vertical velocity GoM

[Rodrigo Duran]

Hi,

I was planning on using the GoM reanalysis 50.1, however the vertical velocity is not available. Can the vertical velocity for this reanalysis be recovered?

 I was thinking about using 20.1, 30.1, 31, 32.5 and 90.1m000 in lieu of the reanalysis. However, the "Legacy" (20.1 and 30.1) experiments suggest using GoM Analysis or Reanalysis instead. Is there a problem with these experiments?

For the Gulf of Mexico and with a 1/25 deg resolution, I need the three velocity components plus ssh, temperature and salinity, for a period of time as long as possible. 

Thanks!

Rodrigo. 

[Alan Wallcraft]

The native HYCOM archives for 50.1 are at http://data.hycom.org/datasets/GOMl0.04/expt_50.1/data/ or via anonymous ftp to ftp.hycom.org.

Then use archv2ncdf3z to extract whatever fields you want on your own fixed vertical grid.  Note that the blkdat option 'intfwv' has recently been added and you should set this to 1 (true) for the best vertical velocity calculation.  The vertical velocity is a very noisy field, so I don't know if it will be useful for your application.

Alan.

[Rodrigo Duran]

Thanks very much, Alan, sounds like a good option. 

I am trying to understand the usefulness of vertical velocity, I hope you can help me assess my thoughts.  Would you agree with these statements? Any other suggestions or comments?

1) The vertical velocity is fundamental to ocean dynamics and the numerical technique, therefore even if the instantaneous fields are difficult to interpret, there must be a physics-based signal that is useful behind the noise. 

2) Perhaps daily averaging is enough to extract the signal from the noise.

Thanks again.

Rodrigo.

[Alan Wallcraft]

HYCOM solves the layer continuity equation (i.e. it is Lagrangian in the vertical) and then regrids in the vertical if necessary (Arbitrary Lagrangian Eulerian), so it never explicitly invokes w.  Alistair Adcroft summarizes this for HYCOM and MOM6 in https://adcroft.github.io/assets/pdf/ALE_workshop_NCWCP_2016.pdf.

Since you want an Eulerian solution, w is needed and it is calculated as a diagnostic field by the "3z" program.  Taking a daily average may be sufficient for what you want.

Alan.