Abstract
Abstract. The first comprehensive statistical study of large-amplitude (> 100%) transient enhancements of the magnetosheath dynamic pressure reveals events of up to ~ 15 times the ambient dynamic pressure with durations up to 3 min and an average duration of around 30 s, predominantly downstream of the quasi-parallel shock. The dynamic pressure transients are most often dominated by velocity increases along with a small fractional increase in the density, though the velocity is generally only deflected by a few degrees. Superposed wavelet transforms of the magnetic field show that, whilst most enhancements exhibit changes in the magnetosheath magnetic field, the majority are not associated with changes in the Interplanetary Magnetic Field (IMF). However, there is a minority of enhancements that do appear to be associated with solar wind discontinuities which cannot be explained simply by random events. In general, it is found that during periods of magnetosheath dynamic pressure enhancements the IMF is steadier than usual. This suggests that a stable foreshock and hence foreshock structures or processes may be important in the generation of the majority of magnetosheath dynamic pressure enhancements.
Highlights
Model DGeevoeslocipemnteifnicthseiniiattgnyhceianernmcidnreecnavrsetesealossa.ceriseItnyoinrr(odAgueemgcnhreaelrtyaaasl7Meed0stuw%oaelhd.t,oiolef2svt0tlaht1hreD1Giea)j,tleeiaetottsvhtnoeeresresfpiglnoocoeDrrnbimpiteseoecermdtnauhrlsbtlsetsyyihhifoenosiSnchwdstaoivewnnign--et al (2008) in the flank magnetosheath, peaks in the den-The magnetosheath acts as an interface between the so- sity and velocity did not coincide and the peak in the dylar wind and the magnetopause and it is Htheyrdefrooreloimgpyor-andnamic pressure more often than notHcoyrrdesrpoolnodgedytoathnedpeak tant to in this ruengdieorns.taInndphaortwicusloalrarthweinmdagpnroeptoesrhtieeEastaharrpetrhemsosSudriyefiesidstemin density.Archer et al.(E20a1r2t)hshSowyesd tdeymnamic relevant in terms of the position and motion of tShecmieang-cesPublished by Copernicus Publications on behalf of the European Geosciences Union
Horbury: Magnetosheath dynamic pressure enhancements pressure pulses observed in the subsolar magnetosheath that were dominated by the velocity
It is unlikely that the enhancements can be explained by the “magnetic slingshot” effects described by Chen et al (1993), Lavraud et al (2007) and Lavraud and Borovsky (2008), which come into play predominantly downstream of the Earth under lowMach-number solar wind and northward Interplanetary Magnetic Field (IMF)
Summary
Model DGeevoeslocipemnteifnicthseiniiattgnyhceianernmcidnreecnavrsetesealossa.ceriseItnyoinrr(odAgueemgcnhreaelrtyaaasl7Meed0stuw%oaelhd.t,oiolef2svt0tlaht1hreD1Giea)j,tleeiaetottsvhtnoeeresresfpiglnoocoeDrrnbimpiteseoecermdtnauhrlsbtlsetsyyihhifoenosiSnchwdstaoivewnnign--et al (2008) in the flank magnetosheath, peaks in the den-The magnetosheath acts as an interface between the so- sity and velocity did not coincide and the peak in the dylar wind and the magnetopause and it is Htheyrdefrooreloimgpyor-andnamic pressure more often than notHcoyrrdesrpoolnodgedytoathnedpeak tant to in this ruengdieorns.taInndphaortwicusloalrarthweinmdagpnroeptoesrhtieeEastaharrpetrhemsosSudriyefiesidstemin density.Archer et al.(E20a1r2t)hshSowyesd tdeymnamic relevant in terms of the position and motion of tShecmieang-ces. Et al (2008) in the flank magnetosheath, peaks in the den-. The magnetosheath acts as an interface between the so- sity and velocity did not coincide and the peak in the dylar wind and the magnetopause and it is Htheyrdefrooreloimgpyor-andnamic pressure more often than notHcoyrrdesrpoolnodgedytoathnedpeak tant to in this ruengdieorns.taInndphaortwicusloalrarthweinmdagpnroeptoesrhtieeEastaharrpetrhemsosSudriyefiesidstemin density. (E20a1r2t)hshSowyesd tdeymnamic relevant in terms of the position and motion of tShecmieang-ces. S. Horbury: Magnetosheath dynamic pressure enhancements pressure pulses observed in the subsolar magnetosheath that were dominated by the velocity
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