Tuesday, October 27, 2009

Characteristics Temperate cyclones

Characteristics Temperate cyclones have the following, characteristics.
Size and Shape The temperate cyclQnes are asymmetri cal and shaped like an inverted 'V'. They stretch from 50 km to 600 km. They may go upto 2,500 km over Norf America. They have a height of 8 to 11 km.

Wind Velocity and Strength These aspects of a temperat cyclone vary with season, location and from cyclone t cyclone, and the wind is directed a little to the right c the centre, rather than into it. The wind strength is mOl in eastern and southern portions, more over North Americ compared to Europe. The wind velocity increases with th approach but decreases after the cyclone has passed.

Orientation and Movement Since these cyclones mov with the westerlies, they are oriented east-west. If the storr front is east-west, the centre moves swiftly eastwards. : the storm front is directed northwards, the centre mov€ towards the north, but after two or three days, the pressuI difference declines and the cyclone dissipates. In case th storm front is directed southwards, the centre moves qui! deep southwards---even upto the Mediterranean regio (sometimes causing the. Mediterranean cyclones).

Structure The north-western sector is the cold sector and the north-eastern sector is the warm sector. As 011 moves eastwards in the northern sector, dark nimbI; clouds and altrostratus are foUowed by cirrostratus highl up with cirrus clouds finally at the storm front. In t~ eastern sector, the extent of cloudiness and rainfall limited. This sector is generally dominated by cumulonin bus which cause heavy downpour, thunderstorm, lightnil1 and hail-storm.
Associated Weather The approach of a temperate cyclor is marked by fall in temperature, fall in the mercury level wind shifts and a halo around the sun and the moon, and a thin veil of cirrus clouds.

A light drizzle follows which turns into a heavy downpour. These conditions change with the arrival of the warm front which halts the fall in mercury level and the rising temperature. Rainfall stops and clear weather prevails until the cold front of an anticyclonic character arrives which causes a fall in temperature, brings cloudiness and rainfall with thunder. After this, once again, clear weather is established.

The temperate cyclones experience more rainfall when there is slower movement and a marked difference in rainfall and temperature between the front and rear of the cyclone. These cyclones are generally accompanied by anti­cyclones.

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