Scientific Program Overview (SPO): Cold Air Outbreak Experiment in the Sub-Arctic Region

北极是地球上变暖最快的地区，海冰迅速消失和气温上升相互促进。不断变化的冰盖给北极冬季天气带来了极大的不确定性，并对沿海社区和当地交通产生了重大影响。此外，高纬度变化如何与中纬度和全球气候系统联系起来是另一个具有挑战性的问题。一种特别鲜为人知的天气状况是，当北极冷空气在相对温暖的开阔海域上空流动时，冷空气爆发。在冷空气爆发期间，相对温暖潮湿的空气以云线的形式向上输送。关于云层的性质以及它们的雨量和降雪量与伴随的垂直空气运动和海面条件的关系，人们知之甚少。冷空气爆发偶尔会产生强烈的环流气流，也就是“极地低压”。冷空气爆发对全球热量和水的运输以及海洋环流都有重大影响。尽管冷空气爆发对天气和气候有影响，但仍然很难预测。这一获奖项目是为了计划一项专门的实地研究，即次北极地区的冷空气爆发实验(CAESAR)，目的是收集必要的测量数据，以了解与冷空气爆发相关的神秘云制度。计划中的实地活动将与斯堪的纳维亚科学家合作，为学生提供成为下一代大气科学家的独特培训机会。凯撒的野战预计将于2022年2月至3月在挪威海上空进行，挪威海是冷空气爆发的常见地。NSF/NCARC C-130飞机将从瑞典或挪威北部部署，配备一套雷达、激光雷达、辐射计、气溶胶、云、降水和痕量气体探测器。目标是研究冷空气爆发期间海洋边界层云的结构，重点是对云粒的微物理(液体和冰)特性及其伴随的动力学进行充分采样。飞行计划旨在调查冷空气爆发的整个演变过程，从北冰洋海冰边缘开始，到遥远的下游发育良好的云结构。凯撒的测量不仅将为细尺度云结构的发展提供新的见解，还将约束一系列数值模型，从能够捕捉细微差别的小尺度云和动力过程的涡流模拟到数值天气和气候模型。一个专门的模型-观测对比项目被计划用来改进数值模型，特别是它们在灰色地带的表现，在灰色地带，最先进的天气模型未能捕捉到相关的云和动力过程。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Arctic is the region on planet Earth warming the most rapidly with rapid sea ice loss and increasing air temperatures reinforcing each other. Changing ice cover posts great uncertainties on Arctic winter weather and significant impacts upon coastal communities and local transportation. In addition, how the high-latitude changes connect to the mid-latitude and the global climate system is another challenging question. One particularly poorly understood weather regime is cold-air outbreaks when cold Arctic air streaming over relatively warm open ocean water. During cold-air outbreaks, relatively warm moist air is transported up in forming lines of clouds. Little is known about the cloud properties and their rain and snowfall amount in relation with the accompanying vertical air movement and sea surface conditions. Cold air outbreaks occasionally spawn into intense circular air movements, “polar lows”. Cold-air outbreaks have significant impacts on the global heat and water transport as well as ocean circulations. Despite their impacts on weather and climate, cold-air outbreaks remain difficult to predict. This awarded project is to plan a dedicated field study, Cold Air Outbreak Experiment in the Sub Arctic Region (CAESAR) that has the goal to gather the necessary measurements to understand the mysterious cloud regime associated with cold-air outbreaks. The planned field campaign will be in collaboration with Scandinavian scientists and provide unique training opportunities to students to be the next generation of atmospheric scientists. The CAESAR field campaign is anticipated in February-March 2022 over the Norwegian Sea, a spot where cold-air outbreaks are prevalent. The NSF/NCAR C-130 aircraft with a suite of radars, Lidars, radiometers, aerosol, cloud, precipitation and trace gas probes will be deployed from northern Sweden or Norway. The goal is to study the structure of marine boundary layer clouds during cold-air outbreaks with a focus on fully sampling microphysical (liquid and ice) properties of cloud particles and the accompanying dynamics. Flight plans are designed to investigate cold-air outbreaks throughout their entire evolution from their initiation over the Arctic sea ice edge to well-developed cloud structures far downstream. The CAESAR measurements will not only afford new insights of development of fine-scale cloud structures but also constrain a hierarchy of numerical models ranging from eddy simulations capable of capturing the nuanced small-scale cloud and dynamical processes to numerical weather and climate models. A dedicated model-observational intercomparison project is planned to improve numerical models particularly their performance in the ‘grey-zone’ where state-of-the-art weather models fail to capture the relevant cloud and dynamical processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.