Anticyclones The calm and still ones

Characteristics of anticyclones  You know the routine – pens and the whiteboard  Just think opposite of depressions

Characteristics of anticyclones  Relatively high pressure  On weather maps they are closed isobars with pressure increasing towards the centre.  Anticyclones move slowly and remain stationary over an area for several days or weeks  The air subsides (sinks). It warms which leads to a decrease in relative humidity = lack of cloud & dry conditions.

Anticyclones  Anticyclones which establish themselves over UK & Western Europe are called blocking anticyclones  They deflect depressions away from UK & Western Europe  Extreme conditions are then produced – dry and freezing in winter and heat waves in summer.

Anticyclones Anticyclone summerwinter Unlike depressions there are two distinct types of anticyclone There are some similarities but in other ways are very different

Anticyclones Winter  Cold day time temps, from below 0 o c to c 5 o c  Very cold night time temps – frosts below 0 o c  Generally clear skies by day & night Summer  Hot day time temp, over 25 o c  Warm night time temps May not fall below 15 o c  Generally clear skies by day & night WinterSummer

Anticyclones Winter  low level cloud may linger and radiation fog may remain in low lying areas  Causes high levels of air pollution in urban areas as pollutants are trapped by temperature inversion Summer  Hazy sunshine in some areas  Early morning mists which disperse quickly  Heavy dew in the mornings  East coast has sea frets or haars (onshore winds)  Thunder storms can occur when RH is high