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  • 1.
    Buehler, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Courcoux, N.
    Universität Bremen, Institute of Environmental Physics.
    John, Viju Oommen
    University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami.
    Radiative transfer calculations for a passive microwave satellite sensor: comparing a fast model and a line-by-line model2006In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, no 20, p. 20304-Article in journal (Refereed)
    Abstract [en]

    A comparison between the fast radiative transfer model Radiative Transfer for the TIROS Operational Vertical Sounder (RTTOV-7) and the physical radiative transfer model Atmospheric Radiative Transfer Simulator ( ARTS) was carried out. Radiances were simulated for the sounding channels of the Advanced Microwave Sounding Unit B (AMSU-B) for the whole globe for a single time of a single day ( 1 January 2000, 0000 UT). Temperature, pressure, and specific humidity profiles from the reanalysis data set ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF) were used as input for both models; geopotential height profiles were also used but only as input for ARTS. The simulations were made for two different surface emissivities, 0.60 and 0.95. The low surface emissivity case exhibits the larger radiance differences. Although the global values of the mean difference and standard deviation are small ( for example, the global mean difference for channel 18 is 0.014 K and the standard deviation is 0.232 K), the examination of the geographical distribution of the differences shows that large positive or negative values are observed over dry regions of high northern and southern latitudes and over dry elevated regions. The origin of these differences was found to be due to errors introduced by the transmittance parametrization used in RTTOV.

  • 2. Buehler, Stefan
    et al.
    John, V. O.
    Universität Bremen, Institute of Environmental Physics.
    A simple method to relate microwave radiances to upper tropospheric humidity2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 110, no 2, p. D02110-Article in journal (Refereed)
    Abstract [en]

    A brightness temperature (BT) transformation method can be applied to microwave data to retrieve Jacobian weighted upper tropospheric relative humidity (UTH) in a broad layer centered roughly between 6 and 8 km altitude. The UTH bias is below 4% RH, and the relative UTH bias below 20%. The UTH standard deviation is between 2 and 6.5% RH in absolute numbers, or between 10 and 27% in relative numbers. The standard deviation is dominated by the regression noise, resulting from vertical structure not accounted for by the simple transformation relation. The UTH standard deviation due to radiometric noise alone has a relative standard deviation of approximately 7% for a radiometric noise level of 1 K. The retrieval performance was shown to be of almost constant quality for all viewing angles and latitudes, except for problems at high latitudes due to surface effects. A validation of AMSU UTH against radiosonde UTH shows reasonable agreement if known systematic differences between AMSU and radiosonde are taken into account. When the method is applied to supersaturation studies, regression noise and radiometric noise could lead to an apparent supersaturation even if there were no supersaturation. For a radiometer noise level of 1 K the drop-off slope of the apparent supersaturation is 0.17% RH−1, for a noise level of 2 K the slope is 0.12% RH−1. The main conclusion from this study is that the BT transformation method is very well suited for microwave data. Its particular strength is in climatological applications where the simplicity and the a priori independence are key advantages.

  • 3. Buehler, Stefan
    et al.
    Kuvatov, M.
    Universität Bremen, Institute of Environmental Physics.
    John, V. O.
    Universität Bremen, Institute of Environmental Physics.
    Leiterer, U.
    Meteorological Observatory Lindenberg, German Weather Service, Lindenberg.
    Dier, H.
    Meteorological Observatory Lindenberg, German Weather Service, Lindenberg.
    Comparison of microwave satellite humidity data and radiosonde profiles: a case study2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no 13, p. S13103-Article in journal (Refereed)
    Abstract [en]

    This article documents a case study comparing radiosonde humidity data to Advanced Microwave Sounding Unit (AMSU) satellite humidity data. The study had two goals: first, to develop a robust method for such a comparison, and second, to check the quality and mutual consistency of radiosonde data, radiative transfer model, and AMSU data. The radiosonde data used are Vaisala RS80 data from the station Lindenberg of the German Weather Service (DWD), which have been subject to several corrections compared to the standard data processing. The radiative transfer model is the Atmospheric Radiative Transfer Simulator ( ARTS), and the AMSU data are those of the satellites NOAA 15 and 16 for the time periods 2001 and 2002. The comparison was done in radiance space, using a radiative transfer model to simulate AMSU radiances from the radiosonde data. The overall agreement is very good, with radiance biases below 1.5 K and standard deviations below 2 K. The main source of "noise'' in the comparison is atmospheric inhomogeneity on the 10-km scale. While the radiosonde correction performed at Lindenberg significantly reduces the bias between simulated and measured AMSU radiance, there still remains a slope in the radiance difference. Possible reasons for this were investigated. Most likely, the radiosondes underestimate the relative humidity under extremely dry conditions, showing 0 % RH when the true value is 2 - 4 % RH.

  • 4.
    Buehler, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuvatov, M.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    John, V. O.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Milz, Mathias
    Soden, B.J.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Jackson, D.L.
    Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, NOAA Earth System Research Laboratory.
    Norholt, J.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    An upper tropospheric humidity data set from operational satellite microwave data2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no 14, p. D14110-Article in journal (Refereed)
    Abstract [en]

    183.31 GHz observations from the Advanced Microwave Sounding Unit B (AMSUB) instruments onboard the NOAA 15, 16, and 17 satellites were used to derive a new data set of Upper Tropospheric Humidity (UTH). The data set consist of monthly median and mean data on a 1.5 degrees latitude-longitude grid between 60 degrees S and 60 degrees N, and covers the time period of January 2000 to February 2007. The data from all three instruments are very consistent, with relative difference biases of less than 4% and relative difference standard deviations of 7%. Radiometric contributions by high ice clouds and by the Earth's surface affect the measurements in certain areas. The uncertainty due to clouds is estimated to be up to approximately 10%RH in areas with deep convection. The uncertainty associated with contamination from surface emission can exceed 10%RH in midlatitude winter, where the data therefore should be regarded with caution. Otherwise the surface influence appears negligible. The paper also discusses the UTH median climatology and seasonal cycle, which are found to be broadly consistent with UTH climatologies from other sensors. Finally, the paper presents an initial validation of the new data set against IR satellite data and radiosonde data. The observed biases of up to 9%RH (wet bias relative to HIRS) were found to be broadly consistent with expectations based on earlier studies. The observed standard deviations against all other data sets were below 6%RH. The UTH data are available to the scientific community on http://www.sat.ltu.se.

  • 5.
    Dieval, Catherine
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Kallio, E.
    Finnish Meteorological Institute.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Y.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Holmström, M.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Fedorov, A.
    Institut de Recherche en Astrophysique et Planetologie, Toulouse.
    Frahm, R.A.
    Southwest Research Institute, San Antonio, Texas.
    Jarvinen, R.
    Finnish Meteorological Institute, Helsinki.
    Brain, D.A.
    Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado.
    A case study of proton precipitation at Mars: Mars Express observations and hybrid simulations2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    Using the data from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) experiment on board Mars Express and hybrid simulations, we have investigated the entry of protons into the Martian induced magnetosphere. We discuss one orbit on the dayside with observations of significant proton fluxes at altitudes down to 260 km on 27 February 2004. The protons observed below the induced magnetosphere boundary at an altitude of less than 700 km have energies of a few keV, travel downward, and precipitate onto the atmosphere. The measured energy flux and particle flux are 108–109 eV cm−2 s−1 and 105–106 H+ cm−2 s−1, respectively. The proton precipitation occurs because the Martian magnetosheath is small with respect to the heated proton gyroradius in the subsolar region. The data suggest that the precipitation is not permanent but may occur when there are transient increases in the magnetosheath proton temperature. The higher-energy protons penetrate deeper because of their larger gyroradii. The proton entry into the induced magnetosphere is simulated using a hybrid code. A simulation using a fast solar wind as input can reproduce the high energies of the observed precipitating protons. The model shows that the precipitating protons originate from both the solar wind and the planetary exosphere. The precipitation extends over a few thousand kilometers along the orbit of the spacecraft. The proton precipitation does not necessarily correlate with the crustal magnetic anomalies.

