RTOFS SSH data/inverse barometric effect

[Parisa Heidary - NOAA Affiliate]

Hello,

I'm new to this field and interested in using RTOFS SSH data. Before proceeding, I need to understand how these data account for the inverse barometric effect, and if RTOFS has air pressure forcing. Could you please provide more details on this? I found some explanation here, but I'm also looking for any specific documents or references that could help me delve deeper into this topic.

Thank you!

[Alan Wallcraft]

HYCOM often reads in atmospheric pressure as a forcing field, but this is usually only applied to the bulk parameterization for wind stress and heat flux.  If  blkdat variable 'mslprf' is set to 1 then atmospheric pressure is used directly to force the model.  This gives what is in effect an inverse barometer, but is more accurate because it is a model forcing term rather than a simple scale factor of pressure.

If RTOFS is like GOFS 3.1, it has 'mslprf' = 0. i.e. no direct pressure forcing and no inverse barometer.

Typically,  'mslprf'=1 is only used in cases with tides because atmospheric pressure contributes to the S2 "tidal" signal, although this effect is from solar heating of the atmosphere rather than gravity.

Alan.

[Dmitry Dukhovskoy - NOAA Federal]

RTOFS does not have inverse barometer effect, from the blkdat input file used for operational RTOFS forecasts:

   0      'mslprf' = msl pressure forcing flag            (0=F,1=T)

[Parisa Heidary - NOAA Affiliate]

Thank you so much for your detailed explanation. I have two more questions:

1. Can you please share any documents that explain this in detail? I couldn't find any comprehensive documents by searching online.

2. I am planning to download RTOFS SSH using this link: NOAA NWS RTOFS. I downloaded a netCDF file, but it doesn't contain SSH. Should I be looking at rtofs_glo.t00z.f01.archs.a.tgz or rtofs_glo.t00z.f01.archs.b instead?

Best,
Parisa

[Alan Wallcraft]

See page 16 of the following for a brief description of Atmospheric pressure forcing in HYCOM.

2018: B.K. Arbic, M.H. Alford, J.K. Ansong, M.C. Buijsman, E.J. Metzger, H.E. Ngodock, J.G. Richman, J.F. Shriver, I. Souopgui, A.J. Wallcraft, L. Zamudio, et. al.

A Primer on Global Internal Tide and Internal Gravity Wave Continuum Modeling in HYCOM and MITgcm

Alan.

[Parisa Heidary - NOAA Affiliate]

Thank you so much Alan.

Dmitry-- I first downloaded rtofs_glo_3dz_n024_6hrly_hvr_US_west.nc, but then tried to get archive files. Now I am downloading rtofs_glo_2ds_f***_diag.nc. But the github link that you shared with me is really helpful. I will need to read those archive files as well. Thanks so much.

Thank you!

On Mon, Jul 8, 2024 at 3:55 PM Dmitry Dukhovskoy - NOAA Federal <dmitry.d...@noaa.gov> wrote:

Parisa, 

what file(s) did you download? I'm checking 

rtofs_glo.t00z.f06.archv.[ab]

in the *.b (a text file) you can see:

srfhgt   =   64731240  44952.250  0  0.000  -1.8124247E+01   1.3719835E+01

To get ssh in m , you will need to do: srfhgt/9.806 

If you use python, see example:

https://github.com/DmitryDukhovskoy/RTOFS_utilities/blob/master-hera/validation_rtofs/plot_sshGS_rtofs.py

lines 91-93

and functions to read HYCOM binary:

https://github.com/DmitryDukhovskoy/RTOFS_utilities/blob/master-hera/MyPython/hycom_utils/mod_read_hycom.py

You will need the one that starts on line 255

Dmitry

[Dmitry Dukhovskoy - NOAA Federal]

Parisa, 

what file(s) did you download? I'm checking 

rtofs_glo.t00z.f06.archv.[ab]

in the *.b (a text file) you can see:

srfhgt   =   64731240  44952.250  0  0.000  -1.8124247E+01   1.3719835E+01

To get ssh in m , you will need to do: srfhgt/9.806 

If you use python, see example:

https://github.com/DmitryDukhovskoy/RTOFS_utilities/blob/master-hera/validation_rtofs/plot_sshGS_rtofs.py

lines 91-93

and functions to read HYCOM binary:

https://github.com/DmitryDukhovskoy/RTOFS_utilities/blob/master-hera/MyPython/hycom_utils/mod_read_hycom.py

You will need the one that starts on line 255

Dmitry