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Effects of cloud shape and water vapor distribution on solar absorption in the near infrared
Author(s) -
Podgorny Igor A.,
Vogelmann Andrew M.,
Ramanathan V.
Publication year - 1998
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/98gl01444
Subject(s) - water vapor , zenith , solar zenith angle , absorption (acoustics) , liquid water content , radiative transfer , atmospheric sciences , environmental science , cloud top , infrared , computational physics , materials science , meteorology , physics , cloud computing , optics , astronomy , satellite , computer science , operating system
A 3D Monte Carlo radiative transfer model is used to demonstrate the importance of cloud shape and water vapor distribution on narrow‐band solar absorption at 0.93 and 2.0 µm. Diurnally averaged absorption for wavy‐topped broken cloud fields can exceed that based on conventional climate model assumptions (plane‐parallel cloud geometry and an unsaturated water vapor distribution in gaps between cloud elements) by 2–10% of the top‐of‐atmosphere insolation. Plane‐parallel clouds often underestimate the absorption by non‐flat‐top clouds, particularly at 2.0 µm and large solar zenith angles. Ambiguities in assigning the above‐cloud water vapor profile create uncertainties in the absorption comparisons between the plane‐parallel and non‐flat‐top clouds, which increase with solar zenith angle and may be as large as 5 to 8%. A thin saturated water vapor layer (0.4 km) above the cloud top systematically enhances column absorption, the magnitude depends on cloud altitude and wavelength. Thus, realistic 3‐D distributions of cloud shape, brokenness and water vapor are needed to quantify the role of clouds in excess absorption.