Water-following characteristics of a mixed layer drifter

Measuring surface currents with Surface Velocity Program drifters: the instrument, its data, and some recent results

“…The subsurface float has been omitted in the recent mini drifter redesign. The most important design characteristics that minimize slip are low tension between the surface buoy and drogue, which avoids aliasing wave motion, and a large drag area ratio (Niiler et al, 1987). As long as the drogue remains attached to the drifter, the downwind slip is estimated at 0.7 cm/s per 10 m/s of wind speed (Niiler and Paduan, 1995).…”

“…Several drogue designs were examined and various problems identified. For example, windowshade drogues could twist and sail across a current; parachute drogues could collapse and subsequently provide very little drag; the line-and-chain FGGE drogue provided too little area compared to the surface float, resulting in significant slip with respect to the currents at the drogue depth (Niiler et al, 1987Niiler and Paduan, 1995;Pazan and Niiler, 2001). Other factors were also considered; for example the rigid three-dimensional tristar drogue was found to have somewhat better water-following characterists than the holey-sock drogue developed at AOML, but the increased manufacturing and shipping costs and more difficult deployments for the tristar outweighted this benefit.…”

“…During the 1980s these designs continued to evolve, and in 1985-89 they were rigorously evaluated on a number of criteria including their water-following characteristics, quantified by attaching vector-measuring current meters to the tops and bottom of the drogues (Niiler et al, 1987. Several drogue designs were examined and various problems identified.…”

“…Slip is caused by direct wind forcing on the surface float, drag on the float and tether induced by wind-driven shear, and surface gravity wave rectification (Niiler et al, 1987;Geyer, 1989). In order to reduce wave rectification, the surface float is spherical (Niiler et al, 1987.…”

Some High-Frequency Variability of Currents Obtained by "GeoDrifters" in the Tsushima Current Region

“…The satellite-tracking drifters have long been proved to be effective tools for examining ocean dynamics over a wide range of time and space scales, the WOCE surface drifter project being a good example (McNally et al 1983;Niiler et al 1987;Krauss and Böning 1987;Thomson et al 1997). Most of studies using satellite drifters have focused on large-scale features or low frequency variability, such as ocean circulations and mesoscale eddies.…”