One‐dimensional radiative transfer solvers are computationally much more efficient than full three‐dimensional radiative transfer solvers but do not account for the horizontal propagation of radiation and thus produce unrealistic surface irradiance fields in models that resolve clouds. Here, we study the impact of using a 3‐D radiative transfer solver on the direct and diffuse solar irradiance beneath clouds and the subsequent effect on the surface fluxes. We couple a relatively fast 3‐D radiative transfer approximation (TenStream solver) to the Dutch Atmosphere Large‐Eddy Simulation (DALES) model and perform simulations of a convective boundary layer over grassland with either 1‐D or 3‐D radiative transfer. Based on a single case study, simulations with 3‐D radiative transfer develop larger and thicker clouds, which we attribute mainly to the displaced clouds shadows. With increasing cloud thickness, the surface fluxes decrease in cloud shadows with both radiation schemes but increase beneath clouds with 3‐D radiative transfer. We find that with 3‐D radiative transfer, the horizontal length scales dominating the spatial variability of the surface fluxes are over twice as large as with 1‐D radiative transfer. The liquid water path and vertical wind velocity in the boundary layer are also dominated by larger length scales, suggesting that 3‐D radiative transfer may lead to larger convective thermals. Our case study demonstrates that 3‐D radiative effects can significantly impact dynamic heterogeneities induced by cloud shading. This may change our view on the coupling between boundary‐layer clouds and the surface and should be further tested for generalizability in future studies.

中文翻译：

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浅积云对植被表面动态非均质性的三维辐射效应

一维辐射传递求解器的计算效率比完整的三维辐射传递求解器要高得多，但不考虑辐射的水平传播，因此在解析云的模型中会产生不切实际的表面辐照场。在这里，我们研究了使用3D辐射转移求解器对云层下方直接和漫射太阳辐照度的影响以及对表面通量的后续影响。我们将相对快速的3D辐射传递近似（TenStream求解器）耦合到荷兰大气大涡模拟（DALES）模型，并通过1D或3D辐射传递对草地上的对流边界层进行仿真。基于单个案例研究，利用3D辐射传递进行的模拟会形成更大或更厚的云，我们主要归因于流离失所的云影。随着云层厚度的增加，两种辐射方案中的云阴影中的表面通量都减小，但是随着3D辐射传递，云层下方的通量增加。我们发现，对于3D辐射传递，控制表面通量空间变化的水平长度尺度是1D辐射传递的两倍。边界层中的液态水路径和垂直风速也受较大长度尺度的支配，这表明3D辐射传递可能导致较大的对流热。我们的案例研究表明，3D辐射效应可以显着影响由云阴影引起的动态异质性。