The Interannual Variability of Tropical Precipitation and Interhemispheric Energy Transport

Abstract

The interannual variability of the location of the intertropical convergence zone (ITCZ) is strongly (R = 0.75) correlated with the atmospheric heat transport across the equator (AHTEQ) over the satellite era (1979–2009). A 1° northward displacement of the ITCZ is associated with 0.34 PW of anomalous AHTEQ from north to south. The AHTEQ and precipitation anomalies are both associated with an intensification of the climatological Hadley cell that is displaced north of the equator. This relationship suggests that the tropical precipitation variability is driven by a hemispheric asymmetry of energy input to the atmosphere at all latitudes by way of the constraint that AHTEQ is balanced by a hemispheric asymmetry in energy input to the atmosphere.

A 500-yr coupled model simulation also features strong interannual correlations between the ITCZ location and AHTEQ. The interannual variability of AHTEQ in the model is associated with a hemispheric asymmetry in the top of the atmosphere radiative anomalies in the tropics with the Northern Hemisphere gaining energy when the ITCZ is displaced northward. The surface heat fluxes make a secondary contribution to the interannual variability of AHTEQ despite the fact that the interannual variability of the ocean heat transport across the equator (OHTEQ) is comparable in magnitude to that in AHTEQ. The OHTEQ makes a minimal impact on the atmospheric energy budget because the vast majority of the interannual variability in OHTEQ is stored in the subsurface ocean and, thus, the interannual variability of OHTEQ does not strongly impact the atmospheric circulation.