Intercomparison of drogued and undrogued drift buoys

Abstract

In order to model the wind and wave forced slip of drift buoys, Ocean Prospects has acquired and quality controlled drogued and undrogued WOCE/TOGA drifting buoy observations and naval AN/WSQ-6 drifting buoy observations; the authors then estimated buoy survivabilities and made some initial intercomparisons of buoy positions. Ocean Prospects obtained, archived and interpolated to synoptic times observations of position and time from: 706 METOCEAN Compact Meteorological and Oceanographic Drifter (CMOD) buoys deployed in the Atlantic, Pacific and Indian Oceans; 2013 WOCE/TOGA Lagrangian drifters deployed during the same period: and 1632 of these same WOCE/TOGA drifters after they lost their drogues. Intercomparisons of the distributions of drogued and undrogued WOCE/TOGA and the Navy's AN/WSQ-6 buoys were made. The distributions of naval and WOCE/TOGA buoys are spatially complementary, meaning that estimation and removal of naval buoy slip and the subsequent inclusion of the naval AN/WSQ-6 data into the Lagrangian drift buoy data base will greatly improve the observation of upper ocean currents in the Indian Ocean and the western Pacific and western Atlantic. The behaviour of undrogued WOCE drift buoys can be expected to be similar to naval AN/WSQ-6 buoys and estimation of undrogued WOCE/TOGA drifting buoy slip should increase the database by almost 40%. The WOCE/TOGA global drifter datasets are comprised of 1,844,144 drogued buoy observations and 848,416 undrogued buoy observations at synoptic time intervals, while naval AN/WSQ-6 buoy global drifter datasets are comprised of 334,944 buoy observations at time intervals determined by ARGOS satellite reception times. Three interpolation procedures were compared before interpolating the naval drifting buoy data to synoptic 4-daily time intervals for consistency with the WOCE/TOGA dataset, the interpolated dataset has 196,885 buoy observations at 4-daily synoptic time intervals. Survivability of WOCE/TOGA buoys against drogue loss exceeds 400 days: survivability of WOCE/TOGA buoys against all modes of failure exceeds 200 days; survivability of naval AN/WSQ-6 buoys against all modes of failure exceeds 40 days. These survivability values fluctuate but there is no substantial trend over the 5 year period from 1990 through 1994. Meridional and zonal surface wind velocity components from the global synoptic FNMOC model have been interpolated to each naval AN/WSQ-6 and WOCE/TOGA buoy position and date/time in the datasets. Ensembles of pairs of drogued and undrogued buoys observed within 3 days of one another have been assembled for 5/spl deg/ latitude bands in the western Pacific: 600 pairs are available, on average, for ensembles of pairs located within 20 km of each other. This data demonstrates the linear relationship between the mean difference in drogued and undrogued buoy drift velocity (slip) in different latitude bands.