Interannual, decadal, and transient greenhouse simulation of tropical cyclone-like vortices in a regional climate model of the South Pacific

Tropical cyclone-like vortices (TCLVs) in the South Pacific Ocean are studi ed using the CSIRO Division of Atmospheric Research Limited Area Model (DAR LAM), nested in a transient carbon dioxide simulation of the CSIRO Mark2 gl obal coupled GCM. This GCM is able to simulate El Nino-Southern Oscillation (ENSO)-like interannual variations, although the amplitude of these is con siderably smaller than observed. A comparison is made between observed geog raphical variations of cyclone formation caused by ENSO and similar variati ons simulated by DARLAM. An analysis of the simulated interannual variabili ty of TCLV formation suggests that under La Nina conditions TCLVs tend to o ccur closer to the coast of Australia, whereas under El Nino conditions TCL Vs tend to occur farther eastward, in agreement with observations. Under en hanced greenhouse conditions, this geographical variation continues. In add ition, the total number of TCLVs in the South Pacific region decreases in a warmer world. As in previous simulations using DARLAM, there is a southwar d movement in TCLV occurrence under enhanced greenhouse conditions, althoug h this has not been simulated to date by other climate models. The GCM simu lation of sea surface temperatures also exhibits coherent decadal variabili ty that has some similarities to the observed ENSO-like decadal variability . This variability forces decadal variations in TCLV formation that, like E NSO-forced variations, have geographically distinct centers of action.