Speaker
Description
Geomagnetic disturbances (GMDs) are rapid changes in the magnetic field of the Earth that can cause electric currents to be induced at the surface of Earth. These geomagnetically induced current (GICs) can cause damage to infrastructure such as pipelines and power grids. Previous studies have shown that there are three main populations of GMDs, one in the pre-midnight sector, one in the dawn sector and a smaller day side population. These studies have related the pre-midnight GMDs to the substorm current wedge, the day population to storm sudden commencement impacts or Pc5 wave activity, and the dawn GMDs to omega bands or Kelvin-Helmholtz activity. Recent models suggest the formation of a “dawnside current wedge” (DCW) during the main phase of storms that could lead to dawn sector GMDs. Recently the dawn GMDs have been found to occur during multiple intensification events, which are related to rapid changes in the AL index with little change in the size of the polar cap. Previously multiple intensification events had only been identified for 2010. We adapt the SOPHIE substorm algorithm to identify more instances of multiple intensifications throughout the period 2010-2022. We investigate the ring current 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. Between 2010 and 2022 a list of global GMDs identified in 10 second averaged ground magnetometer data from SuperMAG is used to investigate the presence of a dawn side current wedge during GMDs. The high temporal resolution of this data is important in capturing the most rapid magnetic field changes associated with extreme GIC events. 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. This finding suggests that dawn and pre-midnight GMDs form through different processes but can occur at the same time.
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