Seasonal and QBO-related Variations in Gravity Wave Activities Observed with Radiosondes at Bandung, Indonesia.

Abstract

The Radio Science Center for Space and Atmosphere (RASC) and the Indonesian National Institute of Aeronautics and Space (LAPAN) conducted daily radiosonde soundings continuously for about 30 months during October 19, 1993 and March 11, 1996, at Bandung, Indonesia (6.9°S, 107.6°E). We obtained a total of 785 profiles of winds and temperatures at 0-38 km, and the same number of humidity profiles below 10 km. In this paper, we first discuss the climatological characteristics of winds, precipitable water vapor content (PWC) and Brunt-Vaisala frequency squared, N2, in the troposphere and lower stratosphere. An annual PWC cycle was clearly observed with sharp contrasts between dry and rainy seasons, centered in July-October and December-March, respectively. The N2 variations were particularly enhanced in the upper troposphere (11-14 km), and the seasonal cycle of N2 is anti-phase to that of PWC. We have further analyzed the seasonal variations in wind velocity and temperature perturbations with a vertical scale of 2 km, which are used as indices of gravity wave activity. The annual cycle of the gravity wave activity is clearly recognized in the entire troposphere, which is anti-phase to the seasonal variations of PWC, that is, in-phase with the N2 variation in the upper troposphere. The gravity wave energy seems to be proportional to the background N2 value, as suggested by a saturated gravity wave model. In the lower stratosphere the annual cycle of the gravity wave activity disappears, but the long-term variations are related to the quasi-biennial oscillation (QBO) structure.