Statistical Characteristics of Inertial Gravity Waves Over a Tropical Station in the Western Pacific Based on High-Resolution GPS Radiosonde Soundings

The characteristics of gravity wave activity in tropical areas have been extensively explored, but at present, less attention has been paid to the activity of inertial gravity waves (IGWs) in the Western Pacific based on in-situ detection data. Based on the radiosonde data over Guam (13.3 degrees N, 144.4 degrees E) for 6 years (2013-2018), the hodograph method and spectrum analysis are used to analyze the statistical characteristics of IGWs in the troposphere (2-14 km) and stratosphere (18-28 km). The gravity wave (GW) energy in the troposphere has clear annual cycle, with the strongest activity in winter and the weakest in monsoon. In the stratosphere, the periodic variation of wave energy is interrupted due to the 2016 quasi-biennial oscillation (QBO) disruption reflected in the zonal wind field. In the troposphere, the quantity of up-propagating GWs is close to that of the down-propagating GWs, while in the stratosphere, they are almost up-propagating GWs. The horizontal propagation direction of GWs is mainly northeast and southwest in both the troposphere and the stratosphere, since the weak background wind field does not produce significant filtering effect. The spectral amplitude based on the normalized temperature perturbation has clear uniform annual variations in the troposphere and stratosphere, which are the largest in winter and the smallest in monsoon. Due to the "saturation" process in the up-propagating process of GWs, the spectral slope is more negative in the stratosphere.