Line-by-Line Calculations of Atmospheric Fluxes and Cooling Rates: Application to Water Vapor
Line-by-Line Calculations of Atmospheric Fluxes and Cooling Rates: Application to Water Vapor
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DOI：
10.1029/92jd01419
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发表时间：
1992-10
影响因子：
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通讯作者：
S. Clough;M. Iacono;J. Moncet
中科院分区：
文献类型：
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作者：
S. Clough;M. Iacono;J. Moncet
基于逐线辐射模型FASCODE开发了一个加速计算晴天通量的模型，并将其应用于大气水汽冷却率的计算。该模型实现了长波上升流和下降流通量的计算精度为0.2%的顺序，以及在目前的限制内的光谱参数，线形的不确定性，和相关的连续精度。对于同样的线形处理，即截断值为10 cm−1的Voigt廓线，没有连续体，本模式的结果与另外两个逐线模式的结果是可以接受的一致，这两个逐线模式是气候模式中使用的辐射代码相互比较的一部分（ICRCCM）。对于这条线的轮廓和中纬度夏季大气，从我们的模式和戈达德大气实验室（GLA）模型的结果之间的最大差异发生在地面的下降流通量，与本模型提供的值大于从GLA。这些差异通常与本模型中更大的大气不透明度一致，这归因于水半宽的自增宽分量和低压区更精细的光谱采样。利用FASCODE中的线形和相关的连续体模型给出的结果与其他两个模型提供的结果有显着不同。这种辐射模型，包括外国的连续以及从修改后的自连续的贡献，已收到广泛的验证对测量的辐射光谱，其中的一个例子。对于中纬度夏季大气，外来连续谱的主要贡献出现在对流层上部250-350 cm−1的光谱区域，而自连续谱的贡献取决于水汽密度的平方，在对流层下部最大。对于中纬度夏季大气，外来连续谱对对流层上部的冷却贡献了0.4 Kd−1或20%，而自连续谱对地表水汽冷却率的贡献为1.9 K d−1。后者比GLA模型的冷却速率小0.17 K d−1，这主要是由于自连续谱的修改。一个重要的结果，已经从目前的工作是洞察大气辐射过程提供的冷却率的光谱剖面。在光谱域中，存在由普朗克函数加权的高度和分子吸收强度之间的映射。大气顶部的出射光谱辐射率与光谱冷却率廓线之间极高的相关性表明，对出射光谱辐射率的测量可以提供光谱积分量所不能提供的关于大气状态的重要信息。我们的研究结果还表明，从100到600 cm−1的光谱区域与大气水蒸气相关的辐射传输的关键重要性。
A model for the accelerated calculation of clear sky fluxes based on the line-by-line radiance model FASCODE has been developed and applied to the calculation of cooling rates for atmospheric water vapor. The model achieves computational accuracies for the longwave upwelling and downwelling fluxes of the order of 0.2%, an accuracy well within current limitations imposed by uncertainties in the spectral parameters, the line shape, and the associated continua. For the same treatment of line shape, the Voigt profile with a 10 cm−1 cutoff and no continuum, the results from the present model are in acceptable agreement with those from two other line-by-line models reported as part of the intercomparison of radiation codes used in climate models (ICRCCM). For this line profile and the mid-latitude summer atmosphere, the largest difference between the results from our model and the Goddard Laboratory for Atmospheres (GLA) model occurs for the downwelling flux at the surface, with the present model providing a value greater than that from GLA. The differences are generally consistent with greater atmospheric opacity from the present model, attributable to the inclusion of a self-broadening component for the half width for water and to finer spectral sampling in the lower-pressure regime. Utilization of the line shape and associated continuum model included in FASCODE gives results that are significantly different from those provided by the other two models. This radiance model, including contributions from the foreign continuum as well as from a modified self-continuum, has received extensive validation against measured radiance spectra, an example of which is provided. For the mid-latitude summer atmosphere the principal contribution from the foreign continuum occurs in the upper troposphere in the 250–350 cm−1 spectral region, whereas the contribution from the self-continuum, dependent on the square of the water vapor density, is greatest in the lower troposphere. For the mid-latitude summer atmosphere the foreign continuum contributes 0.4 Kd−1 or 20% to the cooling in the upper troposphere and the self-continuum contributes 1.9 K d−1 to the cooling rate at the surface due to water vapor. The latter is 0.17 K d−1 less than the cooling rate from the GLA model which is principally due to a modification of the self-continuum. A significant result that has developed from the present work is the insight into atmospheric radiative processes provided by spectral profiles of the cooling rate. In the spectral domain there exists a mapping between the altitude and the molecular absorption strength as weighted by the Planck function. The extremely high correlation between the outgoing spectral radiance at the top of the atmosphere and the spectral cooling rate profile suggests that measurement of the outgoing spectral radiance can provide important information about atmospheric state that is not available from spectrally integrated quantities. Our results also indicate the critical importance of the spectral region from 100 to 600 cm−1 for the radiative transfer associated with atmospheric water vapor.