Collaborative Research: Physics of Stratocumulus Top (POST)

合作研究：层积云顶部物理学（POST）

• 批准号: 0735121
• 负责人: Hermann Gerber
• 金额: --
• 依托单位: Gerber Scientific Inc.
• 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: 2008-01-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0735121&HistoricalAwards=false
• 关键词: Collaborative; Research; Physics; Stratocumulus; Top

Stratocumulus clouds (Sc) off the west coast of California will be studied using a combination of aircraft measurements and modeling. The objective is to improve the understanding of the physical processes that occur near Sc top, and that influence the cloud-top entrainment process and overall boundary-layer evolution. These processes include wind shear, entrainment rate, CTEI (cloud-top entrainment instability), solar and infrared radiation, hydrometeor and CCN (cloud condensation nuclei) effects, and the formation and role played by the EIL (entrainment interface layer). The study is a combination of field measurements and modeling. For the former, the CIRPAS Twin Otter research aircraft will be deployed out of Monterey for ~20 flights in Sc. It will carry a full complement of sensors to produce measurements related to these physical processes. Sensors include the UFT (ultra-fast temperature probe), PVM (fast particulate volume monitor), fast Lyman-Alpha hygrometer, PDI (phased Doppler interferometry probe), other droplet probes, gust probe, solar and infrared radiometers, and the standard set of Twin-Otter probes recording meteorology and aircraft operating properties. The aircraft will be deployed primarily in fields of unbroken Sc with an emphasis on porpoising maneuvers vertically above, through, and below the Sc top level to detect fine-scale changes in conditions. Boundary layer profiles and near-surface horizontal legs will be flown to deduce flux profiles through the sub-cloud boundary layer. NexSat and CloudSat products will be compared to aircraft measurements in real-time and used to help vector the aircraft to fields of Sc. The analysis phase of the field study includes comparisons between the measured physical processes and the calculated cloud-top entrainment velocities with the purpose of clarifying the influence of various processes on the entrainment velocities. The modeling phase of the study will cover a wide range of scales associated with these physical processes. The LEM (linear eddy model) looks at the finest scales associated with droplet size changes. New fine-scale LES (large-eddy simulation) will be applied with grid resolution comparable to the several-meters scale associated the expected typical entrained parcel size. A mesoscale model (COAMPS) will be used to study the larger-scale behavior of the Sc and the boundary layer, and also will be used in real-time to provide predictions for deploying the aircraft. Parameterizations of the cloud top entrainment velocity will be evaluated and improved. The intellectual merit of the project will be improved prediction of the behavior and evolution of Sc found over large areas of the sub-tropical oceans. This has proved to be difficult because of the imperfect understanding of the physical processes involved and the inability to measure them accurately. High on the priority list for better understanding is the entrainment process. The literature shows a lack of measurement success and predictive capability for this important process that affects Sc lifetime. This study uses a unique combination of aircraft measurements and modeling to focus on this deficiency. For the first time co-located high-rate microphysical, thermodynamic, and turbulence probes are used on a fixed-wing aircraft deployed for unraveling the physical interactions near Sc top. Broader impacts derive from this improved understanding of Sc behavior and evolution will be the ability to predict the behavior of low-level stratocumulus found over large ocean areas. This is needed given their major contribution to the planetary albedo that affects the planetary radiation balance and thus global warming.

将结合飞机测量和建模来研究加利福尼亚州西海岸的层积云(SC)。其目的是为了提高对SC顶部附近发生的物理过程的理解，这些物理过程影响云顶卷吸过程和整个边界层的演变。这些过程包括风切变、夹卷速率、云顶夹带不稳定(CTEI)、太阳和红外辐射、水流星和云凝结核(CCN)效应以及夹带界面层(EIL)的形成和作用。这项研究是现场测量和建模相结合的。对于前者，CIRPAS双水獭研究飞机将部署在蒙特利以外的南卡罗来纳州进行约20次飞行。它将携带一整套传感器，以产生与这些物理过程相关的测量结果。传感器包括UFT(超快温度探头)、PVM(快速颗粒体积监测器)、FAST Lyman-Alpha湿度计、PDI(相控多普勒干涉探头)、其他水滴探头、阵风探头、太阳和红外辐射计，以及记录气象和飞机运行特性的标准双水口探头。该飞机将主要部署在未中断的SC领域，重点是在SC顶层上方、穿过和下方垂直移动，以检测条件的细微变化。边界层廓线和近地面水平支路将被飞行，以推断通过次云边界层的通量廓线。NEXSAT和CloudSat产品将与飞机的实时测量进行比较，并用于帮助将飞机引导到SC的领域。现场研究的分析阶段包括将测量的物理过程与计算的云顶卷吸速度进行比较，目的是澄清各种过程对卷吸速度的影响。这项研究的建模阶段将涵盖与这些物理过程相关的各种尺度。LEM(线性涡流模型)着眼于与液滴大小变化相关的最精细尺度。新的细比例尺LES(大涡模拟)将被应用，其网格分辨率可与与预期的典型包裹大小相关的几米尺度相媲美。中尺度模式(COAMPS)将被用来研究SC和边界层的更大尺度行为，也将被实时用于为飞机的部署提供预测。将对云顶卷吸速度的参数进行评估和改进。该项目的学术价值将是改进对在亚热带海洋大片区域发现的SC的行为和演变的预测。这已被证明是困难的，因为对所涉及的物理过程的了解还不完善，而且无法准确地测量它们。为了更好地理解，优先考虑的是夹带过程。文献表明，对于影响SC寿命的这一重要过程，缺乏测量成功率和预测能力。这项研究使用了独特的飞机测量和建模相结合的方法来关注这一不足。首次在固定翼飞机上使用共置的高速微物理、热力学和湍流探测器来解开SC顶部附近的物理相互作用。这种对SC行为和演化的更好理解将产生更广泛的影响，即能够预测在大片海洋地区发现的低层积云的行为。鉴于它们对影响行星辐射平衡从而影响全球变暖的行星反照率的主要贡献，这是必要的。