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

Seasonal variations of different tides in the mesosphere and lower thermosphere (MLT) are investigated from wind observations of a four-station meteor radar chain located at middle- and low-latitudes along the 120°E meridian in the Northern Hemisphere on the basis of Hough mode decomposition. Firstly, 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-depended seasonal variation is found in the semidiurnal and terdiurnal components. At the low/mid- latitude 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 Sep. equinox). Based on the extracted results we further propose a technique to map the three-dimensional distribution (latitude × altitude × season) of MLT tidal components from the observations the meteor radar chain located at middle- and low-latitudes along the 120_E meridian in the Northern Hemisphere. The mapped results are finally compared with the corresponding values observed by the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) 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. Thus, we conclude that the meteor radar chain is useful to monitor and study the regional characteristics of the tidal winds in the MLT region.