New Studies Linking Ice Nucleation and Precipitation

降水是地球上产生淡水的唯一最重要的来源，但我们在微物理层面上对其形成和演化的过程水平的了解还很粗糙，仍然高度不确定。特别是，从冰的起始和生长到冰的分裂，冰微物理过程的相对作用受到很少的约束。这项研究的目的是应用一种新的方法来测量单个雨滴和毛毛雨的冻结行为，目的是将降雨率对冰核数量浓度的敏感度参数化。当雨滴碰撞和合并时，层间降水形成，迅速将云中的水分流成毛毛雨和雨。为了启动这一过程，必须存在少量较大的水流星，通常认为它们是云层中的冰晶，温度足够低，足以形成异质冰核。如果没有发生冰增殖或液滴破裂等次级过程，每个降水颗粒都包含这种种子。为了分析初级和次级过程的相对重要性，单个雨滴将被收集在液氮中，并储存在石蜡中。每个雨滴都将被放置在一个寒冷的舞台上，并将测量其冻结的温度。对流风暴、天气尺度冬季风暴、锋面通道和热带气旋残余降水的雨滴冰点温度分布将作为降水系统演变的函数进行分析。所有数据将在更大的气象和微物理背景下进行分析，即降雨率、云顶温度、云滴数量浓度，并用于限制降水对冰核的敏感性，以便纳入数值天气和气候预测模式。假设人为活动产生的气溶胶会影响冰川过程，进而改变降水。令人惊讶的是，尽管它对社会具有根本的重要性，但在本杰明·富兰克林之后200多年？关于冰过程与降水形成有关的猜想，我们仍然不了解所涉及的微物理过程的相对重要性。这里的实验将有助于约束这个问题。除了典型的传播渠道(会议和同行评议对文献的贡献)外，调查人员还将举办公开讲座，让罗利/达勒姆地区的非科学界参与这一专题。北卡罗来纳州立大学的一些本科生和研究生将在这个项目上与首席研究员合作。

Precipitation is the single most important source of freshwater generation on Earth, but our process-level understanding of its formation and evolution at the microphysical level is crude and remains highly uncertain. In particular, the relative roles of ice microphysical processes, from ice initiation and growth to ice splintering are poorly constrained. The goal of this study is to apply a new method that measures the freezing behavior of individual rain and drizzle drops, with the objective to parameterize the susceptibility of rain rate to ice nuclei number concentrations.INTELLECTUAL MERITPrecipitation forms when drops collide and coalesce, rapidly shunting cloud water into drizzle and rain. To initiate this process a small number of larger hydrometeors must be present, usually assumed to be ice crystals in clouds that are cold enough for heterogeneous ice nucleation to occur. Each precipitation particle contains this seed, provided secondary processes such as ice multiplication or drop breakup did not occur. To analyze the relative importance of primary and secondary processes, individual rain drops will be collected in liquid nitrogen and stored in paraffin. Each raindrop will be placed on a cold stage and the temperature at which it freezes will be measured. The distribution of raindrop freezing temperatures for precipitation from convective storms, synoptic scale winter storms, frontal passages, and remnants of tropical cyclones will be analyzed as a function of the evolution of the precipitating system. All data will be analyzed in the larger meteorological and microphysical context, i.e. rain rate, cloud-top temperature, cloud droplet number concentration, and used to constrain the susceptibility of precipitation to ice nucleation for inclusion in numerical weather and climate prediction models.BROADER IMPACTSThe investigation, although fundamental in nature, touches on questions with important societal implications. It is hypothesized that aerosols from anthropogenic activity affect ice processes and in turn modify precipitation. It is surprising that despite its fundamental importance to society, and more than 200 years after Benjamin Franklins? conjecture implicating ice processes in precipitation formation, we still do not understand the relative importance of the microphysical processes involved. The experiments here will help to constrain this question. In addition to the typical dissemination channels (conferences and peer reviewed contributions to the literature), the investigators will host public lectures to engage the non-science community in the Raleigh/Durham area with this topic. A number of undergraduate and graduate students at N.C. State University will work with the principal investigator on this project.