Sensitivity of shortwave radiative flux density, forcing, and heating rates to the aerosol vertical profile

Journal Article · Wed Mar 31 04:00:00 EDT 2010 · Journal of Geophysical Research. D. (Atmospheres), 115:Art. No. D06209

DOI:https://doi.org/10.1029/2009JD012907· OSTI ID:978936

Guan, Hong; Schmid, Beat; Bucholtz, Anthony; Bergstrom, Robert

The effect of the aerosol vertical distribution on the solar radiation profiles, for idealized and measured profiles of optical properties (extinction and single-scattering albedo (SSA)) during the May 2003 Atmospheric Radiation Measurement (ARM) Aerosol Intensive Observation Period (AIOP), has been investigated using the Rapid Radiative Transfer Model Shortwave (RRTM_SW) code. Calculated profiles of down-welling and up-welling solar fluxes during the AIOP have been compared with the data measured by up- and down-looking solar broadband radiometers aboard a profiling research aircraft. The measured profiles of aerosol extinction, SSA, and water vapor obtained from the same aircraft that carried the radiometers served as the inputs for the model calculations. It is noteworthy that for this study, the uplooking radiometers were mounted on a stabilized platform that kept the radiometers parallel with respect to the earth’s horizontal plane. The results indicate that the shape of the aerosol extinction profiles has very little impact on direct radiative forcings at the top of atmosphere and surface in a cloud-free sky. However, as long as the aerosol is not purely scattering, the shape of the extinction profiles is important for forcing profiles. Identical extinction profiles with different absorption profiles drastically influence the forcing and heating rate profiles. Using aircraft data from 19 AIOP profiles over the Southern Great Plains (SGP), we are able to achieve broadband down-welling solar flux closure within 0.8% (bias difference) or 1.8% (rms difference), well within the expected measurement uncertainty of 1 to 3%. The poorer agreement in up-welling flux (bias -3.7%, rms 10%) is attributed to the use of inaccurate surface albedo data. The sensitivity tests reveal the important role accurate, vertically resolved aerosol extinction data plays in tightening flux closure. This study also suggests that in the presence of a strongly absorbing substance, aircraft flux measurements from a stabilized platform have the potential to determine heating rate profiles. These measurement-based heating rate profiles provide useful data for heating rate closure studies and indirect estimates of single scattering albedo assumed in radiative transfer calculations.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 978936
• Report Number(s): PNNL-SA-67886; KP1701000
• Journal Information: Journal of Geophysical Research. D. (Atmospheres), 115:Art. No. D06209, Journal Name: Journal of Geophysical Research. D. (Atmospheres), 115:Art. No. D06209 Vol. 115
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AEROSOLS
ATMOSPHERIC CIRCULATION
FLUX DENSITY
HEATING RATE
OPTICAL PROPERTIES
R CODES
RADIANT HEAT TRANSFER
RADIOMETERS
SENSITIVITY
SOLAR RADIATION