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  • 1.
    Blomberg, Lars G.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Primdahl, F.
    Brauer, P.
    Bylander, Lars
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments, Alfvén Laboratory.
    Cumnock, Judy
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments, Alfvén Laboratory.
    Eriksson, Stefan
    KTH, Superseded Departments, Alfvén Laboratory.
    Ivchenko, Nickolay V.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments, Alfvén Laboratory.
    Merayo, J. M. G.
    Pedersen, E. B.
    Petersen, J. R.
    EMMA - the electric and magnetic monitor of the aurora on Astrid-22004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 1, p. 115-123Article in journal (Refereed)
    Abstract [en]

    The Astrid-2 mission has dual primary objectives. First, it is an orbiting instrument platform for studying auroral electrodynamics. Second, it is a technology demonstration of the feasibility of using micro-satellites for innovative space plasma physics research. The EMMA instrument, which we discuss in the present paper, is designed to provide simultaneous sampling of two electric and three magnetic field components up to about 1 kHz. The spin plane components of the electric field are measured by two pairs of opposing probes extended by wire booms with a separation distance of 6.7 m. The probes have titanium nitride (TiN) surfaces. which has proved to be a material with excellent properties for providing good electrical contact between probe and plasma. The wire booms are of a new design in which the booms in the stowed position are wound around the exterior of the spacecraft body. The boom system was flown for the first time on this mission and worked flawlessly. The magnetic field is measured by a tri-axial fluxgate sensor located at the tip of a rigid. hinged boom extended along the spacecraft spin axis and facing away from the Sun. The new advanced-design fluxgate magnetometer uses digital signal processors for detection and feedback, thereby reducing the analogue circuitry to a minimum. The instrument characteristics as well as a brief review of the science accomplished and planned are presented.

  • 2.
    Blomberg, Lars
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory.
    Primdahl, F.
    Brauer, P.
    Bylander, Lars
    KTH, Superseded Departments, Alfvén Laboratory.
    Cumnock, Judy
    KTH, Superseded Departments, Alfvén Laboratory.
    Eriksson, S.
    Ivchenko, Nickolay
    KTH, Superseded Departments, Alfvén Laboratory.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Kullen, Anita
    KTH, Superseded Departments, Alfvén Laboratory.
    Merayo, J. M. G.
    Pedersen, E. B.
    Petersen, J. R.
    The EMMA Instrument on the Astrid-2 Micro-Satellite2003Report (Other academic)
  • 3. Carter, J. A.
    et al.
    Milan, S. E.
    Fear, R. C.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hairston, M. R.
    Dayside reconnection under interplanetary magnetic field B-y-dominated conditions: The formation and movement of bending arcs2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 4, p. 2967-2978Article in journal (Refereed)
    Abstract [en]

    Based upon a survey of global auroral images collected by the Polar Ultraviolet Imager, Kullen etal. (2002) subdivided polar cap auroral arcs into a number of categories, including that of bending arcs. We are concerned with those bending arcs that appear as a bifurcation of the dayside auroral oval and which subsequently form a spur intruding into the polar cap. Once formed, the spur moves poleward and antisunward over the lifetime of the arc. We propose that dayside bending arcs are ionospheric signatures of pulses of dayside reconnection and are therefore part of a group of transient phenomena associated with flux transfer events. We observe the formation and subsequent motion of a bending arc across the polar cap during a 30 min interval on 8 January 1999, and we show that this example is consistent with the proposed model. We quantify the motion of the arc and find it to be commensurate with the convection flows observed by both ground-based radar observations and space-based particle flow measurements. In addition, precipitating particles coincident with the arc appear to occur along open field lines, lending further support to the model.

  • 4.
    Cumnock, Judy A.
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Blomberg, Lars G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sundberg, K. Å. Torbjörn
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Small-scale characteristics of extremely high latitude aurora2009In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, no 9, p. 3335-3347Article in journal (Refereed)
    Abstract [en]

    We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF B-y. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

  • 5.
    Ivchenko, Nickolay
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Eglitis, P
    Berthomier, M
    Peticolas, L
    Kullen, Anita
    KTH, Superseded Departments, Alfvén Laboratory.
    Marklund, G
    KTH, Superseded Departments, Alfvén Laboratory.
    Kauristie, K
    Brittnacher, M
    Field aligned current structures and associated pulsations during substorm recovery2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202Article in journal (Refereed)
  • 6.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Eriksson, A. I.
    Odelstad, E.
    Andre, M.
    Dickeli, G.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per Arne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, H.
    Richter, I.
    Rosetta measurements of lower hybrid frequency range electric field oscillations in the plasma environment of comet 67P2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 4, p. 1641-1651Article in journal (Refereed)
    Abstract [en]

