Surface current trajectories in the Southern California Bight: Model results and observations
Carter Ohlmann, Satoshi Mitarai
University of California, Santa Barbara
(Abstract received 08/14/2009 for session D)
ABSTRACT
Many applied problems in coastal oceanography are inherently Lagrangian, requiring trajectories to determine the “fate and transport” of passive tracers. Probability distributions of water parcel location as a function of initial position and advection time are the primary quantities of interest. In the turbulent ocean, numerical model derived trajectories must be relied upon for the extreme number of realizations needed to calculate probability density functions (pdfs). The model-derived trajectories must be shown to be suitably representative. A model-data comparison between Lagrangian pdfs from ROMS simulations and historical drifter observations is presented. The two dimensional Kolmagorov-Smirnov (K-S) statistical model for comparing sampled data with a known pdf is the basis of the comparison. Data are from surface current trajectories collected primarily in the Santa Barbara Channel from 1996 through 1999 with one-meter CODE style drifters. Modeled pdfs come from trajectories (at one meter depth) computed with one-kilometer resolution ROMS simulations for the Southern California Bight for the same time period. Deployments within 10 kilometers of the coast throughout the Santa Barbara Channel with one to four day advection times are evaluated. In general, in situ data lie within the area given by model pdfs and K-S statistics rarely disprove the null hypothesis (H0: data are from the model pdf) for the relatively small data samples available. Both the underlying assumptions and power of the K-S test are discussed. The Lagrangian based comparison elucidates an improved understanding of model performance and ocean circulation beyond that offered with a Eulerian comparison.
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