秋季大气质量海陆间迁移与南北涛动年际变化不同位相配置及其对中国气温异常的影响

Circulation anomalies and their impacts on autumn temperature variations over China in association with different phase combinations of atmospheric mass migration between lands and oceans and inter-hemispheric oscillations

中文关键词:  大气质量海陆间迁移(MAMLO)  南北涛动(IHO)  环流异常  中国气温  秋季

英文关键词:Migration of atmospheric mass between lands and oceans (MAMLO)  Interhemispheric oscillation (IHO)  Circulation anomalies  Surface air temperature changes in China  Boreal fall

中文摘要:

      利用NCEP/NCAR逐月再分析资料,通过构建秋季欧亚大陆-太平洋区域的大气质量海陆间迁移(MAMLO)指数和大气质量南北涛动(IHO)指数,对大气质量海陆间迁移和南北涛动的不同位相配置下环流特征及其对中国秋季气温的影响进行了研究。结果表明,大气质量海陆间迁移与南北涛动指数相关系数仅为-0.06,二者在统计学意义上相互独立。二者存在4种位相配置类型,即大气质量海陆间迁移和南北涛动均为正位相(第Ⅰ类配置);大气质量海陆间迁移和南北涛动均为负位相(第Ⅱ类配置);大气质量海陆间迁移为正位相而南北涛动为负位相(第Ⅲ类配置);大气质量海陆间迁移为负位相而南北涛动为正位相(第Ⅳ类配置)。大气质量海陆间迁移和南北涛动呈现不同位相配置类型时,大气质量的重新分布造成了不同的地表气压场分布并显著地影响到了中国北方地区秋季气温异常分布。当二者为第Ⅰ类配置时,南北涛动削弱北太平洋地区大气质量的负异常,减弱了该区域的异常低压,增强欧亚地区大气质量正异常并加强了欧亚地区的地面高压环流,共同造成中国秋季气温异常成东西反位相型分布,东部暖而西部冷;当二者为第Ⅱ类配置时,南北涛动削弱欧亚大陆大气质量的正异常,增强北太平洋地区大气质量负异常。此时大气质量海陆间迁移和南北涛动通过影响地表风场使得气温异常成全国一致型分布,全区偏暖;而第Ⅲ类配置与第Ⅰ类配置对气温的影响类似,但为东部冷而西部暖,第Ⅳ类配置与第Ⅱ类配置的影响类似。这些表明大气质量海陆间迁移对秋季欧亚地区气温异常起到主要作用,而南北涛动则在大气质量海陆间迁移影响中国北方气温异常分布中起到干扰作用。这些结果对深刻认识秋季大气环流变化机理及中国北方乃至欧亚地区秋季气温异常具有重要意义。

英文摘要:

      Using the NECP/NCAR monthly reanalysis for the period of 1961-2010, circulation anomalies and their possible influences on variations of surface air temperature in China during the boreal fall in association with different phase combinations of migration of atmospheric mass between lands and oceans (MAMLO) and interhemispheric oscillations (IHO) have been investigated. Two indices including MAMLO and IHO are defined to describe the sea-saw-like surface air pressure oscillations between Eurasia and North Pacific and between the southern and northern hemispheres. It is found that the MAMLO and IHO are almost independent of each other in a statistical sense. Four types of phase combination of MAMLO and IHO have been configured. These four types are respectively defined as type-Ⅰ for both MAMLO and IHO in positive phases, type-Ⅱ for both in negative, type-Ⅲ for the MAMLO in positive and IHO in negative, and type-Ⅳ for the MAMLO in negative and IHO in positive. The mean climatological surface air pressure distribution in the boreal fall can be affected by these four types of anomalous surface air pressure patterns, and hence the surface air temperature in China and even in Eurasia-North Pacific can be modulated significantly. When type-Ⅰ cases occur, IHO tends to weaken the low pressure in North Pacific and intensify the high pressure in Eurasia by piling more than normal atmospheric mass in these two places, inducing an east-warm-west-cold pattern in North China when the MAMLO is in its positive phase. In type-Ⅱ cases, IHO weakens the positive air mass anomaly in Eurasia and strengthens the negative air mass anomaly in North Pacific, which leads to a consistent warm pattern in China. In Type-Ⅲ cases, an east-cold-west-warm pattern contrary to that for type-Ⅰ forms in North China. In type-Ⅳ cases, the spatial pattern of temperature is similar to that in type-Ⅱ cases. The above results indicate that MAMLO plays a primary role in the distribution of temperature anomaly in Eurasia during the boreal fall, whereas IHO imposes a disturbing effect superimposed on the influence of MAMLO on the temperature anomaly in North China. Results of the present study are helpful for our better understanding of the mechanisms for atmospheric circulation variations and related temperature changes in North China and even in Eurasia.