Characteristics of inertia gravity waves over the South Pacific as revealed by radiosonde observations

[1] Using horizontal wind and temperature data with fine vertical resolution obtained by radiosondes, we investigate the characteristics of parameters and propagation properties of inertia gravity waves in the upper troposphere and lower stratosphere in the subtropics and extratropics over the South Pacific where very few observations have so far been done. Components extracted by a band-pass filter having cutoff vertical wavelengths of 0.5 and 5 km are analyzed as gravity waves. Gravity wave parameters such as intrinsic frequency (omega) over cap, vertical and horizontal wavelengths, and phase and group velocities are estimated by hodograph analysis. The statistics on such parameters are presented for both the stratosphere and troposphere for the three latitudinal ranges 17 degrees - 24 degrees S, 25 degrees - 33 degrees S, and 34 degrees - 48 degrees S. The horizontal wavelengths decrease and (omega) over cap increases with increasing latitude south. The dominant values for the Coriolis parameter f divided by (omega) over cap are similar to 0.5 in the lower stratosphere and similar to 0.3 in the troposphere, with little dependence on latitude. The dominant vertical wavelengths for upward propagating waves are longer in the troposphere than in the lower stratosphere. The most dominant direction of horizontal propagation is southward, with a little bias toward southeastward. A case study using ray tracing suggests that the major source of such southeastward waves is located in the upper troposphere. Notable northward propagation of gravity waves is also found in the subtropical lower stratosphere. The source of the gravity waves is considered to be a cutoff cyclone developing in the upper troposphere.