  • 6.
    Dieval, Catherine
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    A statistical study of proton precipitation onto the Martian upper atmosphere: Mars Express observations2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, p. 1972-1983Article in journal (Refereed)
    Abstract [en]

    Due to the small size of the Martian magnetic pile-up region, especially at the subsolar point, heated protons with high enough energy can penetrate the induced magnetosphere boundary (IMB) without being backscattered, i.e., they precipitate. We present a statistical study of the downgoing ~ keV proton fluxes measured in the Martian ionosphere by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) experiment onboard the Mars Express spacecraft. We find that on the dayside, the events of proton penetration occur during 3% of the observation time: the precipitation is an intermittent phenomenon. The proton events carry on average ~0.2% of the incident solar wind flux. Therefore, the induced magnetosphere is an effective shield against the magnetosheath protons. The events are more frequent during fast solar wind conditions than during slow solar wind conditions. The sporadic proton penetration is thought to be caused by transient increases in the magnetosheath temperature. The precipitating flux is higher on the dayside than on the nightside, and its spatial deposition is controlled by the solar wind convective electric field. The largest crustal magnetic anomalies tend to decrease the proton precipitation in the Southern hemisphere. The particle and energy fluxes vary in the range 104-106 cm-2 s-1 and 107-109 eVcm-2 s-1, respectively. The corresponding heating for the dayside atmosphere is on average negligible compared to the solar extreme ultraviolet heating, although the intermittent penetration may cause local ionization. The net precipitating proton particle flux input to the dayside ionosphere is estimated as 1.2 · 1021 s-1.

  • 7.
    Dieval, Catherine
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Edberg, N.J.T.
    Swedish Institute of Space Physics, Uppsala.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Reduced proton and alpha particle precipitations at Mars during solar wind pressure pulses: Mars Express results2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3421-3429Article in journal (Refereed)
    Abstract [en]

    1] We performed a statistical study of downward moving protons and alpha particles of ~keV energy (assumed to be of solar wind origin) inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package on board Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low-altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent, and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses, the occurrence frequency of observed proton precipitation events is reduced by a factor of ~3, and for He2+ events the occurrence frequency is reduced by a factor of ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pileup of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H+/He2+ precipitations.

  • 8.
    Dim, J.R.
    et al.
    Earth Observation Research Center, JAXA, 2-1-1 Sengen, Tsukuba.
    Murakami, H.
    Earth Observation Research Center, JAXA, 2-1-1 Sengen, Tsukuba.
    Nakajima, T.Y.
    Earth Observation Research Center, JAXA, 2-1-1 Sengen, Tsukuba.
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Heidinger, A.K.
    CIMSS, University of Wisconsin-Madison/NOAA, Madison.
    Takamura, T.
    Center for Environmental Remote Sensing, Chiba University.
    The recent state of the climate: Driving components of cloud-type variability2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no 11Article in journal (Refereed)
    Abstract [en]

    To reduce the Earth's radiation budget uncertainty related to cloud types' changes, and better understand the climate constraints resulting from long-term clouds' variability, frequent and finer (than actually existing) observations are necessary. This is one of the aims of future satellite programs such as the Global Change Observation Mission-Climate (GCOM-C) satellite, to be launched by the Japan Aerospace Exploration Agency (JAXA). To facilitate the transition from past to future observations, the actual state of climate variables (e.g., cloud types) needs to be evaluated. This evaluation is attempted in the present work with the analysis of long-term cloud types' distribution and amounts. The data set used for this study is 25 years (1982-2006) of global daytime cloud properties observed by the National Oceanic and Atmospheric Administration- Advanced Very-High-Resolution Radiometer (NOAA-AVHRR) satellites sensors. Though various calibrations have been applied on NOAA-AVHRR data, the effects of the orbit drift experienced by these satellites need to be corrected. A signal processing decomposition method allowing the filtering of the cloud types' amount trend affected by the orbit drift is used to perform the necessary corrections. The results obtained show a quantifiable improvement of the cloud amount estimation and trends of the individual NOAA satellites initial observations, at the global and regional scales. The corrected global cloud amount shows a slight decrease in its linear trend. The driving factors of this trend are the decrease in mid and low clouds overwhelming the increase in high clouds (+0.04% cloud amount/yr). A comparison with other cloud climatology studies such as the International Cloud Satellite Climatology Project (ISCCP) data set shows that the global cloud decrease noticed in NOAA-AVHRR's data is smaller. And, contrary to the NOAA-AVHRR's data, the driving force of the ISCCP linear trend is a sharp decrease in low clouds (-0.20% cloud amount/yr).

  • 9.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holl, Gerrit
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Stengel, M.
    Iturbe-Sanchez, F.
    Johnston, M.
    Systematic and random errors between collocated satellite ice water path observations2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 2629-2642Article in journal (Refereed)
    Abstract [en]

    There remains large disagreement between IWP in observational datasets, largely because the sensors observe different parts of the ice particle size distribution. A detailed comparison of retrieved IWP from satellite observations in the Tropics ({plus minus}30{degree sign} latitude) in 2007 is made using collocated measurements. The DARDAR IWP dataset, based on combined Radar/Lidar measurements, is used as a reference as it provides arguably the best estimate of the total column IWP. For each dataset, usable IWP dynamic ranges are inferred from this comparison. IWP retrievals based on solar reflectance measurements, MODIS, and AVHRR-based CMSAF, and PATMOS-x, were found to be correlated with DARDAR over a large IWP range (~20-7000 g/m-2;). The random errors of the collocated datasets have a close to log-normal distribution, and the combined random error of MODIS and DARDAR is less than a factor of 2, which also sets the upper limit for MODIS alone. In the same way the upper limit for the random error of all considered datasets is determined. Datasets based on passive microwave measurements,MSPPS, MiRS, and CMO, are largely correlated with DARDAR for IWP values larger than approximately 700 g/m². The combined uncertainty between these datasets and DARDAR in this range is slightly less MODIS-DARDAR, but the systematic bias is nearly an order of magnitude.

  • 10.
    Emde, Claudia
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Davis, C.
    University of Edinburgh, Institute of Atmospheric and Environmental Science.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Sreerekha, T.R.
    Universität Bremen, Institute of Environmental Physics.
    Teichmann, C.
    Universität Bremen, Institute of Environmental Physics.
    A polarized discrete ordinate scattering model for simulations of limb and nadir long-wave measurements in 1-D/3-D spherical atmospheres2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no 24, p. 24207-Article in journal (Refereed)
    Abstract [en]

    This article describes one of the scattering algorithms of the three-dimensional polarized radiative transfer model ARTS (Atmospheric Radiative Transfer Simulator) which has been implemented to study for example the influence of cirrus clouds on microwave limb sounding. The model uses the DOIT (Discrete Ordinate Iterative) method to solve the vector radiative transfer equation. The implementation of a discrete ordinate method is challenging due to the spherical geometry of the model atmosphere which is required for the simulation of limb radiances. The involved numerical issues, which are grid optimization and interpolation methods, are discussed in this paper. Scattering simulations are presented for limb- and down-looking geometries, for one-dimensional and three-dimensional spherical atmospheres. They show the impact of cloud particle size, shape, and orientation on the brightness temperatures and on the polarization of microwave radiation in the atmosphere. The cloud effect is much larger for limb radiances than for nadir radiances. Particle size is a very important parameter in all simulations. The polarization signal is negligible for simulations with completely randomly oriented particles, whereas for horizontally aligned particles with random azimuthal orientation the polarization signal is significant. Moreover, the effect of particle shape is only relevant for oriented cloud particles. The simulations show that it is essential to use a three-dimensional scattering model for inhomogeneous cloud layers.

  • 11.
    Engeln, Axel von
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Temperature profile determination from microwave oxygen emissions in limb sounding geometry2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no 19, p. 12-1Article in journal (Refereed)
    Abstract [en]

    We present a theoretical investigation of the temperature profile retrieval capabilities of oxygen emission lines in the microwave. The main focus is on two strong lines, both allowing temperature retrieval throughout the mesosphere. One is within the oxygen cluster at 61.15 GHz, the other one is isolated at 118.75 GHz. A thorough comparison of these two lines is presented. Several instrumental parameters such as system noise temperature, antenna beam width, filter width, and coverage of the line are assessed, as well as the possible impact of an error in the spectroscopic parameters. The instrumental setup follows roughly the specifications for the Millimeter Wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER) instrument, serving as a basis for a modern passive microwave instrument. The instrumental parameters have also been varied in order to allow comparisons with two instruments that use the 118.75-GHz line for temperature profile determination, the Odin submillimeter radiameter (SMR) and the EOS microwave limb sounder (MLS). Simultaneous retrieval of temperature and pointing bias is performed with the Optimal Estimation Method. We find temperature retrieval errors of

  • 12.
    Engeln, Axel von
    et al.
    Naval Research Laboratory, Washington, DC.
    Nedoluha, Gerald
    Naval Research Laboratory, Washington, DC.
    Kirchengast, Gottfried
    University of Graz, Institute for Geophysics, Astrophysics and Meteorology.
    Buehler, Stefan
    One-dimensional variational (1-D Var) retrieval of temperature, water vapor, and a reference pressure from radio occultation measurements: A sensitivity analysis2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no 11, p. 4337-Article in journal (Refereed)
    Abstract [en]

