Geographic variations in intensity of the North Atlantic and North Pacific oceanic eddy fields

Abstract

The geographic variations in the oceanic baroclinic eddy field intensity, as indicated by the structure function of the dynamic height across the thermocline after seasonal and large scale trends are removed, is examined using historical data from the North Atlantic and North Pacific oceans. An inverse relationship between eddy field intensity and distance from the western boundary current is found in each region, confirming that the western boundary currents are major energy sources for baroclinic eddies in mid-ocean regions. Eddy energy is largely confined to the northern and western areas of the North Atlantic and North Pacific sub-tropical gyres, with significantly reduced energy levels both in the eastern areas and north of the Sub-Arctic Frontal Region. Dominant eddy field length scales of energy variability consistent in magnitude with those of more recently observed eddies also are confirmed for the North Pacific. Spatial statistics similarly computed from selected Mid-Ocean Dynamics Experiment (MODE-I) hydrographic data are consistent with those determined from the historical data. The statistical characteristics of the structure function are evaluated empirically to estimate the confidence levels of the historical data statistics.