• Issues Analysis 360o

Foehn, Depression and Richter Scale

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  • Katabatic or the gravity flow winds system of Alps across the geographical expanses of Switzerland, Liechtenstein and Italy.
  • it is a local or tertiary wind system.
  • It is a warm and relatively dry wind which descends on the leeward sides of a mountain range.
  • The moist air when is forced to ascend and experiences an orographic lift, gets cold by wet adiabatic lapse rate, heavy condensation takes place, develops sky high cloud walls, sheds maximum of the moisture on windward side.
  • Across the crest line, its character changes, turn relatively dry, warmer and compressed. Precipitation possibilities are either reduced to the minimum or ruled out. Sudden increase in temperature by 10 degrees or more results into snow melt and quick thaw. On occasions, it also results into snow avalanches.

Such foehn effects are named differently in the rest of the world: Chinook over Rockies in USA, Birg over Drakensberg in RSAfrica, Santa Ana in California of USA and Zonda across Andes in Argentina

DEPRESSION (Temperate Meteorology)

  • It is an atmospheric disturbance of middle latitudes, a low air pressure cell of extra tropical regions.
  • It is surrounded by high air pressure conditions, holds converging wind system with anticlockwise direction in northern hemisphere and clockwise direction in southern hemisphere. Most of the depressions trot from west to east. They are driven by the Westerlies. There wavy tracks are determined by Subtropical Westerly Jet Stream.
  • North western India receives such western disturbances during winters which add sufficient moisture to the agronomics of Rabi crops and temperate plantations of the Himalayan region. Their advent is seen interms of extensive cloud covers. The term depression is loosely used for all tropical and temperate cyclones.

Depressions have large areal extent. Distinct parts of a depression: warm sector, warm front, cold sector, cold front and a well pronounced eye.


  • It is an open ended, logarithmic scale, devised by American CF Richter in 1935 to calibrate magnitude of an earthquake.
  • Richter Scale has been accepted universally. Its recorded magnitude draws an exact picture of possible devastation and damages.
  • It is more popular than Modified Mercalli Scale and MSK-64 Scale.
  • The RS reflects the total amount of elastic energy released when constrained and contorted rocks suddenly rebound to give a seismic shock.
  • Its normal reading ranges between 1 and 8.9. The magnitude can extend beyond 8.9 Valdivian 1960 earthquake in Chile was of 9.5 on Richter scale while 64 million years before present(Ma), Chikxulub in Mexico had a meteoritic fall and an earthquake of 12.55 on RS. Dec 26, 2004 Bay of Bengal tsunami was triggered by Banda Aceh earth quake of 9.1 on RS. Sendai-Tohaku earthquake, 2011, Japan was of 9.1 on Richter Scale.

R P Singh By - R P Singh
Posted On - 12/13/2018 8:35:48 AM

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