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  • 51. Mailyan, B.
    et al.
    Shi, Q. Q.
    Kullen, Anita
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Maggiolo, R.
    Zhang, Y.
    Fear, R. C.
    Zong, Q. -G
    Fu, S. Y.
    Gou, X. C.
    Cao, X.
    Yao, Z. H.
    Sun, W. J.
    Wei, Y.
    Pu, Z. Y.
    Transpolar arc observation after solar wind entry into the high-latitude magnetosphere2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 5, s. 3525-3534Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, Cluster observations have revealed the presence of new regions of solar wind plasma entry at the high-latitude magnetospheric lobes tailward of the cusp region, mostly during periods of northward interplanetary magnetic field. In this study, observations from the Global Ultraviolet Imager (GUVI) experiment on board the TIMED spacecraft and Wideband Imaging Camera imager on board the IMAGE satellite are used to investigate a possible link between solar wind entry and the formation of transpolar arcs in the polar cap. We focus on a case when transpolar arc formation was observed twice right after the two solar wind entry events were detected by the Cluster spacecraft. In addition, GUVI and IMAGE observations show a simultaneous occurrence of auroral activity at low and high latitudes after the second entry event, possibly indicating a two-part structure of the continuous band of the transpolar arc.

  • 52. Matsui, H.
    et al.
    Torbert, R. B.
    Spence, H. E.
    Argall, M. R.
    Alm, L.
    Farrugia, C. J.
    Kurth, W. S.
    Baker, D. N.
    Blake, J. B.
    Funsten, H. O.
    Reeves, G. D.
    Ergun, R. E.
    Khotyaintsev, Yu. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Relativistic Electron Increase During Chorus Wave Activities on the 6-8 March 2016 Geomagnetic Storm2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 11, s. 11302-11319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There was a geomagnetic storm on 6-8 March 2016, in which Van Allen Probes A and B separated by similar to 2.5 h measured increase of relativistic electrons with energies approximately several hundred keV to 1 MeV. Simultaneously, chorus waves were measured by both Van Allen Probes and Magnetospheric Multiscale (MMS) mission. Some of the chorus elements were rising tones, possibly due to nonlinear effects. These measurements are compared with a nonlinear theory of chorus waves incorporating the inhomogeneity ratio and the field equation. From this theory, a chorus wave profile in time and one-dimensional space is simulated. Test particle calculations are then performed in order to examine the energization rate of electrons. Some electrons are accelerated, although more electrons are decelerated. The measured time scale of the electron increase is inferred to be consistent with this nonlinear theory.

  • 53. Musacchio, Fabrizio
    et al.
    Saur, Joachim
    Roth, Lorenz
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Retherford, Kurt D.
    McGrath, Melissa A.
    Feldman, Paul D.
    Strobel, Darrell F.
    Morphology of Ganymede's FUV auroral ovals2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 3, s. 2855-2876Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the morphology of Ganymede's FUV aurora by analyzing spectral images obtained over the past two decades by the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. The observations cover the eastern and western elongation as well as various magnetic latitudes of Ganymede within the Jovian plasma sheet. We find both asymmetries in the spatial distribution of auroral brightness on the observed moon disk and temporal variation correlated to Ganymede's changing magnetic latitude. The total disk brightness is on average 1.42 +/- 0.07 times brighter on the leading side (95.4 +/- 2.1R) than on the trailing side (67.2 +/- 2.9R). The brightness ratio of the sub-Jovian hemisphere to the anti-Jovian hemisphere is 1.81 +/- 0.06 on the leading side and 1.41 +/- 0.14 on the trailing side, respectively. Inside the Jovian current sheet, the brightness of the auroral ovals increases by a factor of 1.45 +/- 0.02 on the leading side and decreases by a factor of 0.80 +/- 0.02 on the trailing side. At the current sheet center, the auroral ovals shift 4.1 degrees +/- 0.7 degrees latitude toward Ganymede's planetographic equator on the leading side and 2.9 degrees +/- 1.5 degrees toward the poles on the trailing side. Both effects, the variation of brightness and the movement of the ovals are correlated to a stronger interaction of Jupiter's magnetospheric plasma with Ganymede's minimagnetosphere inside the current sheet. Finally, we calculate the latitudinal difference of the northern and southern ovals from Ganymede's magnetic equator. The result suggests a farther westward orientation of Ganymede's dipole magnetic moment at approximately 47 degrees + 58 degrees/-43 degrees west longitude compared to previous estimates.

  • 54.
    Nakamura, Rumi
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Genestreti, Kevin J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria.;Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA..
    Naltamora, Takuma
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Varsani, Ali
    Univ Coll London, Mullard Space Sci Lab, Dorking, Surrey, England..
    Nagai, Tsugunobu
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Bessho, Naoki
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Denton, Richard E.
    Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA..
    Eastwood, Jonathan P.
    Imperial Coll London, Blackett Lab, London, England..
    Ergun, Robert E.
    Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO USA..
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, Arbara L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Hasegaw, Iroshi
    Japan Aerosp Explorat Agcy, Inst Space & Astronaut Sci, Sagamihara, Kanagawa, Japan..
    Hesse, Michael
    Univ Bergen, Dept Phys & Technol, Bergen, Norway..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Russell, Hristopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Stawarz, Ulia E.
    Imperial Coll London, Blackett Lab, London, England..
    Strangeway, Robert J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Torber, Roy B.
    Univ New Hampshire, Space Sci Ctr, Durham, NH 03824 USA.;Southwest Res Inst, San Antonio, TX USA..
    Structure of the Current Sheet in the 11 July 2017 Electron Diffusion Region Event2019Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 2, s. 1173-1186Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The structure of the current sheet along the Magnetospheric Multiscale (MMS) orbit is examined during the 11 July 2017 Electron Diffusion Region (EDR) event. The location of MMS relative to the X-line is deduced and used to obtain the spatial changes in the electron parameters. The electron velocity gradient values are used to estimate the reconnection electric field sustained by nongyrotropic pressure. It is shown that the observations are consistent with theoretical expectations for an inner EDR in 2-D reconnection. That is, the magnetic field gradient scale, where the electric field due to electron nongyrotropic pressure dominates, is comparable to the gyroscale of the thermal electrons at the edge of the inner EDR. Our approximation of the MMS observations using a steady state, quasi-2-D, tailward retreating X-line was valid only for about 1.4 s. This suggests that the inner EDR is localized; that is, electron outflow jet braking takes place within an ion inertia scale from the X-line. The existence of multiple events or current sheet processes outside the EDR may play an important role in the geometry of reconnection in the near-Earth magnetotail. Plain Language Summary Magnetic reconnection is the process by which magnetic field lines coming from one region are broken and reconnected with magnetic field lines coming from another region. The simplest descriptions of magnetic reconnection are two dimensional, and a number of theoretical predictions have been made using the two-dimensional assumption. We study a magnetic reconnection event observed by the Magnetospheric Multiscale spacecraft on 11 July 2017 and find approximate agreement between the observations and the predictions of a two-dimensional model. The agreement includes the scale size of the reconnection region, details of the particle orbits, and the rate of reconnection.

