Annual Variation and Global Structures of The DE3 Tide

The SABER/TIMED temperatures taken in 2002--2006 are used to delineate the tidal signals in the middle and upper atmosphere. Then the Hough mode decomposition is applied with the DE3 tide, and the overall features of the seasonal variations and the complete global structures of the tide are observed. Investigation results show that the tide is most prominent at 110km with the maximal amplitude of >9K, and exhibits significant seasonal variation with its maximum amplitude always occurring in July every year. Results from the Hough mode decomposition reveal that the tide is composed primarily of two leading propagating Hough modes, i.e., the (-3, 3) and the (-3, 4) modes, thus is equatorially trapped. Estimation of the mean amplitude of the Hough modes show that the (-3, 3) mode and (-3, 4) mode exhibit maxima at 110km and 90km, respectively. The (-3, 3) mode plays a predominant role in shaping the global latitude--height structure of the tide, e.g., the vertical scale of>50km at the equator, and the annual course. Significant influence of the (-3, 4) mode is found below 90km, where the tide exhibits anti-symmetric structure about the equator; meanwhile the tide at northern tropical latitudes exhibits smaller vertical wavelength of about 30km