南大洋南奥克尼群岛的极端温暖事件：大气河流和焚风条件的复合影响,Quarterly Journal of the Royal Meteorological Society

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南大洋南奥克尼群岛的极端温暖事件：大气河流和焚风条件的复合影响
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2023-09-18 , DOI: 10.1002/qj.4578
Hua Lu ₁ , Andrew Orr ₁ , John King ₁ , Tony Phillips ₁ , Ella Gilbert ₁ , Steve Colwell ₁ , Thomas J. Bracegirdle ₁

Affiliation

利用 Signy 和 Orcadas 站分别 1947-1994 年和 1956-2019 年的天气观测对南奥克尼群岛 (SOI) 的极端温暖事件进行了调查。将极端温度定义为超过温度分布的第 95 个百分位数，我们揭示了温暖事件的特征和相关驱动因素，特别是夏季和冬季的十大事件。在这两个监测站，极端温暖事件通常涉及大气河流 (AR) 和局部焚风变暖的综合影响，由于监测站位置相对于 SOI 中最大和最高的岛屿加冕岛，因此具有明显的特征。例如，西尼的温暖事件比奥卡达斯的相应同期温度要高（平均约 3°C）。在这两个站的记录期内，每年的温暖事件数量显着增加，这可能会通过增加冰雪融化来影响生态系统。西格尼的极端温暖事件主要是焚风变暖与源自南大西洋的暖气相结合，南大西洋温暖、富含水分的空气在增强的北风的作用下迅速平流向岛屿。相比之下，奥卡达斯的极端温暖事件涉及暖空气平流和焚风变暖，这些变暖与源自太平洋、穿过德雷克海峡的西北风/西风带增强有关。使用仅大气的英国气象局统一模型的 1 公里网格间距配置对 Signy 站的十大温暖事件之一进行模拟，以理清局部与大规模强迫的作用。我们发现，在案例研究中，大部分变暖可归因于焚风效应。这些结果证明了南极极端温度的复杂性。

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Extreme warm events in the South Orkney Islands, Southern Ocean: Compounding influence of atmospheric rivers and föhn conditions

Extreme warm events in the South Orkney Islands (SOIs) are investigated using synoptic observations from Signy and Orcadas stations for 1947–1994 and 1956–2019 respectively. Defining the extremes as temperatures exceeding the 95th percentile of the temperature distribution, we reveal the characteristics and associated drivers of the warm events, especially the top 10 events in both summer and winter. At both stations, extreme warm events often involve a combined effect of atmospheric rivers (ARs) and localised föhn warming, with distinct characteristics due to the station locations relative to Coronation Island, the largest and highest island of the SOIs. For example, warm events at Signy are warmer (by an average of around 3°C) than the corresponding concurrent temperatures at Orcadas. The number of warm events per year has significantly increased over the record periods at both stations, which could potentially impact ecosystems by increasing melting of snow and ice. Extreme warm events at Signy are dominated by föhn warming in combination with ARs originating from the Southern Atlantic Ocean, where warm, moisture-rich air is rapidly advected towards the islands by enhanced northerly winds. By contrast, the Orcadas warm extremes involve both warm-air advection and föhn warming associated with enhanced northwesterlies/westerlies with ARs originating in the Pacific Ocean that travel across the Drake Passage. Simulation of one of the top 10 warm events for Signy station using a 1-km grid spacing configuration of the atmosphere-only UK Met Office Unified Model is used to disentangle the role of local versus large-scale forcing. We find that the majority of the warming can be attributed to föhn effects for the case study. These results demonstrate the complexity of Antarctic temperature extremes.

更新日期：2023-09-18

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