Relationship between SST Patterns and the Hadley circulation in CMIP5

Abstract:

While observational studies demonstrate poleward expansion of the Hadley circulation in the past few decades, the CMIP5 historical simulations generate much weaker trends. One question is whether the weaker trends in the width of the Hadley circulation are caused by inconsistent SST patterns and trends between CMIP5 and observations. Using CMIP5 historical simulations, we study the relationship between SST patterns and the width of the Hadley circulation. It is found that there are close correlations between the climatological width of the Hadley circulation and tropics-extratropics SST contrasts for the CMIP5 models. That is, models with weaker meridional SST contrasts have wider Hadley cells and vice versa. Furthermore, we also carry out similar analyses for trends in SST and the width of the Hadley circulation. Our results show that models with stronger equatorial SST warming generate weak equatorial retreat of the Hadley circulation, whereas models with stronger subtropical/extratropical SST warming generate poleward expansion of the Hadley circulation. These results suggest that model performance in simulating SST patterns and trends has important influences on trends in the Hadley circulation.