Properties of spatial temperature derivatives in the atmospheric surface layer

Abstract

A pair of parallel cold wires separated in either the vertical or lateral direction was used to obtain the three components 0,, 8,., 0. of the temperature derivative in the streamwise, lateral and vertical directions, respectively. The average absolute skewness values of 0, and 0, are nonzero and approximately equal, while the skewness of eY is approximately zero. These results appear to be consistent with the presence of a large, three-dimensional organised structure in the surface layer. There is an apparent low-frequency contamination in the spectral density of 0, and f?* due mainly to small errors in estimating the sensitivity of the cold wires. The temperature derivatives were high-pass filtered, the filter being set to remove possible contributions from the large structure and to minimise low-frequency sensitivity contamination. The filtered rms ratios gX/& and gX/iZ were in the range 0.7 to 0.9, a result in qualitative agreement with that obtained in the laboratory boundary layer by Sreenivasan eral. (1977). The skewness of filtered .9, or 8, is negligible, consistent with local isotropy of small-scale temperature fluctuations and in support of the high wavenumber spectral isotropy discussed in .

Streamwise heat flux budget in the atmospheric surface layer

“…c I . of local isotropy, perhaps by high-pass filtering the derivative signals (e.g., Antonia et al, 1979b), would be desirable. The magnitude of the viscous term, obtained from (9) using isotropic estimates for E and N, is small ( Figure 5) and approximately independent of z/L.…”

Note on the viscous heating term in the temperature variance equation

“…(1978) obtained 0.84. Clearly, further experiments are required to validate (2), especially of the type where direct measurements of all the components of 2 (e.g., Antonia et al, 1979b) are made.…”

“…obtained by comparing the statistics of e(ae/at)' with those of 13x since the direct measurement of all components of jj seems possible (Antonia et al, 1979b). The correlation ,9(&/at)' was measured at a height of 4 m above ground at the Bungendore field site of the C.S.I.R.O.…”

“…Division of Environmental Mechanics. A brief description of the site and experimental conditions may be found in Antonia et al (1979b). Fluctuations u and 0 were measured with a single hot'wire and a cold wire, respectively, both approximately 1 mm long, placed vertically with a separation of about 1 mm.…”

Taylor's hypothesis and spectra of velocity and temperature derivatives in a turbulent shear flow

“…Division of Environmental Mechanics. Details of the experimental site and conditions can be found in Antonia et al (1979a). The laboratory plane jet facility, described in Rajagopalan and Antonia (1979), has provisions for both heating and cooling which are provided by electric elements and a conventional vapour compression unit, respectively.…”