Relevance of Relative Sea Surface Temperature for Tropical Rainfall Interannual Variability

Abstract

The coupling between sea surface temperature (SST) anomalies and rainfall is an important driver of tropical climate variability. Observations however reveal inconsistencies, such as decreased convective rainfall in regions with positive SST anomalies in the tropical Indian and Atlantic Oceans during and after El Niño–Southern Oscillation (ENSO) events. The upper troposphere warms during El Niño events, stabilizing the atmosphere. SST anomalies only account for the influence of the surface. Using theoretical arguments, we show that relative SST (RSST; defined as SST minus its tropical mean) anomalies, by also accounting for the influence of upper tropospheric temperature anomalies on gross moist stability, explain tropical convection interannual variations better than SST anomalies in observations and climate models. This relation further improves when RSST anomalies are weighted by the precipitation climatology to account for low and high-precipitation regimes. Using RSST is thus essential to understand El Niño–Southern Oscillation teleconnections and interactions between modes of tropical climate variability.