Mechanisms associated with winter intraseasonal extreme sea ice extent in the Weddell Sea

Fabio Ullmann Furtado de LIMA; Leila M. V. CARVALHO

摘要

Previous studies have shown evidence of atmospheric extratropical wave trains modulating sea ice area in the Weddell and Amundsen/Bellingshausen seas on intraseasonal time-scales (20–100 d). Here we investigate mechanisms relating intraseasonal extreme sea ice extent and Ekman layer dynamics with emphasis on the Weddell Sea. This study extends from 1989 to 2013 and focuses on the winter season. Wind stress τ is calculated with winds from the Climate Forecast System reanalysis (CFSR) to evaluate momentum transfer between the atmosphere and the Ekman layer. Lag-composites of the anomalies of Ekman transport and the Ekman pumping indicate that divergence of mass in the Ekman layer and upwelling lead the occurrence of extreme sea ice contraction on intraseasonal time-scales in the Weddell Sea. Opposite conditions (i.e., convergence of the mass and downwelling) lead extreme sea ice expansion on intraseasonal time-scales. This study suggests that the Ekman pumping resulting from the anomalous wind stress on intraseasonal time-scales can transport these warmer waters to the surface contributing to sea ice melting. Additionally, high resolution sea ice fraction and ocean currents obtained from satellite and in situ data are used to investigate in detail mechanisms associated with persistent extreme sea ice expansion and contraction on intraseasonal time-scales. These case studies reveal that atmospheric circumpolar waves on intraseasonal time-scales can induce contrasting anomalies of about ±20% in sea ice concentration at the Weddell and western Antarctica Peninsula margins within less than 30 d. This study shows that extreme anomalies in sea ice may lag between 5–25 d (1–5 pentads) the ocean-atmospheric forcing on intraseasonal time-scales.

机译：先前的研究表明，在季节内时间尺度上（20-100 d），大气温带波列调节了Weddell和Amundsen / Bellingshausen海中的海冰面积。在这里，我们研究有关季节内极端海冰范围和埃克曼层动力学的机制，重点是韦德尔海。这项研究从1989年持续到2013年，重点是冬季。风应力τ是根据气候预测系统再分析（CFSR）的风计算得出的，以评估大气层与埃克曼层之间的动量传递。 Ekman输运和Ekman抽水异常的滞后复合资料表明，Ekman层和上升流中的质量散布导致在韦德尔海的季节内时间尺度上发生极端的海冰收缩。相反的条件（即质量和下降流的收敛）导致了季节内时间尺度上的极端海冰膨胀。这项研究表明，季节内时标上异常风应力引起的埃克曼抽水可以将这些较暖的水运到地表，促进海冰融化。另外，从卫星和原位数据获得的高分辨率海冰分数和洋流用于详细研究与季节内时间尺度上持续的极端海冰扩张和收缩有关的机制。这些案例研究表明，在不到30 d内，季节内时间尺度上的大气绕极波可引起Weddell和南极西部半岛边缘海冰浓度的约20％的对比异常。这项研究表明，在季节内时间尺度上，海冰中的极端异常可能滞后于海洋大气强迫的5-25 d（1-5个五单元组）之间。

Mechanisms associated with winter intraseasonal extreme sea ice extent in the Weddell Sea

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