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Most radiative transfer parameterizations in numerical cloud models transfer radiation in the vertical direction only, utilizing the independent pixel approximation. This method cannot correctly simulate neither the location nor the shape of cloud shadows because shortwave radiation only propagates vertically, and thus it does not account for the slanted path the direct solar beam takes through the atmosphere. Herein, the tilted independent pixel approximation, which more properly accounts for the geometry of the direct solar beam, is applied to a cumulonimbus cloud field. This computationally inexpensive method results in a more accurately modeled cloud shadow at the surface, allowing for more accurate computations of near-surface air temperatures. |
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