GulfFlow: A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements

This dataset is comprised of mean and variance of the surface velocity field of the Gulf of Mexico, obtained from a large set of historical surface drifter data from the Gulf of Mexico—3770 trajectories spanning 28 years and more than a dozen data sources— which were uniformly processed and quality controlled, and assimilated into a spatially and temporally gridded dataset. A gridded product, called GulfFlow, is created by averaging all available data from the GulfDrifters dataset within quarter-degree spatial bins, and within overlapping monthlong temporal bins having a semimonthly spacing. The dataset spans monthly time bins centered on July 16, 1992 through July 1, 2020, for a total of 672 overlapping time slices. Odd- numbered slices correspond to calendar months, while even-numbered slices run from halfway through one month to halfway through the following month. A higher spatial resolution version, GulfFlow-1/12 degree  is created in the identical way but using 1/12 degree bins instead of quarter-degree bins. In addition to the average velocities within each 3D bin, the count of sources contributing to each bin is also distributed, as is the subgridscale velocity variance. The count variable is a four-dimensional array of integers, the fourth dimension of which has length 45. This variable gives the number of hourly observations from each source dataset contributing to each three-dimensional bin. Values 1–15 are the count of velocity observations from drifters from each of the 15 experiments that are flagged as having retained their drogues, values 16–30 are for observation from drifters that are flagged as having lost their drogues, and values 31–45 are for observations from drifters of an unknown drogue status. In defining averaged quantities, we represent the velocity as a vector, u = [u v]^T , where the superscript “T” denotes the transpose. Let an overbar, \(\overline {\bf u}\) , denote an average over a spatial bin and over all times, while angled brackets, <u>, denote an average over a spatial bin and a particular temporal bin. Thus, <u>, is a function of time while \(\overline {\bf u}\) is not. We refer to <u>, as the local average, \(\overline {\bf u}\) as the global average, and \(\overline {<\bf u>}\) as the double average. Given the inhomogeneity of the drifter data, turns out the global average is biased towards intensive but short duration programs, hence the double average results in a much better representation of the true mean velocity field. The dataset includes the global average \(\overline {<\bf u>}\), the local covariance defined as

\(\bf{ε}=<(u − <u>)(𝐮−< 𝐮 >)^T>\)

and \(\epsilon^2\)which is the trace of \(\overline{\bf ε}\)

\(\epsilon^2\)=\(tr\{\overline{\bf ε}\}\)

The data is distributed in two separate netcdCDF files, one for each grid resolution. 

Here the article describing this dataset.

Lilly, J. M. and P. Pérez-Brunius (2021).  A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements. Earth System Science Data, 13: 645–669.  https://doi.org/10.5194/essd-13-645-2021.