HAO Colloquium - Wenbin Wang, HAO

The dynamics and effects of Subauroral Polarization Streams (SAPS): From empirical specification to physics modeling

Subauroral polarization stream (SAPS) are latitudinally narrow flow channels of large westward plasma drifts that occur mostly in the evening to dusk sector in the subauroral ionosphere. They are confined to a latitudinally narrow (~5o) region just equatorward of auroral electron precipitation. This region is the interface where the boundaries of the inner magnetosphere, plasmasphere, and field-aligned currents meet and where steep ionospheric electron density gradients occur. SAPS are observed during all phases of magnetic activity, and thus a significant part of storm-time space weather. They affect the thermosphere and ionosphere (T-I) system through enhanced ion drag and Joule heating not only directly in the SAPS channel, but also in other regions as a result of global ion-neutral dynamic coupling. In this talk, we will first discuss simulation results of the stand-alone thermosphere ionosphere electrodynamics global circulation model (TIEGCM) driven by an empirical SAPS model. For the major storm event on St. Patrick’s day in 2015, the model shows that there are large changes in both neutral winds and temperature when SAPS are included in the simulation. These changes are not limited to just the SAPS region, but global. Associated with wind and temperature changes are large neutral composition variations that lead to a deeper and expanded mid-latitude ionospheric density trough and a much weakened positive storm effect in the afternoon sector. This then results in both significantly diminished storm enhanced densities at high latitudes and a weaker tongue of ionization inside the polar cap. We will then discuss our advances in understanding the global structure and dynamic evolution of SAPS using the recently developed, high resolution coupled magnetosphere ionosphere thermosphere model that includes global magnetosphere, ring current, ionosphere and thermosphere. The model predicts strong westward ion drifts of SAPS equatorward of the auroral electron precipitation boundary on the duskside. These modeled ion drift velocity and aurora electron precipitation are in good agreement with the DMSP F18 satellite measurements. This is the first time that the global distribution and temporal evolution of SAPS with external solar wind driving conditions are investigated using a first-principles model. Our simulation results are consist with statistical studies, but illustrate the highly dynamic behavior of SAPS, which cannot be readily described using statistical analysis. Finally, we will discuss some of the topics for future SAPS studies. 

Date and time: 
Wednesday, January 8, 2020 - 2:00pm to 3:00pm