The Disturbing Effects of Probes in Meteorological Fluid-Model Experiments

Abstract

Detailed measurements of the complete vector-velocity and temperature fields have been carried out for an upper symmetrical (Hadley regime) flow in a rotating, differentially heated annulus of water in order that precise comparison could be made with numerical integrations by G. Williams. To make the measurements, small hypodermic probes must be inserted into the fluid from above. Definite and significant alterations of the torque-angular momentum balance of the fluid, and associated alterations of other field variables have been detected experimentally and shown to be due to the probes. Measurements have been made that allow extrapolation from the altered state to a ?no-probe? state and the determination of correction fields for the temperature and velocity. Evidence that the drag on the probes in the upper westerly zonal flow may be the main source of the flow alteration is given. Important implications of the existence of such effects for quantitative meteorological experiments are pointed out, including clear indications that, for the low probe Reynolds numbers involved, the drag values cannot be greatly reduced by reducing probe sizes.