The Influence Of The Daily Variation Of SST In The Coupled Mode On The ENSO Simulation

In the ocean-atmosphere coupled model,the air-sea interaction is mainly carried out in the form of turbulent flux(heat flux/fresh water flux/wind stress).In the ocean-atmosphere coupled model,the daily mean turbulent flux is mainly used which neglects the diurnal variation of ocean-atmosphere interactions.This paper uses the Chinese Academy of Sciences Earth System Model(CAS-ESM),through two experiments: the benchmark experiment(Ctrl)the coupling frequency is 1 day once;the comparison experiment(Exp),the coupling frequency is 2h once.The difference between the mean climatic states of the physical quantities of the atmosphere and the ocean is studied in two experiments.The difference between the sea surface heat budget in the two experiments,the diurnal change process of the sea surface temperature(SST)and the heat flux in Exp,and its impact on ENSO cycle and amplitude simulation.The results show that:(1)CAS-ESM simulates the average climatic state well,and the average morphological of morphology and observation are basically the same in the two experimental simulations.There is an inevitable connection between the errors of each physical quantity simulation.Exp simulation Compared with the Ctrl experiment,the results are mainly improved in the tropics;(2)Maximum of the daily variation SST can exceed 0.2°C,especially in the equatorial central and eastern Pacific;CAS-ESM can simulate the daily variation of SST,The simulated minimum value of SST appeared around 7:00 am,and the maximum occurs around 5:00 pm;(3)The minimum value of net SST heat flux and short-wave radiant flux appears at night,and the maximum appears at 1:00 pm.Around 00,which is basically same as the observation,but the size is slightly different;the diurnal variation of latent heat is quite different from the observation,and the latent heat of the simulation has a“double peak” structure,that is,the peak is reached at two times in one day,but There is no such embodiment in observation;(4)After increasing the coupling frequency,it has a great impact on the thermal budget of the sea surface,mainly reflected in the absorption of short-wave radiation and the release of latent heat.;(5)At the same time,the simulation of ENSO cycle and amplitude is greatly improved by considering the diurnal variation of turbulent flux: the cycle is changed from Ctrl(coupling frequency is 1 day)to quasi-four years of simulation is close to the observation;the amplitude simulation is reduced.in addition,the simulation of the asymmetry of ENSO is also improved well.