Abstract
In this paper we analyse the material coherence of oceanic eddies
sampled by ships during 9 oceanographic campaigns, 8 of which were
conducted in the Atlantic Ocean (EUREC4A-OA, M124, MSM60, MSM74, M160,
HM2016611, KB2017606, KB2017618) and one in the Indian Ocean (Physindien
2011). After reviewing previous definitions of coherence, we perform a
relative error analysis of our data. To identify the eddy cores and
assess the material coherence of the well-sampled eddies (19 out of 28
eddies in total), we use criteria based on active tracers (potential
vorticity, temperature, salinity). The maximum tracer anomaly is often
below the pycnocline (below the frequency stratification maximum).
Therefore, some eddies are not considered to be materially coherent
using only surface data, whereas they are when we study their
three-dimensional structure. Two methods are then presented to
extrapolate eddy volumes from a single ship section. The horizontal and
vertical resolutions of the data are critical for this determination.
Our results show that the outermost closed contour of the Brunt-Vaisala
frequency is a good approximation for the materially coherent eddy core
to determine the eddy volume.