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.

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:

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