[MITgcm-support] 'repeatPeriod' in data.exf

Tue Jun 22 11:47:14 EDT 2010

Suneet, I added repeatPeriod more than 7 years ago, when we were still using daily-mean surface forcing fields.  If your forcing fields are daily means (or greater), just set repeatperiod to 365.25 (or 365.24219 for very long integrations) and you will be all set.

As far as I can tell from exf_getffieldrec.F, repeatPeriod was never updated to deal with leap years for sub-daily forcing period.  So if your forcing is sub-daily and leap years matter, do not use repeatPeriod (or modify exf_getffieldrec.F to add leap-year capability).  Your best bet is to go with Martin's suggestion.

There is another (undocumented) pkg/exf option for carrying out very long integrations.  If you want to use monthly-mean climatological forcing fields, you can set hfluxperiod, atempperiod, etc., to -12.

Dimitris

On Jun 22, 2010, at 7:13 AM, David Hebert wrote:

Suneet,

I have not run multi-year simulations, so I am not familiar with the handling of leap years with cal. With repeatPeriod = 366 days, when a year with 365 days carries over to the next year I'm wondering if  the 'repeat' of the boundary file will be lagged by a day. For example, in consecutive 365 day years, when crossing a year will  January 1 using Dec. 31st from the boundary file since there is an extra day in the repeatPeriod?. If so, this shift in time would manifest itself greatly over 50 years.  Is there a place one can specify how many days/hours/seconds in a model year? Again, I'm not sure but perhaps others have more experience in this area.

David

On 06/22/10 08:58, Suneet Dwivedi wrote:
Hi David,

Thanks for your reply. This is exactly what i had in mind for 'repeatPeriod'.

Though I am not very sure about your last question, I think a forcing file with 366 days will take care of both leap years (of 366 days) and normal years (of 365 days). But a file with lesser number of days (for example 365 days) will give an error for a leap year (no data on 31st Dec, in this case).

Thanks,
Suneet

On Tue, Jun 22, 2010 at 3:45 PM, David Hebert <david.hebert at nrlssc.navy.mil<mailto:david.hebert at nrlssc.navy.mil>> wrote:
Suneet,

I believe repeatPeriod is the period in which the model will go back to the beginning of the forcing file. So if you wish to use the same forcing for each year (one file with 366 days according to your last post), I don't see why you couldn't specify repeatPeriod=31622400.0 in data.exf. Also, you would need to specify the period between records in your file in data.exf, &EXF_NML_02. For your case if they are daily I would think it would be 86400.0. Example for wind stress would be...

 &EXF_NML_02
 ustressfile        = 'taux.bin',
 vstressfile        = 'tauy.bin',
#
 ustressstartdate1   = 20080628,
 ustressstartdate2   = 000000,
 ustressperiod       = 3600.0,
#
 vstressstartdate1   = 20080628,
 vstressstartdate2   = 000000,
 vstressperiod       = 3600.0,
 &

where ?stressperiod is the period between records. My case was one hour. Your case could be 86400.0 for one day.

A question that arises (for me anyway) is how to handle leap years, particularly with calendar package? Does assuming 366 days cover this?

David

On 06/22/10 08:22, Suneet Dwivedi wrote:
Hi Martin,

Thanks for your reply. Your suggestion is helpful. However, if i follow what you suggested for 60 years of simulation, for example, then for 8 air/sea forcing fields i will have to create 480 (60*8) yearly forcing files, which is possible, but cumbersome. An alternative that I could think of may be to run the model for somewhat shorter duration and restart from there...., for example, running the model for 15 years at a time and restart from there again for 15 years and so on.....Thus rather than splitting forcing fields into years, one may split time window.

I guess in this case, i should set repeatPeriod = 0 in data.exf, if i am using continuous in time daily forcing fields for 15 years. But I am not sure how to set namelist parameters in input/data while restarting from pickup files. What i could gather from looking at verification directory examples and mitgcm manual is that it is possible to restart the model from pickup files by setting nIter0 equal to number as suffix in pickup file, but i am not sure how to set data.cal in this case. Probably, I should not include data.cal in my input directory when I am restarting. Is this right? Any suggestions....

Thanks again,
Suneet

On Tue, Jun 22, 2010 at 8:19 AM, Martin Losch <Martin.Losch at awi.de<mailto:Martin.Losch at awi.de>> wrote:
Suneet,

you can split you forcing fields into years. They have to follow this naming convention:
forcingFile_year, where "year" is a 2 or 4-digit year (e.g. myatemp_1996, myatemp_1997, etc).

In data.exf set:
 useExfYearlyFields= .TRUE.,
 twoDigitYear      = .FALSE.,

and
atempfile = myatemp,
etc. If you want to use a Gregorian calendar the data.cal should look like this:
 &CAL_NML
 TheCalendar='gregorian',
# here you insert your start date, of course
 startDate_1=19920101,
 startDate_2=000000,
# this makes the model interpret output "freqs" (e.g. dumpFreq) close to 1 month (say 2592000.) as a "real" month, the same for a year.
 calendarDumps = .TRUE.,
 &

There are a few examples in the MITgcm_contrib area (arctic, high_res_cube)

Martin

On Jun 22, 2010, at 1:38 AM, Suneet Dwivedi wrote:

> Hi Everybody,
>
> Could anyone of you please tell me what is the exact meaning of parameter 'repeatPeriod' in exf package/data.exf?
>
> I wish to perform a long run of 50-55 years with daily air/sea forcing values over Indian Ocean. Matlab is unable to store and process such a long matrix of dimension [250 150 20000] ~ O(1e+10) with 64 bit precision. An alternative way to do this may be to use climatological daily forcing values (averaged over all available years) of dimension [250 150 366] and use the climatological values for each year of simulation. In this case, i need to know the variable that does this in MITgcm. I wonder 'repeatPeriod' does this. Am I right? For example, if i set 'repeatPeriod' to something like 31622400.0 (for 1 year), will I be able to use same values of forcing on same days of each year after completing one year of simulation? Please suggest.
>
> Thanks,
> Suneet
>
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