DOI: 10.5281/zenodo.3978794
title: GulfFlow: A gridded surface current product for the Gulf of Mexico from consolidated drifter measurements

description: 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—3761 trajectories spanning 27 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 data set runs from August 16, 1992 to August 1, 2019, for a total of 648 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 discussed in the next section. The count variable is a four-dimensional array of integers, the fourth dimension of which has length 30. 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 velocities from drifters from each of the 15 experiments that have not been flagged as having lost their drogues, while values 16–30 are for observation from drifters that have been flagged as having lost their drogue. Values above 15 are only populated for the GDP, HARGOS, LASER and some of the DWDE drifters, as a drogue presence flag is not always available. It is useful at this stage to introduce notation for different types of averages. For convenience we represent the velocity as a vector, <strong>u</strong> = [u v]<sup>T</sup> , where the superscript “T” denotes the transpose. Let an overbar, <strong>\(\overline {\bf u}\)</strong> , denote an average over a spatial bin and over all times, while angled brackets, &lt;<strong>u</strong>&gt;, denote an average over a spatial bin and a particular temporal bin. Thus, &lt;<strong>u</strong>&gt;, is a function of time while \(\overline {\bf u}\) is not. We refer to &lt;<strong>u</strong>&gt;, as the local average, \(\overline {\bf u}\) as the global average, and \(\overline {&lt;\bf u&gt;}\) 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 \(\overline {&lt;\bf u&gt;}\), the local covariance defined as \(\bf{ε}=&lt;(u − &lt;u&gt;)(𝐮−&lt; 𝐮 &gt;)^T&gt;\) 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.
description: The GulfFlow database is a product of the Gulf of Mexico Research Consortium (CIGoM) and was partially funded by the CONACYT-SENER-Hydrocarbons Sector Fund, Mexico, project 201441. See database webpage with additional information, as well as request for download form (https://giola.cicese.mx/database/GulfFlow).