The Dense Sheath Region of Magnetic Clouds as an Interplanetary Trigger of Geomagnetic Storms

Details The Dense Sheath Region of Magnetic Clouds as an Interplanetary Trigger of Geomagnetic Storms The Dense Sheath Region of Magnetic Clouds as an Interplanetary Trigger of Geomagnetic Storms

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh42a0476f&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH42A-0476

Physics

2111 Ejecta, Driver Gases, And Magnetic Clouds, 2784 Solar Wind/Magnetosphere Interactions, 2788 Storms And Substorms

Scientific paper

Interplanetary coronal mass ejections and, in particular, their subset magnetic clouds, are known to cause the strongest geomagnetic disturbances, as measured by storm intensity, substorm recurrence rate, etc. Past work has shown that, through compression of pre-existing pre-shock Bz < 0 fields, the sheath region ahead of the ejecta may elicit geomagnetic activity in its own right. We present here a case where a combination of these two triggers are present. The interval of negative Bz in the sheath is separated from that in the ejecta by a strong northward turning. The example leads to an extreme manifestation of the above: the storm main phase occurs exclusively during Earth passage of the sheath region and the recovery phase has already set in when the magnetic cloud, the initial part of which had an even more strongly negative Bz than the sheath, arrives. We find that the popular "energy coupling" functions ɛ and VBs give an erroneous prediction of the geoeffects. The data suggest the need of including the solar wind momentum flux in so-called energy coupling functions. A link between substorms and storms is suggested by the data: The density of the plasma sheet is enhanced episodically at each substrom onset. In sum, the dense sheath region of ejecta is a further interplanetary source of goeffects at times exceeding those of the ejecta itself. This work is a contribution to the study of interplanetary sources of geomagnetic dusturbances. This work is supported in part by NASA grant NAG5-13512.

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