RETRIEVAL OF SURFACE HEAT AND MOISTURE FLUXES FROM SLOW-LAUNCHED RADIOSONDES

Recently, there has been growing emphasis on improving surface flux inputs to mesoscale models and general circulation models. Since there is presently no operational network providing this information, we have conducted a feasibility experiment to determine whether the Bowen ratio (and indirectly surface heat and moisture fluxes) can be reasonably and accurately derived from thermodynamic measurements obtained from balloon-launched radiosondes. The experiment took place during July 1988 at the Regional Airport in Tallahassee, Florida using an Atmospheric Instrumentation Research, Inc. (AIR) airsonde system and a surface radiation and energy budget station (SREBS) developed at Florida State University. The AIR system consists of a balloon-launched airsonde, which measures vertical profiles of atmospheric pressure, temperature, and relative humidity, and an automatic data acquisition system, which receives and records sensor output from the airsonde package. The SREBS is a compact, self-contained, battery-powered system used to measure approximately 100 surface parameters. For this experiment, the system was used to monitor in situ surface energy fluxes at the time of the radiosonde flights. The data recorded from the airsonde launches were used to create mixing-line profiles for each launch. Using the profiles, an objective technique for choosing the appropriate surface-layer mixing lines was developed, and from these the associated Bowen ratios within the surface layer were deduced. Intercomparisons were made between Bowen ratios derived from the airsonde profiles and the Bowen ratios measured directly by the surface radiation and energy budget station. The results show that this technique produces estimates of the Bowen ratios within 9% of measured values, and a sensitivity analysis indicates that estimates of sensible and latent heat fluxes have root-mean-square differences of less than 6 W m-2.