Main conclusion
As in the snapshot of the 1/30th OFES simulation, submesoscale features, defined as large Rossby number, appear around and east of station ALOHA but they are confined to the surface mixed layer (0-100 m) above the nutricline (150-200 m). These submesoscale features appear near station ALOHA in February and March when the mixed layer is the deepest.
The next step would be to check if the statistics of the model along the track of HOT cruises are consistent with the observations or not.
Results
In Fig. 1 is shown the animation of the Rossby number R = ζ / f at the surface, where ζ is the vertical component of the relative vorticity and f is the Coriolis parameter, during one year in the HYCOM simulation. We see that submesoscale structure with Rossby number of the order 1 appears after about mid-December until March. It would be nice to know if these structures appear because of the weakened stratification of the surface mixed layer.
You can see an updated animation in the following link:
animation of R at the surface between Oct. 2009 and Mar. 2011
Fig. 2 shows the snapshot for Jan. 15, 2010, and Figs. 3 to 5 show the zonal sections at three different latitudes. In all cases, the submesoscale structures are confined to the upper 100 m, well above the nutricline, confirming the result from the 1/30th OFES simulation.
Fig. 6 shows the maximum of absolute value of R in latitude along the HOT track during 2009/2010 in the HYCOM simulation and Fig. 7 the corresponding stratification averaged along the track. We see that statistically, there is more chance to find submesoscale features in February and March when the surface mixed layer is the deepest.
See rel_vort_HOT_track.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/HYCOM/analysis/rel_vort_HOT_track on ipu1.