    Electric field measurements from cometary environments are very rare but can provide important information on how plasma waves help fashion the plasma environment. The long dwelling time of the Rosetta spacecraft close to comet 67P/Churyumov-Gerasimenko promises to improve this state. We here present the first electric field measurements from 67P, performed by the Rosetta dual Langmuir probe instrument LAP. Measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of plasma density changes. Persistent wave activity around the local H2O+ lower hybrid frequency is observed, with the largest amplitudes observed at sharp plasma gradients. We demonstrate that the necessary requirements for the lower hybrid drift instability to be operating are fulfilled. We suggest that lower hybrid waves are responsible for the creation of a warm electron population, the origins of which have been unknown so far, by heating ambient electrons in the magnetic field-parallel direction.

  • 7.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Hamrin, M.
    Nilsson, H.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pitkänen, T.
    Magnetic forces associated with bursty bulk flows in Earth's magnetotail2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 9, p. 3122-3128Article in journal (Refereed)
    Abstract [en]

    We present the first direct measurements of magnetic forces acting on bursty bulk flow plasma in the magnetotail. The magnetic forces are determined using Cluster multispacecraft measurements. We analyze 67 bursty bulk flow (BBF) events and show that the curvature part of the magnetic force is consistently positive, acting to accelerate the plasma toward Earth between approximately 10 and 20 RE geocentrical distances, while the magnetic field pressure gradient increasingly brakes the plasma as it moves toward Earth. The net result is that the magnetic force accelerates the plasma at distances greater than approximately 14 RE, while it acts to decelerate it within that distance. The magnetic force, together with the thermal pressure gradient force, will determine the dynamics of the BBFs as they propagate toward the near-Earth tail region. The determination of the former provides an important clue to the ultimate fate of BBFs in the inner magnetosphere. Key Points Direct measurements of magnetic force acting on BBF plasma BBF plasma is accelerated toward Earth until it reaches 15 RE, then braked Knowledge of the forces on BBFs provides clue to their fate close to Earth.

  • 8.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Liljeblad, Elisabet
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Brenning, Nils
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, H.
    Gunell, H.
    Hamrin, M.
    On the origin of magnetosheath plasmoids and their relation to magnetosheath jets2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 9, p. 7390-7403Article in journal (Refereed)
    Abstract [en]

    We investigate localized magnetosheath and solar wind density enhancements, associated with clear magnetic field changes, and therefore referred to as magnetosheath/solar wind plasmoids, respectively. Using Cluster data, we show that there are two distinct populations of magnetosheath plasmoids, one associated with a decrease of magnetic field strength (diamagnetic plasmoids), and one with an increased magnetic field strength (paramagnetic plasmoids). The diamagnetic magnetosheath plasmoids have scale sizes of the order of 1-10 R-E, while the paramagnetic ones are an order of magnitude smaller. The diamagnetic plasmoids are not associated with any change in the magnetosheath plasma flow velocity, and they are classified as embedded plasmoids in the terminology of Karlsson et al. (2012). The paramagnetic plasmoids may either be embedded or associated with increases in flow velocity (fast plasmoids). A search for plasmoids in the pristine solar wind resulted in identification of 62 diamagnetic plasmoids with very similar properties to the magnetosheath diamagnetic plasmoids, making it probable that the solar wind is the source of these structures. No paramagnetic plasmoids are found in the pristine solar wind, indicating that these are instead created at the bow shock or in the magnetosheath. We discuss the relation of the plasmoids to the phenomenon of magnetosheath jets, with which they have many properties in common, and suggest that the paramagnetic plasmoids can be regarded as a subset of these or a closely related phenomenon. We also discuss how the results from this study relate to theories addressing the formation of magnetosheath jets.

  • 9.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Dawn-dusk asymmetries in auroral morphology and processes2017In: Dawn-Dusk Asymmetries in Planetary Plasma Environments, Wiley Blackwell , 2017, p. 295-305Chapter in book (Other academic)
    Abstract [en]

    We address the dawn-dusk asymmetries in auroral emissions in the main auroral oval, and discuss their origins in terms of the underlying asymmetries of the precipitating particles. These, in turn, are associated with asymmetries in the mechanisms responsible for the transport and acceleration of the precipitating particles. We briefly discuss the reasons for the asymmetries of these processes, which include dawn-dusk asymmetries in particle drifts and in the ionospheric conductivity, the direction of the interplanetary magnetic field, and substorm-related asymmetries in field-aligned currents and flows. Finally, we briefly discuss dawn-dusk asymmetries associated with auroral emissions in the polar cap. 

