Diurnal Cycles of the Refractive Index Structure Function Coefficient
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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The refractive index structure function coefficient, C sub n squared, is an atmospheric parameter needed to describe scintillation and small- scale phase fluctuations of electromagnetic radiation propagated in the atmospheric surface layer. Since systematic direct measurements of C sub n for many climates and seasons are not available, an indirect method is developed where C sub n is calculated from the estimates of sensible and latent heat flux components of the surface energy budgets. This indirect method is primarily for heights less than 4 meters, because low intermittency and KHKM about equal to 1 are assumed. Diurnal variations of C sub n at several heights above land for six combinations of climates, seasons, and surface conditions are calculated from heat fluxes measured by different investigators at many locations, for moderate to high wind velocities. These predictions of C sub n agree well with some direct measurements of C sub n when assumptions of nearly ideal weather and sites are met. The effect of water vapor on C sub n is usually a reduction of about 3Beta per cent and thus is usually negligible above land, but can be significant above tropical oceans.
- Atmospheric Physics