All‐Sky Tracking of Sporadic Field‐Aligned Irregularities as a Novel Probe of Thermospheric Winds

Abstract

AbstractThis paper presents the results of an analysis of a unique observing campaign that tracks groups of irregularities associated with sporadic ( ) via their coherent backscattering of a very high frequency transmitter of opportunity (an analog TV station). The unique all‐sky imaging capability of the first station of the Long Wavelength Array used in this campaign, allowed for the identification and tracking of multiple groups of irregularities, or “clouds,” over the entire visible sky. This all‐sky tracking yielded horizontal wind measurements from 75 distinct clouds observed within 18, 1‐hr collections from May–September 2014 within the 90‐ to 150‐km altitude range. While unusually strong winds of 100–200 m s or more were observed, the winds generally agree with predictions from the updated Horizontal Wind Model. The exception to this was an offset in premidnight zonal winds, which the Long Wavelength Array observations indicated were systematically more westerly than predicted by the Horizontal Wind Model. We postulate that this may be due to a local excess in mountain waves, which is partially supported by tropospheric and stratospheric wind data from the National Oceanic and Atmospheric Administration North American Regional Reanalysis. In three out of the 18 collections, we also observe evidence of significant horizontal zonal wind shears (positive and negative) with magnitudes on the order of 1 m s km .