Dependence of Global Tropical Cyclones on the Tropical Pacific Mean State in the HighResMIP Models

Abstract Global tropical cyclone (TC) activity is influenced by the tropical Pacific mean state, which is modulated by the El Niño–Southern Oscillation (ENSO) phenomenon at interannual time scales. In recent decades, observations show a La Niña–like trend in the tropical Pacific, while most global climate models simulate a more El Niño–like trend. The cause of this inconsistency remains under debate, but it is likely quite consequential for global TC activity. This study examines the response of global TC activity to sea surface temperature (SST) warming patterns using historical simulations from the High Resolution Model Intercomparison Project (HighResMIP): atmosphere-only simulations forced by observed SSTs, which exhibit a La Niña–like SST trend in the tropical Pacific; and coupled simulations, showing a weaker La Niña–like SST trend. TC activity is compared between the two sets of simulations using multiple statistics of TC activity, along with TC-relevant large-scale environmental fields. The TC genesis index (TCGI) is used to quantify the contributions of each environmental field to changes in TC activity. Results show that the forced global TC response is sensitive to the tropical Pacific mean state and varies by basin. In SST-forced simulations, TC activity’s trend patterns resemble the TC anomalies during La Niña events. In those simulations, thermodynamic environmental fields, namely, potential intensity and column-relative humidity, induce zonal variations in TC frequency, while dynamical fields, namely, vertical wind shear and absolute vorticity, induce meridional variations in TC frequency. In contrast, coupled simulations show no consistent TC response across HighResMIP models. Significance Statement Global tropical cyclone (TC) activity is influenced by the sea surface temperature pattern in the tropical Pacific. In recent decades, observations show strengthening zonal (west minus east) and meridional (off-equator minus equator) sea surface temperature gradients, whereas most climate models simulate the opposite trends. This study examines how global TC activity responds to the sea surface warming patterns using climate model simulations. Results show that TC activity is sensitive to changes in the tropical Pacific mean state, with basin-dependent responses. In models forced with strengthening gradients, TC activity changes resemble those during La Niña events, featuring anomalously positive zonal and meridional gradients in sea surface temperature. However, no consistent signals for TC activity have been found in models with weakening gradients.