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首页> 外文期刊>Atmospheric chemistry and physics >High ice water content at low radar reflectivity near deep convection – Part 2: Evaluation of microphysical pathways in updraft parcel simulations
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High ice water content at low radar reflectivity near deep convection – Part 2: Evaluation of microphysical pathways in updraft parcel simulations

机译：在深对流附近，雷达反射率低时冰水含量高-第2部分：上升气流包裹模拟中的微物理路径的评估

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The aeronautics industry has established that a threat to aircraft is posed by atmospheric conditions of substantial ice water content (IWC) where equivalent radar reflectivity (Ze) does not exceed 20–30 dBZ and supercooled water is not present; these conditions are encountered almost exclusively in the vicinity of deep convection. Part 1 (Fridlind et al., 2015) of this two-part study presents in situ measurements of such conditions sampled by Airbus in three tropical regions, commonly near 11 km and ?43 °C, and concludes that the measured ice particle size distributions are broadly consistent with past literature with profiling radar measurements of Ze and mean Doppler velocity obtained within monsoonal deep convection in one of the regions sampled. In all three regions, the Airbus measurements generally indicate variable IWC that often exceeds 2 g m-3 with relatively uniform mass median area-equivalent diameter (MMDeq) of 200–300 μm. Here we use a parcel model with size-resolved microphysics to investigate microphysical pathways that could lead to such conditions. Our simulations indicate that homogeneous freezing of water drops produces a much smaller ice MMDeq than observed, and occurs only in the absence of hydrometeor gravitational collection for the conditions considered. Development of a mass mode of ice aloft that overlaps with the measurements requires a substantial source of small ice particles at temperatures of about ?10 °C or warmer, which subsequently grow from water vapor. One conceivable source in our simulation framework is Hallett–Mossop ice production; another is abundant concentrations of heterogeneous ice freezing nuclei acting together with copious shattering of water drops upon freezing. Regardless of the production mechanism, the dominant mass modal diameter of vapor-grown ice is reduced as the ice-multiplication source strength increases and as competition for water vapor increases. Both mass and modal diameter are reduced by entrainment and by increasing aerosol concentrations. Weaker updrafts lead to greater mass and larger modal diameters of vapor-grown ice, the opposite of expectations regarding lofting of larger ice particles in stronger updrafts. While stronger updrafts do loft more dense ice particles produced primarily by raindrop freezing, we find that weaker updrafts allow the warm rain process to reduce competition for diffusional growth of the less dense ice expected to persist in convective outflow.
机译：航空业已经确定，飞机的威胁是由大量冰水含量（IWC）的大气条件构成的，其中等效雷达反射率（ Z e ）不超过20– 30 dBZ，不存在过冷水;这些条件几乎只在深对流附近遇到。这项由两部分组成的研究的第1部分（Fridlind等人，2015）介绍了空中客车在三个热带地区（通常在11 km和？43°C附近）采样的这种状况的原位测量结果，并得出结论，测得的冰粒尺寸分布与过去的文献 Z e 的廓线雷达测量值以及在其中一个区域的季风深对流中获得的平均多普勒速度大致上一致。在所有三个区域中，空中客车公司的测量结果通常都显示出可变的IWC，其通常超过2 gm -3 ，相对均匀的质量中位面积当量直径（MMD eq ）为200-300微米在这里，我们使用具有大小解析的微观物理学的宗地模型来研究可能导致这种情况的微观物理学途径。我们的模拟表明，水滴均匀冻结所产生的冰MMD eq 比观察到的要小得多，并且仅在考虑到条件的情况下不存在水凝引力的情况下才会发生。与测量结果重叠的高空冰块质量模式的发展需要大量的小冰粒源，其温度约为10°C或更高，随后会从水蒸气中生长出来。在我们的模拟框架中可以想到的一个来源是Hallett-Mossop制冰。另一个原因是，大量的非均质冰晶核在冻结时会与大量的水滴破碎一起起作用。不管生产机制如何，随着冰源的强度增加以及与水蒸气的竞争增加，蒸气生长的冰的主要质量模态直径减小。夹带和增加气溶胶浓度均会降低质量和模态直径。较弱的上升气流会导致更大的质量和更大的蒸气生长冰的模态直径，这与对较大的上升气流中更大的冰粒浮起的预期相反。尽管较高的上升气流确实能腾出更多主要由雨滴冻结产生的致密冰粒，但我们发现较弱的上升气流可使暖雨过程减少竞争较弱的冰的扩散生长的竞争，这种扩散预计会持续对流流出。

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