How are anticyclones formed
Surrounded by circular isobars anticyclone is such a wind system which has highest air pressure at the centre and lowest at the outer margin and winds blow from the centre outward in clockwise direction in the northern hemisphere and anticlockwise in the southern hemisphere. Thus, anticyclones are high-pressure systems and more common in the subtropical high pressure belts but are practically absent in the equatorial regions.
Types of Anticyclones
Types of anticyclones were classified into (i) warm anticyclones, and (ii) cold anticyclones by Hanzilk in 1909.
Characteristics of Anticyclones
1. They are usually circular in shape. The difference of pressure between the centre and periphery of anticyclone ranges between 10-20 mb.
2. They are much larger in size and area than temperate cyclones.
3. Anticyclones follow cyclones. They move very sluggishly. The average velocity of anticyclones is 30-50 km per hour.
4. Winds descend from above at the centre and thus weather becomes clear and rain less because the descending winds cause atmospheric stability.
5. Temperature in anticyclones depends on weather, nature of environment air mass and humidity in the air.
6. Anticyclones do not have fronts.
Wind Systems of Anticyclones
Wind system is not fully developed in anticyclones because of weak pressure gradient. On an average, wind circulation is of divergent system wherein winds spread in all directions from high-pressure centre to low-pressure periphery. The winds are very much sluggish in the rear portion in comparison to the front portion. The centre is characterized by light breeze.
Temperature of Anticyclones
These arise due to the descent of either polar cold air mass or warm tropical air mass. Cold anticyclones are associated with extremely low temperature and they cause cold waves during winter season but when they come in summer season, weather becomes pleasant.
Generalized representation of air pressure and wind system in an anticyclone.
Shapes and Size of Anticyclones
Anticyclones are generally of circular shape but are very large in size. They become so large in size that their diameters become 9,000 km.
Weather Conditions of Anticyclones
Generally, anticyclones are rainless and sky is free of clouds because of the fact that descending air in the centre of anticyclone is warmed up at dry adiabatic rate due to subsidence. This causes rise in temperature, which reduces normal lapse rate of temperature, with the result the stability of air increases resulting into marked increase in the aridity of air. This is why anticyclones are indicative of dry weather.