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

根据ECMWF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的参数化的敏感性，该项目的继续项目旨在扩展该模式对高纬度卷云的辐射影响的评估。对于北极卷云，分析需要扩展到热红外辐射收支，由于太阳辐射的滞后，热红外辐射收支占主导地位，并取决于云的高度、厚度和冰晶特性。因此，该项目被嵌入拟议的Halo任务Cirrus-HL(高纬度)和Halo-(AC)³(北极放大：与气候有关的大气和地面过程以及反馈机制)，这两个任务的目的都是通过最先进的机载遥感(主动和被动)和云微物理现场观测来调查北极云。在观测的基础上，将根据卷云的宏观物理和微观物理特性以及北极特殊环境(海冰、持续的低云)对卷云的辐射效应进行推导和评估。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情况。比较将在辐照度和辐射度的观测空间内进行，而不是在云层属性上。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辐射量。将测试操作和实验辐射方案，并将其与观测的辐射量进行比较，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样的假设：“北极卷云的辐射效应在很大程度上取决于它们的宏观物理和微观物理性质，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有多大变化(例如，轨迹卷云、气团转换中的卷云)？(B)辐射效应在多大程度上取决于海冰和低云的存在？(C)观测到的北极卷云的冰晶形状是否导致云辐射效应的显著变化？(D)数值预报模式是否真实地反映了北极卷云的辐射效应？(E)我们能否使用太阳光谱和热红外辐射测量来限制数值预报模式的潜在不确定性？

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?