Subsuns and Low Reynolds Number Flow

J. I. Katz Department of Physics and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri

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Abstract

The phenomenon called the subsun is the specular reflection of sunlight by horizontally oriented plates of ice. Although well known in meteorological optics, the hydrodynamics of the orientation is not quantitatively understood. The theory of torques on objects at low Reynolds numbers is reviewed; coefficients Co, Cp, and Cψ that describe the orienting torques on discs, rods, and hexagonal prisms are defined; and the results of experiments to measure Co and Cp are reported.

Corresponding author address: Dr. J. I. Katz, Dept. of Physics and McDonnell Center for Space Sciences, Washington University, Box 1105, St. Louis, MO 63130-4899.

Email: katz@wuphys.wustl.edu

Abstract

The phenomenon called the subsun is the specular reflection of sunlight by horizontally oriented plates of ice. Although well known in meteorological optics, the hydrodynamics of the orientation is not quantitatively understood. The theory of torques on objects at low Reynolds numbers is reviewed; coefficients Co, Cp, and Cψ that describe the orienting torques on discs, rods, and hexagonal prisms are defined; and the results of experiments to measure Co and Cp are reported.

Corresponding author address: Dr. J. I. Katz, Dept. of Physics and McDonnell Center for Space Sciences, Washington University, Box 1105, St. Louis, MO 63130-4899.

Email: katz@wuphys.wustl.edu

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