Cloud and Precipitation Studies Using Millimeter-Wavelength Radars

云通过调节进出的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）将云及其复杂反馈确定为未来气候预测的主要不确定性来源，因为它们在全球气候模型中的适当代表仍然是一个挑战。为了充分理解云的作用并改进其在数值模式中的参数化，需要在所有尺度上对云和降水的形成、演化和消散进行基本（过程）研究。

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.