Large hemispheric differences in the Hadley cell strength variability due to ocean coupling

Abstract

By modulating the distribution of heat, precipitation and moisture, the Hadley cell holds large climate impacts at low and subtropical latitudes. Here we show that the interannual variability of the annual mean Hadley cell strength is ~ 30% less in the Northern Hemisphere than in the Southern Hemisphere. Using a hierarchy of ocean coupling experiments, we find that the smaller variability in the Northern Hemisphere stems from dynamic ocean coupling, which has opposite effects on the variability of the Hadley cell in the Southern and Northern Hemispheres; it acts to increase the variability in the Southern Hemisphere, which is inversely linked to equatorial upwelling, and reduce the variability in the Northern Hemisphere, which shows a direct relation with the subtropical wind-driven overturning circulation. The important role of ocean coupling in modulating the tropical circulation suggests that further investigation should be carried out to better understand the climate impacts of ocean-atmosphere coupling at low latitudes.