资源环境科技发展态势分析平台

We investigate variability and trends of the Southern Hemisphere quasi-stationary planetary waves over 1979-2013 using the European Centre for Medium-range Weather Forecasts (ECMWF) Interim reanalyses. The effects of tropical and extra-tropical forcing factors on the phase and amplitude of the planetary waves are identified. The amplitudes of wave numbers 1-3 exhibit an annual cycle with a minimum in summer and maximum over the extended austral winter period. The phase of wave number 1 has a semi-annual cycle, moving east in austral spring/autumn and west in summer/winter as a result of differences in the phase of the semi-annual oscillation across the Pacific sector of the Southern Ocean. The phase of wave number 3 has an annual cycle, being more eastward (westward) in summer (winter). Year-to-year variability of the amplitude of wave number 1 is found to be strongly associated with the Amundsen Sea Low, which in turn is known to be strongly influenced by the El Nino-Southern Oscillation, with the consequence that the amplitude of wave number 1 is larger during the El Nino phase of the cycle. Regarding trends for the year as a whole, the amplitude of wave number 1 has decreased since 1979 (p < 0.1), while the amplitudes of wave numbers 2 and 3 have increased. These changes are consistent with the warming trends in sea surface temperatures across much of the tropical oceans. However, the factors associated with longer-term trends are less clear than for year-to-year variability.