  • 10.
    Karlsson, Tomas
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Liljeblad, Elisabet
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Raines, Jim M.
    Slavin, James A.
    Sundberg, Torbjorn
    Isolated magnetic field structures in Mercury's magnetosheath as possible analogues for terrestrial magnetosheath plasmoids and jets2016In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 129, p. 61-73Article in journal (Refereed)
    Abstract [en]

    We have investigated MESSENGER magnetic field data from the Mercury magnetosheath and near solar wind, to identify isolated magnetic field structures (defined as clear, isolated changes in the field magnitude). Their properties are studied in order to determine if they may be considered as analogues to plasmoids and jets known to exist in Earth's magnetosheath. Both isolated decreases of the magnetic field absolute value ('negative magnetic field structures') and increases ('positive structures') are found in the magnetosheath, whereas only negative structures are found in the solar wind. The similar properties of the solar wind and magnetosheath negative magnetic field structures suggests that they are analogous to diamagnetic plasmoids found in Earth's magnetosheath and near solar wind. The latter have earlier been identified with solar wind magnetic holes. Positive magnetic field structures are only found in the magnetosheath, concentrated to a region relatively close to the magnetopause. Their proximity to the magnetopause, their scale sizes, and the association of a majority of the structures with bipolar magnetic field signatures identify them as flux transfer events (which generally are associated with a decrease of plasma density in the magnetosheath). The positive magnetic field structures are therefore not likely to be analogous to terrestrial paramagnetic plasmoids but possibly to a sub-population of magnetosheath jets. At Earth, a majority of magnetosheath jets are associated with the quasi-parallel bow shock. We discuss some consequences of the findings of the present investigation pertaining to the different nature of the quasi-parallel bow shock at Mercury and Earth.

  • 11. Kullen, A
    et al.
    Blomberg, Lars
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The influence of IMF B-y on the mapping between the Earth's magnetotail and its ionosphere1996In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 23, no 18, p. 2561-2564Article in journal (Refereed)
    Abstract [en]

    It is well known that the dawn-dusk component of the interplanetary magnetic field (IMF) creates asymmetries in the magnetotail. The main effects are a weak nonuniform penetration of IMF B-y into the tail and a rotation of the whole tail current sheet. In this study we modify the Tsyganenko (1989) model to simulate the IMF B-y induced tail effects. By field line mapping we examine how different regions of the magnetosphere and ionosphere are influenced by the IMF By tail effects. The plasma sheet is shown to rotate around the central axis of the magnetotail. The mapping from the plasma sheet to the ionosphere for nonzero IMF B-y shows a change in the geometry of the auroral oval. The whole oval rotates, a local bulge occurs near midnight and the thickness of the oval is different in the morning and the evening sector. Simple geometrical considerations show that the tilting of the field lines caused by IMF B-y leads to a rotation of the oval, whereas the rotation of the tail current sheet is reponsible for the thickness variations along the oval. These results fit very well with the observed auroral distribution for an IMF with a dawnward or duskward direction.

  • 12.
    Kullen, A.
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Brittnacher, M.
    Cumnock, J. A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. KTH, Superseded Departments (pre-2005), Alfvén Laboratory.
    Blomberg, Lars G.
    KTH, Superseded Departments (pre-2005), Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Solar wind dependence of the occurrence and motion of polar auroral arcs: A statistical study2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no A11Article in journal (Refereed)
    Abstract [en]

    [1] Polar UV images from a 3-month period in winter 1998-1999 are used for a statistical study of polar arcs. The study covers all auroral arcs that are located poleward of the northern auroral oval, and which are detectable by the UV imager. The arcs are examined with respect to their spatial and temporal behavior as well as to a possible connection to solar wind parameters using ACE satellite data. It is found that the majority of polar arcs appear during northward IMF, strong IMF magnitude, and high solar wind speed. A modified Akasofu-Perreault epsilon parameter with a cosine function instead of a sine function (nuB(2) cos(4) (theta/2)(l(0)(2)/mu(0))) combines these results. It correlates well with the occurrence frequency of polar arcs for long timescales. The location of polar arcs is strongly dependent on the sign of the IMF B-y component. Static polar arcs occur in the Northern Hemisphere on the dawn (dusk) side of the oval for negative (positive) IMF B-y, whereas poleward-moving arcs separate from the opposite side of the oval, and then move in the direction of IMF B-y. All polar arcs are sorted into five different categories according to their spatial structure and evolution: oval-aligned, bending, moving, midnight, and multiple arcs. Each polar arc type occurs for a characteristic combination of solar wind parameters. IMF clock angle changes seem to have a strong influence on what type of arc occurs. Oval-aligned arcs appear mainly during steady IMF, bending arcs after an IMF B-z sign change, and moving arcs after an IMF B-y sign change. For the rare midnight and multiple arc events, no characteristic IMF clock angle dependence has been found. The different types of clear polar arcs are discussed in the context of existing observational studies and transpolar arc models.

