Atmospheric Rivers and The Onset of Sea-Ice Melt (ARTofMELT)

北极气候变暖的速度比整个世界快得多。全球模型显示了变暖加剧的总趋势，但通常无法再现观测到的海冰急剧减少。这部分是由于表面能量预算中的显著偏差。能量收支不确定性的最大来源是低空云的表示问题以及由此产生的地表太阳和红外辐射通量，以及近地表大气中湍流热通量。在暖空气入侵的强强迫的极端条件下，模型偏差最大-在区域事件中，温暖，潮湿的空气被输送到海冰上，冷却接近表面，形成浅，稳定的分层，其中雾和云的形成。温度、湿度和湍流的浅层和陡峭的垂直梯度是全球模式难以解决的问题。随着时间的增加，在海冰上，作为垂直热力学配置文件，云液体和冰水含量，湍流结构的变化，它们的演变强烈依赖于小尺度的过程，必须在模型中参数化。现有的参数化是基于低纬度的测量，不能充分代表极地条件。由此产生的模式偏差可以在100 W/m2的暖空气入侵。ARTofMELT是第一个观测研究集中在暖空气入侵。由我们在斯德哥尔摩大学的合作伙伴提出的对一个国际项目的支持已获得瑞典极地研究秘书处的批准，瑞典破冰船奥登号计划于2023年春季进行一次研究巡航。这提供了一个独特的机会，使所需的测量提供新的理解的过程中控制空气质量的修改，在这些事件，并制定新的参数化全球模型适合极地环境。在之前几个合作项目的基础上，我们将与斯德哥尔摩的合作伙伴作为一个团队合作，为Oden仪器提供低层大气，云和表面能量预算组成部分的广泛原位和遥感测量。在ECMWF专门预报的指导下，Oden将定位于从大西洋或欧亚地区进入北极的暖空气入侵样本。我们预计在巡航期间采样3-5个事件，并使用事件期间以外的观测结果作为基线，以评估暖空气入侵对低层大气结构，云和地表能量收支的影响。其他与会者将评估海冰对大气强迫的反应。

Arctic climate is warming much faster than that of the world as a whole. Global models show the general trend of enhanced warming, but generally fail to reproduce the observed dramatic reduction in sea ice. This results in part from significant biases in the surface energy budget. The largest source of uncertainty in the energy budget results from problems in the representation of low level clouds and the resulting solar and infra-red radiation fluxes at the surface, and of turbulent heat fluxes within the near-surface atmosphere. The model biases are greatest under the extreme conditions of strong forcing by warm air intrusions - regional events where warm, humid air is transported in over sea ice, cooling close to the surface to form shallow, stably stratified layers within which fog and cloud form. The shallow layers and steep vertical gradients of temperature, humidity, and turbulence are difficult for global models to resolve. Their evolution with increasing time over the sea ice, as the vertical thermodynamic profiles, cloud liquid and ice water contents, and turbulent structure change, depends strongly on small scale processes that must be parameterized within the models. Existing parameterizations are based on measurements at lower latitudes, and fail to adequately represent polar conditions. The resulting model biases can be 100s of W/m2 during warm air intrusions.ARTofMELT is the first observational study focussed on warm air intrusions. Support for an international project, proposed by our partners at Stockholm University, has been approved by the Swedish Polar Research Secretariat, and a research cruise is scheduled for spring 2023 on the Swedish icebreaker Oden. This provides a unique opportunity to make the measurements needed to provide new understanding of the processes controlling air mass modification during these events, and develop new parameterizations for global models appropriate to polar environments. Building on several previous collaborative projects we will work as a single team with our partners in Stockholm to instrument Oden for extensive in situ and remote sensing measurements of the lower atmosphere, clouds, and the components of the surface energy budget. Directed by dedicated forecasts made at ECMWF, Oden will be positioned to sample warm air intrusions entering the Arctic from the Atlantic or Eurasian sectors. We anticipate sampling 3-5 events during the cruise, and use the observations from outside the event periods as a baseline to evaluate the impact of warm air intrusions on lower-atmosphere structure, clouds, and the surface energy budget. Other participants will assess the response of sea ice to the atmospheric forcing.