Does Weakening Vertical Ocean Mixing Contribute to the Poleward Shift of Tropical Cyclone Maximum Intensity?

Abstract:

Although a poleward migration of the location of tropical cyclone (TC) lifetime-maximum intensity (LMI) during the past several decades had been identified recently, the underlying mechanism is still unclear. Using a global coupled model and a high-resolution regional atmosphere model, here we demonstrate that the weakening ocean vertical mixing in the ocean after mid-1970s could be the main cause of the poleward migration. Results from sensitivity experiments of the coupled model show that, with weakening tidal mixing, the sea surface temperature (SST) has an increasing trend over the mid-latitude coastal regions of both northwestern Pacific and the northwestern Atlantic, which is consistent with the observations. The increasing SST over the mid-latitude coastal regions provides more potential energy for the TC development and favors a poleward shift of the TC LMI from the tropics. The high-resolution regional atmosphere model forced with this SST variation produces a 1~2-latitute migration of the location of TC LMI away from the tropics. Our finding that the variation of the location of TC LMI is constrained by the decadal change of ocean forcing contributes to the projection of TC activity in the future.