  • 13. Kullen, A.
    et al.
    Buchert, S.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Johansson, T.
    Lileo, S.
    Eriksson, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Nilsson, H.
    Marchaudon, A.
    Fazakerley, A. N.
    Plasma transport along discrete auroral arcs and its contribution to the ionospheric plasma convection2008In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 26, no 11, p. 3279-3293Article in journal (Refereed)
    Abstract [en]

    The role of intense high-altitude electric field (E-field) peaks for large-scale plasma convection is investigated with the help of Cluster E-field, B-field and density data. The study covers 32 E-field events between 4 and 7 R-E geocentric distance, with E-field magnitudes in the range 500 1000 mV/m when mapped to ionospheric altitude. We focus on E-field structures above the ionosphere that are typically coupled to discrete auroral arcs and their return current region. Connected to such E-field peaks are rapid plasma flows directed along the discrete arcs in opposite directions on each side of the arc. Nearly all the E-field events occur during active times. A strong dependence on different substorm phases is found: a majority of intense E-field events appearing during substorm expansion or maximum phase are located on the night-side oval, while most recovery events occur on the dusk-to-dayside part of the oval. For most expansion and maximum phase cases, the average background plasma flow is in the sunward direction. For a majority of recovery events, the flow is in the anti-sunward direction. The net plasma flux connected to a strong E-field peak is in two thirds of the cases in the same direction as the background plasma flow. However, in only one third of the cases the strong flux caused by an E-field peak makes an important contribution to the plasma transport within the boundary plasma sheet. For a majority of events, the area covered by rapid plasma flows above discrete arcs is too small to have an effect on the global convection. This questions the role of discrete auroral arcs as major driver of plasma convection.

  • 14. Kullen, A.
    et al.
    Cumnock, Judy A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Seasonal dependence and solar wind control of transpolar arc luminosity2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A8Article in journal (Refereed)
    Abstract [en]

    The influence of the solar wind and the interplanetary magnetic field (IMF) on the luminosity of transpolar arcs (TPAs) is examined by taking into account seasonal effects. The study focuses on those transpolar arcs that appear after an IMF By sign change during steady northward IMF. It includes 21 northern hemisphere events identified in a previous study from global UV images taken by the Polar spacecraft between 1996 and 2000. Sorting the TPA events by sign of the Earth dipole tilt we find that the TPAs which appear in the dark hemisphere are on average much weaker than TPAs in the sunlit hemisphere. For the dark hemisphere events, no clear correlation between solar wind parameters and TPA luminosity is found. However, in the sunlit hemisphere, a clear dependence on solar wind and IMF conditions is seen. The TPA brightness is strongly influenced by IMF magnitude, northward IMF Bz and solar wind speed. A weak, negative correlation with the ion density is found. The TPA luminosity in the sunlit hemisphere is much more strongly controlled by the magnetic energy flux than by the kinetic energy flux of the solar wind. This explains the absence of transpolar arcs for the two By sign change cases for positive dipole tilts with lowest magnetic energy flux values. The strong influence of the Earth dipole tilt on the transpolar arc luminosity appears due to the dependence of the ionospheric conductivity on solar EUV emissions.

  • 15. Kullen, A.
    et al.
    Ohtani, S.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Geomagnetic signatures of auroral substorms preceded by pseudobreakups2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114Article in journal (Refereed)
    Abstract [en]

    The evolution of ten growth-phase pseudobreakups and subsequent substorms, identified in Northern Hemisphere Polar UV images during winter 1998-1999, are compared to the AE index, the unified PC indices, and GOES B field data. Comparing substorm onset (auroral breakup) with GOES data and AE and PC indices, it is found that an exact onset determination from these parameters is in most cases not possible. The three weakest substorms leave no clear signatures in the auxiliary parameters. For the other events, the AE increase appears with a time delay of 5-15 min after onset. The PC indices increase, as expected, before the AE index. The time span between PC increase and onset varies widely (-26 to 5 min). A tail dipolarization is seen in GOES data with a time delay of 2-31 min after onset. The dipolarization delay at geosynchronous orbit appears because of the GOES displacement from the tail onset region. Using the mapped GOES distance from the auroral breakup region as an estimate of GOES displacement from the breakup source region, we find that the tail dipolarization region expands in average with an azimuthal speed of 0.22 MLT min(-1) and an equatorward speed of 0.09 degrees min(-1). Pseudobreakups leave hardly any signature in AE or PC index data except in the four strongest substorm cases. In these cases, a bump appears in the PC indices during the pseudobreakup. A bump in geosynchronous B field data is found only in those two cases where GOES is located very close to the pseudobreakup tail source region.

