SIXTH INTERNATIONAL WORKSHOP on TROPICAL CYCLONES Topic 4.1 : Variability of Tropical Cyclone Activity/Intensity on Intraseasonal and Interannual Scales

Topic 4.1 reviews the current status of the understanding on variability of tropical cyclone (TC) activity/intensity on intraseasonal to interannual time scales around the globe. Annually, approximately 80−90 TCs occur over the tropical oceans (Neumann 1993). The TC activities depend on thermodynamic parameters (e.g., sea surface temperature (SST), atmospheric stability, and mid-tropospheric moisture) and dynamic parameters (e.g., low-level vorticity, vertical wind shear, and upper-tropospheric momentum flux convergence) (Gray 1979). In many cases, thermodynamic parameters are closely linked with each other in the tropics; the atmosphere overlying high SSTs tends to be humid, and humid air with high atmospheric temperature inevitably becomes unstable.