Physical oceanographic research using the attended profiling current meter (APCM) and the Cyclesonde

Abstract

About half the physical oceanographic observations at the University of Miami are current profile measurements. These measurements are gathered by two distinct methods: the Attended Profiling Current Meter (APCM), which has been primarily developed and used by Dr. Walter Duing in his studies of intense ocean currents such as the Gulf Stream, the Equatorial Current and the Somali Current where near-surface current meter moorings are impractical or high vertical resolution velocity data are required; the second method involves the use of an automatic unattended current profiler--the Cyclesonde. The Cyclesonde, developed by John Van Leer, has been used to study current profiles on continental shelves and in the upper 300 meters where long time series of CTD/velocity profiles are desired or where profile array data with a single ship are available. Time Series profiles are particularly useful in studying inertial waves, mixing processes, bottom and surface boundary layers or complex mean flow patterns associated with fronts. About 20,000 velocity profiles have been collected by APCM and Cyclesonde techniques. The principal source of error in the APCM is navigational uncertainty in the ship's position, which is required to convert the velocity profile relative to the ship into absolute velocity profiles. Other errors include time lag, angle offset, rotor shading and surface wave pump up. The roller coupling used in both methods greatly reduces the surface wave noise introduced in the speed sensor at depths below the zone of direct wave orbital influence. Typical APCM errors are 3-5 cm and Cyclesonde errors are 1-3 cm/sec, compared to fixed level current meters or Other profiling techniques.