This paper describes a newly designed Sun and Aureole Measurement (SAM) aureolegraph and the first results obtained with this instrument. SAM measurements of solar aureoles produced by cirrus and cumulus clouds were taken at the Atmospheric Radiation Measurement Program (ARM) Central Facility in Oklahoma during field experiments conducted in June 2007 and compared with simultaneous measurements from a variety of other ground-based instruments. A theoretical relationship between the slope of the aureole profile and the size distribution of spherical cloud particles is based on approximating scattering as due solely to diffraction, which in turn is approximated using a rectangle function. When the particle size distribution is expressed as a power-law function of radius, the aureole radiance as a function of angle from the center of the solar disk also follows a power law, with the sum of the two powers being 25. This result also holds if diffraction is modeled with an Airy function. The diffraction approximation is applied to SAM measurements with optical depths &2 to derive the effective radii of cloud particles and particle size distributions between ;2.5 and ;25 mm. The SAM results yielded information on cloud properties complementary to that obtained with ARM Central Facility instrumentation. A network of automated SAM units [similar to the Aerosol Robotic Network (AERONET) system] would provide a practical means to gain fundamental new information on the global statistical properties of thin (optical depth & 10) clouds, thereby providing unique information on the effects of such clouds upon the earth's energy budget.

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The EXCEDE III rocket experiment successfully produced an artificial aurora on April 27, 1990, with an injected ∼ 18‐A beam of ∼ 2.5‐keV electrons. The experiment consisted of an accelerator module and a sensor module in a mother‐daughter configuration. The beam was fired along the Earth's magnetic field lines between the altitudes of ∼62 and 115 km during the flight. A major concern prior to the flight was that the injection of such an overdense electron beam into the lower ionosphere would charge the accelerator module to a significant fraction of the beam potential. To monitor the primary electrons remote from the rocket, two X ray proportional counters were included as part of the sensor module. X ray spectra from bremsstrahlung emission yield a direct measure of the primary electron beam energy outside the plasma sheath surrounding the accelerator module. Analysis of these spectra yields a beam energy of 2.2 ± 0.5 keV which indicates no substantial charging of the accelerator module for the entire time that the beam was on. We also find that the X ray intensity was modulated at the few percent level by firings of the attitude control jets.

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