Sensible Heat Flux From Arid Regions: A Simple Flux‐Variance Method

Abstract

Similarity models in the inner region of the unstable atmospheric boundary layer (ABL) are generally based on four dimensional parameters: buoyancy, friction velocity, surface heat flux, and the height above the land surface. In the free convection limit the friction velocity can be neglected, thus reducing the measurement needs in practical applications. Some field measurements of the second moment of temperature have indicated that free convection scaling of this statistic may be extended into more dynamic regimes, namely, the "dynamic-convective" and, perhaps, the "dynamic" regions of the ABL. An advantage of this approach is that the sensible heat flux can be estimated without shear stress measurements. This temperature variance similarity model is applied for a wide range of unstably stratified flows over the dry Owens Lake, in southeastern California. The simple free convection model of the temperature variance is accurate for sensible heat flux estimation across the full range of unstable atmospheric stability conditions.

Probability density functions of turbulent velocity and temperature in the atmospheric surface layer

“…The fetch surrounding the instrumented site is uniform for several kilometers. The surface is crusty sand with a mean surface roughness length z o of 0.13 mm; however, the variation around this estimate is large [see Katul, 1994;Albertson et al, 1995].…”

“…The short sampling period was necessary to ensure steady state in the mean meteorological conditions. The mean meteorological parameters such as net radiation, soil heat flux, surface temperature, mean wind speed, and wind direction were also measured during the experiment [see Katul, 1994;Katul et al, 1995a, b;Albertson et al, 1995].…”

On the Anomalous Behaviour of Scalar Flux–Variance Similarity Functions Within the Canopy Sub-layer of a Dense Alpine Forest

“…where C 3 ≈ 0.99 (corrected for κ = 0.4) originally determined elsewhere (Wyngaard et al 1971) and verified over a semi-arid area in the region called 'La Crau' in southern France , over a uniform and flat and dry lakebed (Albertson et al 1995), and for several canopies (Wesson et al 2001). Although the φ s (−ζ ) function was experimentally shown to be the same for T , q, and C over a uniform wheat field (Ohtaki 1985), De Bruin et al (1999) studied the correlation coefficient between T and q over a dry vineyard in Spain and concluded that if non-local effects are of the same order as local effects, T and q will be dissimilar.…”

“…The function φ s (−ζ ) must satisfy two limits (De Bruin 1982;De Bruin et al 1993Albertson et al 1995;Wesson et al 2001):…”

“…Over the past two decades, a large number of studies have shown that flux-profile and FV similarity functions for scalars such as temperature (T ) and water vapour concentration (q) mainly differ due to source inhomogeneity at the ground (Thom et al 1975;Garratt 1978;Raupach 1979;Raupach et al 1979;Padro 1993;Kustas et al 1994;Katul et al 1995;Bink 1996;Bink and Meesters 1999;Andreas et al 1998;Mölder et al 1999;Lyons et al 2001). However, even over a homogeneous surface, several studies did not find FV functions for T to be identical to those for q .…”