Measured Spectral Optical Depths and Derived Column Aerosol Size Distributions Obtained From the NCAR C-130 During ACE-1

A. Bucholtz, and F. P. J. Valero (Both at: Atmospheric Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093,

Measurements of the spectral optical depth were made during ACE-1 (Nov.-Dec. 1995) using a Total Direct Diffuse Radiometer (TDDR) mounted in a zenith port of the NCAR C-130. The TDDR is a shadow-band radiometer with a hemispheric field of view and 7 channels (380, 412,500,675,862,1064, and 1640 nm). Each channel has a bandpass of approximately 10 nm. As its name implies, the TDDR measures the total, direct, and diffuse components of the solar radiation field from which the optical depth is obtained. The optical depth, as a function of wavelength, can then be inverted to derive an estimate of the column aerosol size distribution.

During ACE-1, a series of flights were conducted in which the C-130 flew at multiple, stacked altitudes throughout the lower troposphere. These column closure flights allowed the measurement of the spectral optical depth and column aerosol size distribution at multiple levels in the atmosphere. While the TDDR operated on almost all flights of the C-130, results from selected column closure case study days will be presented here.