  • 55.
    Nakamura, Rumi
    et al.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Varsani, Ali
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Genestreti, Kevin J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Le Contel, Olivier
    UPMC Univ Paris 06, Univ Paris Sud, Observ Paris, Ecole Polytech,CNRS,Lab Phys Plasmas, Paris, France..
    Nakamura, Takuma
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Baumjohann, Wolfgang
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Nagai, Tsugunobu
    Tokyo Inst Technol, Earth & Planetary Sci, Tokyo, Japan..
    Artemyev, Anton
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Birn, Joachim
    Space Sci Inst, Boulder, CO USA..
    Sergeev, Victor A.
    St Petersburg State Univ, Earths Phys Dept, St Petersburg, Russia..
    Apatenkov, Sergey
    St Petersburg State Univ, Earths Phys Dept, St Petersburg, Russia..
    Ergun, Robert E.
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Fuselier, Stephen A.
    Southwest Res Inst, San Antonio, TX USA..
    Gershman, Daniel J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, Barbara J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Khotyaintsev, Yuri V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Magnes, Werner
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Mauk, Barry
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Petrukovich, Anatoli
    RAS, Space Res Inst IKI, Moscow, Russia..
    Russell, Christopher T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Stawarz, Julia
    Imperial Coll London, Dept Phys, London, England..
    Strangeway, Robert J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Anderson, Brian
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Burch, James L.
    Southwest Res Inst, San Antonio, TX USA..
    Bromund, Ken R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Cohen, Ian
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Fischer, David
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Jaynes, Allison
    Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80309 USA..
    Kepko, Laurence
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le, Guan
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Plaschke, Ferdinand
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Reeves, Geoff
    CSES, LANL, Los Alamos, NM USA..
    Singer, Howard J.
    NOAA, Space Weather Predict Ctr, Boulder, CO USA..
    Slavin, James A.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Torbert, Roy B.
    Southwest Res Inst, San Antonio, TX USA.;Univ New Hampshire, Inst Study Earth Oceans & Space, Durham, NH 03824 USA..
    Turner, Drew L.
    Aerosp Corp, Space Sci Dept, POB 92957, Los Angeles, CA 90009 USA..
    Multiscale Currents Observed by MMS in the Flow Braking Region2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 2, s. 1260-1278Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold ExB drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

  • 56. Nilsson, Hans
    et al.
    Hamrin, Maria
    Pitkanen, Timo
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Slapak, Rikard
    Andersson, Laila
    Gunell, Herbert
    Schillings, Audrey
    Vaivads, Andris
    Oxygen ion response to proton bursty bulk flows2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 8, s. 7535-7546Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have used Cluster spacecraft data from the years 2001 to 2005 to study how oxygen ions respond to bursty bulk flows (BBFs) as identified from proton data. We here define bursty bulk flows as periods of proton perpendicular velocities more than 100 km/s and a peak perpendicular velocity in the structure of more than 200 km/s, observed in a region with plasma beta above 1 in the near-Earth central tail region. We find that during proton BBFs only a minor increase in the O+ velocity is seen. The different behavior of the two ion species is further shown by statistics of H+ and O+ flow also outside BBFs: For perpendicular earthward velocities of H+ above about 100 km/s, the O+ perpendicular velocity is consistently lower, most commonly being a few tens of kilometers per second earthward. In summary, O+ ions in the plasma sheet experience less acceleration than H+ ions and are not fully frozen in to the magnetic field. Therefore, H+ and O+ motion is decoupled, and O+ ions have a slower earthward motion. This is particularly clear during BBFs. This may add further to the increased relative abundance of O+ ions in the plasma sheet during magnetic storms. The data indicate that O+ is typically less accelerated in association with plasma sheet X lines as compared to H+.

  • 57.
    Norgren, C.
    et al.
    Univ Bergen, Birkeland Ctr Space Sci, Dept Phys & Technol, Bergen, Norway.;Swedish Inst Space Phys, Uppsala, Sweden..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Khotyaintsev, Yu, V
    Swedish Inst Space Phys, Uppsala, Sweden..
    Andre, M.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Vaivads, A.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Hesse, M.
    Univ Bergen, Birkeland Ctr Space Sci, Dept Phys & Technol, Bergen, Norway..
    Eriksson, E.
    Swedish Inst Space Phys, Uppsala, Sweden.;Uppsala Univ, Dept Phys & Astron, Uppsala, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Lavraud, B.
    Univ Toulouse, Inst Rech Astrophys & Planetol, CNES, UPS,CNRS, Toulouse, France..
    Burch, J.
    Southwest Res Inst, San Antonio, TX USA..
    Fuselier, S.
    Southwest Res Inst, San Antonio, TX USA.;Univ Texas San Antonio, Dept Phys & Astron, San Antonio, TX USA..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Gershman, D. J.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA.;NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Space Sci, Los Angeles, CA 90024 USA..
    Electron Reconnection in the Magnetopause Current Layer2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 11, s. 9222-9238Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electron dynamics within thin current sheets plays a key role both for the process of magnetic reconnection and other energy transfer mechanisms but, from an observational point of view, is not well understood. In this paper we report observations of a reconnecting current sheet with intermediate guide field B-G = 0.5B(in), where B-in is the magnetic field amplitude in the inflow regions. The current sheet width is comparable to electron spatial scales. It shows a bifurcated structure and is embedded within the magnetopause current layer with thickness of several ion scales. The electron scale current sheet has strong out-of-plane and in-plane currents, Hall electric and magnetic fields, a finite magnetic field component normal to the current sheet, and nongyrotropic electron distributions formed due to finite gyroradius effects at the boundary of the current sheet. Comparison between test particle simulations and electron data shows that electrons approaching from the edge of the largest magnetic curvature are scattered to perpendicular pitch angles in the center of the current sheet while electrons entering from the opposite side remain close to field aligned. The comparison also shows that an observed depletion in phase space at antiparallel pitch angles can be explained if an out-of-plane electric field, which due to the guide field is close to antiparallel to the magnetic field, is present in the center of the current sheet. This electric field would be consistent with the reconnection electric field, and we therefore interpret the depletion of electron phase space density as a manifestation of ongoing reconnection.

  • 58. ORSINI, S
    et al.
    AMATA, E
    CANDIDI, M
    BALSIGER, H
    STOKHOLM, M
    HUANG, C
    LENNARTSSON, W
    Lindqvist, Per-Arne
    KTH. Plasma fysik.
    COLD STREAMS OF IONOSPHERIC OXYGEN IN THE PLASMA SHEET DURING THE CDAW-6 EVENT OF MARCH 22, 19791985Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 90, nr NA5, s. 4091-4098Artikel i tidskrift (Refereegranskat)
  • 59.
    Partamies, Noora
    et al.
    Univ Ctr Svalbard, Dept Arctic Geophys, Longyearbyen, Norway. artamies, Noora.
    Blomgren, Karl
    KTH. Department of Electronic and Electrical Engineering, University of Bath, Bath, United Kingdom.
    Heino, Erkka
    Ivchenkoo, Nickolay
    KTH.
    Borovsky, Joseph E.
    Hedberg, Hanna
    KTH. FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Patch Size Evolution During Pulsating Aurora2019Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 6, s. 4725-4738Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report both decreasing and increasing trends in the patch sizes during pulsating aurora events. About 150 pulsating auroral events over the Fennoscandian Lapland have been successfully analyzed for their average patch size, total patch area, and number of patches as a function of event time, typically 1-2 hr. An automatic routine has been developed to detect patches in the all-sky camera images. In addition to events with decreasing and increasing average patch size evolution over the course of the pulsating aurora, events with no size trends and events with intermittently increasing and decreasing patch size trends were also found. In this study, we have analyzed a subset of events for which the average and total patch size systematically increase or decrease. The events with increasing patch size trend do not experience a decrease in the peak emission height, which was previously associated with the behavior of pulsating aurora precipitation. Furthermore, the events with increasing patch sizes have shorter lifetimes and twice as many substorm-injected energetic electrons at geosynchronous orbit as the events with decreasing patch sizes. Half of the events with increasing patch sizes occur during substorm expansion phases, while a majority (64%) of the ones with decreasing patch sizes take place during the recovery phase. These findings suggest that the visual appearance of pulsating aurora may be used as an indication of the pulsating aurora energy deposition to the atmosphere.

