Characteristics of Gravity Waves over the Tibetan Plateau during the PRC-Japan Cooperative JICA Project in 2008

Abstract

Using wind and temperature data with high vertical resolution obtained from Global Positioning System (GPS) radiosondes which were launched four times a day at Gerze (32.2°N, 84.4°E) and Litang (30.0°N, 100.3°E) stations during the People’s Republic of China (PRC)-Japan cooperative JICA project in 2008, the characteristics of gravity waves such as vertical energy propagation directions, intrinsic frequencies, vertical wave-lengths, and horizontal propagation directions over the Tibetan Plateau are investigated by hodograph method. The statistic characteristics of the gravity waves show that the activities of the gravity waves over the western and eastern Tibetan Plateau have significant spatial variations except for horizontal propagation directions, and that the gravity waves over the eastern Tibetan Plateau are easier to be triggered. The energy propagates upward for almost half of the observed gravity waves, and the energy propagation is downward for the other half of the gravity waves, indicating that the wave sources in lower and upper troposphere are equally important over the Tibetan Plateau. The dominant gravity wave frequencies lie in the frequency range of 2-2.5 times of Coriolis parameter f at Gerze station, while the dominant gravity wave frequencies are in the range of 1.5-2 times of f at Litang station. The dominant vertical wavelengths are 1.5-2.5 km over Gerze and Litang. For Gerze station, the dominant gravity waves propagate along the west-southwestward directions, while the dominant gravity wave propagating directions are north-northwestward for Litang station.