Improvement of a snow albedo parameterization in the Snow–Atmosphere–Soil Transfer model: evaluation of impacts of aerosol on seasonal snow cover
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The presence of light-absorbing aerosols (LAA) in snow profoundly influence the surface energy balance and water budget. However, most snow-process schemes in land-surface and climate models currently do not take this into consideration. To better represent the snow process and to evaluate the impacts of LAA on snow, this study presents an improved snow albedo parameterization in the Snow–Atmosphere–Soil Transfer (SAST) model, which includes the impacts of LAA on snow. Specifically, the Snow, Ice and Aerosol Radiation (SNICAR) model is incorporated into the SAST model with an LAA mass stratigraphy scheme. The new coupled model is validated against in-situ measurements at the Swamp Angel Study Plot (SASP), Colorado, USA. Results show that the snow albedo and snow depth are better reproduced than those in the original SAST, particularly during the period of snow ablation. Furthermore, the impacts of LAA on snow are estimated in the coupled model through case comparisons of the snowpack, with or without LAA. The LAA particles directly absorb extra solar radiation, which accelerates the growth rate of the snow grain size. Meanwhile, these larger snow particles favor more radiative absorption. The average total radiative forcing of the LAA at the SASP is 47.5 W m−2. This extra radiative absorption enhances the snowmelt rate. As a result, the peak runoff time and “snow all gone” day have shifted 18 and 19.5 days earlier, respectively, which could further impose substantial impacts on the hydrologic cycle and atmospheric processes.
Key wordslight-absorbing aerosols snow albedo SAST SNICAR
积雪中的吸光性气溶胶可以对地表能量平衡和水平衡产生显著的影响. 然而, 在当前考虑了积雪过程方案的陆面和气候模式中, 大多数方案却忽视了气溶胶带来的这些影响. 为了更好地再现积雪过程并评估吸光性气溶胶对积雪的影响, 本文采用了雪-冰-气溶胶辐射模型(SNICAR)来改进雪-大气-土壤传输模型(SAST)中的积雪反照率参数化方案, 并使用美国科罗拉多 SASP 站点观测资料验证了该耦合模式. 结果表明, 相比原始模式, 新耦合的模式可以更好地再现积雪反照率和雪深的变化, 特别是在融雪期间. 此外, 为了进一步评估气溶胶对积雪的影响, 本文利用新耦合模式分别模拟了干净的雪和含吸光性气溶胶的积雪的季节变化特征. 模拟结果显示, 吸光性气溶胶可以吸收额外的太阳辐射, 使得积雪粒子粒径增长, 而同时, 粒径的增长有利于积雪粒子吸收更多的辐射能量. 在 SASP站, 吸光性气溶胶的平均辐射强迫为47.5 W m−2. 该额外辐射吸收量提高了积雪融化率, 使得径流峰值时间和积雪完全融化的时间分别提前了平均 18 和 19.5 天, 而这将对后续的水文和大气过程产生重要影响.
关键词吸光性气溶胶 积雪反照率 SAST SNICAR
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We acknowledge the Center for Snow and Avalanche Studies and Mr. Jeff DERRY for the data availability. We also thank the two anonymous reviewers for their helpful comments, which improved the paper. This work was supported jointly by projects from the National Natural Science Foundation of China (Grant No. 41275003) and the National Key Basic Research and Development Projects of China (Grant No. 2014CB953903).
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