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

• Published in: Journal of geophysical research. Space physics 2022-05, Vol.127 (5), p.n/a
• Main Authors: Lane, J. H., Grocott, A., Case, N. A.
• Format: Article
• Language: English
• Subjects: Asymmetry; convection; Convective flow; dusk‐dawn; dynamics; Interplanetary magnetic field; localized; Magnetic fields; magnetotail; Magnetotails; Neutral sheets; Penetration; Perturbation; transient
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA030057

Previous work has shown that earthward convective flow bursts in the magnetotail have a dusk‐dawn (v⊥y ${v}_{\perp y}$) 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 By. 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 (Bx = 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 By, regardless of whether the fast flow itself agrees or disagrees. Key Points Magnetotail fast flows with a dusk‐dawn direction inconsistent with IMF By can occur irrespective of the sense of IMF By penetration These inconsistent flows occur within a slower “background” convection that is consistent with the expected IMF By sense Localized, transient dynamics can override or prevent IMF By control of the flow, notably when IMF By is weaker