Effect of sudden solar wind dynamic pressure changes at subauroral latitudes: Change in magnetic field

Abstract

The observations obtained during the International Magnetospheric Study (IMS) from the magnetometers of the IGS network extending from Cambridge, England, to Tromso, Norway, are used to study the response of subauroral current systems to sudden changes in solar wind dynamic pressure. Observations show that the response is very strong at subauroral latitudes. The preliminary response in the H component is a brief, small increase in the dayside morning sector and a decrease in the afternoon and night sectors. The main response in the horizontal field (the H and D components) is toward the pole except in the dayside morning sector. The inferred ionospheric current is mainly a circulatory system flowing counterclockwise when viewed from the north pole everywhere at subauroral latitudes except the dayside morning sector.

Interactions of the heliospheric current and plasma sheets with the bow shock: Cluster and Polar observations in the magnetosheath

“…The International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain, located postnoon between 1400 and 1500 MLT in Scandinavia, saw a positive change of nearly 100 nT, peaking near 1220 UT and then decaying (not shown). Similar to results reported by Le et al [1993], the prenoon responses observed by the magnetometer at Narsarsauq, Greenland, were negative.…”

“…[59] A further consequence of the HPS-HCS passage is a sudden impulse in the northward magnetic field recorded by subauroral dayside ground magnetometers [e.g., Le et al, 1993;Russell and Ginskey, 1995], an ionospheric current response to the HPS density increase. The International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain, located postnoon between 1400 and 1500 MLT in Scandinavia, saw a positive change of nearly 100 nT, peaking near 1220 UT and then decaying (not shown).…”

Some aspects of the geomagnetic response to solar wind pressure variations: a case study at low and middle latitudes

“…The differences between groups include, in our opinion, several aspects of the more generic "morning/afternoon asymmetry" proposed by previous analysis. Indeed, a visual inspection of the experimental observations reported in the scientific literature suggests that, as for the present case, the transition between structures with different characteristics of the H component typically occurs at later MLTs for higher latitudes (namely, in the early morning hours at ∼30 • -35 • , around noon at ∼55 • -60 • ; Le et al, 1993;Russell and Ginskey, 1995;Tsunomura, 1998). Our results also reveal that the different responses at different sites basically reflect a close correspondence between the magnetospheric and the ground signals which occur along an axis that progressively rotates from N/S (night events) to an E/W orientation (dawn events).…”

“…At subauroral latitudes (∼54 • -58 • ), the asymptotic response shows a different pattern, with strongly depressed (and even negative) values in the morning, and enhanced values in the afternoon (∼30 nT/(nPa) 1/2 ; Russell and Ginskey, 1995). Previous analysis of the latitudinal dependence of the asymptotic variation (H component) showed a negative gradient between ∼5 • -50 • , both in diurnal and nocturnal sectors (Le et al, 1993;Russell et al, 1994a, b); more recently, however, Francia and Lepidi (2002) found a positive gradient between ∼36 • -65 • , in the afternoon sector. On the other hand, since early investigations (Matsushita, 1962;Nishida and Jacobs, 1962) different waveforms of the H component were detected at different stations.…”

“…We focused specific attention on the correspondence between the magnetospheric field (B) observed at geostationary orbit in the noon quadrant and geomagnetic field measurements at different sites. Following previous investigations (Russell et al, 1992(Russell et al, , 1994aLe et al, 1993;Russell and Ginskey, 1995;Francia et al, 1999, we carefully examined the aspects of the MLT and latitudinal dependence of the asymptotic response.…”