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

概述：在卫星时代(1979年至今)，南极洲周围的海冰面积缓慢增加，与全球冰冻圈其他组成部分的普遍下降相反，也与全球耦合气候模式(CCM)的现代负海冰面积趋势相反。以前的假设侧重于影响海冰质量平衡的大尺度机制：平流层臭氧消耗引起的风应力场的变化；南大洋水文循环能量更强；下流长波辐射增加；以及冰架下淡水产量增加。还将检验另一个假设：未在CCM中分解的中尺度海洋过程在控制边缘冰区的冰缘位置和海冰特征方面发挥着重要作用，海洋中尺度活动的年际变化和趋势可以推动海冰范围的变化，而这些变化与南极绕极流锋的位置等年平均南大洋状态并不密切相关。智力优势：将分析卫星得出的每日海冰浓度场，以确定海洋中尺度变化对影响真实和卫星测量的海冰范围的海冰边缘特征的影响。统计数据将包括中尺度过程造成的冰缘长度增加，以此作为边缘冰带暴露于“公海”过程增加的量度。将对从不同海冰集中格网数据集得出的海冰范围进行比较，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。如果以前的工作证明是正确的，那么近同时期的环境ASAR高分辨率雷达图像将与AMSR-E的海冰浓度场进行比较。还将对追踪到的涡旋数据库进行分析，以确定南极绕极洋流锋面不稳定性以及与地形的相互作用所产生的涡旋是否有助于冰缘的可变性。这些分析将在环南极和区域尺度上进行，以年度分辨率解决年际变化和趋势。将分析允许涡流的耦合海冰三维区域海洋模式或数据约束的海洋状态模式(南大洋状态估计)的输出，以调查这些模式在多大程度上反映海洋中尺度对冰缘扰动的贡献。研究人员还将发展他们自己的冰缘海洋/冰/大气相互作用的理想化模式，以研究冰缘锋面的产生机制，冰缘锋面的不稳定性可能是冰缘中尺度场的重要贡献因素。广泛影响：本研究将阐明高能南大洋中尺度场与海冰耦合的机制。南极海冰对反照率、海洋/大气热湿通量和气体交换有着深远的影响，是全球耦合气候系统的重要组成部分。对现有数据和允许涡流的海洋/海冰模型的同时分析将有助于解释现代海冰模型中的海冰变异性，从而确定改进其海冰表示所需的关键发展。对边缘冰区的仔细检查将有助于解释卫星对冰缘位置的反演。调查人员将继续参与当地的外联活动，包括在太平洋科学中心(西雅图)和华盛顿大学罗宾逊青年学者中心的演讲，在俄勒冈州的公开演讲，经常向Corvallis报纸观点页面投稿气候科学，开发一个针对普通受众的项目网页，并更新他们的外联网站，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.