The Dynamics of Shelf Forcing in Greenlandic Fjords
The Dynamics of Shelf Forcing in Greenlandic Fjords
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DOI：
10.1175/jpo-d-18-0057.1
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发表时间：
2018-11-01
影响因子：
3.5
通讯作者：
Straneo, Fiamma
中科院分区：
文献类型：
--
作者：
Jackson, Rebecca H.;Lentz, Steven J.;Straneo, Fiamma
连接格陵兰冰川和海洋的峡湾是进口热量融化冰和出口融水进入海洋的门户。热量和融水的运输可以通过峡湾环流的各种驱动因素进行调节，包括淡水、当地风和陆架变化。陆架强迫流动（也称为中介流通）是格陵兰岛东部两个主要峡湾的主要变化模式，但我们缺乏对峡湾对陆架强迫的响应的动态理解。从东格陵兰岛的观测的基础上，我们使用数值模拟和分析模型来探索货架驱动流的动态。对于格陵兰峡湾的参数空间，我们发现，峡湾的响应主要是一个函数的三个无量纲参数：峡湾宽度的变形半径（W/R-d），迫使时间尺度的峡湾调整时间尺度，和强迫振幅（货架密度跃层位移）的上层厚度。数值模拟和观测中的陆架强迫流在很大程度上可以用一个简单的开尔文波在峡湾周围传播的分析模型来解释。对于W/R-d > 0.5的峡湾（大多数格陵兰峡湾），三维动力学是理解陆架强迫不可或缺的，峡湾动力学不能用忽略跨峡湾结构的二维模型来近似。峡湾和大陆架之间交换的体积通量增加狭窄的峡湾和共振强迫频率附近的峰值，在较高和较低的频率强迫显着下降。
The fjords that connect Greenland's glaciers to the ocean are gateways for importing heat to melt ice and for exporting meltwater into the ocean. The transport of heat and meltwater can be modulated by various drivers of fjord circulation, including freshwater, local winds, and shelf variability. Shelf-forced flows (also known as the intermediary circulation) are the dominant mode of variability in two major fjords of east Greenland, but we lack a dynamical understanding of the fjord's response to shelf forcing. Building on observations from east Greenland, we use numerical simulations and analytical models to explore the dynamics of shelf-driven flows. For the parameter space of Greenlandic fjords, we find that the fjord's response is primarily a function of three nondimensional parameters: the fjord width over the deformation radius (W/R-d), the forcing time scale over the fjord adjustment time scale, and the forcing amplitude (shelf pycnocline displacements) over the upper-layer thickness. The shelf-forced flows in both the numerical simulations and the observations can largely be explained by a simple analytical model for Kelvin waves propagating around the fjord. For fjords with W/R-d > 0.5 (most Greenlandic fjords), 3D dynamics are integral to understanding shelf forcingthe fjord dynamics cannot be approximated with 2D models that neglect cross-fjord structure. The volume flux exchanged between the fjord and shelf increases for narrow fjords and peaks around the resonant forcing frequency, dropping off significantly at higher- and lower-frequency forcing.