Inferences of weekly cycles in summertime rainfall
Inferences of weekly cycles in summertime rainfall
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夏季降雨周周期的推论
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
R. Carbone
中科院分区：
文献类型：
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作者：
J. Tuttle;R. Carbone
[1]在几个大陆区域，已观察到空气污染气溶胶的周循环。它通常以周末（星期六和星期日）的浓度最小值和工作日（星期二-星期五）的浓度最大值为特征。有几项研究将不同的气溶胶浓度与降水量联系起来，并试图确定是否存在相应的每周降水周期。迄今为止的结果好坏参半。在这里，我们研究了12年的国家合成雷达数据集的证据，每周降水周期在温暖的季节（6月至8月）。计算各种统计量并进行“自助”检验以评估显著性。在美国的许多地区，暖季降水相对较少，少数极端事件占12年总降雨量的很大比例。因此，统计数字往往难以解释。密西西比河以东和37°N以北的一般地区包含的地区，在工作日（星期二-星期五）相对于周末的日降雨量增加25%-50%。统计数据表明，宾夕法尼亚州西部是最大的，最有可能连续的地区有一个每周的周期。北方佛罗里达和东南沿海地区的部分地区推断一个反相周期，在一周内的降雨量比周末少。对地面雨量计数据的抽查证实了宾夕法尼亚州和佛罗里达州这些雷达观测到的异常现象的阶段。虽然有迹象表明，在美国的其他地方每周一次的周期，信心的程度是相当低的。有一个强有力的统计推断，工作日降雨量最大超过净8%的地区检查，这是大约两倍的城市面积。为了评估人为气溶胶如何影响城市和区域尺度的降雨，需要进一步研究气溶胶含量、相关的凝结/冰核谱和对流动力学机制。如果雷达是主要的观测方法，则还需要研究可变气溶胶含量对降雨率和雷达反射率因子之间的参数关系的影响。偏振雷达观测也可用于验证关于降水产生的微物理动力学假设。
[1] In several continental regions a weekly cycle of air pollution aerosols has been observed. It is usually characterized by concentration minima on weekends (Saturday and Sunday) and maxima on weekdays (Tuesday–Friday). Several studies have associated varying aerosol concentrations with precipitation production and attempted to determine whether or not there is a corresponding weekly cycle of precipitation. Results to date have been mixed. Here we examine a 12 year national composited radar data set for evidence of weekly precipitation cycles during the warm season (June–August). Various statistical quantities are calculated and subjected to “bootstrap” testing in order to assess significance. In many parts of the United States, warm season precipitation is relatively infrequent, with a few extreme events contributing to a large percentage of the total 12 year rainfall. For this reason, the statistics are often difficult to interpret. The general area east of the Mississippi River and north of 37°N contains regions where 25%–50% daily rainfall increases are inferred for weekdays (Tuesday–Friday) relative to weekends. The statistics suggest that western Pennsylvania is the largest and most likely contiguous region to have a weekly cycle. Parts of northern Florida and southeastern coastal areas infer a reverse-phase cycle, with less rainfall during the week than on weekends. Spot checks of surface rain gauge data confirm the phase of these radar-observed anomalies in both Pennsylvania and Florida. While there are indications of a weekly cycle in other locations of the United States, the degree of confidence is considerably lower. There is a strong statistical inference of weekday rainfall maxima over a net 8% of the area examined, which is approximately twice the area of cities. Future examination of lofted aerosol content, related condensation/ice nuclei spectra, and knowledge of the convective dynamical regime are needed in order to assess how anthropogenic aerosols may affect rainfall at urban and regional scales. If radar is the primary method of observation, it is also necessary to examine the effects of variable aerosol content on the parametric relationship between rainfall rate and radar reflectivity factor. Polarimetric radar observations could also serve to verify microphysical-dynamical hypotheses regarding precipitation production.