SAPS and Traveling Ionospheric Disturbances

Abstract:

SAPS (subauroral polarization stream) is a strong sunward plasma convection often observated equatorward of the auroral convection and coincident with the ionospheric main trough. The ion-neutral coupling effect associated with SAPS is very significant due to strong ion drag forcing. Some of the known SAPS impacts include frictional heating to ions and neutrals and enhanced thermospheric zonal winds (being muchmore westward), and the zonal wind enhancement induced disturbance in meridional winds (being more poleward through Coriolis forcing). Auroral heating through Joule heating and particle precipitation during storm and substorm periods excites atmospheric waves that propagated into lower latitudes. Traveling ionospheric disturbances (TIDs) are manefistation of these neutral waves. When they arrive in the subauroral region and encouter the SAPS, questions regarding the SAPS impact and the TID response are raise. In this presetation, we provide evidence of concurrent LSTIDs and MSTIDs during the presence of SAPS. LSTIDs are of auroral origin whilerase the MSTIDs appear SAPS-related. Once landing in the SAPS region, LSTID wave fronts and their propagation direction rotate clockwise, creating NW-SE fluctuation bands and SW propagation. These structures are evolved into meso-scale propagating strcutures which can be characterized as MSTIDs. We suggest the strong SAPS poleward electric field is responsible for the evolution of these TIDs, and in particular, excitation of MSTIDs by triggering the Pekins instability with a fairly large instability growth rate. In this presentation, we provide two case studies to demonstrate the SAPS impact on TIDs using geospace storm observations from GNSS differential TEC and the Millstoen Hill incoherent scatter radar.