Long-term energy flux measurements over an irrigation water storage using scintillometry

Abstract

An analysis is presented of the long-term energy balance of a small water body in south-east Queensland, Australia. The main focus of this study was on the use of scintillometry to determine the turbulent fluxes of sensible and latent heat. A novel approach is utilized for identifying periods where the scintillometry measurement footprint extends beyond the water surface. This approach relies on comparison of ‘inferred’ water surface temperature and measured skin temperature. The ‘inferred’ temperature is an independent assessment of water skin temperature derived through rearrangement of key equations in the scintillometry calculation scheme. An extensive dataset is used to investigate the processes controlling heat and vapour fluxes and to develop simple relationships that can be used for reliable predictions. These relationships are used to fill missing measurements in the dataset and to construct a complete energy balance for an 18 month period. The long-term data set is used to describe the diurnal, seasonal and annual variations in energy fluxes and to explore issues related to energy balance closure. Average energy balance closure across the study was 82%, however closure was much better during the winter than the summer. The key factors likely to lead to errors in energy balance closure are considered and it is concluded that the most likely causes are underestimation of latent heat fluxes, advection of energy that is not measured by the scintillometer, or overestimation of net radiation.