Jupiter's Great Red Spot has been raging for at least 340 years
Earth's storms last from about half a day to a little over a week. Jupiter's Great Red Spot, a swirling system bigger than our whole planet with winds beyond hurricane strength, has persisted for at least 340 years, ever since Giovanni Domenico Cassini first spotted it. Storms are a feature of any world with enough atmosphere.
A storm is any major disturbance of an atmosphere, whether driven by wind, rain, snow, ice, lightning or airborne dust. The English word traces to the Proto-Germanic sturmaz, meaning noise or tumult. Storms form when a pocket of low pressure develops inside surrounding high pressure, generating wind and towering cumulonimbus clouds; on a smaller scale, hot air rising off sunbaked ground spins up dust devils. Meteorologists strictly reserve the word for winds of force 10 or more on the Beaufort scale, at least 89 kilometres per hour, though everyday speech is looser, and storms on Earth last roughly 12 to 200 hours.
The vocabulary is rich. A gale brings sustained winds of 34 to 48 knots, a squall a sudden jump of at least 16 knots held for a minute. A derecho is a long-lived band of straight-line winds racing ahead of thunderstorms, while a microburst is a violent downdraught lasting only minutes. A bomb cyclone deepens so fast its winds can rival a hurricane. Ice storms are among the most dangerous winter events: just 8 millimetres of glaze can start bringing down power lines. Some fires grow so intense that they generate their own winds, becoming firestorms, as in the Peshtigo Fire.
Thunderstorms occur worldwide but most often over tropical rainforests, where heat and humidity drive air upward to the top of the troposphere; single storm clouds span 2 to 10 kilometres. Tropical cyclones are warm-core systems fed by heat released as moist air condenses, and depending on strength and region they are called tropical storms, hurricanes or typhoons. Storms can do good too, easing droughts and bringing the snow that makes skiing possible.
Other worlds offer spectacular examples. Neptune once showed a Great Dark Spot, and in 1994 the Hubble Space Telescope imaged a Saturn storm known as the Dragon Storm, first seen in 1990. On Mars, dust storms can engulf the entire planet, usually when it swings closest to the Sun, and they raise global temperatures. When Mariner 9 became the first spacecraft to orbit another planet, in November 1971, it arrived to find Mars shrouded in dust.
Source: Storm
