Effect of Tropical Cyclones on Ocean Heat Transport as simulated by a High Resolution Coupled GCM

Abstract

This study investigates the Tropical Cyclone (TC) effect on the northern hemisphere Ocean Heat Transport (OHT) and the possible changes that greenhouse induced global warming might generate in the characteristics of the TC-induced OHT (TCiOHT). The analysis has been performed using 20C3M (20th Century) and A1B (21st Century) IPCC scenario climate simulations obtained running a fully coupled high-resolution global general circulation model named CMCC_MED. The Atmospheric model component has a T159 horizontal resolution and 31 vertical levels. The Ocean model component has a horizontal resolution ranging from 2 degrees to 0.5 degrees near the equator and 31 vertical levels. The capability of the model to reproduce a reasonably realistic TC climatology has been assessed by comparing the model results from the simulation of the 20th Century with observations. TC detection method has been implemented thanks to the TC-MIP project. The model appears to be able to simulate tropical cyclone-like vortices with many features similar to the observed TCs. The simulated TC activity exhibits realistic structure, geographical distribution and interannual variability, suggesting that the model is able to reproduce the major basic mechanisms that link the TC activity with the large scale circulation. The TC-induced ocean cooling is well represented and the resulting column-integrated ocean heating makes the poleward OHT larger in the subtropics and decreases the poleward heat transport out of the deep tropics. This effect, investigated looking at the 100 most intense Northern Hemisphere TCs, is strongly correlated to the TC-induced momentum flux at the surface of the ocean: the winds associated to the TCs significantly weaken the trade winds in the 5-18N latitude belt and reinforce them in the 18-30N band. TCs frequency and intensity appear to be substantially stationary through the whole 1950-2069 period. The effect of the TCs on the OHT is overall less pronounced in the 21st century when compared to the 20th century.