Intraseasonal oscillations over the tropical western Pacific and eastern Indian Ocean for the northern summers of 1989-1991

Abstract

In this study we used data analyzed by the Navy Operational Global Analysis and Prediction System to study the intraseasonal oscillations other than Madden and Julian oscillation over the tropical western Pacific and eastern Indian ocean. The period of study is May-September of 1989, 1990 and 1991. Multiple-set canonical correlation (MCC), single point correlation and composite analyses were used to determine the structure of the disturbances. The results show that MCC mode#l describes both the seasonal change and a near 20 day oscillation with a zonal half-wavelength around 3000-4000 km. The single point correlation and composites indicate that these oscillations are in gradient wind balance, transporting moisture northward, having upper level divergence over a surface low and a warm-core structure. The seasonal change composite shows a quasi-stationary oscillation with May and June corresponding to the negative phase of MCC mode#l, and August corresponding to the positive phase of MCC mode#l. The near 20 day composite describes a westward propagation of 2.5 - 3' per day, with phase 2 corresponding to the negative phase of MCC mode#l and phase 5 corresponding to the positive phase of MCC mode#1