We discuss two phases of the substorm‐associated magnetospheric dynamics in terms of the particles and fields at synchronous orbit. The first phase corresponds to the ‘decreases’ of energetic ...particle flux first identified by Erickson and Winckler (1973) and discussed by Walker et al. (1976) and Erickson et al. (1979). This phase begins one‐half hour to one hour before the substorm onset and is characterized by (1) a distortion of the magnetosphere to a more taillike configuration caused by (2) an intensification and/or motion toward the earth of the cross‐tail current and of its earthward part, the partial ring current, (3) a shift of trapped particle trajectories closer to the earth on the nightside following contours of constant B causing the particle ‘decreases,’ accompanied by a change in the pitch angle distributions from ‘pancake’ to ‘butterfly’ as observed at geostationary orbit, (4) an initiation of a response of the auroral electrojet (AE) index. The decreases of energetic particle flux can correspond to the substorm growth phase as defined initially by McPherron (1970) or the growth or precursor phase of Erickson et al. (1979). Plasma motions and currents during decreases tend to be variable, but the description above nevertheless characterizes the large‐scale trend. It is suggested that the electric field induced by the increasing tail current near the earth acts opposite to the cross‐tail convection field and can temporarily inhibit convection near the geostationary orbit. The second phase is the conventional expansion phase that begins with the ‘onset,’ characterized in our study by (1) a sudden decrease in the tail current and a return of the inflated magnetosphere to a dipolelike configuration, (2) a sudden shift of trapped high‐energy particles toward the tail again following contours of constant B, and at the same time (3) a surge of tail plasma toward the earth as the induced electric field now increases the total convection field. Separate effects thus result in the dramatic increases of both high energy and plasma particles seen at substorm expansion phase onset, (4) an AE index response and the appearance of bays at stations near midnight local time accompanied by very active aurora as well as the precipitation of high‐energy particles. The different appearance of the responses at ATS 1 (on the magnetic equator) and ATS 6 (off the magnetic equator) can be well explained by the above description. True diamagnetic effects of the particle population are clearly evident at the ATS 6 region and must be carefully distinguished from the effects of distant currents. The use of oppositely directed detectors on ATS 6 that permit the evaluation of the guiding center particle density gradients has been of great use in this analysis.
ASPERA-4 (Analyzer of Space Plasmas and Energetic Atoms) is a package of an electron spectrometer, ion mass analyzer, and two energetic neutral atom imagers. In this talk we report the first ASPERA-4 ...observations during the period April - December 2006. The structure of the Venus - solar wind interaction region as characterized by the ASPERA-4 experiment includes the following regions and boundaries bow shock, magnetosheath, induced magnetosphere boundary and induced magnetosphere, pho-toelectron boundary. The similar structure is identified at Mars. However, at Venus the flux of the planetary ions is more stable and better reproducible over the observational period. Similar to Mars the photoelectron peaks observed when the spacecraft entries the ionosphere. Photoelectrons result from the photodissociation of CO sub(2) and have the typical energy around 22 - 28 eV. Observations of the photoelectrons shows that the satellite is magnetically connected with the Venus ionosphere. Photoelectrons are used to introduce a new boundary not detected at Venus before, a photoelectron boundary similar to Mars. ASPERA-4 established for the first time composition of the escaping planetary ions. The main escaping ion is O super(+) in contrast to Mars where the escaping plasma consists of approximately equal amounts of O super(+), O super(+) sub(2) and 20-50% submixure of CO super(+) sub(2). This results from higher gravity at Venus which bounds heavier components such as CO super(+) sub(2) closer to the surface. The induced magnetosphere is also filled by low energy protons from 10 eV (the instrument lower limit) to the solar wind energy. The observed escaping He super(+) has never been detected at Venus before. However, to constrain the escape rate of this gas is critical for establishing helium balance at Venus that, in turn, is needed to estimate the radiogenic production rate. The detected fluxes of He super(+) exceed the ones at Mars on more than an order.
Magnetopause Kelvin-Helmholtz (KH) waves are believed to mediate solar wind plasma transport via small-scale mechanisms. Vortex-induced reconnection (VIR) was predicted in simulations and recently ...observed using NASA's Magnetospheric Multiscale (MMS) mission data. Flux Transfer Events (FTEs) produced by VIR at multiple locations along the periphery of KH waves were also predicted in simulations but detailed observations were still lacking. Here we report MMS observations of an FTE-type structure in a KH wave trailing edge during KH activity on 5 May 2017 on the dawnside flank magnetopause. The structure is characterised by (1) bipolar magnetic BY variation with enhanced core field BZ and (2) enhanced total pressure with dominant magnetic pressure. The cross-section size of the FTE is found to be consistent with vortex-induced flux ropes predicted in the simulations. Unexpectedly, we observe an ion jet (VY), electron parallel heating, ion and electron density enhancements, and other signatures that can be interpreted as a reconnection exhaust at the FTE central current sheet. Moreover, pitch angle distributions of suprathermal electrons on either side of the current sheet show different properties, indicating different magnetic connectivities. This FTE-type structure may thus alternatively be interpreted as two interlaced flux tubes with reconnection at the interface as reported by Kacem et al. (2018) and Øieroset et al. (2019). The structure may be the result of interaction between two flux tubes, likely produced by multiple VIR at the KH wave trailing edge, and constitutes a new class of phenomenon induced by KH waves.
The Cluster mission is intended for the study of the Earth’s magnetosphere and Sun-Earth relationships. Four satellites fly in a tetrahedral formation sending data that can separate spatial from ...temporal effects for the first time. This formation will provide a better understanding of microscopic and macroscopic features in the magnetosphere and the solar wind. As an illustration we discuss the CIS data during a large magnetic storm.
We report evidence of a long-lasting reconnection event during which the accelerated plasma flow direction changes in response to an interplanetary magnetic field (IMF) B sub(y) reversal, indicating ...a change in the reconnection site location. The observations were made by Equator-S on the dawn flank of the magnetopause and consist of a large number of plasma jets detected mostly within magnetospheric flux transfer events. The plasma jets were found in quantitative agreement with the theoretical predictions for reconnection. The reversal of the plasma flow direction in the jets following the reversal of the B sub(y) component not only confirms that the dayside reconnection configuration is controlled by the IMF, as opposed to local control, but also stresses the importance of the IMF dawn-dusk component, in addition to the north-south component, in determining the global configuration of the reconnection.
The Salammbo 3D code was applied to the January 25, 1991 event in an attempt to reproduce the radiation belt response to a geomagnetic storm on the 10 hr-10 day time scale. The model can successfully ...reproduce flux variations that occur over a time scale on the order of half a day. The electron dynamics is characterized, and results obtained from the model are presented. Finally, simulation results are compared with CRRES measurements of electron fluxes. (AIAA)
The objective of the study was to reproduce the radiation belt response to a geomagnetic storm on the 10 min-10 hr scale. For this purpose, the new Salammbo 4D code was applied to the January 24, ...1991 event. The model is capable of reproducing flux variations on a time scale on the order of ten minutes. The proton dynamics is examined, and simulation results are compared against CRRES measurements. (AIAA)
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