Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT Leeds, United Kingdom;
Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, LS2 9JT Leeds, United Kingdom.
Proc Natl Acad Sci U S A. 2018 Mar 13;115(11):2687-2692. doi: 10.1073/pnas.1721627115. Epub 2018 Feb 28.
Large biases in climate model simulations of cloud radiative properties over the Southern Ocean cause large errors in modeled sea surface temperatures, atmospheric circulation, and climate sensitivity. Here, we combine cloud-resolving model simulations with estimates of the concentration of ice-nucleating particles in this region to show that our simulated Southern Ocean clouds reflect far more radiation than predicted by global models, in agreement with satellite observations. Specifically, we show that the clouds that are most sensitive to the concentration of ice-nucleating particles are low-level mixed-phase clouds in the cold sectors of extratropical cyclones, which have previously been identified as a main contributor to the Southern Ocean radiation bias. The very low ice-nucleating particle concentrations that prevail over the Southern Ocean strongly suppress cloud droplet freezing, reduce precipitation, and enhance cloud reflectivity. The results help explain why a strong radiation bias occurs mainly in this remote region away from major sources of ice-nucleating particles. The results present a substantial challenge to climate models to be able to simulate realistic ice-nucleating particle concentrations and their effects under specific meteorological conditions.
大尺度的气候模式模拟在南大洋上空云辐射特性方面存在较大偏差，导致模拟海表温度、大气环流和气候敏感性出现较大误差。在这里，我们结合云分辨模式模拟和该区域冰核浓度的估计，表明我们模拟的南大洋云反射的辐射远多于全球模式预测的，这与卫星观测结果一致。具体来说，我们表明，对冰核浓度最敏感的云是在温带气旋冷区的低层混合相云，这些云先前被确定为南大洋辐射偏差的主要贡献者。南大洋上空普遍存在的极低冰核浓度强烈抑制云滴冻结，减少降水，并提高云反射率。研究结果有助于解释为什么主要远离冰核来源的这个偏远地区会出现强烈的辐射偏差。研究结果对气候模型提出了重大挑战，需要能够模拟特定气象条件下实际的冰核浓度及其影响。