  • 60. Peng, F. Z.
    et al.
    Fu, H. S.
    Cao, J. B.
    Graham, D. B.
    Chen, Z. Z.
    Cao, D.
    Xu, Y.
    Huang, S. Y.
    Wang, T. Y.
    Khotyaintsev, Y. V.
    Andre, M.
    Russell, C. T.
    Giles, B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Torbert, R. B.
    Ergun, R. E.
    Burch, J. L.
    Quadrupolar pattern of the asymmetric guide-field reconnection2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 6, s. 6349-6356Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With high-resolution data of the recently launched Magnetospheric Multiscale mission, we report a magnetic reconnection event at the dayside magnetopause. This reconnection event, having a density asymmetry N-high/N-low approximate to 2 on the two sides of the reconnecting current sheet and a guide field B-g approximate to 0.4B(0) in the out-of-plane direction, exhibit all the two-fluid features: Alfvenic plasma jets in the outflow region, bipolar Hall electric fields toward the current sheet center, quadrupolar Hall magnetic fields in the out-of-plane direction, and the corresponding Hall currents. Obviously, the density asymmetry N-high/N-low approximate to 2 and the guide field B-g approximate to 0.4B(0) are not sufficient to dismiss the quadrupolar pattern of Hall reconnection. This is different from previous simulations, where the bipolar pattern of Hall reconnection was suggested.

  • 61. Perry, G. W.
    et al.
    Dahlgren, Hanna
    Univ Southampton, England.
    Nicolls, M. J.
    Zettergren, M.
    St-Maurice, J. -P
    Semeter, J. L.
    Sundberg, T.
    Hosokawa, K.
    Shiokawa, K.
    Chen, S.
    Spatiotemporally resolved electrodynamic properties of a Sun-aligned arc over Resolute Bay2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 11, s. 9977-9987Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Common volume measurements by the Resolute Bay Incoherent Scatter Radar-North (RISR-N) and Optical Mesosphere and Thermosphere Imagers (OMTI) have been used to clarify the electrodynamic structure of a Sun-aligned arc in the polar cap. The plasma parameters of the dusk-to-dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of RISR-N. Multipoint line-of-sight RISR-N measurements of the plasma drift are inverted to construct a time sequence of the electric field and field-aligned current system of the arc. Evidence of dramatic electrodynamic and plasma structuring of the polar cap ionosphere due to the arc is described. One notable feature of the arc is a meridionally extended plasma density depletion on its leading edge, located partially within a downward field-aligned current region. The depletion is determined to be a by-product of enhanced chemical recombination operating on a time scale of 15 min. A similarly shaped electric field structure of over 100 mV/m and line-of-sight ion temperatures nearing 3000 K were collocated with the depletion.

  • 62.
    Pitkanen, T.
    et al.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China.;Umea Univ, Dept Phys, Umea, Sweden..
    Kullen, Anita
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Shi, Q. Q.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China..
    Hamrin, M.
    Umea Univ, Dept Phys, Umea, Sweden..
    De Spiegeleer, A.
    Umea Univ, Dept Phys, Umea, Sweden..
    Nishimura, Y.
    Boston Univ, Ctr Space Phys, Boston, MA 02215 USA..
    Convection Electric Field and Plasma Convection in a Twisted Magnetotail: A THEMIS Case Study 1-2 January 20092018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 9, s. 7486-7497Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate THEMIS satellite measurements made in a tail-aligned constellation during a time interval on 1-2 January 2009, which has previously been attributed to an interval of an interplanetary magnetic fieldB(y)-driven magnetotail twisting. We find evidence for that the orientation of the convection electric field in the tail is twist-mode dependent. For earthward flow and a negative twist (induced tail B-y < 0), the electric field is found to have northward E-z and tailward E-x components. During a positive twist (induced tail B-y > 0), the directions of E-z and E-x are reversed. The E-y component shows the expected dawn-to-dusk direction for earthward flow. The electric field components preserve their orientation across the neutral sheet, and a quasi-collinear field is observed irrespective to the tail distance. The electric field associated with the tailward flow has an opposite direction compared to the earthward flow for the negative twist. For the positive twist, the results are less clear. The corresponding plasma convection and thus the magnetic flux transport have an opposite dawn-dusk direction above and below the neutral sheet. The directions depend on the tail twist mode. The hemispherically asymmetric earthward plasma flows are suggested to be a manifestation of an asymmetric Dungey cycle in a twisted magnetotail. The role of tailward flows deserve further investigation.

  • 63. Plaschke, F.
    et al.
    Karlsson, T.
    Hietala, H.
    Archer, M.
    Voeroes, Z.
    Nakamura, R.
    Magnes, W.
    Baumjohann, W.
    Torbert, R. B.
    Russell, C. T.
    Giles, B. L.
    Magnetosheath High-Speed Jets: Internal Structure and InteractionWith Ambient Plasma2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 10, s. 10157-10175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the first time, we have studied the rich internal structure of a magnetosheath high-speed jet. Measurements by the Magnetospheric Multiscale (MMS) spacecraft reveal large-amplitude density, temperature, and magnetic field variations inside the jet. The propagation velocity and normal direction of planar magnetic field structures (i.e., current sheets and waves) are investigated via four-spacecraft timing. We find structures to mainly convect with the jet plasma. There are indications of the presence of a tangential discontinuity. At other times, there are small cross-structure flows. Where this is the case, current sheets and waves overtake the plasma in the jet's core region; ahead and behind that core region, along the jet's path, current sheets are overtaken by the plasma; that is, they move in opposite direction to the jet in the plasma rest frame. Jet structures are found to be mainly thermal and magnetic pressure balance structures, notwithstanding that the dynamic pressure dominates by far. Although the jet is supermagnetosonic in the Earth's frame of reference, it is submagnetosonic with respect to the plasma ahead. Consequently, we find no fast shock. Instead, we find some evidence for (a series of) jets pushing ambient plasma out of their way, thereby stirring the magnetosheath and causing anomalous sunward flows in the subsolar magnetosheath. Furthermore, we find that jets modify the magnetic field in the magnetosheath, aligning it with their propagation direction.

  • 64. POTEMRA, TA
    et al.
    ZANETTI, LJ
    BYTHROW, PF
    ERLANDSON, RE
    LUNDIN, R
    Marklund, Göran T.
    KTH.
    BLOCK, LP
    Lindqvist, Per-Arne
    KTH.
    RESONANT GEOMAGNETIC-FIELD OSCILLATIONS AND BIRKELAND CURRENTS IN THE MORNING SECTOR1988Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 93, nr A4, s. 2661-2674Artikel i tidskrift (Refereegranskat)
  • 65.
    Roth, Lorenz
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik. Southwest Research Institute, United States.
    Saur, J.
    Retherford, K. D.
    Strobel, D. F.
    Feldman, P. D.
    McGrath, M. A.
    Spencer, J. R.
    Blöcker, A.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Europa's far ultraviolet oxygen aurora from a comprehensive set of HST observations2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 3, s. 2143-2170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyze a large set of far ultraviolet oxygen aurora images of Europa's atmosphere taken by Hubble's Space Telescope Imaging Spectrograph (HST/STIS) in 1999 and on 19 occasions between 2012 and 2015. We find that both brightness and aurora morphology undergo systematic variations correlated to the periodically changing plasma environment. The time variable morphology seems to be strongly affected by Europa's interaction with the magnetospheric plasma. The brightest emissions are often found in the polar region where the ambient Jovian magnetic field line is normal to Europa's disk. Near the equator, where bright spots are found at Io, Europa's aurora is faint suggesting a general difference in how the plasma interaction shapes the aurora at Io and Europa. The dusk side is consistently brighter than the dawnside with only few exceptions, which cannot be readily explained by obvious plasma physical or known atmospheric effects. Brightness ratios of the near-surface OI] 1356 Å to OI 1304 Å emissions between 1.5 and 2.8 with a mean ratio of 2.0 are measured, confirming that Europa's bound atmosphere is dominated by O2. The 1356/1304 ratio decreases with increasing altitude in agreement with a more extended atomic O corona, but O2 prevails at least up to altitudes of ∼900 km. Differing 1356/1304 line ratios on the plasma upstream and downstream hemispheres are explained by a differing O mixing ratio in the near-surface O2 atmosphere of ∼5% (upstream) and ≲1% (downstream), respectively. During several eclipse observations, the aurora does not reveal any signs of systematic changes compared to the sunlit images suggesting no or only weak influence of sunlight on the aurora and an optically thin atmosphere.

