Open AccessSpectral characteristics of solar near‐infrared absorption in cloudy atmospheres
Author(s) -
Ridgway William,
Ramaswamy V.,
Freidenreich S. M.,
Batey Michael
Publication year - 1998
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1998jd200013
Subject(s) - water vapor , atmosphere (unit) , radiative transfer , liquid water content , atmospheric sciences , absorptance , absorption (acoustics) , infrared , cloud fraction , cloud top , wavenumber , troposphere , physics , environmental science , computational physics , cloud cover , optics , meteorology , cloud computing , satellite , astronomy , reflectivity , computer science , operating system
Theoretical and experimentally derived estimates of the atmospheric absorption of solar energy in the presence of clouds have been reported to be at variance for quite a long time. A detailed set of near‐monochromatic computations of the reflectance, transmittance, and absorptance of a standard midlatitude atmosphere with embedded water clouds is used to identify spectral features in the solar near‐infrared that can be utilized to study this discrepancy. The results are framed in terms of the cloud radiative forcing both at the surface and at the top of the atmosphere, and it is shown that water vapor windows are the most sensitive to variations in cloud optical properties and cloud placement in the vertical. The ratio of the cloud radiative forcing at the surface to that at the top of the atmosphere, R , varies from near zero in the band centers at small wavenumbers for high clouds to ∼1 in the band centers at larger wavenumbers for low clouds and to values in excess of 2 in the water vapor windows at small wavenumbers. The possibility of using measurements from space with the future Moderate Resolution Imaging Spectroradiometer (MODIS) and simultaneous surface measurements is discussed. It is also shown that horizontal inhomogeneities in the cloud layers do not alter appreciably the estimates of the R factor, but areal mean cloud absorption is lower for an inhomogeneous cloud having the same mean liquid water as the corresponding homogeneous cloud.