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2019 , Vol. 42 >Issue 6: 1229 - 1238

DOI: https://doi.org/10.12118/j.issn.1000-6060.2019.06.01

气候与水文

乌鲁木齐城区一次极端东南大风的形成机制——重力波与超低空急流耦合

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  • 1新疆维吾尔自治区气象台，新疆乌鲁木齐830002；2中国气象局乌鲁木齐沙漠气象研究所，新疆乌鲁木齐830002；3新疆维吾尔自治区人工影响天气办公室，新疆乌鲁木齐830002；4新疆维吾尔自治区气象局，新疆乌鲁木齐830002
汤浩（1972-），男，高级工程师，本科，从事中尺度数值天气预报模式应用和客观天气预报技术研究.E-mail: tanghao72@163.com〖ZK)

收稿日期: 2019-05-31

  修回日期: 2019-08-27

  网络出版日期: 2019-11-15

基金资助

新疆自治区科技计划项目（201433112）资助

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Formation mechanism of a southeast gale event in Urumqi urban area: The coupling of gravity wave and ultra-low level jet

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  • 1 Xinjiang Meteorological Observatory,Urumqi 830002,Xinjiang,China;2 Institute of Desert Meteorology,China Meteorological Administration,Urumqi 830002,Xinjiang,China;3 Weather Modification Office of Xinjiang,Urumqi 830002, Xinjiang China;4 Xinjiang Meteorological Bureau,Urumqi 830002,Xinjiang,China

Received date: 2019-05-31

  Revised date: 2019-08-27

  Online published: 2019-11-15

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摘要

东南大风是乌鲁木齐城区独有的强灾害性天气，通过研究发现东南大风是天山峡谷特殊地形造成的大振幅重力波与超低空急流耦合触发的强下坡风暴。针对2012年3月30日乌鲁木齐城区出现的近10 a最强的一次东南大风天气过程，使用中尺度WRF模式进行数值模拟，分析模式输出的高时空分辨率产品发现：在气压梯度力作用下，气流从天山峡谷南端进入，一方面由于狭管效应在峡谷内300~400 m高度形成超低空急流；另一方面气流在进入峡谷过程中，因爬坡强迫抬升形成重力波。重力波在峡谷内与超低空急流发生耦合，在峡谷北端背风坡形成大曲率背风波，背风波的下沉运动引起动量下传，将超低空急流的能量输送到地面，形成水跃型下坡风暴即东南大风。在此过程中背风坡上空风向切变的临界层吸收上层波能量加强了超低空急流，对流层低层稳定层结对背风波的下沉运动起到加速作用。

关键词： 超低空急流; 重力波; 下坡风暴; 临界层; 层结稳定度

本文引用格式

汤浩, 王旭, 储长江, 孙鸣婧 . 乌鲁木齐城区一次极端东南大风的形成机制——重力波与超低空急流耦合[J]. 干旱区地理, 2019 , 42(6) : 1229 -1238 . DOI: 10.12118/j.issn.1000-6060.2019.06.01

Abstract

There is a northwest-southeast-oriented canyon in the middle of the Tianshan Mountains, Xinjiang, China, the length of the canyon is about 80 km, the altitude at the bottom of the valley is about 1 200 m, and the height of the mountains is about 3 000 m. Urumqi is located in the northwest opening downhill of the canyon, the Turpan Basin is located at the southeast opening. This paper uses the mesoscale WRF model to simulate the strongest southeastern gale in the past 10 years in Urumqi City which occurred on March 30, 2012.The simulated output of high temporal-spatial resolution is analyzed. With the simulation and the diagnostic analysis we concluded that the southeast gale in Urumqi is a strong downslope windstorm triggered by the combination of gravity wave and ultra-low level jet which was caused by the special landform in Tianshan canyon. The formation mechanism is summarized as follows: (1) The cold air at the bottom of the Mongolian high pressure flows back into the basin from the eastern part of the Tarim Basin, accumulates and forms a ground high pressure on the south side of the Tianshan Mountains. On the north side of the Tianshan Mountains, the front decompression occurs due to the intrusion of cold front, and thus pressure field on both sides of the Tianshan Mountains is high in the South and low in the North. Under the action of the pressure-gradient force, the cold air enters the Tianshan Gorge, and the airflow gradually accelerates due to the funneling effects. In the middle of the canyon, the wind is southeast and the wind speed exceeds 8 at a distance of 300 meters from the ground. (2) During the process of cold air at the southern end of the canyon climbing into the canyon, gravity waves are formed by the forced lifting due to the terrain. As the pressure gradient on both sides of the canyon increases, the amplitude of the gravity wave increases and is coupled with the ultra-low-level jet, the gravity wave forms a leeward wave hydraulic jump at the northern end of the canyon, triggering a strong downhill storm on the ground, that is the southeast gale in Urumqi. (3) There are two factors complementing each other and thus enhancing the ultra-low-level jet energy. One of them is the critical layer of the shear of southeast and southwest winds above the ultra-low-level jet stream absorbs the upper-layer wave energy and transmits it downward to the ultra-low-level jet stream; the other is the gravity wave breaking turbulence exacerbates the downward transfer of energy in the rapids. In this process, the stable atmospheric stratification of the lower troposphere over the leeward slope exacerbates the sinking motion of lee wave and the energy transmission caused by it.

Key words： ultra-low level jet; gravity wave; downhill storm; critical layer; stratification stability

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