    A 1-D Var retrieval study of simulated radio occultation measurements is presented. Temperature and a water vapor profile are retrieved along with a reference pressure to generate the pressure profile by applying the hydrostatic equation. High-resolution European Center for Medium-Range Weather Forecasts (ECMWF) atmospheric fields are used by a ray tracing tool to calculate the exact positions of the tangent point. The 1-D atmospheric profiles following the calculated tangent point trajectory in the 3-D ECMWF fields are used to simulate bending angle measurements with a 1-D forward model. Assimilation of these bending angles in a 1-D Var tool employing the same 1-D forward model is performed. We analyze the sensitivity of the retrieval to changes in vertical resolution, horizontal smearing of the tangent point trajectory, and the assumption of hydrostatic equilibrium for a nonvertical atmospheric scan. We find that retrievals calculated without adequate vertical resolution can have significant errors in temperature and water vapor. Errors in the retrieval by assuming hydrostatic equilibrium for a nonvertical scan generally cause only minor errors in the retrieved profiles. A study into the occurrence of rays curving down toward the Earth surface indicates that about 5–10% of the profiles could experience so-called critical refraction at altitudes between 0.5 km and 2 km in case of the applied high-resolution ECMWF data.

  • 13.
    Fatemi, Shahab
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    The effects of lunar surface plasma absorption and solar wind temperature anisotropies on the solar wind proton velocity space distributions in the low-altitude lunar plasma wake2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no 10Article in journal (Refereed)
    Abstract [en]

    We study the solar wind proton velocity space distribution functions on the lunar nightside at low altitudes (∼100 km) above the lunar surface using a three-dimensional hybrid plasma solver, when the Moon is in the unperturbed solar wind. When the solar wind encounters a passive obstacle, such as the Moon, without any strong magnetic field and no atmosphere, solar wind protons that impact the obstacle's surface are absorbed and removed from the velocity space distribution functions. We show first that a hybrid model of plasma is applicable to study the low-altitude lunar plasma wake by comparing the simulation results with observations. Then we examine the effects of a solar wind bi-Maxwellian velocity space distribution function and the lunar surface plasma absorption on the solar wind protons' velocity space distribution functions and their entry in the direction parallel to the interplanetary magnetic field lines into the low-altitude lunar wake. We present a backward Liouville method for particle-in-cell solvers that improves velocity space resolution. The results show that the lunar surface plasma absorption and anisotropic solar wind velocity space distributions result in substantial changes in the solar wind proton distribution functions in the low-altitude lunar plasma wake, modifying proton number density, velocity, and temperature there. Additionally, a large temperature anisotropy is found at close distances to the Moon on the lunar nightside as a consequence of the lunar surface plasma absorption effect

  • 14.
    Fatemi, Shahab
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Holmström, Mats
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Futaana, Yoshifumi
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Lue, Charles
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Collier, Michael R.
    NASA Goddard Space Flight Center.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, Gabriella
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Effects of protons deflected by lunar crustal magnetic fields on the global lunar plasma environment2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 8, p. 6095-6105Article in journal (Refereed)
    Abstract [en]

    Solar wind plasma interaction with lunar crustal magnetic fields is different than that of magnetized bodies like the Earth. Lunar crustal fields are, for typical solar wind conditions, not strong enough to form a (bow)shock upstream but rather deflect and perturb plasma and fields. Here we study the global effects of protons reflected from lunar crustal magnetic fields on the lunar plasma environment when the Moon is in the unperturbed solar wind. We employ a three-dimensional hybrid model of plasma and an observed map of reflected protons from lunar magnetic anomalies over the lunar farside. We observe that magnetic fields and plasma upstream over the lunar crustal fields compress to nearly 120% and 160% of the solar wind, respectively. We find that these disturbances convect downstream in the vicinity of the lunar wake, while their relative magnitudes decrease. In addition, solar wind protons are disturbed and heated at compression regions and their velocity distribution changes from Maxwellian to a non-Maxwellian. Finally, we show that these features persists, independent of the details of the ion reflection by the magnetic fields.

  • 15.
    Haberle, R. M.
    et al.
    NASA Ames Research Center.
    Gõmez-Elvira, J.
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Juárez, M. De La Torre
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Harri, A. M.
    Finnish Meteorological Institute.
    Hollingsworth, J. L.
    NASA Ames Research Center.
    Kahanpää, H.
    Finnish Meteorological Institute.
    Kahre, M. A.
    NASA Ames Research Center.
    Lemmon, M.
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Mischna, M.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Martin-Torres, Javier
    Centro de Astrobiologia, Madrid.
    Moores, J. E.
    Department of Earth and Space Science and Engineering, York University.
    Newman, C.
    Ashima Research, Pasadena.
    Rafkin, S. C R
    Southwest Research Institute, San Antonio, Texas.
    Rennõ, N.
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor.
    Richardson, M. I.
    Ashima Research, Pasadena.
    Rodríguez-Manfredi, J. A.
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Vasavada, A. R.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Zorzano-Mier, M. P.
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Preliminary interpretation of the REMS pressure data from the first 100 sols of the MSL mission2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 3, p. 440-453Article in journal (Refereed)
    Abstract [en]

    We provide a preliminary interpretation of the Rover Environmental Monitoring Station (REMS) pressure data from the first 100 Martian solar days (sols) of the Mars Science Laboratory mission. The pressure sensor is performing well and has revealed the existence of phenomena undetected by previous missions that include possible gravity waves excited by evening downslope flows, relatively dust-free convective vortices analogous in structure to dust devils, and signatures indicative of the circulation induced by Gale Crater and its central mound. Other more familiar phenomena are also present including the thermal tides, generated by daily insolation variations, and the CO2 cycle, driven by the condensation and sublimation of CO2 in the polar regions. The amplitude of the thermal tides is several times larger than those seen by other landers primarily because Curiosity is located where eastward and westward tidal modes constructively interfere and also because the crater circulation amplifies the tides to some extent. During the first 100 sols tidal amplitudes generally decline, which we attribute to the waning influence of the Kelvin wave. Toward the end of the 100 sol period, tidal amplitudes abruptly increased in response to a nearby regional dust storm that did not expand to global scales. Tidal phases changed abruptly during the onset of this storm suggesting a change in the interaction between eastward and westward modes. When compared to Viking Lander 2 data, the REMS daily average pressures show no evidence yet for the 1-20 Pa increase expected from the possible loss of CO 2 from the south polar residual cap. Key Points REMS pressure sensor is operating nominally New phenomena have been discovered Familiar phenomena have been detected ©2014. American Geophysical Union. All Rights Reserved.

  • 16.
    Hamilton, Victoria E.
    et al.
    Department of Space Studies, Southwest Research Institute.
    Vasavada, Ashwin R.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Sebastián, Eduardo
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Juárez, Manuel De La Torre
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena.
    Ramos, Miguel
    Departamento de Física y Matemática, University of Alcalá.
    Armiens, Carlos
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Arvidson, Raymond E.
    Department of Earth and Planetary Sciences, Washington University, St. Louis.
    Carrasco, Isaías
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Christensen, Philip R.
    School of Earth and Space Exploration, Arizona State University.
    Pablo, Miguel A. De
    Departamento de Geología, Geografía y Medio Ambiente, University of Alcalá.
    Goetz, Walter
    Max-Planck-Institut für Solar System Research.
    Gõmez-Elvira, Javier
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Lemmon, Mark T.
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Madsen, Morten B.
    Niels Bohr Institute, Copenhagen University.
    Martin-Torres, Javier
    Centro de Astrobiologia, INTA-CSIC, Madrid , Instituto Andaluz de Cienccias de la Tierra (CSIC-UGR), Grenada.
    Martínez-Frías, Jesús
    Centro de Astrobiologia, INTA-CSIC, Madrid , Instituto de Geociencias (CSIC-UCM), Ciudad Universitaria.
    Molina, Antonio
    Centro de Astrobiologia, INTA-CSIC, Madrid , Departamento de Física y Matemática, University of Alcalá.
    Palucis, Marisa C.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Rafkin, Scot C R
    Department of Space Studies, Southwest Research Institute.
    Richardson, Mark I.
    Ashima Research, Pasadena.
    Yingst, R. Aileen
    Planetary Science Institute, Tucson.
    Zorzano, María-Paz
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Observations and preliminary science results from the first 100 sols of MSL Rover Environmental Monitoring Station ground temperature sensor measurements at Gale Crater2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 4, p. 745-770Article in journal (Refereed)
    Abstract [en]