  • 16.
    Kullen, Anita
    KTH, Superseded Departments, Alfvén Laboratory.
    The Connection Between Transpolar Arcs and Magnetotail Rotation2000In: Geophysical Research Letters, ISSN 0094-8276, Vol. 27, p. 73-76Article in journal (Refereed)
    Abstract [en]

    Recent observations show that the evolution of transpolar arcs (TPA's) are often associated with a sign change of the dawn-dusk component of the interplanetary magnetic field (IMF). It is known that a nonzero IMF B-y causes a twist of the tail plasma sheet. In this study it is assumed that a sign change of IMF B-y causes the magnetotail to rotate until the entire tail is twisted in the opposite direction. To examine a possible connection between TPA's and tail rotation the Tsyganenko 1989 model is modified such that the near-Earth tail and the far tail are twisted in opposite directions. Mapping from the tail current sheet to the ionosphere shows a separated region of closed field lines that extends into the polar cap. This separated part may be interpreted as the mapped region of a TPA.

  • 17.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Transpolar Arcs: Summary and Recent Results2012In: Auroral Phenomenology And Magnetospheric Processes: Earth And Other Planets, American Geophysical Union (AGU), 2012, p. 69-80Conference paper (Refereed)
    Abstract [en]

    This review summarizes the current understanding of transpolar arcs. The following topics are covered: (1) transpolar arc (TPA) types, (2) influence of interplanetary magnetic field (IMF) B-y and B-z on shape and motion of TPAs, (3) temporal intensifications of TPAs, (4) substorms and TPAs, (5) solar wind energy coupling, (6) ionospheric convection and source regions of TPAs, (7) interhemispheric differences caused by IMF B-x, (8) interhemispheric differences caused by the Earth dipole tilt, and (9) magnetotail topology during TPAs.

  • 18.
    Kullen, Anita
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fear, R. C.
    Milan, S. E.
    Carter, J. A.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The statistical difference between bending arcs and regular polar arcs2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 12, p. 10443-10465Article in journal (Refereed)
    Abstract [en]

    In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) B-y direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook-shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during B-y-dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90 degrees about 20min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF B-y and initial arc location. In our data set, the highest correlations are found with IMF B-y appearing at least 1-2 h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.

  • 19.
    Kullen, Anita
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Janhunen, P
    Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 3, p. 951-970Article in journal (Refereed)
    Abstract [en]

    We investigate with the help of a magnetohydro-dynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF B-y sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results. The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF B-y. The tail becomes longer and at its tailward end stronger twisted for IMF B-z > \B-y\ than for IMF B-z < \B-y\. The field lines originating in the high-latitude flank of the far-tail plasma sheet map into the near-Earth tail lobes and to a strongly poleward displaced polar cap boundary. A comparison with observations suggests that an oval-aligned arc may occur on the high-latitude part of the polar cap boundary. An IMF B-y sign change causes large deformations of the tail. After the IMF B-y flip the near-Earth and far-tail plasma sheet regions are oppositely twisted which causes in the near-Earth tail a bifurcation of the closed field line region that moves from one flank to the other. The bifurcated part of the closed field line region maps to a bridge of closed field lines moving over the entire polar cap. This moving bridge may be interpreted as the mapped region of a moving transpolar arc. Based on earlier observations, such a type of polar arcs is expected to occur after an IMF B-y sign change.

