MF radar observation of mean wind and tides of winter mesopause (80-98 km) region over Wuhan (30°N, 114°E)

Data obtained from the medium-frequency radar at Wuhan (30degreesN, 114degreesE) from 11 to 25 February and from 28 February to 13 March have been used to study the mean wind and tidal oscillations at mesopause (80-98 km) region over Wuhan in winter. The observed zonal and meridional mean winds show obvious temporal variation and usually decrease with the increasing heights. In most observational time, the zonal mean wind is eastward. A dynamic spectral analysis of disturbance amplitude illustrates a prominent peak at a period of 24 h at all heights and almost uninterrupted, and there are occasionally slightly strong semidiurnal and weak terdiurnal tidal disturbances, indicating that in the mid-latitude regions, the diurnal tide is the dominant tidal disturbance at mesopause in winter. The temporal variation of tidal amplitudes and their wave kinematical energies illustrates that there may be significant resonant interaction among the diurnal, semidiurnal and terdiurnal tides. A quantitative comparison with the global-scale wave model (GSWM) demonstrates that the observed diurnal and semidiurnal tidal amplitudes are less and larger than the results of GSWM-02, respectively. The essentially linear GSWM cannot predict the decrease of diurnal tidal amplitude at higher heights, which may be due to several possible nonlinear processes, such as wave-wave interaction and wave break. Although the height variations of tidal phases are consistently well with the predictions of GSWM, there are evident phase differences between our observation and the model. The profiles of the diurnal tidal phases show obvious decrease trend with the increasing height, indicating the observed diurnal tide is propagating upward. The vertical wavelength of the observed diurnal tide is estimated to be about 37 km, and the corresponding downward phase velocity is about 1.5 km(-1) h. (C) 2003 Elsevier Ltd. All rights reserved.