The Observation Analysis And Simulations Of Summer Land-sea Thermal Contrast Over Asian Monsoon Region

Observations form NCEP/NCAR and ERA-40 are used to contrast and analyze the feature of summer land-sea thermal contrast over Asian monsoon region, and define the land-sea thermal contrast index. It is indicated that the temperature over land is decreased, over sea is increasing, and the contrast tends to decrease. On this basis, the model simulations of it given by 20 climate models historical simulations from Phase 5 of the Coupled Model Inter-comparison Project(CMIP5) are used to compare with observation analysis. And we use the best and worst selected models in the RCP4.5 scenario to forecast it. The main results are as follows:(1)The observation data show that the average temperature of upper-middle troposphere has a remarkable trend feather over Asian monsoon region from 1955 to 2005, which is the temperature over land is decreasing and temperature over sea is increasing. According to the selected area, we define a land index、sea index and land-sea thermal contrast index respectively. They have a large rate of inter-annual change; the land-sea thermal contrast index is reducing; the land-sea thermal contrast index can be able to reflect the features of the difference between strong and weak monsoon. NCEP is consistent with the ERA-40; however, NCEP has an obvious linear trend.(2)The CMIP5 models have a better simulation performance on the climate condition of zonal-wind field, the height field in 500hPa、200hPa and a poor simulation performance on the temperature field. Models could not perform well enough in the simulation of the index inter-annual change. The simulations of interdecadal change are that:sea index is increasing and the land-sea thermal contrast index is decreasing, but the land index is both increasing. Combined with statistical computing, we can draw a conclusion that GFDL-ESM2G、MPI-ESM-LR. MPI-ESM-MR have a better simulation performance, on the contrary, bcc-csml-1-m、MRI-CGCM3、MIROC5 perform bad. The models capability to simulate land-sea thermal contrast can reflect the ability of simulating the summer monsoon.(3)In the situation of RCP4.5, the simulation temperature of upper-middle troposphere over Asian monsoon region by CMIP5 models indicates that it will increase on the 21th century. The degree of temperature increase over sea is bigger than over land in simulation data, land index、sea index are both increasing, the land-sea thermal contrast index is decreasing. The worse models have a slightly higher simulation data to the future temperature field than the better models, especially which is over sea, besides, the worse models cannot simulate the decreasing trend of land-sea thermal contrast.