Foehn jets over the Larsen C Ice Shelf, Antarctica
Foehn jets over the Larsen C Ice Shelf, Antarctica
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DOI：
10.1002/qj.2382
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发表时间：
2015-04-01
影响因子：
8.9
通讯作者：
Gray, Sue L.
中科院分区：
文献类型：
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作者：
Elvidge, Andrew D.;Renfrew, Ian A.;Gray, Sue L.
在拉森C冰架上方南极半岛(AP)以东发现了此前不为人知的喷流。这些喷流对美联社东海岸有重大影响，该地区气候迅速变暖，近年来那里的两大块冰架已经坍塌。在AP的三次Fehn事件期间，在新飞机的观测中可以看到背风变暖和干燥，并在大约1.5公里的网格间距处用气象局统一模式(MetUM)进行了很好的模拟。在个例A中，弱西南风气流和上升的逆风逆风是具有上风阻塞的高度非线性流型的特征。在C个例中，较强的西北风表现为相对线性的个例，上风气流阻塞较少。情况B位于流型线性度介于两者之间的某个位置。在飞机观测和对所有三种情况的MetUM模拟中都能明显看到的烟尘急流是源自背风入口处的中尺度特征(宽度可达60公里)。通过反轨迹分析，确定它们属于缝隙流类型。在A和B两种情况下，喷流是不同的，相对于背景流被强烈加速，并被限制在拉森C冰架上方的低水平。它们就像阿尔卑斯山浅浅的沼泽。情况C类似于深渊的情况，只是喷流不太明显。与邻近的较平静的沼气区域相比，烟尘急流的温度要低得多，也更潮湿。这是由于急流区的减弱的烟尘效应：在A情况下，急流具有较低的迎风源区，而在更线性的情况C中，由于穿过山口的地形抬升减少，沿急流轨迹的非绝热增温和降水减少。
Previously unknown foehn jets have been identified to the east of the Antarctic Peninsula (AP) above the Larsen C Ice Shelf. These jets have major implications for the east coast of the AP, a region of rapid climatic warming and where two large sections of ice shelf have collapsed in recent years. During three foehn events across the AP, leeside warming and drying is seen in new aircraft observations and simulated well by the Met Office Unified Model (MetUM) at approximate to 1.5 km grid spacing. In case A, weak southwesterly flow and an elevated upwind inversion characterise a highly nonlinear flow regime with upwind flow blocking. In case C strong northwesterly winds characterise a relatively linear case with little upwind flow blocking. Case B resides somewhere between the two in flow regime linearity. The foehn jets - apparent in aircraft observations where available and MetUM simulations of all three cases - are mesoscale features (up to 60 km in width) originating from the mouths of leeside inlets. Through back trajectory analysis they are identified as a type of gap flow. In cases A and B the jets are distinct, being strongly accelerated relative to the background flow, and confined to low levels above the Larsen C Ice Shelf. They resemble the shallow foehn' of the Alps. Case C resembles a case of deep foehn', with the jets less distinct. The foehn jets are considerably cooler and moister relative to adjacent regions of calmer foehn air. This is due to a dampened foehn effect in the jet regions: in case A the jets have lower upwind source regions, and in the more linear case C there is less diabatic warming and precipitation along jet trajectories due to the reduced orographic uplift across the mountain passes.