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

Abstract

Previous studies have shown that there is a correlation between the By component of the interplanetary magnetic field (IMF) and the By component observed in the magnetotail lobe and in the plasma sheet. However, studies of the effect of IMF By on several magnetospheric processes have indicated that the By component in the tail should depend more strongly on the recent history of the IMF By rather than on the simultaneous measurements of the IMF. Estimates of this timescale vary from ∼25 min to ∼4 h. We present a statistical study of how promptly the IMF By component is transferred into the neutral sheet, based on Cluster observations of the neutral sheet from 2001 to 2008, and solar wind data from the OMNI database. Five thousand nine hundred eighty‐two neutral sheet crossings during this interval were identified, and starting with the correlation between instantaneous measurements of the IMF and the magnetotail (recently reported by Cao et al. (2014)), we vary the time delay applied to the solar wind data. Our results suggest a bimodal distribution with peaks at ∼1.5 and ∼3 h. The relative strength of each peak appears to be well controlled by the sign of the IMF Bz component with peaks being observed at 1 h of lag time for southward IMF and up to 5 h for northward IMF conditions, and the magnitude of the solar wind velocity with peaks at 2 h of lag time for fast solar wind and 4 h for slow solar wind conditions.

Conjugate Observations of the Evolution of Polar Cap Arcs in Both Hemispheres

“…Note that the PCA showed clear dawn-dusk motions corresponding to the IMF B y variations (seen in Figures 1 and 2) and the PCAs, observed by the ASI at the YRS in the nightside sectors, suddenly brightened at least around the two typical IMF B y polarity changes and faded during their evolutions (seen in Figure 2). Figure 1, the PCA dawn-dusk motions responded to IMF B y polarity changes after about 69 min, which is consistent with the timescales for magnetospheric convection and/or the IMF B y penetration into the magnetotail and consequent tail reconfiguration (twists) (Browett et al, 2017;Cowley, 1981;Fear & Milan, 2012;Kullen et al, 2015;Rong et al, 2015;Walker et al, 1999;Zhang et al, 2015). A few previous observational results and MHD simulations suggested that the tail twist was stronger during northward IMF than that during southward IMF (Kullen & Janhunen, 2004;Walker et al, 1999).…”

How Much Flux Does a Flux Transfer Event Transfer?

“…Therefore, although Russell and Elphic (1979) argued that their estimates should be treated as a lower limit to the true total rate of reconnection at the time (due to the possibility of missed events if the satellite was poorly situated), we argue that their estimates should be considered as being an upper limit of the flux estimates per event that can reasonably be derived in this way from spacecraft observations. Given the mean repetition rate of FTE signatures of ∼8 min (Lockwood & Wild, 1993; and taking a typical cross polar cap convection time of ∼2 h for moderately or strongly southward interplanetary magnetic field (IMF) conditions (Browett et al, 2017;Cowley, 1981;Rong et al, 2015;Zhang et al, 2015), in which time the polar cap is entirely refreshed, this implies that flux transfer events are typically capable of providing 1.5-15% of the flux transfer into the magnetotail; the implication of this estimate is that the balance is contributed by quasi-steady reconnection, in which case flux transfer events form a relatively minor part of the Dungey cycle (as argued by Newell & Sibeck, 1993, though their assumptions and conclusions were disputed by Lockwood et al, 1995).…”

Detailed Regression Model of Plasma Sheet By

“…This publication also contains a detailed review of other relevant issues. Browett et al (2017) directly addressed penetration delay in the magnetotail as measured by correlation coefficients and suggested that the times about 1 hr are more typical for the southward IMF and up to 3-5 hr for the northward IMF.…”