URAHFREP project (1998-2001)

The purpose of the field trials is to study the possible influence of HF thermodynamics on the dispersion of atmospheric HF clouds. Models predict both negative buoyancy (heavy gas) effects and positive buoyancy effects depending on concentration, humidity and other factors. The main question addressed by the experiments is whether these effects in reality are strong enough to dominate naturally occurring uctuations. If so plume lift-off can be expected, and even without lift-off it is possible that vertical mixing is enhanced.

In order to test if the lift-off or enhanced mixing created by the HF release was strong enough compared to the naturally uctuations the HF releases were accompanied by passive smoke release, made shortly after to obtain a reference to the HF release. The instrumentation included various types of HF sensors, thermocouple arrays, a fully instrumented release rig, a passive smoke machine, a meteorological mast and a lidar backscatter system. In addition video and photography was deployed. Pots with grass were set out in the far range for the purpose of studying environmental effects.

The trials cover a range meteorological conditions. These include neutral conditions with relatively high windspeed and low humidity as well as unstable conditions with low windspeed and high humidity, the most favorable conditions for lift-off to occur. The lidar was used to scan vertical cross-plume slices 100 meter downwind of the source. The scan rate was about 1 scan per second. From these measurements various indicators of the plume geometry have been extracted. A comparison of plume characteristics for HF clouds and passive smoke clouds has been made. The analysis shows no sign of any difference between the dispersion of HF and passive smoke except for one release, where a positive buoyancy effect cannot be excluded. An enhanced mixing effect of HF was not observed.

Dowload reports, pictures and data.

The field experiment dispersion data are distributed in Rediphem database format. Read more about this database and associated software.