Postdoctoral researcher studying surface gravity waves.
Gwendal Marechal is a postdoctoral researcher at the Colorado School of Mines studying surface gravity waves in the S-MODE campaign.
SWOT-AdAC: What is your field of research and how did you choose it?
Gwendal Marechal: I am a physical oceanographer focusing on surface gravity waves. I try to understand what are the roles of these waves at the air-sea transition zone, and how they mediate the heat, momentum, and mass exchanges between the upper ocean and the lower atmosphere. For this aim, I mostly use remote-sensing data (airplane and satellites) and wave numerical models. I chose this field of research certainly because I grew up close to the sea, in Brittany, France, and I’ve always been passionate about field work at sea, whether it was during fishing off-shore during my childhood or instrument deployment on platforms/vessel during my Master. My choice was oriented to physical oceanography because these were the courses where my grades were not the worst during high school. The choice of surface gravity waves field of study was certainly motivated because of the surf that I started when I was 12.
SWOT-AdAC: How is your field of research related to SWOT?
GM: During my PhD I focused on the effects of surface currents on the wave height and I realized that the operational current products that were available at the time were not sufficiently resolved, especially in space, leading to the fact that a lot of the current-induced spatial variability of the wave height were not captured in numerical model. Thanks to the new geostrophic currents derived from the Sea-Surface-Height (SSH) measured by SWOT, we hope that we will be able to capture current effects on the wave at shorter scales. It will be the opportunity to model how surface currents modify the spatial variability of the wave-induce-air-sea fluxes (wave breaking, gas emission, …)
Also, waves represent a source of noise in the SSH measurements (sea-stats bias, layover effects). One of the goals of the next IOP S-MODE campaign is the SWOT CalVal. In addition to current and water property measurements (lagrangian floats, CTD, GPS-buoy, …), waves and current will be measured at the same time with two airplanes. It will be the opportunity to estimate the effects of the waves on the bias in the SWOT SSH.
SWOT-AdAC: What do you find exciting about SWOT and the SWOT-AdAC campaign you will be participating? How will you contribute to the campaign?
GM: I’m really looking forward to using SWOT data for my research. As said before, I want to have a better idea about the effects of currents on the wave height. However, today we do not have access to high-resolution surface current measurements, so characterization of the current-induced wave property spatial gradients is very limited.
Numerical models suggested that the statistics of the wave field is proportional to the surface Kinetic Energy. One consequence of this relationship is that it would be possible to infer current properties from waves measurements. SWOT measurements will provide a ground truth to confirm, or not, this inversion. Something crucial to know, we have a very poor knowledge of surface currents, whereas this variable is crucial for a wide range of application (climate, marine debris, food chain, …)
During the S-MODE campaign I will work on wave measurements provided by lidar. On the boat, I will be in the night shift in charge of CTD casts. This part of the experiment will focus on the three-dimensional characterization of submesoscale fronts (oceanic feature with a horizontal scale smaller than few kilometers). This is also a topic that I care about as a wave-guy; actually, high resolved oceanic simulations suggest that wave-induced circulations modify the submesoscale dynamics down to the first meters of the ocean.
SWOT-AdAC: What are your plans after the SWOT-AdAC campaign
GM: I plan, first, to get closer to the sea. Although Colorado mountains are amazing, I miss too much the sea. I plan to start a new project about wave effects on the upper ocean from the data acquired during the S-MODE campaign (Pilot, IOP-1, IOP-2). During the previous campaign we were able to see strong inhomogeneities in the wave field at scale associated to submesoscale fronts as whitecap fronts. At these locations we expect a strong three-dimensional dynamic with a large effect of waves-induced circulation on the underlying flow. This study will be the opportunity to see where goes the energy from the wind, how it drives ocean currents, it grows surface waves, and forces vertical mixing.