  • 20.
    Kullen, Anita
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Janhunen, P
    Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study (Vol 22, pg 951, 2004)2004In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, no 8, p. 2655-2655Article in journal (Refereed)
  • 21.
    Kullen, Anita
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory.
    On the relation between solar wind, pseudobreakups, and substorms2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no A12Article in journal (Refereed)
    Abstract [en]

    A statistical study of pseudobreakups and substorms is performed using Polar UV images from a 3-month period in winter 1998-1999. Data from the ACE solar wind monitor are examined in order to determine the influence of solar wind parameters on the occurrence of different substorm and pseudobreakup types. The results confirm that the IMF clock angle and the amount of solar wind energy flux control the strength of a substorm. The majority of large substorms appear when the IMF is strongly southward and the solar wind energy flux is high. Most small substorms occur during weakly positive or zero IMF B-z and low solar wind energy flux values. Pseudobreakups are associated with even lower energy fluxes than small substorms and appear typically for weakly positive IMF B-z. These results are in agreement with the scenario that pseudobreakups essentially are very weak substorms. Pseudobreakups appear during quiet times and during the growth phase or the recovery phase of weak or medium strong substorms. Time periods of enhanced geomagnetic activity with recurrent substorms are devoid of pseudobreakups. A detailed analysis of the different pseudobreakup types reveals that quiet time pseudobreakups appear predominantly during northward IMF. At least 20 percent of these appear at the poleward oval boundary. Optically, they do not differ much from very weak substorms. Growth phase pseudobreakups develop typically at the end of a 1 to 2 hour long excursion from northward to weakly southward IMF and are followed by quite weak substorms. A large majority of recovery phase pseudobreakups occur at a strongly polewardly displaced oval boundary at the end of a very active recovery phase. A considerable decrease of the polar cap size during the preceding substorm is connected to a northward turning of the IMF.

  • 22.
    Kullen, Anita
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sundberg, Torbjörn
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Occurrence and properties of substorms associated with pseudobreakups2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. A12310-Article in journal (Refereed)
    Abstract [en]

    We investigate how substorms with and without growth-phase pseudobreakups are affected by solar wind and ionospheric conditions. The study is based on 874 events identified with Polar UVI. An AE index analysis shows that substorms with growth-phase pseudobreakups are typically weak and appear as isolated events after hours of low geomagnetic activity. During the hours before onset the average solar wind merging field E-m is weaker, and the length of time with enhanced values shorter than for regular substorms. Integrating E-m over the last southward IMF period before onset shows an upper limit above which these substorms do not occur. To estimate how much E-m reaches the ionosphere, polar cap potential drop and unified PC indices are examined. It is found that substorms with growth-phase pseudobreakups have on average lower PC index values than regular substorms. The temporal evolution of the PC indices is similar for both substorm groups; the summer index correlates better with E-m, the winter index with AE. Also the average polar cap potential drop curves for both types of substorms resemble one other; the dayside and nightside curves are mainly influenced by E-m and AE, respectively. Comparing growth-phase, isolated and recovery pseudobreakups shows that solar wind and ionospheric conditions around the first substorm after a pseudobreakup are similar, independent of whether the last pseudobreakup appeared hours (recovery and isolated pseudobreakups) or minutes before substorm onset (growth-phase pseudobreakups). Isolated and recovery pseudobreakups are less often associated with a northward IMF rotation than growth-phase pseudobreakups or substorms.

  • 23.
    Kullen, Anita
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Thor, Simon
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    The Difference Between Isolated Flux Transfer Events and Flux Transfer Event Cascades2019In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 10, p. 7850-7871Article in journal (Refereed)
    Abstract [en]

    This flux transfer event (FTE) study is based on 984 FTEs originally identified by Wang et al. (2005, ) in Cluster data. Due to Cluster's orbit, the FTE list exclusively contains events detected at the high-latitude dayside magnetopause and low-latitude flanks. The focus of this study is on FTE separation time. The results show that FTEs appearing in cascades are mainly located at the northern dusk and southern dawn magnetopause, while isolated FTEs are equally spread over the region covered by Cluster. This difference may be explained by the different interplanetary magnetic field (IMF) conditions during which the subsets occur. For isolated FTEs, average IMF B-y is close to zero. During such conditions, FTEs are expected to form at arbitrary longitudes along an equatorial merging line. After formation, they propagate northward and southward, causing an equal distribution at higher latitudes. In contrast, FTE cascades typically occur during weakly southward IMF with a negative B-y component. Their asymmetric distribution at higher latitudes is consistent with both the component and the antiparallel merging model for nonzero B-y. In both scenarios, newly formed FTEs are expected to move to the northern dusk and southern dawn regions, as observed. Many FTE cascades appearing during northward IMF are located close to the low-latitude flanks, confirming previous reports. We discovered that such FTEs appear during large IMF values. Another new result is that 16% of all isolated FTEs appear during small IMF cone angles, suggesting that these may form as a result of magnetosheath jets impacting on the magnetopause.

