Modulation of Monsoon Circulations by Cross-Equatorial Ocean Heat Transport.

(Lutsko, N, Marshall, J., and Green, B.), Journal of Climate, vol. 32, no. 12, pp. pages, 2019.

Abstract

Motivated by observations of southward ocean heat transport (OHT) in the northern Indian Ocean duringsummer, the role of the ocean in modulating monsoon circulations is explored by coupling an atmosphericmodel to a slab ocean with an interactive representation of OHT and an idealized subtropical continent.Southward OHT by the cross-equatorial cells is caused by Ekman flow driven by southwesterly monsoonwinds in the summer months, cooling sea surface temperatures (SSTs) south of the continent. This increasesthe reversed meridional surface gradient of moist static energy, shifting the precipitation maximum over theland and strengthening the monsoonal circulation, in the sense of enhancing the vertical wind shear. However,the atmosphere’s cross-equatorial meridional overturning circulation is also weakened by the presence ofsouthward OHT, as the atmosphere is required to transport less energy across the equator. The sensitivity ofthese effects to varying the strength of the OHT, fixing the OHT at its annual-mean value, and to removing theland is explored. Comparisons with more realistic models suggest that the idealized model used in this studyproduces a reasonable representation of the effect of OHT on SSTs equatorward of subtropical continents,and hence can be used to study the role of OHT in shaping monsoon circulations on Earth.

doi = 10.1175/JCLI-D-18-0623.1