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Nilsson, Hans
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Publications (10 of 35) Show all publications
Schillings, A., Slapak, R., Nilsson, H., Yamauchi, M., Dandouras, I. & Westerberg, L.-G. (2019). Earth atmospheric loss through the plasma mantle and its dependence on solar wind parameters. Earth, Planets and Space, 71(70)
Open this publication in new window or tab >>Earth atmospheric loss through the plasma mantle and its dependence on solar wind parameters
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2019 (English)In: Earth, Planets and Space, Vol. 71, no 70Article in journal (Refereed) Published
Abstract [en]

Atmospheric loss and ion outfow play an important role in the magnetospheric dynamics and in the evolution of the atmosphere on geological timescales—an evolution which is also dependent on the solar activity. In this paper, we investigate the total O+ outfow [s−1 ] through the plasma mantle and its dependency on several solar wind param‑ eters. The oxygen ion data come from the CODIF instrument on board the spacecraft Cluster 4 and solar wind data from the OMNIWeb database for a period of 5 years (2001–2005). We study the distribution of the dynamic pressure and the interplanetary magnetic feld for time periods with available O+ observations in the plasma mantle. We then divided the data into suitably sized intervals. Additionally, we analyse the extreme ultraviolet radiation (EUV) data from the TIMED mission. We estimate the O+ escape rate [ions/s] as a function of the solar wind dynamic pressure, the interplanetary magnetic feld (IMF) and EUV. Our analysis shows that the O+ escape rate in the plasma mantle increases with increased solar wind dynamic pressure. Consistently, it was found that the southward IMF also plays an important role in the O+ escape rate in contrast to the EUV fux which does not have a signifcant infuence for the plasma mantle region. Finally, the relation between the O+ escape rate and the solar wind energy transferred into the magnetosphere shows a nonlinear response. The O+ escape rate starts increasing with an energy input of approxi‑ mately 1011W.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
O+ outfow/escape, Plasma mantle, Solar wind, Interplanetary magnetic feld (IMF), Extreme ultraviolet (EUV), Coupling functions
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Atmospheric science; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-74886 (URN)10.1186/s40623-019-1048-0 (DOI)000472492500001 ()2-s2.0-85067844890 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-15 (johcin)

Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-10-11Bibliographically approved
Schillings, A., Slapak, R., Nilsson, H., Yamauchi, M., Dandouras, I. & Westerberg, L.-G. (2019). Earth atmospheric loss through the plasma mantle and its dependence onsolar wind parameters. In: : . Paper presented at EGU General Assembly 2019, 7–12 April 2019, Vienna, Austria.
Open this publication in new window or tab >>Earth atmospheric loss through the plasma mantle and its dependence onsolar wind parameters
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2019 (English)Conference paper (Refereed)
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Atmospheric science; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-73466 (URN)
Conference
EGU General Assembly 2019, 7–12 April 2019, Vienna, Austria
Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-04-05Bibliographically approved
Alho, M., Wedlund, C. S., Nilsson, H., Kallio, E., Jarvinen, R. & Pulkkinen, T. (2019). Hybrid modeling of cometary plasma environments: II. Remote-sensing of a cometary bow shock. Astronomy and Astrophysics, 630, Article ID A45.
Open this publication in new window or tab >>Hybrid modeling of cometary plasma environments: II. Remote-sensing of a cometary bow shock
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A45Article in journal (Refereed) Published
Abstract [en]

Context. The ESA Rosetta probe has not seen direct evidence of a fully formed bow shock at comet 67P/Churyumov–Gerasimenko (67P). Ion spectrometer measurements of cometary pickup ions measured in the vicinity of the nucleus of 67P are available and may contain signatures of the large-scale plasma environment.

Aims. The aim is to investigate the possibility of using pickup ion signatures to infer the existence or nonexistence of a bow shock-like structure and possibly other large-scale plasma environment features.

Methods. A numerical plasma model in the hybrid plasma description was used to model the plasma environment of a comet. Simulated pickup ion spectra were generated for different interplanetary magnetic field conditions. The results were interpreted through test particle tracing in the hybrid simulation solutions.

