Time delay of interplanetary magnetic field penetration into Earth's magnetotail

Abstract

Many previous studies have demonstrated that the interplanetary magnetic field (IMF) can control the magnetospheric dynamics. Immediate magnetospheric responses to the external IMF have been assumed for a long time. The specific processes by which IMF penetrates into magnetosphere, however, are actually unclear. Solving this issue will help to accurately interpret the time sequence of magnetospheric activities (e.g., substorm and tail plasmoids) exerted by IMF. With two carefully selected cases, we found that the penetration of IMF into magnetotail is actually delayed by 1-1.5 h, which significantly lags behind the magnetotail response to the solar wind dynamic pressure. The delayed time appears to vary with different auroral convection intensity, which may suggest that IMF penetration in the magnetotail is controlled considerably by the dayside reconnection. Several unfavorable cases demonstrate that the penetration lag time is more clearly identified when storm/substorm activities are not involved.

The statistical difference between bending arcs and regular polar arcs

“…Although the precise peak of the Spearman's rank correlation shifts depending on data set and time period over which IMF B y is averaged over, there is a common trend in all three plots: A stronger correlation is obtained for any hour chosen between 1 and 7 h before the arc formed than in the hour immediately before formation. Considering that the formation of polar arcs is according to several polar arc models tightly connected to IMF B y induced changes in the magnetotail, the 1–2 h time delay between IMF B y and its effect on initial arc location is in agreement with a recent report by Rong et al [] of a 60–90 min time delay until IMF B y penetrates the inner magnetotail. The small differences in the results of Figure and (top left) indicate the case‐to‐case variation in the time taken for the IMF B y component to influence the initial arc location.…”

Timescales for the penetration of IMF By into the Earth's magnetotail

“…The patches were tracked as they convected across the polar cap and returned at lower latitudes as part of the Dungey cycle. The timescales taken for the polar cap patches to convect from noon to midnight in MLT were approximately 1–2 h, in agreement with Rong et al [] but slightly shorter than those found by Fear and Milan []. One possible explanation for the apparent disagreement with the convection timescales from these three studies is the differences in the IMF conditions.…”

Magnetospheric response and reconfiguration times following IMF By reversals

“…Rong et al [] reported 1–1.5 h lag time between the IMF B y and magnetotail B y , based on two events. Both events are chosen to coincide with a strong solar wind dynamic pressure pulse, and in both cases the IMF B z is northward.…”

“…However, we do not know how efficient this will be and what the associated time scales would be. In the events studied by Rong et al [] there is a pressure pulse coinciding with the IMF B y change which may mask earlier signatures of any change in IMF‐induced B y . Analyzing such events and separating spatiotemporal changes from IMF‐induced effects is problematic.…”

“…Rong et al [] reported the penetration of IMF into the magnetotail to be delayed by 1–1.5 h, based on two events. Motoba et al [] analyzed one event and found the highest correlation between IMF B y and B y in the central magnetotail measured by Cluster when lagging the solar wind by 51 (57 from bow shock reference) min (reconfiguration time defined by maximum correlation).…”