Seasonal Variation of Upper Tropospheric and Lower Stratospheric Equatorial Waves over the Tropical Pacific

Abstract

Abstract Upper tropospheric and lower stratospheric wind data spanning 31 years from 1964 to 1994 were analyzed at rawinsonde stations in the central/western Pacific. Traditional spectral and cross-spectral analysis led to the conclusion that there is a significant signal with periods between 3 and 4.5 days, which the authors link with the dominant antisymmetric waves predicted by theory to have these periods, mixed Rossby–gravity waves, and equatorial Rossby waves. Then the authors applied the seasonally varying spectral analysis method developed by Madden to study the average seasonal variation of these waves. The seasonally varying analysis suggested that there are significant twice-yearly maxima in equatorial wave activity throughout the upper troposphere and lower stratosphere, with peaks occurring in late winter–spring and in late summer–fall. The twice-yearly signal was most prominent at the 70-hPa and 100-hPa levels. Similar and consistent results were also shown by an autoregressive cyclic spectr...