William Collins

This research assesses the influences of Atlantic Multidecadal Variability (AMV) on global tropical cyclones (TCs) using two large ensembles of idealized global climate model simulations with opposite signs of AMV forcings superimposed (i.e., AMV+ and AMV–). We first detect TCs and then compare TC activity by basin in the two AMV experiments. We find contrasting responses of Atlantic and Pacific TC frequency to the AMV anomalies. Compared to AMV–, AMV+ significantly increases TC frequency in the North Atlantic, including those making landfalls. The increase is explained by warmer sea surface temperature, higher relative humidity, increased relative vorticity, and weaker vertical wind shear under AMV+. By contrast, AMV+ decreases TC occurrence over the western North Pacific and South Pacific, which is tied to stronger vertical wind shear and lower relative humidity. The opposite responses of TC activity to AMV+ are attributed to strengthened Walker Circulation between the Atlantic and Pacific.