- May 8, 2022
- Posted by: OptimizeIAS Team
- Category: DPN Topics
- This year, the La Nina is being blamed for worsening perhaps the longest spell of heatwaves from March to April in north, west and Central India.
- La Nina is a climate pattern that describes the cooling of surface ocean waters along the tropical west coast of South America.
- La Nina means Little Girl in Spanish.
- La Nina is also sometimes called El Viejo (in Spanish), anti-El Niño, or simply “a cold event.”
- La Nina has the opposite effect of El Nino.
- La Niña is caused by a build-up of cooler-than-normal waters in the tropical eastern Pacific due to stronger south-east trade winds than usual
- And pushing more warm water towards Asia from the west coast of the South Americas.
- La Nina events are indicated by sea-surface temperature decreases of more than 0.5 for at least five successive three-month seasons.
- Upwelling increases, bringing cold, nutrient-rich water to the surface in off the coast of peru
- Atmospheric stability and cold and dry conditions prevail over West Coast of South America and instability and low pressure conditions in tropical western pacific
- La Nina brings greater than normal rainfall over northern Australia, Indonesia, New-guinea and India during monsoon
- La Nina events may lastbetween one and three years, unlike El Niño, which usually lasts no more than a year
- La- Nina is a cold phase of EnSo( El-Nino Southern Oscillation)
- La-Nina affects the position and intensity of jet streams and storms outside of the tropics
La-Nina and heat waves:
- IMD defines a heat wave as a condition when the average maximum temperature exceeds 45°C, or if the temperature is higher than normal by 4.5°-6.4°C on at least two consecutive days
- While heat waves are expected to peak in May, the ongoing heat wave first occurred early in March and the spring season felt like summer.
- Heat waves in mountain states of Himachal Pradesh, Uttarakhand and UT of J&K are unprecedented this year.
- Persistence of La-Nina is believed to be an early and prolonged heat waves in India this year
How La-Nina induces Heat waves?
- Every summer, the formation of a low pressure over India pulls in high-pressure winds from the Arabian Sea, causing the monsoon.
- However, the formation of a ridge in the subtropical jet stream over India resulted in a high-pressure zone that trapped heat within the subcontinent, creating a persistent heat wave.
- The hot air over land is being boxed in from all sides by the jet stream’s high pressure, resulting in the formation of a ‘heat dome’.
- The resultant overall high-pressure region prevents other winds from being pulled into the subcontinent.
- Within the heat dome, the jet stream moves air from west to east, but this air sinks back hot, leading to a heat wave.
- This anomaly was likely triggered by persistent La Niña conditions
- Moreover, the La Niña produced a north-south pressure pattern over India as expected during the winter that normally influences trade winds that bring monsoon rains to India.
- However, because of persistence of La-Nina, drove hot westerly winds and blasts of hot air from the Middle East into Pakistan and India.
- Western disturbances, or moisture from the Mediterranean region that fall as rain over north-western India brings rainfall in march during rise in temperature.
- Temperature difference between Europe and India causes this Western disturbance
- Partly due to La Nina, the temperature difference was week and resulted in weak western disturbances with hardly any rain
- The similar effect has been seen even during 1998-2000 when La Nina had persisted for three years,