1979—2013年ERA-Interim资料的青藏高原低涡活动特征分析

为了更好地了解青藏高原多尺度地形的动力作用,并为改良数值模式中地形的表示方法奠定基础,通过采用2010年青藏高原西南部6个地面台站的观测资料以及4种不同分辨率的分析(再分析)资料,分别估算了冈底斯山及整个青藏高原主体范围内的地表气压拖曳,得出了青藏高原可能存在的拖曳类型,并且分析了青藏高原气压拖曳的一些特征。得出如下主要结论:由罗斯贝波产生的波动拖曳作为行星尺度的拖曳对青藏高原地区总拖曳的贡献最大;同时,青藏高原范围内存在着大量与天气过程密切相关的天气尺度的拖曳;对于冈底斯山对气流的中尺度动力作用的进一步分析可知,夏季基本全为气流分离,冬季500 hPa以下为气流分离,500—200 hPa为气流分离和波动破碎的混合区,而200 hPa以上的平流层则为重力波的产生及其破碎区域;冈底斯山地区的地表气压拖曳主要集中在3000—5000 m高度,并且,冈底斯山总拖曳的方向近乎与山脊垂直;地表气压和地形高度资料的分辨率越高,所能分辨出的更小波长的气压拖曳也越多,估算出的高原主体范围内的拖曳值也越大;变压梯度和地形梯度是影响气压拖曳的基本因子,但地形梯度对拖曳的影响最终是通过气压梯度来实现的。

An objective analysis of the Tibetan Plateau vortexes based on the ERA-interim reanalysis data: 1979-2013

The purpose of this research is not only to further understand the dynamic effect of the Tibetan Plateau but also to provide a good benchmark to verify the representation of mountain drag in numerical models. In order to explore the possible pressure drag types over the Tibetan Plateau, the observational data at the six synoptic stations and the analysis (re-analysis) data at the four different resolutions are used to estimate the surface pressure drag over the Gangdise range and the main body of the Tibetan Plateau in 2010 respectively. Meanwhile, some characteristic analysis of the pressure drag over the Tibetan Plateau is discussed. The preliminary conclusions are generalized as follows: Wave drag excited by the Rossby wave plays a dominant role in the Tibetan Plateau's total drag; there still exists significant synoptic-scale drag associated with the synoptic processes over the Tibetan Plateau. As to the meso-scale dynamic influence on the airflow over the Gangdise range, flow spitting is the main type in summer; in winter, surface pressure drag is mainly generated by the flow splitting below 500 hPa and by both the flow splitting and wave breaking between 500 hPa and 200 hPa, while the generation of mountain wave and its breaking is the primary drag type in the stratosphere above 200 hPa. Also, the pressure drag of the Gandise is mainly concentrated on between 3000-5000 m and its direction seems to be roughly perpendicular to the mountain ridge. Moreover, the magnitude of the surface pressure drag on the main body of the Plateau increases with the increase of the horizontal resolution of the data. At last, the allobaric gradient and topographic gradient are the two influencing factors of the pressure drag, but the impact of the topographic gradient on pressure drag is finally realized through the impact of pressure gradient.