Observing fine-scale ocean structures in the NW Mediterranean Sea from altimetry, gliders and HF radar

Rosemary Morrow (CTOH / LEGOS, France)


Alice Carret (CTOH / LEGOS, France); Florence Birol (CTOH / LEGOS, France); Fernando Niño (CTOH / LEGOS, France)

Event: 2015 Ocean Surface Topography Science Team Meeting

Session: Science II: Mesoscale and sub-mesoscale ocean processes: current understanding and preparation for SWOT

Presentation type: Type Poster

The NW Mediterranean Sea has distinct ocean dynamics, with relatively strong boundary currents and moderate eddy energy, but with variations at small Rossby radius which are difficult to detect with conventional satellite altimetry. In this study, we analyse alongtrack altimetry from 3 different missions and measurement systems : Jason-2 Ku-band data, SARAL Ka-band data, and Cryosat-2 SAR data. We apply spectra analysis over short, 300-500 km sections in the NW Mediterranean Sea and estimate the mesoscale capabilities of the ocean dynamics here. The « white noise » background error levels differ between the 3 missions and for different seasons. This limits our ability to detect alongtrack mesoscale structures, and we quantify the typical length scales we can detect with each mission, depending on their seasonal signal to noise levels.

In the second part of the study, we also look at the observational capabilities of gliders and HFradar to study the geostrophic variability in the NW Mediterranean Sea. The high-frequency noise of the gliders limits us to observing signals greater than the Rossby radius (10-15 km). Only a few colocated glider and alongtrack altimetry data are available and these provide good results for the larger mesoscale structures. Validation of smaller-scale ocean variations is more difficult : with weaker amplitudes they are close to the noise levels for both observation types, and their rapid evolution means only a few days of short glider tracks are usefully colocated. The final data set we use is HFradar, which provides good synoptic 2D data coverage which can be easily colocated with the altimeter passes. In calm weather, the geostrophic currents associated with boundary currents and eddies are well detected and we can estimate their spatial and temporal characteristics. However, in periods of strong wind forcing (Mistral, Tremontagne), the surface currents become ageostrophic and fail to monitor the depth-integrated geostrophic flow.


Poster show times:

RoomStart DateEnd Date
Grand Ballroom Foyer Thu, Oct 22 2015,11:00 Thu, Oct 22 2015,18:00
Rosemary Morrow