摘要
The consistency of global atmospheric mass and water budget performance in 20 state-of-the-art ocean-atmosphere Coupled Model Intercomparison Project Phase 5(CMIP5) coupled models has been assessed in a historical experiment. All the models realistically reproduce a climatological annual mean of global air mass(AM) close to the ERA-Interim AM during 1989-2005. Surprisingly, the global AM in half of the models shows nearly no seasonal variation,which does not agree with the seasonal processes of global precipitable water or water vapor, given the mass conservation constraint. To better understand the inconsistencies, we evaluated the seasonal cycles of global AM tendency and water vapor source(evaporation minus precipitation). The results suggest that the inconsistencies result from the poor balance between global AM tendency and water vapor source based on the global AM budget equation. Moreover, the cross-equatorial dry air mass flux, or hemispheric dry mass divergence, is not well represented in any of the 20 CMIP5 models, which show a poorly matched seasonal cycle and notably larger amplitude, compared with the hemispheric tendencies of dry AM in both the Northern Hemisphere and Southern Hemisphere. Pronounced erroneous estimations of tropical precipitation also occur in these models. We speculate that the large inaccuracy of precipitation and possibly evaporation in the tropics is one of the key factors for the inconsistent cross-equatorial mass flux. A reasonable cross-equatorial mass flux in well-balanced hemispheric air mass and moisture budgets remains a challenge for both reanalysis assimilation systems and climate modeling.
The consistency of global atmospheric mass and water budget performance in 20 state-of-the-art ocean-atmosphere Coupled Model Intercomparison Project Phase 5（CMIP5） coupled models has been assessed in a historical experiment. All the models realistically reproduce a climatological annual mean of global air mass（AM） close to the ERA-Interim AM during 1989-2005. Surprisingly, the global AM in half of the models shows nearly no seasonal variation,which does not agree with the seasonal processes of global precipitable water or water vapor, given the mass conservation constraint. To better understand the inconsistencies, we evaluated the seasonal cycles of global AM tendency and water vapor source（evaporation minus precipitation）. The results suggest that the inconsistencies result from the poor balance between global AM tendency and water vapor source based on the global AM budget equation. Moreover, the cross-equatorial dry air mass flux, or hemispheric dry mass divergence, is not well represented in any of the 20 CMIP5 models, which show a poorly matched seasonal cycle and notably larger amplitude, compared with the hemispheric tendencies of dry AM in both the Northern Hemisphere and Southern Hemisphere. Pronounced erroneous estimations of tropical precipitation also occur in these models. We speculate that the large inaccuracy of precipitation and possibly evaporation in the tropics is one of the key factors for the inconsistent cross-equatorial mass flux. A reasonable cross-equatorial mass flux in well-balanced hemispheric air mass and moisture budgets remains a challenge for both reanalysis assimilation systems and climate modeling.
基金
Natural Science Foundation of Jiangsu Province grant(BK2012465)
National Natural Science Foundation of China(41205065,41475045,41005046)
National Basic Research Program of China(2010CB428602)
Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institution
