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与大气科学界高度相关的一个广泛的开放问题领域。气专委(2014)认识到需要作出更多的科学努力，以理清各种相互作用的过程及其在不断变化的气候中的作用。这项提议旨在开发和测试一种新的气溶胶-云相互作用遥感概念。气溶胶对辐射收支有直接影响，并通过改变云微物理以及随后对云动力学、降水、云寿命、水循环的影响，甚至改变区域和全球环流格局，造成间接影响。气溶胶本身受到云的影响：气溶胶的性质和空间分布受到颗粒膨胀以及云中动力和化学过程的影响。活化的云凝聚核(Ccnc)的浓度起着至关重要的作用。Ccnc可通过现场测量直接确定，覆盖范围有限。然而，由于它们的大小范围远远低于可见光辐射的波长，因此无法用传统的光学遥感方法进行定量测量。为此，提出了另一个概念：云端测量，即测量在云端反射的光谱太阳辐射，目的是得出云粒大小和相位的轮廓。据推测，这些观测结果可以研究气溶胶对云微物理垂直发展的影响，甚至可以得出Ccnc。Ccnc也可以直接从气溶胶光学性质测量中得到。然而，它们与Ccnc之间的相关性已被确定，但存在重大不确定性。这项建议旨在将这两种方法结合起来，以检验涉及的假说。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。为了这个项目的目的，一个高光谱成像仪将配备偏振能力。利用同样的仪器，可以推导出对流云的微观物理性质以及无云天空中的气溶胶光学性质。这项工作被组织成两个博士项目。重点1)检验对开发飞行器和拟议的卫星遥感飞行任务至关重要的两个假设：CCN浓度能否通过对气溶胶特性和云微物理剖面的遥感得出？2)快速高光谱扫描能够对变化的云进行微物理反演；如果这种信息能够得出微物理特性随距离云边缘的变化，将对其进行检验。3)从有云的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.