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，气温升高，两者相互促进。冰盖的变化对北极冬季天气具有很大的不确定性，并对沿海社区和当地交通产生重大影响。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。一个特别不为人所知的天气状况是，当寒冷的北极空气流过相对温暖的开阔海水时，冷空气爆发。在冷空气爆发期间，相对温暖的潮湿空气以形成云线的形式向上输送。人们对云的性质及其雨雪量与伴随的垂直空气运动和海面条件的关系知之甚少。冷空气的爆发偶尔会产生强烈的循环空气运动，即“极低”。冷空气爆发对全球热和水运以及海洋环流产生重大影响。尽管它们对天气和气候有影响，但冷空气的爆发仍然难以预测。这个获奖项目是计划一个专门的实地研究，即亚北极地区冷空气爆发实验（CAESAR），其目标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层状况。计划中的实地活动将与斯堪的纳维亚科学家合作，并为学生提供成为下一代大气科学家的独特培训机会。凯撒实地行动预计将于2022年2月至3月在挪威海上空进行，那里是冷空气暴发普遍的地方。NSF/NCAR C-130飞机将从瑞典北部或挪威部署，配备一套雷达、激光雷达、辐射计、气溶胶、云、降水和微量气体探测器。目的是研究冷空气爆发期间海洋边界层云的结构，重点是对云粒子的微物理（液体和冰）特性及其伴随的动力学进行全面采样。飞行计划的设计是为了调查冷空气爆发的整个演变过程，从北极海冰边缘开始，到下游发育良好的云层结构。凯撒的测量不仅提供了对精细尺度云结构发展的新见解，而且还限制了从能够捕捉细微的小规模云和动力过程的涡模拟到数值天气和气候模式的数值模式的层次。一个专门的模式-观测相互比较项目正在计划中，以改进数值模式，特别是它们在“灰色地带”的性能，在那里，最先进的天气模式无法捕捉到相关的云和动力过程。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.