A detailed description of the solar wind triggers of two dayside transients: Events of 25 July 1997

Details A detailed description of the solar wind triggers of two dayside transients: Events of 25 July 1997 A detailed description of the solar wind triggers of two dayside transients: Events of 25 July 1997

Jan 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004jgra..10901201z&link_type=abstract

Journal of Geophysical Research, Volume 109, Issue A1, CiteID A01201

Physics

Magnetospheric Physics: Solar Wind/Magnetosphere Interactions, Magnetospheric Physics: Magnetopause, Cusp, And Boundary Layers, Interplanetary Physics: Discontinuities, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions

Scientific paper

Traveling Convection Vortices (TCVs), a specific type of dayside transient event, offer a good opportunity to study the modes of interaction between the solar wind, bow shock and the magnetosphere/ionosphere system. We study here in detail the solar wind triggers of two TCV events that occurred at 1500 UT and 1835 UT on 25 July 1997. During these two events there was a fortuitous conjunction of four solar wind monitors near the Earth's magnetosphere. We were able to identify the exact solar wind discontinuity that triggered each ground TCV. We found that the 1500 UT TCV was triggered by the density (and thus dynamic pressure) enhancement accompanying a tangential discontinuity. We were able to determine the orientation of the discontinuity plane and thus predict, in good agreement with observations, the propagation of the discontinuity between the four spacecraft as well as the propagation of the transient in the magnetosphere (geosynchronous) and ionosphere. The ground transient was generated in the early afternoon local time and then propagated westward, first toward local noon and then away from noon toward dawn. The 1835 UT TCV, which was stronger, was triggered by a more complicated solar wind discontinuity that exhibited significant spatial structure and an unusual propagation pattern. A detailed analysis of the orientation of the discontinuity fronts explained the propagation of the discontinuity in the solar wind. Even though the discontinuity did not carry a significant dynamic pressure enhancement, it had the properties required to generate a hot flow anomaly (HFA) or a foreshock cavity at the bow shock. The corresponding pressure reduction in the magnetosheath interacted with the magnetosphere to generate the transient near local noon that propagates eastward toward dusk. Geosynchronous observations confirm these conclusions. To strengthen our conclusions, we compared the discontinuity that triggered the ground TCV event with four other discontinuities that occurred in the same 2-hour window. We found that none of the other four discontinuities carried significant dynamic pressure enhancements or had properties required to create a HFA at the bow shock. They did not trigger detectable transients on the ground. It thus seems that TCVs can be triggered by solar wind discontinuities that either carry dynamic pressure enhancements (or alternatively reductions) or by discontinuities that create HFAs or foreshock cavities at the bow shock.

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