Cloud and Precipitation Studies Using Millimeter-Wavelength Radars

云在地球气候系统中起着至关重要的作用，它调节辐射的传入和传出，并影响大气水文循环。政府间气候变化专门委员会（IPCC，2013年）的报告指出，云及其复杂的反馈是未来气候预测不确定性的主要来源，因为它们在全球气候模型中的适当表现仍然是一个挑战。为了充分了解云的作用并改进其在数值模式中的参数化，需要对云和降水的形成、演变和消散进行所有重要尺度的基础（过程）研究。 毫米波长（云）雷达通过充分探测云和降水，弥补了地球水文循环观测的空白，从而提供了对水循环的独特和更全面的看法。使用云雷达作为云尺度过程的钥匙孔，并与其他光学或微波传感器的协同作用，我们建议在两个简单的，层状云系统，发挥最大的影响，在地球的气候：海洋层积云和北极混合相云的降水生产和反馈。 在-40 ° C到0°C之间的温度下，过冷液态水滴和固态冰晶共存的混合相云特别有问题。在世界各地的许多地方，在所有季节都可以观察到混合相云，可以覆盖广泛的区域，并且可以长期存在。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层状形式出现，在云-表面辐射相互作用中发挥主导作用，其出现的增加增加了净表面长波辐射，并可能减少冬季海冰厚度和夏季海冰稳定性。正是大气垂直运动、水汽、液体和冰之间复杂的相互作用使得混合相云的相分离和垂直结构的正确表征变得困难。拟议的研究将调查微物理过程，确定冰从混合相云底部沉淀的速度。 拟议的研究还旨在增加我们对大气研究中一个长期存在的问题的理解;什么物理过程是导致浅暖云降水开始的原因。综合数据和模式分析的主要目标是了解在不同时间和空间尺度上海洋层积云中引起降水的过程的内部运作，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.