A dual perspective on cloud-aerosol-radiation interaction using novel polarimetric and hyper-spectral measurements

云和气溶胶的相互作用是一个与大气科学界高度相关的开放问题的广泛领域。IPCC（2014）认识到需要进一步的科学努力，以理清各种相互作用的过程及其在气候变化中的作用。本提案旨在开发和测试气溶胶-云相互作用遥感的新概念。气溶胶对辐射收支有直接影响，它们通过改变云微物理和随后对云动力学、降水、云寿命、水循环甚至对区域和全球环流模式的变化产生间接影响。气溶胶本身受云的影响：气溶胶的性质和空间分布受到粒子膨胀以及云中的动力和化学过程的影响。活化云凝结核（CCNC）的浓度起着至关重要的作用。CCNC可以通过有限覆盖范围的原位测量直接确定。但是，由于它们的尺寸范围远低于可见辐射的波长，因此无法用常规光学遥感方法进行定量测量。因此，提出了另一种概念：云侧测量，测量在云侧反射的光谱太阳辐射，目的是推导云颗粒大小和相位的轮廓。据推测，这些观测可以研究气溶胶对云微物理垂直发展的影响，甚至可以推导出CCNC。CCNC也可以直接从气溶胶光学特性测量中得出。然而，它们与CCNC之间的相关性已被确定，具有显著的不确定性。本建议旨在将这两种方法结合起来，以检验所涉及的假设。快速扫描光谱观测将是解决这些问题的关键，因为云在时间上变化很快。本项目将配备具有偏振能力的高光谱成像仪。利用相同的仪器推导对流云的微物理特性以及两者之间无云天空中的气溶胶光学特性。这项工作分为两个博士项目。1)对飞机和拟议的卫星遥感任务发展至关重要的两个假设的检验：CCN浓度能否从气溶胶特性和云微物理剖面的遥感中得到？2)快速高光谱扫描允许对变化的云进行微物理检索；将测试该信息是否允许导出微物理特性随距离云边缘的变化。3)在有云的情况下，从偏振高光谱辐射观测中反演气溶胶。

Interaction of clouds and aerosols is a wide field of open questions highly relevant to the atmospheric scientific community. IPCC (2014) recognizes the need for additional scientific efforts to disentangle the variety of interacting processes and their role in a changing climate. This proposal aims at developing and testing a novel concept for remote sensing of the aerosol-cloud interaction. Aerosols have direct effects on the radiation budget and they cause indirect effects by alteration of cloud microphysics and subsequent effects on cloud dynamics, precipitation, cloud lifetime, water cycle, and even changes on regional and global circulation patterns. Aerosol itself is affected by clouds: Aerosol properties and spatial distribution are affected by swelling of particles as well as by dynamical and chemical processes in the cloud. The concentration of activated cloud condensation nuclei (CCNC) plays a crucial role. CCNC can be directly determined by in-situ measurements with limited coverage. However, they cannot be measured quantitatively by conventional optical remote sensing methods since their size range is far below the wavelengths of visible radiation. For that reason an alternative concept was proposed: Cloud side measurements, measuring spectral solar radiance reflected at cloud sides, aim at deriving profiles of cloud particle size and phase. It was hypothesized that these observations allow to study the impact of aerosol on vertical development of cloud microphysics, and even to derive CCNC. CCNC may also be derived directly from aerosol optical property measurements. Correlations between them and CCNC have been identified, however, with significant uncertainy. This proposal aims at bringing together these two approaches to test the involved hypotheses. Fast scanning spectral observations will be key to address these issues, since clouds change rapidly in time. For the purpose of this project, a hyper-spectral imager will be equipped with polarization capability. With the same instrumentation derivation of microphysical properties of convective clouds as well as aerosol optical properties in the cloudless sky in between is aimed at. The work is structured into two PhD projects. Highlights 1) Test of two hypotheses which are key for the development of aircraft and proposed satellite remote sensing missions: Can CCN concentration be derived from remote sensing of aerosol properties and cloud microphysics profiles? 2) Rapid hyper-spectral scanning allows for microphysics retrievals of changing clouds; it will be tested if this information allows deriving changes of microphysical properties with distance from the cloud edge. 3) Retrieval of aerosol from polarized hyper-spectral radiance observations in presence of clouds will be expored.