Thermospheric poleward wind surge at midlatitudes during great storm intervals

Abstract

We report a significant poleward surge in thermospheric winds at subauroral and midlatitudes following the 17-18 March 2015 great geomagnetic storm. This premidnight surge is preceded by strong westward winds. These disturbances were observed over three sites with geodetic latitudes 35-42°N in the American sector by Fabry-Perot interferometers at 630nm wavelength. Prior to the wind disturbances, subauroral polarization streams (SAPS) were measured by the Millstone Hill incoherent scatter radar between 20 and 02UT. We identify the observed neutral wind variations as driven by SAPS, through a scenario where strong ion flows cause a westward neutral wind, subsequently establishing a poleward wind surge due to the poleward Coriolis force on that westward wind. These regional disturbances appear to have prevented the well-known storm time equatorward wind surge from propagating into low latitudes, with the consequence that the classic disturbance dynamo mechanism failed to occur. Key Points Premidnight poleward wind surge at 100m/s, preceded by 300m/s westward winds No equatorward wind surge developed throughout the night Disturbance wind driven by strong westward ion flow near dusk and Coriolis force.