Dependence of Antarctic sea-ice extent on mesoscale ocean variability in the Southern Ocean

概述：南极洲周围的海冰范围在卫星时代（1979年至今）缓慢增加，与其他全球冰冻圈成分的普遍下降相反，与全球耦合气候模式（CCM）中的现代负海冰范围趋势相反。以前的假设集中在影响海冰质量平衡的大规模机制：由于平流层臭氧消耗导致的风应力场的变化;更活跃的南大洋水文循环;下沉流长波辐射增加;以及冰架下的淡水生产增加。将检验另一个假设：CCM中未解决的中尺度海洋过程在控制边缘冰区的冰边缘位置和海冰特征方面起着重要作用，海洋中尺度活动的年际变化和趋势可以驱动海冰范围的变化，而这些变化与年度变化并不密切相关。南大洋的平均状态，如南极绕极流锋的位置。将分析每日卫星得出的海冰浓度场，以确定海洋中尺度变化对海-影响真实海冰范围和卫星测量海冰范围的冰缘特征。统计数据将包括由于中尺度过程而增加的冰缘长度，作为边缘冰区更多地暴露于“开阔洋”过程的一个衡量标准。将比较从不同海冰密集度网格数据集得出的海冰范围，以确定海冰范围的年际变化和趋势是否对测量方法和空间分辨率敏感。如果先前的工作证明是正确的，那么将把近同期的环境卫星ASAR高分辨率雷达图像与AMSR-E的海冰浓度场进行比较。还将分析一个跟踪的涡流数据库，以确定南极绕极流锋面不稳定性和与地形的相互作用产生的涡流是否有助于冰缘变化。这些分析将在环南极和区域尺度上以年度分辨率进行，以解决年际变化和趋势，将分析带有海冰耦合的允许涡流的三维区域海洋模式或数据约束海洋状态模式（南大洋状态估计）的输出，以调查这些模式如何代表海洋中尺度对冰缘扰动的贡献。研究人员还将开发自己的理想化模式的海洋/冰/大气在冰边缘的相互作用，以调查机制产生的冰边缘锋的不稳定性可能是显着的贡献者的冰边缘mesoscale field.Broader影响：这项研究将阐明耦合机制的高能南大洋中尺度场与海冰。南极海冰是全球耦合气候系统的重要组成部分，对南极海冰、海洋/大气热湿通量和气体交换有着重要的影响。对现有数据和允许涡流的海洋/海冰模型的并行分析将为现代CCM中海冰变化的解释提供信息，从而确定改善海冰代表性所需的关键发展。对边缘冰区的仔细检查将有助于为解释卫星对冰缘位置的检索提供信息。调查人员将继续参与当地的外展活动，包括在太平洋科学中心（西雅图）和华盛顿大学的罗宾逊青年学者中心的演讲，在俄勒冈州的公开演讲，并经常向科瓦利斯报纸的意见页面提供气候科学方面的内容，开发针对普通观众的项目网页，并更新他们的外展网站，包括极地照片服务器。

Overview: Sea ice extent around Antarctica has slowly increased over the satellite era (1979-present), against the general decline of other global cryosphere components and contrary to modern negative sea ice extent trends in global coupled climate models (CCMs). Previous hypotheses have focused on large-scale mechanisms that impact the sea ice mass balance: changes in wind stress fields due to stratospheric ozone depletion; a more energetic Southern Ocean hydrologic cycle; increased downwelling long wave radiation; and enhanced freshwater production under ice shelves. An additional hypothesis will be tested: Mesoscale ocean processes that are not resolved in CCMs play a significant role in controlling ice edge position and sea-ice characteristics in the marginal ice zone and that inter-annual variability and trends in ocean mesoscale activity can drive changes in sea ice extent that are not closely correlated with the annual-averaged Southern Ocean state such as position of Antarctic Circumpolar Current fronts.Intellectual Merit: Daily satellite-derived sea-ice concentration fields will be analyzed to determine the effect of ocean mesoscale variability on sea-ice edge characteristics that influence true and satellite-measured sea-ice extent. Statistics will include the increase in ice-edge length due to mesoscale processes as a measure of increased exposure of the Marginal Ice Zone to "open-ocean" processes. Sea ice extent derived from different gridded datasets of sea-ice concentration will be compared to determine whether inter-annual variability and trends in sea ice extent are sensitive to measurement methodology and spatial resolution. If justified by prior work, near-contemporaneous Envisat ASAR high-resolution radar images will then be compared with sea-ice concentration fields from AMSR-E. A database of tracked eddies will also be analyzed to determine whether eddies generated by Antarctic Circumpolar Current frontal instabilities and interactions with topography contribute to ice-edge variability. These analyses will be performed on circum-Antarctic and regional scales, at annual resolution to resolve inter-annual variability and trends.The output from an eddy-permitting three-dimensional regional ocean model with coupled sea ice or a data-constrained ocean state model (Southern Ocean State Estimate) will be analyzed to investigate how well these models represent the ocean mesoscale contribution to ice-edge perturbations. The investigators will also develop their own idealized models of ocean/ice/atmosphere interactions at the ice edge to investigate mechanisms for generation of ice-edge fronts whose instabilities may be significant contributors to the ice-edge mesoscale field.Broader Impacts: This study will elucidate the mechanisms coupling the highly energetic Southern Ocean mesoscale field with sea ice. Antarctic sea ice has a profound effect on albedo, ocean/atmosphere heat and moisture fluxes and gas exchange, and so is an important component of the global coupled climate system. The concurrent analyses of existing data and eddy-permitting ocean/sea-ice models will inform interpretation of sea-ice variability in modern CCMs, and so identify critical developments needed to improve their representation of sea ice. Careful examination of the marginal ice zone will help inform the interpretation of satellite retrievals of ice-edge position. The investigators will continue their participation in local outreach activities including presentations at Pacific Science Center (Seattle) and the Robinson Center for Young Scholars at the University of Washington, public talks in Oregon and frequent contributions on Climate Science to the Corvallis newspaper Opinion Page, development of a project web page targeted at a general audience, and updating their outreach web site including polar photo server.