Cyclones and Anticyclones

Abstract

The terms cyclone and anticyclone are used to describe organized atmospheric systems with circular flow areas with low and high atmospheric pressure (e.g. Martin 2006; Russell and Thompson 2002; Wallace and Hobbs 2006; Holton 2004). In the Northern Hemisphere, wind in the low-pressure systems (cyclones) is blowing counterclockwise, while anticyclones spin clockwise in the Northern Hemisphere and counterclockwise in the Southern. The main structure and the circulation of the cyclone and anticyclone are shown on Fig. 17.1. In the case of the cyclones, the pressure is lowest the centre (depression), while in the case of the anticyclones, the pressure is highest at the centre. In the first case, the pressure gradient is directed towards the centre, while in the latter case, the pressure gradient force is directed from the centre of high pressure to the periphery. When cyclone or anticyclone is associated with the wave front, then it is called a wave or frontal storm or mid-latitude anticyclone. Cyclones are associated with unstable atmospheric conditions and vertical movements of air. In cyclones, the air near the Earth moves towards the inside, the centre of the cyclone, where pressure is lowest, and then it starts rising. At the same height, the lifted air starts to diverge to the surrounding environment, away from the centre of cyclone.