Comparison of CERES SYN1deg Radiative Fluxes with Those Derived from Observations at The ARM ENA Site

Profiles of radiative fluxes simulated from thermodynamic and cloud observations made at the Atmospheric Radiation Measurement (ARM) Eastern North Atlantic (ENA) site for a 6-year period are termed as ENARad. ENARad radiative fluxes are compared to those from the Clouds and the Earth's Radiant Energy System (CERES) 1°-resolution synoptic product (SYN1deg) simulated radiative flux profiles as well as the CERES instrument observed top-of-atmosphere (TOA) fluxes, and ground site broadband radiometer measurements. Monthly average differences between ENARad and surface radiometer reported fluxes as well as differences between ENARad, SYN1deg and observed fluxes at TOA were statistically insignificant. SYN1deg significantly overestimated surface downwelling shortwave flux by 12±52 W m −2 and surface downwelling longwave flux by 5±20 W m −2 on monthly timescales. Such overestimations were traced to moister and warmer sub-cloud layer, drier cloud layer, and moister and colder above-cloud free troposphere in the ancillary thermodynamic and cloud properties used by SYN1deg than observed. Similarly, low cloud coverage, boundaries, and liquid water paths utilized by SYN1deg were also significantly higher than observed. Intramodel differences in the hourly values of shortwave fluxes exceeded 100Wm −2 at the TOA and the surface. These differences were also due to inaccuracies in representation of low cloud properties within the SYN1deg product relative to those determined by ENA ARM instrumentation and used as ENARad ancillary data. Results presented are relevant to investigations employing the CERES SYN1deg data product, studies that estimate radiative fluxes from surface-based or satellite-borne observations, and comparative analyses of radiative fluxes derived using different methodological approaches.