● Teleconnection refers to climate anomalies being related to each other at large distances.
● Atlantic Zonal Mode (AZM) and Indian summer monsoon rainfall (ISMR) are known to have an inverse relationship, which means that the cold (warm) phases of AZM result in strong (weak) ISMR.
● This paper reports that the inverse relationship between AZM and ISMR has significantly strengthened in recent decades.
● The findings have been featured in Geophysical Research Letters.
Abu Dhabi, UAE – May 19, 2019: A new study at NYU Abu Dhabi (NYUAD) has discovered a growing teleconnection in a warming world between the Indian Summer Monsoon Rainfall, which affects millions of people in India, and the Atlantic Zonal Mode.
Led by senior scientist at NYUAD's Center for Prototype Climate Modeling (CPCM) Ajaya Ravindran, the research team found a robust increase in the interannual variability of the Sea Surface Temperature (SST) over the eastern tropical Atlantic Ocean as a result of global warming.
This increase in variability implies an increase in the number of Atlantic Zonal Mode (AZM) events, inducing strong Kelvin waves - disturbances seen near the earth's equatorial atmosphere - into Indian Ocean. This, as a result, leads to strengthening the teleconnection between the Atlantic Zonal Mode and the Indian Summer Monsoon Rainfall.
Consequently, the cold phases of the Atlantic Zonal Mode enhance the Indian Summer Monsoon Rainfall whereas the warm phases of the Atlantic Zonal Mode weaken the Indian Summer Monsoon Rainfall. Atlantic Zonal Mode is defined as the year to year variability of the sea surface temperature anomalies (departure from mean) over the eastern tropical Atlantic Ocean.
Researchers documented the evolving changes in the relationship between the Atlantic Zonal Mode and the Indian Summer Monsoon Rainfall in various decades. They examined the possible physical mechanism behind such changes by analyzing century-long observed rainfall and Sea Surface Temperature data.
The study suggests that El Niño variability, which refers to the warming phase of the sea surface temperature, as the most important teleconnection that affects the Indian Summer Monsoon. It is found that El Nino-Monsoon teleconnection weakens in several years. The present study suggests that the teleconnection between Atlantic Zonal Mode and Monsoon also plays a crucial role in deciding the fate of the monsoon, especially after the 1980s.
'Our discovery of the growing role of tropical Atlantic sea surface temperature anomalies on Indian summer monsoon in a warming world brightens the prospect of Indian summer monsoon prediction,” explains Ravindran.