[MITgcm-support] Barotropic ocean gyre tutorial

Jeremy Miller jeremysharonmiller at gmail.com
Sun Apr 4 09:13:26 EDT 2021


Dear Oliver,
P.S. I am re-attaching the plot here, because it wasn't in a readable form
the last time.
Best
Jeremy

On Sun, 4 Apr 2021 at 16:00, Jeremy Miller <jeremysharonmiller at gmail.com>
wrote:

> Dear Oliver,
>
> Thanks for coming back to me. I did just that. I now get a plot for "eta"
> that appears to be two sets of constant values, on the left and right of
> the line x=0.6*1e6 m (see the attached plot in
> fig_bar_gyre_windx_siny.png). I also notice that the output bin file
> (tau_2_1) still shows different values to the original numpy array (tau_2).
> I have attached the latest version of the python script used to generate
> the data (gendata_tut4.1.py) and the script used to generate the plots (
> tut_4.1_plots.py).
>
> Best
> Jeremy
>
> On Sun, 4 Apr 2021 at 13:48, Oliver Jahn <jahn at mit.edu> wrote:
>
>> Hi Jeremy,
>>
>> this will not work:
>>
>> > if sys.byteorder == 'little': tau_2.byteswap(True)
>> > fid = open('windx_siny.bin', 'wb')
>> > tau_2.astype('float32').tofile(fid)
>>
>> Can you instead try Jeff's suggestion:
>>
>> tau_2.astype('>f4').tofile('windx_siny.bin')
>>
>> and NOT use the byteswap command?  Mixing byteswap and astype is a bad
>> idea as byteswap will create a mismatch between the data in memory and
>> numpy's assumption of the data type.
>>
>> Best,
>> Oliver
>>
>>
>> > as you suggested, the plot still came out blank.
>> > Regarding Jeffrey Scott's comment that the reason I could not read back
>> > the bin file was due to a mismatch between float32 and float64, I
>> > followed his advice and read in the
>> > bin file using the snippet
>> >
>> > tau_2_1 = np.fromfile('windx_siny.bin',dtype='float32')
>> >
>> > and I got back an array with every entry being 'inf' except the
>> > penultimate column, being all '0'.
>> >
>> > Is it possible that the snippet
>> >
>> > # X=X.astype('float128')
>> > # Y=Y.astype('float128')
>> >
>> > (which is commented) needs to be included but with 'float128' replaced
>> > with 'float32'?
>> >
>> > Best
>> > Jeremy
>> >
>> >
>> >
>> >
>> >
>> > On Thu, 1 Apr 2021 at 16:47, Jan Klaus Rieck <jan.rieck at mail.mcgill.ca
>> > <mailto:jan.rieck at mail.mcgill.ca>> wrote:
>> >
>> >     Hello Jeremy Miller,
>> >
>> >     I also use python to to generate input data for the MITgcm. I found
>> >     that, to generate files that can be read by the MITgcm consistently,
>> >     I needed to specify the type explicitly.
>> >     My way of saving the files would look like this in your case:
>> >
>> >     if sys.byteorder == 'little': tau_2.byteswap(True)
>> >     fid = open(''windx_siny.bin', 'wb')
>> >     tau_2.astype('float32').tofile(fid)
>> >
>> >     Of course, 'float32' could be replaced by 'float64' if you require
>> >     double precision.
>> >
>> >     I hope this helps,
>> >     Jan Rieck
>> >
>> >     On Thu, 2021-04-01 at 10:22 +0300, Jeremy Miller wrote:
>> >>     Dear MITGCM forum,
>> >>
>> >>     I am Jeremy Miller, I am new to MITgcm and I've been going through
>> >>     the tutorials. I have a question about the "Barotropic Ocean Gyre"
>> >>     tutorial (section 4.1).
>> >>
>> >>     I managed to compile and run the code, and re-produce the first
>> >>     two plots shown in section 4.1.5 for  wind stress of τ = τ0 cos(
>> >>     πy/Ly), for both the advection and non-advection cases (with the
>> >>     provided input binary files).
>> >>     I ran into problems when trying to produce the third plot, for the
>> >>     case where τ = τ0 sin( πy/Ly). I am a python user, so I translated
>> >>     gendata.m into python to write the input binary
>> >>     files 'windx_cosy.bin' 'windx_siny.bin' (see the file
>> >>     gendata_tut4.1py attached).  As explained in section 3.9 I've
>> >>     included the snippet
>> >>
>> >>     if sys.byteorder == 'little': tau_2.byteswap(True)
>> >>
>> >>     where "tau2" is the array to be output. There was no issue in the
>> >>     cosine wind stress, and I managed to reproduce the results that I
>> >>     got with the original 'windx_cosy.bin' provided in the tutorial.
>> >>     However, with the sine wind stress case, the output in
>> >>     'Eta.0000077760.001.001' is all zeros.
>> >>
>> >>     When I attempt to read  'windx_siny.bin' with python into a new
>> >>     array called tau2_1. I get absurdly big numbers back, which do not
>> >>     match the original array tau2 that I created. If I Remove the
>> >>     snippet " if sys.byteorder == 'little': tau_2.byteswap(True) ", in
>> >>     the python gendata code, tau2_1 and tau2 match. But, then when I
>> >>     run the code again, the file output.txt contains a long list of
>> NaNs.
>> >>
>> >>     I have also included the python code used to generate the plots in
>> >>     the file tut_4.1_plots.py <http://tut_4.1_plots.py/>
>> >>
>> >>     Look forward to hearing from you.
>> >>     Yours sincerely
>> >>     Jeremy Miller
>> >>     _______________________________________________
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>> >>
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>> >>
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