冬季青藏高原大气热状况分析Ⅱ:年际变化

An analysis of the diabatic heating characteristic of atmosphere over the Tibetan Plateau in winter Ⅱ: Interannual variation.

  • 摘要: 在分析了冬季高原上空气候平均热力特征的基础上,文中继续讨论冬季高原上空非绝热加热年际变化的特征及其与北半球大气环流场异常的联系。结果发现,冬季高原上空非绝热加热的年际异常主要表现为高原西侧至东南侧潜热加热的异常。且与夏季不同,冬季高原上空非绝热加热异常偏大(偏小)时,在高原上空从上至下,出现一致的气旋性(反气旋)性差异环流,表现出相当正压的异常结构;数值试验的结果进一步指出,高原冬季热力异常主要与高原上游的西风环流异常紧密相连,高原西南侧西风急流增强时,因高原阻挡在高原西北部易形成气旋性差异环流,且高原南侧绕流增加,围绕高原主体形成气旋性差异环流,最终导致高原西部及南侧的潜热加热增加,总的非绝热加热变大。高原冬季非绝热加热的异常是大尺度环流异常与高原动力作用的结果,是整个北半球异常模态的局地响应,与北半球一支从西北到东南的遥相关波列密切相关。

     

    Abstract: The climatological characteristic of diabatic heating over the Tibetan Plateau (TP) during winter was analyzed in Part Ⅰ. This paper is Part Ⅱ of the work, which discusses the interannual variation of the diabatic heating over the TP during winter and its relationship with atmospheric circulation anomalies in the Northern Hemisphere by means of data diagnoses and numerical simulations. The mode of the most prominent interannual variations of atmospheric diabatic heating over the TP during winter is mostly due to the abnormal latent heating over the western and southeastern side of the TP. Different from the interannual variation in summer, there appear consistent cyclonic (or anticyclonic) deflection circulations over the TP from the upper troposphere down to the lower troposphere when the columnintegrated diabatic heating over the TP is above (below) normal, showing an equivalentbarotropic structure. The results of numerical experiments show the heating abnormality over the TP during winter is closely related with the westerly wind variation on the southwest side of the TP. When the westerly there is stronger than normal, there appears a cyclonic circulation over the northwestern TP due to the topography blocking, and the detouring flow around the south side of the TP also becomes stronger, forming a remarkable cyclonic deviation circulation around the main part of the TP. These then lead to the increase of latent heating and total heating over the west part of the TP and its south side. It is further demonstrated that the abnormality of diabatic heating in winter over the TP is a consequence of the atmospheric circulation abnormality in the Northern Hemisphere and the mechanical forcing of the TP. The heating anomaly over the TP is closely related with the teleconnection wave ray emanating from northwest to southeast in the Northern Hemisphere. Therefore, it can be considered as a local response to the atmospheric circulation anomaly in the Northern Hemisphere.

     

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