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The maritime traffic around the Loop current of the Gulf of Mexico is large enough to help retrieving the oceanic surface current. Using Automatic Identification System (AIS) data streams for the period 2019-2020, a distance-weighted least-squares approach [Le Goff et al 2021] is used to estimate ocean surface currents at a depth corresponding to the mean draught of the commercial vessels (about 7m). The calculated gridded data product has spatial resolution of 0.125⁰ × 0.125⁰ and daily temporal resolution. These estimations provide a valuable resource to investigate the ageostrophic processes that altimeter-based data are not sufficient to resolve. However, the limited coverage of the AIS Data (limited to the main maritime routes), prevents studies from reaching regional basins and thus limits potential applications of the collected data at larger scales where altimetry data is sufficient. As such, synergy between AIS-derived sea surface currents and altimetry data needs to be considered to increase the accuracy of sea surface currents in the Gulf of Mexico. The merging is done through the Multiscale Inversion for Ocean Surface Topography (MIOST) [Ubelmann et al., 2020] variational tool to retrieve both geostrophic and ageostrophic current. This tool allows the decomposition of the signal into different components representing different time and space scales (i.e., mesoscale to large-scale) and different physical signals (i.e., geostrophic, internal waves, near-inertial oscillations, Ekman current…). The resulting improved ocean surface current estimates will be compared to the intensity of surface currents estimated from the AOML drifters. Comparisons with high-resolution Sea Surface Temperature (SST) images from infrared instruments will be focused on the eddy separation events for the Gulf of Mexico loop current and on the associated eddy paths. Identification of warm rings with an eddy tracking algorithm (e.g., AMEDA [Le Vu et al 2018]) will allow the determination of the characteristics and life cycle of these eddies. [Le Goff et al 2021] : Le Goff, C., Boussidi, B., Mironov, A., Guichoux, Y., Zhen, Y., Tandeo, P., et al. (2021). Monitoring the greater Agulhas Current with AIS data information. Journal of Geophysical Research: Oceans, 126, e2021JC017228. https://doi.org/10.1029/2021JC017228 [Ubelmann et al 2021]: Ubelmann, C., Dibarboure, G., Gaultier, L., Ponte, A., Ardhuin, F., Ballarotta, M., & Faugère, Y. (2021). Reconstructing ocean surface current combining altimetry and future spaceborne Doppler data. Journal of Geophysical Research: Oceans, 126, e2020JC016560. https://doi.org/10.1029/2020JC016560 [Le Vu et al 2018]: Le Vu, B., Stegner, A., & Arsouze, T. (2018). Angular Momentum Eddy Detection and tracking Algorithm (AMEDA) and its application to coastal eddy formation. Journal of Atmospheric and Oceanic Technology, 35(4), 739-762.

The Mean Dynamic Topography (MDT) is a key reference surface for altimetry. It is needed for the calculation of the ocean absolute dynamic topography, and under the geostrophic approximation, the estimation of surface currents. The MDT is the missing component for the optimal assimilation of altimeter data into operational ocean system. However, in coastal areas, where in-situ measurements are sparse, mainly on the shelf, the global MDT solutions are often less accurate than in the open ocean. Considering the availability of long time-series of high-quality HF-Radar velocity measurements in the Mid Atlantic Bight, the main objective is to include these data to calculate an improved MDT is this area. The prerequisites for the computation of this new Mean Dynamic Topography are to remove the non-geostrophic signal from the HF radar measured velocities. The first step is thus to pre-process these data. We used average currents from December 2006 through November 2016, estimated from HF radars and processed by Rutgers University (https://tds.marine.rutgers.edu/thredds/cool/codar/cat_totals.html ; Roarty et al, 2021). Then the mean wind-driven currents modelized as in Mulet et al (2021), were removed. Besides, the first guess MDT computed from altimetry and gravimetry was improved by using a dedicated filter along the coast. Finally, the improved MDT was estimated from the first guess MDT and the processed in-situ data (HF-radars, drifters and T/S profiles) through a multivariate objective analysis. This new regional MDT defines better currents near the coast. In particular, the MDT shows more organized across-shelf gradient following the shelf-break, and a more continuous mean flow on the shelf. Mulet, Sandrine, Marie-Hélène Rio, Hélène Etienne, Camilia Artana, Mathilde Cancet, Gérald Dibarboure, Hui Feng, et al. « The New CNES-CLS18 Global Mean Dynamic Topography ». Ocean Science 17, nᵒ 3 (17 juin 2021): 789‑808. https://doi.org/10.5194/os-17-789-2021. Roarty, Hugh, Scott Glenn, Joseph Brodie, Laura Nazzaro, Michael Smith, Ethan Handel, Josh Kohut, et al. « Annual and Seasonal Surface Circulation Over the Mid-Atlantic Bight Continental Shelf Derived From a Decade of High Frequency Radar Observations ». Journal of Geophysical Research: Oceans 125, nᵒ 11 (2020): e2020JC016368. https://doi.org/10.1029/2020JC016368.

The Stokes drift is the main contribution from ocean surface waves to particles drift in the ocean's upper layer. At the moment, estimates of the Stokes drift at the global scale rely on numerical models, due to the unavailability of such measurements from space. CFOSAT is a new mission concept, carrying SWIM, a rotating scatterometer, operating both at nadir and off-nadir. It aims at measuring the ocean surface waves slopes spectrum, from which the Stokes drift can be estimated. Potential for Stokes drift estimation from SWIM is illustrated using statistical diagnostics on SWIM ocean waves spectra. Although the Stokes drift is carried in majority by waves which are not resolved by SWIM, it is shown that an algorithm based on the extrapolation of SWIM waves spectra could be thought of. Such potential combined with the characteristics of SWIM make the effort to design and qualify a Stokes drift product interesting. Such a product would be of particular interest in areas such as the Southern Ocean, where Stokes drift is significant and poorly known, and where the observational conditions are favorable to SWIM (resolved wind sea, favorable wave direction)