New methods for estimating poleward eddy heat transport using satellite altimetry

The role of ocean eddies in redistributing heat from the tropics to the poles remains a poorly constrained feature of the global energy balance. Attempts to monitor poleward eddy heat transport using satellite altimetry are severely limited by the sparseness of the observations in the vertical and the horizontal as well as in time, and consequently underrepresent heat transport by mesoscale eddies, particularly at high latitudes. In this study, we examine a suite of cheap, skillful, and robust filtering strategies for estimating poleward heat transport in idealized, eddy-resolving simulations of oceanic turbulence at high and low latitudes. A range of observation scenarios are considered, allowing us to explore the interplay of eddy length and time scales with the spatiotemporal resolution capability of satellite observations.

We show that, by extracting high-wavenumber information aliased into the low wavenumber band, one can derive ``superresolved'' velocity fields from sparse satellite observations, increasing the effective resolution of altimetric maps by a factor of four or more. As a result, the measured magnitude and temporal variability of the poleward eddy heat transport is much closer to the true value. The speed and stability of the filters are also dramatically increased by employing stochastic turbulence models for the unresolved scales, effectively parameterizing them with a model that can be learned ``on-the-fly'' from the satellite observations themselves. Implications for estimating poleward eddy heat transport using current and next-generation altimeters are discussed.