Simulations and projections of the western Pacific subtropical high in CMIP5 models

This work examined the performance of 26 coupled climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in the simulation of the present-day temporal variability and spatial pattern of the western Pacific subtropical high (WPSH). Results show that most models are able to capture the spatial distribution and variability of the 500 hPa geopotential height and zonal wind fields in the western subtropical Pacific, with the underestimation of the mean intensities of WPSH. The underestimation may be associated with the cold bias of sea surface temperature in the tropical Indian and western Pacific Oceans in the models. To eliminate the impact of the climatology biases, the climatology of these models is replaced by that of the NCEP/NCAR reanalysis in the verification. It is noted that at interdecadal time scales, the models reproduce the shift of WPSH with enhancement and westward extension after the late 1970s. According to assessment of the simulations of the WPSH indices, it is found that some models (CNRM-CM5, FGOALS-g2, FIO-ESM, MIROC-ESM and MPI-ESM-P) are better than others in simulating WPSH. Then the ensemble mean of these better models are used to project the future changes of WPSH under three typical Representation Concentration Pathway scenarios (RCP8.5, RCP4.5, RCP2.6). It is suggested that the WPSH enlarges and strengthens, and its position extends westward under the scenarios, with the largest linear growth trend in RCP8.5, smallest in RCP2.6, and in between in RCP4.5; while the ridge line of WPSH does not show obvious long-term trend. These results may have implications for the attribution and prediction of climate variations and changes in East Asia.