INFORMATION-CONTENT OF AVHRR CHANNELS 4 AND 5 WITH RESPECT TO THE EFFECTIVE RADIUS OF CIRRUS CLOUD PARTICLES
INFORMATION-CONTENT OF AVHRR CHANNELS 4 AND 5 WITH RESPECT TO THE EFFECTIVE RADIUS OF CIRRUS CLOUD PARTICLES
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DOI：
10.1175/1520-0450-30.7.973
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发表时间：
1991-07-01
期刊：
影响因子：
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通讯作者：
FOUQUART, Y
中科院分区：
文献类型：
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作者：
PAROL, F;BURIEZ, JC;FOUQUART, Y
本文研究了11 μ m和12 μ mAVHRR资料在亮温与透明卷云微物理特性关系上的重要差异。 在非散射近似中，通道4和5的发射度通过吸收系数比相关，吸收系数比是获得云粒子尺寸的关键参数。 观测到的该参数的平均值对应于多分散球体的有效半径为18 μ m，多分散无限长冰柱的有效半径为12 μ m。 考虑到多次散射，亮度温度差的增加更大的圆柱体比球，由于事实上，散射的前向峰是较小的圆柱体。 为了获得云粒子的大小，在非散射情况下开发的方法仍然是适用的，如果一个使用的有效发射度，隐含地包括散射的影响。 因此，一个有效的吸收系数比的定义，我们得出这个比例和云粒子的光学性质之间的直接关系。 有效吸收系数比的平均值对应于有效半径为26 μ m或稍小的冰球的情况下的水球（过冷液滴），但没有协议可以获得完全随机取向的圆柱体。
This paper investigates the important difference in the relationship between brightness temperatures between the 11-mu-m and the 12-mu-m AVHRR data and the microphysical properties of the semitransparent cirrus clouds. In the nonscattering approximation, the emittance for channels 4 and 5 are related through the absorption coefficient ratio that is the key parameter giving access to the size of cloud particles. The observed mean value of this parameter corresponds to effective radius of 18-mu-m for polydisperse spheres and 12-mu-m for polydisperse infinitely long ice cylinders. Taking the multiple scattering into account, the brightness temperature difference enhances much more for cylinders than for spheres owing to the fact that the forward peak of scattering is less large for cylinders. To obtain the size of cloud particles, the method developed in the nonscattering case is still applicable if one makes use of the effective emittance that implicitly includes the effects of scattering. Thus, an effective absorption coefficient ratio is defined and we derive a direct relationship between this ratio and the optical properties of the cloud particles. The mean value of the effective absorption coefficient ratio corresponds to ice spheres of effective radius of 26-mu-m or a bit less in the case of water spheres (supercooled droplets), but no agreement can be obtained for fully randomly oriented cylinders.