Influence of the ice crystal shape on radiative effects of Arctic cirrus: Observations and representation in numerical weather prediction models

基于欧洲中期天气预报中心辐射方案对已完成的中纬度冰云项目中观测到的冰晶辐射特性参数化的敏感性，该项目的继续旨在将这一模式评估扩展到高纬度卷云的辐射效应。对于北极卷云，分析需要扩展到热红外辐射预算，由于太阳辐射的滞后，并取决于云的高度，厚度和冰晶的特性。因此，该项目被纳入拟议的HALO飞行任务Cirrus-HL（High Latitude）和HALO-（AC）³（ArctiC放大：气候相关的大气和表面过程，以及反馈机制），这两个项目的目的都是通过最先进的航空遥感技术来调查北极地区的云层（主动和被动）和云微物理原位观测。在该项目中，测量云反射的太阳和发射的热红外辐射率和辐照度与一个新的宽带辐射计系统，光谱反照率计，和热红外成像仪提出了量化的辐射能量收支以上和以下的北极卷云。在观测的基础上，将推导出卷云辐射效应，并根据卷云对云的宏观物理和微观物理特性以及特殊的北极环境（海冰、持续低云）的依赖性进行评估。我们将评估卷云及其辐射效应在数值天气预报模式中的表现。比较将在辐照度和辐射度的观测空间而不是云的特性中进行。因此，数值天气预报（NWP）模式的输出将通过辐射传输模式转换为观测到的辐射量。将对操作和实验辐射方案进行测试，并与观测到的辐射量进行比较，以确定模型和观测之间可能存在差异的原因。空中观测和辐射传输模拟将被用来证实这一假设：“北极卷云的辐射效应，这在很大程度上取决于它们的宏观物理和微观物理特性，如冰晶形状，可以用来验证数值天气预报模型。为了解决这一假设，拟议的研究将侧重于五个具体的科学问题：（A）北极卷云在不同水平尺度上的辐射效应如何变化（例如，凝迹卷云，气团转变中的卷云）？(B)辐射效应有多强取决于海冰和低云的存在？(C)观测到的北极卷云冰晶形状是否导致云辐射效应的显著变化？(D)数值预报模式真实地反映了北极卷云的辐射效应吗？(E)我们能使用光谱太阳和热红外辐射测量来限制NWP模式的潜在不确定性吗？

Based on the sensitivity of the ECMWF radiation scheme to the parametrization of ice crystal radiative properties observed in the completed project for ice clouds in mid-latitudes, the continuation of the project aims to extends this model evaluation for the radiative effects of cirrus in high-latitudes. For Arctic cirrus, the analysis needs to be extended to the thermal-infrared radiation budget, which dominates due to the lag of solar radiation and depends on cloud altitude, thickness and ice crystal properties. Therefore, the project is embedded in the proposed HALO missions Cirrus-HL (High Latitude) and HALO-(AC)³ (ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms), which both aim to investigate Arctic clouds by state of the art airborne remote sensing (active and passive) and cloud microphysical in situ observations.Within this project, measurements of the cloud-reflected solar and emitted thermal infrared radiance and irradiance with a new broadband radiometer system, a spectral albedometer, and a thermal-infrared imager are proposed to quantify the radiative energy budget above and below Arctic cirrus. Based on the observations, the cirrus radiative effect will be derived and evaluated with respect to its dependence on cloud macrophysical and microphysical properties, and the special Arctic environment (sea ice, persistent low clouds). We will evaluate how well the cirrus and their radiative effects are represented in numerical weather prediction models. The comparison will be performed in the observational space of irradiances and radiances instead of cloud properties. Therefore, the output of the numerical weather prediction (NWP) models will be converted by radiative transfer models into the observed radiation quantities. Operational and experimental radiation schemes will be tested and compared to the observed radiation quantities to identify the reasons of potential differences between model and observation. The airborne observations and the radiative transfer simulations will be used to corroborate the hypothesis: “The radiative effects of Arctic cirrus, which significantly depend on their macrophysical and microphysical properties such as the ice crystal shape, can be used to validate numerical weather prediction models.” To address this hypothesis, the proposed study will focus on five specific science questions: (A) How variable are the radiative effects by Arctic cirrus on different horizontal scales (e.g., contrail cirrus, cirrus in air mass transformation)? (B) How strong the radiative effects depend on the presence of sea ice and low clouds? (C) Do observed ice crystal shapes of Arctic cirrus lead to a significant change of cloud radiative effects? (D) Do NWP models realistically represent the radiative effects of Arctic cirrus? (E) Can we use spectral solar and thermal-infrared radiation measurements to constrain potential uncertainties of NWP models?