Thermal low

Thermal lows, or heat lows, are non-frontal low-pressure areas that occur over the continents in the subtropics during the warm season, as the result of intense heating when compared to their surrounding environments.^[1] Thermal lows occur near the Sonoran Desert, on the Mexican plateau, in California's Great Central Valley, in the Sahara, in the Kalahari, over north-west Argentina, in South America, over the Kimberley region of north-west Australia, over the Iberian peninsula, and over the Tibetan plateau.

On land, intense, rapid solar heating of the earth's surface causes the heating of the lowest layers of the atmosphere, via re-radiated energy in the infrared spectrum. The hotter air is less dense than surrounding cooler air and rises, leading to the formation of a low pressure area. Elevated areas can enhance the strength of the thermal low because they warm more quickly than the atmosphere which surrounds them at the same altitude. Over water, instability lows form during the winter when the air overlying the land is colder than the warmer water body.

Thermal lows can extend to 3,100 metres (10,200 ft) in height and tend to have weak circulations. Thermal lows over the western and southern portions of North America, northern Africa, and Southeast Asia are strong enough to lead to summer monsoon conditions. Thermal lows inland of the coastline lead to the development of sea breezes which, combined with rugged topography near the coast, can lead to poor air quality. Owing to the very high temperatures in the centre of heat lows, there are relatively few direct observations of thermal lows.