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

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 µm increments from 0.4 µm to 0.9 µm 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.