Understanding and constraining extratropical clouds in Earth's present and changing climate

了解和限制地球当前和不断变化的气候中的温带云

• 批准号: RGPIN-2021-02720
• 负责人: Tan, Ivy
• 金额: $ 2.55万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742176
• 关键词: Understanding; constraining; extratropical; clouds; Earth

The surface temperature-mediated response of clouds to global warming, known as "cloud feedback", continues to contribute the largest spread in climate projections by climate models. Previous work led by the PI has demonstrated using a single climate model that low biases in the proportion of supercooled liquid to total cloud water content in mixed-phase clouds causes underestimates in climate sensitivity --- a metric that quantifies the ultimate change in global mean surface air temperature in response to a doubling of atmospheric carbon dioxide concentrations. Recently, the newest generation of climate models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) predicts an increase in climate sensitivity that has been linked to general improvements to the same mixed-phase cloud biases identified by the PI's work. Establishing whether the higher climate sensitivity is realistic is of utmost importance for the development of climate change policy and mitigation strategies. The proposed five-year program will address the question of whether the higher climate sensitivity values of the latest generation of climate models are realistic by addressing the unresolved issues stemming from the PI's previous work in two distinct but parallel research themes. The first research theme strives to diagnose and constrain the extratropical cloud feedback in climate models using satellite remote sensing observations. This will be achieved by (i) applying the PI's methodology to evaluate the simulation of cloud optical depth in the CMIP6 models against observations from two different satellite instruments, (ii) performing single-model perturbed parameter ensemble simulations to identify the most important constrainable physical processes in a community climate model, and (iii) determining the impact of precipitation as a constrainable process rate in the extratropical cloud feedback based on satellite observations of precipitation. The second research theme strives to properly account for the most prominent long-standing mixed-phase cloud bias in climate models. This will be achieved by (i) characterizing the spatial distribution of cloud thermodynamic phase in mixed-phase clouds using two different approaches, (ii) calculating the covariability of ice nucleating particles with the spatial distribution of cloud thermodynamic phase, and (iii) using in situ observations to develop the first explicit parameterization of ice depositional growth in climate models that accounts for the spatial distribution of cloud thermodynamic phase in mixed-phase clouds based on observations. The overarching goal of the proposed five-year program is to constrain the extratropical cloud feedback in order to assess whether the higher climate sensitivity in the CMIP6 models is realistic. The implications are particularly pertinent to Canada, and especially our vulnerable Arctic, which has seen rapid climate change in the past few decades.

云层对全球变暖的表面温度介导的响应（称为“云反馈”）继续在气候模型的气候预测中发挥最大的作用。 PI领导的先前工作已经证明，使用单一气候模型，混合相云中过冷液体与总云水含量的比例的低偏差会导致气候敏感性的低估——气候敏感性是量化全球平均值最终变化的指标大气二氧化碳浓度加倍导致地表空气温度升高。最近，参与耦合模型比对项目 (CMIP6) 第六阶段的最新一代气候模型预测气候敏感性的增加，这与 PI 工作确定的相同混合相云偏差的总体改善有关。确定更高的气候敏感性是否现实对于制定气候变化政策和缓解战略至关重要。 拟议的五年计划将通过解决 PI 之前在两个不同但平行的研究主题中的工作所产生的未解决问题来解决最新一代气候模型的更高气候敏感性值是否现实的问题。第一个研究主题致力于利用卫星遥感观测来诊断和约束气候模型中的温带云反馈。这将通过以下方式实现：(i) 应用 PI 的方法根据两个不同卫星仪器的观测来评估 CMIP6 模型中云光学深度的模拟，(ii) 执行单模型扰动参数集合模拟以确定最重要的受约束物理社区气候模型中的过程，以及（iii）根据卫星降水观测确定降水的影响作为温带云反馈中的可约束过程速率。 第二个研究主题致力于正确解释气候模型中最突出的长期混合相云偏差。这将通过以下方式实现：（i）使用两种不同的方法表征混合相云中云热力学相的空间分布，（ii）计算冰成核粒子与云热力学相空间分布的协变性，以及（iii）使用现场观测，以开发气候模型中冰沉积增长的第一个明确参数化，该模型根据观测解释混合相云中云热力学相的空间分布。拟议的五年计划的总体目标是限制温带云反馈，以评估 CMIP6 模型中较高的气候敏感性是否现实。其影响尤其与加拿大有关，尤其是我们脆弱的北极地区，过去几十年来，气候变化迅速。