Monday, September 26, 2011
WATERSPOUT. (Part 2).
A waterspout is an intense columnar vortex (usually appearing as a funnel-shaped cloud) that occurs over a body of water, and it is connected to a cumuliform cloud. In the common form, it is a non-supercell tornadoe over water. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur. Waterspouts do not suck up water; the water seen in the main funnel cloud is actually water droplets formed by condensation. While many waterspouts form in the tropics, locations at higher latitude within temperate zones also report waterspouts, such as Europe and the Great Lakes in the USA. Although rare, waterspouts have been observed in connection with lake-effect snow precipitation bands. Waterspouts have a five-part life cycle: formation of a dark spot on the water surface, spiral pattern on the water surface, formation of a spray ring, development of visible condensation funnel, and ultimately decay.
Waterspouts exist on a microscale, where their environment is less than two kilometers in width. The cloud that develops them can be as innocuous as a moderate cumulus, or as great as a supercell. While some waterspouts are strong and tornadic in nature like their land-based counterpart, most are much weaker and caused by different atmospheric dynamics. They normally develop in moisture-laden environments as their parent clouds are in the process of development, and it is theorized that they spin up as they move up the surface boundary from the horizontal shear near the surface, and then stretch upwards to the cloud once the low level shear vortex aligns with a developing cumulus or thunderstorm. Weak tornadoes, known as landspouts, have been shown to develop in a similar manner. TYPES:
Waterspouts that are not associated with a rotating updraft of a supercell thunderstorm, are known as "non-tornadic" or "fair-weather waterspouts," and are by far the most common type. Fair-weather waterspouts occur in coastal waters and are associated with dark, flat-bottomed, developing convective cumulus towers. Waterspouts of this type rapidly develop and dissipate, having life cycles shorter than 20 minutes. They are most frequently seen in tropical and sub-tropical climates, with upwards of 400 per year observed in the Florida Keys. Fair-weather waterspouts are very similar in both appearance and mechanics to landspouts, and largely behave as such if they move ashore.
"Tornadic waterspouts," also accurately referred to as "tornadoes over water," are formed from mesocyclonic action in a manner essentially identical to traditional land-based tornadoes in connection with severe thunderstorms, but simply occuring over water. A tornadoe which travels from land to a body of water would also be considered a tornadic waterspout. Since the vast majority of mesocyclonic thunderstorms occur in land-locked areas of the United States, true tornadic waterspouts are correspondingly rarer than their fair-weather counterparts.
A winter-waterspout, also known as a snow devil, an icespout, an ice devil, a snonado, or a snowspout, is an extremely rare instance of a waterspout forming under the base of a snow squall. The term "winter waterspout" is used to differentiate between the common warm season waterspout and this rare winter season event. Very little is known about this phenomenon and only six known pictures of this event exist to date, four of which were taken in Ontario, Canada. There are a couple of critical criteria for the formation of a winter waterspout. Extremely cold temperatures need to be present over a body of warm water enough to produce a fog resembling steam above the water's surface; this requires a 19 degrees Celsius or 34 degrees Farenheit temperature difference between the water and the invading surface air mass. Like the more efficient lake-effect snow events, winds focusing down the axis of long lakes enhance wind convergence and likely enhance their development.
A family of four waterspouts seen on the Great Lakes (Lake Huron) on September 9, 1999. Four waterspouts seen in the Florida Keys on June 5, 2009. Though the majority occur in the tropics, they can seasonally appear in temperate areas throughout the world, and are common across the western coast of Europe as well as the British Isles and several areas of the Mediterranean and Baltic Sea. They are not restricted to saltwater; many have been reported on lakes and rivers including the Great Lakes and the St. Lawrence River.
Waterspouts are common along the southeast U.S. coast, especially off southern Florida, the Keys, and can happen over seas, bays, and lakes worlwide.
Approximately 160 waterspouts are currently reported per year across Europe, with the Netherlands reporting the most at 60, followed by Spain and Italy at 25, and the United States at 15. They are most common in late summer.
Waterspouts are frequently observed off the east coast of Australia.
Waterspouts have long been recognized as serious marine hazards. Stronger waterspouts are usually quite dangerous, posing threats to ships, planes, helicopters, and swimmers. It is recommended to keep a considerable distance from these phenomena, and to always be on alert through weather reports. The United States National Weather Service will often issue special marine warnings when waterspouts are likely or have been sighted over coastal waters, or tornadoe warnings when waterspouts are expected to move onshore. When close to shorelines, waterspouts can devastate nearby coral reefs and marine organisms close to the surface.
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