The Potential Importance of Correlated Humidity and Temperature Variations for Atmospheric Acoustic Backscatter

Abstract

The dependence of the velocity of sound on temperature and humidity mixing ratio is derived and the commonly applied expression of Wesely (1976) corrected. Variations in the acoustic refractive index produced by turbulent fluctuations in temperature, humidity mixing ratio and vapor pressure or density are examined. The resulting expressions are used in a simple approach to the structure function constant for acoustic refractive index. Wesely's (1976) conclusions (using expressions for structure constants in the surface boundary layer) about the relative importance of terms dependent on humidity structure are confirmed. The importance of the correlation between variations in temperature and humidity for the strength of echoes detected by monostatic sodar is discussed.