Foehn warming distributions in nonlinear and linear flow regimes: a focus on the Antarctic Peninsula
Foehn warming distributions in nonlinear and linear flow regimes: a focus on the Antarctic Peninsula
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DOI：
10.1002/qj.2489
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发表时间：
2016-01-01
影响因子：
8.9
通讯作者：
Lachlan-Cope, Tom A.
中科院分区：
文献类型：
--
作者：
Elvidge, Andrew D.;Renfrew, Ian A.;Lachlan-Cope, Tom A.
本文研究焚风事件中背风面暖化的结构与跨障流区线性的关系。两个对比的情况下，西风气流在南极半岛（AP）被认为是一个高度非线性，其他相对线性。撞击AP的西风气流为研究焚风提供了世界上最好的天然实验室之一，这是由于其海洋环境和拉森C冰架（LCIS）在其东侧提供了广阔，均匀和光滑的表面。利用气象局统一模型（网格尺寸为1.5公里）和飞机观测的数值模拟。在情况A中，相对较弱的西南跨半岛流和升高的逆风逆温决定了高度非线性焚风事件，观察到山波破碎。随之而来的强烈加速下坡流导致高振幅变暖和冰架融化直接背风的AP。然而，由于焚风气流通过水跃向上上升，焚风变暖在顺风方向迅速减弱。在情况C中，强烈的西北风决定了相对线性的流态。没有水跃，强烈的焚风能够在整个冰架的低层流动，机械地混合近地表流，防止强烈的地表逆温的发展，并向冰架输送大量的感热。因此，在情况C中，整个LCIS上的融冰速率比情况A中的大得多。我们的研究结果意味着，虽然非线性焚风事件会导致强烈的变暖，在直接的背风山脉，线性焚风事件通常会导致更广泛的背风面变暖，并在冰面上，更高的融化率。这对美联社有重大影响，最近东海岸变暖导致LCIS以北的两个冰架崩溃。
The structure of lee-side warming during foehn events is investigated as a function of cross-barrier flow regime linearity. Two contrasting cases of westerly flow over the Antarctic Peninsula (AP) are considered - one highly nonlinear, the other relatively linear. Westerly flow impinging on the AP provides one of the best natural laboratories in the world for the study of foehn, owing to its maritime setting and the Larsen C Ice Shelf (LCIS) providing an expansive, homogeneous and smooth surface on its east side. Numerical simulations with the Met Office Unified Model (at 1.5 km grid size) and aircraft observations are utilized. In case A, relatively weak southwesterly cross-Peninsula flow and an elevated upwind inversion dictate a highly nonlinear foehn event, with mountain wave breaking observed. The consequent strongly accelerated downslope flow leads to high-amplitude warming and ice-shelf melt in the immediate lee of the AP. However this foehn warming diminishes rapidly downwind due to upward ascent of the foehn flow via a hydraulic jump. In case C, strong northwesterly winds dictate a relatively linear flow regime. There is no hydraulic jump and strong foehn winds are able to flow at low levels across the entire ice shelf, mechanically mixing the near-surface flow, preventing the development of a strong surface inversion and delivering large fluxes of sensible heat to the ice shelf. Consequently, in case C ice-melt rates are considerably greater over the LCIS as a whole than in case A. Our results imply that although nonlinear foehn events cause intense warming in the immediate lee of mountains, linear foehn events will commonly cause more extensive lee-side warming and, over an ice surface, higher melt rates. This has major implications for the AP, where recent east-coast warming has led to the collapse of two ice shelves immediately north of the LCIS.