Definition of anticyclones

Anticyclone which is commonly known as high is 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; anticyclones are high-pressure systems where air moves away and sink, they are very common in the subtropical high pressure belts but are practically absent in the equatorial regions. Anticyclones are generally surrounded by circular isobars, they are circular in shape but are very large in size; they can become so large in size such that their diameters could reach up to 9000km.

According to Hanzilk in 1909, anticyclones are classified into two types such as

1. Warm anticyclones
2. Cold anticyclones.

Warm anticyclones over land areas typically bring calm and often warm weather. Cold anticyclones take place where there is extremely low temperature and they bring about cold waves during the day and colder nights due to lack of cloud cover during winter season but when they occur in summer season, there is presence of light wind and a pleasant weather.

How are anticyclones formed?

The formation of anticyclones in higher position occurs in warm core cyclones such asthe tropical cycloneswhen latent heat caused by the formation ofcloudsis released thereby increasing the air temperature; the resultant thickness of the atmospheric layer increases high pressure above which empties their outflow.

Anticyclones formation depend on few factors such as its size, intensity, moist-convection, Coriolis force for instance. In anticyclones, the wind system is very light and not fully developed due to weak pressure gradient. On an average, wind circulation is of divergent system whereby the winds circulate in all directions from high-pressure centre to low-pressure periphery. The winds are very much sluggish in the rear portion when compared to the front portion, however, the centre is dominated by light breeze; these take place due to the descent of either polar cold air mass or warm tropical air mass.

Generally, anticyclones are rainless and the 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 a rise in temperature, which lowers normal lapse rate of temperature, with this, the stability of air increases resulting into marked increase in the aridity of air. This is why anticyclones comes with dry weather.

Characteristics of Anticyclones

• They are usually circular in shape. The difference of pressure between the centre and periphery of anticyclone ranges between 10-20 mb.
• They are much larger in size and area than temperate cyclones.
• Anticyclones follow cyclones. They move very sluggishly. The average velocity of anticyclones is 30-50 km per hour.
• Winds descend from above at the centre and thus weather becomes clear and rain less because the descending winds cause atmospheric stability.
• Temperature in anticyclones depends on weather, nature of air mass and humidity in the air.
• Anticyclones do not have fronts.

Difference between Anticyclones and cyclones

1. One major difference between cyclone and anticyclone is that a cyclone is a system of low pressure while an anticyclone is a system of high pressure.
2. There is the presence of storm in cyclone and a light cool wind in anticyclone.
3. In cyclone, the winds converge at the eye (central low pressure) and moves in a spiral motion, while in anticyclone the winds diverge from the central high pressure to the surrounding low pressure.
4. Winds blow in an anti-clockwise direction in the Northern hemisphere and clockwise in the Southern hemisphere while they blow in a clockwise direction in the Northern hemisphere and counterclockwise in the Southern Hemisphere.