Synoptic climatology of thermal low-pressure systems over south-western north America
Synoptic climatology of thermal low-pressure systems over south-western north America
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北美西南部热低压系统的天气气候学
DOI：
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发表时间：
1992
期刊：
影响因子：
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通讯作者：
S. Colucci
中科院分区：
文献类型：
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作者：
David R. Rowson;S. Colucci
本文分析了美国西南部和墨西哥西北部1974-1984年11年期间的闭合等压线、非迁移热低压频率。平均发病和故障日期，首选的位置，和系统的垂直范围。上层（500毫巴）流的热低压的存在和系统之间的关系和降水在亚利桑那州和墨西哥西部的影响也进行了研究。分析表明，美国西南海岸和墨西哥西海岸附近的热低压的形成和维持的首选区域。在这一区域内，有两个频率最高点，集中在美洲西南部和墨西哥西北部的沙漠地区以及西马德雷山脉西方的高原高地。该系统在6月中旬至9月中旬最为普遍，并在7月和8月初达到最大垂直范围，接近700毫巴。这种变化可能归因于太阳的天顶移动，尽管夏季期间系统强度的短期波动可能与低层云量的变化有关。具体而言，降水提前500毫巴槽通过北部的系统似乎与减弱的热低，这表明负反馈关系，值得进一步研究。
Analyses of closed-isobar, non-migratory, thermal low-pressure frequencies are presented for an 11-year period, 1974–1984, over the south-western USA and north-western Mexico. Average onset and breakdown dates, preferred locations, and the vertical extent of the system are presented. The effect of upper level (500 mbar) flow on the presence of the thermal low and relationships between the system and precipitation in Arizona and western Mexico also are investigated. The analyses suggest a preferred region for the formation and sustenance of the thermal low near the south-west coast of the USA and the west coast of Mexico. Within this region exist two frequency maxima, centred over the desert regions of the American South-west and north-western Mexico and over the plateau highlands of the Sierra Madre Occidental. The system is most prevalent from mid-June until mid-September and reaches its maximum vertical extent near 700 mbar in July and early August. This variation may be attributed to the zenithal progression of the sun, although short-term fluctuations in the strength of the system during the summer period probably are related to changes in cloud cover over the low. Specifically, precipitation in advance of 500-mbar troughs passing to the north of the system appears to be associated with the weakening of the thermal low, suggesting a negative feedback relationship that deserves further investigation.