Seasonal variations of MLT tides revealed by a meteor radar chain based on Hough mode decomposition

摘要

Seasonal variations of different tides in the mesosphere and lower thermosphere are investigated from wind observations of a meteor radar chain on the basis of Hough mode decomposition. First, the observed winds are decomposed into different (diurnal, semidiurnal, and terdiurnal) tidal components. Different seasonal patterns are revealed for each component. Pronounced semiannual oscillation (SAO) is presented in the diurnal component, while latitude-dependent seasonal variation is found in the semidiurnal and terdiurnal components. At the low/midlatitude stations, the semiannual/annual oscillation is relatively stronger. Then, Hough mode decomposition is utilized to extract the dominant tidal modes of each decomposed component. It is found that each component is dominated by one of its symmetric tidal modes with strong seasonal dependency. Apparent SAO is observed in the dominant (1, 1) mode; (2, 4) mode is strong in the autumn and winter months (after the September equinox). Based on the extracted results we further map the three-dimensional distribution (latitude × altitude × season) of each tidal component. The mapped results are finally compared with the corresponding values observed by the Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer (TIDI) and modeled from the global scale wave model (GSWM). Each mapped tidal component agrees well with corresponding TIDI observation in the seasonal variation. Meanwhile, coincidences are found in the seasonal dependency of the diurnal component between the mapped values and the modeled results from GSWM, while difference between them exists in that of the semidiurnal one.