    We describe preliminary results from the first 100 sols of ground temperature measurements along the Mars Science Laboratory's traverse from Bradbury Landing to Rocknest in Gale. The ground temperature data show long-term increases in mean temperature that are consistent with seasonal evolution. Deviations from expected temperature trends within the diurnal cycle are observed and may be attributed to rover and environmental effects. Fits to measured diurnal temperature amplitudes using a thermal model suggest that the observed surfaces have thermal inertias in the range of 265-375?J m-2 K-1 s-1/2, which are within the range of values determined from orbital measurements and are consistent with the inertias predicted from the observed particle sizes on the uppermost surface near the rover. Ground temperatures at Gale Crater appear to warm earlier and cool later than predicted by the model, suggesting that there are multiple unaccounted for physical conditions or processes in our models. Where the Mars Science Laboratory (MSL) descent engines removed a mobile layer of dust and fine sediments from over rockier material, the diurnal temperature profile is closer to that expected for a homogeneous surface, suggesting that the mobile materials on the uppermost surface may be partially responsible for the mismatch between observed temperatures and those predicted for materials having a single thermal inertia. Models of local stratigraphy also implicate thermophysical heterogeneity at the uppermost surface as a potential contributor to the observed diurnal temperature cycle. Key Points Diurnal ground temperatures vary with location Diurnal temperature curves are not well matched by a homogeneous thermal model GTS data are consistent with a varied stratigraphy and thermophysical properties.

  • 17.
    Harri, A. M.
    et al.
    Finnish Meteorological Institute, Division of Earth Observation.
    Genzer, M.
    Finnish Meteorological Institute, Division of Earth Observation.
    Kemppinen, O.
    Finnish Meteorological Institute, Division of Earth Observation.
    Kahanpää, H.
    Finnish Meteorological Institute, Division of Earth Observation.
    Gomez-Elvira, J.
    Centro de Astrobiología (CAB).
    Rodriguez-Manfredi, J. A.
    Centro de Astrobiología (CAB).
    Haberle, R.
    NASA Ames Research Center.
    Polkko, J.
    Finnish Meteorological Institute, Division of Earth Observation.
    Schmidt, W.
    Finnish Meteorological Institute, Division of Earth Observation.
    Savijärvi, H.
    Finnish Meteorological Institute, Division of Earth Observation.
    Kauhanen, J.
    Finnish Meteorological Institute, Division of Earth Observation.
    Atlaskin, E.
    Finnish Meteorological Institute, Division of Earth Observation.
    Richardson, M.
    Ashima Research, Pasadena.
    Siili, T.
    Finnish Meteorological Institute, Division of Earth Observation.
    Paton, M.
    Finnish Meteorological Institute, Division of Earth Observation.
    Juarez, M. De La Torre
    NASA Jet Propulsion Laboratory, Pasadena.
    Newman, C.
    Ashima Research, Pasadena.
    Rafkin, S.
    Southwest Research Institute, Boulder.
    Lemmon, M. T.
    Texas A&M University.
    Mischna, M.
    NASA Jet Propulsion Laboratory, Pasadena.
    Merikallio, S.
    Finnish Meteorological Institute, Division of Earth Observation.
    Haukka, H.
    Finnish Meteorological Institute, Division of Earth Observation.
    Martin-Torres, Javier
    Centro de Astrobiologia, INTA-CSIC, Madrid.
    Zorzano, María-Paz
    Centro de Astrobiología (CAB).
    Peinado, V.
    Centro de Astrobiología (CAB).
    Rennõ, N.
    University of Michigan.
    Pressure observations by the curiosity rover: Initial results2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 1, p. 82-92Article in journal (Refereed)
    Abstract [en]

    REMS-P, the pressure measurement subsystem of the Mars Science Laboratory (MSL) Rover Environmental Measurement Station (REMS), is performing accurate observations of the Martian atmospheric surface pressure. It has demonstrated high data quality and good temporal coverage, carrying out the first in situ pressure observations in the Martian equatorial regions. We describe the REMS-P initial results by MSL mission sol 100 including the instrument performance and data quality and illustrate some initial interpretations of the observed features. The observations show both expected and new phenomena at various spatial and temporal scales, e.g., the gradually increasing pressure due to the advancing Martian season signals from the diurnal tides as well as various local atmospheric phenomena and thermal vortices. Among the unexpected new phenomena discovered in the pressure data are a small regular pressure drop at every sol and pressure oscillations occurring in the early evening. We look forward to continued high-quality observations by REMS-P, extending the data set to reveal characteristics of seasonal variations and improved insights into regional and local phenomena. Key Points The performance and data quality of the REMS / MSL pressure observations. MSL pressure observations exhibit local phenomena of the Gale crater area. Small pressure oscillations possibly linked to gravity waves. ©2013. American Geophysical Union. All Rights Reserved.

  • 18.
    Hong, Gang
    et al.
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Yang, Ping
    Department of Atmospheric Sciences, Texas A&M University, College Station, Texas.
    Baum, Bryan A.
    Space Science and Engineering Center, University of Wisconsin, Madison, Wisconsin.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Weng, Fuzhong
    Satellite Meteorology and Climatology Division, Center for Satellite Applications and Research, NOAA NESDIS, Camp Springs, Maryland.
    Liu, Quanhua
    Joint Center for Satellite Data Assimilation, NOAA NESDIS, Camp Springs, Maryland.
    Heygster, Georg
    Institute of Environmental Physics, University of Bremen.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Scattering database in the millimeter and submillimeter wave range of 100-1000 GHz for nonspherical ice particles2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. D06201-Article in journal (Refereed)
    Abstract [en]

    The inference of ice cloud properties from spaceborne sensors is sensitive to the retrieval algorithms and satellite sensors used. To approach a better understanding of ice cloud properties, it is necessary to combine satellite measurements from multiple platforms and sensors operating in visible, infrared, and millimeter and submillimeter-wave regions of the electromagnetic spectrum. The single-scattering properties of ice particles with consistent ice particle models are the basis for estimating the optical and microphysical properties of ice clouds from multiple satellite sensors. In this study, the single-scattering properties (extinction efficiency, absorption efficiency, single-scattering albedo, asymmetry factor, and scattering phase matrix) of nonspherical ice particles, assumed to be hexagonal solid and hollow columns, hexagonal plates, 3D bullet rosettes, aggregates, and droxtals, are computed from the discrete dipole approximation method for 21 millimeter and submillimeter-wave frequencies ranging from 100 to 1000 GHz. A database of the single-scattering properties of nonspherical ice particles are developed for 38 particle sizes ranging from 2 to 2000 μm in terms of particle maximum dimension. The bulk scattering properties of ice clouds consisting of various ice particles, which are the fundamental to the radiative transfer in ice clouds, are developed on the basis of a set of 1119 particle size distributions obtained from various field campaigns.

  • 19.
    John, Viju O.
    et al.
    Met Office Hadley Centre, Exeter.
    Allan, Richard P.
    Department of Meteorology, University of Reading.
    Bell, William
    Met Office Hadley Centre, Exeter.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kottayil, Ajil
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Assessment of intercalibration methods for satellite microwave humidity sounders2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 10, p. 4906-4918Article in journal (Refereed)
    Abstract [en]

    Three methods for ntercalibrating humidity sounding channels are compared to assess their merits and demerits. The methods use the following: (1) natural targets (Antarctica and tropical oceans), (2) zonal average brightness temperatures, and (3) simultaneous nadir overpasses (SNOs). Advanced Microwave Sounding Unit-B instruments onboard the polar-orbiting NOAA 15 and NOAA 16 satellites are used as examples. Antarctica is shown to be useful for identifying some of the instrument problems but less promising for intercalibrating humidity sounders due to the large diurnal variations there. Owing to smaller diurnal cycles over tropical oceans, these are found to be a good target for estimating intersatellite biases. Estimated biases are more resistant to diurnal differences when data from ascending and descending passes are combined. Biases estimated from zonal-averaged brightness temperatures show large seasonal and latitude dependence which could have resulted from diurnal cycle aliasing and scene-radiance dependence of the biases. This method may not be the best for channels with significant surface contributions. We have also tested the impact of clouds on the estimated biases and found that it is not significant, at least for tropical ocean estimates. Biases estimated from SNOs are the least influenced by diurnal cycle aliasing and cloud impacts. However, SNOs cover only relatively small part of the dynamic range of observed brightness temperatures

  • 20.
    John, Viju O
    et al.
    Met Office Hadley Centre, Exeter.
    Holl, Gerrit
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Allen, Richard P.
    Department of Meteorology, University of Reading.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Parker, David E.
    Met Office Hadley Centre, Exeter.
    Soden, Brian J.
    Rosenstiel School of Marine and Atmospheric Science, University of Miami.
    Clear-sky biases in satellite infrared estimates of upper tropospheric humidity and its trends2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116Article in journal (Refereed)
    Abstract [en]

    We use microwave retrievals of upper tropospheric humidity (UTH) to estimate the impact of clear-sky-only sampling by infrared instruments on the distribution, variability, and trends in UTH. Our method isolates the impact of the clear-sky-only sampling, without convolving errors from other sources. On daily time scales, IR-sampled UTH contains large data gaps in convectively active areas, with only about 20-30 % of the tropics (30 degrees S-30 degrees N) being sampled. This results in a dry bias of about -9 % RH in the area-weighted tropical daily UTH time series. On monthly scales, maximum clear-sky bias (CSB) is up to -30 % RH over convectively active areas. The magnitude of CSB shows significant correlations with UTH itself (-0.5) and also with the variability in UTH (-0.6). We also show that IR-sampled UTH time series have higher interannual variability and smaller trends compared to microwave sampling. We argue that a significant part of the smaller trend results from the contrasting influence of diurnal drift in the satellite measurements on the wet and dry regions of the tropics.

