Short-Term and Interannual Variations of Migrating Diurnal and Semidiurnal Tides in the Mesosphere and Lower Thermosphere

Abstract

Among the broad spectrum of vertically propagating tides, migrating diurnal (DW1) and semidiurnal (SW2) are prominent modes of energetic and dynamical coupling between the mesosphere and lower thermosphere and the upper thermosphere and ionosphere. DW1 and SW2 tides are modulated on time scales ranging from days to years. NASA Thermosphere-Ionosphere-Mesosphere Energetic and Dynamics (TIMED) is the first observational platform to perform global synoptic observations of these fundamental tides (for nearly two decades) overcoming previous observational limitations. Here we utilize the extensive archive of TIMED Doppler Interferometer wind measurements and exploit the capabilities of tidal theory to estimate short-term (<1 month), seasonal (intra-annual), long-term (>1 year), and climatological variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes and then compare with tidal estimates derived from the Navy Global Environmental Model-High Altitude version data assimilation system. Overall, the tidal estimates from TIMED Doppler Interferometer and Navy Global Environmental Model-High Altitude version are similar and exhibit significant short-term and intra-annual variability. The short-term variability can induce ∼64% change in the DW1 amplitude. Statistically, the short-term variability in DW1 (1,1), SW2 (2,2), and SW2 (2,3) modes is of the order of ∼9, 33, and 20 m/s, respectively. The biennial oscillations in DW1 and SW2 modes suggest a systematic correlation with the equatorial quasi-biennial oscillation in the stratosphere and are more apparent in DW1 amplitudes. Although there is significant interannual variability in addition to the apparent biennial signal, there is no clear evidence of any solar cycle dependence or long-term trend in either DW1 or SW2 modes.