Analysis of short-term closure of the surface energy balance above short vegetation

Abstract

A detailed study of the surface energy balance was performed at a Mediterranean site in southern Italy. Two data sets of measurements of surface heat fluxes taken in the spring and autumn were tested with emphasis on the short-term (h) closure of the surface energy budget. The analysis shows that correction of the wind speed measurement sonic anemometer error at large angles of attack has influence on the energy budget closure; an important contribution also comes from heat storage between the soil flux sensor and the ground surface, not only for the amplitude but also for the relative phases of the measured fluxes. An analysis of the time series stationarity did not show appreciable effects on the energy budget. Instead, it appeared to be sensitive to the length of the averaging period for the coordinate rotation system. The use of a ‘long term coordinate system’, together with spectral analysis indicated that the usual 30-min averaging time is too short to include the entire contribution of the turbulent heat fluxes and that a 2-h averaging period is more suitable if larger scale motion effects are to be included.