Eddy Generation Mechanisms in the Eastern Boundary Current Systems

Mesoscale eddy generation mechanisms in the Northeastern Pacific (NEP) are investigated using merged altimetry data from 1993 to 2013 and solutions of a nonlinear, 1½-layer reduced-gravity model as well as MITgcm. We estimate the relative roles of local wind forcing and the remote forcing from the equator in eddy generation in the NEP.

In order to extract mesoscale variability, a 10-600 km band-pass filter is used according to the diameter range of most of mesoscale eddies. We find that mesoscale variation contributes a lot to the change of the SSHA in the NEP. The results of statistical analyses indicate that the number of mesoscale eddies in the NEP does not show any seasonality and the generation location is related to the shape of coastline.

Model solutions show that local wind explains about 43% of the mesoscale eddies generated in the NEP and the low-frequency wind is more important to eddy generation, while equatorial wind explains 20% of the mesoscale eddies in the NEP and high-frequency wind is more important. The equatorial wind-driven SSHA signals reach the west coast of California in the form of coastal Kelvin waves, which can affect the generation of mesoscale eddies in the NEP. By more analyses to the numerical experiments, we find that local wind contributes more to the generation of mesoscale eddies north of 35°N than south of 35°N, while the signals driven by equatorial wind are more important to the generation of mesoscale eddies south of 35°N in the NEP.

Mesoscale eddy generation mechanisms in the Northeastern Pacific (NEP) are investigated using merged altimetry data from 1993 to 2013 and solutions of a nonlinear, 1½-layer reduced-gravity model as well as MITgcm. We estimate the relative roles of local wind forcing and the remote forcing from the equator in eddy generation in the NEP.

In order to extract mesoscale variability, a 10-600 km band-pass filter is used according to the diameter range of most of mesoscale eddies. We find that mesoscale variation contributes a lot to the change of the SSHA in the NEP. The results of statistical analyses indicate that the number of mesoscale eddies in the NEP does not show any seasonality and the generation location is related to the shape of coastline.

Model solutions show that local wind explains about 43% of the mesoscale eddies generated in the NEP and the low-frequency wind is more important to eddy generation, while equatorial wind explains 20% of the mesoscale eddies in the NEP and high-frequency wind is more important. The equatorial wind-driven SSHA signals reach the west coast of California in the form of coastal Kelvin waves, which can affect the generation of mesoscale eddies in the NEP. By more analyses to the numerical experiments, we find that local wind contributes more to the generation of mesoscale eddies north of 35°N than south of 35°N, while the signals driven by equatorial wind are more important to the generation of mesoscale eddies south of 35°N in the NEP.