"IMD's Monsoon Forecast Falls Short Despite Technical Accuracy"
El Niño
warming of the central and eastern equatorial Pacific Ocean that typically suppresses the Indian monsoon.
Indian Ocean Dipole (IOD)
a sea-surface temperature difference between the western and eastern Indian Ocean affecting monsoon strength.
The India Meteorological Department (IMD) issues two seasonal monsoon forecasts each year, in April and May, ahead of the June-to-September season. These forecasts classify expected rainfall against the Long Period Average (LPA), a benchmark computed over a fixed base period, currently 1971-2020. IMD's categories run from 'deficient' (below 90% of LPA) to 'below normal' (90%-95%), 'normal' (96%-104%), 'above normal', and 'excess'.
The single biggest driver of year-to-year monsoon variability is the El Niño-Southern Oscillation. During an El Niño, the central and eastern equatorial Pacific Ocean warms. This weakens the Walker Circulation, the east-west atmospheric circulation over the tropical Pacific. It reduces the moisture flow that normally feeds the Indian monsoon. However, El Niño's effect is not fixed. A positive Indian Ocean Dipole (IOD), a difference in sea-surface temperature between the western and eastern Indian Ocean, can partly offset El Niño's suppressing effect. This is why two El Niño years can produce very different monsoon outcomes. It is also why forecasting the exact scale of a shortfall is harder than forecasting its direction.
IMD also uses other indicators. Ocean Mean Temperature (OMT), measured in the south-western Indian Ocean during January-March, helps assess early whether the coming monsoon is likely to fall above or below the long-term mean. Separately, Western disturbances, extra-tropical weather systems linked to the subtropical westerly jet stream, traditionally bring winter rain to north-west India. In recent years they have increasingly influenced rainfall during the monsoon months too, adding a layer of unpredictability that El Niño-based forecasting alone cannot capture.
A seasonal monsoon forecast is a probabilistic exercise built on a handful of ocean-atmosphere indicators: El Niño status, the IOD, OMT readings, and increasingly, Western disturbance activity. Because these indicators can reinforce or cancel each other, a forecast issued in April or May carries real uncertainty, even when the broad direction, above or below normal, is clear.
This season, IMD's internal models pointed towards 'deficient' rainfall, but the department's public forecast used the more conservative 'below normal' category. The final national tally came close enough to call it a technical success. But that success held only at the all-India aggregate level. …
Which of the following statements with regard to India's indigenous new high resolution weather model, the 'Bharat Forecast System,' is/are correct?
1.Its objective is to generate forecasts at the Panchayats cluster level.
2.It was developed by IIT Delhi.
Select the answer using the code given below:
With reference to 'Indian Ocean Dipole (IOD)' sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?
1.IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2.An IOD phenomenon can influence an El Nino's impact on the monsoon.
Select the correct answer using the code given below:
With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct?
1.OMT is measured up to a depth of 26°C isotherm which is 129 metres in the south-western Indian Ocean during January-March.
2.OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.
Which of the statements given above is/are correct?
Consider the following statements:
1.The winds which blow between 30° N and 60° S latitudes throughout the year are known as westerlies.
2.The moist air masses that cause winter rains in North-Western region of India are part of westerlies.
Which of the statements given above is/are correct?
With reference to monsoon-related phenomena, match List-I with List-II and select the correct answer using the code given below:
List-I: 1. El Niño 2. Positive Indian Ocean Dipole 3. Western Disturbance 4. Ocean Mean Temperature (OMT)
List-II: a. Suppresses Indian monsoon rainfall b. Offsets El Niño's suppressing effect c. Brings moisture to north-west India and increasingly to monsoon months too d. Used as a pre-monsoon forecasting indicator
Consider the following statements regarding IMD's seasonal monsoon rainfall categories: 1. 'Below normal' rainfall is defined as 90% to 95% of the Long Period Average. 2. 'Deficient' rainfall refers to rainfall below 90% of the Long Period Average. How many of the above statements are correct?
Consider the following statements about Western Disturbances: 1. They are extra-tropical weather systems linked to the subtropical westerly jet stream. 2. They traditionally bring winter rainfall to north-west India. 3. Their influence is now limited exclusively to the winter season. Which of the statements given above is/are correct?
The Centre classifies a national-level 'agricultural drought' when the all-India rainfall deficit crosses which of the following thresholds?
The India Meteorological Department issues its operational seasonal monsoon forecasts in which two months, ahead of the monsoon season?
Want the full note, Prelims Facts & MCQ answers?
Create a free account — takes less than a minute.
Create free account