Introducing a Global SST Gradient and Fronts Dataset Based on 20 Years of L2 MODIS SST Fields

The 2002-2021 MODerate-resolution Imaging Spectroradiometer (MODIS) Aqua L2 Sea Surface Temperature (SST) data product, originally generated by the National Aeronautics and Space Administration (NASA) Ocean Biology Processing Group (OBPG), has been restructured from 5-minute granules, the file size produced by the OBPG, to full orbits. Cloud screening issues in the vicinity of strong SST gradients were then corrected and the geometry of pixels modified to address the bow-tie effect. Each orbit starts at 78° S and is 40,271 scan lines long with 1,354 pixels per scan line and each orbit overlaps the preceeding orbit by 100 scan lines. The overall dataset consists of approximately 100,000 orbital files for the 20 year period considered.Regridding the SST fields to a slightly modified Level-2 (L2) structure to address the bow-tie effect and combining the 5-minute granules to full orbits allowed for the straight-forward determination of the SST gradient field as well as the location of fronts. The Sobel gradient operator was used for the former and the Cayula-Cornillon edge detection algorithm for the latter. The eastward and northward components of the SST gradients are included in the netCDF file of corrected SST fields described in the first paragraph while the output of the Cayula-Cornillon algorithm consists of a netCDF file for each orbit with the latitude and longitude of all frontal data points found by the algorithm along with a number of characteristics associated with each frontal point, such as, a 15 element vector of SST values along a line centered on and locally normal to the front, similar vectors of eastward and northward gradients (described above),... For each orbit, a binary 1354 × 40271 array of frontal locations is also included in the file containing the preprocessed SST field and the component fields of the gradient vector.