Impact of Sahara Dust Layers on Convective Cloud Development and Precipitation over the Tropical Eastern Atlantic Ocean

在所有已知的气候强迫机制中，间接影响目前在气候预测中产生了最大的不确定性。尽管热带深对流云系对大尺度大气环流有很大的影响，但很少有人研究气溶胶对深对流云系的影响。为了提高我们对气溶胶间接影响的理解，并更好地量化它们在区域和全球气候变化中的作用，需要创新的方法。本研究的总体目标是利用天气研究和预报(WRF)模式的综合观测分析和云分辨模拟，结合光谱面元微物理(SBM)计划，评估矿物尘埃如何影响热带深对流云系的发展，并了解沙尘间接影响观测变化的机制。我们的综合卫星和来自多个仪器/平台的现场数据与我们的创新分析技术相结合，将极大地有利于研究界解决气溶胶-云相互作用的关键问题，并在区域和全球气候模型-网格尺度上开发和验证高级模式中气溶胶-云-降水相互作用的真实表示。预期这项研究工作将取得两项成果，即：(1)造成观测到的对流核心、层状/砧状和从无尘区到尘埃区的降水变化的机制，以及(2)估计沙尘对深对流云造成的云性质和降水量的变化。沙尘通过改变辐射加热的半直接作用和作为云凝结核(CCN)和冰核(IN)的间接作用影响云的性质。在温度较高的深对流云中，尘埃造成的非均匀成核可能会改变潜热的垂直分布和过冷水的垂直分布。热带深对流系统的这些变化也将对大尺度环流产生重大影响。然而，气溶胶-云相互作用是气候系统中最不了解的方面，我们对气溶胶作为冰核(IN)对混合相云和冰云的影响的了解是最差的。必须进行全面的观测和模式模拟，以评估和了解沙尘气溶胶对云的间接和半直接影响的物理过程。这项工作的结果将补充我们对气溶胶-云-气候相互作用的理解，并有利于气候界估计沙尘对气候变化的贡献。通过学生培训和教育外展，不同层次的学生将对当前的气候问题有一些了解。

The indirect effect currently produces the greatest uncertainty in climate predictions among all known climate forcing mechanisms. Although tropical deep-convective cloud systems have great impacts on large-scale atmospheric circulation, few studies investigate the aerosol impacts on deep convective cloud systems. To improve our understanding of the aerosol indirect effect, and to better quantify their role in regional and global climate changes requires innovative approaches.Intellectual MeritThe overarching goal of this research is to utilize comprehensive observation analysis and cloud resolving simulations using Weather Research and Forecast (WRF) model coupled with a spectral bin microphysics (SBM) scheme to assess how mineral dust affects the development of tropical deep-convective cloud systems, and to understand mechanisms responsible for the observed changes of dust indirect effect. The combination of our integrated satellite and in-situ data from multiple instruments/platforms and our innovative analysis techniques will greatly benefit research community to address key questions of aerosol-cloud interaction and to develop and validate the realistic representation of aerosol-cloud-precipitation interactions in advanced models on regional and global climate model-grid scales. Two outcomes are expected from this research effort, i.e., (1) the mechanisms responsible for the observed changes in convective core, stratiform/anvil, and precipitation from the dust-free sector to the dust sector, and (2) an estimation of the changes in cloud properties and precipitation imposed by dusts on the deep convective clouds.Broader ImpactAs one of the major sources of aerosols, Saharan dust can be transported across the tropical North Atlantic and into the Caribbean region as well as into Europe. Dust affects cloud properties by the semi-direct effect through changing the radiative heating, and by the indirect effect through acting as cloud condensation nuclei (CCN) and ice nuclei (IN). The heterogeneous nucleation imposed by dust occurs at warmer temperature in a deep convective cloud could potentially change the vertical profile of latent heat and the vertical distribution of supercooled water. These changes in the tropical deep convective systems will have substantial impacts on large scale circulation as well. Nevertheless, the aerosol-cloud interaction is the least understood aspect in the climate system, of which our understanding of the impact of aerosols on mixed-phase and ice clouds by acting as ice nuclei (IN) is the poorest. It is vital to have comprehensive observations and model simulation to assess and understand the physical processes of the indirect and semi-direct effects of dust aerosols on clouds. The outcomes of this work will complement our understanding of aerosol-cloud-climate interactions and benefit the climate community to estimate of the contribution of dust to climate change. Through student training and education outreach, students from various levels will gain some understanding on current climate issues.