  • 66.
    Roth, Lorenz
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Saur, Joachim
    Retherford, Kurt D.
    Bloecker, Aljona
    Strobel, Darrell F.
    Feldman, Paul D.
    Constraints on Io's interior from auroral spot oscillations2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 2, s. 1903-1927Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The morphology of Io's aurora is dominated by bright spots near the equator that oscillate up and down in approximate correlation with the oscillating orientation of the Jovian magnetospheric field. Analyzing Hubble Space Telescope images, we find that the auroral spots oscillate in phase with the time-variable Jovian magnetic field at Io and that the amplitude of the spot oscillations is reduced by 15% (+/- 5%) with respect to the amplitude of the magnetic field oscillation. We investigate the effects of Io's plasma interaction and magnetic induction in the moon's interior on the magnetic field topology and the aurora oscillations using a magnetohydrodynamic (MHD) simulation and an analytical induction model. The results from the MHD simulation suggest that the plasma interaction has minor effects on the oscillations, while the magnetic induction generally reduces magnetic field oscillations near the surface. However, the analytical model shows that induction in any near-surface layer for which the skin depth is larger than the thickness-like a conductive magma ocean-would induce a phase shift, in conflict with the observations. Under the assumption that the spot oscillations represent the magnetic field oscillation, we constrain the conductance of a near-surface layer to 1 x 10(3) S or lower. A magma ocean with conductances of 10(4) S or higher as derived from Galileo magnetometer measurements would cause overly strong attenuation of the amplitude in addition to the irreconcilable phase shift. The observed weakly attenuated, in-phase spot oscillation is consistent with induction in a deep, highly conductive layer like Io's metallic core.

  • 67. Russell, A. J. B.
    et al.
    Karlsson, Tomas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Wright, A. N.
    Magnetospheric signatures of ionospheric density cavities observed by Cluster2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 3, s. 1876-1887Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present Cluster measurements of large amplitude electric fields correlated with intense downward field-aligned currents, observed during a nightside crossing of the auroral zone. The data are reproduced by a simple model of magnetosphere-ionosphere coupling which, under different conditions, can also produce a divergent electric field signature in the downward current region, or correlation between the electric and perturbed magnetic fields. We conclude that strong electric field associated with intense downward field-aligned current, such as this observation, is a signature of ionospheric plasma depletion caused by the downward current. It is also shown that the electric field in the downward current region correlates with downward current density if a background field is present, e.g., due to magnetospheric convection. Key Points Correlated electric field and downward current density seen in Cluster data The signature is reproduced in a model of magnetosphere-ionosphere coupling It implies an ionospheric cavity embedded in a larger-scale current system

  • 68. Saur, J.
    et al.
    Duling, S.
    Roth, Lorenz
    KTH, Skolan för elektro- och systemteknik (EES).
    Jia, X.
    Strobel, D. F.
    Feldman, P. D.
    Christensen, U. R.
    Retherford, K. D.
    McGrath, M. A.
    Musacchio, F.
    Wennmacher, A.
    Neubauer, F. M.
    Simon, S.
    Hartkorn, O.
    The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals2015Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 3, s. 1715-1737Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new approach to search for a subsurface ocean within Ganymede through observations and modeling of the dynamics of its auroral ovals. The locations of the auroral ovals oscillate due to Jupiter's time-varying magnetospheric field seen in the rest frame of Ganymede. If an electrically conductive ocean is present, the external time-varying magnetic field is reduced due to induction within the ocean and the oscillation amplitude of the ovals decreases. Hubble Space Telescope (HST) observations show that the locations of the ovals oscillate on average by 2.0 ±1.3. Our model calculations predict a significantly stronger oscillation by 5.8 ± 1.3 without ocean compared to 2.2±1.3 if an ocean is present. Because the ocean and the no-ocean hypotheses cannot be separated by simple visual inspection of individual HST images, we apply a statistical analysis including a Monte Carlo test to also address the uncertainty caused by the patchiness of observed emissions. The observations require a minimum electrical conductivity of 0.09 S/m for an ocean assumed to be located between 150 km and 250 km depth or alternatively a maximum depth of the top of the ocean at 330 km. Our analysis implies that Ganymede's dynamo possesses an outstandingly low quadrupole-to-dipole moment ratio. The new technique applied here is suited to probe the interior of other planetary bodies by monitoring their auroral response to time-varying magnetic fields. Key Points New technique to search for a subsurface ocean in Ganymede with a telescope Ocean affects auroral oscillation caused by time-varying external magnetic field HST observations reveal weak auroral oscillation and imply existence of ocean

  • 69.
    Schlatter, Nicola Manuel
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ivchenko, Nickolay
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Haggstrom, I.
    On the relation of Langmuir turbulence radar signatures to auroral conditions2014Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, nr 10, s. 8499-8511Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a statistical study of anomalous radar echoes observed in the auroral ionosphere thought to be signatures of Langmuir turbulence (LT). Data obtained with the European Incoherent Scatter Svalbard radar during the international polar year (IPY) were searched for these anomalous echoes in the auroral Fregion. In incoherent scatter radar experiments LT may in certain circumstances be observed as enhanced backscattered radar power at the ion line frequencies, plasma line frequencies, and at zero Doppler shift. The power enhancement at zero Doppler shift could arise due to Bragg scattering from nonpropagating density fluctuations caused by strong LT. In the IPY data set, around 0.02% of the data comply with our search criteria for altitudes above 190 km based on the ion line spectrum including enhancement at zero Doppler shift. The occurrence frequency of the identified events peaks in the premidnight sector and increases with local geomagnetic disturbance. Enhanced backscattered power is observed with limited altitude extent (below 20 km in 70% of the events), and the altitude distribution of identified radar signatures in the ion line channel has a peak at about 220 km. Enhancement of the plasma line is observed with the ion line enhancements in more than 60% of the events. Two classes of enhanced plasma lines occur. In the first class, plasma lines are limited in frequency and altitude and occur at altitudes of ion line enhancements. In the second class, the plasma lines are spread in frequency and range and are observed at lower altitudes than the first class (at about 170 km) with frequencies close to 3 MHz. Available optical data available indicate that the identified events to occur during auroral breakup with high-energy electron precipitation.

  • 70. Stasiewicz, K
    et al.
    Gustafsson, G
    Marklund, Göran T.
    Lindqvist, Per-Arne
    KTH.
    Clemmons, J
    Zanetti, L
    Cavity resonators and Alfven resonance cones observed on Freja1997Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 102, nr A2, s. 2565-2575Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multiresolution wavelet analysis of magnetic field, electric field, and plasma density records taken on Freja during strong auroral events shows evidence for cavity Alfven resonators in the topside ionosphere. The cavity (or transverse) resonators consist of standing perpendicular wave modes which are trapped inside plasma cavities of different perpendicular scales. The smallest size cavities have perpendicular widths comparable to the electron skin depth, lambda(s) = 2 pi c/omega(pe), and are presumably associated with the resonance cones of Alfven waves launched by a magnetospheric source. The Alfven resonance cones (ARCs) carry intense field-aligned currents, support strong parallel electric fields and represent discharge and heating channels for auroral particles. We have made a detailed analysis of the electromagnetic properties of two singular auroral structures associated with ARCs. Field-aligned currents at the resonance structures reach intensities of 100-300 rho Am-2 in the upward and downward directions and are carried mainly by cold ionospheric plasma in both directions. The parallel electric field of ARCs is observed at amplitudes up to 100 mV/m, which is 2 orders of magnitude larger than expected for the unbounded Alfven waves. Field-aligned electron beams accelerated inside ARCs are observed to drive Langmuir waves with parallel electric field occasionally exceeding 1 V/m. One of the analyzed ARC structures has electromagnetic and particle properties characteristic of ''black aurora'' with electric field diverging from the center of the cavity; the other has converging electric field.

