Collaborative Research: Physics of Stratocumulus Top (POST)

将用飞机测量和模拟相结合的方法研究加州西海岸的层积云。其目的是提高对发生在Sc顶附近的物理过程的理解，并影响云顶夹带过程和整体边界层演变。这些过程包括风切变、卷吸率、CTEI（云顶卷吸不稳定性）、太阳和红外辐射、水凝物和CCN（云凝结核）效应以及卷吸界面层的形成和作用。这项研究是实地测量和建模的结合。对于前者，CIRPAS Twin Otter研究飞机将部署在蒙特雷，在旧金山进行约20次飞行，它将携带完整的传感器，以产生与这些物理过程相关的测量结果。传感器包括UFT（超快速温度探测器）、PVM（快速颗粒体积监测器）、快速莱曼-阿尔法湿度计、PDI（相位多普勒干涉测量探测器）、其他液滴探测器、阵风探测器、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獭探测器。该飞机将主要部署在未中断的Sc领域，重点是在Sc顶部水平上方，通过和下方垂直地进行海豚式机动，以检测条件的细微变化。边界层廓线和近地面水平支腿将被用来推断穿过云下边界层的通量廓线。将把NexSat和CloudSat产品与飞机的实时测量结果进行比较，并用来帮助引导飞机进入Sc场。实地研究的分析阶段包括比较测量的物理过程和计算的云顶卷吸速度，目的是澄清各种过程对卷吸速度的影响。该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）着眼于与液滴尺寸变化相关的最精细尺度。新的细尺度LES（大涡模拟）将应用网格分辨率相媲美的几米规模相关的预期典型夹带包裹的大小。中尺度模型（COAMPS）将用于研究Sc和边界层的大尺度行为，也将用于实时提供飞机部署的预测。云顶卷吸速度的参数化将得到评价和改进。该项目的智力价值将是改进对在亚热带海洋大面积发现的钪的行为和演变的预测。事实证明，这是困难的，因为对所涉及的物理过程的理解不完善，无法准确测量。为了更好地理解，优先考虑的是夹带过程。文献表明，缺乏测量成功和预测能力，这一重要的过程，影响钪寿命。 本研究采用了一种独特的飞机测量和建模相结合的方法来关注这一不足。第一次共同定位的高速率微物理，热力学和湍流探头上使用的固定翼飞机部署解开附近的Sc顶部的物理相互作用。更广泛的影响来自于对Sc行为和演化的更好理解，将是预测在大海洋区域发现的低层层积云行为的能力。这是必要的，因为它们对影响行星辐射平衡从而影响全球变暖的行星辐射的主要贡献。

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.