Dynamics of the snow grain size in a windy coastal area of Antarctica from continuous in situ spectral-albedo measurements

IF 4.4 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Cryosphere Pub Date : 2023-06-08 DOI:10.5194/tc-17-2323-2023
Sara Arioli, G. Picard, L. Arnaud, V. Favier
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引用次数: 1

Abstract

Abstract. The grain size of the superficial snow layer is a key determinant of the surface albedo in Antarctica. Its evolution is the result of multiple interacting processes, such as dry and wet metamorphism, melt, snow drift, and precipitation. Among them, snow drift has the least known and least predictable impact. The goal of this study is to relate the variations in surface snow grain size to these processes in a windy location of the Antarctic coast. For this, we retrieved the daily grain size from 5-year-long in situ observations of the spectral albedo recorded by a new multi-band albedometer, unique in terms of autonomy and described here for the first time. An uncertainty assessment and a comparison with satellite-retrieved grain size were carried out to verify the reliability of the instrument, and an RMSE up to 0.16 mm in the observed grain size was found. By relating these in situ measurements to time series of snow drift, surface temperature, snow surface height and snowfall, we established that the evolution of the grain size in the presence of snow drift is complex and follows two possible pathways: (1) a decrease in the grain size (about half of our measurements) resulting from the deposition of small grains advected by the wind (surprisingly, this decrease is often – 2/3 of the cases– associated with a decrease in the surface height, i.e., a net erosion over the drift episode), (2) an increase in the grain size (the other half) due to either the removal of the surface layer or metamorphism. However, we note that this increase is often limited with respect to the increase predicted by a theoretical metamorphism model, suggesting that a concomitant deposition of small grains is likely. At last, we found that wind also completely impedes the deposition of snowfall during half of the observed precipitation events. When this happens, the grain size evolves as if precipitation were not occurring. As a result of all these processes, we conclude that the grain size in a windy area remains more stable than it would be in the absence of snow drift, hence limiting the variations in the albedo and in the radiative energy budget.
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根据连续的现场光谱反照率测量,南极洲多风沿海地区雪粒大小的动力学
摘要表层积雪的粒度是决定南极地表反照率的关键因素。它的演化是干湿变质、融化、雪漂、降水等多种相互作用的结果。其中,积雪漂移的影响是最不为人所知和最不可预测的。这项研究的目的是将南极海岸多风地区表面雪颗粒大小的变化与这些过程联系起来。为此,我们从一种新的多波段反照率计记录的光谱反照率的5年原位观测中检索了每日颗粒大小,这种反照率计在自主性方面是独一无二的,在这里是第一次描述。为了验证仪器的可靠性,进行了不确定度评估并与卫星反演的粒度进行了比较,发现观测到的粒度的RMSE高达0.16 mm。通过将这些原位测量结果与积雪漂移、地表温度、雪面高度和降雪量的时间序列相关联,我们确定了积雪存在下粒度的演变是复杂的,并遵循两种可能的途径:(1)由风平流的小颗粒沉积引起的颗粒尺寸减小(约占我们测量值的一半)(令人惊讶的是,这种减小通常- 2/3的情况-与地表高度的降低有关,即,漂移期间的净侵蚀),(2)由于表层的去除或变质作用而导致的颗粒尺寸增大(另一半)。然而,我们注意到,相对于理论变质模型预测的增加,这种增加往往是有限的,这表明可能伴随有小颗粒的沉积。最后,我们发现在观测到的一半降水事件中,风也完全阻碍了降雪的沉积。当这种情况发生时,颗粒大小的变化就好像降水没有发生一样。由于所有这些过程,我们得出结论,有风地区的颗粒尺寸比没有积雪的地区更稳定,因此限制了反照率和辐射能量收支的变化。
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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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