Effects of Subauroral Polarization Streams on the Upper Thermospheric Winds During Non-Storm Time

Intense sunward (westward) plasma flows, named Subauroral Polarization Stream (SAPS), have been known to occur equatorward of the electron auroras for decades, yet their effect on the upper thermosphere has not been well understood. On the one hand, the large velocity of SAPS results in large momentum exchange upon each ion-neutral collision. On the other hand, the low plasma density associated with SAPS implies a low ion-neutral collision frequency. We investigate the SAPS effect during non-storm time by utilizing a Scanning Doppler Imager (SDI) for monitoring the upper thermosphere, SuperDARN radars for SAPS, all-sky imagers and DMSP Spectrographic Imager for the auroral oval, and GPS receivers for the total electron content. Our observations suggest that SAPS at times drives substantial (>50 m/s) westward winds at subauroral latitudes in the dusk-midnight sector, but not always. The occurrence of the westward winds varies with AE index, plasma content in the trough, and local time. The latitudinally averaged wind speed varies from 60 to 160 m/s, and is statistically 21% of the plasma. These westward winds also shift to lower latitude with increasing AE and increasing MLT. We do not observe SAPS driving poleward wind surges, neutral temperature enhancements, or acoustic-gravity waves, likely due to the somewhat weak forcing of SAPS during the non-storm time.

Thermally stable monolithic Doppler asymmetric spatial heterodyne interferometer: optical design and laboratory performance

We report on a thermally stable monolithic Doppler asymmetric spatial heterodyne (DASH) interferometer with field-widening prisms for thermospheric wind measurements by observing the Doppler shift of the airglow emission. Analytical deduction and numerical simulation are applied to determine the central optical path difference, the thermal compensation condition and the field-widening design. A monolithic interferometer with optimized configuration was built and tested in the laboratory. Laboratory tests show that the best visibility of 0.94 was realized with the 9 ^° field-of-view illumination, while the thermal responses of the spatial frequency and the optical phase offset are 0.0154 cm^-1/^°C and 0.469 rad/^°C, respectively.