Horizontal and vertical distribution of air temperature in a vegetation [maize] canopy.

Abstract

Air temperature measurements within a maize row canopy were carried out to investigate the horizontal and vertical variability of the mean air temperature. Attention was given to finding adequate scaling parameters of the within-canopy air temperature profiles under various atmo spheric stratification states. It appeared that in a narrow-row crop the horizontal mean air temperature can vary between 0.1 °C (night time) and 0.35 °C (daytime) from its spatial mean value. Exceptions can occur around noon under daytime situations when direct irradiation dominates and where the direct beam illuminates the within-row space of the canopy. Then differences to the spatial mean value of 1 °C or more can be observed. During daytime, the within-canopy temperature profiles scale well with the above-canopy temperature scale, T*, for 'constant' irradiation and wind speed regimes. During calm evenings, however, the rela tive within-canopy temperature profile scales very well with the within-canopy free convec tion temperature scale, 0*. It appeared that the within-row and across-row heat advection is of minor importance within dense row canopy.

Quantifying the Clear‐Sky Bias of Satellite Land Surface Temperature Using Microwave‐Based Estimates

“…Over vegetated areas, satellite LST derived from MW observations corresponds to the temperature of the canopy top (or first few centimeters, depending on penetration depth), and therefore, the LST‐ T air differences depend not only on vegetation density but also on canopy height. As a result, LST‐ T air differences may depend on local lapse rate (Flerchinger et al, ; Jacobs et al, , ). Although this effect is in line with the negative LST‐ T air values observed over tropical forests (Figure ), it should be noted that spatial coverage of stations used in the CRU data set is very limited over tropical forests.…”

Simulating of leaf wetness duration within a potato canopy

“…During night-time and around sunrise and sunset the air within the canopy is well mixed. This results in a within-canopy temperature profile that is more or less constant with height (Jacobs et al, 1992). In the present study the air temperature at two heights within the canopy was measured and for the within-canopy air temperature a linear profile was used.…”

“…Figure I furthermore shows that during night-time the within-canopy air temperature was somewhat higher than the above-canopy air temperature. During night-time a well mixed air layer is present within the canopy (Jacobs et a!., 1992), i.e., a layer with a more or less constant temperature. In contrast, the temperature in the air layer just above the canopy is stable, i.e., the temperature increases with height (Jacobs et a!., 1994)•…”