Nonclassic evolution of a cold-frontal system across the western United States during the Intermountain Precipitation Experiment
Nonclassic evolution of a cold-frontal system across the western United States during the Intermountain Precipitation Experiment
复制标题
山间降水实验期间美国西部冷锋系统的非经典演化
DOI：
10.1175/waf-d-19-0166.1
复制
发表时间：
2020
影响因子：
2.9
通讯作者：
Steenburgh, W. J.
中科院分区：
文献类型：
--
作者：
Schultz, D. M.;Steenburgh, W. J.
利用 2000 年 2 月 14 日至 15 日山间降水实验 (IPEX) 第 4 期密集观测期间收集的观测数据，对穿越犹他州北部的冷锋通道进行了研究。为了说明其一些非经典特征，我们考虑其起源。锋面在太平洋沿岸的两个地表特征（以下简称冷锋系统）登陆后形成。第一个特征是与降水带和绳状云相关的表面压力槽和风移，几乎没有表面斜压。第二次是在 4 小时后登陆，是与降水减弱相关的风向变化，登陆时气温下降较弱（9 小时内下降 1°C），但当它向加利福尼亚州中部内陆移动时，气温下降幅度更大（9 小时内下降 4°–6°C）。当第一个特征进入大盆地时，由于下坡气流和白天加热，槽前面的表面温度升高，而槽后面的温度随着降水冷却近地表空气而下降。再加上内华达山脉背风处的汇合，该槽发展成为冷锋系统的主要斜压区（不到一小时就达到8°C），而第二个特征的降温进一步减弱。表面气压槽的运动比槽后表面风更快，并且与高空短波槽的运动有关。该案例与之前发表的西部山间案例一起，挑战了冷锋术语、结构和演化的传统概念模型。
A cold-frontal passage through northern Utah was studied using observations collected during intensive observing period 4 of the Intermountain Precipitation Experiment (IPEX) on 14–15 February 2000. To illustrate some of its nonclassic characteristics, its origins are considered. The front developed following the landfall of two surface features on the Pacific coast (hereafter, the cold-frontal system). The first feature was a surface pressure trough and wind shift associated with a band of precipitation and rope cloud with little, if any, surface baroclinicity. The second, which made landfall 4 h later, was a wind shift associated with weaker precipitation that possessed a weak temperature drop at landfall (1°C in 9 h), but developed a stronger temperature drop as it moved inland over central California (4°–6°C in 9 h). As the first feature moved into the Great Basin, surface temperatures ahead of the trough increased due to downslope flow and daytime heating, whereas temperatures behind the trough decreased as precipitation cooled the near-surface air. Coupled with confluence in the lee of the Sierra Nevada, this trough developed into the principal baroclinic zone of the cold-frontal system (8°C in less than an hour), whereas the temperature drop with the second feature weakened further. The motion of the surface pressure trough was faster than the posttrough surface winds and was tied to the motion of the short-wave trough aloft. This case, along with previously published cases in the Intermountain West, challenges the traditional conceptual model of cold-frontal terminology, structure, and evolution.