Proof-of-Concept Study for Ground-based Millimetre-wave Observations of Horizontal Winds in the Polar Stratosphere and Mesosphere

Abstract:

Detailed observations of horizontal winds in the Polar Regions are essential to understand chemical transport, atmospheric dynamics, waves and tides, and improve knowledge of polar and global climate systems. New measurement techniques for the altitude range 20‑70 km are needed to address the current sparse wind observations for the upper stratosphere and mesosphere that limits our understanding of vertical wave propagation and its impact on planetary‑scale circulation. We demonstrate the feasibility of remote sensing stratospheric and mesospheric zonal and meridional winds using ground‑based passive millimetre wave spectroradiometry. Vertical profiles of horizontal winds are retrieved from simulations of line‑of‑sight Doppler‑shifted atmospheric emission lines above Halley station (75°37’S, 26°14’W), Antarctica. Using the 231.28 GHz ozone line, or the pair of ozone lines at 249.79 GHz and 249.96 GHz, and a radiometer system temperature of 1400 K we estimate that daily mean wind profiles over the altitude range 25‑75 km could be observed with a measurement uncertainty of 4‑8 ms^-1 and vertical resolution of 10‑15 km. Under optimal observing conditions at Halley the temporal resolution is predicted to improve to 1‑3 hrs, allowing studies of planetary and large‑scale gravity waves. Combining observations of the 231.28 GHz ozone line and the 230.54 GHz carbon monoxide line extends the altitude coverage to ~95 km. The effects of clear‑sky seasonal mean winter/summer conditions, zenith angle of the received atmospheric emission, and spectrometer frequency resolution on the altitude coverage, measurement uncertainty, and height and time resolution of the retrieved wind profiles have been determined.