Sources and Role of Dry Vortex Merger for Tropical Cyclone Genesis over the Atlantic Ocean

A strong, convective African tropical disturbance has a greater chance to develop into a Tropical Depression (TD) if it merges with a shallow, dry vortex (D-vortex) from the north of the African easterly jet (AEJ) after leaving the western coast. Using 11-year reanalysis data we found that the D-vortex merger process occurred for 63.5% of tropical cyclones (TCs) or developing systems over the main development region of the Atlantic Ocean, while it occurred for 54% of non-developing systems. TC genesis could be largely controlled by the large-scale environment, but the differences in characteristics of vortices associated with the D-vortex merger between developing and non-developing systems could potentially help determine their destinies; in general, developing systems were dominated by a more intense and moist south vortex, while non-developing systems were dominated by a north vortex which was more intense, drier, and larger in size. Analysis also shows that 74% of intense developing systems were involved with the D-vortex merger process. More attention needs to be paid to the D-vortex merger and the characteristics of those vortices as they can play significant roles or have a strong indication in Atlantic TC genesis.