SuperDARN Observations During Geomagnetic Storms, Geomagnetically Active Times, and Enhanced Solar Wind Driving

M.‐T Walach,A Grocott

doi:10.1029/2019ja026816

M.‐T Walach, A Grocott

Open Access

https://doi.org/10.1029/2019ja026816

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Abstract

AbstractThe Super Dual Auroral Radar Network (SuperDARN) was built to study ionospheric convection at Earth and has in recent years been expanded to lower latitudes to observe ionospheric flows over a larger latitude range. This enables us to study extreme space weather events, such as geomagnetic storms, which are a global phenomenon, on a large scale (from the pole to magnetic latitudes of 40°). We study the backscatter observations from the SuperDARN radars during all geomagnetic storm phases from the most recent solar cycle and compare them to other active times to understand radar backscatter and ionospheric convection characteristics during extreme conditions and to discern differences specific to geomagnetic storms and other geomagnetically active times. We show that there are clear differences in the number of measurements the radars make, the maximum flow speeds observed, and the locations where they are observed during the initial, main, and recovery phase. We show that these differences are linked to different levels of solar wind driving. We also show that when studying ionospheric convection during geomagnetically active times, it is crucial to consider data at midlatitudes, as we find that during 19% of storm time the equatorward boundary of the convection is located below 50° of magnetic latitude.

Highlights

Geomagnetic storms are one of the more extreme examples of geomagnetic responses to solar wind driving
We show the measurements made during storms with SuperDARN, which we compare to measurements during times of high solar wind driving when no geomagnetic storm occurs and to measurements made during times when geomagnetic activity is high, irrespective of storm phases
We have studied geomagnetic storms from 2010-2016 statistically, in terms of the solar wind driving and ionospheric convection and compared this to geomagnetically active times, as well as times when solar wind driving is high, but geomagnetic activity is very low

Summary

Introduction

Geomagnetic storms are one of the more extreme examples of geomagnetic responses to solar wind driving. Cowley & Lockwood, 1992; Milan, 2015; Milan, Gosling, & Hubert, 2012; Walach, Milan, Yeoman, Hubert, & Hairston, 2017, and references therein) This is relevant for geomagnetic storms, as it has been shown that the recovery phase of a storm, when the geomagnetic activity decreases, is coupled to a decrease in southward IMF and solar wind driving (Gonzalez et al, 1999). Whilst substorms may be critical in energising the ring current (Kamide et al, 1998), it has been shown that the Dst ring current index, which is similar to the Sym-H index (Wanliss & Showalter, 2006), can be simulated well using solar wind data alone (O’Brien & McPherron, 2000). This is no coincidence, as substorms are driven by the solar wind

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