Clouds have been recognized to enhance surface melt on the Greenland Ice Sheet (GrIS). However, quantitative estimates of the effects of clouds on the GrIS melt area and ice-sheet-wide surface mass balance are still lacking. Here we assess the effects of clouds with a state-of-the-art regional climate model, conducting a numerical sensitivity test in which adiabatic atmospheric conditions as well as zero cloud water/ice amounts are assumed (i.e., clear-sky conditions), although the precipitation rate is the same as in the control all-sky simulation. By including or excluding clouds, we quantify time-integrated feedbacks for the first time. We find that clouds were responsible for a 3.1%, 0.3%, and 0.7% increase in surface melt extent (of the total GrIS area) in 2012, 2013, and 2014, respectively. During the same periods, clouds reduced solar heating and thus daily runoff by 1.6, 0.8, and 1.0 Gt day−1, respectively: clouds did not enhance surface mass loss. In the ablation areas, the presence of clouds results in a reduction of downward latent heat flux at the snow/ice surface so that much less energy is available for surface melt, which highlights the importance of indirect time-integrated feedbacks of cloud radiative effects.
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机译:人们已经认识到云可以增强格陵兰冰原(GrIS)的表面融化。但是,仍缺乏对云层对GrIS融化面积和冰盖范围的表面质量平衡的影响的定量估计。在这里,我们使用最新的区域气候模型评估云的影响,并进行了数值敏感性测试,假设绝热的大气条件以及零的云水/冰量(即晴朗的天空条件),尽管降水率与全天空模拟中的降水率相同。通过包含或排除云,我们首次量化了时间积分反馈。我们发现,云在2012年,2013年和2014年分别使表面融化程度(占GrIS总面积的)增加了3.1%,0.3%和0.7%。在同一时期,云减少了太阳采暖,因此每日径流量分别减少了1.6、0.8和1.0 Gt day -1 sup>:云并没有增加表面质量损失。在消融区域中,云的存在会导致雪/冰表面向下的潜热通量减少,从而使表面融化所用的能量更少,这突出了云辐射效应的时间积分反馈的重要性。
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