Upper ocean flow statistics estimated from superresolved sea‐surface temperature images

Abstract

AbstractOcean turbulence on scales of 10–50 km plays a key role in biogeochemical processes, frontal dynamics, and tracer transport in the upper ocean, but our understanding of these scales is limited because they are too small to be resolved using extant satellite altimetry products. By contrast, microwave imagery of the sea‐surface temperature field does resolve these scales and can be used to estimate the upper ocean flow field due to the strong correlation between the surface density field and the interior potential vorticity. However, because the surface density (or temperature) is a smoothed version of the geostrophic stream function, the resulting velocity field estimates are limited to scales of 100–300 km in the first few hundred meters of the water column. A method is proposed for generating superresolved sea‐surface temperature images using direct low‐resolution (microwave) temperature observations in combination with an empirical parameterization for the unresolved scales modeled on statistical information from high‐resolution (infrared) imagery. Because the method relies only on the statistics of the small‐scale field, it is insensitive to data outages due to cloud cover that affect infrared observations. The method enhances the effective resolution of the temperature images by exploiting the effect of spatial aliasing and generates an optimal estimate of the small‐scale temperature field using standard Bayesian inference. The technique is tested in quasigeostrophic simulations driven by realistic climatological shear and stratification profiles for three contrasting regions at high, middle, and low latitudes. The resulting superresolved sea‐surface temperature images are then used to estimate the three‐dimensional velocity field in the upper ocean on scales of 10–50 km.