Calculations of free atmospheric shortwave spectral characteristics over the desert (from the CAENEX-70 data)

Abstract

This report presents a summary of a joint Soviet/American exchange program to compare calculations with observations in the real atmosphere, in order to determine and study the diabatic processes that are important for tropospheric energetics. The primary purpose of the present investigation was to determine the effect of aerosols upon radiation characteristics in the real atmosphere. Spectral measurements of the radiation field as a function of height have been made in 0.01 pm increments from 0.4 pm to 0.9 pm along with aerosol optical properties. Using these data, radiative transfer calculations have been performed using the 4-term expansion of the spherical harmonics method in order to provide an independent check on the accuracy of the previous measurements as well as provide recommendations for improved observations. The effect of a small amount of highly absorbing material, such as hematite, has been demonstrated. Extensive data are presented giving spectral shortwave radiation flux and flux divergence values as a function of height in the atmosphere. Because no "best fit" overall spectral regions were obtained, further studies were performed to test the sensitivity of the theoretical results to small variations in the input parameters. The results indicate that the major reason for discrepancies between measured and calculated radiation fields is difficulties with the radiative and aerosol measurements, rather than shortcomings of the calculational scheme.

Light Absorption Properties of Inhomogeneous Spherical Aerosol Particles

“…The size of soot particles produced by combustion processes ranges from the submicron to visible (Finfer, 1967), though particles with radii larger than a few microns will quickly fall out. As for hematite particles, Kondratyev et al (1979) found their sizes to be about 0.1*m; however, the existence of hematite particles in the supermicron size range is also reported (Klappenbach and Goranson, 1979). In spite of these reports, our knowledge of the size distribution of these absorbing particles is still very incomplete.…”

“…In the real atmosphere, however, such microphysical processes as coagulation, adsorption of reactive gases onto the particle surface, and incorporation in the cloud forming process eventually lead to a mixed nature of individual aerosol particles (i.e., internal mixing becomes predominant). From the analysis of the CAENEX data, Kondratyev et al (1979) suggested a possibility that hematite was embedded within other less absorbing particles in the atmosphere. The absorption property of an inhomogeneous particle which contains both absorbing and nonabsorbing substances may be different from that of a homogeneous particle composed of the absorbing substance only; therefore it is of interest to inquire into the optical properties of these inhomogeneous aerosol particles.…”