Collaborative Research: Physics of Stratocumulus Top (POST)

加利福尼亚西海岸外的层积云（Sc）将使用飞机测量和建模相结合的方法进行研究。目的是提高对Sc顶附近发生的物理过程的理解，这些物理过程影响云顶夹带过程和整体边界层演化。这些过程包括风切变、夹带速率、CTEI（云顶夹带不稳定性）、太阳和红外辐射、水流星和CCN（云凝结核）效应，以及EIL（夹带界面层）的形成和作用。这项研究结合了实地测量和建模。对于前者，CIRPAS双水獭研究飞机将部署在蒙特利，在南卡罗来纳州进行约20次飞行。它将携带全套传感器，以产生与这些物理过程相关的测量。传感器包括UFT（超快速温度探头），PVM（快速颗粒体积监测仪），快速莱曼-阿尔法湿度计，PDI（相控多普勒干涉测量探头），其他液滴探头，阵风探头，太阳和红外辐射计，以及记录气象和飞机操作特性的双水獭探头标准集。该飞机将主要部署在不间断的Sc领域，重点是在Sc顶层的上方、上方和下方垂直进行鼠式机动，以探测条件的细微变化。边界层剖面和近地表水平分支将被用来推导通过亚云边界层的通量剖面。NexSat和CloudSat产品将与飞机实时测量结果进行比较，并用于帮助飞机向Sc场方向移动。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夹带速度进行比较，目的是澄清各种过程对夹带速度的影响。研究的建模阶段将涵盖与这些物理过程相关的广泛尺度。LEM（线性涡流模型）着眼于与液滴尺寸变化相关的最细尺度。新的精细尺度LES（大涡模拟）将被应用，其网格分辨率可与预期典型夹带包裹尺寸相关的几米尺度相媲美。中尺度模型（COAMPS）将用于研究Sc和边界层的更大尺度行为，也将用于实时预测飞机的部署。将对云顶夹带速度的参数化进行评估和改进。该项目的知识价值将是改进对亚热带海洋大面积上发现的Sc的行为和进化的预测。这已被证明是困难的，因为对所涉及的物理过程的理解并不完善，而且无法准确地测量它们。为了更好地理解，最重要的是娱乐过程。文献表明，缺乏测量成功和预测能力的这一重要过程，影响Sc寿命。本研究使用飞机测量和建模的独特组合来关注这一缺陷。首次在固定翼飞机上使用了同步定位的高速微物理、热力学和湍流探头，用于揭示Sc顶部附近的物理相互作用。更广泛的影响源于对Sc行为和进化的更好理解，将是预测在大海域发现的低层层积云行为的能力。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。

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.