The Seasonal Changes Of Atmospheric Mass Redistributions Between The Northern Hemispheric Continents And Oceans In Both Reanalysis And CMIP5Model Data And Errors In Simulated Surface Air Pressure

Using NCEP/NCAR for the period of1979-2011, ERA-40reanalysis data and getting ready for IPCC AR5(Intergovernmental Panel on Climate Change,the Fifth Assessment Report) climate models, the seasonal characteristics of redistribution of air mass changes over the Northern hemispheric areas between continents and oceans are studied. Moreover, CMIP5(the fifth phase of the Coupled Model Intercomparison Project) climate models are evaluated in performance in simulating the surface pressure. Our results demonstrate that:(1) Using NCEP/NCAR and ERA-40reanalyses, Our results demonstrate that air mass in the Norhern hemisphere shifts remarkably between continents and oceans as the season cycles. In July, the air mass reaches lowest over Eurasia and highest over Pacific, and vice versa in January. However, different scenario is observed over north Atlantic; the accumulated air mass reaches its maximum there in May. The maintenance of the accumulation or loss of air mass in a region is found to be related to the area mean air mass flux divergence along with the difference of evaporation from precipitation in the air column. The zonal-vertical circulations change with season varies with the simultaneous ascent and decent of the air between continents and oceans, linking up with the atmospheric motion between lands and seas. Besides, there also exist apparent differences of water vapor content of the air in regions between continents and oceans, and these differences change with season cycles. Physically, the vapor content is able to affect significantly the atmosphere to absorb solar short and long-wave radiations, and hence to affect atmospheric thermal conditions. The land-sea thermal contrasts including diabatic heating change their signs with seasons going on, resulting in the reversal of orientations of the temperature gradient. These thermal forcings facilitate not only the formation of the monsoons but also indirectly induce the seasonal cycling of the air mass exchanges over regions between continents and oceans.(2) The data of CMIP5models are used to investigate the seasonal characteristics of air mass changes over the Northern hemispheric areas between continents and oceans. The results indicate that the Norhern hemispheric air mass shifts remarkably between continents and oceans as the seasons cycling. The air mass changes over the continents and oceans are related to the differences of regional mean mass flux divergence, evaporations and precipitations. Changing with the seasons, air mass flow pattern shows interesting temporal and spatial variability. Multi-models ensembled mean zonal-vertical circulation exist obvious changes with the seasons, which connects the air motion between the continents and oceans. Meanwhile vapor quality plays an importent role in air mass changes over the Northern hemispheric areas between continents and oceans. Driven by the land-sea thermal differences, the modifying high-level and low-level atmospheric circulation systems are conductive to the seasonal air mass shifting between the continents and oceans.(3)22CMIP5models can basically simulate the surface pressure characteristics of changing with the seasons. But the most values of models are higher than the observations. Due to the deviation of orographic height between the models and the observations, the large-value of errors in these22models are mainly distributed in the plateau terrain areas. After deducting the Ps errors of22models caused by the topography, the distribution of the errors of22models ensemble mean error are significantly different between continents and oceans with season varies. The ps errors of all models are analyzed by EOF, the abilities of "reappear" the Ps seasonal variation are markedly different as the season cycles among all modes.