Global View of the Origin of Tropical Disturbances Revisited

A thirty-year climatology of global tropical disturbances is presented. The climatology is generated from ERA-Interim reanalysis data using the Okubo-Weiss parameter as a kinematic criterion and the column relative humidity as a thermodynamic criterion. The tracking algorithm is trained on the 2010 Pre-Depression Investigation of Cloud-systems in the Tropics dataset and yields a global probability of detection rate of approximately 80% when compared to 2005-2009 Joint Typhoon Warning Center and National Hurricane Center INVEST tracks.

The tropical disturbance climatology is viewed from both global and regional perspectives. Globally, there is very little interseasonal variability in the number of tropical disturbances. The low variability suggests some global constraint on the number of tropical disturbances despite the variety of formation mechanisms. The global genesis productivity, or the percentage of tropical disturbances that develop, ranges between 15-25% and has been relatively stable over the thirty-year period. Regionally, there is more variability in the genesis productivity, with the northeast and northwest Pacific basins being the most prolific. Within some of the basins, there exist climatological genesis “hotspots.”