Inter-annual variability of mesosphere and lower thermosphere tides

Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become prominent dynamical features. The momentum deposition from upward propagating waves is thought to generate the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. Five years of measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite and longer time series from the Super Dual Auroral Radar Network (SuperDARN) HF radars are analyzed to examine the seasonal and inter-annual variations of the diurnal, semidiurnal and terdiurnal tides in the mesosphere and lower thermosphere. We present estimates of both the migrating and nonmigrating of these tides from the lower stratosphere to the lower thermosphere and discuss evidence of nonlinear interaction between the tides and other wave modes. We also examine the inter-relationship the tides may have with lower and middle atmosphere variability (e.g., QBO, SAO, and stratospheric warmings) and tidal impacts on the zonal mean structure of the upper atmosphere and ionosphere.