Cyclone is a system of low atmospheric pressure in which the barometric gradient is steep. Winds circulate, blowing inwards in an anticlockwise direction in the Northern hemisphere and clockwise direction in the Southern hemisphere. Cyclones are classified into two parts: (l)Tropical Cyclone (2)Temperate or Extra-tropical Cyclone
(l)Tropical Cyclone: A system of low pressure occurring in tropical latitudes, characterized by its very strong winds; found mainly in Indian Ocean , Indonesia , and Australia
(a)A Tropical Depression is a system with low pressure enclosed within few isobars and the wind speed is. 33 knot or 61 tens and it lacks a marked circulation.
(a)A Tropical Depression is a system with low pressure enclosed within few isobars and the wind speed is. 33 knot or 61 tens and it lacks a marked circulation.
(b)A Tropical Storm is a system with several closed isobars and a wind circulation of 115 Kms.
(c)A Tropical Cyclones is a warm core vortex circulation of tropical origin with a small diameter often of an approximately circular shape; they occur only in oceanic areas where the sea temperatures exceed 27 degree C.
Different Names of Tropical Cyclones:
Hurricanes -N. America & Caribbean
Willy willies- Australia
Bagulo- Philippine Islands
Typhoon- Japan, Western North Pacific
Cyclones- Indian Ocean
Bagulo- Philippine Islands
Typhoon- Japan, Western North Pacific
Cyclones- Indian Ocean
Structure of the Tropical Cyclones:
► It is essentially radially symmetrical
► It has six regions (1) The eye is the centre of the storm which is characterised by more or less circular with comparatively clear skies, lowest pressure, the highest temperature and highest relative humidities;
(2) The eye is surrounded by a wall of cumulonimbus known as eyeball. Strongest wind is found;
(3) Spiral bands or Rainbands or Feeder bands contain many individual thunderstorms which produce heavy rainfall;
(4)Annular zone is characterized by cloudiness and high temperatures and low humidities;
(5) Outer Convective band;
(6) Main cloudmass. Horizontal structure of tropical cyclone
► It is essentially radially symmetrical
► It has six regions (1) The eye is the centre of the storm which is characterised by more or less circular with comparatively clear skies, lowest pressure, the highest temperature and highest relative humidities;
(2) The eye is surrounded by a wall of cumulonimbus known as eyeball. Strongest wind is found;
(3) Spiral bands or Rainbands or Feeder bands contain many individual thunderstorms which produce heavy rainfall;
(4)Annular zone is characterized by cloudiness and high temperatures and low humidities;
(5) Outer Convective band;
(6) Main cloudmass. Horizontal structure of tropical cyclone
Eye: the innermost or central portion of the mature cyclone is the 'eye'. It is about 10 to 30 km in diameter, depending upon the size of the.storm and is a more.or less calm region with little or no clouds and some subsidence. The eye or the calm centre can be described variously as the: Pressure eye (where mean sea level pressure is lowest), Wind eye (light or calm wind conditions), Radar eye (the eye seen in radar echoes) and the Satellite eye (clear or dark spot seen in the cloud mass in satellite imagery).
Eye Wall or Inner Ring Surrounding the eye is a tight 'inner ring' of hurricane winds. This core of maximum winds is at the center of a solid thick wall of towering Cumulonimbus clouds and is called the 'eye wall'.
Outer Ring An outer ring of cyclonic circulation lies beyond the eye wall, where the speed decreases steeply and clouds and rain diminish rapidly outwards.
(2) Temperate Cyclone: It is also called 'Depressions'. It has low pressure at the centre and increasing pressure outward. It has varying shapes such as near circular, elliptical or wedge, therefore, it is also called Low or Troughs or Mid Latitude Depressions. Secondly, they are formed in the regions extending between 35 degree to 65 degree latitudes in both the hemispheres. Thirdly, Tropical Cyclone is confined strictly over sea, whereas Temperate Cyclone form over both land and sea. Fourthly, Tropical cyclone is produced in summer and autumn and Temperate cyclone largely in winter. Fifthly, Temperate cyclone has low pressure gradient, whereas tropical cyclone has steep pressure gradient; and finally, rainfall in temperate cyclones is slow and continuous, whereas in tropical cyclone the rainfall is violent and torrential.
Anticyclone: A system of atmospheric pressure in which the isobars on a synoptic chart indicate a relatively, highpressure in the center and decreasingly low pressures outwards to the periphery of the system. The isobars are generally widely spaced, indicating light winds which may be absent near the centre. Air movement is clockwise in the Northern hemisphere and anticlockwise in the Southern hemisphere. The term anticyclone was coined by Galton in 1861 Anticyclones do not experience any precipitation and tend to be dry. It is characterized by larger, slow moving and more persistent with a high pressure at the centre but with a weaker pressure gradient and light variable winds diverging from the center.
► They are usually circular in shape but sometimes also assume 'V shape.
► They are much larger in size and area than temperate cyclones as their diameter is 75% larger than that of the latter.
► Anticyclones do not have fronts.
► Winds descend from above at the centre and thus weather becomes clear and rainless.
► They are much larger in size and area than temperate cyclones as their diameter is 75% larger than that of the latter.
► Anticyclones do not have fronts.
► Winds descend from above at the centre and thus weather becomes clear and rainless.
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