Interannual, Decadal, and Transient Greenhouse Simulation of Tropical Cyclone–like Vortices in a Regional Climate Model of the South Pacific

Abstract

Tropical cyclone?like vortices (TCLVs) in the South Pacific Ocean are studied using the CSIRO Division of Atmospheric Research Limited Area Model (DARLAM), nested in a transient carbon dioxide simulation of the CSIRO Mark2 global coupled GCM. This GCM is able to simulate El Niño?Southern Oscillation (ENSO)?like interannual variations, although the amplitude of these is considerably smaller than observed. A comparison is made between observed geographical variations of cyclone formation caused by ENSO and similar variations simulated by DARLAM. An analysis of the simulated interannual variability of TCLV formation suggests that under La Niña conditions TCLVs tend to occur closer to the coast of Australia, whereas under El Niño conditions TCLVs tend to occur farther eastward, in agreement with observations. Under enhanced greenhouse conditions, this geographical variation continues. In addition, the total number of TCLVs in the South Pacific region decreases in a warmer world. As in previous simulations using DARLAM, there is a southward movement in TCLV occurrence under enhanced greenhouse conditions, although this has not been simulated to date by other climate models. The GCM simulation of sea surface temperatures also exhibits coherent decadal variability that has some similarities to the observed ENSO-like decadal variability. This variability forces decadal variations in TCLV formation that, like ENSO-forced variations, have geographically distinct centers of action.