A global morphology of gravity wave activity in the stratosphere revealed by the GPS occultation data (GPS/MET)

Using temperature profiles obtained by the GPS/MET (GPS Meteorology) experiment from April 1995 to February 1997, we have extracted mesoscale temperature perturbations with vertical wavelengths ranging from 2 to 10 km and background Brunt-Väisälä frequency squared, N 2. For each occultation event, we can evaluate a potential energy Ep which is assumed to be caused by atmospheric gravity waves. The monthly mean values of Ep at 15 - 20 km around Japan showed an annual variation with an enhancement in winter, which is consistent with the climatological behavior of the kinetic energy of gravity waves observed with the MU (middle and upper atmosphere) radar (34.9°N, 136.0°E) from 1985 to 1989. We have then derived the global distribution of Ep at 20 - 30 km during Northern Hemisphere winter (from November to February). Our analysis shows that the largest Ep values are generally centered around the equator between 25°N and 25°S with considerable longitude variations. Longitudinal variations of Ep at 20 - 30 km in a latitude range of 30° - 60°N are also analyzed, resulting in larger Ep values over the continents than over the Pacific Ocean. Using GPS/MET data without antispoofing, latitudinal variations of Ep are determined in 15 - 45 km. Although large Ep values are concentrated near the equator at 20 - 30 km, Ep tends to become larger at midlatitudes at 30 - 40 km and higher-altitude regions. At midlatitudes, Ep is found to be larger in winter months in both hemispheres. Height variations of Ep indicate a decrease at 25 - 30 km and a monotonic increase above 30 km.