An oceanic pathway for Madden\u2013Julian Oscillation influence on Maritime Continent Tropical Cyclones

Karthik Balaguru,Sujith Krishnakumar,Samson M Hagos,L Ruby Leung

doi:10.1038/s41612-021-00208-4

Karthik Balaguru, Sujith Krishnakumar + Show 2 more

Open Access

https://doi.org/10.1038/s41612-021-00208-4

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Abstract

While the Madden–Julian Oscillation (MJO) has been shown to affect tropical cyclones (TCs) worldwide through its modulation of large-scale circulation in the atmosphere, little or no role for the ocean has been identified to date in this influence of MJO on TCs. Using observations and numerical model simulations, we demonstrate that MJO events substantially impact TCs over the Maritime Continent (MC) region through an oceanic pathway. While propagating across the MC region, MJO events cause significant sea surface cooling with an area-averaged value of about 0.35 ± 0.12 °C. Hence, TCs over the MC region immediately following the passage of MJO events encounter considerably cooler sea surface temperatures. Consequently, the enthalpy fluxes under the storms are reduced and the intensification rates decrease by more than 50% on average. These results highlight an important role played by the ocean in facilitating MJO-induced sub-seasonal variability in TC activity over the MC region.

Highlights

The Madden–Julian Oscillation (MJO), a 30–60 days period oscillation is a dominant mode of variability in the tropical atmosphere
It was found that strong MJO events weaken subsequent events that immediately follow them through their sea surface temperature (SST) footprints[28]
Stronger MJOs tend to induce more sea surface cooling as they pass over the Maritime Continent (MC) region (Supplementary Fig. 2a)

Summary

Introduction

The Madden–Julian Oscillation (MJO), a 30–60 days period oscillation is a dominant mode of variability in the tropical atmosphere. It is one of the most important meteorological phenomena at intraseasonal timescales with wide-ranging impacts on global weather and climate[1,2,3]. When the active phase of the MJO happens over a region, the large-scale environment becomes more favorable for cyclogenesis, leading to the formation and intensification of tropical cyclones (TCs) in that region[5,6]. It has been observed that TCs tend to form in clusters in different basins coinciding with the favorable or active phase of the MJO7. Reduction in vertical wind shear, enhancement of low-level cyclonic vorticity and an increase in mid-tropospheric humidity are found to be the main factors behind the MJO’s positive influence on TCs in various regions[8,9,10,11,12,13,14,15,16,17,18,19]

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