south-west monsoon Current Affairs - 2019
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The India Meteorological Department (IMD) predicts near-normal monsoon, at 96% of long period average. IMD in its first stage operational forecast for the southwest monsoon season (June to September) rainfall has made the following predictions:
- The South-west monsoon seasonal (June to September) rainfall over the country as a whole is likely to be near normal.
- The monsoon seasonal (June to September) rainfall is likely to be 96% of the Long Period Average (LPA) with a model error of 5%.
- The LPA of the season rainfall over the country as a whole for the period 1951-2000 was 89 cm.
- Even though weak El Nino conditions are likely to prevail during the monsoon season its intensity is expected to be reduced in the later part of the season.
IMD will issue the second stage Monsoon-2019 Forecast during the first week of June 2019.
Monsoon Predictions are made using a set of algorithms and climate models, both analytical and numerical. Monsoon Mission, an initiative launched by the Ministry of Earth Sciences in 2017 has two state-of-the-art dynamical prediction systems for short range to medium, extended range and seasonal forecasts.
Meteorologists keep a track on five important parameters that can dictate the fate of India monsoon:
- The gradient in the sea surface temperatures between the North Atlantic and North Pacific Oceans.
- The sea surface temperature over the Equatorial Indian Ocean.
- Sea-level pressure in East Asia.
- Air temperature of the land surface in Northwest Europe.
- The heat content over Equatorial Pacific measured by its warm water volume.
Studies have proposed including various other indicators, such as surface pressure over the Arabian Sea, in such forecasting models to eliminate biases and to make the predictions accurate.
A study conducted by the University of Hyderabad and the Indian Institute of Technology – Bombay has found out that the extreme El Nino conditions and warming of the Bay of Bengal had resulted in unprecedented heavy rainfall in Chennai for three days between November 30th to December 2nd in 2015.
El Nino usually causes less than normal rainfall in the case of south-west monsoon. However, it does the reverse in the case of the northeast monsoon. It causes above-normal rainfall during the northeast monsoon. This is due to the difference in seasonal wind patterns between the two monsoons.
The researchers had carried out a simple linear correlation analysis that points out that the sea surface temperature at the Bay of Bengal is positively correlated with northeast monsoon rainfall. It has been found out that the magnitude of correlations of northeast monsoon rainfall with El Nino conditions and the Bay of Bengal warming to be almost same.
Based on several experiments, the scientists have attributed around 21% of the intensity of the extreme Chennai rainfall to the extreme El Nino condition
The consistent warming of the Bay of Bengal off the coast of Tamil Nadu and Andhra Pradesh is also considered as an important factor for the floods by the scientists.
However, scientists are yet to ascertain whether the contribution from the tropical Pacific to extreme rainfall during the northeast monsoon occurs only at the time of extreme El Nino or whether normal El Ninos too are capable of causing them.
El-Nino is a weather phenomenon, during which temperature at sea surface is warmer than normal sea-surface temperatures. El Nino is a warming of the Pacific Ocean between South America and the Date Line, centred directly on the Equator, and typically extending several degrees of latitude to either side of the equator. It accompanies high air surface pressure in the western Pacific. El Niño occurs when tropical Pacific Ocean trade winds die out and ocean temperatures become unusually warm