Results. Features of the observed pickup ion energy spectrum were reproduced, and the model was used to interpret the observation to be consistent with a shock-like structure. We identify (1) a spectral break related to the bow shock, (2) a mechanism for generating the spectral break, and (3) a dependency of the energy of the spectral break on the interplanetary magnetic field magnitude and bow shock standoff distance.

Place, publisher, year, edition, pages
EDP Sciences, 2019
Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, methods: numerical / plasmas / shock waves, techniques: miscellaneous
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-76347 (URN)10.1051/0004-6361/201834863 (DOI)000486989400044 ()
Note

Validerad;2019;Nivå 2;2019-10-10 (johcin)

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10Bibliographically approved
Wedlund, C. S., Bodewits, D., Alho, M., Hoekstra, R., Behar, E., Gronoff, G., . . . Beth, A. (2019). Solar wind charge exchange in cometary atmospheres: I. Charge-changing and ionization cross sections for He and H particles in H2O. Astronomy and Astrophysics, 630, Article ID A35.
Open this publication in new window or tab >>Solar wind charge exchange in cometary atmospheres: I. Charge-changing and ionization cross sections for He and H particles in H2O
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A35Article in journal (Refereed) Published
Abstract [en]

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet, mass-loading the solar wind through an effective conversion of fast light solar wind ions into slow heavy cometary ions.

Aims. To understand these processes and place them in the context of a solar wind plasma interacting with a neutral atmosphere, numerical or analytical models are necessary. Inputs of these models, such as collision cross sections and chemistry, are crucial.

Methods. Book-keeping and fitting of experimentally measured charge-changing and ionization cross sections of hydrogen and helium particles in a water gas are discussed, with emphasis on the low-energy/low-velocity range that is characteristic of solar wind bulk speeds (<20 keV u−1/2000 km s−1).

Results. We provide polynomial fits for cross sections of charge-changing and ionization reactions, and list the experimental needs for future studies. To take into account the energy distribution of the solar wind, we calculated Maxwellian-averaged cross sections and fitted them with bivariate polynomials for solar wind temperatures ranging from 105 to 106 K (12–130 eV).

Conclusions. Single- and double-electron captures by He2+ dominate at typical solar wind speeds. Correspondingly, single-electron capture by H+ and single-electron loss by H dominate at these speeds, resulting in the production of energetic neutral atoms (ENAs). Ionization cross sections all peak at energies above 20 keV and are expected to play a moderate role in the total ion production. However, the effect of solar wind Maxwellian temperatures is found to be maximum for cross sections peaking at higher energies, suggesting that local heating at shock structures in cometary and planetary environments may favor processes previously thought to be negligible. This study is the first part in a series of three on charge exchange and ionization processes at comets, with a specific application to comet 67P/Churyumov-Gerasimenko and the Rosetta mission.

Place, publisher, year, edition, pages
EDP Sciences, 2019
Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, instrumentation: detectors / solar wind, methods: data analysis / plasmas
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-76348 (URN)10.1051/0004-6361/201834848 (DOI)000486989400034 ()
Note

Validerad;2019;Nivå 2;2019-10-10 (johcin)

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10Bibliographically approved
Wedlund, C. S., Behar, E., Kallio, E., Nilsson, H., Alho, M., Gunell, H., . . . Hoekstra, R. (2019). Solar wind charge exchange in cometary atmospheres: II. Analytical model. Astronomy and Astrophysics, 630, Article ID A36.
Open this publication in new window or tab >>Solar wind charge exchange in cometary atmospheres: II. Analytical model
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A36Article in journal (Refereed) Published
Abstract [en]

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided a unique opportunity to study charge-changing processes in situ.

Aims. To understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

Methods. An extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. It is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas.

Results. After presenting a general 1D solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (He2+, He+, He0) and (H+, H0, H) on solar wind parameters at comet 67P. We show that double charge exchange for the He2+−H2O system plays an important role below a solar wind bulk speed of 200 km s−1, resulting in the production of He energetic neutral atoms, whereas stripping reactions can in general be neglected. Retrievals of outgassing rates and solar wind upstream fluxes from local Rosetta measurements deep in the coma are discussed. Solar wind ion temperature effects at 400 km s−1 solar wind speed are well contained during the Rosetta mission.

Conclusions. As the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of Rosetta, forming in effect a solar wind ion cavity. This study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67P and the Rosetta mission.

