WHOI PO

Mesoscale eddy fluxes play an important role in ocean transport. Coarse resolution climate models parameterize these fluxes in terms of diffusion coefficients, and improving such parameterizations remains an active topic of research. Recently, significant progress has been made in both describing and understanding the spatial variability in mesoscale diffusivity. The latter has mainly been in terms of monochromatic models, which describe eddy fluxes in terms of a single length scale and phase speed. This approach seems at odds with the broad spectrum of variability in the ocean. In order to better understand the spectral nature of eddy fluxes in the ocean, in this study we calculate wavenumber-frequency spectra in a broad sector of the eastern Pacific from satellite SST and altimetry data. The cross-spectra from these two datasets gives the eddy heat flux, which is then integrated to give wavenumber, frequency, and phase speed spectra at each latitude. These distributions are examined and compared with eddy properties as described by an eddy census. The same analysis is also performed on a high-resolution coupled climate model, providing a glimpse at spatial and temporal scales unresolved by the satellite data. The agreement between the model and the data provides validation for the model and confirms the underlying physics. In the extra-tropics, the dominant length scale that emerges from the cross spectral analysis is consistently proportional to the average diameter of individually tracked coherent eddies. The phase speed cross spectra peak rather narrowly around the long Rossby wave phase speed. Both these conclusions support the notion of parameterizations of eddy fluxes in terms of a single length scale and phase speed.