DisEntangling Quasi-geostrophic motions and INternal waves in high resolution satellite observations of the Ocean – EQUINOX
Caracterize and distinguish slow and fast oceanic variability for wide-swath altimetry
Upcoming wide-swath altimetric missions (CNES/NASA SWOT, launch date 2021) is an exceptional opportunity for the observation of the ocean. The project adresses a challenge that appeared with this novel instrument and related to the superimposition of oceanic slow (week or longer) and fast (day or faster) variabilities. This project aims at developing methods in order to distinguish slow and fast motions and map their geographical distributions.
A new altimeter for the ocean: challenge and opportunity
The incoming years will see an unprecedented wealth in altimetric data (up to 6 satellite flying at one time) and the emergence of a new instrument (SWOT) that will revolutionize our ability to map ocean sea level and currents at fine scales (<100km). The SWOT technological breakthrough is however jeopardized by a novel issue, identified as prioritary by the mission science team, which results from the superimpositions of two different signals: slow Mesoscale eddies and SubMesoscale front and filaments (M/SM) on one hand and fast Internal Gravity Waves (IGW) on the other hand. The limited temporal resolution of SWOT and altimeters in general prevents a separation based on temporal filtering of M/SM and IGW signals which are thus effectively entangled in the sea level measured. <br /><br />EQUINOx aims at improving our ability to distinguish M/SM and IGS in SWOT data and altimetric data in general. The project aims in particular at innovating developing methods that combine data (altimetry, surface temperature and currents) as well as statistical and dynamical hypotheses about M/SM and IGW processes. EQUINOx's objectives are to elevate such approach to a state where they could be used in an operational manner with satellite and in situ data. One goal is to obtain a regional description of our ability to distinguish these signals.
Idealized and realistic numerical simulations.
Evaluation of realistic numerical simulations thanks to original comparisons with in situ observations
The project is improving our understanding of high frequency motions in the ocean: how do these motions sign in observations? what dynamics govern their evolution? what is their geographical distribution? how are they represented in numerical model prediction?
Mapping of the oceanic surface expression of slow and fast variability
Methodological development allowing to distinguish both types of processes.
Improved operational predictions of the oceanic circulation
The project lead to the publications of the following articles:
- Y. Morel, J. Gula, and A. Ponte. «Potential Vorticity diagnostics based on balances between volume integral and boundary conditions.« Ocean Modelling, 2019. doi: 10.1016/j.ocemod.2019.04.004
- R. Morrow, L. Fu, F. Ardhuin, M. Benkiran, B. Chapron, E. Cosme, F. D'Ovidio, J. Thomas Farrar, S. T. Gille, G. Lapeyre, P.-Y. Le Traon, A. Pascual, A. Ponte, B. Qiu, N. Rascle, C. Ubelmann, J. Wang, E. Zaron, Global observations of fine-scale ocean surface topography with the Surface Water and Ocean Topography (SWOT) Mission. Front. Mar. Sci., 2019. doi: 10.3389/fmars.2019.00232
- X. Yu, A. L. Ponte, S. Elipot, D. Menemenlis, E. D. Zaron, R. Abernathey, Surface kinetic energy distributions in the global oceans from a high-resolution numerical model and surface drifter observations. submitted to Geophysical Research Letters
- C. Haro-Gonzalez, A. Ponte and E. Autret. Quantifying Tidal Fluctuations in Remote Sensing Infrared SST Observations. Submitted to Remote Sensing.
No patent was obtained.
The incoming years will see an unprecedented wealth in altimetric data (up to 6 satellite flying at one time) and the emergence of a new instrument (SWOT) that will revolutionize our ability to map ocean sea level and currents at fine scales (<100km). The SWOT technological breakthrough is however jeopardized by a novel issue, identified as prioritary by the mission science team, which results from the superimpositions of two different signals: slow Mesoscale eddies and SubMesoscale front and filaments (M/SM) on one hand and fast Internal Gravity Waves (IGW) on the other hand. The limited temporal resolution of SWOT and altimeters in general prevents a separation based on temporal filtering of M/SM and IGW signals which are thus effectively entangled in the sea level measured.
EQUINOx aims at improving our ability to disentangle M/SM-IGW signals in future SWOT data and in altimetric data in general. The project builds up on an innovative method developed recently by the PI. It combines sea level and surface temperature data and assumptions about M/SM and IGW statistical signatures on observable variables and on a fundamentally dynamical variable called potential vorticity that condensate the M/SM field. The objectives of EQUINOx are to raise this type of approach to a state where they could be used operationally with satellite and in situ observations. One objective is also to regionally describe our ability to disentangle IGW and M/SM.
EQUINOx is organized around a progressive work plan that will first consist in testing the method in configurations with gradual realism and improving it thanks to a reformulation in a framework that will combine and objectively weigh statistical and dynamical constraints. Models predicting the evolution of IGW and M/SM will also be leveraged in order to design a unique assimilation system performing the disentanglement of IGW and M/SM signatures. The analysis of state of the art high resolution realistic numerical simulations will improve our knowledge about the distributions of IGW-M/SM relative signatures on surface variables and about the accuracy of IGW-M/SM dynamical models. Observing System Simulation Experiment (OSSE) will be performed in order to test the methods developed and prepare their application to real data. Finally, satellite observations of sea level and sea surface temperature will be analyzed and the methods of disentanglement developed within the project will be tested in areas where tidal IGW are stationary and predictable.
EQUINOx will have a significant impact on our understanding of M/SM and IGW dynamics and of their manifestations on satellite and in situ observations, and, on their geographical distributions. The project will improve our ability to distinguish these processes in observations and estimate the ocean circulation at scales where most of the ocean kinetic energy lies. These results will benefit to the validation of innovative high resolution numerical modeling studies as well as to biochemical and ecological studies. If funded, the timing of EQUINOx would be ideal with respect to SWOT launch date (2021). EQUINOx fits well within challenge 1 - axis 1 of the ANR 2017 Work Programme and SNR challenge 1 - orientation 1. EQUINOx aims at strengthening the team and the research of A. Ponte who is bringing a novel expertise on IGW and on IGW-M/SM interactions to the laboratory (LOPS) where he was recently been hired. The project will facilitate dissemination of his team's work. A public conference will be performed in order to broadcast this research to a public audience.
Monsieur Aurélien Ponte (Laboratoire d'Océanographie Physique et Spatiale (LOPS))
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IFREMER-LOPS Laboratoire d'Océanographie Physique et Spatiale (LOPS)
Help of the ANR 171,828 euros
Beginning and duration of the scientific project: December 2017 - 36 Months