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Nilsson, Hans
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Publications (10 of 30) 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: 2019-08-15Bibliographically 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
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
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
Behar, E., Tabone, B. & Nilsson, H. (2018). Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko. Monthly notices of the Royal Astronomical Society, 478(2), 1570-1575
Open this publication in new window or tab >>Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 2, p. 1570-1575Article in journal (Refereed) Published
Abstract [en]

When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.

Place, publisher, year, edition, pages
Royal Astronomical Society, 2018
National Category
Fusion, Plasma and Space Physics Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-68782 (URN)10.1093/mnras/sty1111 (DOI)000439547400010 ()2-s2.0-85048857464 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-06-19 (andbra)

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-08-09Bibliographically approved
Yamauchi, M., Sergienko, T., Enell, C.-F., Schillings, A., Slapak, R., Johnsen, M. G., . . . Nilsson, H. (2018). Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview. Space Weather: The international journal of research and applications, 16(9), 1437-1450
Open this publication in new window or tab >>Ionospheric Response Observed by EISCAT During the 6–8 September 2017 Space Weather Event: Overview
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2018 (English)In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, no 9, p. 1437-1450Article in journal (Refereed) Published
Abstract [en]

We present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner magnetosphere, and an AL < −2,000 substorm took place. (1) Both X flares caused enhancement of ionospheric electron density for about 10 min. The X9.3 flare also increased temperatures of both electrons and ions over 69°–75° geomagnetic latitude until the X‐ray flux decreased below the level of X‐class flares. However, the temperature was not enhanced after the previous X2.2 flare in the prenoon sector. (2) At around 75° geomagnetic latitude, the prenoon ion upflow flux slightly increased the day after the X9.3 flare, which is also after the first ICME and a SEP event, while no outstanding enhancement was found at the time of these X flares. (3) The upflow velocity sometimes decreased when the interplanetary magnetic field (IMF) turned southward. (4) Before the first ICME arrival after the SEP event under weak IMF with Bz ~0 nT, a substorm‐like expansion of the auroral arc signature took place without local geomagnetic signature near local midnight, while no notable change was observed after the ICME arrival. (5) AL reached <−2,000 nT only after the arrival of the second ICME with strongly southward IMF. Causality connections between the solar/solar wind event and the ionospheric responses remain unclear.

Place, publisher, year, edition, pages
John Wiley & Sons, 2018
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-71230 (URN)10.1029/2018SW001937 (DOI)2-s2.0-85053439748 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-18 (johcin) 

Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2019-03-27Bibliographically approved
Schillings, A., Nilsson, H., Slapak, R., Wintoft, P., Yamauchi, M., Wik, M., . . . Carr, C. (2018). O+ Escape During the Extreme Space Weather Event of 4–10 September 2017. Space Weather: The international journal of research and applications, 16(9), 1363-1376
Open this publication in new window or tab >>O+ Escape During the Extreme Space Weather Event of 4–10 September 2017
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2018 (English)In: Space Weather: The international journal of research and applications, ISSN 1542-7390, E-ISSN 1542-7390, Vol. 16, no 9, p. 1363-1376Article in journal (Refereed) Published
Abstract [en]

We have investigated the consequences of extreme space weather on ion outflow from the polar ionosphere by analyzing the solar storm that occurred early September 2017, causing a severe geomagnetic storm. Several X-flares and coronal mass ejections were observed between 4 and 10 September. The first shock—likely associated with a coronal mass ejection—hit the Earth late on 6 September, produced a storm sudden commencement, and began the initial phase of the storm. It was followed by a second shock, approximately 24 hr later, that initiated the main phase and simultaneously the Dst index dropped to Dst = −142 nT and Kp index reached Kp = 8. Using COmposition DIstribution Function data on board Cluster satellite 4, we estimated the ionospheric O+ outflow before and after the second shock. We found an enhancement in the polar cap by a factor of 3 for an unusually high ionospheric O+ outflow (mapped to an ionospheric reference altitude) of 1013 m−2 s−1. We suggest that this high ionospheric O+ outflow is due to a preheating of the ionosphere by the multiple X-flares. Finally, we briefly discuss the space weather consequences on the magnetosphere as a whole and the enhanced O+ outflow in connection with enhanced satellite drag.

Place, publisher, year, edition, pages
Blackwell Publishing, 2018
National Category
Aerospace Engineering
Research subject
Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-71026 (URN)10.1029/2018SW001881 (DOI)2-s2.0-85053442508 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-10-17 (johcin) 

Available from: 2018-09-28 Created: 2018-09-28 Last updated: 2018-10-17Bibliographically approved
Behar, E., Tabone, B., Saillenfest, M., Henri, P., Deca, J., Lindkvist, J., . . . Nilsson, H. (2018). Solar wind dynamics around a comet: A 2D semi-analytical kinetic model. Astronomy and Astrophysics, 620, Article ID A35.
Open this publication in new window or tab >>Solar wind dynamics around a comet: A 2D semi-analytical kinetic model
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, article id A35Article in journal (Refereed) Published
Abstract [en]

Aims.We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometaryatmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics.Methods.We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-stateis assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced byindividual solar wind protons during the interaction.Results.A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to acomet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar winddeflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular regionis found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, togetherwith the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of theRosettamission.Conclusions.The qualitative match between the model and thein situdata highlights how dominant the motional electric field isthroughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic descriptionof how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical modelfor a systematic quantitative comparison to the data.

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-68781 (URN)10.1051/0004-6361/201832736 (DOI)000451249600003 ()2-s2.0-85051991586 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-12-05 (svasva)

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2019-01-10Bibliographically approved
Schillings, A., Slapak, R., Nilsson, H., Yamauchi, M. & Westerberg, L.-G. (2017). Atmospheric loss during major geomagnetic storms: Cluster observations. In: : . Paper presented at European Geosciences Union General Assembly 2017, Vienna, Austria, 23-28 April 2017.
Open this publication in new window or tab >>Atmospheric loss during major geomagnetic storms: Cluster observations
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2017 (English)Conference paper, Oral presentation with published abstract (Refereed)
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Research subject
Fluid Mechanics; Atmospheric science
Identifiers
urn:nbn:se:ltu:diva-62336 (URN)
Conference
European Geosciences Union General Assembly 2017, Vienna, Austria, 23-28 April 2017
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-11-24Bibliographically approved
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