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Abstract We present a statistical investigation of the effects of interplanetary magnetic field (IMF) on hemispheric asymmetry in auroral currents. Nearly 6 years of magnetic field measurements from Swarm A and C satellites are analyzed. Bootstrap resampling is used to remove the difference in the number of samples and IMF conditions between the local seasons and the hemispheres. Currents are stronger in Northern Hemisphere (NH) than Southern Hemisphere (SH) for IMF Bin NH (Bin SH) in most local seasons under both signs of IMF B. For Bin NH (Bin SH), the hemispheric difference in currents is small except in local winter when currents in NH are stronger than in SH. During Band Bin NH (Band Bin SH), the largest hemispheric asymmetry occurs in local winter and autumn, when the NH/SH ratio of field aligned current (FAC) is 1.180.09 in winter and 1.170.09 in autumn. During Band Bin NH (Band Bin SH), the largest asymmetry is observed in local autumn with NH/SH ratio of 1.160.07 for FAC. We also find an explicit Beffect on auroral currents in a given hemisphere: on average Bin NH and Bin SH causes larger currents than vice versa. The explicit Beffect on divergence‐free current during IMF Bis in very good agreement with the Beffect on the cross polar cap potential from the Super Dual Auroral Radar Network dynamic model except at SH equinox and NH summer.
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Statistical Study of Favorable Foreshock Ion Properties for the Formation of Hot Flow Anomalies and Foreshock Bubbles
Abstract Hot flow anomalies (HFAs) and foreshock bubbles (FBs) are frequently observed in Earth's foreshock, which can significantly disturb the bow shock and therefore the magnetosphere‐ionosphere system and can accelerate particles. Previous statistical studies have identified the solar wind conditions (high solar wind speed and high Mach number, etc.) that favor their generation. However, backstreaming foreshock ions are expected to most directly control how HFAs and FBs form, whereas the solar wind may partake in the formation process indirectly by determining foreshock ion properties. Using Magnetospheric Multiscale mission and Time History of Events and Macroscale Interactions during Substorms mission, we perform a statistical study of foreshock ion properties around 275 HFAs and FBs. We show that foreshock ions with a high foreshock‐to‐solar wind density ratio (>∼3%), high kinetic energy (>∼600 eV), large ratio of kinetic energy to thermal energy (>∼0.1), and large ratio of perpendicular temperature to parallel temperature (>∼1.4) favor HFA and FB formation. We also examine how these properties are related to solar wind conditions: high solar wind speed and oblique bow shock (angle between the interplanetary magnetic field and the bow shock normal) favor high kinetic energy of foreshock ions; foreshock ions have large ratio of kinetic energy to thermal energy at large(>30°); small(<30°), high Mach number, and closeness to the bow shock favor a high foreshock‐to‐solar wind density ratio. Our results provide further understanding of HFA and FB formation.
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- Award ID(s):
- 1941012
- PAR ID:
- 10372593
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 127
- Issue:
- 8
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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