Polar Cap Patches: Investigation of Formation Mechanisms and Source Plasma

While polar cap ionospheric patches have been studied for over two decades, there remains no general agreement to which of many proposed patch-production mechanisms are important or dominate. An experiment was designed and implemented to search for transient events redirecting subauroral ionospheric plasma from its subauroral flow to transient injection into the polar cap, as would occur for the Lockwood and Carlson 1992 mechanism of patch creation. An earlier experiment provided compelling evidence of this mechanism acting within the cusp, but only smoking gun evidence regarding the source-reservoir for the plasma injected into the polar cap. The work here, for the first time, tracks the bullet continuously from subauroral latitudes before the event fires, through the cusp and into the polar cap. We conclude that this mechanism must be a dominant patch generation mechanism and highlight that poleward-moving-form research has direct application to polar cap patch generation by magnetopause reconnection.