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- Title
Quantifying Transition Zone Radiative Effects in Longwave Radiation Parameterizations.
- Authors
Jahani, Babak; Calbó, Josep; González, Josep‐Abel
- Abstract
The change in the state of sky from cloudy to cloudless (or vice versa) comprises an additional phase called "transition zone," in which the characteristics of the particle suspension lay between those corresponding to pure clouds and atmospheric aerosols. This phase, however, is usually considered, in atmospheric monitoring and modeling, as an area containing either aerosol or thin clouds. A sensitivity analysis has been performed to assess the longwave radiative effects resulting from different approximations to the transition zone for three radiation parameterizations included in the Weather Research and Forecasting Model. The parameterizations produce important differences (up to 60 W m−2) between radiative effects of optically thin layers of aerosols and clouds (as surrogates for transition zone suspensions) in the longwave region, both at the top and bottom of the atmosphere. Also, differences are greater if the suspension of particles is located at higher altitudes, but smaller in high humidity conditions. Plain Language Summary: The change in the state of sky from cloudy to cloudless (or vice versa) comprises an additional phase called "transition zone," in which the characteristics of the particle suspension lay between those corresponding to a pure cloud and those of atmospheric aerosols. This phase, however, is usually considered, in atmospheric monitoring and modeling, as an area containing either aerosol or thin clouds. This study quantifies the uncertainties that this binary assumption may introduce to the estimation of longwave radiative effects at the top and bottom of the atmosphere by using the Fu‐Liou‐Gu (FLG), NewGoddard, and Rapid Radiative Transfer Model for General Circulation Model (RRTMG) radiative parameterizations included in the Weather Research and Forecasting Model. The results show that there are important differences between optically thin clouds and aerosols in longwave region, which may cause substantial uncertainties in the radiative effects at the top and bottom of the atmosphere (up to 60 W m−2) if they are used to approximate transition zone conditions. Results are important due to the role that longwave radiation plays in the radiative balance that drives the Earth's climate. Key Points: The LW radiation parameterizations RRTMG, FLG, and NGO included in WRF‐ARW were used for idealized one‐dimensional vertical simulationsDifferent approximations to transition zone cause substantial uncertainty in the LW radiative effects at top and bottom of the atmosphereNeglecting transition zone conditions at high altitudes contributes to larger uncertainties in the total column energy budget
- Subjects
RADIATIVE transitions; GENERAL circulation model; ATMOSPHERIC aerosols; METEOROLOGICAL research; WEATHER forecasting; STRATOCUMULUS clouds
- Publication
Geophysical Research Letters, 2020, Vol 47, Issue 22, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2020GL090408