  • 21.
    John, Viju O.
    et al.
    Met Office Hadley Centre, Exeter.
    Holl, Gerrit
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Candy, Brett
    Met Office Hadley Centre, Exeter.
    Saunders, Roger W.
    Met Office Hadley Centre, Exeter.
    Perker, David E.
    Met Office Hadley Centre, Exeter.
    Understanding intersatellite biases of microwave humidity sounders using global simultaneous nadir overpasses2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D02305-Article in journal (Refereed)
    Abstract [en]

    Simultaneous nadir overpasses (SNOs) of polar-orbiting satellites are most frequent in polar areas but can occur at any latitude when the equatorial crossing times of the satellites become close owing to orbital drift. We use global SNOs of polar orbiting satellites to evaluate the intercalibration of microwave humidity sounders from the more frequent high-latitude SNOs. We have found based on sensitivity analyses that optimal distance and time thresholds for defining collocations are pixel centers less than 5 km apart and time differences less than 300 s. These stringent collocation criteria reduce the impact of highly variable surface or atmospheric conditions on the estimated biases. Uncertainties in the estimated biases are dominated by the combined radiometric noise of the instrument pair. The effects of frequency changes between different versions of the humidity sounders depend on the amount of water vapor in the atmosphere. There are significant scene radiance and thus latitude dependencies in the estimated biases and this has to taken into account while intercalibrating microwave humidity sounders. Therefore the results obtained using polar SNOs will not be representative for moist regions, necessitating the use of global collocations for reliable intercalibration.

  • 22.
    Karig, D. E.
    et al.
    Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York.
    Ask, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Geological perspectives on consolidation of clay-rich marine sediments2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no B4, p. 2197-Article in journal (Refereed)
    Abstract [en]

    Experimental consolidation of uncemented clay-rich marine sediments provides information concerning their stress history. A main finding is that some of the well-known behavior of soft sediment deformation in geotechnical applications cannot validly be extrapolated to sediments that have been subjected to higher stresses and longer times of geologic conditions. This study confirms that the yield stress of the uncemented sediment accurately reflects its previous maximum consolidation state. Furthermore, we have identified a new phase of post-yield strain that is associated with higher values of the modified compression index (the slope of the porosity versus the logarithm of effective vertical stress) than that of elastic deformation, but with much lower values than that for primary consolidation. This post-yield behavior is a linear, non-elastic deformation, and is termed tertiary consolidation. Yield stress appears independent of creep time or strain rate, whereas the tertiary-primary consolidation transition is sensitive to these parameters. During post-yield creep (secondary consolidation) the slope of the porosity versus the logarithm of time curve, or the secondary consolidation index, is generally assumed constant. However, this is not valid for claystones at effective vertical stresses above about 1 MPa, where the secondary consolidation index increases with stress. At a given effective vertical stress, the secondary consolidation index also increases with creep times greater than about 105 s (28 h).

  • 23.
    Kaufmann, M.
    et al.
    Department of Physics, University of Wuppertal , Research Center Jülich.
    Gusev, O. A.
    Department of Physics, University of Wuppertal.
    Grossmann, K. U.
    Department of Physics, University of Wuppertal.
    Martin-Torres, Javier
    Analytical Services and Materials Inc., Hampton.
    Marsh, D. R.
    National Center for Atmospheric Research, Boulder, Colorado.
    Kutepov, A. A.
    Max-Planck-Institute for Extraterrestrial Physics-Institute for Astronomy and Astrophysics, University of Munich.
    Satellite observations of daytime and nighttime ozone in the mesosphere and lower thermosphere2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no 9Article in journal (Refereed)
    Abstract [en]

    The global distribution of mesospheric and lower thermospheric ozone 9.6 μm infrared emissions was measured by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment during two Space Shuttle missions in November 1994 and August 1997. The radiances measured by CRISTA have been inverted to O3 number densities in the 50-95 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved O3 number densities has been carried out. The ozone abundance profiles show volume mixing ratios of 1-2 ppmv at the stratopause, 0.5 ppmv or less around 80 km, and typically 1 ppmv during daytime and 10 ppmv during nighttime at the secondary maximum. The agreement with other experiments is typically better than 25%. The global distribution of upper mesospheric ozone shows significant latitudinal gradients and an enhancement in the equatorial upper mesosphere. At the polar night terminator a third ozone maximum is observed. Three-dimensional model results indicate that the latitudinal gradients are significantly influenced by solar tides.

  • 24.
    Kottayil, Ajil
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    John, V.O.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Correcting diurnal cycle aliasing in satellite microwave humidity sounder measurements2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, p. 101-113Article in journal (Refereed)
    Abstract [en]

    Microwave humidity measurements from polar orbiting satellites are affected by diurnal sampling biases which are caused by changes in the local observation time of the satellites. The long term data records available from these satellites thus have spurious trends, which must be corrected. Diurnal cycles of the microwave measurements have been constructed by combining data over the period 2001--2010 from five different satellite platforms (NOAA-15, -16, -17, -18, and MetOpA). This climatological diurnal cycle has been used to deduce and correct the diurnal sampling bias in AMSU-B and MHS measurements. Diurnal amplitudes for channels which are sensitive to surface temperature variations show a sharp land-sea contrast with the amplitudes exceeding 10 K for land regions, but less than one Kelvin for oceanic regions. The humidity channels sensitive to the upper and middle troposphere exhibit a seasonal variation with large diurnal amplitudes over convective land regions (often above 3 K) in comparison to oceanic regions. The diurnal peak times of these channels over land occur in the early mornings. The diurnal sampling bias correction has a greater impact over land regions when compared to oceanic regions due to the large diurnal amplitudes over land. The diurnal cycle of humidity generated as a part of this study could be used to evaluate diurnal cycles in climate models.

  • 25.
    Moradi, Isaac
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    John, Viju
    Met Office Hadley Centre, Exeter.
    Eliasson, Salomon
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Comparing upper tropospheric humidity data from microwave satellite instruments and tropical radiosondes2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no 24, article id D24310Article in journal (Refereed)
    Abstract [en]

    Atmospheric humidity plays an important role in the Earth's climate. Microwave satellite data provide valuable humidity observations in the upper troposphere with global coverage. In this study, we compare upper tropospheric humidity (UTH) retrieved from the Advanced Microwave Sounding Unit (AMSU-B) and the Microwave Humidity Sounder (MHS) against radiosonde data measured at four of the central facilities of the Atmospheric Radiation Measurement (ARM) program. The Atmospheric Radiative Transfer Simulator (ARTS) was used to simulate satellite brightness temperatures from the radiosonde profiles. Strong ice clouds were filtered out, as their influence on microwave measurements leads to incorrect UTH values. Day and night radiosonde profiles were analyzed separately, to take into account the radiosonde radiation bias. The comparison between radiosonde and satellite is most meaningful for data in cloud free, night time conditions, and with a time difference of less than 2 hours. We found good agreement between the two data sets. The satellite data are slightly moister than the radiosonde data, with a mean difference of 1-2.3 %RH, depending on the radiosonde site. Monthly gridded data were also compared, and showed slightly larger mean difference of up to 3.3 %RH, which can be explained by sampling issues.

