Impact of the location of tropical convection on climate variability

The Equatorial Mode, characterized by the anomalous warming of the sea surface temperature (SST) in the eastern equatorial Atlantic region, leads the interannual variability of the tropical Atlantic during the boreal summer causing impacts both in tropical and extratropical regions. However, this pattern and its teleconnections, are not stationary; and the origin of such changes continues to be subject of enquiry and debate.

With this premise, in the present work, we evaluate the possible influence of a displacement of the ITCZ (Intertropical Convergence Zone), mediated by a radiative perturbation, on the pattern of the Equatorial Mode and its connection with the Pacific. More particularly, we examine two perturbation experiments that reduce the incident shortwave radiation in two latitude bands: NEXT in the northern extratropics and STRO in the southern tropics. The analysis is carried out from a multi-model perspective, using the data of 8 CMIP5 coupled climate models from the Extratropical-Tropical Interaction Model Intercomparison Project (ETIN-MIP).

Our results suggest that the strengthening of the ITCZ over the Atlantic equatorial band, is capable of generating changes in the mean state of the equatorial Atlantic, as well as conditions of enhanced variability on the interannual scale. In addition, it is found that the westward shift of the SST warm anomalies in the Equatorial Mode and the existence of a more variable mean state in the equatorial Atlantic and Pacific, are key in the intensification of the Atlantic-Pacific connection.