Seoul National University, Republic of Korea

• Main Authors: C H Sui, Gerry Bell, Jeff Callaghan
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.175.5783; http://severe.worldweather.org/iwtc/document/Topic_4_1_Chang_Hoi_Ho.pdf

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. Over the tropical oceans prone to frequent TCs, the thermodynamic factors for TC formation are most often satisfied. Also, the dynamic parameters—positive low-level vorticity and weak vertical wind shear—give rise to environments favorable for the generation of TCs. In the case of changes in the large-scale circulation in the tropical oceans, the thermodynamic and/or dynamic parameters may be modified. These modifications, in turn, may alter the TC activity/intensity. The variation of the TC activity is to some extent associated with the El Nino–Southern Oscillation (ENSO), quasi-biennial oscillation (QBO), Arctic Oscillation (AO), North Atlantic Oscillation (NAO)