Atlantic Zonal Mode: An Emerging Source of Indian Summer Monsoon Variability in a Warming World

Abstract

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. Here, we report that the inverse relationship between AZM and ISMR has significantly strengthened in recent decades. The cause of this strengthening relationship has been investigated. We find a robust increase in interannual variability of sea surface temperature over the eastern tropical Atlantic Ocean in recent decades, which implies an increase in the number of strong AZM events toward the end of the twentieth century. The increase in strong AZM events alters the large‐scale monsoon circulation over the Indian subcontinent by enhancing the Kelvin wave response into the Indian Ocean, leading to an enhanced AZM‐ISMR teleconnection. This demands a better representation of the AZM‐ISMR teleconnection in climate models for improving seasonal monsoon prediction in a warming world.

The synergistic impact of ENSO and IOD on Indian summer monsoon rainfall in observations and climate simulations – an information theory perspective

“…The dipole mode (EOF2) explains about 15 % of the total variance, which is associated with the IOD. Our results for the Indian Ocean EOF patterns and their respective contribution to the total variance are consistent with the study by Saji et al (1999). Similarly, the PCs associated with the first EOF over the Pacific Ocean are highly correlated against the observed Niño 3.4 index, with a correlation value greater than 0.8 for both datasets, indicating that EOF1 captures the ENSO-like variability.…”

“…In the observations and reanalysis datasets, empirical orthogonal function (EOF) analysis of the detrended SST anomalies is performed over the tropical Indian Ocean From the two SST datasets, it is observed that both ENSOand IOD-like structures are captured with the second EOF and the first EOF patterns, i.e., a zonal dipole-like structure in the Indian Ocean and the Pacific Ocean, respectively. We use EOF analysis as opposed to standard indices such as the dipole mode index, known as DMI (Saji et al, 1999), and Niño 3.4 to allow each model to exhibit its own patterns as opposed to an imposed structure (Saji et al, 2006;Cai et al, 2009a,b;Liu et al, 2011).…”

“…Another important source that is linked to ISMR interannual variability is a dipole-like structure in the Indian Ocean surface temperature known as IOD (Saji et al, 1999). During a positive (negative) IOD, the southeastern part of the Indian Ocean is cooler (warmer) than normal, while the western part of the Indian Ocean is warmer (cooler).…”

La Niña's Diminishing Fingerprint on the Central Indian Summer Monsoon

“…One cannot neglect other potential factors for observed rainfall changes during post-1980 La Niña, such as the role of Pacific decadal oscillation (Krishnamurthy & Krishnamurthy, 2014), Atlantic zonal mode (Sabeerali et al, 2019), poleward shift of the jet stream over the north Atlantic (Chang et al, 2001),…”

Can Short and Partial Observations Reduce Model Error and Facilitate Machine Learning Prediction?

“…In fact, the MISO pattern of year 2010 is similar to that of year 1998 with a weak amplitude. Note that the winter of both year 1998 and year 2010 corresponds to a strong positive phase of the Atlantic Zonal Mode (AZM) [ 36 , 37 ]. The results here confirm the negative correlation between the MISO and the AZM as well as the relatively short predictability of the MISO at the positive phase of the AZM.…”