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首页> 外文学位 >Mixed-layer models and large-eddy simulations of stratocumulus-topped marine boundary layers: Their nonlinear dynamics and sensitivity to cloud droplet concentration.
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Mixed-layer models and large-eddy simulations of stratocumulus-topped marine boundary layers: Their nonlinear dynamics and sensitivity to cloud droplet concentration.

机译：层积云顶海洋边界层的混合层模型和大涡模拟：它们的非线性动力学和对云滴浓度的敏感性。

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摘要

Due to their high albedo and weak greenhouse effects, low stratiform clouds have a strong tendency to cool the earth and are an important factor in predicting global climate. However, they are difficult to accurately simulate in global climate models, leading to large disparities between the responses of leading global climate models to increased greenhouse gases and aerosols. Marine subtropical stratocumulus-topped boundary layers that persist over cool ocean waters such as off the coast of California or Chile are particularly challenging due to a strong and sharp capping inversion that is difficult for the grids of numerical models to resolve, as well as the clouds themselves being thin, radiatively active, and sometimes drizzling.;We use a simple model problem to look at effects of aerosols on the properties of stratocumulus cloud-topped boundary layer, which can help us better understand the effect of human-generated aerosols on climate. We compare simulations with two models, a simple Mixed-Layer Model (MLM) and a much more complex and computationally intensive Large-Eddy Simulations (LES). Our model problem is idealized from an observed case, Research Flight 1 of the Second Dynamics and Chemistry of Marine Stratocumulus Experiment (DYCOMS-II) 300 km southwest of San Diego. Simulations with different values of cloud droplet condensations are run to steady state and compared to each other.;The MLM is a 3-variable autonomous system of ordinary differential equations which we study using phase plane analysis. This leads to the idea of a one-dimensional slow manifold and multiple long-term evolutions depending on the initial boundary layer depth, which prove to be very helpful in understanding the LES as well as the MLM. For high droplet concentrations, the LES displays two slow manifolds leading into two stable steady states, a well-mixed stratocumulus layer and a decoupled boundary layer with thin, broken cloud. This is the first time that an LES of boundary layer clouds has been shown to have multiple equilibria, which has important consequences for the sensitivity of cloud-topped boundary layers to their initial and boundary conditions as well as their sensitivity to climate perturbations.
机译：由于层状反照率高和温室效应弱，低层状云很容易使地球降温，并且是预测全球气候的重要因素。但是，很难在全球气候模型中准确模拟它们，从而导致领先的全球气候模型对温室气体和气溶胶增加的响应之间存在巨大差异。持续存在于诸如加利福尼亚或智利海岸之类的凉爽海洋水域上的海洋亚热带平流层顶边界层特别具有挑战性，这是因为强大而尖锐的封盖反演难以使数值模型的网格以及云层难以解析自身薄，辐射活跃，有时会下毛毛雨;;我们使用一个简单的模型问题来研究气溶胶对平积云云顶边界层性质的影响，这可以帮助我们更好地了解人为产生的气溶胶对气候的影响。我们将模拟与两个模型进行比较，一个是简单的混合层模型（MLM），另一个是复杂得多且计算量大的大涡模拟（LES）。我们的模型问题是根据观察到的案例理想化的，该案例是圣地亚哥西南300公里处的第二次海洋层积云动力学和化学实验（DYCOMS-II）的研究飞行1。具有不同值的云滴凝结的模拟运行到稳态并相互比较。MLM是一个三变量的常微分方程的自治系统，我们将使用相平面分析进行研究。这导致一维缓慢流形和依赖于初始边界层深度的多次长期演化的思想，这被证明对理解LES和MLM非常有帮助。对于高液滴浓度，LES显示两个缓慢的歧管，通向两个稳定的稳态，一个混合均匀的平流层和一个解耦的边界层，其中有薄而破碎的云。这是首次证明边界层云的LES具有多重平衡，这对云层顶边界层对其初始条件和边界条件的敏感性以及对气候扰动的敏感性具有重要意义。

著录项

  • 作者

    Uchida, Junya.;

  • 作者单位

    University of Washington.;

  • 授予单位 University of Washington.;
  • 学科 Applied Mathematics.;Atmospheric Sciences.;Meteorology.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 141 p.
  • 总页数 141
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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