Dynamic Response of the Spring Wyrtki Jet to the Monsoon Onset Over the Bay of Bengal

The dynamic response of the spring Wyrtki Jet (WJ), one of the dominant wind‐driven surface currents in the Indian Ocean, to the abrupt onset of the Bay of Bengal (BoB) summer monsoon is investigated. The results indicate that the spring WJ tends to approach a maximum around the monsoon onset time, with the zonal current exhibiting a rapid acceleration prior to and a gradual deceleration soon after the onset. The diagnosis demonstrates that the geostrophic term fundamentally driven by the equatorial westerlies primarily accounts for the WJ evolution. Before the monsoon onset, the burst of equatorial westerlies forces the rapid WJ acceleration. While accompanying the monsoon onset, the equatorial regime switches from westerlies to cross‐equatorial flows, leading to the gradual WJ reduction in spring. In physics, the first‐branch northward‐propagating intraseasonal oscillation, inducing both the equatorial westerlies burst and the BoB monsoon onset, powerfully factors into the spring WJ‐monsoon onset relationship.