Collaborative Research: Inhibition of Snowfall by Pollution Aerosols

这是一个合作项目，研究空气污染对降雪率和降雪量的影响。两名研究人员（Borys和Lowenthal）先前的工作发现了证据，表明污染空气中的颗粒物会降低降雪率和降雪量。这一机制没有得到充分的记录，但在早期的工作中得到了明确的建议，即与空气污染相关的较高颗粒浓度包含了更多的云凝结核（CCN），即云滴形成的颗粒。因此，污染增加了云滴的浓度，但降低了它们的平均大小，从而降低了下落的冰晶与过冷云滴碰撞而生长的效率。因此，污染通过减少从云中收集并沉积在降雪中的过冷水的数量来减少降水。这项研究将采取额外的步骤，以确定在沙漠研究所风暴峰实验室观察到的冬季地形云降雪如何被与污染相关的高浓度气溶胶颗粒所减少。这项工作将包括对云凝结核的直接测量，对降雪和降水的持续观测，以及建立污染和降雪量之间物理联系的建模。该项目将使用一个中尺度模型，该模型在预测降水率和降水量方面表现出了技能。主要目标是：* 确定污染气溶胶负荷和降雪率之间的关系;* 确定雾凇、雪晶大小、晶体习性和大尺度气象特征在确定降雪率方面的相对重要性;* 利用RAMS中尺度模式和箱模拟微物理学对上述影响进行敏感性研究;及 * 利用中尺度模式估算污染气溶胶对研究区降雪量和降雪率的定量影响，为预测大气污染对山区降雪的影响提供了新的能力，改变了水资源至关重要的地区的分水岭。该项目还应有助于更好地了解如何在天气和气候模型中体现空气污染的影响，特别是在它们影响降水的情况下。

This is a collaborative project to study the effect of air pollution on snowfall rates and amounts. Previous work by two of the investigators (Borys and Lowenthal) developed evidence suggesting that the particles in polluted air decrease snowfall rates and amounts. The mechanism, not fully documented but clearly suggested by earlier work, is that the higher particle concentrations associated with air pollution contain increased numbers of cloud condensation nuclei (CCN), the particles on which cloud droplets form. Pollution thus increases the concentration of cloud droplets but decreases their average size, and so decreases the efficiency with which falling ice crystals grow by collision with the supercooled droplets. Pollution therefore reduces precipitation by reducing the amount of supercooled water collected from clouds and deposited in snowfall. The study will take additional steps toward determining how snowfall from winter orographic clouds, observed at the Desert Research Institute's Storm Peak Laboratory, is reduced by the high concentration of aerosol particles associated with pollution. This extension of previous work will include direct measurement of the CCN, continued observations of snowfall and precipitation, and modeling to establish the physical links between pollution and snowfall amount. The project will use a mesoscale model that has demonstrated skill in predicting precipitation rates and amounts. Key objectives are these:* To determine the relationship between pollution-aerosol loading and snowfall rate;* To determine the relative importance of riming, snow crystal size, crystal habit, and large-scale meteorological features in determining the snowfall rate;* To conduct sensitivity studies of effects including the above using the RAMS mesoscale model with bin-emulating microphysics; and* To estimate the quantitative effect of pollution aerosol on snowfall rate and amount in the study region through use of the mesoscale model.The anticipated result is a new ability to predict how air pollution affects snowfall in pristine mountainous areas and so changes the watershed in areas where water resources are critically important. The project should also lead to improved understanding of how to represent the effects of air pollution in models of weather and climate, especially as they influence precipitation.