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CYCLONES

Temperate Cyclone
Q.Compare the origin and weather conditions associated with the tropical and temperate   cyclones. (15/16)
Q.Compare and contrast tropical cyclone and temperate cyclone. (12/12)
 
  • Temperate cyclones are low pressure meteorological system which develops in mid latitudes due to convergence of cold air mass and warm air mass.
  • Norwegian scientist Jacob Bjerknes is attributed to giving elaborate theory on temperate cyclone which is known as polar front theory.
  • Polar front theory
    1.Stage I: incipient stage (dilatory motion,stationary front)
    2.Stage II:Frontogenesis stage(cold & warm front,Rossby waves)
    3.Stage III:Mature stage
    4.Stage IV occlusion stage
    5.Stage V Dissipation stage.
  • weather
    1.cold sector
    2.Warm front
    3.warm sector
    4.Cold front

Tropical Cyclone

Low Pressure meteorological system
CONDITIONS
  • Sea surface temperature (> 27 degree cent , so April -Sept.)
  • Coriolis force not less than a minimum value ( so, rarely between 5 N and 5 S)
  • upper air anti cyclogenesis.
  • A Minimum vertical wind shear required,so difficult in sub tropical high pressure zone i.e 30-35 degree latitudes.
  • Pre-existing vortices
  • Sufficient Wind Velocity to move on sea surface


STAGE
1.Stage1 (Incipient stage)
  • Air starts to move in circular motion;isobars away from centers are ill defined;these vortices moves into ITCZ  where intense convection takes place and incipient cyclone develops; core develops which act as zone of convergence.
2.Stage 2(Infantile stage)
  • Eye and eyewall develops;in the upper layer thunder and lightning due to development of cumulonimbus clouds
3.Stage 3(Juvenile stage)
  • Eye,eyewall are developed and rings are in the stage of formation;convection system become prominent and vertical clouds (cumulonimbus) are fully developed;now cyclone can be traced moving over sea and they become   predictable.
4.Stage 4(Mature stage)
  • Eye, eyewall ,inner ring and outer rings are fully developed; clouds are fully developed with nimbo-stratus at lower level and cumulonimbus in the upper layer while cirrus below the tropopause. characterized by high velocity winds over 120 km/hr, thunder and lightning with heavy downpour.
5.Stage 5(Dissipient stage)
  • As they reach ground  , they dissipate as favourable conditions of water vapour not available; Also dissipate as they reach subtropical high pressure belts.




VERTICAL STRUCTURE
1.Eye:
  • Diameter: 2 to 5 Km, Calm Zone, clear sky with bright sunshine, no rainfall, air subsidence;
2.Eye wall:
  • Diameter 20 times the Eye- 30-40 Km; very high speed wind called hurricane with speed 140 Km/hr -400 Km/hr; thunder & lightning; Heavy rainfall due to cumulo-nimbus clouds;Cloud Bursts; Zone of convection.
 3.Inner Ring:
  • Dia:50-60 Km;wind speed around 60-80 Km/hr;rainfall due to cumulus cloud;
 4.Outer Ring:
  • wind speed around 40 Km/hr; Gentle breeze; Pleasant whether; some drizzles by strato-cumulus cloud;
 5.Annular Zone

  • Radius from center is 500-600 Km; surrounds whole cyclone; zone of subsidence and high pressure
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