Intraseasonal oscillation in the tropical Indian Ocean

The features of the intraseasonal oscillation (ISO) of the tropical Indian Ocean are studied using several sources of observational data. It is shown that there are intraseasonal oscillations in the tropical Indian Ocean, but their periods vary with latitude: the major period is about 20–30 days in the equatorial region, about 30–50 days at 10°N/10°S latitude and 60–90 days at 20°N/20°S latitude. The intensity of the ISO increases with latitude but the speed of the westward propagation of the ISO decreases with latitude. The intensity and propagation speed of the ISO have clear interannual variation features. The atmospheric intraseasonal oscillation over the tropical Indian Ocean is also analyzed and compared with the oceanic intraseasonal oscillation. It is shown that the major period is in the range 30–60 days and the intensity and period of the atmospheric ISO decrease with latitude slightly. The zonal propagation of the atmospheric ISO also has some differences with the oceanic ISO. It is necessary to study the relationship between the atmospheric ISO and oceanic ISO in the tropical Indian Ocean deeply.