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Indian monsoon derailed by a North Atlantic wavetrain
P J Borah1,2, V Venugopal3,2,4, J Sukhatme1,2
1Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore 560012, India.
Science (New York, N.Y.)
|December 11, 2020
Summary
Indian monsoon droughts are often predicted by warm Pacific conditions. However, nearly half of past droughts show near-neutral Pacific temperatures and abrupt late-season rainfall declines, linked to mid-latitude Rossby waves.
Area of Science:
- Climatology
- Atmospheric Science
- Meteorology
Background:
- Indian monsoon drought forecasting traditionally relies on season-long rainfall deficits linked to a warm equatorial Pacific.
- This paradigm, however, does not account for a significant portion of historical drought events.
Purpose of the Study:
- To investigate the characteristics and underlying mechanisms of Indian monsoon droughts that deviate from the traditional warm Pacific paradigm.
- To identify alternative predictors for improved drought forecasting.
Main Methods:
- Analysis of historical drought data over the past century.
- Identification of subseasonal rainfall patterns and their correlation with Pacific and Atlantic climate variability.
- Investigation of atmospheric teleconnections, specifically Rossby wave dynamics and vorticity anomalies.
Main Results:
- Nearly half of observed Indian monsoon droughts over the past century occurred with near-neutral Pacific temperatures.
- These droughts were characterized by subseasonal, abrupt late-season rainfall deficits.
- A significant atmospheric teleconnection was identified, involving Rossby waves originating from mid-latitudes, specifically linked to North Atlantic vorticity anomalies.
Conclusions:
- Indian monsoon droughts can be driven by mechanisms independent of equatorial Pacific conditions.
- Subseasonal rainfall deficits associated with mid-latitude atmospheric teleconnections represent a critical, yet underappreciated, drought-driving factor.
- This identified atmospheric teleconnection offers a new pathway for enhancing the predictability of Indian monsoon droughts, particularly when Pacific signals are absent.
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