A MODEL FOR A MODIFIED CARBORUNDUM BLOCK ATMOMETER

Abstract

The potential evapotranspiration continues to be a difficult quantity to estimate. A modified carborundum block atmometer, designed to integrate the effects of the various meteorological elements and to give an estimate of the related latent evaporation, is discussed. A description of the instrument and its routine operation is given. Then the mechanics of the atmometer are discussed using an energy balance approach and a model describing the physics of the instrument evaporation is presented. The available data can then be fitted with the appropriate empirical choice of one constant parameter in the model. These data are then outlined to demonstrate the performance of the atmometer and the model under a range of operating conditions. Test periods of lengths 7.5, 16.5 and 24 h were used during two summers of observations. Each summer was treated separately with the largest mean difference between the average observed evaporation and the calculated evaporation being 0.2 ml and the largest standard deviation of this difference being 2.0 ml.