A cyclone is an area of low atmospheric pressure. The term was originally applied to the violent storms which occur in the Bay of Bengal and other parts of the tropics, generally after an ominous calm and a sudden drop in atmospheric pressure. In a region where a cyclone exists, the pressure decreases from the outside inwards, so that the pressure reading of a barometer is always low near the centre. The steeper the pressure gradient, the higher the wind velocity. The winds blow spirally inwards towards the centre, counter-clockwise in the northern hemisphere, and clockwise in the southern. Outside of the tropics a cyclone is usually called a depression, in allusion to the lowering of the barometer height. Depressions vary greatly in size. the diameter may be as low as 160 km, but they average nearer 1600 km in diameter. A depression is, as a rule, accompanied by a lot of cloud and rain. The air in front of a depression feels humid, but towards the rear it becomes fresh and chilly. depressions are not stationary. The velocities and paths of their
centres depend on many factors. They move faster in winter than in summer, and deep depressions faster than shallow ones. The average velocity varies from region to region, in the USA the average being about 40 kmh, in Europe closer to 25 kmh, the winter velocity being roughly double the summer. The term anticyclone was first used by Sir Francis Galton to describe a condition of pressure and circulation just the reverse of the cyclonic condition. Research Cyclone
Abbreviations
SciTech
Research Cyclone