Seasonal and interannual variations of global tides in the mesosphere and lower thermosphere neutral winds: II. Semidiurnal and terdiurnal tides

In the mesosphere and lower thermosphere (MLT) region, semidiurnal and terdiurnal tides are dominant at middle and high latitudes and are important for the dynamics and structures. Using the global neutral horizontal wind data in the MLT region observed by TIMED Doppler interferometer from 2002 to 2021, the seasonal and interannual variations of six semidiurnal and terdiurnal tidal components (SW2, SW3, SW4, TW3, TW2 and TW4) are investigated. Particularly, the responses of these tidal components to the stratospheric quasi-biennial oscillation (SQBO) and the solar cycle are presented. The results indicate that: (a) seasonal and interannual variations of these tidal components are pronounced in their peak regions. The peak region is defined as the region where the ratio of the annual mean amplitude to the maximum annual mean amplitude is larger than 0.8. (b) In their peak regions, migrating tidal components exhibit strong seasonal variations at annual (annual oscillations (AO)), semiannual (semiannual oscillations (SAO)) and terannual (terannual oscillations (TAO)) periods, whereas nonmigrating tidal components only exhibit prominent AO and SAO. (c) In their peak regions, the responses of the annual mean amplitudes of these tidal components to SQBO are negative; the responses of migrating tidal components to solar cycle are negative whereas those of nonmigrating tidal components are positive. (d) For these tidal components, the responses of the amplitudes of seasonal variations to SQBO and solar cycle are weaker than their annual mean amplitudes, and the latitude x altitude response patterns are not always consistent with those of the annual mean amplitudes.