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04.26.11: Coherence between snapshots of SST, SSH and FSLE for the Gulf Stream region

To have an idea if my calculation of SSH and FSLE on a specific day is coherent with the SST from the MUR SST product, I choose a snapshot for the Gulf Stream (GS) region where the eddies and SST gradient are strong surface signals. Both the SSH and FSLE fields appear to be coherent with the SST field (Fig. 1 and 2). Nearly all SST filaments are associated with a FSLE filament (Fig. 3), with the exception of the nearly-linear SST filament near the coast in the southwest corner of the figure. This exception might be a real feature and an example where a quasi-linear geostrophic flow is not associated with a stretching velocity field. There are also minor SST filaments north of the GS that are not associated with FSLE filaments; no a priori reason for these. On the other hand, not all FSLE filaments are associated with SST filaments (not even the weak ones) as it is the case south of the GS. There, either it is because the SST field is nearly uniform albeit the velocity field being stirring or the estimate of the SST filaments via the SST gradient is dominated by noise. This might be a problem when applying this calculation northeast of Hawaii where SST gradients are much weaker than in the GS region (by about on order of magnitude).

../../../../../../_images/SST_SSH_Feb02_2010_GS.png

Figure 1: SST (colors; deg. C) and SSH (contours; cm) on Feb. 2, 2010. The SST is from the MUR SST product. SSH is from AVISO SSH anomaly of type UPD with MDOT for the mean SSH, interpolated in time for that day.

../../../../../../_images/SST_FSLE_Feb02_2010_GS.png

Figure 2: SST (colors; deg. C) and high FSLE (ci = 0.1:0.05:1.0 1/day) on Feb. 2, 2010. The SST is from the same product as in Fig. 1 and the FSLE have been computed using the same SSH product as in Fig. 1.

../../../../../../_images/SSTgrad_FSLE_Feb02_2010_GS.png

Figure 3: SST gradient (colors; 1e-4 deg. C/m) and high FSLE (ci = 0.1:0.05:1.0 1/day) on Feb. 2, 2010. The SST is from the same product as in Fig. 1 and the FSLE have been computed using the same SSH product as in Fig. 1. The SST gradient is computed after smoothing the SST field with a 0.2°running mean.


To plot Fig. 1:

from pycurrents.plot.maptools import llticks
cs = contour(ssh_lonmat,ssh_latmat,ssh*100,arange(-110,+50,20),colors='k');
clabel(cs, fmt='%1.0f')
contourf(lon, lat, sst, arange(-2,24,2))
axis([360-80, 360-40, 35, 45])
llticks(gca(), 'lon', 'lat')
title('SST on Feb. 2, 2010 (colors) and SSH (contours)')
colorbar()

The SSH and FSLE were computed using manifold_SSH_AVISO.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/SSH_AVISO on the central disk. The SST gradient is computed with gradSST_FSLE.py in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/MUR_SST/analysis again on the central disk.