Based on the reanalysis dataset ERA40 of European Center of Medium Range Weather Forcast （ECMWF）, winter climate change and characteristics of sea ice-atmosphere interaction at high northern latitudes for recent sev...Based on the reanalysis dataset ERA40 of European Center of Medium Range Weather Forcast （ECMWF）, winter climate change and characteristics of sea ice-atmosphere interaction at high northern latitudes for recent several tens of years are analyzed. Superposed upon the background of global warming, the amplitude of temperature increase in winter at high northern latitudes is bigger and it exhibits different features in different regions. From the end of 1970 s, the Greenland Sea, the Barents Sea and most part of Euro-Asian continent and North American continent are getting warmer, whereas the Labrador Sea, the Greenland and the area around the Bering Strait are getting colder. Meanwhile, the sea level pressure in the central part of the northern polar region and the place where the climatic Icelandic low exist decreases, but in places farther southward it increases. Since the 1970 s, the sensible heat flux and latent heat flux sent to the atmosphere from the Greenland Sea and the Barents Sea has increased, this is mainly due to the reduction of sea ice concentration and the weakening of insulator and shield effect of the solid ice accordingly caused by the increase of air temperature. In sea ice free area of the Norwegian Sea, the sensible heat flux and latent heat flux sent to the atmosphere has reduced due to decrease of temperature and humidity differences between the air and the sea surface caused by increase of air temperature and humidity. In the Labrador Sea, due to decrease of air temperature and humidity and increase of temperature and humidity differences between the air and the sea surface accordingly, the sea gives more sensible heat flux and latent heat flux to the air. This will lead to the growth of sea ice extent there. The features of linear regression of sea level pressure, sea ice concentration and sum of sensible heat flux and latent heat flux toward time series of the leading mode of EOF expansion of surface air temperature are close to those of their own EOF expansion for the leading mode, respectively. This shows that these variables share similar features of variation with time linearly.展开更多
深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计...深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计算的大气非绝热加热数据,分析两种资料所反映的高原上大气非绝热加热的时空分布特点,重点比较了二者在高原南麓的差异,并结合TRMM PR降水和潜热资料分析了差异的可能原因.研究发现两种资料之间的差异在夏季最大:ERA40在高原南麓高海拔地区所诊断的非绝热加热显著大于NCEP.ERA40大气强加热区域从高原南部山脚向北延伸、越过海拔4000位势米直至高原主体的南部;而相应NCEP大气强加热区主要位于高原南麓低海拔地区,不超过海拔4000位势米界限.上述差异不仅限于贴地层(地表感热的直接影响区域),而在400~500 h Pa大气层也很显著.同时发现,ERA40所估计的夏季高原南麓降水显著大于NCEP和TRMM PR的观测,这种差异在时间、空间上都与非绝热加热的差异相吻合.这说明降水所释放的潜热是造成上述差异的主要原因.分析大气加热场和大气环流的经向垂直剖面发现,ERA40在南麓高海拔地区所诊断的大气非绝热加热可向上延伸至对流层高层~300 h Pa,而相应NCEP大气非绝热加热主要集中在较低大气层,相应ERA40诊断的大气垂直上升速度明显强于NCEP,200 h Pa的水平辐散也较强.高原南麓深对流降水及其潜热的不确定性是充分理解高原-大气相互作用的主要难点.展开更多
基金The work was supported by Natural Science Foundation of China under grant 40233031.
文摘Based on the reanalysis dataset ERA40 of European Center of Medium Range Weather Forcast （ECMWF）, winter climate change and characteristics of sea ice-atmosphere interaction at high northern latitudes for recent several tens of years are analyzed. Superposed upon the background of global warming, the amplitude of temperature increase in winter at high northern latitudes is bigger and it exhibits different features in different regions. From the end of 1970 s, the Greenland Sea, the Barents Sea and most part of Euro-Asian continent and North American continent are getting warmer, whereas the Labrador Sea, the Greenland and the area around the Bering Strait are getting colder. Meanwhile, the sea level pressure in the central part of the northern polar region and the place where the climatic Icelandic low exist decreases, but in places farther southward it increases. Since the 1970 s, the sensible heat flux and latent heat flux sent to the atmosphere from the Greenland Sea and the Barents Sea has increased, this is mainly due to the reduction of sea ice concentration and the weakening of insulator and shield effect of the solid ice accordingly caused by the increase of air temperature. In sea ice free area of the Norwegian Sea, the sensible heat flux and latent heat flux sent to the atmosphere has reduced due to decrease of temperature and humidity differences between the air and the sea surface caused by increase of air temperature and humidity. In the Labrador Sea, due to decrease of air temperature and humidity and increase of temperature and humidity differences between the air and the sea surface accordingly, the sea gives more sensible heat flux and latent heat flux to the air. This will lead to the growth of sea ice extent there. The features of linear regression of sea level pressure, sea ice concentration and sum of sensible heat flux and latent heat flux toward time series of the leading mode of EOF expansion of surface air temperature are close to those of their own EOF expansion for the leading mode, respectively. This shows that these variables share similar features of variation with time linearly.
文摘深入理解青藏高原上空大气非绝热加热三维结构,有助于揭示高原热动力效应和机械强迫效应在亚洲夏季风系统中的作用机理.然而现有的高原非绝热加热率资料存在较大不确定性.本文详细比较了NCEP和ERA40再分析资料"残差诊断法"计算的大气非绝热加热数据,分析两种资料所反映的高原上大气非绝热加热的时空分布特点,重点比较了二者在高原南麓的差异,并结合TRMM PR降水和潜热资料分析了差异的可能原因.研究发现两种资料之间的差异在夏季最大:ERA40在高原南麓高海拔地区所诊断的非绝热加热显著大于NCEP.ERA40大气强加热区域从高原南部山脚向北延伸、越过海拔4000位势米直至高原主体的南部;而相应NCEP大气强加热区主要位于高原南麓低海拔地区,不超过海拔4000位势米界限.上述差异不仅限于贴地层(地表感热的直接影响区域),而在400~500 h Pa大气层也很显著.同时发现,ERA40所估计的夏季高原南麓降水显著大于NCEP和TRMM PR的观测,这种差异在时间、空间上都与非绝热加热的差异相吻合.这说明降水所释放的潜热是造成上述差异的主要原因.分析大气加热场和大气环流的经向垂直剖面发现,ERA40在南麓高海拔地区所诊断的大气非绝热加热可向上延伸至对流层高层~300 h Pa,而相应NCEP大气非绝热加热主要集中在较低大气层,相应ERA40诊断的大气垂直上升速度明显强于NCEP,200 h Pa的水平辐散也较强.高原南麓深对流降水及其潜热的不确定性是充分理解高原-大气相互作用的主要难点.
