The Role Of Boundary Layer Wind Field In Land-atmosphere Coupling In East Asia

Land-atmosphere(L-A)interaction is an important process in the climate system.In particular,soil moisture has a non-negligible effect on changes in precipitation and temperature.In addition,the atmospheric boundary layer(ABL)is located in the lowest troposphere which is an interface through which the land surface influences the atmosphere,on the one hand,the state and struction of ABL can be influenced by land processes,on the other hand,the land variables have effects on precipitation and temperature mainly through the ABL.Above all,the ABL is crucial for L-A interactions.Winds are an important element of the ABL,ABL winds have great effect on the moisture transport and convergence,However,the role of winds in L-A interactions are still not very clear.Here we use WRF4.0 to investigate L-A interactions in the northern China in the summer of 2013.Besides,we analyze the role of ABL winds.The main results show that:(1)The spatial distributions of variables such as precipitation ? temperature and the height of ABL simulated by WRF4.0 is similar to reanalysis data.Compared with reanalysis data,the time series of variables simulated are relatively accurate,especially for the simulation of the location of the north-to-south retreat of summer rain belt.In addition,the model has errors in the simulation of variables.The surface sensible heat flux simulated is higher than ERA5,the latent heat flux is simulated lower.(2)It is shown that changing the soil moisture in the northern China makes the land variables change.Surface temperature ? sensible heat flux and the height of ABL become higher in the drier area.Because when sensible heat flux increases it can cause more heat transferred to the ABL,which increases the height of ABL and 2 m temperature.In addition,the maximum and minimum temperature are also influenced by soil moisture.The maximum temperature decreases most obviously when soil moisture becomes wet,indicates that soil moisture has a strong effect on the maximum temperature.(3)It is found that after ABL winds are permutated the time series of surface temperature and soil moisture become more similar,especially for the mean values in the semi-arid northern China,but are the opposite over the southern China.This is because the strong L–A positive feedbacks in the northern China,which involves the wind field change in response to land surface change and tends to cause large weather and climate anomalies.The processes are weakened by the permutated winds,Hence the consistency of inter-member variables increases.Contrasting,The L-A interactions in the southern China are weak,the precipitation strongly responds to ABL perturbations and becomes less similar after ABL winds permutated.Thus,the different L-A interactions in these two regions are the main reason for the contrasting responses of local climate to the perturbation of ABL winds.