Thermally driven gap winds into the Mexico City basin
Thermally driven gap winds into the Mexico City basin
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DOI：
10.1175/1520-0450(2000)039
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发表时间：
2000-08-01
期刊：
影响因子：
--
通讯作者：
Zhong, S
中科院分区：
文献类型：
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作者：
Doran, JC;Zhong, S
在 1997 年冬季为期四个星期的野外活动中，一股低空急流形式的东南气流通过盆地东南角的一个山隙进入墨西哥城盆地，持续在下午或傍晚形成。峰值风速经常超过 10 m s(-1)。尽管以前没有研究过这些风，但观察结果表明它们是盆地风系统的常规特征，至少在冬季是这样。在实验的早期阶段，喷流的发现频率更高，当时流域内的条件通常更温暖、更干燥、云量更少，而在实验后期，条件更凉爽、更潮湿、云量更大。早期风力通常也更强。盆地内外发射的无线电探空仪的温度测量显示，间隙风强度依赖于两个区域之间的温差。使用三维数值模型来模拟间隙流的特征，以提供有关其发展机制的信息。急流的最大速度通常在盆地和南部地区之间出现最大温度梯度数小时后达到。动量平衡分析表明，间隙风是由较温暖的盆地和较冷的外部空气之间的温差引起的下边界层间隙上的南北压力梯度引发的。间隙风侵入盆地主要是由水平平流引起的。间隙风对辐合带的形成起着重要作用，辐合带对流域内表面空气污染物的分布产生重要影响。
A southeasterly flow in the form of a low-level jet that enters the Mexico City basin through a mountain gap in the southeast corner of the basin developed consistently in the afternoons or early evenings during a four-week 1997 winter field campaign. Peak wind speeds often exceeded 10 m s(-1). Although these winds have not been studied previously, the observations suggest that they are a regular feature of the basin wind system, at least during the winter months. The jets were found more frequently during the early Dart of the experiment, when conditions in the basin were generally warmer, drier, and less cloudy, than in the later part when conditions were cooler, more humid, and cloudier. The winds usually were stronger during the early period, also. Temperature measurements from radiosondes launched inside and outside the basin showed a dependence of the gap wind strength on the temperature differences between the two regions. A three-dimensional numerical model was used to simulate the characteristics of the gap flows to provide information on the mechanisms responsible for their development. The maximum speed of the jet usually is reached several hours after the occurrence of the maximum temperature gradient between the basin and the region to the south. An analysis of the momentum balance shows that the gap wind is initiated by a north-south pressure gradient across the gap in the lower boundary layer arising from temperature differences between the warmer basin and the cooler exterior air. Penetration of the gap wind into the basin is caused primarily by horizontal advection. The gap wind plays an important role in the formation of a convergence zone, which can have an important effect on surface air pollutant distributions in the basin.