  • 71. Stawarz, J. E.
    et al.
    Eriksson, S.
    Wilder, F. D.
    Ergun, R. E.
    Schwartz, S. J.
    Pouquet, A.
    Burch, J. L.
    Giles, B. L.
    Khotyaintsev, Y.
    Le Contel, O.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Magnes, W.
    Pollock, C. J.
    Russell, C. T.
    Strangeway, R. J.
    Torbert, R. B.
    Avanov, L. A.
    Dorelli, J. C.
    Eastwood, J. P.
    Gershman, D. J.
    Goodrich, K. A.
    Malaspina, D. M.
    Marklund, Göran T.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Mirioni, L.
    Sturner, A. P.
    Observations of turbulence in a Kelvin-Helmholtz event on 8 September 2015 by the Magnetospheric Multiscale mission2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 11, s. 11021-11034Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Spatial and high-time-resolution properties of the velocities, magnetic field, and 3-D electric field within plasma turbulence are examined observationally using data from the Magnetospheric Multiscale mission. Observations from a Kelvin-Helmholtz instability (KHI) on the Earth's magnetopause are examined, which both provides a series of repeatable intervals to analyze, giving better statistics, and provides a first look at the properties of turbulence in the KHI. For the first time direct observations of both the high-frequency ion and electron velocity spectra are examined, showing differing ion and electron behavior at kinetic scales. Temporal spectra exhibit power law behavior with changes in slope near the ion gyrofrequency and lower hybrid frequency. The work provides the first observational evidence for turbulent intermittency and anisotropy consistent with quasi two-dimensional turbulence in association with the KHI. The behavior of kinetic-scale intermittency is found to have differences from previous studies of solar wind turbulence, leading to novel insights on the turbulent dynamics in the KHI.

  • 72. Teh, W. -L
    et al.
    Nakamura, T. K. M.
    Nakamura, R.
    Baumjohann, W.
    Russell, C. T.
    Pollock, C.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Burch, J. L.
    Torbert, R. B.
    Giles, B. L.
    Evolution of a typical ion-scale magnetic flux rope caused by thermal pressure enhancement2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 2, s. 2040-2050Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With high time-resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion-scale magnetic flux ropes (similar to 5 and similar to 11 ion inertial length radius) separated by similar to 14 s are resolved. These two ion-scale flux ropes (FR1 and FR2) show non-frozen-in ion behavior and consist of a strong axial magnetic field at the reversal of the negative-then-positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater-like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force-free but the FR2 seems not. Moreover, the FR2 is time-dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann-Teller frame using the direct measured electric fields, while the FR1 is in quasi-steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater-like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.

  • 73. Toledo-Redondo, Sergio
    et al.
    Andre, Mats
    Khotyaintsev, Yuri V.
    Lavraud, Benoit
    Vaivads, Andris
    Graham, Daniel B.
    Li, Wenya
    Perrone, Denise
    Fuselier, Stephen
    Gershman, Daniel J.
    Aunai, Nicolas
    Dargent, Jeremy
    Giles, Barbara
    Le Contel, Olivier
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, Robert E.
    Russell, Christopher T.
    Burch, James L.
    Energy budget and mechanisms of cold ion heating in asymmetric magnetic reconnection2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 9, s. 9396-9413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cold ions (few tens of eV) of ionospheric origin are commonly observed on the magnetospheric side of the Earth's dayside magnetopause. As a result, they can participate in magnetic reconnection, changing locally the reconnection rate and being accelerated and heated. We present four events where cold ion heating was observed by the Magnetospheric Multiscale mission, associated with the magnetospheric Hall E field region of magnetic reconnection. For two of the events the cold ion density was small compared to the magnetosheath density, and the cold ions were heated roughly to the same temperature as magnetosheath ions inside the exhaust. On the other hand, for the other two events the cold ion density was comparable to the magnetosheath density and the cold ion heating observed was significantly smaller. Magnetic reconnection converts magnetic energy into particle energy, and ion heating is known to dominate the energy partition. We find that at least 10-25% of the energy spent by reconnection into ion heating went into magnetospheric cold ion heating. The total energy budget for cold ions may be even higher when properly accounting for the heavier species, namely helium and oxygen. Large E field fluctuations are observed in this cold ion heating region, i.e., gradients and waves, that are likely the source of particle energization. Plain Language Summary The magnetic field of Earth creates a natural shield that isolates and protects us from the particles and fields coming from our star, the Sun. This natural shield is called the magnetosphere and is filled by plasma. The particles coming from the Sun form another plasma called the solar wind and are usually deviated around the magnetosphere. However, under certain circumstances these two plasmas can reconnect (magnetic reconnection), and part of the energy and mass of the two plasmas is interchanged. Magnetic reconnection is the driver of storms and substorms inside the magnetosphere. In this work, we investigate what occurs to particles of very low energy (cold ions) of ionospheric origin when they reach the reconnecting boundary of the magnetosphere. It is found that they are energized and take an important part of the energy spent in reconnecting the plasmas. The plasma boundary develops spatial structures and emits waves that are able to heat the cold ions. Once heated, these cold ions irreversibly will escape the Earth's magnetosphere to never come back to Earth.

  • 74. Torbert, R. B.
    et al.
    Burch, J. L.
    Argall, M. R.
    Alm, L.
    Farrugia, C. J.
    Forbes, T. G.
    Giles, B. L.
    Rager, A.
    Dorelli, J.
    Strangeway, R. J.
    Ergun, R. E.
    Wilder, F. D.
    Ahmadi, N.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Khotyaintsev, Y.
    Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal-Incidence Magnetopause Crossing2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 12, s. 11901-11916Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On 22 October 2016, the Magnetospheric Multiscale (MMS) spacecraft encountered the electron diffusion region (EDR) when the magnetosheath field was southward, and there were signatures of fast reconnection, including flow jets, Hall fields, and large power dissipation. One rapid, normal-incidence crossing, during which the EDR structure was almost stationary in the boundary frame, provided an opportunity to observe the spatial structure for the zero guide field case of magnetic reconnection. The reconnection electric field was determined unambiguously to be 2-3 mV/m. There were clear signals of fluctuating parallel electric fields, up to 6 mV/m on the magnetosphere side of the diffusion region, associated with a Hall-like parallel current feature on the electron scale. The width of the main EDR structure was determined to be similar to 2 km (1.8 de). Although the MMS spacecraft were in their closest tetrahedral separation of similar to 8 km, the divergences and curls for these thin current structures could therefore not be computed in the usual manner. A method is developed to determine these quantities on a much smaller scale and applied to compute the normal component of terms in the generalized Ohm's law for the positions of each individual spacecraft (not a barocentric average). Although the gradient pressure term has a qualitative dependence that follows the observed variation of E + Ve x B, the quantitative magnitude of these terms differs by more than a factor of 2, which is shown to be greater than the respective errors. Thus, future research is required to find the manner in which Ohm's law is balanced. Plain Language Summary The Magnetospheric Multiscale (MMS) spacecraft observed the spatial structure of the region where magnetic energy is converted to particle flows and heat. New features of currents and fields parallel to the magnetic field are analyzed. Some discrepancies with present computer simulations are found within this region.

