The capacity of Eratosthenes Centre of Excellence to estimate cloud radiative effects: the CyCARE campaign

Abstract

Clouds are one of the most significant factors in the climate system that strongly affect the Earth’s energy budget. Clouds reflect some of the sun's energy back into space, producing a cooling effect at the top of the atmosphere and at the same time trap the longwave radiation producing a warming effect. On average, the cooling effect is stronger than the warming effect, but accurately estimating the effects of clouds on the Earth's energy budget is still a major area of research. The cloud radiative effects (CRE), which is defined as the difference between the radiation under cloudy and cloud-free conditions, are mostly estimated from satellite observations. For accurate estimation from the ground, measurements by a combination of different instruments that provide vertical information about the optical and microphysical cloud and aerosol properties are necessary, to feed this information in radiative transfer models. During the CyCARE campaign, which was a joint initiative between the Cyprus University of Technology (CUT), Limassol and TROPOS, the Leipzig Aerosol and Cloud Remote Observations System (LACROS) operated at the CUT from October 2016 to March 2017. LACROS includes active and passive remote-sensing instruments, such as a PollyXT Raman-polarization lidar to retrieve aerosol vertical distribution, a 35-GHz cloud radar to obtain cloud microphysical properties, a disdrometer to measure precipitation, a Doppler lidar to track aerosol and cloud dynamics, and a microwave radiometer to measure water vapor and liquid water. Using the radiative transfer package LibRadtran the cloudy and clear sky shortwave and longwave radiation fluxes on the surface and the top of atmosphere were calculated during the CyCARE campaign. The aerosol and cloud profiles, along with other microphysical properties of clouds and aerosols were used as input in the radiative transfer model for the above-mentioned calculations. Subsequently, the CRE were obtained as the differences between all sky and clear sky fluxes. Since ERATOSTHENES Centre of Excellence (ERATOSTHENES CoE) is in the process to build up a permanent station named Cyprus Atmospheric Remote Sensing Observatory (CARO), the demonstrated CyCARE campaign depicts the capacity of the Centre to obtain long-term aerosol-cloud-radiation interactions in the sensitive climate area of the Eastern Mediterranean. The CARO constitutes the basic tool to improve the representation of clouds and aerosols in climate models and validate the satellite derived CREs.     Acknowledgments: “The authors acknowledge the ‘EXCELSIOR’: ERATOSTHENES: EΧcellence Research Centre for Earth Surveillance and Space-Based Monitoring of the Environment H2020 Widespread Teaming project (www.excelsior2020.eu). The ‘EXCELSIOR’ project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 857510, from the Government of the Republic of Cyprus through the Directorate General for the European Programmes, Coordination and Development and the Cyprus University of Technology”.