  • 24.
    Liljeblad, Elisabet
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Raines, J.
    Slavin, J.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sundberg, T.
    Zurbuchen, T. H.
    MESSENGER observations of the dayside low-latitude boundary layer in Mercury's magnetosphere2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 10Article in journal (Refereed)
    Abstract [en]

    Observations from MESSENGER's MAG and FIPS instruments during the first orbital year have resulted in the identification of 25 magnetopause crossings in Mercury's magnetosphere with significant low-latitude boundary layers (LLBLs). Of these crossings 72% are observed dawnside, and 65% for northward interplanetary magnetic field.

    The estimated LLBL thickness is 450 ± 56 km, and increases with distance to noon. The Na+-group ion is sporadically present in 14 of the boundary layers, with an observed average number density of 22 ± 11% of the proton density. Furthermore, the average Na+-group gyroradii in the layers is 220 ± 34 km, the same order of magnitude as the LLBL thickness.

    Magnetic shear, plasma β and reconnection rates have been estimated for the LLBL crossings, and compared to those of a control group (non-LLBL) of 61 distinct magnetopause crossings which show signs of nearly no plasma inside the magnetopause. The results indicate that reconnection is significantly slower, or even suppressed, for the LLBL crossings compared to the non-LLBL cases.

    Possible processes that form or impact the LLBL are discussed. Protons injected through the cusp or flank may be important for the formation of the LLBL. Furthermore, the opposite asymmetry in the Kelvin-Helmholtz instability (KHI) as compared to the LLBL, rules out the KHI as a dominant formation mechanism. However, the KHI and LLBL could be related to each other, either by the impact of sodium ions gyrating across the magnetopause, or by the LLBL preventing the growth of KH waves on the dawnside.

  • 25.
    Liljeblad, Elisabet
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sundberg, Torbjörn
    KTH.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Observations of magnetospheric ULF waves in connection with the Kelvin-Helmholtz instability at Mercury2016In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 9, p. 8576-8588Article in journal (Refereed)
    Abstract [en]

    The magnetic field data from the MESSENGER spacecraft is investigated to establish the presence of magnetospheric ultra-low frequency (ULF) waves in connection with 131 previously observed nonlinear Kelvin-Helmholtz (KH) waves at Mercury. Distinct ULF wave signatures are detected in 44 out of the 131 magnetospheric traversals prior to or after observing the KH waves. Of these ULF events, 39 out of 44 are highly coherent at the frequency of maximum power spectral density, and occur more often on the dayside magnetosphere than away from it. The waves observed at the dayside magnetosphere, which appear mainly at the duskside and naturally following the KH wave occurrence asymmetry, are significantly different to the evening- or morningside events, and have the following distinct wave characteristics: a polarization mainly in the perpendicular (azimuthal) direction to the mean magnetic field, a wave normal angle closer to the parallel than the perpendicular direction, an absolute ellipticity increasing away from noon, almost exclusively a right-hand polarization, and frequencies in the narrow range of 0.02 − 0.04 Hz (well below the local Na +  gyrofrequency, and in the same range as the KH waves). The results strongly suggest that the large majority of the ULF waves at the dayside observed in this study are driven by KH waves at the magnetopause, and that they occur in the vicinity of a field line resonance, which in turn manifests the importance of the Kelvin-Helmholtz instability in terms of energy and momentum transport throughout Mercury's magnetosphere.

  • 26.
    Liljeblad, Elisabet
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sundberg, T.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Statistical investigation of Kelvin-Helmholtz waves at the magnetopause of Mercury2014In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 119, no 12, p. 9670-9683Article in journal (Refereed)
    Abstract [en]

    A large study of Kelvin-Helmholtz (KH) waves at the magnetopause of Mercury covering 907 days of data from the MErcury Surface Space ENvironment GEochemistry Ranging spacecraft have resulted in 146 encounters of not only nonlinear KH waves but also linear surface waves, including the first observations of KH waves at the dawnside magnetopause. Most of the waves are in the nonlinear phase (90%) occur at the duskside magnetopause (93%), under northward magnetosheath magnetic field conditions (89%) and during greater magnetosheath Bz (23 nT) values than in general. The average period and amplitude is 30 ± 14 s and 14 ± 10 nT, respectively. Unlike duskside events, dawnside waves do not appear at the magnetopause flank (&lt;6 magnetic local time). This is in agreement with previous observations and modeling results and possibly explained by finite Larmor radius effects and/or a lack of a large-scale laminar flow at the dawnside magnetopause boundary. Key Points Observing Kelvin-Helmholtz waves at the dawnside Mercury magnetopause Confirming a dawn-dusk asymmetry associated with the Kelvin-Helmholtz at Mercury Determine characteristics associated with Kelvin-Helmholtz waves

  • 27. Mailyan, B.
    et al.
    Shi, Q. Q.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    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 magnetosphere2015In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, no 5, p. 3525-3534Article in journal (Refereed)
    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.

