Increased Eddy Activity in the Northeastern Pacific during 1993-2011

The authors study the long-term behaviors of eddy activity in the northeastern Pacific (NEP) and the dynamic mechanism behind them, using the third version of the mesoscale eddy trajectory dataset released by Chelton and Schlax as well as other observation and reanalysis datasets. Both the eddy kinetic energy (EKE) and eddy occurrence number (EON) present prominent increases, with interannual and decadal variabilities northeast of the Hawaiian-Emperor seamounts. The increasing EON is mainly due to the prolongation of eddy lifetimes associated with eddy intensification, particularly for anticyclonic eddies (AEs). The prolongation of eddy lifetimes results from weakened surface winds. The enhanced anticyclonic wind stress curl (WSC) injects more energy into the AEs in the study domain, providing a more suitable environment for their growth. The decadal climate modes, such as the Pacific decadal oscillation (PDO) and the North Pacific Gyre Oscillation (NPGO), may also modulate eddy activity in the NEP by exerting fluctuations in the surface wind system.