Estimation of the advection effects induced by surface heterogeneities in the surface energy budget

Abstract

<p><strong>Abstract.</strong> The effect of terrain heterogeneities in one-point measurements is a continuous subject of discussion. Here we focus on the order of magnitude of the advection term in the equation of the temperature as generated by documented terrain heterogeneities and we estimate its importance as a term in the surface energy budget (SEB). The heterogeneities are estimated from satellite and model fields for scales near 1 kilometer or broader, while the smaller scales are estimated through direct measurements with remotely-piloted aircraft, thermal cameras and also by high-resolution modeling. The variability of the surface temperature fields is not found to decrease clearly with increasing resolution, and consequently the advection term becomes more important as the scales become finer. The advection term provides non-significant values to the SEB at scales larger than few kilometers. On the contrary, surface heterogeneities at the meter scale yield large values of the advection, which are probably only significant in the first centimeters above the ground. The motions that seem to contribute significantly to the advection term in the SEB equation in our case are roughly those around the hectometer scales.</p>

A study of local turbulence and anisotropy during the afternoon and evening transition with an unmanned aerial system and mesoscale simulation

“…Besides, the three sources are reproducing a similar temporal evolution of temperature, being the model 1 K warmer and 1 K colder than the observations during day and night respectively. Although these biases are not large, similar values are found for other studies and they can be attributed to an enhanced mixing of the model at lower levels (Conangla and Cuxart, 2006) or to a misrepresentation of the surface heterogeneities (Cuxart et al, 2016).…”

“…During the AET, spatial inhomogeneities are created, which influence the development of the ABL through the night (Acevedo and Fitzjarrald, 2001;Cuxart et al, 2016). Over complex terrain, temperature gradients at local scales (Conangla and Cuxart, 2006) or larger-scale structures (Bonner, 1968) normally associated with topography are responsible for the generation of a low-level jet (LLJ), first described in Blackadar (1957).…”

Landsat and Local Land Surface Temperatures in a Heterogeneous Terrain Compared to MODIS Values

“…Therefore, in this single scene, it is checked that with lower spatial resolution (1 km 2 ), significant temperature gradients at the hectometre scale are not detectable, pointing to the need of higher horizontal resolution fields to monitor their evolution, something currently out of reach with the satellites at disposal for the scientific community that have these images just once every several days and for a single instant. However, heterogeneities of this size may contribute significantly to measured surface energy and water budgets over land, according to other previous studies ( [11]). …”

“…If LST is obtained from the Atmospheric Surface Layer (ASL), which is a layer of air with a thickness of a few meters above the surface, there are a number of well identified issues that influence LST measurements: (i) the very small scale heterogeneities [11], implying that the radiometer receives radiation from elements of the surface radiating differently; (ii) the determination of the emissivity of the emitting surface, which strongly depends on the amount of water in the upper centimetres of the soil and the state of the vegetation, and, nonetheless; (iii) the possible high-concentration of atmospheric emitters between the radiometer and the surface, such as CO 2 and water vapour, especially on stable nights. The usual strategies are to sample homogeneous surfaces, to determine the emissivity of the sampled area and to measure the radiation emitted through a window partially transparent to CO 2 and to water vapour.…”

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

“…These factors include the inherent horizontal heterogeneity [15,47], the corresponding local advection processes [57,61], slope effects on the available radiant energy [62,63], the potential failure of the vertically-constant-flux assumption in the SL [64], and others.…”