A Modeling Study of Factors that Control the Vigor of Deep Cumulus Convection

观测显示热带和中纬度夏季深层对流（例如雷暴活动）的强度有很大的变化，这些变化不能用基于简单原理的大气不稳定性的现有测量方法很好地解释。这些经典的处理方法解决了从均匀加热的平面上升的未稀释空气相对于周围环境的特性，以确定对流云所达到的最大上升气流强度和高度。本研究将采用能够解决影响此类云的多种因素的模式计算，以更好地理解和量化变化的中层大气湿度、地表加热的异质性和地表地形（即斜坡和高架地形）在决定其活力方面的作用。由此产生的这些复杂效应的简化表示（称为“参数化”）的改进将最终改进全球气候模式。本次探索中使用的主要云分辨数值系统将是天气研究与预报（WRF）模式，该模式将辅以更理想化的计算，以帮助理解对流云活力与简单包理论预测的偏离，并更全面地解开因果关系。该策略将涉及精心设计的WRF模型运行组（集合），以系统地探索云行为作为关键环境因素的函数的变化。这项工作的智力价值在于通过一系列概念和数值模型来推进我们对潮湿浮力驱动的大气对流的基本理解，这将使研究人员能够发展和测试有关控制对流的活力和热传输特性的因素的基本假设，并最终确定这些云在全球大气环流中作为一种“湍流”形式的作用。这项工作的更广泛影响将包括对更精确地模拟局部/区域天气和全球气候的贡献，以及在气候变化存在的情况下更可靠地预测对流活动的预期变化的手段。通过“DEMOS”项目（耶鲁大学的一个本科生组织，在周边地区开展推广活动），对一名本科生进行设计和操作云解析模型的基本要素培训（适合作为该学生选择的气象学职业的介绍），并加强公立学校学生对科学的接触，这将是这一努力的额外影响。

Observations show substantial variations in the intensity of both tropical and midlatitude-summertime deep convection (e.g., thunderstorm activity) that are not well explained by established measures of the atmosphere's instability based on simple principles. These classic treatments address properties of undiluted parcels of air ascending from a uniformly heated flat surface relative to their surrounding environment to determine the maximum updraft intensity and height achieved by convective clouds. This research will employ model calculations capable of resolving multiple factors influencing such clouds to better understand and quantify the role of variable mid-level atmospheric moisture, heterogeneity in surface heating, and surface orography (i.e. sloped and elevated terrain) in determining their vigor. Resulting improvements in simplified representations of these intricate effects (termed "parameterizations") will ultimately improve global climate models. The primary cloud-resolving numerical system used in this exploration will be the Weather Research and Forecasting (WRF) model, which will be supplemented by more idealized calculations to help understand departures of convective cloud vigor from that predicted by simple parcel theory and to more fully disentangle cause and effect. This strategy will involve carefully designed groups (ensembles) of WRF model runs to systematically explore changes in cloud behavior as a function of key environmental factors. The intellectual merit of this work rests on advancing our basic understanding of moist buoyantly-driven atmospheric convection through a hierarchy of conceptual and numerical models, which will allow researchers to develop and test basic hypotheses concerning factors that control the vigor and heat transport properties of convection, and ultimately the role of such clouds as a form of "turbulence" within the global atmospheric circulation.Broader impacts of this work will include contributions toward more accurate simulations of local/regional weather and global climate, as well as means to more reliably anticipate expected changes in convective activity in the presence of climate change. Training of an undergraduate student in basic elements of design and operation of cloud-resolving models (suitable as an introduction to a chosen career in meteorology for that student) and enhanced exposure of public school students to science through the "DEMOS" program (a Yale University undergraduate organization that does outreach in the surrounding area) will be additional impacts of this effort.