Pressure and humidity effects on optical refractive-index fluctuations

Abstract

Although temperature fluctuations dominate the variance of optical refractive index fluctuations it has been shown recently that humidity fluctuations can also be important (e.g., Friehe etal., 1975). This paper reports on simultaneous measurements of temperature, humidity and pressure so that the relative importance of all three can be investigated. For the dry site where the measurements were made, the humidity contribution was less than other investigators had found. The major contribution of the pressure fluctuations was through their covariance with temperature, but this term was found to be between 0.03 and 0.4% of the total variance. The results thus confirmed that pressure fluctuations can be neglected in most circumstances. Both the temperature and humidity spectra displayed -S/3 power laws at small scales while the temperature-humidity cospectrum decreased more rapidly than a -5/3 power law. The temperature-pressure cospectrum decreased even more rapidly than the temperature-humidity cospectrum. The temperature-pressure correlation coefficient was found to be about -0.1. The humiditypressure correlation was typically between *O.OS and the cospectrum poorly defined.

Forecasting atmospheric stability transitions over a high-elevation desert in the southwestern United States

“…They also gathered quantitative evidence of the extended and multiple transitions characteristic of non-ideal conditions. Such observations were consistent with the aerosol dependencies studied by McBean and Elliott (1981) and Sadot and Kopelka (1992).…”

Spectral Measurements in a Disturbed Boundary Layer over Snow

“…Priestley and Hill (1985) measured six positive and six negative t-q cospectra at BAO that behaved as f -513 . McBean and Elliott (1981) and Kohsiek (1982), however, did not find the predicted inertial-convective subrange behavior in the t-q cospectra that they obtained over dry land. Figure 13 α is thus important confirmation of the existence of an f-5/3 inertial-convective subrange in negative t-q cospectra.…”

“…The temperature spectrum always contributed at least 96% to the 0.55-µ m CA value, so I have not provided a similar breakdown for this wavelength in Table 4. McBean and Elliott (1981) also found that temperature fluctuations far outweighed other contributions to C^, in the visible region over land. Over the ocean, on the other hand, Antonia et al (1978) reported that the t-q contribution to CA could be 5-10% even though the q contribution was less than 1%.…”

Inertial subrange correlation between temperature and humidity fluctuations in the unstable surface layer above vegetated terrains

“…On the other hand, some of the observations claiming a deviation from f -5/3 may be explained by sensor separation. McBean and Elliott (1981) who used a 50 cm sensor separation, found a too rapid drop-off of the cospectrum for frequencies above 1 Hz. They do not give wind speeds, but assuming a value of 211 m s-', this corresponds to wavenumbers zz= 1 m-', which compares well with our estimate 0.3 6 -' = 0.6 m-'.…”