East Asian rainfall in summer is closely related to the meridional displacement of the East Asian westerly jet (EAJ) on the interannual timescale. Thus, reasonably reproducing the interannual relationship between the EAJ and rainfall is crucial for improving the capacity to simulate and predict the East Asian monsoon. 
 

A group of scientists from the Institute of Atmospheric Physics, Chinese Academy of Sciences, focused on the interannual variation of the EAJ’s meridional displacement and its relationship with the East Asian summer rainfall, using the historical simulations of CMIP5. Their results indicate that almost all the CMIP5 models depict a weaker interannual jet–rainfall relationship in comparison with observation, and exhibit considerably large spread across the models (Figure 1). "Some models even show negative correlation coefficients, completely different to the observation," says Dr.  LI Chaofan. 

Figure 1. Interannual correlation coefficient between the East Asian westerly jet and rainfall for each model [CC(J, R)]. The black bar represents the correlation coefficient in the observation. Green bars represent the five models that simulate the highest correlation coefficients, and brown bars represent the five models with the lowest correlation coefficients. 
 

Their work, published in Advances in Atmospheric Sciences, further explores the performance of models in simulating the EAJ and rainfall basic state, and suggests that the simulated jet–rainfall relationship is directly related to the climatological location of the westerly jet in Eurasia and the intensity of EAJ variability. “Besides, simulation of the tropical historical rainfall is also worthy of more attention,” adds Dr Li. “The diversity in the modeled jet–rainfall relationship is not related to the simulated climatological rainfall bias locally but connects with the bias in remote regions, i.e., South Asia and the western North Pacific.” These results may serve as a good reference for better simulating the East Asian summer monsoon in climate models. 
 

Citation: Yan, Y. H., C. F. Li, and R. Y. Lu, 2019: Meridional displacement of the East Asian upper-tropospheric westerly jet and its relationship with the East Asian summer rainfall in CMIP5 simulations. Adv. Atmos. Sci., 36(11), https://doi.org/10.1007/s00376-019-9066-1 .

Media Contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn