The Atmospheric Boundary Layer In An Arctic Wintertime On-Ice Air Flow
The Atmospheric Boundary Layer In An Arctic Wintertime On-Ice Air Flow
复制标题
北极冬季冰上气流的大气边界层
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
S. Thiemann
中科院分区：
文献类型：
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作者：
B. Brümmer;S. Thiemann
1998年3月12日，飞机在300公里长的距离上，在最低3公里处，首次系统地测量了弗拉姆海峡北极海冰上来自开放水域的冰上暖气流。在水面上，空气温度低于水温，从而出现对流边界层（CBL）作为初始条件。当CBL通过冰缘时，形成了一个浅的稳定的内边界层。在残留的CBL中，湍流和先前存在的对流云在约20公里内溶解。在相同的距离内，由于不稳定层结向稳定层结的过渡，表面摩擦的影响在IBL内增大，在IBL以上减小，从而在IBL顶部产生低空急流。IBL强烈分层相对于温度和风。风切变约为0.1 s-1，因此IBL中的Richardson数处于亚临界状态，并产生湍流。IBL顶部在230公里的距离上增长到约145米。IBL的增长不是单调的，它受到（a）由不同冰厚和云条件变化引起的不均匀冰面温度和（B）冰面铅的影响。在冰上气流的前侧，温暖空气和北极冷空气之间的气团边界在低层是尖锐的（12 K超过10 km），并随高度倾斜。观测结果表明，分层的IBL被提升为冷空气顶部的平板。
A warm on-ice air flow from the open water over the Arctic sea ice in the Fram Straitwas, for the first time, systematically measured on 12 March 1998 by aircraft in thelowest 3 km over a 300-km long distance. The air mass modification and the processesinvolved are discussed.Over the water, air temperature was lower than water temperature so that a convectiveboundary layer (CBL) was present as initial condition. As soon as the CBL passed theice edge, a shallow stable internal boundary layer (IBL) was formed. In the residual CBL, turbulence and pre-existing convective clouds dissolved within about 20 km. Within about the same distance, due to the transition from unstable to stable stratification, the influence of surface friction increased in the IBL and decreased above the IBL with consequent generation of a low-level jet at IBL top. The IBL was strongly stratified with respect to both temperature and wind. The wind shear was around 0.1 s-1 so that the Richardson number in the IBL was subcritical and turbulence was generated. The IBL top grew to about 145 m over 230 km distance. The growth of the IBL was not monotonic and was influenced by (a) inhomogeneous ice surface temperatures causedby both different ice thickness and changes in the cloud conditions, and (b) leads in theice deck. At the front side of the on-ice flow, the air mass boundary between the warmair and the cold Arctic air was sharp (12 K over 10 km) at low levels and tilted withheight. Observations suggest that the stratified IBL was lifted as a slab on top of thecold air.