  • 26.
    Morgan, Julia K.
    et al.
    Department of Earth Science, Rice University, Houston, TX.
    Ask, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Consolidation state and strength of underthrust sediments and evolution of the décollement at the Nankai accretionary margin: results of uniaxial reconsolidation experiments2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no B03102Article in journal (Refereed)
    Abstract [en]

    Uniaxial reconsolidation experiments conducted on Ocean Drilling Program drill cores along the Muroto Transect of the Nankai accretionary margin demonstrate complex yield and postyield behavior and provide evidence for enhanced strengths within sediments beneath the décollement zone. Tests were conducted on samples collected from similar stratigraphic levels below the décollement and its seaward projection. Consolidation state of the samples increased landward and with depth and was tracked closely by sediment yield stress for all but one of the samples. The sediments, however, exhibited substantial postyield strength: up to 2.8 times the predicted in situ effective vertical stress beneath the protothrust zone. This enhanced strength results from diagenesis that leads to matrix cementation during stable effective stress conditions within the underthrust section. The close correspondence between yield stress and predicted in situ effective stress suggests that despite the cemented state, the sediment matrix remains sensitive to in situ stress conditions. The low yield stress of one sample, collected within ∼40 m of the décollement fault at Site 808, may reflect diagenesis under reduced effective stress conditions, due to postconsolidation increases in pore pressure along the décollement. Due to their cemented state, the strong underthrust sediments resist décollement downcutting beneath the toe of the prism, leading to preferential incorporation of weaker, continuously deforming accreted sediments during shear. Seismogenic slip along the décollement at depth may create stresses in excess of sediment strength, causing shear failure and rapid release of trapped pore fluids feeding high pore fluid pressures along the décollement zone.

  • 27.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barghouthi, Imad A.
    Department of Physics, Al-Quds University, Jerusalem.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Eriksson, A.I
    Swedish Institute of Space Physics, Uppsala.
    André, M.
    Swedish Institute of Space Physics, Uppsala.
    Hot and cold ion outflow: Observations and implications for numerical models2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, p. 105-117Article in journal (Refereed)
    Abstract [en]

    Cluster observations of oxygen ion outflow and low-frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low-altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high-energy O+ ions in the high-altitude cusp and mantle and cold H+ ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high-altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O+ and cold H+, if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low-altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations

  • 28.
    Nilsson, Hans
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Slapak, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Barghouthi, I.A.
    Department of Physics, Al-Quds University, Jerusalem.
    Eriksson, A.I.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    André, M.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Hot and cold ion outflow: Spatial distribution of ion heating2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    Ions apparently emanating from the same source, the ionospheric polar cap, can either end up as energized to keV energies in the high-altitude cusp/mantle, or appear as cold ions in the magnetotail lobes. We use Cluster observations of ions and wave electric fields to study the spatial variation of ion heating in the cusp/mantle and polar cap. The average flow direction in a simplified cylindrical coordinate system is used to show approximate average ion flight trajectories, and discuss the temperatures, fluxes and wave activity along some typical trajectories. It is found that it is suitable to distinguish between cusp, central and nightside polar cap ion outflow trajectories, though O+ heating is mainly a function of altitude. Furthermore we use typical cold ion parallel velocities and the observed average perpendicular drift to obtain average cold ion flight trajectories. The data show that the cusp is the main source of oxygen ion outflow, whereas a polar cap source would be consistent with our average outflow paths for cold ions observed in the lobes. A majority of the cusp O+ flux is sufficiently accelerated to escape into interplanetary space. A scenario with significant oxygen ion heating in regions with strong magnetosheath origin ion fluxes, cold proton plasma dominating at altitudes below about 8 RE in the polar cap, and most of the cusp oxygen outflow overcoming gravity and flowing out in the cusp and mantle is consistent with our observations.

  • 29.
    Nordström, T.
    et al.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Zhang, T.L.
    Austrian Academy of Sciences, Space Research Institute, Graz.
    Venus ion outflow estimates at solar minimum: Influence of reference frames and disturbed solar wind conditions2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, p. 3592-3601Article in journal (Refereed)
    Abstract [en]

    Recent estimates of ion escape rates from Venus, based on ASPERA-4 data, differ by more than a factor of 4. Whereas the ASPERA-4 instrument provides state-of-the art observations, the limited field of view of the instrument and the strongly limited geographical coverage of the spacecraft orbit means that significant assumptions must be used in the interpretation of the data. We complement previous studies by using a method of average distribution functions to obtain as good statistics as possible while taking the limited field of view into account. We use more than 3 years of data, more than any of the previous studies, and investigate how the choice of a geographical reference frame or a solar wind electric field oriented reference frame affects the results. We find that the choice of reference frame cannot explain the difference between the previously published reports. Our results, based on a larger data set, fall in between the previous studies. Our conclusion is that the difference between previous studies is caused by the large variability of ion outflow at Venus. It matters significantly for the end result which data are selected and which time period is used. The average escape rates were found to be 5.2±1.0×1024 s−1for heavy ions (m/q ≥16) and 14±2.6×1024 s−1for protons. We also discuss the spatial distribution of the planetary ion outflow in the solar wind electric field reference frame.

  • 30.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    Electric resistivity in the Gravberg-1 deep well, Sweden1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no 6B, p. 9171-9182Article in journal (Refereed)
    Abstract [en]

    The Siljan impact structure located in central Sweden has been the object of intense geophysical and geological studies for several decades. This paper presents the results of electrical resistivity measurements on the surface, in the hole, and on core samples from shallow coreholes distributed over the whole impact structure. Magnetotelluric data constrain the central part of the structure to be essentially one-dimensional with an upper crustal unit of about 10 000 Ωm followed by a less resistive impact related unit of 1000 Ωm from a depth of about 6 km to a depth of 20 km. The lower crust is a homogeneous unit of about 300 Ωm extending down to about 40 km, where the upper mantle is marked by an increase in resistivity of about 1000 Ωm. Major fracture zones, some of which coincide with the horizontal dolerite sills, known to extend over tens of kilometers, are probably the main carriers of current. Saline fluids recovered below 5.4-km depth and the magnetotelluric results lead us to conclude that pore fluids are highly saline below this depth even on a regional scale.

  • 31.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Section of Solid Earth Physics, Department of Geophysics, University of Uppsala.
    Magnetotellurics in southwestern Sweden: evidence for electrical anisotropy in the lower crust?1988In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 93, no B7, p. 7897-7907Article in journal (Refereed)
    Abstract [en]

    Magnetotelluric data from measurements conducted on the SW part of the Baltic Shield are analyzed with respect to crustal and upper mantle structures. The interpretations have been done using ordinary 2-D and transverse anisotropic layered models in which distortions of the impedance tensors due to near-surface electrical structures are included in the interpretation procedures. The anisotropic model is able to explain the gross features of the data, whereas the 2-D model only displays features observed at long periods. The 2 main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km. The minimum depth to the conductive mantle layer is found from a most squares analysis

  • 32.
    Rona, P.A.
    et al.
    National Oceanic and Atmospheric Administration, Miami.
    Widenfalk, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Boström, K.
    Stockholms Universitet.
    Serpentinized ultramafics and hydrothermal activity at the mid-atlantic ridge crest near 15°N1987In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 92, no B2, p. 1417-1427Article in journal (Refereed)
    Abstract [en]

    The initial occurrence of serpentinized ultramafic rocks at the nontransform intersection of a wall of a rift valley with the wall of a fracture zone is described from a site at the Fifteen Twenty Fracture Zone. The ultramafics crop out in block-faulted terrain on the upper portion of the eastern intersection between the rift valley and fracture zone walls in water depths between 2910 and 3300 m. They comprise cumulate harzburgites, pyroxenites, Iherzolites, and wehrlites, as well as gabbronorites, olivine gabbronorites, gabbropegmatites, and alteration products including serpentinites, bastite serpentinites, and asbestos. The Ti-Zr-Y relations and relatively constant Zr/Ti ratio in basalts recovered with the ultramafic rocks indicate a cogenetic relation from a common magmatic source that has undergone a late stage differentiation in the lower crust. Ongoing hydrothermal activity is indicated by chemical anomalies (δ3He, Mn) in the near-bottom water at the ultramafic outcrop. The upwelling hydrothermal circulation apparently follows crust-penetrating faults that may have controlled the diapiric ascent of the serpentinites and that continue to tap degassing magma and/or mantle. The observations presented indicate that ultramafic cumulates form beneath the rift valley adjacent to long-offset (>100 km) ridge-ridge transform faults, where they are serpentinized by hydrothermal processes within the initial 1 × 106 years of generation of lithosphère at a slow spreading axis. The corners formed by the intersections of the walls of a rift valley with both the transform (RT corner) and the nontransform (RN corner) portions of these fracture zones are principal loci of diapiric emplacement of serpentinized ultramafics.