  • 28. Pitkanen, T.
    et al.
    Hamrin, M.
    Norqvist, P.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, H.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Imber, S. M.
    Milan, S. E.
    Azimuthal velocity shear within an Earthward fast flow - further evidence for magnetotail untwisting?2015In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, no 3, p. 245-255Article in journal (Refereed)
    Abstract [en]

    It is well known that nonzero interplanetary magnetic field B-y conditions lead to a twisted magnetotail configuration. The plasma sheet is rotated around its axis and tail magnetic field lines are twisted, which causes an azimuthal displacement of their ionospheric footprints. According to the untwisting hypothesis, the untwisting of twisted field lines is suggested to influence the azimuthal direction of convective fast flows in the nightside geospace. However, there is a lack of in situ magnetospheric observations, which show actual signatures of the possible untwisting process. In this paper, we report detailed Cluster observations of an azimuthal flow shear across the neutral sheet associated with an Earthward fast flow on 5 September 2001. The observations show a flow shear velocity pattern with a V-perpendicular to y sign change, near the neutral sheet (B-x similar to 0) within a fast flow during the neutral sheet flapping motion over the spacecraft. Firstly, this implies that convective fast flows may not generally be unidirectional across the neutral sheet, but may have a more complex structure. Secondly, in this event tail B-y and the flow shear are as expected by the untwisting hypothesis. The analysis of the flow shear reveals a linear dependence between B-x and V-perpendicular to y close to the neutral sheet and suggests that Cluster crossed the neutral sheet in the dawnward part of the fast flow channel. The magnetospheric observations are supported by the semi-empirical T96 and TF04 models. Furthermore, the ionospheric SuperDARN convection maps support the satellite observations proposing that the azimuthal component of the magnetospheric flows is enforced by a magnetic field untwisting. In summary, the observations give strong supportive evidence to the tail untwisting hypothesis. However, the T96 ionospheric mapping demonstrates the limitations of the model in mapping from a twisted tail.

  • 29.
    Pitkanen, T.
    et al.
    Shandong Univ, Inst Space Sci, Weihai, Peoples R China.;Umea Univ, Dept Phys, Umea, Sweden..
    Kullen, Anita
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    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 20092018In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 9, p. 7486-7497Article in journal (Refereed)
    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.

  • 30. Pitkänen, T.
    et al.
    Hamrin, M.
    Karlsson, Tomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Nilsson, H.
    Kullen, A.
    On IMF By-lnduced dawn-dusk asymmetries in earthward convective fast flows2017In: Dawn-Dusk Asymmetries in Planetary Plasma Environments, Wiley Blackwell , 2017, p. 95-106Chapter in book (Other academic)
    Abstract [en]

    Studies of earthward plasma and magnetic field transport in the Earth's magnetotail plasma sheet have shown that, on the average, Earthward ion flows in the premidnight and midnight sectors exhibit a duskward component while flows in the postmidnight sector are dawnward. The flow pattern is more pronounced for slower flows (&lt;100 km/s) and alters gradually to a more symmetric one with respect to midnight for increasing flow speeds. However, recent ionospheric and magnetospheric studies have suggested that a nonzero By component in the interplanetary magnetic field (IMF) may significantly influence the earthward transport, creating previously unnoticed dawn-dusk asymmetries between the hemispheres. In this article, we give a short overview of the present understanding of the topic, present new results, and briefly discuss the importance of the IMF By component for the Earthward transport processes in the magnetotail plasma sheet.

  • 31. Pitkänen, T.
    et al.
    Hamrin, M.
    Kullen, Anita
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Maggiolo, R.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Nilsson, H.
    Norqvist, P.
    Response of magnetotail twisting to variations in IMF B-y: A THEMIS case study 1-2 January 20092016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 15, p. 7822-7830Article in journal (Refereed)
    Abstract [en]

    Theoretical considerations, observations, and simulations have shown that the B-y component of the interplanetary magnetic field (IMF) may cause twisting of the magnetotail. However, the fundamental issues, the temporal and spatial responses of the magnetotail in the twisting process, are still unresolved. We report unique multipoint observations of the response of the magnetotail to the variations in IMF B-y on 1-2 January 2009. For the first time, estimates of the tail twisting response time at different (Time History of Events and Macroscale Interactions during Substorms, THEMIS) distances in the same event are inferred. Using cross-correlation and timing analyses, we find that the tail twisting propagates from farther out toward the Earth and the response time increases significantly to the inner magnetosphere.

1 - 31 of 31
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