RAPID: What Caused the Record Warmth and Loss of Antarctic Sea ice in the Austral Summer of 2022, and will Sea Ice Remain Low Over 2022-2024?

在2021/2022年的南半球冬季，南极海冰面积急剧下降，2022年2月标志着自1979年卫星海冰观测以来有记录以来的最低海冰面积。再加上海冰的消失，2022年3月，南极东部出现了有史以来最极端的热浪，从气候学角度来看，气温攀升到了+40摄氏度以上。极端事件在社会经济影响中的影响过大，但也是气候预测的试金石。该项目将使用新的工具来诊断导致南极海冰面积和热浪达到创纪录低位的因素，重点是风和海洋温度的影响。目前(2022年6月)，南极海冰面积仍然处于一年中这个时候的创纪录低水平，这增加了低海冰面积长期持续的可能性，但对南极海冰的年度预报尚不存在。为了解决这个问题，该项目还将建立2022-2024年期间的探索性年度海冰预报。南极海冰面积和气温的极端变化对我们目前对南极气候变异性的理解提出了质疑。受这些事件的时间安排和我们最近开发的新分析工具的推动，该项目将解决以下研究问题：(R1)当地风能否解释2021/2022年观测到的海冰损失，或者远程海洋表面温度(SST)异常是必要的因素？(R2)2022-2024年的海冰状况可能保持在异常低的水平吗？(R3)最先进的气候模型能否模拟出与观测到的热浪规模相当的热浪，如果它跟随导致热浪的观测环流？主要方法将是在气候模型中使用推挤技术，气候模型中的一个或几个变量被推向观测值。项目作者使用这一工具将1979-2018年间南极海冰的变化和趋势归因于风和海温异常。该项目将把这一工具应用到2019-2022年期间，通过在这段时间内运行两个不同的模型实验来处理R1和R3，在这段时间里，南极洲和南大洋的海温被推向观测值。此外，我们还将诊断2019-2022年大气变化的已知影响南极海冰的相关模式，以进一步了解2022年海冰面积的减少。为了解决R2问题，我们计划扩展模型模拟，但不使用微调，将模型用作预测模型(因为其2022年的初始条件将从微调模拟的结束处获取，并捕获观测状态的重要方面)。我们预计，如果当前的上层海洋热含量异常高，那么低海冰面积的状况可能会持续到2022-2024年，就像2016/2017年海冰面积创下历史新低后2017-2019年的情况一样。为了进一步解决R3，我们将使用由项目团队开发的新颖的大气热传输计算来比较观测和模型模拟。该奖项反映了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。

In the austral winter of 2021/2022 a drastic decline in Antarctic sea ice extent has taken place, and February 2022 marked the lowest sea ice extent on record since satellite sea ice observations began in 1979. Combined with the loss of sea ice, the most extreme heat wave ever observed took place over East Antarctica in March 2022 as temperatures climbed over +40°C from climatology. Extreme events have an oversized footprint in socioeconomic impacts, but also serve as litmus tests for climate predictions. This project will use novel tools to diagnose the factors that led to the record low Antarctic sea ice extent and heat wave focusing on the impact of winds and ocean temperatures. Currently (June 2022) Antarctic sea ice extent remains at record low levels for the time of year, raising the prospect of a long-lasting period of low sea ice extent, yet annual forecasts of Antarctic sea ice do not yet exist. To address this issue, this project will also create exploratory annual sea ice forecasts for the 2022-2024 period. The extreme changes observed in Antarctic sea ice extent and air temperature have questioned our current understanding of Antarctic climate variability. Motivated by the timing of these events and our recent development of novel analysis tools, this project will address the following research questions:(R1) Can local winds account for the observed 2021/2022 sea ice loss, or are remote sea surface temperature (SST) anomalies a necessary ingredient?(R2) Are sea ice conditions over 2022-2024 likely to remain anomalously low?(R3) Can a state-of-the-art climate model simulate a heat wave of comparable magnitude to that observed if it follows the observed circulation that led to the heat wave?The main approach will be to use a nudging technique with a climate model, in which one or several variables in a climate model are nudged toward observed values. The project authors used this tool to attribute Antarctic sea ice variability and trends over 1979-2018 to winds and SST anomalies. This project will apply this tool to the period 2019-2022 to address R1 and R3 by running two different model experiments over this time period in which the winds over Antarctica and SSTs in the Southern Ocean are nudged toward observed values. In addition, we will diagnose the relevant modes of atmospheric variability over 2019-2022 that are known to influence Antarctic sea ice to gain further insight into the 2022 loss of sea ice extent. To address R2, we plan to extend the model simulations but without nudging, using the model as a forecast model (as its 2022 initial conditions will be taken from the end of the nudged simulations and capture important aspects of the observed state). We expect that if current upper ocean heat content is anomalously high, low sea ice extent conditions may continue over 2022-2024, as happened over 2017-2019 following the previous record low of sea ice extent in 2016/2017. To further address R3, we will compare observations and model simulations using novel atmospheric heat transport calculations developed by the project team.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.