Salinity Variability in the California Current System

A regional model is used to study the interannual to decadal salinity variability in the California Current (CC) system, using multiple simulations of 1950-2005. The model reproduces the mean structure, red variance spectrum, and the spiciness in the CalCoFI observations. However, the model standard deviation is too high by roughly 40%, and has too high positive skewness. The model also fails to reproduce the phase of the salinity time evolution; however the salinity shows variability between different realizations of the model, suggesting intrinsic variability as a contributing cause. To study the generation mechanism for low-frequency anomalies, we first try to remove the effect of isopycnal heave (associated with eddies) by using a density surface. Anomalies on the 1025.6 density surface at 36N have a decorrelation time scale of 23 months. Their generation is consistent with anomalous advection upstream in the CC, such that anomalously salty water in the CC is associated with a southward displacement of the North Pacific Current and weakened inflow from the north. Strong lateral gradients characterize the one-month averages of CC salinity, temperature and density. In the region southwest of the mean CC path, the salinity gradients are compensated and thus lack a strong dynamical signature. We propose that these dynamically passive salinity gradients are displaced by eddies and lead to the intrinsic variability observed there. At the region closer to Cape Mendocino, salinity gradients are associated with a density front and may be an active player in the dynamics.