  • 75. Torkar, K.
    et al.
    Nakamura, R.
    Andriopoulou, M.
    Giles, B. L.
    Jeszenszky, H.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Torbert, R. B.
    Influence of the Ambient Electric Field on Measurements of the Actively Controlled Spacecraft Potential by MMS2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 12, s. 12019-12030Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Space missions with sophisticated plasma instrumentation such as Magnetospheric Multiscale, which employs four satellites to explore near-Earth space benefit from a low electric potential of the spacecraft, to improve the plasma measurements and therefore carry instruments to actively control the potential by means of ion beams. Without control, the potential varies in anticorrelation with plasma density and temperature to maintain an equilibrium between the plasma current and the one of photoelectrons produced at the surface and overcoming the potential barrier. A drawback of the controlled, almost constant potential is the difficulty to use it as convenient estimator for plasma density. This paper identifies a correlation between the spacecraft potential and the ambient electric field, both measured by double probes mounted at the end of wire booms, as the main responsible for artifacts in the potential data besides the known effect of the variable photoelectron production due to changing illumination of the surface. It is shown that the effect of density variations is too weak to explain the observed correlation with the electric field and that a correction of the artifacts can be achieved to enable the reconstruction of the uncontrolled potential and plasma density in turn. Two possible mechanisms are discussed: the asymmetry of the current-voltage characteristic determining the probe to plasma potential and the fact that a large equipotential structure embedded in an electric field results in asymmetries of both the emission and spatial distribution of photoelectrons, which results in an increase of the spacecraft potential.

  • 76. Toth, Gabor
    et al.
    Chen, Yuxi
    Gombosi, Tamas I.
    Cassak, Paul
    Markidis, Stefano
    KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Peng, Ivy Bo
    KTH.
    Scaling the Ion Inertial Length and Its Implications for Modeling Reconnection in Global Simulations2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 10, s. 10336-10355Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the use of artificially increased ion and electron kinetic scales in global plasma simulations. We argue that as long as the global and ion inertial scales remain well separated, (1) the overall global solution is not strongly sensitive to the value of the ion inertial scale, while (2) the ion inertial scale dynamics will also be similar to the original system, but it occurs at a larger spatial scale, and (3) structures at intermediate scales, such as magnetic islands, grow in a self-similar manner. To investigate the validity and limitations of our scaling hypotheses, we carry out many simulations of a two-dimensional magnetosphere with the magnetohydrodynamics with embedded particle-in-cell (MHD-EPIC) model. The PIC model covers the dayside reconnection site. The simulation results confirm that the hypotheses are true as long as the increased ion inertial length remains less than about 5% of the magnetopause standoff distance. Since the theoretical arguments are general, we expect these results to carry over to three dimensions. The computational cost is reduced by the third and fourth powers of the scaling factor in two-and three-dimensional simulations, respectively, which can be many orders of magnitude. The present results suggest that global simulations that resolve kinetic scales for reconnection are feasible. This is a crucial step for applications to the magnetospheres of Earth, Saturn, and Jupiter and to the solar corona.

  • 77. Toth, Gabor
    et al.
    Jia, Xianzhe
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Peng, Ivy Bo
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Chen, Yuxi
    Daldorff, Lars K. S.
    Tenishev, Valeriy M.
    Borovikov, Dmitry
    Haiducek, John D.
    Gombosi, Tamas I.
    Glocer, Alex
    Dorelli, John C.
    Extended magnetohydrodynamics with embedded particle-in-cell simulation of Ganymede's magnetosphere2016Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, nr 2, s. 1273-1293Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have recently developed a new modeling capability to embed the implicit particle-in-cell (PIC) model iPIC3D into the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme magnetohydrodynamic (MHD) model. The MHD with embedded PIC domains (MHD-EPIC) algorithm is a two-way coupled kinetic-fluid model. As one of the very first applications of the MHD-EPIC algorithm, we simulate the interaction between Jupiter's magnetospheric plasma and Ganymede's magnetosphere. We compare the MHD-EPIC simulations with pure Hall MHD simulations and compare both model results with Galileo observations to assess the importance of kinetic effects in controlling the configuration and dynamics of Ganymede's magnetosphere. We find that the Hall MHD and MHD-EPIC solutions are qualitatively similar, but there are significant quantitative differences. In particular, the density and pressure inside the magnetosphere show different distributions. For our baseline grid resolution the PIC solution is more dynamic than the Hall MHD simulation and it compares significantly better with the Galileo magnetic measurements than the Hall MHD solution. The power spectra of the observed and simulated magnetic field fluctuations agree extremely well for the MHD-EPIC model. The MHD-EPIC simulation also produced a few flux transfer events (FTEs) that have magnetic signatures very similar to an observed event. The simulation shows that the FTEs often exhibit complex 3-D structures with their orientations changing substantially between the equatorial plane and the Galileo trajectory, which explains the magnetic signatures observed during the magnetopause crossings. The computational cost of the MHD-EPIC simulation was only about 4 times more than that of the Hall MHD simulation. Key Points

  • 78. Varsani, A.
    et al.
    Nakamura, R.
    Sergeev, V. A.
    Baumjohann, W.
    Owen, C. J.
    Petrukovich, A. A.
    Yao, Z.
    Nakamura, T. K. M.
    Kubyshkina, M. V.
    Sotirelis, T.
    Burch, J. L.
    Genestreti, K. J.
    Voeroes, Z.
    Andriopoulou, M.
    Gershman, D. J.
    Avanov, L. A.
    Magnes, W.
    Russell, C. T.
    Plaschke, F.
    Khotyaintsev, Y. V.
    Giles, B. L.
    Coffey, V. N.
    Dorelli, J. C.
    Strangeway, R. J.
    Torbert, R. B.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R.
    Simultaneous Remote Observations of Intense Reconnection Effects by DMSP and MMS Spacecraft During a Storm Time Substorm2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 11, s. 10891-10909Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During a magnetic storm on 23 June 2015, several very intense substorms took place, with signatures observed by multiple spacecraft including DMSP and Magnetospheric Multiscale (MMS). At the time of interest, DMSP F18 crossed inbound through a poleward expanding auroral bulge boundary at 23.5 h magnetic local time (MLT), while MMS was located duskward of 22 h MLT during an inward crossing of the expanding plasma sheet boundary. The two spacecraft observed a consistent set of signatures as they simultaneously crossed the reconnection separatrix layer during this very intense reconnection event. These include (1) energy dispersion of the energetic ions and electrons traveling earthward, accompanied with high electron energies in the vicinity of the separatrix; (2) energy dispersion of polar rain electrons, with a high-energy cutoff; and (3) intense inward convection of the magnetic field lines at the MMS location. The high temporal resolution measurements by MMS provide unprecedented observations of the outermost electron boundary layer. We discuss the relevance of the energy dispersion of the electrons, and their pitch angle distribution, to the spatial and temporal evolution of the boundary layer. The results indicate that the underlying magnetotail magnetic reconnection process was an intrinsically impulsive and the active X-line was located relatively close to the Earth, approximately at 16-18 R-E.