Place, publisher, year, edition, pages
EDP Sciences, 2019
Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, instrumentation: detectors / waves / solar wind, methods: analytical
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-76349 (URN)10.1051/0004-6361/201834874 (DOI)000486989400035 ()
Note

Validerad;2019;Nivå 2;2019-10-10 (johcin)

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10Bibliographically approved
Wedlund, C. S., Behar, E., Nilsson, H., Alho, M., Kallio, E., Gunell, H., . . . Hoekstra, R. (2019). Solar wind charge exchange in cometary atmospheres: III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 630, Article ID A37.
Open this publication in new window or tab >>Solar wind charge exchange in cometary atmospheres: III. Results from the Rosetta mission to comet 67P/Churyumov-Gerasimenko
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2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 630, article id A37Article in journal (Refereed) Published
Abstract [en]

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ.

Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.

Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas.

Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions.

Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

Place, publisher, year, edition, pages
EDP Sciences, 2019
Keywords
comets: general, comets: individual: 67P/Churyumov-Gerasimenko, instrumentation: detectors, solar wind, methods: analytical, plasmas
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-76342 (URN)10.1051/0004-6361/201834881 (DOI)000486989400036 ()
Note

Validerad;2019;Nivå 2;2019-10-10 (johcin)

Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10Bibliographically approved
Edberg, N. J. T., Eriksson, A. I., Vigren, E., Johansson, F. L., Goetz, C., Nilsson, H., . . . Henri, P. (2019). The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P. Astronomical Journal, 158(2), Article ID 71.
Open this publication in new window or tab >>The Convective Electric Field Influence on the Cold Plasma and Diamagnetic Cavity of Comet 67P
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2019 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 158, no 2, article id 71Article in journal (Refereed) Published
Abstract [en]

We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov–Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the Langmuir Probe instrument and the direction of the convective electric field  conv = − ×  was determined from magnetic field () measurements inside the coma combined with an assumption of a purely radial solar wind velocity . We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the − convhemisphere) compared to when it is away from the nucleus (in the + conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the − conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2019
Keywords
comets, individual (67P), magnetic fields, plasmas, space vehicles, instruments
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-75579 (URN)10.3847/1538-3881/ab2d28 (DOI)000476604700001 ()
Note

Validerad;2019;Nivå 2;2019-08-19 (johcin)

Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2019-08-19Bibliographically approved
Schillings, A., Gunell, H., Nilsson, H., De Spiegeleer, A., Ebihara, Y., Westerberg, L.-G., . . . Slapak, R. (2019). The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations. Annales Geophysicae
Open this publication in new window or tab >>The fate of O+ ions observed in the plasma mantle and cusp: particle tracing modelling and Cluster observations
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2019 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Article in journal (Refereed) Submitted
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:ltu:diva-76359 (URN)
Available from: 2019-10-11 Created: 2019-10-11 Last updated: 2019-10-17
Berecic, L., Behar, E., Nilsson, H., Nicolaou, G., Stenberg-Wieser, G., Wieser, M. & Goetz, C. (2018). Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period. Astronomy and Astrophysics, 613, 1-8
Open this publication in new window or tab >>Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

Place, publisher, year, edition, pages
EDP Sciences, 2018
National Category
Fusion, Plasma and Space Physics Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-68784 (URN)10.1051/0004-6361/201732082 (DOI)000433880200003 ()
Note

Validerad;2018;Nivå 2;2018-06-14 (andbra)

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-06-21Bibliographically approved
Slapak, R., Schillings, A., Nilsson, H., Yamauchi, M. & Westerberg, L.-G. (2018). Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,2017 [Letter to the editor]. Annales Geophysicae
Open this publication in new window or tab >>Corrigendum to Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: Implications for atmospheric escape on evolutionary time scales, published in Ann. Geophys., 35, 721–731,2017
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2018 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576Article in journal, Letter (Refereed) Published
Place, publisher, year, edition, pages
Copernicus Publications, 2018
National Category
Aerospace Engineering Fluid Mechanics and Acoustics
Research subject
Atmospheric science; Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-68587 (URN)10.5194/angeo-35-721-2017-corrigendum (DOI)
Available from: 2018-05-02 Created: 2018-05-02 Last updated: 2018-11-20Bibliographically approved
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