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12.24.10: List of questions and things to do

Questions

  • What is the fundamental difference between mixed layer instabilities and frontogenesis?
  • Why do we use the term frontogenesis when what happens exactly is instabilities that damp that front and re-establish thermal wind balance? Yes, “frontogenesis” is a kind of misnomer; the genesis of the front is due to the background straining flow but the agesotrophic circulation that arises is a response to that front. Maybe I should use the term “frontal processes”, which is more vague but more accurate in the same time. Thanks to Cedric Chavanne for clarifying this issue.
  • Can we and should we use Glider data reported by Nicholson et al.? Other Glider data?
  • In this note, Figs.3 and 4 show the horizontal structure of the potential density and salinity field in the 1/30th deg. OFES simulation. Why does the density field seem to have less energy at the submesoscale than the salinity field? Can we still have the nitrate field having more energy at the submesoscale than the density field? Partial answer: Klein et al. (1998) explain that if the motion follows isopycnal layer but not the contour of salinity (and temperature), then the motion is effective in stirring the latter but not the former. Thus, we can say that in the mixed layer, the motion is perpendicular to all contours (density and salinity) so that it is effective in stirring both quantities but below the mixed layer, the motion is more parallel to the density contours than to the salinity contours (because there is still a strong horizontal gradient of density at these depths) and so is effective in stirring more the latter than the former.

To do

  • Spring events in the 1/10th due to southward advection of mesoscal eddies as in HYCOM?
  • Look at SST in HYCOM and OFES? Do we see these southward advection? If yes, use GHRSST product (available from the APDRC)?
  • Samping the 1/10th OFES (and HYCOM?) as in WHOTS and ARGO data. Compare probability distributions –there are ways to do that. (Do we expect the distribution due to submesoscale stirring to be different though? No, but we are trying to exclude the hypothesis of submesoscale, we are instead trying to exclude the mesoscale hypothesis)
  • Where do we find large vertical velocities in the mixed layer in the HYCOM model? In one quarter of eddies? Do we have generation of submesoscale features other than by horizontal eddy stirring (as in the 1/10th deg. OFES simulation)? What is the effect on the density field?
  • Sensitivity of FSLE to SSH product: FSLE diagnostic useful or not?
  • Okubo-Weiss parameter: Useful or not?
  • Spectrum in the horizontal direction of density, temperature, salinity and nitrate in the 1/10th OFES simulation and varying with depth: How do the slopes vary with depth? How is the slope for nitrate compared to that of density, temperature and salinity? Can scatter plots be enough to estimate how parallel the nitrate and density contours are?
  • In the 1/10th OFES simulation, do we see an anti-correlation between density anomalies and nitrate anomalies –as nitrate anomalies are supposed
  • Look at the nutrient anomaly along an isopycnal in the 1/10th OFES simulation. Does it have a submesoscale structure? Seperate the contribution from the advection by the geostrophic flow (component of the horizontal velocity parallel to depth contours) and the contribution from the advection by the ageostrophic flow (component of the horizontal velocity perpendicular to depth contours, with the assumption that the ageostrophic flow is along isopycnals). Are the structure of each different –so that we can isolate them in the observations? For instance, can we relate the contribution from the ageostrophic flow to proxies for strain (Okubo-Weiss parameter and FSLE)? Is the advection by the ageostrophic flow always in the direction to bring the depth of the density contours back to its resting value?
  • Or, more simple, follow Klein et al. (1998) and compare density at one level and gradient of nitrate. Does the structure of the gradient appears as filaments? Can we relate those to Okubo-Weiss (original or the modified version by Hua and colleagues) and/or FSLE?