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

北极气候变暖的速度比整个世界都快得多。全球模型显示了全球变暖加剧的总体趋势，但通常无法再现观测到的海冰急剧减少的情况。这在一定程度上是由于表面能量收支的显著偏差造成的。能量收支不确定的最大来源是低层云的表示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内的湍流热通量方面的问题。在暖空气入侵的强烈强迫的极端条件下，模型偏差最大。暖空气入侵是指温暖、潮湿的空气通过海冰输送进来，在靠近海面的地方冷却，形成浅而稳定的层状层，在其中形成雾和云。温度、湿度和湍流的浅层和陡峭的垂直梯度对于全球模型来说是很难解决的。随着垂直热力廓线、云液体和冰水含量以及湍流结构的变化，它们在海冰上随着时间的增加而演变，很大程度上依赖于必须在模式中参数化的小尺度过程。现有的参数是基于较低纬度的测量，不能充分代表极地条件。由此产生的模式偏差在暖空气侵入期间可能是100s W/m2。ARTofMELT是第一个专注于暖空气侵入的观察性研究。由我们在斯德哥尔摩大学的合作伙伴提出的一个国际项目的支持已经得到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来进行必要的测量，以提供对这些事件期间控制气团改变的过程的新的理解，并为适用于极地环境的全球模式开发新的参数。在之前几个合作项目的基础上，我们将作为一个单一的团队与我们在斯德哥尔摩的合作伙伴合作，为低层大气、云和地表能量预算的组成部分进行广泛的现场和遥感测量。在ECMWF做出的专门预报的指导下，奥登将对从大西洋或欧亚地区进入北极的暖空气进行采样。我们预计在巡航期间抽样3-5次事件，并使用事件周期外的观测作为基线来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.