A new study has made important strides in understanding a key teleconnection pattern, namely, the Circumglobal teleconnection pattern. It is a type of atmospheric wave activity that can affects climate conditions in mid-latitude regions across the Northern Hemisphere. Better simulations of this pattern could help predict extreme weather events like the 2022 heatwave in China's Yangtze River Valley and 2018 heatwave over Europe.

The photo was taken in July 2023 at a beach in Qinhuangdao, one of the most popular summer resorts in China.  The beach is full of tourists escaping from summer heat. (Photo by QI Yi)

The research, recently published in the Journal of Climate, emphasizes the role of the Indian summer monsoon in improving the representation of CGT in climate models. Climate models are essential tools used by scientists to predict future climate conditions, but how well models can simulate CGT is still an unsolved problem. This new study, led by YU Hanzhao, a Ph.D. student at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, offers fresh insights into how models can be improved.

“Previous studies paid less attention to how well coupled climate models can represent the CGT pattern,” YU explained. “We found that models which accurately capture features of Indian summer monsoon rainfall tend to perform better in simulating CGT.”

The research team examined data from 40 climate models used in two major climate research projects (Coupled Models Intercomparison Project Phase 5 and 6, CMIP5 and CMIP6) and found that models with better accuracy in reproducing Indian monsoon rainfall also did a better job at simulating wave structure over west-central Asia, hence elevating overall performance on representing CGT pattern.

The authors further explored the underlying mechanism using Rossby wave source diagnosis, a method for analyzing the formation of atmospheric wave. Results show that realistic simulation of monsoon rainfall creates upper-level outflow of air mass over the Indian subcontinent and its adjacent regions, which help to excite the CGT pattern over west-central Asia and downstream area. This link between Indian monsoon rainfall and CGT pattern is crucial for improving climate model predictions.

The research also highlighted the influence of El Niño-Southern Oscillation (ENSO), a climate phenomenon that affects weather worldwide. It is found that the ENSO can impact on simulation skill of CGT pattern by modulating Indian summer monsoon rainfall.

“This study provides a valuable reference for climate modelers to improve their simulations,” said Professor ZHOU Tianjun, the corresponding author of the study and a senior research scientist at IAP/CAS and the University of Chinese Academy of Sciences. “Reducing errors in simulating the CGT pattern in coupled climate models will improve our ability to predict regional climate, such as rainfall and temperature, across the Northern Hemisphere.”

By identifying the critical role of the Indian monsoon in global weather patterns, this research opens new avenues for more accurate climate predictions, which could help prepare for and mitigate the impact of extreme weather events in the future.