  • 79.
    Vaverka, Jakub
    et al.
    Umea Univ, Dept Phys, Umea, Sweden.;Natl Inst Polar Res, Tachikawa, Tokyo, Japan.;Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Nakamura, Takuji
    Natl Inst Polar Res, Tachikawa, Tokyo, Japan..
    Kero, Johan
    Swedish Inst Space Phys, Kiruna, Sweden..
    Mann, Ingrid
    Arctic Univ Norway, Tromso, Norway..
    De Spiegeleer, Alexandre
    Umea Univ, Dept Phys, Umea, Sweden..
    Hamrin, Maria
    Umea Univ, Dept Phys, Umea, Sweden..
    Norberg, Carol
    Umea Univ, Dept Phys, Umea, Sweden.;Swedish Inst Space Phys, Kiruna, Sweden..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Pellinen-Wannberg, Asta
    Umea Univ, Dept Phys, Umea, Sweden.;Swedish Inst Space Phys, Kiruna, Sweden..
    Comparison of Dust Impact and Solitary Wave Signatures Detected by Multiple Electric Field Antennas Onboard the MMS Spacecraft2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 8, s. 6119-6129Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dust impact detection by electric field instruments is a relatively new method. However, the influence of dust impacts on electric field measurements is not completely understood and explained. A better understanding is very important for reliable dust impact identification, especially in environments with low dust impact rate. Using data from Earth-orbiting Magnetospheric Multiscale mission (MMS) spacecraft, we present a study of various pulses detected simultaneously by multiple electric field antennas in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe potential measurement) configurations. The study includes data obtained during an impact of a millimeter-sized object. We show that the identification of dust impacts by a single antenna is a very challenging issue in environments where solitary waves are commonly present and that some pulses can be easily misinterpreted as dust impacts. We used data from multiple antennas to distinguish between changes in the spacecraft potential (dust impact) and structures in the ambient plasma or electric field. Our results indicate that an impact cloud is in some cases able to influence the potential of the electric field antenna during its expansion.

  • 80. Vines, S. K.
    et al.
    Fuselier, S. A.
    Trattner, K. J.
    Burch, J. L.
    Allen, R. C.
    Petrinec, S. M.
    Anderson, B. J.
    Webster, J. M.
    Ergun, R. E.
    Giles, B. L.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Russell, C. T.
    Magnetospheric Ion Evolution Across the Low-Latitude Boundary Layer Separatrix2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 10, s. 10247-10262Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    On 20 September 2015, the Magnetospheric Multiscale (MMS) spacecraft crossed the dusk magnetopause after a compression of the magnetosphere. Enhanced densities and fluxes of both colder (≤10 eV) and hotter (&gt;1 keV) magnetospheric and magnetosheath heavy ion species were observed reaching the magnetopause. The evolution of the velocity distributions for H+, He+, and O+ measured by the Hot Plasma Composition Analyzer on MMS during this magnetopause crossing is presented. In particular, this study focuses on the changes in the species' distribution functions as MMS passes from the magnetosphere through the electron edge of the low-latitude boundary layer (LLBL) separatrix and then into the LLBL. Two types of processes are suggested to play a role in the heating of colder magnetospheric ions across the LLBL separatrix in the region between the separatrix and the electron and ion edges of the LLBL. One mechanism leads to the formation and enhancement of ring distributions in this layer of the LLBL as the magnetospheric ions propagate across the separatrix. A second mechanism leading first to perpendicular heating and then to parallel heating of colder protons may arise from a possible two-stream instability as the magnetospheric ions first encounter the warmer magnetosheath electrons in the electron layer and then the warmer magnetosheath ions between the electron and ion edges of the LLBL separatrix. Perpendicular heating of He+ and O+ is seen more so in the main reconnection exhaust, due to nonadiabatic behavior of these ions as they are accelerated up to the bulk flow speed.

  • 81. Voros, Z.
    et al.
    Yordanova, E.
    Varsani, A.
    Genestreti, K. J.
    Khotyaintsev, Yu. V.
    Li, W.
    Graham, D. B.
    Norgren, C.
    Nakamura, R.
    Narita, Y.
    Plaschke, F.
    Magnes, W.
    Baumjohann, W.
    Fischer, D.
    Vaivads, A.
    Eriksson, E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Ergun, R. E.
    Leitner, M.
    Leubner, M. P.
    Strangeway, R. J.
    Le Contel, O.
    Pollock, C.
    Giles, B. J.
    Torbert, R. B.
    Burch, J. L.
    Avanov, L. A.
    Dorelli, J. C.
    Gershman, D. J.
    Paterson, W. R.
    Lavraud, B.
    Saito, Y.
    MMS Observation of Magnetic Reconnection in the Turbulent Magnetosheath2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 11, s. 11442-11467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we use the full armament of the MMS (Magnetospheric Multiscale) spacecraft to study magnetic reconnection in the turbulent magnetosheath downstream of a quasi-parallel bow shock. Contrarily to the magnetopause and magnetotail cases, only a few observations of reconnection in the magnetosheath have been reported. The case study in this paper presents, for the first time, both fluid-scale and kinetic-scale signatures of an ongoing reconnection in the turbulent magnetosheath. The spacecraft are crossing the reconnection inflow and outflow regions and the ion diffusion region (IDR). Inside the reconnection outflows D shape ion distributions are observed. Inside the IDR mixing of ion populations, crescent-like velocity distributions and ion accelerations are observed. One of the spacecraft skims the outer region of the electron diffusion region, where parallel electric fields, energy dissipation/conversion, electron pressure tensor agyrotropy, electron temperature anisotropy, and electron accelerations are observed. Some of the difficulties of the observations of magnetic reconnection in turbulent plasma are also outlined.

  • 82. Wang, Rongsheng
    et al.
    Lu, Quanming
    Nakamura, Rumi
    Baumjohann, Wolfgang
    Russell, C. T.
    Burch, J. L.
    Ergun, R. E.
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Wang, Shui
    Giles, Barbara
    Gershman, Dan
    Interaction of Magnetic Flux Ropes Via Magnetic Reconnection Observed at the Magnetopause2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 10, s. 10436-10447Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the high-resolution field and plasma data obtained from the Magnetospheric Multiscale mission at the magnetopause, a series of three flux transfer events was observed one after another inside southward ion flows, without time gap between any two successive flux ropes. Using the plasma measurements, the current densities within the flux ropes were studied in detail. The currents within the first two flux ropes, dubbed Fr1 and Fr2, were composed of a series of well-separated filamentary currents. The thickness of the filamentary currents and the gap between them were sub ion scale, occasionally dropped down to electron scale. In the third flux rope Fr3 which was closest to the expected reconnection X line, the current displayed a singular compact current layer, was ion scale in width and concentrated on its center. Considering the location of the flux ropes relative to the reconnection X line, we suggested that the current density could be a singular structure when the flux rope was just created and then fragmented into a series of filamentary currents as time. By examining the interregions between Fr1 and Fr2, and between Fr2 and Fr3, reconnection was only confirmed to occur between Fr2 and Fr3 and no reconnection signature was found between Fr1 and Fr2. It seems that magnetic field compression resulted from collision of two neighboring flux ropes is one necessary condition for the occurrence of the coalescence.

  • 83.
    Wilder, F. D.
    et al.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Ergun, R. E.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA.;Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80309 USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Ahmadi, N.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Eriksson, S.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Goodrich, K. A.
    Univ Colorado, Atmospher & Space Phys Lab, Campus Box 392, Boulder, CO 80309 USA..
    Shuster, J.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Univ Maryland, College Pk, MD 20742 USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Plaschke, F.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Magnes, W.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Khotyaintsev, Y. V.
    Swedish Inst Space Phys, Uppsala, Sweden..
    The Role of the Parallel Electric Field in Electron-Scale Dissipation at Reconnecting Currents in the Magnetosheath2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 8, s. 6533-6547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report observations from the Magnetospheric Multiscale satellites of reconnecting current sheets in the magnetosheath over a range of out-of-plane "guide" magnetic field strengths. The currents exhibit nonideal energy conversion in the electron frame of reference, and the events are within the ion diffusion region within close proximity (a few electron skin depths) to the electron diffusion region. The study focuses on energy conversion on the electron scale only. At low guide field (antiparallel reconnection), electric fields and currents perpendicular to the magnetic field dominate the energy conversion. Additionally, electron distributions exhibit significant nongyrotropy. As the guide field increases, the electric field parallel to the background magnetic field becomes increasingly strong, and the electron nongyrotropy becomes less apparent. We find that even with a guide field less than half the reconnecting field, the parallel electric field and currents dominate the dissipation. This suggests that parallel electric fields are more important to energy conversion in reconnection than previously thought and that at high guide field, the physics governing magnetic reconnection are significantly different from antiparallel reconnection.

