Silber Israel, Fridlind Ann M, Verlinde Johannes, Ackerman Andrew S, Chen Yao-Sheng, Bromwich David H, Wang Sheng-Hung, Cadeddu Maria, Eloranta Edwin W
Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, Pennsylvania, USA.
NASA Goddard Institute for Space Studies, New York, New York, USA.
J Geophys Res Atmos. 2019 Oct 27;124(20):10878-10895. doi: 10.1029/2019jd030882. Epub 2019 Sep 11.
The rarity of reports in the literature of brief and spatially limited observations of drizzle at temperatures below -20°C suggest that riming and other temperature-dependent cloud microphysical processes such as heterogeneous ice nucleation and ice crystal depositional growth prevent drizzle persistence in cold environments. In this study, we report on a persistent drizzle event observed by ground-based remote-sensing measurements at McMurdo Station, Antarctica. The temperatures in the drizzle-producing cloud were below -25°C and the drizzle persisted for a period exceeding 7.5 hours. Using ground-based, satellite, and reanalysis data we conclude that drizzle was likely present in parts of a widespread cloud field, which stretched more than ~1000 km along the Ross Ice Shelf coast. Parameter space sensitivity tests using two-moment bulk microphysics in large-eddy simulations constrained by the observations suggest that activated ice freezing nuclei (IFN) and accumulation-mode aerosol number concentrations aloft during this persistent drizzle period were likely on the order of 0.2 L and 20 cm, respectively. In such constrained simulations, the drizzle moisture flux through cloud base exceeds that of ice. The simulations also indicate that drizzle can lead to the formation of multiple peaks in cloud water content profiles. This study suggests that persistent drizzle at these low temperatures may be common at the low aerosol concentrations typical of the Antarctic and Southern Ocean atmospheres.
文献中关于在温度低于-20°C时出现短暂且空间范围有限的毛毛雨观测报告很少，这表明淞附及其他与温度相关的云微物理过程，如异质冰核形成和冰晶沉积增长，会阻止毛毛雨在寒冷环境中持续存在。在本研究中，我们报告了在南极洲麦克默多站通过地基遥感测量观测到的一次持续毛毛雨事件。产生毛毛雨的云层温度低于-25°C，毛毛雨持续了超过7.5小时。利用地基、卫星和再分析数据，我们得出结论，毛毛雨可能出现在一个广泛云场的部分区域，该云场沿着罗斯冰架海岸延伸超过约1000公里。在由观测数据约束的大涡模拟中使用双矩体微物理学进行的参数空间敏感性测试表明，在这次持续毛毛雨期间，高空的活性冰核（IFN）和积聚模态气溶胶数浓度可能分别约为0.2 L和20 cm⁻³。在这种约束模拟中，通过云底的毛毛雨水汽通量超过了冰的水汽通量。模拟还表明，毛毛雨可导致云水含量剖面形成多个峰值。这项研究表明，在南极和南大洋大气典型的低气溶胶浓度条件下，这些低温下的持续毛毛雨可能很常见。
