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Dust devils and dust storms | Thunderstorms, lightning and tornadoes Hurricanes and great spots | Space weather and solar winds
Hurricanes From the ground, you might not recognise a hurricane till it's almost upon you. Looking down from a satellite, the distinctive swirl of cloud with the clear eye near its centre reveals the presence of one of the most devastating weather systems on Earth. Hurricanes - called typhoons and tropical cyclones in some parts of the world - are violent depressions (lows) that start out over the Earth's tropical oceans in late summer or autumn. They're driven by the heat of the Sun, and always move from warmer to cooler areas of the Earth, acting as giant temperature regulators. Unlike the depressions that are a major feature of European weather, hurricanes have no warm or cold fronts circulating around them. In Europe, the pressure at the centre of a depression rarely falls below about 970 millibars. In a hurricane, warm, wet, fast-rising air can reduce the pressure to 890 millibars or less. In the eye of a hurricane, falling air produces cloudless skies and light winds. The eye shrinks as the hurricane intensifies. Around the eye, rising air creates a 10,000ft (3,000m) wall of cloud that throws out spiralling bands of clouds and powerful winds extending up to 75 miles (120km) from the storm centre. Hurricane force winds have speeds of 75mph (120kph) or above. In intense hurricanes, wind speed can be more than 150mph (240kph). Hurricanes build up their energy as they travel over the warm ocean surface. But, once a hurricane moves over dry land, its source of energy is cut off, so the storm weakens and dies. Generally, most damage is done within about 125 miles (200km) of the coastline. On Earth, hurricanes nearly always bring death and destruction to ships at sea and to communities on land. In 1900, the hurricane that swept ashore at Galveston, Texas, claimed 6,000 lives. More recently, in 1988, Hurricane Gilbert claimed 265 lives in Jamaica and Mexico, and caused more than $4bn (£2.7bn) of damage. Great spots On Jupiter, the Great Red Spot puts Earth hurricanes to shame. This anti-cyclonic (high-pressure) storm could swallow three entire Earths without trace. The storm redistributes not solar heat but heat rising from deep within the planet itself. It's the longest-lasting weather system ever recorded - first observed in 1664 - and it's still going strong. Wind speeds around the anti-cyclone reach 250mph (400kph), with little or no wind at the centre. In Jupiter's bands of clouds, other hurricane-like storms are constantly forming - and being absorbed into more powerful neighbours. Neptune has its own Great Dark Spot, a giant anti-cyclone with 700mph (1,100kph) winds blasting out from its centre. On Saturn, temporary yellowish-white spots appear in the cloud bands from time to time, often lasting for several months. These too may be giant hurricane-like structures. |
How Earth compares with Jupiter's Great Red Spot (This movie typically takes 30 seconds to download. You may require the RealPlayer plug-in for your browser.)
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