stylistic:style_transfer, structural:scholar_edition
Wind circulation in the northern and southern hemispheres

The direction of wind flow around an atmospheric high-pressure area and a low-pressure area, as seen from above, depends on the hemisphere. High-pressure systems rotate clockwise in the northern Hemisphere; low-pressure systems rotate clockwise in the southern hemisphere.

High pressure systems in the temperate latitudes generally bring warm weather in spring and summer, when the amount of heat received from the Sun during daytime exceeds what is lost at night, and cold weather in fall and winter when the amount of heat lost at night exceeds what is gained during daytime (with low pressure systems it is the reverse--lows in fall and winter bring warmer weather and cooler weather in spring and summer).

The latitudes of 30N and 30S, the so-called "horse latitudes", have semi-permanent high pressure around them known as the subtropical ridge, although their size and exact location varies with the seasons. On the West Coast of the United States, the subtropical ridge expands in spring and brings the region's characteristic rainless summer weather. As it shrinks in fall, the West Coast is subject to cold fronts from the Pacific which bring rain during the cool months. On the East Coast, it brings warm, humid air in late spring and throughout summer. In fall, as the subtropical ridge retreats, cold air from Canada takes over. In Europe, the effect is similar as the subtropical ridge brings the Mediterranean hot, dry summer weather and cool, wet winters. Europe north of the Pyrenees is at a higher latitude so the effect of the ridge is somewhat less significant and this region is mainly characterized by a cooler maritime climate. However, a particularly hot summer such as 2003 or 2019 which sees the subtropical ridge expand more than usual can bring heat waves as far north as Scandinavia—conversely, while Europe had record-breaking summer heat in 2003 due to a particularly strong subtropical ridge, its counterpart in North America was unusually weak and temperatures across the continent that spring and summer were wet and well below normal.

In the Southern Hemisphere the result is similar. Australia and the southern cone of South America get hot, dry summer weather from the subtropical ridge and cooler wetter winter weather as cold fronts from the southern oceans take over.

Winter sees the dominance of cold highs from the sub-Arctic. In Western Europe and the West Coast of North America, these originate in the Gulf of Alaska or the Greenland/Iceland area and move south to southeast. Since they are principally masses of ocean air, they will bring cool, damp conditions with widespread fog. In East Asia and interior North America, these air masses come from Siberia or Canada and bring very cold, dry air in their wake.

The scientific terms in English used to describe the weather systems generated by highs and lows were introduced in the mid-19th century, mostly by the British. The scientific theories which explain the general phenomena originated about two centuries earlier.

The term cyclone was coined by Henry Piddington of the British East India Company to describe the devastating storm of December 1789 in Coringa, India. A cyclone forms around a low-pressure area. Anticyclone, the term for the kind of weather around a high-pressure area, was coined in 1877 by Francis Galton to indicate an area whose winds revolved in the opposite direction of a cyclone. In British English, the opposite direction of clockwise is referred to as anticlockwise, making the label anticyclones a logical extension.

A simple rule is that for high-pressure areas, where generally air flows from the center outward, the coriolis force given by the earth's rotation to the air circulation is in the opposite direction of earth's apparent rotation if viewed from above the hemisphere's pole. So, both the earth and winds around a low-pressure area rotate counter-clockwise in the northern hemisphere, and clockwise in the southern. The opposite to these two cases occurs in the case of a high. These results derive from the Coriolis effect; that article explains in detail the physics, and provides an animation of a model to aid understanding.