A Foehn Event Enhanced by the Synoptic Scale Dry Intrusion
A Foehn Event Enhanced by the Synoptic Scale Dry Intrusion
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因天气规模干入侵而增强的焚风事件
DOI：
10.2151/jmsj.82.229
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发表时间：
2004
影响因子：
3.1
通讯作者：
M. Yamamoto
中科院分区：
文献类型：
--
作者：
Y. Ogura;Ryoji Kumabe;M. Yamamoto
本文的目的是报告我们努力揭示2003年3月2日上午在Totigi县Yaita市造成一些人员和财产损失的大风的性质和可能原因的结果。我们的方法是通过对观测数据的分析，所有使用的数据都是常规的。结果表明，造成灾害的大风是一股类似焚风的下坡风，它是一个炸弹级中纬度气旋经过关东地区时产生的，而八分市位于该气旋后侧强西北气流的山脉背风面。这次大风事件的独特之处在于，它之后是另一个类似焚风的事件，即表面温度高于前一次焚风，露点温度低于前一次焚风，而风则不那么猛烈。通过对降水场的分析，得出第一次焚风是湿的（热力学），而第二次焚风是干的（动力学）。此外，在我们寻求理解为什么地面空气是温暖和干燥的第二焚风，它被发现，到第二焚风开始的时候，异常强烈的中层下降运动的区域，代表干入侵，已经接近关东地区，这有助于降低空气具有高的潜在温度和低混合比进入下坡风在第二焚风。最后指出，在气旋中心后的西北气流中存在一个边界清晰的低空急流，与低空急流相联系的强风对这次焚风事件起了重要作用。因此，这里提出的文件显示的事件序列与连续焚风的形成，发生在一个相当有限的局部地区，但与天气尺度的中纬度气旋的演变和结构密切相关。
The purpose of this article is to report the result of our effort to uncover the nature, and possible cause(s), of the high wind that was responsible for some human and property damage in the morning of 2 March 2003 in Yaita city, Totigi prefecture. Our approach is through the analysis of observed data and all data used are conventional. It is found that the damage-causing high wind was a foehn-like downslope wind, which occurred when a bomb-class midlatitude cyclone passed over the Kanto area, and Yaita city was situated on the lee side of the mountain range in the strong northwesterly flow in the back side of the cyclone. The unique feature of the present high wind event is that it was followed by another foehn-like episode, in that surface temperature was higher and dewpoint temperature was lower than in the preceding foehn, while the wind was less violent. It is concluded, through the analysis of the precipitation field, that the first foehn was wet (thermodynamic), whereas the second foehn was dry (dynamic). Further, in our quest to understand why the surface air was warmer and dryer in the second foehn, it is found that, by the time of the commencement of the second foehn, the region of the unusually strong mid-level descending motion, representing the dry intrusion, had approached the Kanto area and this helped bring down the air possessing high potential temperature and low mixing ratio into the downslope wind in the second foehn. Finally, it is pointed out that a well-defined low-level jet was present in the northwesterly flow behind the cyclone center and the strong wind associated with the low level jet was instrumental in the present foehn event. Thus, presented here are documentations showing the sequence of events associated with successive foehn formations, that occurred in a quite limited local area but was intimately linked with the evolution and structure of a synoptic-scale midlatitude cyclone.