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Numerical simulations of upslope fog observed at Beppu Bay in Oita Prefecture, Japan
Meteorological Applications ( IF 2.7 ) Pub Date : 2021-05-28 , DOI: 10.1002/met.2003
Yukitaka Ohashi 1 , Makoto Suido 2
Affiliation  

The present study focussed on the formation of upslope fog. This fog causes chronic expressway closures near Beppu Bay (BB) in Oita Prefecture, Japan. A dense fog event, occurring on 3 and 4 May 2020, resulting from the passage of an extratropical cyclone through the southern Japanese islands, was simulated using the Weather Research and Forecasting (WRF) numerical model. The simulation results indicated that warm and humid air with a lifting condensation level less than 20 m flowed into a plain from BB. Simulated fog and poor visibility were more severe on mountain slope adjacent to BB than on the surroundings. Here, the westward horizontal flux of water vapour by the wind flow was prolonged at lower heights. Analyses of the simulated elements verified that the upslope fog was induced by moist adiabatic cooling of the air lifted by the upslope winds. At the mature stage of upslope fog, a simulated local vertical circulation generated in conjunction with the upper synoptic flow extended the dense fog into the upper atmosphere over BB. During the decaying stage of upslope fog on mountain, a fog covered on the entire BB. This was associated with weakening winds at lower heights. Sensitivity experiments for model boundary conditions supported the importance of mountain steepness and the rectangular shape of BB for the generation of upslope fog. Finally, an application possibility of dense fog forecasts was discussed by using a simulated difference in the equivalent potential temperature between the base of the mountain and Beppuwan expressway interchange located midslope.

中文翻译:

日本大分县别府湾上坡雾的数值模拟

目前的研究重点是上坡雾的形成。这种雾导致日本大分县别府湾 (BB) 附近的高速公路长期关闭。使用天气研究和预报 (WRF) 数值模型模拟了 2020 年 5 月 3 日至 4 日发生的浓雾事件,该事件由温带气旋穿过日本南部岛屿引起。模拟结果表明,抬升凝结高度小于20 m的暖湿空气从BB流入平原。BB 附近的山坡上的模拟雾和能见度比周围更严重。在这里,由风流引起的水汽向西水平通量在较低高度处延长。对模拟元素的分析证实,上坡雾是由上坡风吹起的空气的湿绝热冷却引起的。在上坡雾的成熟阶段,结合上层天气流产生的模拟局部垂直环流将浓雾扩展到BB上方的上层大气。山上上坡雾消退阶段,整个BB笼罩着一层雾气。这与较低高度的风减弱有关。模型边界条件的敏感性实验支持山陡度和 BB 矩形形状对上坡雾生成的重要性。最后,
更新日期:2021-05-28
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