Radiative closure study for cloud free cases and cloud radiative effect at Lindenberg Meteorological Observatory

Clouds modulate the surface radiation budget by interacting with both shortwave and longwave fluxes and their impact is quantified by the cloud radiative effect (CRE), obtained as the difference between the observed and the estimated cloud-free fluxes. In this work, we will present a radiative closure study for cloud-free cases using LibRadtran radiative transfer model (Emde et al., 2016) conducted at the Lindenberg Observatory, Germany (52.21°N, 14.12°E; 127 m a.s.l.). The observatory operates as a Baseline Surface Radiation Network (Driemel et al. 2018) station since 1994 and collects high quality broadband irradiance measurements. It is also a so-called supersite, where a large number of remote sensing and in-situ surface measurements are available, including: GRUAN radiosonde data (Seidel et al., 2009), AERONET (Giles et al., 2019) measurements for aerosol characterisation, CloudNet (Illingworth et al., 2007) data for information on profiles of cloud micro- and macrophysical properties. Vertical profiles of temperature and relative humidity are available from both radiosonde and microwave radiometer. The synergy of these observations enables the possibility to perform a sensitivity study of the cloud-free irradiance estimates obtained with LibRadtran. Once determined the best input set-up to obtain such estimates making use of surface measurements, CRE will be evaluated from the start of observations to present day: as the data set collected at the Lindenberg Observatory spans almost 30 years, it allows to assess potential climatological variations/trend in cloud conditions and their impact on the surface radiative fluxes. Additionally, estimated cloud free irradiances and CRE as obtained with libRadtran will be compared to those from simple parametrisations, e.g. Dupont et al. (2008) for the downwelling longwave flux.  

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