How Cyclones Form |
In meteorology, a cyclone is a large scale circulation of winds (or air mass) that rotates around a strong center of low atmospheric pressure rotating counterclockwise
in the Northern Hemisphere, clockwise in the Southern Hemisphere.
By contrast an anticyclone is a large scale circulation of winds (or air mass) that rotates around a central region of high atmospheric pressure, rotating clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere.
Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices (an upper-level low-pressure area lying near one of the Earth's poles) and extratropical cyclones (sometimes called mid-latitude cyclones or wave cyclones). Cyclones along with the anticyclones drive the weather over much of the Earth. The largest low-pressure systems of the synoptic scale are polar vortices and extratropical cyclones. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones (storm-scale region of rotation in diameter, within a thunderstorm), tornadoes, and dust devils lie within the smaller mesoscale.
Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification.
Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones (generally found in the central latitudes, or tropics). These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream (fast flowing, narrow, meandering air currents in the atmosphere).
Weather fronts mark the boundary between two masses of air of different temperature, humidity, and densities, and are associated with the most prominent meteorological phenomena. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines (a line of thunderstorms forming along or ahead of a cold front) or dry lines (a line across a continent that separates moist air and dry air; also called a dew point line). Such fronts form west of the circulation center and generally move from west to east; warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. Warm fronts move poleward ahead of the cyclone path. Occluded fronts (when a cold front overtakes a warm front) form late in the cyclone's life cycle near the center of the cyclone and often wrap around the storm center.
Tropical cyclogenesis describes the development and strengthening of a tropical cyclone in the atmosphere of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core. Cyclones can transition between extratropical, subtropical, and tropical phases. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear (the difference in wind speed or direction over a relatively short distance in the atmosphere).
In the Atlantic and the northeastern Pacific oceans, a tropical cyclone is generally referred to as a hurricane (from the name of the ancient Central American deity of wind, Huracan), in the Indian and south Pacific oceans it is called a cyclone, and in the northwestern Pacific it is called a typhoon. Regardless of how it is referred to it is the same weather phenomena. The growth of instability in the vortices is not universal. For example, the size, intensity, moist-convection, surface evaporation, the value of potential temperature at each potential height can affect the nonlinear evolution of a vortex.
By contrast an anticyclone is a large scale circulation of winds (or air mass) that rotates around a central region of high atmospheric pressure, rotating clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere.
Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices (an upper-level low-pressure area lying near one of the Earth's poles) and extratropical cyclones (sometimes called mid-latitude cyclones or wave cyclones). Cyclones along with the anticyclones drive the weather over much of the Earth. The largest low-pressure systems of the synoptic scale are polar vortices and extratropical cyclones. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones (storm-scale region of rotation in diameter, within a thunderstorm), tornadoes, and dust devils lie within the smaller mesoscale.
Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars, Jupiter, and Neptune. Cyclogenesis is the process of cyclone formation and intensification.
Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones (generally found in the central latitudes, or tropics). These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream (fast flowing, narrow, meandering air currents in the atmosphere).
Weather fronts mark the boundary between two masses of air of different temperature, humidity, and densities, and are associated with the most prominent meteorological phenomena. Strong cold fronts typically feature narrow bands of thunderstorms and severe weather, and may on occasion be preceded by squall lines (a line of thunderstorms forming along or ahead of a cold front) or dry lines (a line across a continent that separates moist air and dry air; also called a dew point line). Such fronts form west of the circulation center and generally move from west to east; warm fronts form east of the cyclone center and are usually preceded by stratiform precipitation and fog. Warm fronts move poleward ahead of the cyclone path. Occluded fronts (when a cold front overtakes a warm front) form late in the cyclone's life cycle near the center of the cyclone and often wrap around the storm center.
Tropical cyclogenesis describes the development and strengthening of a tropical cyclone in the atmosphere of tropical cyclones. Tropical cyclones form due to latent heat driven by significant thunderstorm activity, and are warm core. Cyclones can transition between extratropical, subtropical, and tropical phases. Mesocyclones form as warm core cyclones over land, and can lead to tornado formation. Waterspouts can also form from mesocyclones, but more often develop from environments of high instability and low vertical wind shear (the difference in wind speed or direction over a relatively short distance in the atmosphere).
In the Atlantic and the northeastern Pacific oceans, a tropical cyclone is generally referred to as a hurricane (from the name of the ancient Central American deity of wind, Huracan), in the Indian and south Pacific oceans it is called a cyclone, and in the northwestern Pacific it is called a typhoon. Regardless of how it is referred to it is the same weather phenomena. The growth of instability in the vortices is not universal. For example, the size, intensity, moist-convection, surface evaporation, the value of potential temperature at each potential height can affect the nonlinear evolution of a vortex.
