Comparisons between CMIP5 and CMIP6 models in simulations of the climatology and interannual variability of the east asian summer Monsoon

The climatology and interannual variability of East Asian summer monsoon (EASM) is evaluated based on the outputs from the phase 6 of the Coupled Model Inter-comparison Project (CMIP6) models and then compared to that in the phase 5 (CMIP5) models. Results show that the CMIP6 models tend to reproduce more reasonably climatological atmospheric circulation and precipitation over East Asia, with smaller inter-model spreads compared with the CMIP5 models. In addition, the multi-model ensemble mean of CMIP6 is more skillful than CMIP5 in both the summertime climatological wind and precipitation. For the interannual variation of EASM, the general bias of weak western North Pacific anticyclone (WNPAC) is significantly improved from the CMIP5 to CMIP6 models, contributing to alleviated dipole rainfall bias in CMIP6. The simultaneous warm sea surface temperature (SST) anomalies in the North Indian Ocean (NIO) and tropical North Atlantic Ocean (TNA) are suggested to play important roles in reproducing the reasonable WNPAC in CMIP6 through intensifying the suppression of convection activities over the western North Pacific. Moreover, those warm SST anomalies in the NIO and TNA are verified to be tied closely to the preceding El Nino. More realistic El Nino-Southern Oscillation (ENSO) SST pattern may be associated with more realistic SST evolutions in both the NIO and TNA. The results indicate that the improvement of EASM interannual variation depends highly on ENSO and the resultant NIO and TNA SST anomalies in models.