A case-study of cold-air pool evolution in hilly terrain using field measurements from COLPEX
A case-study of cold-air pool evolution in hilly terrain using field measurements from COLPEX
复制标题
使用 COLPEX 现场测量进行丘陵地形冷空气池演变的案例研究
DOI：
10.1002/qj.3499
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发表时间：
2019
影响因子：
8.9
通讯作者：
Jemmett-Smith B
中科院分区：
文献类型：
--
作者：
Jemmett-Smith B
利用冷气池实验(COLPEX)的IOP-16观测资料，对丘陵地区冷空气池(CAP)的演变进行了个例研究。COLPEX是为了研究英国典型的小规模山谷(∼深100-200 m，∼1 公里宽)中的冷空气汇集而设计的。16年眼压期间的天气条件是夜间形成冰帽所需的典型天气条件，具有高压、晴朗的天空和低环境风。最初，CAP在日落前后形成，并不间断地生长了几个小时。然而，从日落后的4 小时开始，这种稳定的冷却速度会发生多次中断。从观测中突出了三个事件和中断的原因，归因于：(A)以重力波和/或开尔文-亥姆霍兹(KH)不稳定形式的波活动，(B)夜间低空急流(NLLJ)发展导致的山谷上方风的增加，(C)NLLJ不稳定导致的切变引起的混合。一个弱稳定的残留层为第一集中的波浪活动提供了条件。在第二集中，这个残留层被一个发展中的NLLJ自上而下地侵蚀。由于NLLJ的作用，山顶风的持续增加继续扰乱了第三集的CAP。尽管降温中断，但CAP在夜间永远不会完全被侵蚀。CAP的完全解体发生在当地日出后约3.5hr. 。这个案例研究突出了一些气象现象，这些气象现象即使在理想的CAP条件下也可能扰乱CAP的演变。目前的业务天气预报模式不太可能充分反映这些过程，即使对高分辨率的研究模式也可能具有挑战性。
A case‐study investigation of cold‐air pool (CAP) evolution in hilly terrain is conducted using field measurements made during IOP 16 of the COLd‐air Pool EXperiment (COLPEX). COLPEX was designed to study cold‐air pooling in small‐scale valleys typical of the UK (∼100–200 m deep, ∼1 km wide). The synoptic conditions during IOP 16 are typical of those required for CAPs to form during the night, with high pressure, clear skies and low ambient winds. Initially a CAP forms around sunset and grows uninterrupted for several hours. However, starting 4 hr after sunset, a number of interruptions to this steady cooling rate occur. Three episodes are highlighted from the observations and the cause of disruption attributed to (a) wave activity, in the form of gravity waves and/or Kelvin–Helmholtz (KH) instability, (b) increases in the above‐valley winds resulting from the development of a nocturnal low‐level jet (NLLJ), (c) shear‐induced mixing resulting from instability of the NLLJ. A weakly stable residual layer provides the conditions for wave activity during Episode 1. This residual layer is eroded by a developing NLLJ from the top down during Episode 2. The sustained increase in winds at hill‐top levels – attributed to the NLLJ – continue to disrupt the CAP through Episode 3. Although cooling is interrupted, the CAP is never completely eroded during the night. Complete CAP break‐up occurs some 3.5 hr after local sunrise. This case‐study highlights a number of meteorological phenomena that can disrupt CAP evolution even in ideal CAP conditions. These processes are unlikely to be sufficiently represented by current operational weather forecast models and can be challenging even for high‐resolution research models.