Subsurface Oceanic Structure Associated With Atmospheric Convectively Coupled Equatorial Kelvin Waves in the Eastern Indian Ocean

Abstract

17 Atmospheric convectively coupled equatorial Kelvin waves (CCKWs) are a major trop18 ical weather feature strongly influenced by ocean–atmosphere interactions. However, pre19 diction of the development and propagation of CCKWs remains a challenge for models. 20 The physical processes involved in these interactions are assessed by investigating the 21 oceanic response to the passage of CCKWs across the eastern Indian Ocean and Mar22 itime Continent using the NEMO ocean model analysis with data assimilation. Three23 dimensional life cycles are constructed for “solitary” CCKW events. As a CCKW prop24 agates over the eastern Indian Ocean, the immediate thermodynamic ocean response in25 cludes cooling of the ocean surface and subsurface, deepening of the mixed layer depth, 26 and an increase in the mixed layer heat content. Additionally, a dynamical downwelling 27 signal is observed two days after the peak in the CCKW westerly wind burst, which prop28 agates eastward along the Equator and then follows the Sumatra and Java coasts, con29 sistent with a downwelling oceanic Kelvin wave with an average phase speed of 2.3 m s−1. 30 Meridional and vertical structures of zonal velocity anomalies are consistent with this 31 framework. This dynamical feature is consistent across distinct CCKW populations, in32 dicating the importance of CCKWs as a source of oceanic Kelvin waves in the eastern 33 Indian Ocean. The subsurface dynamical response to the CCKWs is identifiable up to 34 11 days after the forcing. These ocean feedbacks on time scales longer than the CCKW 35 life cycle help elucidate how locally driven processes can rectify onto longer time-scale 36 processes in the coupled ocean–atmosphere system. 37 Plain Language Summary 38 We investigate the effects that the passage of a weather system (an atmospheric 39 convectively coupled equatorial Kelvin wave, CCKW) along the Equator has in the east40 ern Indian Ocean. CCKWs can intensify precipitation and cause extreme weather, such 41 as flooding, over the islands of the Maritime Continent, which include Indonesia and Malaysia. 42 CCKWs affect the ocean and which can then feedback onto the CCKWs. A better un43 derstanding of the physical processes connecting the atmosphere and ocean during a CCKW 44 passage is still needed to improve its prediction by models. More accurate CCKW pre45 diction will then help to mitigate some of the consequences of the weather-related nat46 ural disasters in the region. We show that the effects of the passage of the CCKW on 47 the ocean are relatively long-lived. For example, the increase in the amount of heat avail48