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Thunderstorms develop as warm, moist air rises turning into rain or hail. As the thunderstorm reaches its mature stage, violent updrafts are noted and precipitation begins. At the onset of precipitation, strong downdrafts develop. Falling precipitation reverses rising air columns by frictional drag and cooling, and the storm eventually begins to dissipate or collapse.
This image shows the remains of a collapsed thunderstorm in the southern Pacific Ocean northwest of Easter Island and northeast of Henderson Island. The surrounding arc cloud marks the edge of the cold air surge which developed when the storm collapsed. Such an arc cloud might be associated with a gust front. The mass of cooled air spreads out from downdrafts and often becomes organized into a small, high-pressure area called a bubble high, which persists for some time as an entity that can sometimes be seen on the surface chart. Or, for example, from space, as an almost circular cloud-free area. Bubble highs are a so-called mesoscale features, i.e. having a size of typically 80 to 300 km across. They are relatively cold and often have the characteristics of a different air mass.
However, downdraft may also originate from neighboring thunderstorms and the high pressure bubble adopts quasi-frontal characteristics if it originates from a supercell or squall line. Such bubble highs may be a mechanism for controlling the direction in which new cells form, especially if the bubble high is overrun by unstable air.
Related features:
Thunderstorm
Air-mass thunderstorm
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