EUREC4A-UK: Elucidating the role of cloud-circulation coupling in climate

EUREC4A-UK是一个观测和模拟研究方案，旨在研究浅层尾积云生命周期中详细的气溶胶和云过程，以及云过程和大尺度动力学之间的双向相互作用。这些云对全球气候模式(GCM)变暖的不同反应解释了大部分模型间的差异，但这些反应的物理作用仍然很差。该计划的重点是英国科学家和BAS双水獭飞机在EUREC4A中的参与(阐明云-环流耦合在气候中的作用)。EUREC4A是一项协调一致的国际运动，旨在解决目前对控制信风积云对气候变暖环境条件变化的反应过程缺乏了解的问题。EUREC4A的目标是研究云、大气环流和气候敏感性之间的相互作用。EUREC4A-UK将通过以下方式为国际方案作出独特而自给自足的贡献：(1)提供作为协调实地活动一部分所需的观测设施；(2)开展和领导对浅层尾积云生命周期中的气溶胶、云微物理和边界层过程的分析；(3)通过模拟云过程和大尺度动力学之间的双向相互作用，将分析置于EUREC4A问题的背景下；(4)应用结果，在UM检验新的对流方案，并利用改进的模式来确定控制云场的主要过程。国际伙伴将补充这项研究，重点是观测和模拟贸易积云的宏观物理性质和环境，以确定：(1)控制对流质量通量、中尺度结构和浅层积云深度的因素；(2)贸易积云的比例如何随湍流、对流混合和大尺度环流而变化；(3)这种变化对大气辐射的影响。热带海洋上普遍存在的贸易积云的辐射特性对地球辐射收支有重大影响。因此，这些云对全球变暖的响应对全球平均云反馈至关重要。正是对气候变暖的不同反应解释了气候模型中气候敏感性的大部分传播。因此，需要更好地了解控制低层云量的机制。世界气候研究计划署支持支持云、环流和气候敏感性大挑战的EUREC4A实地项目，这一事实清楚地表明了研究的紧迫性。EUREC4A-UK显然是有必要的，因为气溶胶、云和降水过程影响着不同环境中云的宏观物理性质。例如，雨量的垂直分布可以影响上层减速层中云滴的浓度和大小，从而影响云的辐射特性。雨的强度和雨滴的蒸发影响阵风锋面的强度，从而影响二次云的产生。然而，由于气溶胶、卷吸、湍流和巨云凝结核(GCCN)的复杂相互作用，模式计算的降水产生率和降雨量是不确定的。这些过程依赖于环境条件，受大尺度动态控制。同样，气溶胶-云-降水过程可以影响更大尺度的动力学，例如通过辐射传输。事实上，在一系列尺度上的过程之间存在许多相互作用，需要在模型中加以理解和表示。

EUREC4A-UK is a programme of observational and modelling research which aimsto study the detailed aerosol and cloud processes in the life cycle of shallow tradecumulus clouds and the two-way interactions between the cloud processes and thelarge-scale dynamics. The different responses of these clouds to warming in globalclimate models (GCM) explain most of the inter-model differences, yet the physicsof these responses remains poorly constrained. The programme is focussed onthe participation of UK scientists and the BAS Twin Otter aircraft in EUREC4A(Elucidating the Role of Clouds-Circulation Coupling in Climate). EUREC4A isa coordinated international campaign that aims to address the current lack of understanding ofthe processes controlling the response of trade-wind cumulus clouds to changing environmentalconditions in a warmer climate. The goal of EUREC4A is to examine the interplay between theclouds, atmospheric circulations and climate sensitivity. EUREC4A-UK will make a unique and self-contained contribution to the international programme by: (i) providing observational facilities whichare needed as part of the coordinated field campaign; (ii) conducting and leading the analysis ofthe aerosols, cloud microphysics and boundary-layer processes in the life cycle of shallow tradecumulus clouds; (iii) placing the analysis in the context of the EUREC4A problems by modelling thetwo-way interactions between the cloud processes and the large-scale dynamics; and (iv) applyingthe results by testing the new convection scheme in the UM and using the improved model to determinethe dominant processes controlling the cloud fields. International partners will complement the re-search with a focus on observing and modelling the macrophysical properties and the environmentof trade-cumulus clouds in order to determine: (i) what controls the convective mass flux, mesoscaleorganization and depth of shallow-cumulus clouds; (ii) how the trade-cumulus cloud fraction varieswith turbulence, convective mixing and large-scale circulations; and (iii) the impact this variation hason atmospheric radiation.The radiative properties of the trade-wind cumulus clouds that are ubiquitous over the tropical oceans have a major influence on the Earth's radiation budget. The response to global warming of these clouds is therefore critical for global mean cloud feedbacks. It is the differing response to warming that explains most of the spread of climate sensitivity in climate models. Hence, a better understanding is required of the mechanisms that control the low-level cloud fraction. The urgency of the research is made clear by the fact that the World Climate Research Programme endorses the EUREC4A field project which supports the Grand Challenge on Clouds, Circulation and Climate Sensitivity.There is a clear need for EUREC4A-UK because the aerosol,cloud and precipitation processes influence the macrophysical properties of the clouds in differentenvironments. For example, the vertical distribution of raincan affect the concentration and size of cloud drops in the upper detrainment layers, which influ-ences cloud radiative properties. The intensity of rain and evaporation of raindrops influences thestrength of gust fronts and hence secondary cloud-production. However, model calculations of therate of production of rain and hence the quantity of rain are uncertain due to the complex interactionsof aerosols, entrainment, turbulence and giant cloud condensation nuclei (GCCN). These processesdepend on the environment conditions, controlled by the large-scale dynamics. Equally, the aerosol-cloud-precipitation processes can influence the larger-scale dynamics, for example through radiativetransfer. Indeed there are many interactions between processes on a range of scales that need to beunderstood and represented in models.