Radiative sensitivities of tropical anvils to small ice crystals
Radiative sensitivities of tropical anvils to small ice crystals
复制标题
热带砧对小冰晶的辐射敏感性
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
J. Kiehl
中科院分区：
文献类型：
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作者：
C. Zender;J. Kiehl
模拟了热带对流层上部的层状铁砧，以确定其辐射特性对小冰晶存在的敏感性。云的演变模拟在一个一维（垂直）的框架，包括上升气流，沉积，升华，沉降，成核和辐射。云辐射强迫、反照率、发射率和加热率的敏感性是从一项测试中得出的，该测试包括然后排除了大量小晶体的存在。这些晶体尺寸（3 < L < 20 μm）在最近的观测中已经测量到，但小于大多数过去观测的检测极限。短波强迫和短波强迫对小晶体的存在非常敏感，即使这些晶体占总云质量的不到2%。对于光学厚砧的长波强迫和发射率，在一般情况下，小冰晶比他们的短波同行的敏感性低得多。假设六方晶体习性的辐射处理产生了与球形习性相同的灵敏度。结果与先前的研究一致，因为六方晶体的反向散射增加了行星的散射，增加了10- 15%。小晶体的加热速率的敏感性取决于垂直位置的云和长波和短波加热扰动之间的抵消。小晶体改变加热率高达50%，在云顶和底部。
Stratiform anvils in the upper tropical troposphere were simulated to determine the sensitivities of their radiative properties to the presence of small ice crystals. Cloud evolution was modeled in a one-dimensional (vertical) framework incorporating an updraft, deposition, sublimation, sedimentation, nucleation, and radiation. The sensitivities of cloud radiative forcing, albedo, emissivity, and heating rate were derived from a test that included and then excluded the presence of numerous small crystals. These crystals sizes (3 < L < 20 μm) have been measured in recent observations but are smaller than the detection limit of most past observations. The shortwave forcing and albedo were very sensitive to the presence of the small crystals, even though these crystals accounted for less than 2% of total cloud mass. For optically thick anvils the longwave forcing and emissivity were, in general, much less sensitive to the small ice crystals than their shortwave counterparts. Radiative treatments assuming a hexagonal crystal habit yielded the same sensitivities as the spherical habit. The results agreed with previous studies in that the increased backscatter from hexagonal crystals enhanced the planetary albedo by ∼10–15%. The heating rate sensitivity to the small crystals depended on vertical location within the cloud and showed cancelation between the longwave and the shortwave heating perturbations. The small crystals changed heating rates by up to 50% at cloud top and base.