Indirect Aerosol Effects on Tropical Convection

气溶胶对热带对流的间接影响

• 批准号: 0820557
• 负责人: Susan van den Heever
• 金额: $ 32.22万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0820557&HistoricalAwards=false
• 关键词: Indirect; Aerosol; Effects; Tropical; Convection

The impact of aerosols--both naturally occurring and anthropogenic--upon clouds has been long recognized. In the case of more widespread stratiform type clouds (e.g., subtropical stratocumulus) and isolated convective clouds, these impacts have been rather extensively examined. Such is not the case for systems of deep clouds over broad equatorial regions, which are subject to incursions of wind-driven dust from emanating from continental deserts and urbanized areas. Work supported by this grant will be unique in examining groups of deep tropical convective cloud systems in considerable detail in order to better understand their sensitivity to incursions of microphysically active aerosol including cloud condensation nuclei (CCN) and ice nuclei (IN), which in turn influence the precipitation development and cloud-radiation interactions. Model runs will be conducted over large horizontal regions (~9600 km x 180 km at 38 vertical levels) integrated over long periods (~100 days), which will allow the simulated atmosphere to achieve a state of radiative-convective equilibrium and subsequent assessment of responses to variable amounts and vertical distributions of aerosols. Specific goals include analysis of the impacts that variable CCN and IN concentrations have upon: (1) the tropical water budget, including precipitation processes and distribution of latent heat release; (2) differentiation between the so-called "first" and "second" indirect aerosol effect, which relate to droplet sizes and number concentrations influencing radiative transfer through cloud layers; (3) cloud dynamics, such as those that may favor a previously noted tendency toward tri-modal distribution of convective cloud depth and including updrafts, downdrafts, development of low-level cold pools and other factors influencing cloud organization; (4) radiative-convective equilibrium across the tropics; (5) partitioning of water substance between liquid and ice; and (6) the anvil-cirrus properties of deep tropical convection. Simulated cloud statistics will also be compared with observed cloud properties emerging from NASA's CloudSat satellite to better assess model performance and ultimately identify those physical processes implicit in the observations.The intellectual merit of this study rests in developing an improved description of physics governing the behavior of tropical cloud systems and their role in the global climate system via a combination of cloud microphysical and radiative feedbacks. It will also advance understanding of the "radiative-convective equilibrium" paradigm thought to characterize much of the tropical atmosphere, and will facilitate extracting maximum value from newly emerging datastreams such as provided by CloudSat.Broader impacts of this work include improvement of techniques needed for medium-range forecasts of tropical cloud systems (such as those that occasionally engender tropical cyclones) as well as longer-term prediction of the earth's climate, and include graduate student education and increased involvement by underrepresented groups (viz. women in science).

气溶胶-自然产生的和人为的-对云的影响早已得到承认。在更广泛的层状云的情况下（例如，在热带层积云和孤立对流云的影响下，这些影响已经得到了相当广泛的研究。 但赤道地区上空的深云系统却并非如此，这些系统容易受到来自大陆沙漠和城市化地区的风吹尘埃的侵袭。这项赠款支持的工作将是独特的，在相当详细地检查热带深对流云系统组，以更好地了解他们的微物理活性气溶胶入侵的敏感性，包括云凝结核（CCN）和冰核（IN），这反过来又影响降水的发展和云辐射相互作用。模型运行将在长时间（约100天）综合的大面积水平区域（约9 600公里x180公里，38个垂直高度）进行，这将使模拟的大气达到辐射-对流平衡状态，并随后评估对气溶胶的可变数量和垂直分布的反应。具体目标包括分析不同的云凝结核和无机氮浓度对以下方面的影响：（1）热带水收支，包括降水过程和潜热释放的分布;（2）区分所谓的“第一”和“第二”间接气溶胶效应，这与影响通过云层的辐射传输的液滴大小和数量浓度有关;（3）云的动力学，如有利于前面提到的对流云深度的三模态分布的趋势，包括上升气流、下降气流、低空冷池的发展和其它影响云组织的因素;（4）横跨热带的辐射-对流平衡;（5）水物质在液体和冰之间的分配;（6）热带深对流的砧卷云特征。 模拟的云统计数据也将与从美国宇航局的CloudSat卫星观测到的云特性进行比较，以更好地评估模式性能，并最终确定观测中隐含的物理过程。反馈它还将促进对“辐射-对流平衡”范式的理解，这种范式被认为是热带大气的特征，这项工作的更广泛影响包括改进热带云系中期预报所需的技术（如偶尔产生热带气旋的那些）以及对地球气候的长期预测，并包括研究生教育和增加代表性不足的群体（即科学界的妇女）的参与。