UNCERTAINTY OF BOUNDARY-LAYER HEAT BUDGETS COMPUTED FROM WIND PROFILER-RASS NETWORKS

Uncertainties in the evaluation of the atmospheric heat budget, in whi ch the turbulent heat flux divergence term is calculated as a residual , are investigated for a triangular array of 915-MHz wind profilers-ra dio acoustic sounding systems (RASS) using a surface-integral method. A scaling analysis of the residual error heat budget equation reveals the basic characteristics and magnitudes of the uncertainties. These v alues are verified with a Monte Carlo simulation technique for synthet ic datasets in which the triangle size is of the order of 30 km (meso- gamma scale). The uncertainties depend on measurement errors. atmosphe ric stability, mean wind speed, triangle size, and averaging time. In addition, we estimate the effects of baroclinity and mean wind diverge nce on the accuracy of the calculation of the heat budget. Idealized, barotropic, and divergence-free conditions are studied to investigate the influence of various instrument accuracies on profiles of the turb ulent virtual potential temperature flux divergence term. Results show that this term can be computed as a residual of the other terms with an uncertainty that varies from approximately 0.4 to 1.6 K h(-1) for t ypical ranges of mean wind speed and stability, given current accuraci es for l-h averages of wind profiler-RASS. Uncertainties of the remain ing terms in the equation are smaller. Although the uncertainties foun d are of about the same magnitude as typical maximum daytime boundary layer turbulent sensible heat flux divergences, 1.2 K h(-1), it is fou nd that under favorable conditions meaningful turbulent heat flux dive rgences can be obtained. The computations, however, become very uncert ain under conditions of strong baroclinity or wind divergence.