Based on the multi-model output data in CMIP5,the seasonal cycle of air mass(AM) migration between land and sea in the Northern Hemisphere(NH) and its driving factors are investigated.Results show that the land-sea exchange of AM in NH exhibits notable seasonal variation.The annual minimum AM deficit of the Pacific Ocean and the Atlantic Ocean happens in January.The annual maximum AM pile-up of the Pacific Ocean happens in July,while the annual maximum AM pile-up of the Atlantic does in June,one month later than the result explored by the reanalysis data.The annual maximum AM pile-up of the Eurasian continent happens in December,while the minimum appears in July.Consistent with the seasonal variation of AM,the vertically integrated air mass fluxes also emerge notable seasonal cycle.In particular,there is an anti-phase variation between the low and upper level columnar-integrated AM fluxes,which affects the seasonal inversion of zonal vertical circulation and the atmospheric motion and mass transport between land and sea.The columnar water vapor shows a contrast seasonal variation compared to the AM,and its spatial distribution shows a clear zonal deviation between land and sea in NH.This implies that the corresponding changes of air density and zonal pressure gradient may be favorable for the land-sea exchange of AM.In addition,the climatology of surface air temperature in January(July) exhibits a negative-positive-negative-positive (positive-negative-positive-negative) pattern from west to east in NH,suggesting that the heating contrast between land and sea drives the land-sea exchange of AM during the seasonal change.