CR 12:29-37 (1999)  -  doi:10.3354/cr012029

ABSTRACT: Aerodynamic measurements of latent (λE) and sensible heat (H) exchange were made in an intensively managed peat pasture during 2 consecutive years; the fetch was approximately 1.5 km. The surface conductance (g_s) was calculated from the Penman-Monteith equation. The analysis focused on 2 successive aspects of g_s: g_s as a function of environment (primarily vapour pressure deficit [D]) and the energy balance as a function of g_s. The effect of D on g_s consisted of 2 components: the range of D over which g_s was reduced (beyond inflection point D_i) and the reducing effect per unit D. As average D increased, so did inflection point D_i and the range of D over which g_s was reduced; the reducing effect per unit D decreased. g_s was a strong mediator in the energy balance. λE increased with D upto the inflection point D_i, beyond which g_s increasingly offset the positive effect of D. As g_s impaired λE, the surface to air temperature difference (ΔT) and consequently H increased. With increasing g_s, λE and H added up to progressively lower values, suggesting an increasing soil heat flux. Hysteresis in the diurnal patterns of the energy balance showed that the positive effect of D on λE remained stronger than the consequent negative effect of g_s. λE was higher after than before noon, whereas ΔT and H were lower.

KEY WORDS: Aerodynamic technique · Surface conductance · Energy exchange · Latent heat · Sensible heat · Pasture · Grassland