Aice marine Science as level nasa earth Observatory by Steve Graham and Holli Riebeek · November 1, 2006
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Increasing Organization Given favorable conditions, the tropical disturbance can become better organized into a more unified storm system. As the storm organizes, surface air pressures fall in the area around the storm and winds begin to spin in a cyclonic circulation (counter-clockwise in the Northern Hemisphere). Surface pressures fall when water vapor condenses in rising air and releases energy, or latent heat, into areas within the tropical disturbance. The heat boosts the air (increases the buoyancy), so it continues rising. To compensate for the rising air, surrounding air sinks. As this air sinks towards the surface, it is compressed by the weight of the air above it and warms. The pressure rises at the top of the layer of warming air, pushing air at the top of the layer outward. Because there is now less air in the layer, the weight of the entire layer is less, and the pressure at the ocean surface drops. The drop in pressure draws in more air at the surface, and this air converges near the center of the storm to form more clouds. 
Hurricanes intensify when condensation of water vapor in rising air releases heat energy into storm, setting off a chain reaction. The heat makes the surrounding air more buoyant, causing it to rise further. To compensate for the rising air, surrounding air sinks. The sinking air is compressed by the weight of the air above it, and it warms. The pressure rises at the top of the layer of warmed air, pushing air outward. As the air spreads outward, the total air pressure at the surface drops. The more the pressure drops, the more the winds intensify, drawing more heat and moisture from the ocean surface. (Graphic by Robert Simmon, NASA GSFC.) Like an ice skater whose body spins faster as his arms are drawn inward, air near the surface speeds up as it spirals in towards the center of the low pressure area. The increasing winds that spin around the center of the storm draw heat and moisture from the warm ocean surface, providing more fuel for the rising motions that produce the clouds and increase the temperatures. A chain reaction (or feedback mechanism) is now in progress, as the rising temperatures in the center of the storm cause surface pressures to drop even more. The lower the surface pressure, the more rapidly air flows into the storm at the surface, increasing the winds and causing more thunderstorms. More thunderstorms release more heat, forcing air at higher altitudes outward. The air pressure at the surface drops even more, triggering stronger winds, and so on. The storm takes the distinctive, spiraling hurricane shape because of the Coriolis Force, generated by the rotation of the Earth. This is the same force that causes the south-blowing African jet to bend westward over the Atlantic, spawning easterly waves. In the Northern Hemisphere, the Earth’s rotation causes moving air to veer to the right. As air rushes towards the low-pressure center of the storm at the Earth’s surface, it curves right. If the storm is far enough from the equator (generally at least 8 degrees of latitude), the deflection or curvature is great enough that the air starts spinning counterclockwise around the center of the storm. Once sustained wind speeds reach 37 kilometers (23 miles) per hour, the tropical disturbance is called a tropical depression. As winds increase to 63 kilometers (39 miles) per hour, the cyclone is called a tropical storm and receives a name, a tradition started with the use of World War II vintage code names such as Able, Baker, Charlie, etc. For a number of years beginning in 1953, female names were used exclusively until the late 1970s, when storm names began to be alternated between male and female names. Finally, when wind speeds reach 119 kilometers (74 miles) per hour, the storm is classified as a hurricane. Weakening Factors Even when the conditions are ripe for hurricane formation at the surface, the storm may not form if the atmospheric conditions five to ten kilometers above the surface are not favorable. For example, around the area of 20 degrees latitude, the air aloft is often sinking, due to the presence of the sub-tropical high—a semi-permanent high pressure system in the subtropical regions. The high pressure pushes air towards the surface. The sinking air warms and creates a temperature inversion, an extremely stable air layer in which temperature increases with altitude, the opposite of the usual temperature profile in the lower atmosphere. Called the trade wind inversion, this warm layer is very stable, which makes it difficult for air currents to rise and form thunderstorms and (eventually) hurricanes. In addition, strong upper-level winds tend to rip apart developing thunderstorms by dispersing the latent heat and preventing the warming temperatures that lead to lower air pressure at the surface. At the surface, hurricanes can diminish rather quickly given the right conditions. These conditions include the storm moving over cooler water that can’t supply warm, moist tropical air; the storm moving over land, again cutting off the source of warm, moist air; and finally, the storm moving into an area where strong winds high in the atmosphere disperse latent heat, reducing the warm temperatures aloft and raising the surface pressure. AICE Marine Science NASA Earth Observatory Hurricane Anatomy During hurricane development, certain characteristics become more prominent as the storm strengthens. At the center of the hurricane is the eye, a cloud-free area of sinking air and light winds that is usually from 10 to 65 kilometers in diameter. As air rises in the thunderstorms surrounding the eye, some of it is forced towards the center, where it converges and sinks. As this air sinks, it compresses and warms to create an environment (mostly) free of clouds and precipitation. The eye is the calmest part of the storm because the strong surface winds converging towards the center never actually reach the exact center of the storm, but instead form a cylinder of relatively calm air. 
(Top) Surrounding the eye of the hurricane is a ring of thunderstorms, called the eyewall. Rainbands surround the eye of the storm in concentric circles. In the eyewall and in the rainbands, warm, moist air rises, while in the eye and around the rainbands, air from higher in the atmosphere sinks back toward the surface. The rising air cools, and water vapor in the air condenses into rain. Sinking air warms and dries, creating a calm, cloud-free area in the eye. (Middle) Low pressure at the ocean surface in the heart of the hurricane draws in surrounding air. These spiraling winds pick up speed as they approach the eye, pulling more heat and moisture from the ocean surface. (Bottom). The stronger the convection in the thunderstorms becomes, the more rain they produce. The more rain they produce, the more heat they release into the surrounding atmosphere, further fueling the storm. (Graphics Copyright © National Center for Atmospheric Research/The COMET Program.) Bordering the eye of a mature hurricane is the eye wall, a ring of tall thunderstorms that produce heavy rains and very strong winds. The most destructive section of the storm is in the eye wall on the side where the wind blows in the same direction as the storm’s forward motion. For example, in a hurricane that is moving due west, the most intense winds would be found on the northern side of the storm, since the hurricane’s winds are added to the storm’s forward motion. Surrounding the eye wall are curved bands of clouds that trail away in a spiral fashion, suitably called spiraling rain bands. The rain bands are capable of producing heavy bursts of rain and wind, perhaps one-half or two-thirds the strength of those associated with the eye wall. Directory: ourpages -> auto -> 2016 2016 -> Typhoon (the Northwest Pacific Ocean west of the dateline) 2016 -> A kq2a: What is the pattern of air movement in the troposphere? Variations in global insolation 2016 -> District 26 family night at citi field september 20, 2016 New York Mets vs. Atlanta Braves 2016 -> C/Linux Programming Syllabus – Fall 2016 Instructor: Carol Yarbrough, asfa computer Science Email 2016 -> Mid-term exam schedule january 2017 Mon., Jan. 23 – 8: 30am 2016 -> Science Skills Center High School Dr. Dahlia McGregor, Principal ap computer Science A 2016 -> Short Essay Response to Emily Dickinson's Poetry (1 page minimum, 1 ½ page maximum) Due Date: Tuesday, March 8th 2016 -> Program: University of Illinois Chicago Chance & stem academy University Name 2016 -> Fourth Grade ela/ss winter Packet Thursday, December 22 2016 -> Chapter Questions Download 448.17 Kb. Share with your friends:
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