What are anti-cyclones?

Answer 1

An anticyclone, also known as a 'high' can be identified on a weather chart as an often large area of widely spaced isobars, where pressure is higher than surrounding areas. In the Northern Hemisphere winds blow in a clockwise direction around high pressure. The highest pressure occurs at the centre and is known as the 'high pressure centre'. Anticyclones can bring warm and sunny weather in summer, but cold and foggy weather in winter.

A depression, also known as a 'low' can be recognised on a weather chart by an area of closely spaced isobars, often in a roughly circular shape, where pressure is lower than surrounding areas. They are often accompanied by fronts. In the Northern Hemisphere winds blow around depressions in an anticlockwise direction. The lowest pressure occurs at the middle of a depression, this is known as the 'low pressure centre'. Depressions are often associated with strong winds and heavy rain and are nearly always accompanied by fronts.

Troughs Troughs are elongated extensions of areas of low pressure. They bring similar weather to that associated with depressions. Ridges Ridges are elongated extensions of areas of high pressure. They bring similar weather to that associated with anticyclones. Col A col can be identified as an area of slack pressure between two anticyclones and two depressions. The following diagram summarises the appearance on a weather chart of the main types of pressure systems. Cold fronts and warm fronts Cold fronts can be identified on weather charts as bold lines with triangles. These are blue when displayed on colour charts. The points of the triangle indicate the direction in which the front is moving. A cold front indicates a change in air mass, where warmer air is being replaced by colder air. They often bring short spells of heavy rainfall in the form of showers and squally winds, and are accompanied by a decrease in temperature, a veer in wind direction and a change to brighter showery conditions. Warm fronts can be identified on weather charts as bold lines with semi-circles or humps. These are coloured red when displayed on colour charts. The direction of the humps indicates the direction in which the front is moving. A warm front indicates a change from a colder to a warmer air mass. They often bring spells of prolonged and sometimes heavy rainfall, with strong winds. Occluded fronts Occluded fronts can be identified on weather charts as bold lines with sets of triangles and semi-circles. These are coloured purple on coloured weather charts. The direction in which the symbols face indicates the direction in which the front is travelling. Occlusions are formed when the cold front overtakes the warm front, therefore they have similar characteristics to a cold front, but less intense. Warm Sector The warm sector of a depression is located behind the warm front and ahead of the cold front. It often brings mild temperatures but the weather can be overcast with drizzle.

Answer 2

An anticyclone is an area of high pressure rather than low pressure ("cyclone"). Weather associated with anticyclones features clear skies and relatively calm winds.

This remains true in both hemispheres, however, the rotation of air is what differs. Anticyclonic motion is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Cyclonic motion is the opposite.