Augmented Bowen Ratio Analysis –I: Site Adequacy, Fetch and Heat Storage (ABRA)

Abstract

The addition of measurements of downward-looking infrared surface temperature to the standard suite of Bowen Ratio Energy Balance observations permits a direct examination of the adequacy of fetch. Furthermore, when the observed rates of change of surface temperature are examined (using multiple regression) in the light of the total turbulent heat exchange (the sum of sensible and latent heats) and the total heat energy available (due to net radiation, corrected for the ground heat exchange) a quantification of the rate of heat storage otherwise unaccounted for (e.g. by the canopy) is revealed. The statistical methodology minimizes the difficulties often encountered near dawn and dusk when the ratio of sensible to latent heat fluxes approaches -1. Analysis making use of all available data is then possible, without data exclusions being applied. Four months of data obtained at a site in the Zimbabwe highland region in 2014 are used to illustrate this augmented Bowen Ratio analysis methodology. The analysis reveals that the heat storage terms tend to dominate the heat energy budget for periods following dawn and dusk, and that most of the heat storage is associated with the uppermost layers of soil rather than the vegetative canopy.