来自高分辨率可见卫星图像的Terra Nova Bay Polynya frazil条纹的空间特征

IF 4.4 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Cryosphere Pub Date : 2023-05-17 DOI:10.5194/tc-17-2073-2023
K. Bradtke, A. Herman
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引用次数: 1

摘要

摘要南极大陆周围的沿海波利尼西亚是海洋-大气热量和水分交换非常强烈的区域,这对当地和区域天气、海冰产生和水团形成非常重要。由于极端的大气条件(非常强的离岸流、低空气温度和湿度),波利尼西亚的表层海洋高度湍流,由于Langmuir、风致和浮力驱动的组合湍流而混合。混合层动力学和形成的海冰之间复杂相互作用的一个明显迹象是frazil条纹,这是由开阔水域隔开的高冰浓度的细长斑块。尽管frazil条纹无处不在,但其观测和建模分析一直非常有限,这在很大程度上是因为它们对热通量和冰产生的意义才刚刚变得明显。在本研究中,首次对Terra Nova Bay Polynya(TNBP)的地表frazil浓度的空间变异性进行了综合分析。Frazil条纹以高分辨率(像素大小为10-15 m) 可见卫星图像及其特性(表面积、宽度、间距和方向)与气象强迫(风速和气温)有关。这为估计给定气象条件下高冰产量地区的范围和冰覆盖率提供了一个简单的统计工具。研究还表明,窄条纹的方向往往与风向一致,这表明局部风力在其形成中起主导作用。非常宽的条纹反过来偏离了这种模式,因为它们可能受到几个其他因素的影响,包括地表水循环和相关的辐合带。与用光谱波模型计算的模拟开放水域波长相比,对图像中确定的峰值波长和方向的分析表明,TNBP中观测到的波增长显著放缓。这表明frazil条纹在改变波阵中的风浪增长和/或消散方面发挥了重要作用。
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Spatial characteristics of frazil streaks in the Terra Nova Bay Polynya from high-resolution visible satellite imagery
Abstract. Coastal polynyas around the Antarctic continent are regions of very strong ocean–atmosphere heat and moisture exchange that are important for local and regional weather, sea ice production, and water mass formation. Due to extreme atmospheric conditions (very strong offshore winds, low air temperature, as well as humidity) the surface ocean layer in polynyas is highly turbulent, with mixing due to combined Langmuir, wind-induced, and buoyancy-driven turbulence. One of the visible signs of complex interactions between the mixed-layer dynamics and the forming sea ice are frazil streaks, elongated patches of high ice concentration separated by areas of open water. In spite of their ubiquity, observational and modelling analyses of frazil streaks have been very limited largely due to the fact that their significance for heat flux and ice production is only just becoming apparent. In this study, the first comprehensive analysis of the spatial variability of surface frazil concentration is performed for the Terra Nova Bay Polynya (TNBP). Frazil streaks are identified in high-resolution (pixel size 10–15 m) visible satellite imagery, and their properties (surface area, width, spacing, and orientation) are linked to the meteorological forcing (wind speed and air temperature). This provides a simple statistical tool for estimating the extent and ice coverage of the region of high ice production under given meteorological conditions. It is also shown that the orientation of narrow streaks tends to agree with the wind direction, suggesting the dominating role of the local wind forcing in their formation. Very wide streaks, in turn, deviate from that pattern, as they are presumably influenced by several additional factors, including local water circulation and the associated convergence zones. An analysis of peak wavelengths and directions determined from the images, compared to analogous open-water wavelengths computed with a spectral wave model, demonstrates a significant slow-down in the observed wave growth in TNBP. This suggests an important role of frazil streaks in modifying wind-wave growth and/or dissipation in polynyas.
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来源期刊
Cryosphere
Cryosphere GEOGRAPHY, PHYSICAL-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
8.70
自引率
17.30%
发文量
240
审稿时长
4-8 weeks
期刊介绍: The Cryosphere (TC) is a not-for-profit international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on all aspects of frozen water and ground on Earth and on other planetary bodies. The main subject areas are the following: ice sheets and glaciers; planetary ice bodies; permafrost and seasonally frozen ground; seasonal snow cover; sea ice; river and lake ice; remote sensing, numerical modelling, in situ and laboratory studies of the above and including studies of the interaction of the cryosphere with the rest of the climate system.
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