Fig. 3. Mean velocity field, optimized with variational technique.
Limitation in data causes a high level of noise and errors in mean velocity estimates. To get more representative mean velocity field without oversmoothing by direct statistical methods (i.e. to remove uncorrelated noise in the central areas of large-scale gyres, poorly covered with drifter measurements, and to remain, at the same time, reliably observed and well-resolved narrow strong jets, like KE) we employed original variational interpolation technique. Main advantage of our scheme is the inclusion of advective nonlinear term into the cost function soft constraints. This idea is based on estimates of weakness of ageostrophic currents, obvious difference in cross- and along-stream decorrelation scales in the western boundary currents and frontal areas, and, mathematically, results in a preference of along-stream velocity averaging, when cross-stream flow structure is mostly remained unchanged. Other terms of our cost function provided smoothness and non-divergence of the solution as well as its fitting averaged data. Results are shown in Fig. 3. Indeed, optimized mean velocities not only keep parameters of main jets, but even allow discussion of KE and SF interaction with Shatsky Rise and Emperor Seamounts.
