Short-term variability and summer-2009 averages of the mean wind and tides in the mesosphere and lower thermosphere over Langfang, China (39.4°N, 116.7°E)

Abstract: Data obtained from the newly installed MF radar at Langfang (39.4°N, 116.7°E), China, during the summer months of 2009 are used to study the short-term variability and summer averages of the mean wind and tidal oscillations in the mesosphere and lower thermosphere (MLT). Both the zonal and meridional daily winds between 80km and 98km show considerable day-to-day variability; their Lomb–Scargle spectra reveal active quasi-2-day and quasi-16-day planetary waves. The tidal large day-to-day variations have time scales of days or longer, which could be attributed to the contribution of planetary waves. The summer-averaged zonal wind is westward below 82km and eastward above 88km with the transition altitude at ∼85km. The meridional wind is dominated by the southward wind. The summer-averaged zonal and meridional semidiurnal tides exhibit amplitudes of 10–15m/s; they are larger than the diurnal tides, whose amplitudes are 5–10m/s. The phase tilt of the semidiurnal tide is downward, indicating this component is excited below the MLT. For the diurnal tide, the phase propagation is downward above 86km but it is upward below 86km, which indicates that the tide is evanescent or a mixture of evanescent and propagating modes. These wind and tide observations are compared with data from other mid-latitude stations at ∼40°N and with the HWM and GSWM models. Comparisons show that HWM-93 is better than HWM-07 in delineating the 2009 summer-averaged zonal wind over Langfang while both have systematic discrepancy in delineating the meridional mean winds. The prediction of the 2009 summer-averaged diurnal tide over Langfang by GSWM-09 is better than that from GSWM-02 but not the semidiurnal tide. [Copyright &y& Elsevier]