Glossary

A tropical cyclone is a low-pressure system characterised by structured convection, severe storms, and a closed low-level atmospheric circulation at its centre. Depending on the region in which it forms, it may be referred to as a typhoon (Central and West Pacific), hurricane (Atlantic and East Pacific), cyclone (India, Bangladesh), tropical cyclone (southern Indian Ocean) or willy-willy (Australia). Cyclone activity in the tropics is of a fundamentally different nature than in the middle and high latitudes. Disturbances in the tropical easterlies occasionally result in low-pressure cells that can even be felt at the surface (tropical disturbances) and whose additional convergence in the friction layer promotes conditional instability through convection and, through the condensation heat released from the moist-warm tropical air, provides cyclones with substantial energy. When this happens, tropical storms can develop.