Solar irradiance computations compared with observations at the Baseline Surface Radiation Network Payerne site

Abstract

[1] Radiative transfer model calculations of solar fluxes during cloud-free periods often show considerable discrepancies with surface radiation observations. Many efforts have been undertaken to explain the differences between modeled and observed shortwave downward radiation (SDR). In this study, MODTRAN4v3r1TM (designed later simply as MODTRAN TM ) was used for model simulations and compared with high-quality radiation observations of the Baseline Surface Radiation Network (BSRN) site at Payerne, Switzerland. Results are presented for cloud-free shortwave downward radiation calculations. The median differences of modeled minus observed global SDR are small (<1%) and within the instrumental error. The differences of modeled and observed direct and diffuse SDR show larger discrepancies of À1.8% and 5.2%, respectively. The diffuse SDR is generally overestimated by the model, and more important, the model to observation linear regression slope and zero intercept differ significantly from their ideal values of 1 and 0. Possible reasons for the discrepancies are presented and discussed, and some modifications are investigated for decreasing such differences between modeled and observed diffuse SDR. However, we could not resolve all the discrepancies. The best agreement is obtained when comparing model simulations whose 550-nm aerosol optical depth input is inferred from observations using nine spectral channels and using BSRN observations performed with a new and more precise shading disk and Sun-tracking system. In this case, the median bias between model simulations and observed diffuse SDR is À0.4 W m À2 (<1%).

Complex experiment on studying the microphysical, chemical, and optical properties of aerosol particles and estimating the contribution of atmospheric aerosol-to-earth radiation budget

“…The analysis also shows that the average differences between empirical data and model calculations are close to results obtained by other authors in other regions (Kato et al, 1997;Henzing et al, 2004;Michalsky et al, 2006;Nowak et al, 2008;Wang et al, 2009;Halthore et al, 1998Halthore et al, , 2004Plakhina et al, 1998;Chubarova et al, 1999). It is important that our results were obtained under the conditions of high and moderate atmospheric transmittance, where the optical depth, scattering phase function, and aerosol single scattering albedo errors increase significantly.…”

Clear‐sky shortwave radiative closure for the Cabauw Baseline Surface Radiation Network site, Netherlands

“…The authors report biases between models and measurements of generally less than 1% for direct irradiances and less than 1.9% for diffuse irradiances. A recent study performed by Nowak et al [2008], however, demonstrates that closure can still be a challenge; the authors find biases of −1.8% for direct irradiances and 5.2% for diffuse irradiances. In general, the number of studies reporting a satisfactory degree of closure for both direct and diffuse irradiances is still limited, which motivated us to perform the study presented here.…”

Solar radiation measurements compared to simulations at the BSRN Izaña station. Mineral dust radiative forcing and efficiency study

“…For this purpose, the BSRN establishes exigent quality controls for its products [Long and Dutton, 2002;Long and Shi, 2006]. The BSRN high-quality data have been already used for validating solar shortwave downward radiation (SDR) estimates in the last years [e.g., García et al, 2008;Nowak et al, 2008]. These studies document disagreements between instantaneous simulations and measurements less than 2% for global and direct measurements, and 5% for the diffuse solar component, which agree well with the expected instrumental uncertainties.…”