Intraseasonal Variability of Surface Circulation in the Indo-Pacific Warm Pool Induced by Summer Monsoon Intraseasonal Oscillations

Abstract

The Indian summer monsoon intraseasonal oscillation (MISO) is the most influential mode of tropical atmospheric intraseasonal variability in boreal summer (May-October). This study investigates how the MISO drives the intraseasonal variability (ISV) of zonal currents (U) in the Indo-Pacific warm pool (IPWP) region. An analysis of satellite observations confirms a close association between U ISV and the MISO, with MISO-induced surface U anomalies reaching 16-19 cm s(-1) near the equator and 4-5 cm s(-1) in the Northern Hemisphere portion of the IPWP. These ISVs account for 15%-35% of the intensity changes in the major zonal currents. The spatial distribution of U ISV shows coherent enhancement and suppression of MISO convections with a lag of approximately 7 days as a delayed response to the tropical wind forcing. ISV anomalies show northward emanation following propagation of the MISO. Ocean model experiments confirm that large-scale ISV in surface U is primarily caused by the wind forcing of the MISO. Owing to the convergence/divergence of MISO-induced U ISV, significant warm water volume anomalies occur in the western-to-central equatorial Pacific.