Forcings and Feedbacks: Arctic Sea Ice and the Atmosphere

近几十年来，北极和次北极的北大西洋部分的海冰集中出现了明显的趋势。尽管在很大程度上是由大气流动的变化推动的，直到过去几年，大气流动一直显示出北大西洋/北极涛动(NAO/AO)积极阶段的显著趋势，但海冰的趋势对大气环流产生了重大反馈。在初步的模拟研究中，PI发现，与海洋表面温度相比，海冰趋势的反馈很强，而且是负的。这一反馈对强迫区的位置非常敏感，最敏感的地区是格陵兰以东和巴伦支海，这些地区的海冰密度变化很大。PI将对分季节(月度)反馈的性质进行更详细的评估，特别是冬末至春季和夏季的反馈，包括海冰面积覆盖率，这在她的初步研究中没有体现出来。工作假设是，大气对强迫的响应仍然突出地投射到主导气候模式上，因此响应可以被分解为一级，代表对大气变率主导模式的投影，以及“直接”部分，代表对强迫区域更局部的响应部分。PI将采用国家大气研究中心(NCAR)社区气候系统模型(CCSM)的版本。该模型将强制大气二氧化碳(CO2)浓度每年增加1%，并将检验大气CO2浓度加倍和四倍对海冰浓度模式的影响。这些模式是否与过去一个世纪观测记录的不同时期所观察到的趋势模式相似？即使它们表面上类似于任何观察到的趋势，将这种强迫模式(从强迫耦合模式获得)应用到大气环流模式(AGCM)将是很有趣的，因为这种响应对关键位置强迫区域的微小差异非常敏感。这项研究的动机是需要将自然/人为原因造成的强迫/反应分开。这项活动的学术价值在于，它寻求了解和量化海冰对大气环流及其变异性的反馈，这一点人们知之甚少，同时提出了关于温带变异性的新的动力学概念。这项活动的更广泛影响是，它将增进我们对北极气候系统，甚至整个气候系统中根本感兴趣的现象的理解，同时教育和培训博士生以及本科生。

Sea-ice concentration in the Arctic and the North-Atlantic part of the sub-Arctic has undergone pronounced trends in recent decades. Although driven in large part by changes in atmospheric flow, which had shown pronounced trends toward the positive phase of the North-Atlantic/Arctic Oscillation (NAO/AO) until the past couple of years, the trend in sea ice exerts a significant feedback upon the atmospheric circulation. In a preliminary modeling study the PIs found that the feedback due to sea-ice trends was strong, compared to that of sea surface temperature, and negative. This feedback was very sensitive to the location of the area of forcing, the most sensitive area being immediately east of Greenland and in the Barents Sea, areas that have highly variable sea-ice concentrations. The PI will carry out a more detailed evaluation of the nature of the subseasonal (monthly) feedback, especially late winter into spring and summer, including fractional sea ice area coverage, which was not represented in her preliminary study. The working hypothesis is that the atmospheric response to the forcing is still prominently projected onto the dominant climate pattern so that the response may be decomposed to first order into an "indirect" part, representing the projection onto the dominant pattern of atmospheric variability, and a "direct" part, representing the part of the response that is more local to the area of forcing. The PI will employ versions of the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM). The model will be forced with a 1% increase per year in atmospheric carbon dioxide (CO2) concentration and the effects of doubled and quadrupled atmospheric CO2 concentration on sea ice concentration patterns will be examined. Do the patterns resemble the patterns of the observed trend during different periods of the observational record over the past century? Even if they superficially resemble any of the observed trends, it will be interesting to apply this pattern of forcing (obtained from the forced coupled model) to the atmospheric general circulation model (AGCM), since the response is highly sensitive to small differences in the area of forcing at key locations. The motivation of the study is the need to detangle forcing/response due to natural/anthropogenic causes. The intellectual merit of the activity is that it seeks to understand and quantify the feedback of sea ice on the atmospheric circulation and its variability, which is poorly understood, while developing novel dynamical ideas regarding extratropical variability. The broader impacts of the activity are that it will improve our understanding of phenomena that are of fundamental interest in the Arctic climate system, indeed the entire climate system, while educating and training a PhD student, as well as undergraduate students.