The Spatial Extent of Magnetopause Magnetic Reconnection From In Situ THEMIS Measurements

Magnetic reconnection at the magnetopause has long been studied with multi‐spacecraft observations. In this work, data from the five satellite THEMIS mission during the years of 2008–2010 are used to generate statistics regarding the spatial extent of magnetopause reconnection. The presence of a reconnecting magnetopause is determined with the Walén relation as two satellites cross the magnetopause simultaneously. In some cases both satellites measure reconnection whereas in others one satellite measures reconnection and the other does not. This study finds that two spacecraft are more likely to observe a contiguous reconnection region the closer they are spatially, and that reconnection is not always extended around the entire magnetopause. Plasma β gradient drifts are investigated as a cause of local reconnection suppression. Spacecraft position along the magnetopause flanks is also investigated as a possible spatial limitation to reconnection due to changes in shear flow or boundary thickness.