The synergistic impact of ENSO and IOD on the Indian Summer Monsoon Rainfall in observations and climate simulations - an information theory perspective

Abstract

Abstract. El-Niño southern oscillation (ENSO) and Indian Ocean Dipole (IOD) are two well-know temporal oscillations in the sea surface temperature (SST), which both are thought to influence the interannual variability of the Indian Summer Monsoon Rainfall (ISMR). Until now, there has been no measure to assess the simultaneous information exchange (IE) from both ENSO and IOD to ISMR. This study explores the information exchange from two source variables (ENSO and IOD) to one target (ISMR). First, in order to illustrate the concepts and quantification of two-source IE to a target, we use idealized test cases consisting of linear as well as non-linear dynamical systems. Our results show that these systems exhibit net synergy (i.e., the combined influence of two sources on a target is greater than the sum of their individual contributions), even with uncorrelated sources in both the linear and non-linear systems. We test IE quantification with various estimators (the Linear, Kernel, and Kraskov estimators) for robustness. Next, the two-source IE from ENSO and IOD to the ISMR is investigated in observations, reanalysis, three global climate model (GCM) simulations, and three nested, higher-resolution simulations using a regional climate model (RCM). This (1) quantifies IE from ENSO and IOD to ISMR in the natural system, and (2) applies IE in the evaluation of the GCM and RCM simulations. The results show that both ENSO and IOD contribute to the ISMR interannual variability. Interestingly, significant net synergy is noted in the central parts of the Indian subcontinent, which is India's monsoon core region. This indicates that both ENSO and IOD are synergistic predictors in the monsoon core region. But, they share significant net redundant information in the southern part of Indian subcontinent. The IE patterns in the GCM simulations differ substantially from the patterns derived from observations and reanalyses. Only one nested RCM simulation IE pattern adds value to the corresponding GCM simulation pattern. Only in this case, the GCM simulation shows realistic SST patterns and moisture transport during the various ENSO and IOD phases. This confirms, once again, the importance of the choice of the GCM in driving a higher-resolution RCM. This study shows that two-source IE is a useful metric that helps in better understanding the climate system and in process-oriented climate model evaluation.

Oceanic versus terrestrial origin of El Niño Southern Oscillation–associated continental precipitation anomalies

“…Under the influence of La Niña, which always modulates precipitation of oceanic origin that is the most important source of precipitation in the tropical north and south Atlantic Ocean, an increase in precipitation is usually observed. 52 Likewise, there is a significant relationship between the ENSO and precipitation in Asia; 53 particularly, the ENSO contributes to Indian monsoon interannual variability, 18,54 bringing about an increase in the precipitation over the Indian Peninsula during La Niña events. In this region, the influence of recycling supports the importance of precipitation from terrestrial origin.…”

Evaluation and Projection of Vb-Cyclones and Associated North-Western Mediterranean Sea State in Regional Coupled Climate Simulations

“…These differences might be attributed to the emergence of simulation biases inherited from the driving EC-EARTH GCM, e.g., cold surface & sea surface temperatures over the Mediterranean compared to ERA-20C forcing. A study by Pothapakula et al (2020) showed that the biases in the driving GCMs emerged into the regional climate simulations resulting in unrealistic process chains. Downscaling the EC-EARTH3 (latest version of EC-EARTH) which has smaller bias in the surface air temperatures, SST (Döscher et al, 2021) might assist in further understanding the state and process chains linking the North-West Mediterranean Sea and the Vb-cyclone precipitation in historical & future periods.…”

“…Vb-cyclone precipitation Methods from information theory were recently used in quantifying interactions among sub-systems, especially in climate (Pothapakula et al, 2019(Pothapakula et al, , 2020 Title Suppressed Due to Excessive Length 9 Krug et al, 2021b;Ruddell et al, 2019). Transfer entropy (TE) was especially used in detecting and quantifying the direction of information exchange between two or more sub-systems.…”

“…Thereafter the North-Western Mediterranean Sea state in terms of SST, evaporation & wind speed corresponding to the Vb-cyclone precipitation over the three catchments, the Danube, Elbe and Odra in the two simulations Title Suppressed Due to Excessive Length is analyzed. Finally to quantify the process chain linking the North-Western Mediterranean Sea and the Vb-precipitation over the three catchments we use information theory methods similar to the studies by Pothapakula et al (2019Pothapakula et al ( , 2020; Krug et al (2021b). These studies used information exchange to quantify the Indo-Pacific coupling, the interplay between the Indian Ocean dipole & El-Niño southern oscillations with the Indian Monsoon precipitation, and, the role of North-Western Mediterranean Sea evaporation during the Vb-cyclone precipitation over Odra catchment.…”

Identifying and Using Suitable Oceanic Domains for Prediction of the Indian Monsoon Rainfall over Tamil Nadu

“…Climate teleconnections such as the El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) which are related to SST changes are frequently used to make reliable seasonal forecasts [10]. And both ENSO and IOD are synergistic predictors in the monsoon core region [11]. Sea surface temperature climatology is a crucial prerequisite for ocean modelling.…”