Dayside Auroral Oval Expansion, Magnetic Flux Erosion, and Substorms

Magnetic flux is eroded from the dayside magnetosphere when the interplanetary magnetic field (IMF) turns southward. During this period, the dayside auroral oval shifts equatorward as magnetic flux is transported anti-sunward to the magnetotail. Poleward-Moving Auroral Forms (PMAFs) are thought to be the ionospheric footprints of the flux tubes which are formed and transported tailward. Afterwards, magnetic reconnection occurs in the magnetotail, resulting in a substorm. This study looks at the time between the onset of dayside magnetic reconnection and the onset of a substorm. Rates of dayside auroral oval equatorward shifts after southward turnings of the IMF are presented, along with the number of PMAFs generated during each expansion of the dayside auroral oval. The oval shifts are obtained from the meridian scanning photometer located in Longyearbyen, Svalbard at the Kjell Henriksen Observatory (KHO). This statistical study will provide the: (i) average initial (before expansion) and final (after expansion) latitude of the dayside auroral oval, (ii) the average elapsed time for the dayside auroral oval to shift equatorward after the IMF z-component shifts southward, (iii) the number of PMAFs generated for each equatorward shift of the dayside auroral oval, (iv) the time elapsed between the beginning of the dayside auroral oval equatorward shift and the onset of a substorm, and (v) the associated solar wind parameters: IMF x-, y-, z-components, solar wind speed, solar wind dynamic pressure, and clock angle. Finally, machine learning was used to identify dayside oval expansions and their associated PMAFs.