Long‐term observations of the wind field in the Antarctic and Arctic mesosphere and lower‐thermosphere at conjugate latitudes

摘要

Mean winds, semidiurnal and diurnal tides, and trends and long‐period oscillations spanning a solar cycle (from early 1999 through June 2010) measured by medium frequency (MF) radars at conjugate Antarctic and Arctic latitudes (Syowa, Antarctica, 69°S, 39.6°E, and Andenes, Norway, 69.3°N, 16°E) are described and compared. Zonal mean winds are stronger and more uniform from year to year over the Antarctic, with a stronger eastward winter jet spanning the range of altitudes presented (70 to 96 km). The summer westward jet is also stronger and maximizes at higher altitudes over the Antarctic than over the Arctic. The eastward winter jet over the Arctic, while generally weaker, exhibits a localized maximum in late winter at ～2 to 3 year intervals. Meridional mean winds likewise achieve somewhat stronger maxima at higher altitudes over the Antarctic than over the Arctic. Semidiurnal tide amplitudes are typically somewhat larger over the Antarctic and similar in the two components, with maxima at ～85 km or above and narrow responses that tend to cluster from ～February to May and ～September to November over the Antarctic and from ～December to February and ～June to September over the Arctic. Zonal diurnal tide amplitudes are quite similar between the sites, with maxima extending from ～70 to 90 km and slightly stronger over the Antarctic. Meridional diurnal amplitudes display more significant growth with altitude, achieve stronger maxima at the highest altitudes presented, and typically exhibit a single and narrow maximum during December to February over the Antarctic and double maxima from ～May to September over the Arctic. Also discussed are trends and long‐period oscillations over a solar cycle observed in these mean and tidal wind fields.