冬の準定常プラネタリー波の鉛直構造

Abstract

Zonal harmonic analysis of the structure of quasi-stationary planetary waves in the winter stratosphere of the Northern Hemisphere made by Hirota and Sato (1969) is extended to the cases of eight winters (1963-1970) inclusive of 500mb data. Each winter is formed of three months: January, February and March.From the analysis of monthly mean states of the amplitude, the position of trough and the wave energy, it is found that the ″node-like structure″ of planetary waves of zonal wavenumber 1 appears at about 100mb level at 60°N in many months among 24 months. The presence of nodes and the intensity of the zonal westerlies at upper levels are highly correlated; the node appears when the intensity of the mean zonal wind at 10mb level exceeds about 40meter/sec. This suggests that the node appears as the result of the interferences of waves propagating upwards and downwards. In such situation, reflective indices of amplitudes are simply estimated to be between 35 and 60%. The presence of the node-like structure is not evident in the wave 1 at 40°N. It is not found in waves 2 and 3.The vertical distribution of the wave energy of waves 2 and 3 shows the maximum at about 300-500mb level and decreases with increasing height above the level.The year to year variation of the vertical structure of planetary waves is discussed, and is also compared with the result of van Loon et al. (1973).