A novel method to diagnose model uncertainties in projecting the South Asian summer monsoon

A team of researchers from Sun Yat-sen University has revealed some of the key sources of uncertainty in projections of the South Asian summer monsoon under global warming by models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6).

This study, published in Atmospheric and Oceanic Science Letters, describes findings from CMIP6 model projections. The aim was to reveal the major sources of uncertainty in projecting the South Asian summer monsoon circulation, especially the role of tropospheric meridional thermal contrast. 

One of the key issues in monsoon research is how the South Asian summer monsoon will change in the future, but most current studies focus on the changes in the South Asian summer monsoon precipitation rather than its circulation. However, model uncertainty in the response of the South Asian summer monsoon circulation to increased CO₂ concentration is considered to be the main contributor to uncertainty in projections of the South Asian summer monsoon precipitation.

Previous studies have found that a weakened South Asian summer monsoon circulation can be attributed to a decrease in the meridional gradient of upper-tropospheric temperature between Eurasia and the Indian Ocean. By using the model output from an abrupt quadrupling of CO₂ (abrupt-4×CO2) in 18 CMIP6 models, the authors of this study found that the correlation between the changes in the meridional gradient of upper-tropospheric temperature between Eurasia and the Indian Ocean and the changes in the South Asian summer monsoon circulation intensity is remarkable.

“We applied a novel diagnostic method, called the Climate Feedback-Response Analysis Method, to further diagnose the changes in the meridional gradient of upper-tropospheric temperature between Eurasia and the Indian Ocean and reveal the key processes that contribute to the uncertainty in its changes. We found that it was contributed positively by the predominate atmospheric dynamic process, followed by the cloud shortwave radiative effect, but negatively by the surface latent heat flux and cloud longwave radiative effects,” explains Dr. Xiaoming Hu, Associate Professor of Sun Yat-sen University, one of the study’s corresponding authors.

Other authors who contributed to the study include Yunqi Kong, Yuting Wu, Prof. Song Yang, and Dr. Yana Li.