What is a Hurricane?
Hurricane = Tropical cyclone ...
A cyclone is a circulation in the atmosphere with lower atmospheric pressure that rotates counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere.
We define a tropical cyclone as a non-frontal [absence of the warm and cold fronts typically associated with winter-type storms], "warm-core" storm with a sustained wind speed of at least 34 knots (kt) or 39 mph that forms in or near the tropics.
"Warm-core" means that, on average, the temperature near the center of the cyclone is warmer than the surrounding environment. A tropical cyclone’s strongest wind speeds are generally located about 1500 feet above the surface and the strength of the wind decreases both above and below that level (Franklin et al. 2003).
However, it remains strong enough at the surface to be able to cause considerable damage. This wind structure -- stronger winds in the lower atmosphere than in the upper atmosphere (upper troposphere) -- is a direct consequence of the warm-core structure.
Tropical cyclones usually form within 25° of the Equator, but they can form as far as 40° from the Equator (Elsberry 1995), which is as far north as New York City or as far south as Melbourne, Australia. Regardless of where it originates, in order to form a tropical cyclone requires a relatively small, closed circulation, that is, a low-pressure area less than 500-1000 km in diameter, within 5000 feet of the surface that has a substantial concentration of thunderstorms inside it. It is not currently well understood what quantifies "substantial concentration of convection" in terms of its extent over time or space.
Frequent thunderstorms day after day within this closed circulation concentrate precipitation and the formation of precipitation itself heats the atmosphere. If the closed circulation is sufficiently strong and small and the thunderstorms occur close enough to its center, the heat is focused within the circulation by both the rotation of the circulation itself and the rotation of the Earth (Coriolis deflection).
Read all of Dr. Robert Hart's hurricane primer here. (Note: It is a PDF file.)
A cyclone is a circulation in the atmosphere with lower atmospheric pressure that rotates counter-clockwise in the northern hemisphere and clockwise in the southern hemisphere.
We define a tropical cyclone as a non-frontal [absence of the warm and cold fronts typically associated with winter-type storms], "warm-core" storm with a sustained wind speed of at least 34 knots (kt) or 39 mph that forms in or near the tropics.
"Warm-core" means that, on average, the temperature near the center of the cyclone is warmer than the surrounding environment. A tropical cyclone’s strongest wind speeds are generally located about 1500 feet above the surface and the strength of the wind decreases both above and below that level (Franklin et al. 2003).
However, it remains strong enough at the surface to be able to cause considerable damage. This wind structure -- stronger winds in the lower atmosphere than in the upper atmosphere (upper troposphere) -- is a direct consequence of the warm-core structure.
Tropical cyclones usually form within 25° of the Equator, but they can form as far as 40° from the Equator (Elsberry 1995), which is as far north as New York City or as far south as Melbourne, Australia. Regardless of where it originates, in order to form a tropical cyclone requires a relatively small, closed circulation, that is, a low-pressure area less than 500-1000 km in diameter, within 5000 feet of the surface that has a substantial concentration of thunderstorms inside it. It is not currently well understood what quantifies "substantial concentration of convection" in terms of its extent over time or space.
Frequent thunderstorms day after day within this closed circulation concentrate precipitation and the formation of precipitation itself heats the atmosphere. If the closed circulation is sufficiently strong and small and the thunderstorms occur close enough to its center, the heat is focused within the circulation by both the rotation of the circulation itself and the rotation of the Earth (Coriolis deflection).
Read all of Dr. Robert Hart's hurricane primer here. (Note: It is a PDF file.)
posted by Jake McCafferty at 8:58:00 PM
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