Lagged correlation of dynamic height from the gappy California Cooperative Oceanic Fisheries Investigation (CalCOFI) with monthly San Diego sea level for the period 1949-2001 shows that the dynamic height propagates westward at 4.10 cm/s, about double the speed of the large-scale low frequency Rossby wave (2.2 cm/s). TOPEX/Poseidon/Jason1 along-track sea level height estimates since January 1993, filtered interannually, propagate westward at 4.3 cm/s, verifying that observed westward propagation is about double that expected. Including the effect of the mean California current on the Rossby wave propagation does not explain the discrepancy but rather slightly increases it.
Because of the westward propagation, interannual variations in alongshore geostrophic surface current are proportional to the time derivative of sea level. This means that such large scale interannual current variability can be monitored with appropriate lag, by the time derivative of coastal sea level. The anomalous alongshore flow advects particles, the anomalous alongshore particle displacement being proportional to sea level. Since nutrient concentration is lower in the south, the anomalous alongshore displacement results in lower nutrient concentration when sea level is anomalously high and higher nutrient concentration when the sea level is anomalously low. Vertical displacement also results in a similar relationship between nutrients and sea level.
The anomalous alongshore and vertical particle displacements associated with the Rossby waves also act on the mean temperature and salinity fields to produce temperature and salinity anomalies. Theory suggests that these anomalies should be proportional to the anomalous dynamic height. Consistent with this, observed salinity anomalies at depths of 100-200 m are well correlated with dynamic height anomalies. At depths greater than 200 m the observed anomalies are small and, consistent with a smaller signal to noise ratio, the correlation falls. At depths shallower than 100 m the correlation between salinity and dynamic height anomalies also falls rapidly. The flow anomalies can similarly be used to explain the temperature fluctuations except that the correlation between temperature and dynamic height fluctuations does not fall rapidly in the surface layer as in the salinity case.
