Mixed layer thickness - GOFS 3.1 reanalysis

[Paula Marangoni]

Hi!

I'm using GOFS 3.1 reanalysis data and I need the mixed layer thickness for my study. 

Is this variable avaiable as a reanalysis product or just for analysis?

If it is not avaiable for download, how can I calculate mixed layer thickness?

Thank you.

Paula

[Alan Wallcraft]

We don't have mixed layer for the reanalysis.

The simplest way to calculate a MLD is the shallowest depth at which SST-T is 0.3 degC.  The MLD available for the Analysis uses a criteria similar to this except it also tries to allow for salinity.  You can try a different temperature jump than 0.3 degC if you like, I have seen values between 0.1 and 0.8 degC used.

Alan.

[Paula Marangoni]

Hi, Alan.

That's T (temperature) is the potential temperature, isn't it? I just want to be sure, because I have the in situ temperature. 

And sea surface temperature I have to use is from the first layer (vertical level equal to zero), right?

Thank you very much.

Paula

[Alan Wallcraft]

I don't think potential vs in-situ matters very much near the surface, but yes we would normally use potential temperature.

SST is from the 1st layer, which you will have as 0 m, but it is actually the average over the top 1 m of the water column.

Alan.

[Paula Marangoni]

Hi, Allan. Thank you for your answer. It helped me a lot!

However, as you said that my first layer is the average over the top 1 m, now I have another question. 

In my research, I am calculating the volume transport of a water column in a specific latitude section. To do this, I need to calculate the cell thickness to obtain the area. So, I am calculating the distances between longitudes, and I also need cell thickness (differences between the depth cells). My question is about the cell thickness.

 

In the data I have the following coordinates:

array([0.00e+00, 2.00e+00, 4.00e+00, 6.00e+00, 8.00e+00, 1.00e+01,
       1.20e+01, 1.50e+01, 2.00e+01, 2.50e+01, 3.00e+01, 3.50e+01,
       4.00e+01, 4.50e+01, 5.00e+01, 6.00e+01, 7.00e+01, 8.00e+01,
       9.00e+01, 1.00e+02, 1.25e+02, 1.50e+02, 2.00e+02, 2.50e+02,
       3.00e+02, 3.50e+02, 4.00e+02, 5.00e+02, 6.00e+02, 7.00e+02,
       8.00e+02, 9.00e+02, 1.00e+03, 1.25e+03, 1.50e+03, 2.00e+03,
       2.50e+03, 3.00e+03, 4.00e+03, 5.00e+03])

How can I get the right cell thickness, if these depth coordinates are averages? At first, I was calculating the difference (shown below), believing it to be the thickness.

array([   2.,    2.,    2.,    2.,    2.,    2.,    3.,    5.,    5.,
          5.,    5.,    5.,    5.,    5.,   10.,   10.,   10.,   10.,
         10.,   25.,   25.,   50.,   50.,   50.,   50.,   50.,  100.,
        100.,  100.,  100.,  100.,  100.,  250.,  250.,  500.,  500.,
        500., 1000., 1000.])

Could you help me with this problem?

Thank you in advance.

[Alan Wallcraft]

The original HYCOM model has layers (cells) in the vertical, but these vary in thickness over time.  What we supply is a consistent profile through those layers sampled at the depths specified, with 0m being a special case that is always the original layer 1 which is 1 m thick everywhere.  The best you can do for cells is probably to put the cell interfaces half way between the samples points, this will give you 1 m for the top layer which is what you want.  Values below the bottom will be data void, and the cell interface below the last ocean point is the bottom from depth_GLBv0.08_11.nc.  Note that because we are supplying sampled values the top to bottom sum of the transports may not be exactly correct, but it should not be far off if you allow for the bottom.

Alan.

[mh...@oceani.com]

Will there be GLBy0.08  20240418 _ssh and _ts3z (/datasets/GLBy0.08/expt_93.0/data/hindcasts/2024) posted today?

 

Thanks,

 

Mark

 

[Michael McDonald]

Mark,
Yes. The April 18th data is available now.

https://tds.hycom.org/thredds/catalog/GLBy0.08/expt_93.0/FMRC/runs/catalog.html

--
Michael McDonald
HYCOM.org Administrator

[mh...@oceani.com]

Will there be GLBy0.08  20240612 _ssh and _ts3z (/datasets/GLBy0.08/expt_93.0/data/hindcasts/2024) posted today? These products are not affected by the decommissioning of the GOFS 3.1 analyses, correct?

 

Thanks,

 

Mark

[mh...@oceani.com]

My apologies. It looks like my previous email to the forum preserved an unrelated thread.  Here are the questions submitted via that email:

 

Will there be GLBy0.08  20240612 _ssh and _ts3z files (/datasets/GLBy0.08/expt_93.0/data/hindcasts/2024) posted today?

 

Is the availability of these products directly affected by the decommissioning of the GOFS 3.1 analyses?

 

Thanks again,

 

Mark

 

[mark]

My apologies again.  My previous two messages were getting buried in an older thread for some reason. 

Just curious on the status of the GLBy0.08  _ssh and _ts3z products (/datasets/GLBy0.08/expt_93.0/data/hindcasts/2024). 

Is the availability of these products affected by the decommissioning of the GOFS 3.1 analyses?

 Thanks yet again,

 Mark

 

[Alan Wallcraft]

GLBy0.08/expt_93.0 is GOFS 3.1 and so it will stop when GOFS 3.1 stops.

The computer running GOFS 3.1 is closed to most users, but is still running GOFS 3.1 and is expected to do so until ESPCv2 becomes operational.

Alan.