Meeting Abstracts
Correcting spurious low-frequency variations in drifter velocities
Rick Lumpkin, Semyon Grodsky, Luca Centurioni, Marie-Helene Rio, Jim Carton
NOAA/AOML
(Abstract received 04/05/2012 for session A)
ABSTRACT
Satellite-tracked surface drifters have been collecting near-surface ocean current observations in the tropical Pacific since 1979, with observations in the other basins also now extending more than 15 years. These data allow investigators to explore climate variability of ocean circulation and understand how it responds to changing surface forcing. However, recent studies have reported evidence of spurious variations in drifter-derived surface currents that became noticeable in 2003, reached peak severity in 2005, and subsequently diminished. The spurious variations have a pattern similar to mean surface winds, and may be explained by the presence of undiagnosed drogue loss in drifters whose occurrence changes in time. In this study, we describe a methodology to reassess drogue presence for each drifter in the historical data set since 14 October 1992. We demonstrate the effects of this reanalysis upon time-mean and low-frequency variations in the speed of drifters, and describe how this methodology will be implemented by NOAA's Global Drifter Program for drogue detection.