  • 84. Wilder, F. D.
    et al.
    Ergun, R. E.
    Newman, D. L.
    Goodrich, K. A.
    Trattner, K. J.
    Goldman, M. V.
    Eriksson, S.
    Jaynes, A. N.
    Leonard, T.
    Malaspina, D. M.
    Ahmadi, N.
    Schwartz, S. J.
    Burch, J. L.
    Torbert, R. B.
    Argall, M. R.
    Giles, B. L.
    Phan, T. D.
    Le Contel, O.
    Graham, D. B.
    Khotyaintsev, Y. V.
    Strangeway, R. J.
    Russell, C. T.
    Magnes, W.
    Plaschke, F.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    The nonlinear behavior of whistler waves at the reconnecting dayside magnetopause as observed by the Magnetospheric Multiscale mission: A case study2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 5, s. 5487-5501Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show observations of whistler mode waves in both the low-latitude boundary layer (LLBL) and on closed magnetospheric field lines during a crossing of the dayside reconnecting magnetopause by the Magnetospheric Multiscale (MMS) mission on 11 October 2015. The whistlers in the LLBL were on the electron edge of the magnetospheric separatrix and exhibited high propagation angles with respect to the background field, approaching 40°, with bursty and nonlinear parallel electric field signatures. The whistlers in the closed magnetosphere had Poynting flux that was more field aligned. Comparing the reduced electron distributions for each event, the magnetospheric whistlers appear to be consistent with anisotropy-driven waves, while the distribution in the LLBL case includes anisotropic backward resonant electrons and a forward resonant beam at near half the electron-Alfvén speed. Results are compared with the previously published observations by MMS on 19 September 2015 of LLBL whistler waves. The observations suggest that whistlers in the LLBL can be both beam and anisotropy driven, and the relative contribution of each might depend on the distance from the X line.

  • 85. Zhang, Y. C.
    et al.
    Lavraud, B.
    Dai, L.
    Wang, C.
    Marchaudon, A.
    Avanov, L.
    Burch, J.
    Chandler, M.
    Dorelli, J.
    Duan, S. P.
    Ergun, R. E.
    Gershman, D. J.
    Giles, B.
    Khotyaintsev, Y. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Paterson, W.
    Russell, C. T.
    Schiff, C.
    Tang, B. B.
    Torbert, R.
    Quantitative analysis of a Hall system in the exhaust of asymmetric magnetic reconnection2017Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, nr 5, s. 5277-5289Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Taking advantage of high-resolution measurements from the MMS mission, we find evidence for a complete Hall system in the exhaust of asymmetric magnetic reconnection 40 Di downstream of the X line. The investigation of the fine structure of the Hall system reveals that it displays features in the exhaust similar to those reported previously in the ion diffusion region by simulations and observations. This finding confirms the importance of particle-scale processes in the reconnection exhaust as well. On the magnetospheric side of the exhaust, electrons are strongly accelerated by parallel electric fields. This process significantly contributes to feed the Hall current system, resulting in a nonnegligible Hall magnetic field signature on this side despite an otherwise lower density. Calculation of the induced out-of-plane magnetic field by in-plane currents (based on Biot-Savart law) provides direct quantitative evidence for the process of Hall magnetic field generation by the Hall current system. A strong normal Hall electric field is present only on the magnetospheric side of the exhaust region, consistent with previous works. Multipoint data analysis shows that the ion pressure gradient in the ion momentum equation produces this Hall electric field. This global pattern of the Hall system can be explained by kinetic Alfvén wave theory.

  • 86.
    Zhou, Hongyang
    et al.
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Toth, Gabor
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Jia, Xianzhe
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Chen, Yuxi
    Univ Michigan, Dept Climate & Space Sci & Engn, Ann Arbor, MI 48109 USA..
    Markidis, Stefano
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Beräkningsvetenskap och beräkningsteknik (CST).
    Embedded Kinetic Simulation of Ganymede's Magnetosphere: Improvements and Inferences2019Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 7, s. 5441-5460Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The largest moon in the solar system, Ganymede, is also the only moon known to possess a strong intrinsic magnetic field and a corresponding magnetosphere. Using the new version of Hall magnetohydrodynamic with embedded particle-in-cell model with a self-consistently coupled resistive body representing the electrical properties of the moon's interior, improved inner boundary conditions, and the flexibility of coupling different grid geometries, we achieve better match of magnetic field with measurements for all six Galileo flybys. The G2 flyby comparisons of plasma bulk flow velocities with the Galileo Plasma Subsystem data support the oxygen ion assumption inside Ganymede's magnetosphere. Crescent shape, nongyrotropic, and nonisotropic ion distributions are identified from the coupled model. Furthermore, we have derived the energy fluxes associated with the upstream magnetopause reconnection of similar to 10(-7) W/cm(2) based on our model results and found a maximum of 40% contribution to the total peak auroral emissions.

  • 87.
    Zhou, M.
    et al.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Berchem, J.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Walker, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    El-Alaoui, M.
    Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90095 USA..
    Goldstein, M. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Space Sci Inst, Boulder, CO USA..
    Lapenta, G.
    Katholieke Univ Leuven, Dept Math, Ctr Plasma Astrophys, Leuven, Belgium..
    Deng, X.
    Nanchang Univ, Inst Space Sci & Technol, Nanchang, Jiangxi, Peoples R China..
    Li, J.
    Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA USA..
    Le Contel, O.
    Univ Paris Sud, UPMC Univ Paris 06, CNRS, Lab Phys Plasmas,Ecole Polytech,Observ Paris, Paris, France..
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Lavraud, B.
    Univ Toulouse, CNRS, Inst Rech Astrophys & Planetol, UPS,CNES, Toulouse, France..
    Paterson, W. R.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Burch, J. L.
    Southwest Res Inst, San Antonio, TX USA..
    Torbert, R. B.
    Univ New Hampshire, Dept Phys, Durham, NH 03824 USA.;Univ New Hampshire, Ctr Space Sci, Durham, NH 03824 USA..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Zhao, C.
    Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves2018Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 3, s. 1834-1852Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report Magnetospheric Multiscale (MMS) observations of a reconnecting current sheet in the presence of a weak density asymmetry with large guide field at the dayside magnetopause. An ion diffusion region (IDR) was detected associated with this current sheet. Parallel current dominated over the perpendicular current in the IDR, as found in previous studies of component reconnection. Electrons were preferentially heated parallel to the magnetic field within the IDR. The heating was manifested as a flattop distribution below 400eV. Two types of electromagnetic electron whistler waves were observed within the regions where electrons were heated. One type of whistler wave was associated with nonlinear structures in E-|| with amplitudes up to 20mV/m. The other type was not associated with any structures in E-||. Poynting fluxes of these two types of whistler waves were directed away from the X-line. We suggest that the nonlinear evolution of the oblique whistler waves gave rise to the solitary structures in E-||. There was a perpendicular super-Alfvenic outflow jet that was carried by magnetized electrons. Intense electrostatic lower hybrid drift waves were localized in the current sheet center and were probably driven by the super-Alfvenic electron jet, the velocity of which was approximately equal to the diamagnetic drift of demagnetized ions. Our observations suggest that the guide field significantly modified the structures (Hall electromagnetic fields and current system) and wave properties in the IDR.

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