Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006ihy..worke..51s&link_type=abstract
2nd UN/NASA Workshop on International Heliophysical Year and Basic Space Science. Proceedings of the conference held 27 Novembe
Astronomy and Astrophysics
Astrophysics
Scientific paper
In this talk, I shall endeavor to present a concise review of recent work concerning the equatorial geomagnetic and ionospheric effects of variations in solar wind dynamic pressure, Pd at the sub-solar magnetopause. Though the equatorial effects are the primary concern here, the global perspective will be retained to provide an overall picture of the coupling processes involving the magnetosphere-high latitude ionosphere-low latitude ionosphere domains. Two types of Pd changes are dealt with here. The first one is the sudden step-like increase in Pd representative of interplanetary shocks and other discontinuities in the solar wind that lead to the well-known geomagnetic storm sudden commencements (SSC) and sudden impulses (SI). These abrupt changes in Pd are documented to also initiate, at times, magnetospheric substorms and long-period ( 1hour) magnetospheric and ionospheric oscillations. Variation in Pd on time scales longer that of shocks and discontinuities are the other type. Awareness of the geomagnetic field response to this type of Pd changes is fairly recent and experimental evaluation of the physical situation that prevail at auroral and equatorial regions where the contribution of ionospheric currents may be expected to be as significant as those of magnetopause currents is indeed at a nascent stage now. In contrast, SSC and SI have been extensively studied over the decades using ground and space-borne magnetometers and a credible phenomenological model based on them has been developed, as also numerical modeling. Nonetheless, several fundamental and important questions remain to be settled. Foremost among these are: (1) the origin of the bi-modal response of the equatorial daytime H-field to sudden magnetospheric compressions induced by shocks with the resulting SSC taking two distinct forms, namely, with and without a preliminary reverse impulse (PRI) which occur more or less with equal frequency and (2) the mechanism of extension of the PRI from high latitudes to the dayside dip equator (propagation through the Earth-ionosphere waveguide or following the so-called ‘Tamao path’?). It is argued that to achieve progress in resolving these and other issues, in addition to the existing meridional magnetometer networks, the longitudinal network of equatorial magnetometers (run as a part of Circum-pan Pacific Magnetometer Network, CPMN by Kyushu University, Japan) needs to be strengthened as regards spatial coverage and GPS- time synchronization. New initiatives aimed at establishment of longitudinal networks of well chosen passive diagnostics of the ionosphere medium are also needed for the dip equatorial region. These requirements can be realized under the aegis of International collaborative and cooperative programs such as IHY.
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