  • 33.
    Shematovich, V.I.
    et al.
    Institute of Astronomy, Russian Academy of Sciences, Moscow.
    Bisikalo, D.V.
    Institute of Astronomy, Russian Academy of Sciences, Moscow.
    Dieval, Catherine
    Barabash, Stas
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Nilsson, H.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Furtaana, Y.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Holmström, M.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Gérard, J-C
    Université de Liège.
    Protons and hydrogen atoms transport in the Martian upper atmosphere with an induced magnetic field2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A11320-Article in journal (Refereed)
    Abstract [en]

    We have applied the Direct Simulation Monte Carlo method to solve the kinetic equation for the H/H+ transport in the upper Martian atmosphere. We calculate the upward H and H+ fluxes, values that can be measured, and the altitude profile of the energy deposition to be used to understand the energy balance in the Martian atmosphere. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. We use an energy spectrum of the down moving protons in the altitude range 355–437 km adopted from the Mars Express Analyzer of Space Plasma and Energetic Atoms measurements in the range 700 eV–20 keV. The particle and energy fluxes of the downward moving protons were equal to 3.0 × 106 cm−2 s−1 and 1.4 × 10−2 erg cm−2 s−1. It was found that 22% of particle flux and 12% of the energy flux of the precipitating protons is backscattered by the Martian upper atmosphere, if no induced magnetic field is taken into account in the simulations. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85–500 km, we find that up to 40%–50% of the energy flux of the precipitating protons is backscattered depending on the velocity distribution of the precipitating protons. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.

  • 34.
    Shematovich, V.I.
    et al.
    Institute of Astronomy, Russian Academy of Sciences, Moscow.
    Bisikalo, D.V.
    Institute of Astronomy, Russian Academy of Sciences, Moscow.
    Stenberg, G.
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Barabash, Stas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dieval, Catherine
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Gérard, J-C
    LPAP, Université de Liège.
    He2+ transport in the Martian upper atmosphere with an induced magnetic field2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 3, p. 1231-1242Article in journal (Refereed)
    Abstract [en]

    Solar wind helium may be a significant source of neutral helium in the Martian atmosphere. The precipitating particles also transfer mass, energy, and momentum. To investigate the transport of He2+ in the upper atmosphere of Mars, we have applied the direct simulation Monte Carlo method to solve the kinetic equation. We calculate the upward He, He+, and He2+ fluxes, resulting from energy spectra of the downgoing He2+ observed below 500 km altitude by the Analyzer of Space Plasmas and Energetic Atoms 3 instrument onboard Mars Express. The particle flux of the downward moving He2+ ions was 1–2 × 106 cm–2 s–1, and the energy flux is equal to 9–10 × 10–3 erg cm–2 s–1. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. It was found, that if the induced magnetic field is not introduced in the simulations the precipitating He2+ ions are not backscattered at all by the Martian upper atmosphere. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85–500 km, we find that up to 30%–40% of the energy flux of the precipitating He2+ ions is backscattered depending on the velocity distribution of the precipitating particles. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.

  • 35.
    Slanger, Tom G.
    et al.
    Molecular Physics Laboratory, SRI International, Menlo Park.
    Cosby, P. C.
    Molecular Physics Laboratory, SRI International, Menlo Park.
    Huestis, D. L.
    Molecular Physics Laboratory, SRI International, Menlo Park.
    Saiz-Lopez, A.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Murray, B. J.
    School of Environmental Sciences, University of East Anglia, Norwich, Department of Chemistry, University of British Columbia, Vancouver.
    O'Sullivan, D. A.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Plane, J. M C
    School of Environmental Sciences, University of East Anglia, Norwich.
    Prieto, C. Allende
    McDonald Observatory, Department of Astronomy, University of Texas at Austin.
    Martin-Torres, Javier
    AS&M, Inc., NASA/Langley Research Center, Hampton.
    Jenniskens, P.
    NASA Ames Research Center.
    Variability of the mesospheric nightglow sodium D2/D1 ratio2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 110, no 23, p. 1-8, article id D23302Article in journal (Refereed)
    Abstract [en]

    Measurements of the intensity ratio of the 589.0/589.6 nm sodium doublet in the terrestrial nightglow over an 8-year period, involving >300 separate determinations, have established that it is variable, the value RD = I(D2)/I(D1) lying between 1.2 and 1.8. Sky spectra from the Keck I telescope with the High-Resolution Echelle Spectrometer (HIRES) échelle spectrograph and the Keck II telescope with the Échellette Spectrograph and Imager (ESI) échelle spectrograph were used in this analysis. The result contrasts with the accepted view, from earlier measurements at midlatitude, that the ratio is 2.0, as expected on statistical grounds. The lack of dependence of the ratio on viewing elevation angle, and hence Na slant column, allows self-absorption to be ruled out as a cause of the variability. The data suggest a semiannual oscillation in the ratio, maximum at the equinoxes and minimum at the solstices. Airborne measurements over the North Atlantic (40°-50°N) in 2002 show an even larger range in the nightglow ratio and no correlation with the upper mesospheric temperature determined from the OH 6-2 bands. A laboratory study confirms that the ratio does not depend on temperature; however, it is shown to be sensitive to the [O]/[O2] ratio. It is therefore postulated that the variable ratio arises from a competition between O reacting with NaO(A3∑+), produced from the reaction of Na with O3, to yield D-line emission with a D2/D1 ratio greater than about 2.0, and quenching by O2 to produce NaO(X2II), possibly with vibrational excitation, which then reacts with O to produce emission with a ratio of less than 1.3. Copyright 2005 by the American Geophysical Union.

  • 36.
    Slapak, Rikard
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Nilsson, Hans
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eriksson, Anders
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Observations of oxygen ions in the dayside magnetosheath associated with southward IMF2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    We present a case study of high energy oxygen ions (O+) observed in the dayside terrestrial magnetosheath, in the southern hemisphere. It is shown that the presence of O+ is strongly correlated to the IMF direction: O+ is observed only for Bz<0. Three satellites observe O$^+ immediately at both sides of the magnetopause and about 2 RE outside the magnetopause. These conditions indicate escape along open magnetic field lines. We show that if outflowing O+ is heated and accelerated sufficiently in the cusp, it takes 15-20 minutes for it to reach the magnetopause, allowing the ions to escape along newly opened field lines on the dayside. Earlier studies show evidence of strong heating and high velocities in the cusp and mantle at high altitudes, strengthening our interpretation. The observed magnetosheath O+ fluxes are of the same order as measured in the ionospheric upflow, which indicates that this loss mechanism is significant when it takes place.

  • 37.
    Smith, Anne K.
    et al.
    Atmospheric Chemistry Division, National Center for Atmospheric Research.
    Marsh, Daniel R.
    Atmospheric Chemistry Division, National Center for Atmospheric Research.
    Russell, James M.
    Center for Atmospheric Sciences, Hampton University.
    Mlynczak, Martin G.
    NASA Langley Research Center, Hampton.
    Martin-Torres, Javier
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, Analytical Services and Materials Inc., Hampton.
    Kyrölä, Erkki
    Finnish Meteorological Institute, Helsinki.
    Satellite observations of high nighttime ozone at the equatorial mesopause2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no 17, article id D17312Article in journal (Refereed)
    Abstract [en]

    Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18-50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large-amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars. Copyright 2008 by the American Geophysical Union.

  • 38.
    Takagi, M.
    et al.
    University of Tokyo, Deptartment of Earth & Planetary Science.
    Suzuki, K.
    Tokyo Gakugei University, Department of Astronomy & Earth Science.
    Sagawa, H.
    Max-Planck-Institut für Solar System Research.
    Baron, P.
    National Institute for Information & Communication Technology, Applied Electromagnet Research.
    Mendrok, Jana
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kasai, Y.
    National Institute for Information & Communication Technology, Applied Electromagnet Research.
    Matsuda, Y.
    Tokyo Gakugei University, Department of Astronomy & Earth Science.
    Influence of CO2 line profiles on radiative and radiative-convective equilibrium states of the Venus lower atmosphere2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no E06Article in journal (Refereed)
    Abstract [en]

    Influence of CO2 line profiles on vertical temperature distributions in the radiative and radiative-convective equilibria is examined in the Venus atmosphere. The CO2 opacity obtained by the Voigt (Lorentz) profile without the line cutoff is shown to be excessive since this opacity gives surface temperatures of about 860-1020 K in the radiative-convective equilibrium. On the other hand, the opacity obtained by the extremely sub-Lorentzian profiles of Pollack et al. (1993) and Tonkov et al. (1996) are underestimated; the surface temperature obtained with this opacity remains 600 K even in the radiative equilibrium. In this case, convection does not take place below the cloud layer because of the cloud opacity. It is also shown that Fukabori et al.' s (1986) and Meadows and Crisp's (1996) profiles, both of which have intermediate absorption coefficients, give temperature distributions close to the observed one in the radiative-convective equilibrium. In these cases, the convection layer extends from the surface to 30-50 km altitudes. Then, the temperature distribution below the cloud layer is determined by a dry adiabatic lapse rate and the temperature near the cloud bottom. The surface temperature in the radiative-convective equilibrium is strongly affected by the temperature near the cloud bottom in this situation. The detailed structure of the H2SO4 cloud must be taken into account to construct a realistic radiative transfer model.

