The impacts of the summer Asian Jet Stream biases on surface air temperature in mid-eastern China in IPCC AR4 models

One of the great model biases in simulating the East Asian summer monsoon are the warming bias of the summer surface air temperature (SAT) in mid-eastern China in the late 1970s. Previous studies have found that the summer equatorward displacement of the Asian Jet Stream (AJS) could result in SAT cooling in mid-eastern China in the past half century. This paper focuses on the relationship of the meridional displacement bias of the Asian Jet Stream (AJS) with the SAT bias in mid-eastern China in 22 IPCC AR4 models. On the basis of 20C3M simulation outputs, the bias analyses show that the summer SAT bias in mid-eastern China are closely linked to the bias of the subtropical upper-level zonal wind around the AJS core. Climatologically, the summer AJS cores in more than half of IPCC models are north of the observed one, and most of models underestimate the intensity of the AJS. Ten models (bccr_bcm2_0, cccma_cgcm3_1_t63, cnrm_cm3, gfdl_cm_2_0, gfdl_cm2_1, ipsl_cm4, miroc3_2_hires, mpi_echam5, ncar_ccsm3_0, and ukmo_hadgem1) are able to capture the AJS meridional displacement-the distinct feature of the summer AJS-for the influences of climate in eastern China. Among these ten models, bccr_bcm2_0, cccma_cgcm3_1_t63, miroc3_2_hires, mpi_echam5 and ncar_ccsm3_0 fail to simulate the multi-decadal variations of the AJS and cccma_cgcm3_1_t63, cnrm_cm3, ipsl_cm4, mpi_echam5, and ukmo_hadgem1 underestimate large-scale circulations associated with the AJS over eastern China. Thus, merely two models, gfdl_cm_2_0 and gfdl_cm2_1, have the ability in successfully simulating the SAT cooling in mid-eastern China during the late 1970s. These results imply that a good simulation of the AJS is important for weather and climate forecasts and assessments in eastern China. © 2011 Royal Meteorological Society.