Seasonal variation of gravity wave activity at 5-20 km observed with VHF radar at White Sands Missile Range, New Mexico

Wind observations at altitudes from 5 to 20 km obtained from the VHF wind profiler radar at the White Sands Missile Range (WS), New Mexico, are used to construct a climatology of gravity wave intensities over WS during the nearly 6-year period from January 1991 through September 1996. The kinetic energy densities for both high-frequency gravity waves (ground-based period of 6 min to 2 hours) and low-frequency gravity waves (period from 2 to 21 hours) are considered. These results are compared to earlier results from the middle and upper atmosphere (MU) radar in Japan. Comparisons of gravity wave variability at high and low frequency reveal both similarities and differences between the two sites. The primary differences occur at high frequency. The seasonal cycle in the high-frequency gravity waves is less pronounced and less regular at WS compared to MU. The magnitude of the high-frequency kinetic energy density is generally larger at WS compared to MU, and the relationship between the upper tropospheric jet stream winds and the high-frequency gravity wave activity is not nearly so strong at WS as at MU. The primary high-frequency gravity wave excitation mechanism at WS appears to change with season. There is evidence of a connection in winter and spring between the wind speeds in the middle troposphere and the high-frequency gravity wave activity, suggesting a topographic source for these waves. Strong summertime high-frequency variability at WS in the upper troposphere is most likely linked to waves launched by deep convection during the monsoon season in New Mexico. The results for low-frequency gravity waves are more consistent between WS and MU. Similarities appear in the kinetic energy density, the nature of the seasonal cycle, and the correlation between the kinetic energy density and the mean winds.