Collaborative Research: Isotopic Fractionation in Snow (IFRACS)

这一合作项目力求增进对混合相地形云中的降水过程以及降雪的同位素特征变化的了解，这些变化与气溶胶对云微物理的影响有关。这项研究将使用沙漠研究所(DRI)风暴高峰实验室(SPL，海拔3210米)的水蒸气、云水和雪的同位素含量的测量和模拟来检验以下假设：1)与结冰和结冰抑制相关的雪的同位素组成的变化是显著的；以及2)云底附近云滴和降雪的同位素组成和化学足以解决蒸汽沉积和结冰在雪生长中的相对作用。使用新的启用同位素的天气研究和预报(WRF)模型的模型模拟将用于测试基于观测的推论，即通过结冰和水汽沉积形成积雪，它们发生的海拔高度，以及气溶胶浓度变化对降雪同位素组成的影响。降雪的同位素组成对气溶胶引起的边缘质量分数变化的敏感性将通过模型模拟在一系列气溶胶浓度范围内进行，该模型基于SPL冬季风暴期间代表各种气象和天气条件的观测案例研究。特定地点降水的同位素组成反映了当地的云过程以及上风冷凝、蒸发和混合的历史。在这项工作中，将探索气溶胶引起的混合相地形云变化对降雪同位素含量的影响。在SPL的冬季风暴中，由于气溶胶引起的云滴尺寸的减小而抑制了积雪的增长。更广泛的影响：在本项目期间，使能同位素的微型物理模型对世界资源框架社区的贡献，将使这些方法能够在一般循环和水循环研究中得到更广泛的应用。冰川冰中记录的同位素信号被用作过去气候的替代记录。冰川上的低水平旋转可能会导致与全球温度无关的同位素信号的一部分。该项目涉及来自DRI和哈佛大学的研究生参与和培训实地项目和建模研究。在野外实验季节，SPL将为本科生和研究生主办威斯康星大学、北卡罗来纳州立大学和科罗拉多大学的大气科学野外课程。作为这项工作的一部分，将为每个班级举办一系列关于在环境科学中使用同位素签名的讲座。关于SPL研究项目的报道已经出现在美国有线电视新闻网、美国全国广播公司、国家公共广播电台、国家地理探索者、地方电视台、美国各地的报纸和NCAR EOL频道(http://tinyurl.com/ISPAscience).SPL完整地参与了来自全国各地电视台的气象学家的汽船天气峰会。这些活动将与SPL的冬季实地考察同时进行，并将在气候峰会上介绍有关这项工作的讲座。研究人员还将在蒸汽船温泉举办一个社区讲座，并在SPL举办一个“开放参观”活动，分享这项研究的科学动机。最后，为向中学生提供以气象学和气候为重点的动手学习而开发的课程将继续该项目，并在实地研究期间让班级观察气象气球的发射。

This collaborative project seeks to improve understanding of precipitation processes in mixed phase orographic clouds and the variation in the isotopic signature of snowfall that is associated with aerosol effects on cloud microphysics. The study will use measurements and modeling of the isotopic content of water vapor, cloud water, and snow at the Desert Research Institute's (DRI's) Storm Peak Laboratory (SPL, altitude 3210 m) to test the hypotheses that: 1) variations in the isotopic composition of snow associated with riming and riming inhibition are significant; and 2) the isotopic composition and chemistry of cloud droplets near cloud base and falling snow are sufficient to resolve the relative roles of vapor deposition and riming in snow growth. Model simulations with a new isotope-enabled version of the Weather Research and Forecasting (WRF) model will be used to test observation-based inferences on snow formation by riming and vapor deposition, the altitudes at which they occur, and the effects of variation of aerosol concentration on the isotopic composition of snowfall. The sensitivity of the isotopic composition of snowfall to aerosol-induced changes in the rimed mass fraction will be evaluated with model simulations over a range of aerosol concentration based on observational case studies representing a variety of meteorological and synoptic conditions during wintertime storms at SPL.Intellectual Merit: Riming of ice crystals in wintertime orographic clouds significantly enhances their water content and the amount of water deposited in snowfall. The isotopic composition of precipitation at a given location reflects local cloud processes as well as the history of upwind condensation, evaporation and mixing. In the work, the impact of aerosol-induced changes in mixed phase orographic clouds on the isotopic content of snowfall will be explored. Inhibition of snow growth by riming due to aerosol-induced reduction of cloud droplet size has been observed in wintertime storms at SPL. Broader Impact: The contribution of isotope-enabled microphysical models to the WRF community during this project will allow for broader application of these methodologies in studies of general circulation and the water cycle. The isotopic signal recorded in glacial ice has been used as a proxy record of past climates. Low-level riming over glacial ice may contribute to a component of the isotopic signal that is independent of global temperature. This project involves the participation and training of graduate students from DRI and Harvard in the field program and modeling studies. During the field experiment season, SPL will host atmospheric science field courses from the University of Wisconsin, North Carolina State University, and the University of Colorado for undergraduate and graduate students. As part of this work, a series of lectures will be presented to each of these classes on the use of isotopic signatures in environmental science. Reports on SPL research projects have appeared on CNN, NBC, National Public Radio, National Geographic Explorer, local television stations, in newspapers across the U.S., and the NCAR EOL Channel (http://tinyurl.com/ISPAscience). SPL is integrally involved in the Steamboat Weather Summit of meteorologists from television stations around the country. These activities will coincide with the winter field study at SPL and a talk on this work will be presented at the Weather Summit. The investigators will also present a community lecture in Steamboat Springs and an "open house" at SPL to share the scientific motivation of this research. Finally, a curriculum developed to provide middle school students with hand-on learning focused on meteorology and climate will continue with the project and have classes observe weather balloons launches during the field study.