Anticyclones Studying anticyclonic weather
In contrast to depressions, anticyclones only involve one type of air mass, usually involve large areas and do not involve fronts. An anticyclone is a large mass of subsiding air which produces and area of high pressure. The air converges in the upper troposphere where the air has little moisture content and descends down the air column. As it descends it warms up and so warm, dry air arrives at the ground. It the diverges and winds blow out from the centre spiralling in a clockwise direction (in the northern hemisphere). The pressure gradients in such a feature are gentle, and so there are light winds or calm conditions. Anticyclones can be very large, typically at least 3000 km wide (much bigger than depressions) and, once they become established can give several days of warm settled weather with clear skies. Anticyclones do not always produce fine weather. They sometimes produce temperature inversion. This means that daytime heating may lead to a layer of instability below the inversion giving stratus clouds. This is know as 'anticyclonic gloom; and may produce drizzle. Because anticyclones are very stable and stay in one place they can divert mid latitude low pressure systems around them. Anticyclones often develop (in Europe) over Scandanavia and Siberia in winter and over the Azores in summer. (Anticyclones are never found over the equatorial regions because they are dominated by low pressure.

British Anticyclonic Weather :
In Britian in summer an anticyclone will mean heat waves during the day. But, as there is no cloud cover, the nights will be cold and mist or heavy dews will form. After a few days, a layer of hot air is built up at ground level which will eventually break away giving thunderstorms and ending the anticyclone.

In Britian in winter we have short days with low insolation and long nights. This means that when we have anticyclonic weather there is intense radiation cooling during the night time leading to ground frosts. Over several days, a ground layer of very cold air is built up causing a temperature inversion. In this case we often get fogs, which are slower to clear than the summer mists.

The very stable conditions present in anticyclones means that pollution can be held to the ground giving very poor air quality e.g. smogs. Summer poor air quality is caused by the photochemical reaction of exhaust gases because of intense insolation giving low level ozone and there are no winds to blow it away because of the stable conditions.