Preprints
https://doi.org/10.5194/acp-2021-421
https://doi.org/10.5194/acp-2021-421

  07 Jun 2021

07 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Longwave Radiative Effect of the Cloud-Aerosol Transition Zone Based on CERES Observations

Babak Jahani1, Hendrik Andersen2,3, Josep Calbó1, Josep-Abel González1, and Jan Cermak2,3 Babak Jahani et al.
  • 1Departament de Física, Universitat de Girona, Girona, Spain
  • 2Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 3Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Abstract. This study presents an approach for quantification of cloud-aerosol transition zone broadband longwave radiative effects at the top of the atmosphere (TOA) during daytime over the ocean, based on satellite observations and radiative transfer simulation. Specifically, we used several products from MODIS (Moderate Resolution Imaging Spectroradiometer) and CERES (Clouds and the Earth’s Radiant Energy System) sensors for identification and selection of CERES footprints with horizontally homogeneous transition zone and clear-sky conditions. For the selected transition zone footprints, radiative effect was calculated as the difference between the instantaneous CERES TOA upwelling broadband longwave radiance observations and corresponding clear-sky radiance simulations. The clear-sky radiances were simulated using the Santa Barbara DISORT Atmospheric Radiative Transfer model fed by the hourly ERA5 reanalysis (fifth generation ECMWF reanalysis) atmospheric and surface data. The CERES radiance observations corresponding to the clear-sky footprints detected were also used for validating the simulated clear-sky radiances. We tested this approach using the radiative measurements made by the MODIS and CERES instruments onboard Aqua platform over the south-eastern Atlantic Ocean during August 2010. For the studied period and domain, transition zone radiative effect (given in flux units) is on average equal to 8.0 ± 3.7 W m−2 (heating effect; median: 5.4 W m−2), although cases with radiative effects as large as 50 W m−2 were found.

Babak Jahani et al.

Status: open (until 19 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Babak Jahani et al.

Babak Jahani et al.

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Short summary
The change in the state of sky from cloudy to cloudless (or vice versa) comprises an additional phase called “transition zone” with characteristics laying between those of aerosols and clouds. This study presents an approach for quantification of cloud-aerosol transition zone broadband longwave radiative effects at the top of the atmosphere during daytime over the ocean, based on satellite observations and radiative transfer simulations.
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