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

Abstract

Observations of the temperature-humidity cospectrum and correlation spectrum were made with a cold platinum wire and a Ly-a hygrometer at 3.7 and 10 m above vegetated surfaces during unstable atmospheric conditions. It was found theoretically that a separation 6 between the temperature and humidity sensors causes a drop-off of the correlation spectrum at wavenumbers > 0.3 6-'. The observed drop-off follows the theoretical one reasonably well. Measurements made with the temperature sensor placed in the center of the Ly-a gap reveal a f-5/3 dependence of the temperature-humidity cospectrum in the inertial subrange up to frequencies of20 Hz. The drop-off at higher frequenties is thought to be caused by limitations inherent to the Ly-a humidiometer.

Spectral Measurements in a Disturbed Boundary Layer over Snow

“…For example, McBean's (1971) temperature spectra showed a distinct inertial-convective subrange; but his humidity spectra, though having levels similar to his t spectra at l οω frequency, fell off much more rapidly than f-5"3 at high frequency. Kohsiek (1984) made similar observations; his t spectra went as f-5/3 at high frequency, but his q spectra fell off somewhat more rapidly. The temperature and humidity spectra Schmitt et al (1979) measured over Minnesota farmland behaved, generally, like the Kansas temperature spectra; but, as with their oceanic measurements, the humidity spectra had an unusual hump near fz/U = 1.…”

HNO3 deposition to a deciduous forest

“…The correlation coefficient (r) between temperature and humidity fluctuations over simple surfaces has been observed to be near unity for neutral and unstable conditions (Wesely and Hicks, 1978;Wyngaard et al, 1978;Kohsiek, 1984) implying similarity in the to.3…”

Use of variance techniques to measure dry air-surface exchange rates

“…A number of investigators (Swinbank and Dyer, 1967;Phelps and Pond, 1971;McBean and Miyake, 1972;Thorpe et al, 1973;Friehe et al, 1975;Wesely and Hicks, 1978;Wyngaard et al, 1978) have shown that temperature and humidity fluctuations are highly correlated at frequencies corresponding to the flux-carrying eddies over uniform, warm, wet surfaces, presumably because the surface appears as a uniform source of both heat and water vapor that are mixed upward by practically the same turbulent wind motions. Indeed, this strong correlation can extend to greater frequencies (Kohsiek, 1984). If the high degree of correlation exists between temperature (or humidity) and other scalar quantities, especially at the frequencies of flux-carrying eddies, then the considerable information available on relationships of fluxes to variances for temperature and humidity is probably also applicable to many other scalar quantities.…”

“…The equations used in the adjustments are described by Hicks (1972), except that the adjustments for phase shift caused by sensor separation along the mean flow are omitted. In principle, this approach to accounting for sensor separation should produce adjustments equivalent to those produced with the procedures described by Kohsiek (1984) for sensors separated in a direction transverse to the mean flow. A comparison of the two approaches, however, reveals that Kohsiek's adjustments have a slightly larger effect.…”