Global numerical weather prediction and climate models are subject to long‐standing systematic shortwave radiation errors due to deficiencies in the representation of boundary layer clouds over the ocean. In the subtropics, clouds are typically too reflective in the cumulus regime and not reflective enough in the stratocumulus regime. Potential sources of error include cloud cover, liquid water path, effective radius, and subgrid heterogeneity, but diagnosing the absolute contributions of each to the radiation bias is hampered by uncertainties and sometimes contradictory information from different observational products. This paper draws on a set of ship‐based observations of boundary layer clouds obtained during the ARM MAGIC campaign along a northeast Pacific Ocean transect, crossing both stratocumulus and shallow cumulus cloud regimes. The surface‐based observations of cloud properties are compared with various satellite products, taking account of the diurnal cycle, to provide an improved quantitative assessment of the deficiencies in the European Centre for Medium‐Range Weather Forecasts global numerical weather prediction model. A series of off‐line radiation calculations are then performed to assess the impact on the shortwave radiation bias of correcting each of the model's deficiencies in cloud characteristics along the transect. A reduction in the bias is achieved by improving the agreement between modeled and observed in‐cloud liquid water path frequency distributions. In the cumulus regime, this is accomplished primarily by reducing the all‐sky water path, while for the stratocumulus regime, an underestimate of cloud cover and liquid water and an overestimate in effective radius and subgrid heterogeneity all contribute to a lack of reflected shortwave radiation.

中文翻译：

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了解亚热带海洋边界层云区域中的全局模型系统短波辐射误差

由于海洋边界层云表示的不足，全球数值天气预报和气候模型容易受到长期的系统性短波辐射误差的影响。在亚热带地区，云层通常在积云区中反射过多，而在平积云区中反射不足。错误的潜在来源包括云层覆盖，液态水路径，有效半径和亚网格异质性，但是由于不确定性以及有时来自不同观测产品的矛盾信息的存在，难以诊断出每种对辐射偏差的绝对贡献。本文借鉴了一组基于ARM的MAGIC运动期间沿东北太平洋样带获得的边界层云的观测结果，这些云跨越了平积云和浅积云区域。考虑到昼夜周期，将基于云的表面性质与各种卫星产品的观测值进行比较，以提供对欧洲中距离天气预报中心全球数值天气预报模型中的缺陷的定量评估。然后，进行一系列离线辐射计算，以评估校正模型沿断面云特征的每个缺陷对短波辐射偏差的影响。通过改善模拟和观察到的云中液态水路径频率分布之间的一致性，可以减少偏差。在积云区，这主要是通过减少全天的水路来实现的，而对于平积云区，