Shortwave radiative closure studies for clear skies during the Atmospheric Radiation Measurement 2003 Aerosol Intensive Observation Period

Abstract

[1] The Department of Energy's Atmospheric Radiation Measurement (ARM) program sponsored a large aerosol intensive observation period (AIOP) to study aerosol during the month of May 2003 around the Southern Great Plains (SGP) Climate Research Facility (CRF) in north central Oklahoma. Redundant measurements of aerosol optical properties were made using different techniques at the surface as well as in vertical profile with sensors aboard two aircraft. One of the principal motivations for this experiment was to resolve the disagreement between models and measurements of diffuse horizontal broadband shortwave irradiance at the surface, especially for modest aerosol loading. This paper focuses on using the redundant aerosol and radiation measurements during this AIOP to compare direct beam and diffuse horizontal broadband shortwave irradiance measurements and models at the surface for a wide range of aerosol cases that occurred during 30 clear-sky periods on 13 days of May 2003. Models and measurements are compared over a large range of solar-zenith angles. Six different models are used to assess the relative agreement among them and the measurements. Better agreement than previously achieved appears to be the result of better specification of input parameters and better measurements of irradiances than in prior studies. Biases between modeled and measured direct irradiances are in the worst case 1%, and biases between modeled and measured diffuse irradiances are less than 1.9%.

Initial Assessment of the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR)-Based Aerosol Retrieval: Sensitivity Study

“…The opposite is valid for O: changes of ω 0 are larger than the corresponding changes of g ( Figure 9; right column). Thus, the corresponding errors of the downwelling diffuse (up to 5%, or ±5 W·m ) and upwelling (up to 3%, or ±3 W·m ) [52]; hence, the errors in calculated downwelling diffuse flux presented here are comparable to these uncertainties.…”

Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

“…This decrease in diffuse radiation is not fully compensated for by increases in diffuse radiation in other spectral regions where the surface albedo is relatively high, resulting in a net 6.6 Wm −2 decrease in the integrated downwelling irradiance computed using the spectral albedo. From this analysis, it is clear that the use of a spectrally constant surface albedo was an important factor in past studies (e.g., Halthore et al, 2005) that concluded that radiative transfer models overestimated diffuse irradiance for clear sky conditions, in contrast to those studies that used a spectrally varying surface albedo and found no such discrepancy (e.g., Michalsky et al, 2006).…”

“…Radiative closure calculations, in which radiative transfer model calculations are compared to irradiance (flux) or radiance measurements, can serve as a testbed to evaluate the specification of atmospheric column properties retrieved from measurements (including surface conditions, water vapor amount, and aerosol and cloud properties), radiative transfer model calculations, and the radiative measurements themselves (e.g., Michalsky et al, 2006;McFarlane and Evans, 2004;Turner et al, 2004;Halthore and Schwartz, 2000;Mlawer et al, 2000). Previously, studies using data from the Atmospheric Radiation Measurement (ARM) Program have performed such comparisons in the longwave spectral region to refine treatment of the longwave water vapor continuum and to improve the specification of the atmospheric water vapor column.…”

Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

“…Aerosol-induced decreases in downward solar radiation have been observed in field experiments (e.g. Leiterer et al (1997) in Germany and Russia, Kanaya et al (2003) at Rishiri Island and Michalsky et al (2006) in Oklahoma) or through analysis of long-term ground and satellite observational data (Lee et al, 2005;Hatzianastassiou et al, 2007;Han et al, 2012). During strong air pollution episodes such as wild fire Grell et al, 2011;Jiang et al, 2012) or dust events , it is calculated that aerosols reduced the shortwave radiation and temperature at the surface, and heated the atmosphere at the top of planetary boundary layer (PBL).…”