Studies of the Mesosphere and Lower Thermosphere Dynamics Using Satellite Observations and Numerical Models

NASA UARS and TIMED satellites have enabled global and long-term monitoring of the Earth's middle and upper atmosphere, and thus an unprecedented and comprehensive quantification of mesosphere and lower thermosphere (MLT) variability on large spatial scales and time scales ranging from days to decades. These observations have led to improved theoretical understanding of the MLT dynamics, by inspiring development/improvement of numerical models and analysis methods, and providing more observational constraints to the models. Several studies within the last decade will be reviewed as examples: The observation of the seasonal variation of propagating planetary waves (5-7-day wave and quasi-2-day wave) in the MLT, and TIME-GCM simulations to understand the cause of the seasonality; the study of short-term tidal variability using TIMED satellite, ground-based, and TIME-GCM; the numerical study of the ionospheric effects of these MLT short-term variabilities; and determination of the gravity wave forcing, which is the most dominant driver of MLT circulation, from satellite and ground-based wind measurements, using a momentum balance relation tested by WACCM. Challenges posed by current and future model development will also be discussed, as initiatives for future missions.