The Influence of Localized Dynamics on Dusk-Dawn Convection in the Earth’s Magnetotail

摘要

Previous work has shown that earthward convective flow bursts in the magnetotail have a dusk- dawn (v⊥y) component that is controlled by the historical state of the Interplanetary Magnetic Field (IMF) By component. Here, we analyze 27 years of Cluster, THEMIS and Geotail plasma and magnetic field data and identify 1,639 magnetotail fast flow “detections” that demonstrate a dusk-dawn asymmetry. We find that ~70% has a dusk-dawn direction consistent with that expected from the penetration of IMF B_y. Superposed epoch analysis suggests that the inconsistency of the remaining ~30% is not due to a lack of the expected IMF By penetration. Instead, we find that on average, the expected sense of IMF By penetration is associated with flows irrespective of whether those flows agree or disagree with the expected dusk-dawn asymmetry. IMF By, and the penetrated By do, however, tend to be stronger for “agree” flows. Detections which agree (disagree) tend to be accompanied by a localized perturbation to the By component of the magnetotail magnetic field in the same sign as (opposite to) the prevailing IMF By conditions, which temporarily enhances (overrides) the penetrated field. Agree (disagree) flows also appear to be observed further away from (closer to) the neutral sheet (B_x = 0) and are associated with weaker (stronger) magnetic field dipolarization. Finally, we find that the slower “background” convective flow has an average direction which is consistent with penetration of the expected IMF B_y, regardless of whether the fast flow itself agrees or disagrees.