Outgoing Longwave Radiation due to Directly Transmitted Surface Emission
Outgoing Longwave Radiation due to Directly Transmitted Surface Emission
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DOI：
10.1175/jas-d-11-0248.1
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发表时间：
2012-06-01
影响因子：
3.1
通讯作者：
Shine, K. P.
中科院分区：
文献类型：
--
作者：
Costa, S. M. S.;Shine, K. P.
一个经常使用的图表总结了地球和大气的年平均和全球平均能量收支，表明从地表通过中红外大气窗口到达大气顶部的辐照度为40 W m（-2）;这可以与大约235 W m（-2）的总出射长波辐射（OLR）进行比较。40 W m（-2）的值是以特别的方式估计的。一个更详细的计算这一部分，这里称为表面透射辐照度（STI），提出了，使用逐行辐射代码和三维气候的温度，湿度，云量等没有假设的波长从表面辐射可以到达大气层的顶部。强调了水蒸气连续体的作用。在晴朗的天空中，如果排除连续体，全球和年度平均STI计算为约100 W m（-2），在整个热带和亚热带地区有一个广泛的最大值。当包括连续体时，晴空STI减少到66 W m（-2），具有明显不同的地理分布，热带最小，亚热带沙漠上的局部峰值。云的加入将STI降低到约22 W m（-2）。由于此处忽略了过程，实际值可能会稍小一些，建议STI值为20 W m（-2）（估计不确定性约为+/- 20%）比先前估计的40 W m（-2）更现实。这表明只有不到十分之一的OLR直接来自地表。
A frequently used diagram summarizing the annual- and global-mean energy budget of the earth and atmosphere indicates that the irradiance reaching the top of the atmosphere from the surface, through the midinfrared atmospheric window, is 40 W m(-2); this can be compared to the total outgoing longwave radiation (OLR) of about 235 W m(-2). The value of 40 W m(-2) was estimated in an ad hoc manner. A more detailed calculation of this component, termed here the surface transmitted irradiance (STI), is presented, using a line-by-line radiation code and 3D climatologies of temperature, humidity, cloudiness, etc. No assumption is made as to the wavelengths at which radiation from the surface can reach the top of the atmosphere. The role of the water vapor continuum is highlighted. In clear skies, if the continuum is excluded, the global- and annual-mean STI is calculated to be about 100 W m(-2) with a broad maximum throughout the tropics and subtropics. When the continuum is included, the clear-sky STI is reduced to 66 W m(-2), with a distinctly different geographic distribution, with a minimum in the tropics and local peaks over subtropical deserts. The inclusion of clouds reduces the STI to about 22 W m(-2). The actual value is likely somewhat smaller due to processes neglected here, and an STI value of 20 W m(-2) (with an estimated uncertainty of about +/- 20%) is suggested to be much more realistic than the previous estimate of 40 W m(-2). This indicates that less than one-tenth of the OLR originates directly from the surface.