Anomalous Poleward Transports in the California Current
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Science II: Large Scale Ocean Circulation Variability and Change
Presentation type: Type Oral
Contribution: PDF file
We are using altimeter-derived velocity fields to examine the Lagrangian pathways that move passive water parcels from the southern to the northern regions of the California Current System (CCS) along the Pacific Northwest (Oregon-Washington) coasts. Motivation comes from observations of the appearance of anomalous water properties and larger numbers of “warm-water”, “tropical/subtropical” zooplankton during some years (often El Niño years). These observations have been used to infer transports from far to the south. Use of the altimeter data allows us to address several questions: (1) What are the greatest distances from which to expect passive water parcels to arrive in the PNW from the south during “anomalous” years? (2) What are the spatial and temporal characteristics of the pathways taken by the parcels that reach the farthest north from the south during any single year? (3) What role do the surface wind-forced Ekman transports play in these pathways? (4) What role do smaller-scale mesoscale and sub-mesoscale “eddy diffusivities” play in these transports? We address these questions by calculating Lagrangian trajectories from altimeter-derived surface geostrophic currents, with/without the addition of Ekman transport components; and with/without the inclusion of small-scale eddy diffusivities. Results indicate that smaller-scale eddy diffusivities may enhance northward transports, while Ekman transports may hinder it. The most distant origin of the parcels is within the Southern California Bight. We find significant correlations between northward altimeter-derived transports from central/southern California and the zooplankton anomalies off Oregon. EOF and Principal Estimator Pattern analyses help to quantify the relationship between the anomalous transports and patterns of local and distant forcing.