Australia+Cyclone

= ﻿Australia Cyclone Yasi =

Fierce winds and driving rains brought by the most powerful storm ever to hit Queensland are lashing northern coastal areas of the Australian state.
= = With winds reaching up to 290km/h (181mph), Cyclone Yasi is ripping roofs off buildings and has cut power to at least 100,000 people. The storm struck south of Cairns and is moving inland, with forecasters warning of severe damage and likely deaths. Queensland's premier has warned of devastation on an unprecedented scale.

= Physical structure = All tropical cyclones are areas of low atmospheric pressure in the Earth's atmosphere. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level. Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation, which occurs when moist air is carried upwards and its water vapor condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.

Eye and center
A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent.The eye is normally circular in shape, and may range in size from 3 kilometres (1.9 mi) to 370 kilometres (230 mi) in diameter.Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble a football stadium; this phenomenon is thus sometimes referred to as the stadium effect.

Size
One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar, also known as its ROCI. If the radius is less than two degrees of latitude or 222 kilometres (138 mi), then the cyclone is "very small" or a "midget". A radius between 3 and 6 latitude degrees or 333 kilometres (207 mi) to 670 kilometres (420 mi) are considered "average-sized". "Very large" tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (552 mi). Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with Atlantic tropical cyclones roughly half their size. Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relative vorticity field decreases to 1×10−5 s−1 from its center.
 * ~ Size descriptions of tropical cyclones ||
 * ~ ROCI ||~ Type ||
 * Less than 2 degrees latitude || Very small/midget ||
 * 2 to 3 degrees of latitude || Small ||
 * 3 to 6 degrees of latitude || Medium/Average ||
 * 6 to 8 degrees of latitude || Large anti-dwarf ||
 * Over 8 degrees of latitude || Very large ||