Cloud and Precipitation Studies Using Millimeter-Wavelength Radars

云通过调节进出辐射和影响大气水文循环，在地球气候系统中发挥着至关重要的作用。政府间气候变化专门委员会报告(IPCC，2013)指出，云层及其复杂的反馈是未来气候预测的一个主要不确定性来源，因为它们在全球气候模型中的适当表现仍然是一个挑战。为了充分理解云的作用并改进其在数值模式中的参数化，需要在所有尺度上进行对云和降水的形成、演变和消散具有重要意义的基础(过程)研究。 毫米波(云)雷达通过充分探测云和降水，弥补了地球水循环中的观测空白，从而提供了水循环实际情况的独特和更全面的看法。利用云雷达作为云尺度过程中的一个钥匙孔，并与其他光学或微波传感器协同工作，我们建议研究对地球气候影响最大的两个简单的层状云系的降水产生和反馈：海洋层积云和北极混合相云。 过冷液态水滴和固体冰晶在-40°C至0°C温度下共存的混合相云尤其成问题。混合相云在世界各地的许多地方随时随地都能观测到，可以覆盖大片区域，而且可以持续很长时间。在对气候变化特别敏感的北极地区，它们以持续的单层或多层形式出现，在云-表面辐射相互作用中起主导作用，它们的出现增加了地表净长波辐射，可能会降低冬季海冰厚度和夏季海冰稳定性。正是大气垂直运动、水汽、液体和冰之间的复杂相互作用，使得对混合相云的相划分和垂直结构的适当描述变得困难。这项拟议的研究将调查微物理过程，这些过程决定了冰从混合相云底部沉淀的速度。 这项拟议的研究还旨在加深我们对大气研究中一个长期存在的问题的理解：什么物理过程导致了浅层暖云中降水的开始。综合数据和模式分析的主要目标将是了解海洋层积云在不同时间和空间尺度上启动降水的过程的内部机制，并通过这种了解，为全球模式中的云参数化发展提供信息。

Clouds play a crucial role in the Earth’s climate system by regulating incoming and outgoing radiation and by influencing the atmospheric hydrological cycle. The Intergovernmental Panel on Climate Change report (IPCC, 2013) identified clouds and their complex feedbacks as a major source of uncertainty for future climate projections because their proper representation in global climate models remains a challenge. In order to adequately understand the role of clouds and improve their parameterization in numerical models, fundamental (process) studies on all scales important to cloud and precipitation formation, evolution and dissipation are required. Millimeter-wavelength (cloud) radars bridge an observational gap in Earth’s hydrological cycle by adequately detecting clouds and precipitation thus offering a unique and more holistic view of the water cycle in action. Using cloud radars as a keyhole in cloud-scale processes and in synergy with other optical or microwave sensors, we propose to work on the precipitation production and feedbacks in two simple, stratiform cloud systems that exert the largest effect in Earth’s climate: marine stratocumulus and Arctic mixed-phase clouds. Mixed-phase clouds in which supercooled liquid water droplets and solid ice crystals coexist at temperatures between -40°C and 0°C are particularly problematic. Mixed-phase clouds are observed in many locations worldwide in all seasons, can cover extensive areas, and can be long-lived. In the Arctic, a region particularly sensitive to climate change, they occur as persistent single- or multiple stratiform layers and play a dominant role in cloud-surface radiative interactions, an increase in their occurrence increases the net surface longwave radiation and probably reduces winter sea ice thickness and summer sea-ice stability. It is the complex interaction between atmospheric vertical motions, water vapor, liquid, and ice that makes the proper characterization of the phase partitioning and vertical structure of mixed-phase clouds difficult. The proposed research will investigate the microphysical processes that determine the rate at which ice is precipitating from the base of mixed-phase clouds. The proposed research also aims to add to our understanding of one of the longstanding problems in atmospheric research; what physical processes are responsible for the onset of precipitation in shallow warm clouds. The primary objective of the combined data and model analyses will be to understand the inner-workings of the processes responsible for precipitation initiation in marine stratocumulus clouds at different time and space scales and, through that understanding, to inform cloud parameterization development in global models.