  • 39.
    Thapliyal, Pradeep K.
    et al.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Shukla, Munn V.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Shah, Shivani
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Joshi, P.C.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Pal, P.K.
    Atmospheric and Oceanic Sciences Group, Space Applications Centre, Indian Space Research Organisation, Ahmedabad.
    Kottayil, Ajil
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    An algorithm for the estimation of upper tropospheric humidity from Kalpana observations: Methodology and validation2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no 1Article in journal (Refereed)
    Abstract [en]

    This study presents a methodology for estimating the upper tropospheric humidity (UTH) for a layer between 500 and 200 hPa from observations in the water vapor channel (5.6–7.2 μm) of the Indian geostationary satellite, Kalpana. Radiative transfer simulations for different UTH conditions have been used to develop the relationship between water vapor channel radiances and UTH. A new technique has been described to include the normalized reference pressure in the algorithm, to account for latitudinal variation of temperature that is derived from a diverse radiosonde profiles data set and is a polynomial function of the latitude for different months. This has an advantage that the forecast or analysis profiles from the operational numerical weather prediction model are not required to compute the normalized reference pressure. The operationally retrieved UTH products have been extensively compared and validated for the period of 1 March to 1 May 2009, using Meteosat-7 UTH products over the Indian Ocean and the UTH computed from the radiosonde profiles. The results suggest that UTH estimates from Kalpana match very well with the Meteosat-7 UTH products having RMS difference of ∼6%. Validation with the UTH computed from the radiosonde observed relative humidity shows that the RMS error of Kalpana UTH is 9.6% and the mean bias is −3.0%. Similar validation of Meteosat-7 UTH with the same set of radiosonde derived UTH shows an RMS error of 13.3% and the bias of −6.5%, which is higher in comparison to the Kalpana UTH.

  • 40.
    Verdes, C.
    et al.
    Universität Bremen, Institute of Remote sensing.
    Buehler, Stefan
    Engeln, Axel von
    Universität Bremen, Institute of Remote sensing.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Universität Bremen, Institute of Environmental Physics.
    Kuenzi, K.
    Universität Bremen, Institute of Remote sensing.
    Eriksson, Patrick
    Chalmers University of Technology, Department of Radio and Space Science, Gothenburg.
    Sinnhuber, Björn-Martin
    University of Leeds, School of the Environment.
    Pointing and temperature retrieval from millimeter-submillimeter limb soundings2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no 16, p. 4299-Article in journal (Refereed)
    Abstract [en]

    Passive microwave limb sounding instruments like the Millimeter-Wave Atmospheric Sounder (MAS) or the Microwave Limb Sounder (MLS) observe dedicated oxygen lines for the derivation of temperature and pointing information, since these quantities are essential for the quality of the retrieval of the trace gas mixing ratio. Emission lines of oxygen are chosen because the volume mixing ratio (VMR) profile is known. In this paper, we demonstrate the capabilities of a new and innovative method by means of which accurate temperature and pointing information can be gathered from other strong spectral features like ozone lines, without including accurate knowledge of the VMR profile of these species. For this purpose, retrievals from two observation bands with a bandwidth of about 10 GHz each, one including an oxygen line, have been compared. A full error analysis was performed with respect to critical instrument and model parameters, such as uncertainties in the antenna pattern, calibration uncertainties, random pointing error, baseline ripples, baseline discontinuities, and spectroscopic parameters. The applied inversion algorithm was the optimal estimation method. For the selected scenario and instrumental specifications we find that the retrieval of a pointing offset and the atmospheric temperature profile can be achieved with a good accuracy. The retrieval precision of the pointing offset is better than 24 m. The retrieval precision of the temperature profile is better than 2 K for altitudes ranging from 10 to 40 km. Systematic errors (due to model parameter uncertainties) are somewhat larger than these purely statistical errors. Investigations carried out for different atmospheric states or different instrumental specifications show similar results.

  • 41.
    Westerberg, Lars-Göran
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Åkerstedt, Hans
    Nilsson, Hans
    Swedish Institute of Space Physics / Institutet för rymdfysik.
    Rème, Henri
    CESR, Toulouse.
    Balogh, Andre
    Imperial College.
    3D MHD reconnection model coupled with Cluster multi-spacecraft data: 3D reconnection model2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113Article in journal (Refereed)
    Abstract [en]

    We present a model where a three-dimensional viscous/resistive analytical model of the large scale plasma flow in the outflow region about a reconnection site at the dayside magnetopause, is coupled with multi-spacecraft measurements from the Cluster satellite armada. A total of ten magnetopause crossings have been analyzed during the period 10:29-11:05 UT January 26, 2001, where nine are shown to be suitable to be coupled with the analytical model. Five of these nine reconnection events results in a successful coupling. By fitting the analytical expressions of the plasma velocity and magnetic field behaviour during the transition of the magnetopause, with data from the Cluster spacecraft we obtain estimates of the location of the X-line together with estimates on the anomalous transport coeffcients of kinematic viscosity (v) and magnetic diffusivity (ηd). We also obtain the development of the magnetopause transition layer away from the X-line. It is shown that the distance from the spacecraft to the X-line varies between 0.01 and 1 Earth radii, while v + ηd have a value between 4 . 104 km2/ s and 4 . 106 km2/ s. Furthermore it is shown that the transition layer thickness follows the analytical pattern where it grows proportional to the square root of the distance from the reconnection site. The estimated thickness obtained from each spacecraft is shown to follow the analytical structure well.

  • 42.
    Zhang, Ping
    et al.
    Department of Geophysics, Uppsala University.
    Rasmussen, Thorkild Maack
    Department of Geophysics, Uppsala University.
    Pedersen, Laust Börsting
    Department of Geophysics, Uppsala University.
    Electric resistivity structure of the Siljan impact region ( Sweden)1988In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 93, no B6, p. 6485-6501Article in journal (Refereed)
    Abstract [en]

    Based on 65 magnetotelluric (MT) measuring stations, a cross section of the electric conductivity structure in the Siljan impact area, located in the central part of Sweden, is presented. Static shift effects due to local near-surface inhomogeneities are present in nearly all of the MT soundings.In an attempt to correct for near-surface distortions, average impedance data and distortion parameters were interpreted. Derived 2-D models show some coincidence with seismic reflection results and support an impact origin of the Siljan area. Fluid migration through the fractures generated by the impact is one possible explanation for the anomalously high conductivity within the upper crust

  • 43.
    Zhou, X-Z
    et al.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Angelopoulos, V.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Poppe, A.R.
    Space Science Laboratory, University of California, Berkeley.
    Halekas, J.S.
    Space Science Laboratory, University of California, Berkeley.
    Khurana, K.K.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Kivelson, M.G.
    Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles.
    Fatemi, Shahab
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Holmström, Mats
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Lunar dayside current in the terrestrial lobe: ARTEMIS observations2014In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 5, p. 3381-3391Article in journal (Refereed)
    Abstract [en]

    We report Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) dual-probe observations of two events in the terrestrial magnetotail lobe, both characterized by upward moving heavy ions of lunar origin at one of the probes that is magnetically connected with the dayside lunar surface. By treating magnetic measurements at the other probe as the unperturbed lobe fields, we obtain background-subtracted magnetic perturbations (most significantly in Bz) when the first probe moved in the dawn-dusk direction across flux tubes magnetically connected to the Moon. These magnetic perturbations indicate the presence of field-aligned current above the lunar surface. By examining possible carriers of field-aligned current, we find that lunar heavy ions and accompanying electrons both contribute considerably to the current. Observations of the field-aligned current also suggest that the charging process at the dayside lunar surface and the associated lobe plasma environment, which have traditionally been viewed as a one-dimensional current balance problem, are actually more complicated. These observations give the first insights into how heavy ions affect the lunar dayside environment in terms of multispecies plasma dynamics.

1 - 43 of 43
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