A global distribution of the stratospheric gravity wave activity from GPS occultation profiles with SAC-C and CHAMP

Abstract

We have analysed the gravity wave activity using temperature profiles retrieved from the GPS occultation experiments on board the SAC-C and CHAMP satellites. By dividing the latitude and longitude ranges, here considered in individual cells, the variability of wave energy as a function of altitude observed in both hemispheres during October, November and December 2001 is presented. Some features were repeatedly observed during the three months. Nevertheless, as most available occultations were occurred during November, we begin showing results from this month. Significant differences detected during October are only pointed out at midlatitudes, provided that sufficient number of occultations are available. A significantly larger wave activity at 40-60°N with respect to 40-60°S is detected during this month. Differences between both the hemispheres are discussed and compared with previous results. Wave activity enhancements at equatorial regions above Brazil, Indonesia and India are found to be correlated with outgoing longwave radiation data. Vertical fluctuations with lengths above and below 3.5 km are considered separately, in order to identify the contribution of Kelvin and Rossby-gravity waves. In both cases, for long and short fluctuations and at the upper troposphere as well as at the lower stratosphere, there is a height interval of several kilometers where a systematic enhanced wave activity is observed. Its average height is progressively decreasing with increasing latitude, same as the height variation in the tropopause location. Longitudinal enhancements are also detected mainly around the equator and at midlatitudes. A clear signature is observed locally in the Southern Hemisphere (SH) at midlatitudes and 70-65°W, for vertical wavelengths longer than 3.5 km. It corresponds to mountain waves forced by the Andes Range, observed whenever occultations are available in this cell. © 2004, Meteorological Society of Japan.