Asymmetry in the Ring Current During Geomagnetic Disturbances

Geomagnetic disturbances (GMDs) are defined as rapid changes in the magnetic field of the Earth that can lead to geomagnetically induced currents (GICs). Recent studies have shown that there are two main populations of GMDs, one in the pre-midnight sector and one in the dawn sector. The pre-midnight GMDs have been related to the substorm current wedge. The dawn population of GMDs has previously been found to occur during multiple intensification events. We adapt the SOPHIE substorm list to identify more instances of multiple intensifications. Recent models suggest the formation of a “dawnside current wedge” (DCW) during the main phase of storms that could lead to dawn sector GMDs. We investigate GMDs at all latitudes using the SuperMAG local time indices (SMR-LT), where SMR-LT are local time measurements of the magnetic field at low latitudes. During multiple intensification events the dawn sector low latitude magnetic field between 3 and 9 MLT (SMR06) is typically higher than the dusk sector between 15 and 21 MLT (SMR18), which is indicative of a DCW. Statistical analysis of the local time ring current indices during the dawn and pre-midnight GMDs shows that the dawn GMDs occur when the difference between the dawn sector and dusk sector SMR values (SMR06-SMR18) is largest and thus when there is a DCW.