A model for the Arctic mixed layer circulation under a summertime lead: implications for the near-surface temperature maximum formation

IF 4.4 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Cryosphere Pub Date : 2023-08-21 DOI:10.5194/tc-17-3343-2023
A. Alvarez
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Abstract

Abstract. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occurs during winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, if any, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically 10–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. These observations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numerical modeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calm and moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells are generated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and the adjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near the surface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surface stresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer is formed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification, and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity is higher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layer formation. According to the results, ice drift is key to the development of the NSTM layer.
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夏季主导下的北极混合层环流模型:对近地表温度最高值形成的影响
摘要由于冬季发生的强烈海洋-大气热交换的气候相关性,海冰覆盖中的铅已被广泛研究。铅也是初夏热交换和融化的首选地点,但它们的海洋学和气候相关性,如果有的话,在夏季仍未得到很大程度的探索。特别是,在不同的北极盆地下,一个典型的10 - 30 m深的近地表最高温度(NSTM)层的发展,在观测上与太阳辐射穿过引线的穿透有关。这些观测结果表明,导联中的平静事件和风事件的串联可以促进NSTM层的发展。利用数值模拟和一个理想化的框架,本研究调查了夏季铅暴露在平静和温和风期的组合下NSTM层的形成。在平静期,太阳热量在铅下的上层积聚。近地表对流单元每天都在产生,从前边一直延伸到中心。对流细胞影响铅和邻近冰盖下的混合层中的热量储存。随后的风事件(以及相应的冰漂移)将新鲜和冷的融水混合并传播到靠近地表的温暖层中。表面混合导致近表层温度低于深层温度,而深层温度受表面应力的影响较弱。此外,最初位于铅表面下的温暖水域伸展并水平扩散。因此,形成了一个NSTM层。该研究分析了NSTM层的深度和温度对浮力强迫、风强度、冰漂移、分层和铅几何形状的敏感性。数值结果表明,NSTM层以中等风和冰漂移出现,当风强度大于9 m s−1时消失。根据背景分层的不同,平静期在NSTM层的形成中会加强或变得至关重要。结果表明,冰的漂移是NSTM层发育的关键。
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来源期刊
Cryosphere
Cryosphere GEOGRAPHY, PHYSICAL-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
8.70
自引率
17.30%
发文量
240
审稿时长
4-8 weeks
期刊介绍: The Cryosphere (TC) is a not-for-profit international scientific journal dedicated to the publication and discussion of research articles, short communications, and review papers on all aspects of frozen water and ground on Earth and on other planetary bodies. The main subject areas are the following: ice sheets and glaciers; planetary ice bodies; permafrost and seasonally frozen ground; seasonal snow cover; sea ice; river and lake ice; remote sensing, numerical modelling, in situ and laboratory studies of the above and including studies of the interaction of the cryosphere with the rest of the climate system.
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