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.

Marine Heatwaves in the East Asian Marginal Seas Facilitated by Boreal Summer Intraseasonal Oscillations

“…The influx of freshwater from precipitation, Yangtze River discharge, and strength of the Taiwan Current, lead to a decrease in SSS to below normal levels during BSISO phases 5 to 7 (Figures 3e-3h, Column E). Although, we have not explicitly investigated all the sources of freshwater influx in this region, apart from precipitation, we mention them in consideration of the major current systems and northward movement of the active BSISO ( (Song et al, 2022). Kim et al (2014) suggested that 80% of the total freshwater in the East China Sea and its neighboring region originates from Changjiang River discharge.…”

Seasonality of the intraseasonal variability in the upper equatorial western Pacific Ocean currents

“…However, in the Pacific region, limited in situ observations have resulted in few systematic studies on the seasonal spatiotemporal distribution of ocean circulation ISVs. Atmospheric ISOs, which exhibit significant seasonal characteristics (Lee et al 2013), strongly influence the upper ocean (Song et al 2019(Song et al , 2022. Besides the external forcing by atmospheric ISOs, ocean internal variability also plays a significant role in surface current ISVs in the western Pacific.…”