Eulerian and Lagrangian eddy statistics of the Tasman Sea and southwest Pacific Ocean

Abstract

Ocean eddy variability dominates many important processes in the ocean at a range of length and timescales. We describe the eddy statistics in the Tasman Sea–New Zealand region using drifter data from the Global Drifter Program (GDP) to derive Lagrangian statistics and TOPEX/Poseidon (T/P) satellite data to derive Eulerian statistics. The ratio η of the Lagrangian to Eulerian timescales is also a measure of length scales in the ocean; when η is high, Lagrangian length scales are short compared with Eulerian length scales and vice versa. We compute η both in the time domain from temporal autocorrelations of drifter and satellite data, and in the frequency domain from drifter and satellite velocity spectra. The zonal component of this ratio appears to be constant in the Tasman Sea, whereas the meridional component shows a latitudinal dependence. We argue that if η is known, all Eulerian and Lagrangian timescales can be determined from relatively easy measurements of the Eulerian timescale and eddy kinetic velocity.