Interannual fluctuations of intraseasonal variance of near‐equatorial zonal winds

Abstract

Interannual fluctuations of intraseasonal variance are investigated in zonal wind time series from six stations in the near‐equatorial eastern Indian and western Pacific Oceans, in order to document the interannual variability of the Madden‐Julian oscillation. Each time series is subjected to band‐pass filtering that retains fluctuations with periods between about 30 and 60 days. The variance of the filtered data is calculated for each season in the data record and is compared with the variance of unfiltered wind anomalies and with the interannual variance of seasonal means. The principal systematic interannual modulation of 30‐ to 60‐day wind variance occurs in time series of lower tropospheric winds (surface and 850 mbar) at the stations between 14°E and the international date line, where intraseasonal variance is enhanced during the well‐developed stages of El Niño‐Southern Oscillation warm events. No systematic interannual modulation of intraseasonal zonal wind variance is found in the records from stations west of 140°E or in 200‐mbar zonal winds.