Multiscale Magnetosphere‐Ionosphere Coupling During Stormtime: A Case Study of the Dawnside Current Wedge
A characteristic feature of the main phase of geomagnetic storms is the dawn‐dusk asymmetric depression of low‐ and mid‐latitude ground magnetic fields, with largest depression in the dusk sector. Recent work has shown, using data taken from hundreds of storms, that this dawn‐dusk asymmetry is stron...
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| Published in: | Journal of geophysical research. Space physics Vol. 128; no. 11 |
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| Main Authors: | , , , , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Washington
Blackwell Publishing Ltd
01-11-2023
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | A characteristic feature of the main phase of geomagnetic storms is the dawn‐dusk asymmetric depression of low‐ and mid‐latitude ground magnetic fields, with largest depression in the dusk sector. Recent work has shown, using data taken from hundreds of storms, that this dawn‐dusk asymmetry is strongly correlated with enhancements of the dawnside westward electrojet and this has been interpreted as a “dawnside current wedge” (DCW). Its ubiquity suggests it is an important aspect of stormtime magnetosphere‐ionosphere (MI) coupling. In this work we simulate a moderate geomagnetic storm to investigate the mechanisms that give rise to the formation of the DCW. Using synthetic SuperMAG indices we show that the model reproduces the observed phenomenology of the DCW, namely the correlation between asymmetry in the low‐latitude ground perturbation and the dawnside high‐latitude ground perturbation. We further show that these periods are characterized by the penetration of mesoscale bursty bulk flows (BBFs) into the dawnside inner magnetosphere. In the context of this event we find that the development of the asymmetric ring current, which inflates the dusk‐side magnetotail, leads to asymmetric reconnection and dawnward‐biased flow bursts. This results in an eastward expansion and multiscale enhancement of the dawnside electrojet. The electrojet enhancement extends across the dawn quadrant with localized enhancements associated with the wedgelet current systems of the penetrating BBFs. Finally, we connect this work with recent studies that have shown rapid, localized ground variability on the dawnside which can lead to hazardous geomagnetically induced currents.
Plain Language Summary
During geomagnetic storms, electric currents in space can have a dramatic effect on the magnetic field on the ground, causing so‐called geomagnetic disturbances (GMDs). Storm‐time GMDs exhibit a lopsided asymmetry: dusk‐biased near the equator and dawn‐biased at high latitudes where aurora usually occur. This asymmetry has been interpreted as a giant wedge‐like current system, a dawnside current wedge (DCW). Using a high‐resolution supercomputer model, we successfully reproduced the DCW and showed that it occurred during a period of intense, localized flow bursts, akin to bubbles, on the nightside of near‐Earth space. The bubbles' buoyancy propels them from the nightside inwards toward dawn, driving intense currents into the Earth's atmosphere. Our simulations suggest that the causal agent of these dawnside bubbles is magnetic reconnection, typically symmetric but skewed dawnward due to asymmetry in the ring current, a crescent‐shaped population of energetic ions in space which intensifies during geomagnetic storms. Understanding the cause of stormtime GMD asymmetry is not only important to characterize how electric currents bind the magnetosphere and upper atmosphere, but also to mitigate space weather hazards, as intense GMDs can disrupt and damage power systems on Earth.
Key Points
Global model reproduces correlation between ring current asymmetry and dawnside electrojet inferred from hundreds of geomagnetic storms
Analysis of the model reveals a dawnside current wedge mediated by mesoscale flow bursts and driven by an asymmetric substorm‐like process
Model reveals multiscale enhancement of dawnside electrojet with space weather implications due to rapid, localized ground variability |
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| ISSN: | 2169-9380 2169-9402 |
| DOI: | 10.1029/2023JA031594 |