Exponential Size Distributions for Snow
Exponential Size Distributions for Snow
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雪的指数尺寸分布
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
A. Bansemer
中科院分区：
文献类型：
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作者：
A. Heymsfield;P. Field;A. Bansemer
利用最近几个现场项目的机载数据，作者再次研究了指数冰颗粒尺寸分布 (PSD) 当 PSD 较宽时的特性。解决了两个主要问题：对于什么范围的冰水含量 (IWC) 和等效雷达反射率 (Ze)，指数可以准确估计 PSD 的这些较高矩，以及为什么 PSD 的指数拟合斜率值存在下限，正如从机载测量中发现的那样？早期在温度主要高于 10°C 的情况下进行的研究发现，在穿过深层冰云层螺旋下降期间，在雪中测量到的雪厚度降低至约 9 cm 1 ，然后保持在该水平。已经提出了几种物理过程来解释这些观察结果。如果可靠，这些数据可用于通过遥感改进冰云特性的检索，并用于冰云微物理特性的云模型表示。对于从 2D 探测器获取的数据，最近的证据表明，大冰粒在探测器的传感区域之前（但归因于探测器的传感区域）破碎，产生探测器随后感知的小晶体。破碎的文物已客观地从数据中删除。去除可疑破碎颗粒前后的尺寸分布比较表明，报告的最小值可能是由于破碎和/或其他仪器误差造成的。修订后的 PSD 表明，对于 40 cm 1 、0 .1 gm 1 IWC 和 5 dB Ze，PSD 的第二个 (IWC) 到第四个 (Ze) 时刻以大于几百微米的颗粒为主。不需要具有比指数更多变量的分析表示（例如，gamma PSD）来从 PSD 准确地导出这些矩。在这些情况下，指数 PSD 的截距参数 N0 1c m 4 比之前假设的大 5 到 30 倍。
Using airborne data from several recent field projects, the authors have taken another look at the properties of exponential ice particle size distributions (PSDs) when the PSDs are broad. Two primary questions are addressed: for what ranges of ice water content (IWC) and equivalent radar reflectivity (Ze) do exponentials produce accurate estimates of these higher moments of the PSD, and why is there a lower limit to the value to the slope of exponential fits to PSD, , as has been found from airborne measurements? Earlier studies at temperatures primarily above 10°C have found that measured in snow during spiral descents through deep ice cloud layers decreases to about 9 cm 1 and then remains there. Several physical processes have been advanced to explain these observations. If reliable, the data could be used to improve retrieval of ice cloud properties through remote sensing and for cloud model representations of ice cloud microphysical properties. For data acquired from 2D probes, recent evidence indicates shattering of large ice particles ahead of, but attributable to, the probe’s sensing area, generating small crystals that the probe then senses. Shattered artifacts have been objectively removed from the data. Comparisons of size distributions before and after removal of suspected shattered particles suggest that the reported minimum may have been due to shattering and/or other instrument errors. The revised PSDs indicate that for 40 cm 1 ,0 .1 gm 1 IWC, and 5 dB Ze, moments two (IWC) through four (Ze) of the PSD are dominated by particles larger than a few hundred microns. Analytical representations with more variables than exponentials (e.g., gamma PSD) are not required to accurately derive these moments from the PSD. In these situations, the intercept parameter of the exponential PSD, N0 1c m 4 , is 5 to 30 times larger than assumed earlier.