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Tuesday, January 26, 2010

Synoptic Systems

Type of system Description

Cyclonic Circulation

(Cycir)

Atmospheric wind flow in upper levels associated with

any low pressure system. The wind flow is counter

clockwise in the Northern Hemisphere and clockwise in

the Southern Hemisphere.

Anticyclonic circulation Atmospheric wind flow in upper levels associated with

any high pressure system. The wind flow is clockwise

in the Northern Hemisphere and counter clockwise in

the Southern Hemisphere.

Low pressure Area

(LOPAR)/ well marked

LOPAR

Area in the atmosphere in which the pressures are

lower than those of the surrounding region at the same

level and is represented on a synoptic chart by a

system of one closed isobar (wind speed on the

surface < 17 Knots (Kts) when the system is at sea or

one closed isobar in the radius of 3 Deg. from the

centre over land).

Depression Intense low pressure system represented on a synoptic

chart by two or three closed isobars at 2 hPa interval

and wind speed from 17 to 27 Kts at sea and two

closed isobars in the radius of 3 Deg. from the centre

over land.

Deep Depression Intense low pressure system represented on a synoptic

chart by two or three closed isobars at 2 hPa interval

and wind speed from 28 to 33 Kts at sea and three to

four closed isobars in the radius of 3 Deg. from the

centre over land.

Cyclonic Storm Intense low pressure system represented on a synoptic

chart by more than four closed isobars at 2 hPa

interval and in which the wind speed on surface level is

in between 34 – 47 Kts.

Severe Cyclonic Strom Intense low pressure system represented on a synoptic chart by more than four closed isobars at 2 hPa interval

and in which the wind speed on surface level is in

between 48 – 63 Kts.

Very Severe Cyclonic

Storm

Intense low pressure system represented on a synoptic

chart by more than four closed isobars at 2 hPa interval

and in which the wind speed on surface level is in

between 64 – 119 Kts.

Super cyclonic storm Intense low pressure system represented on a synoptic

chart by more than four closed isobars at 2 hPa interval

and in which the wind speed on surface level is 120

Kts. and above.

Western Disturbance Weather disturbances noticed as cyclonic

circulation/trough in the mid and lower tropospheric

levels or as a low pressure area on the surface, which

occur in middle latitude westerlies and originate over

the Mediterranean Sea, Caspian Sea and Black Sea

and move eastwards across north India.

Western Depression Weather system which originate over the

Mediterranean Sea, Caspian Sea and Black Sea and

approach northwest India and is defined by two or

more closed isobars on the surface.

Induced low Under the influence of the western disturbance,

sometimes a low is developed to the south of the

system called as induced low.

Induced cyclonic

circulation

Under the influence of the western disturbance,

sometimes a cyclonic circulation is developed to the

south of the system called as induced cyclonic

circulation.

Trough A line or curve along which the atmospheric pressure is

minimum. Pressure increases on both sides of the line

or curve.

Trough in westerlies A moving wave perturbation in mid latitude regions

which are present throughout the year which move

from west to east and entire globe. These systems

generally affect the northern parts of India.

Trough in easterlies A moving wave perturbation in the equatorial easterly

wave, moving from east to west.

Easterly Waves A shallow trough disturbance in the easterly current of

the tropics, more in evidence in the upper level winds

than in surface pressure, whose passage westwards is

followed by a marked intensification of cloudy, showery

weather. The southern peninsular region is affected by

easterly waves.

Shear line A line or narrow zone across which there is an abrupt

change in the horizontal wind component; a line of

maximum horizontal wind shear.

Ridge An elongated area of relatively high atmospheric

pressure almost always associated with and most

clearly identified as an area of maximum anticyclonic

curvature of wind flow.

Wind-discontinuity A line across which there is an abrupt change in wind

direction

Troposphere An atmospheric layer in which all significant weather

phenomena occur. The troposphere is characterized by

decreasing temperature with height.

Lower troposphere

level

Part of the troposphere upto 2.1 km above mean Sea

level (a.s.l)

Mid troposphere level Part of the troposphere from 2.1 km a.s.l. but below 7.6

km a.s.l

Upper troposphere

level

Part of the troposphere from 7.6 km a.s.l to a height

upto which temperature decreases with height

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