Thunderstorms and tornadoes
Although tornadoes and hurricanes are cyclones, the vast majority of cyclones are not hurricanes or tornados. The tern cyclone simply refers to the circulation around any low pressure center no matter how large or intense it is. Thunderstorms, are related in some manner to tornadoes, hurricanes, and midlatitude cyclones. Dynamic thermal instability occurs during the development of thunderstorms, which form when warm, humid air rises in an unstable environment. A number of mechanisms, such as unequal heating of Earth's surface of lifting of warm air along a front or mountain slope, can trigger the upwarm air movement needed to created thunderstorm producing cumulonimbus clouds. Severe thunderstorms produce high winds, damaging hail, flash floods, and tornadoes. In the U.S. air mass thunderstorms frequently occur in maritime tropical air that moves northward from the gulf of Mexico. During the spring and summer when air is heated from below by the warmer land surface, the warn humid air mass becomes unstable and thunderstorms develop. Generally, three stages are involved in the development of a thunderstorm. The cumulus stage is dominated by rising currents of air and the formation of a towering cumulonimbus cloud. Fallin
Tornadoes, sometimes called twisters, or cyclones, are violent windstorms that take the form of a rotating column of air, or vortex, that extends downward from a cumulonimbus cloud. The less common but more dangerous lightning is cloud to ground lightning. Mountainous regions, such as the Rockies in the west and the Appalachians in the East, experience a greater number of air-mass thunderstorms than do the Plains states. They are influenced by strong vertical wind shear - that is, changes in wind direction and/or speed between different heights, and updrafts that become tilted and continue to build upward. The object of lightning is to equalize the electrical difference associated with the formation of a large cumulonimbus cloud by producing a negative flow of current from the region of excess negative charge to the region with excess positive charge, or vice versa. The lightning we see as some single flashes are really several very rapid strokes between the cloud and the ground. The origin of charge separation in clouds, although not fully understood, must hinge on rapid vertical movements within the cloud. The most common type of lightning called sheet lightning occurs within and between clouds. Some tornadoes consist of a single vortex. g precipitation within the cloud causes drag on the air and initiates a downdraft that is further aided by the influx of cool, dry air surrounding the cloud, a process termed entrainment. The vertical wind profile of these cells may produce a mesocyclone, a column of cyclonically rotating air, within which tornadoes sometimes form. An important precondition linked to tornado formation in severe thunderstorms is the development of a mesocyclone that forms in the updraft of the thunderstorm. A squall line with severe thunderstorms can also form along a boundary called a dryline, a narrow zone along which there is an abrupt change in moisture.
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