Momentum and climate governors of the California Undercurrent transport

The California Undercurrent (CUC) transport undergoes significant variability ranging from intraseasonal to interannual time scales, and has both climate and biogeochemical consequences. Using a regional model solution at the mesoscale-resolving resolution, we depict the CUC characteristics (e.g. its path and spatiotemporal variability) and assess the governors of the CUC transport variability. The CUC path is strongly regulated by topography, and the CUC variability has significant latitudinal coherence. The CUC contributes much more to the advection of biogeochemical tracers than eddies and cross-shore mean flow. From a momentum perspective, the top two modulators of the CUC transport are topographic form stress and eddy advection. From a climate perspective, among a range of climate mode variability and local wind forcing, ENSO is a dominant predictor of the interannual variability of the CUC transport. Analysis revealed that the momentum and climate modulators of the CUC transport can be reconciled: the equatorial signal of the ENSO event influences the CUC through the poleward propagation of coastal trapped waves and then the modulation of density fields and consequently the topographic form stress. The role of eddy stress in redistributing the momentum within the CUC is also discussed.