Seasonal variations of the vertical fluxes of heat and horizontal momentum in the mesopause region at Starfire Optical Range, New Mexico

Abstract

Lidar observations of wind and temperature profiles between 85 and 100 km, conducted at the Starfire Optical Range (SOR), New Mexico, are used to characterize the seasonal variations of the vertical fluxes of heat and horizontal momentum and their relationships to gravity wave activity in this region. The wind and temperature variances exhibit strong 6‐month oscillations with maxima during the summer and winter that are about 3 times larger than the spring and fall minima. The vertical heat flux also exhibits strong 6‐month oscillations with maximum downward flux during winter and summer. The downward heat flux peaks near 88 km where it exceeds −3 K m s−1 in mid‐winter and is nearly zero during the spring and fall equinoxes. The heat flux is significantly different from zero only when the local instability probability exceeds 8%, i.e., the annual mean for the mesopause region. The momentum fluxes also exhibit strong seasonal variations, which are related to the horizontal winds. Two‐thirds of the time the horizontal momentum flux is directed against the mean wind field.