Impacts Of Frequency Of Sea Temperature Forcing On Asia Summer Climate Simulation And Prediction

The state of the underlying surface of the ocean is an important factor to determine the short-term climate predictability.For the prediction objects with different time scales,the dynamic prediction model often adopts different forms of ocean boundary conditions.The method of forcing a single atmospheric general circulation model to predict climate based on given sea surface temperature(SST)is still adopted by many operational agencies,but the understanding of the influences of SST forcing at various frequencies on short-term climate prediction and their differences is still insufficient.In view of this,a series of numerical simulations and predictions of SST forcing at different frequencies(month,week and day)have been carried out,using the Beijing Climate Center Atmospheric General Circulation Model(BCC_AGCM3).The possible relationship between SST forcing frequency and Asian summer climate simulation and prediction results has been revealed by comparison.The main conclusions are as follows:(1)The effect of different frequency SST forcing on Asian summer climate simulation results may depend on the error of the climate model itself.For BCC_AGCM3,using the weekly or daily frequency SST forcing field can improve the modeling of summer precipitation and circulation climate to a certain extent,but it also makes the model overestimate the summer climate interannual and intraseasonal variability intensity.There is no consistent correspondence between the monotonic variation of SST forcing field frequency and the difference of model simulation results,which may be because the effect of the SST condition on the summer climate simulation is modulated by the complex internal variability of the model atmosphere.(2)For the prediction experiments that introduce the real atmospheric initial conditions,using the high frequency(weekly or daily frequency)SST forced field will more accurately describe the SST variability characteristics,but also make the model further overestimate the intensity of the boreal summer intraseasonal oscillation(BSISO)and the forcing effect of the underlying surface sea temperature on the atmosphere,which may lead to the model's overallprediction skills for BSISO not improved compared with the monthly frequency SST forcing experiment.However,the statistics of individual events show that the experiment using the high frequency SST forcing will obtain higher prediction skill than the experiment using the monthly frequency SST forcing in the BSISO 5-8 phase where the SST has a significant forcing effect on the atmosphere.(3)Although the simulation and prediction experiments of SST forcing at various frequencies can reasonably describe the climate state and variability center distribution characteristics of summer precipitation and circulation in Asia,the simulation and prediction skills of monsoon interannual evolution are generally low,which may be due to that the coupling process between ocean and atmosphere cannot be accurately described by a single atmospheric model.