Tides in the mesopause region over Antarctica: Comparison of whole atmosphere model simulations with ground‐based observations

Abstract

Listen

Translate article

AbstractAlmost a quarter century ago first optical and radar observations from the South Pole revealed rich dynamics unexpected from classical tidal theory. A strong semidiurnal wind oscillation was detected near the mesopause implying substantial deviations from the classical view that the semidiurnal variation is dominated by the migrating tide. Subsequent systematic observations exhibited large seasonal variations of both the diurnal and semidiurnal tide with dramatic reduction in amplitude from summer to winter. First numerical simulations with a realistic general circulation model extending into the lower thermosphere indicated the presence of nonmigrating tides with substantial amplitudes in the polar regions. However, direct model‐data comparisons have been limited to idealized linear models. Here whole atmosphere model (WAM) simulations for January and July are compared with available wind climatologies based on multiyear radar observations at different locations in Antarctica as well as with first summertime lidar measurements of temperature. The diurnal tide simulation agrees well with most of the independent radar and satellite wind observations in both seasons. The strong semidiurnal tide comprised of migrating and nonmigrating components is well reproduced in summer, while in winter the model tends to overestimate the amplitudes over the continental edge. Besides model validation, a self‐consistent numerical solution also enables cross validation of observations made with different instruments at different locales.