CAREER: The Role of Mineral Dust in Atmospheric Ice Formation, and its Impacts on Past, Present and Future Climate

这是一项职业奖，其中研究部分考察了尘埃颗粒在混合相云(包含液态水滴和冰粒的云)中作为冰核(IN)的作用对气候的影响。矿物尘埃颗粒(由土壤矿物组成的颗粒，而不是烟尘和生物材料)是大气中最重要的IN，它们可以通过增加云冰颗粒的浓度来改变云的辐射特性，但代价是过冷的液态水滴。来自冰芯的测量表明，在冰期和间冰期之间，大气中的尘埃浓度变化了三到四倍，因此尘埃对云层的调制可能会对气候产生重要影响。此外，包括荒漠化在内的土地覆盖变化对大气沙尘的人为贡献估计高达总负荷的25%，因此沙尘在冰核形成中的作用可能导致对气候的人为影响。该项目的第一个任务是改进大气环流模式(AGCM，包括耦合气候模式的大气分量模式)中矿物尘埃对云冰成核影响的表示。该项目的初步工作表明，与卫星观测相比，AGCM模拟的云中缺乏过冷的液态水滴。该项目的工作是基于这样的假设，即这种缺陷是由于Wegener-Bergeron Findeison(WBF)过程的夸大所致，在WBF过程中，由于液态水和冰上的饱和蒸汽压的差异，云冰颗粒的增长以牺牲邻近的过冷液滴为代价。在本质上，这一过程受到对小规模上升气流和下降气流运动的依赖的限制，这些运动造成了当地的大气温度，这可能对该过程不利。在该项目下开展的工作将开发一种参数化法，以确定这些小尺度垂直运动的影响，这些运动发生在空间尺度上太小，无法在目前的AGCMS中分辨。一旦建立了参数，它将被用来处理关于尘埃对云的影响以及这些影响的气候后果的若干问题，包括：当考虑到尘埃-冰云效应时，矿物尘埃扰动在地球大气中的净辐射影响是什么？过去气候中的尘埃扰动是否通过尘埃对含冰云的影响而显著影响了那些气候？二十世纪大气尘埃负荷的变化是否通过对含冰云的影响而成为一种重要的气候强迫？在目前的大气矿物尘埃负荷下，含冰的云层对IN扰动的敏感度如何？这份职业建议书的教育部分是与耶鲁科学合作动手学习和研究(SCHOLAR)计划合作组织的，该计划提供为期两周的STEM领域的校园住宿暑期学习计划。奖学金项目的学生来自纽黑文公立高中系统，超过一半的学生来自代表性较低的群体，在许多情况下，他们来自他们将是第一个完成大学学业的家庭。该奖项下的工作将为SCARTER项目开发一个模块，向学生介绍大气和气候科学领域，更具体地说，介绍气溶胶和云在塑造天气和气候方面所起的作用。该单元包括课堂和实验室活动，每年夏天，四名学生被选为一组，参加来年春季在科罗拉多州斯普林斯的Storm Peak实验室(SPL)的实地体验。学生们在SPL花了四天时间在PI的监督下测量气溶胶和云层，并在他们的学校和下一次学者会议上介绍他们的研究。此外，PI还维护着一个博客，学生们在访问SPL之前、期间和之后都可以在博客上发表意见。

This is a CAREER award in which the research component examines the climatic impacts of dust particles due to their role as ice nuclei (IN) in mixed phase clouds (clouds containing both liquid water droplets and ice particles). Mineral dust particles (particles composed of soil minerals, as opposed to soot and biological materials) are the most important IN in the atmosphere, and they can change the radiative properties of clouds by increasing the concentration of cloud ice particles at the expense of supercooled liquid water droplets. Measurement from ice cores suggest that atmospheric dust concentration varies by a factor of three to four between ice ages and interglacials, thus the modulation of clouds by dust could have important climatic consequences. In addition, the anthropogenic contribution to atmospheric dust, through changes in land cover including desertification, is estimated to be as high as 25% of the total burden, so that the role of dust in ice nucleation could lead to anthropogenic influences on climate.The first task of the project is to improve the representation of the effect of mineral dust on cloud ice nucleation in atmospheric general circulation models (AGCMs, including the atmospheric component models of coupled climate models). Preliminary work for the project shows that AGCM-simulated clouds are deficient in supercooled liquid water droplets in comparison to satellite observations. Work in this project is based on the hypothesis that this deficiency is due to an exaggeration of the Wegener-Bergeron Findeison (WBF) process, in which cloud ice particles grow at the expense of neighboring supercooled droplets due to the difference in saturation vapor pressure over liquid water and ice. In nature the process is limited by its dependence on small-scale updraft and downdraft motions, which create local atmospheric temperatures which can be unfavorable to the process. Work under this project will develop a parameterization the effect of these small-scale vertical motions, which occur on spatial scales too small to resolve in current AGCMs. Once the parameterization is developed, it will be used to address several questions regarding the effects of dust on clouds and the climatic consequences of these effects, including: What is the net radiative effect of mineral dust perturbations in Earth's atmosphere when dust-ice-cloud effects are taken into account? Have the dust perturbations in past climates significantly impacted those climates via dust effects on ice-containing clouds? Have variations in atmospheric dust loadings over the twentieth century acted as an important climate forcing via effects on ice-containing clouds? Under the current atmospheric mineral dust loading, how sensitive are ice-containing clouds to IN perturbations?The educational component of this CAREER proposal is organized in collaboration with the Yale Science Collaborative Hands-On Learning and Research (SCHOLAR) program, which offers a two-week on-campus residential summer learning program in STEM fields. Students in the SCHOLAR program come from the New Haven public high school system, and more than half of the students are from underrepresented groups, in many cases from families in which they would be the first to complete college. Work under this award will develop a module for the SCHOLAR program to introduce students to the fields of atmospheric and climate science, and more specifically to the roles played by aerosols and clouds in shaping weather and climate. The module includes both classroom and laboratory activities, and each summer a group of four students is selected to participate in a field experience at the Storm Peak Laboratory (SPL) in Steamboat Springs Colorado, during the following Spring. The students spend four days at SPL making measurements of aerosols and clouds under the PI's supervision, and make presentations of their research at their schools and at the next SCHOLAR session. In addition, the PI maintains a blog to which students contribute before, during, and after their visit to SPL.