Walker Cell & Modoki: mechanism & impact

WALKER CELL AND MODOKI

Walker Cell refers to air circulation in the Troposphere of Tropics. Unlike Hadley Cell of this region that blows between different latitudes it follows particular latitude near Equator only.

Mechanism of Walker Cell

  • It is caused by difference in heat distribution between oceans and land.
  • Walker Cell moves from eastern ocean to its western part, having subsiding limb on its eastern section and rising limb on its western margin.
  • This drives warm surface water from east to pile it along western part of the ocean.
  • This results in the upwelling of cold water along eastern margin of ocean or western coast of the continent and hence thermocline rises in the eastern margin of the ocean.
  • Thus eastern margin of ocean witness cold condition as compared to its western counterpart.

NORM WC

Impact of normal Walker Cell

  • Eastern Oceans become cold and dry while western part become warm and wet.
  • Warm air in the western part promotes evaporation and convectional rainfall, on the other hand cold and upwelling water in the east promotes planktons and fishing grounds.
  • Moreover, rising moist air of western oceans enhances the intensity and frequency of cyclones in the adjoining areas, whereas subsiding air in the eastern ocean suppress cyclone formation.

normal wc-impacts

Weak or reverse Walker Cell: El Nino

In case of weak Walker Cell, the Thermocline almost remains horizontal and so eastern ocean remain equally warm while in case of reversal of Walker Cell, it even gets warmer than its western part.

el_nino_reversed_walker_circulation

Impact of weak Walker Cell

  • Warming eastern ocean results El Nino like condition in the Pacific Ocean along Ecuador and Peru
  • Creates drought like condition in Australia, S.E. Asia, East Africa, N.E. South America and Central America.
  • Increases precipitation in central Pacific and W. South America while reduces the Monsoon impact in South Asia.
  • Intensifies Hurricanes in the Gulf of Mexico
  • Kills the fishing industry of Ecuador and Peru

Strong Walker Cell

Strong Walker and consequent Strong Trade Wind removes warm tropical water from the eastern oceans, thus enhancing the upwelling rate and cooling that area.

LA LINA

Impact of strong Walker Cell

  • Strong trade wind causes heavy rainfall in the western part of the ocean.
  • It strengthens Monsoon wind in South Asia
  • Fishing industry of Ecuador & Peru gets enriched
  • Promotes strong Typhoons in South China Sea
  • Enhances cyclones’ strength in the Bay of Bengal

El Nino-Modoki

El Nino Modoki refers to condition of warming in the mid-Pacific Ocean and Walker Cell breaks. In this case subsiding limb remains same as that of Walker Cell in the eastern part of the ocean but in the western part Walker Cell’s limb descends as shown in the figure.

ElNino-MODOKI

Impact of El Nino Modoki

  • More rainfall in central Pacific
  • Less or no rainfall in western Pacific
  • More fishing in eastern Pacific
  • More cyclone in Arabian Sea as compared to Bay of Bengal

La Nina Modoki

In this case, central Pacific witness cooling impact resulting in the subsidence of air in the area. This breaks the Walker Cell. So, both the eastern and western Pacific witness rising air.

Impact of La Nina Modoki

  • Rainfall both in the eastern and western oceans
  • Dry condition in the central Pacific
  • Bad for fishing industry in Peru & Ecuador
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