Re: ESMF regrid problem

Hi Mary

I suspect that the file size issue is related to the time dimension rather than just the grid size, so I could try and use a time loop to break things up a bit.

I was reluctant to do this since the script needs to run on all 45 control runs from the CMIP5 models, so it's already a big, slow chunk of processing. Obviously it also needs to be a fairly 'general' regrid, with lots of exception handling, since there are so many different grids to deal with.

Will

From: Mary Haley <haley@ucar.edu<mailto:haley@ucar.edu>>
Date: Wednesday, 9 July 2014 8:01 AM
To: Will Hobbs <will.hobbs@utas.edu.au<mailto:will.hobbs@utas.edu.au>>
Cc: "ncl-talk@ucar.edu<mailto:ncl-talk@ucar.edu>" <ncl-talk@ucar.edu<mailto:ncl-talk@ucar.edu>>
Subject: Re: ESMF regrid problem

Hi Will,

I had to do a little digging to see where we are with this issue (I have filed a new ticket on this, NCL-1989).

In order to support large variables that are > 4 GB, you have to write them to NetCDF-4 file (the pure one, not the classic one). This means that ESMF_RegridWeightGen needs to be able to read these files.

It appears that the latest version of ESMF_RegridWeightGen (6.3.0r) does not support this yet, and I have question into the developers about this.

It does appear that you can *write* the weights file that ESMF_RegridWeightGen creates to a NetCDF-4 file, but this isn't going to help you much.

Are your lat/lon dimensions causing you to have a variable that is > 4 GB, or do you have other dimensions that are contributing to a large variable?

I recall having one user get around a similar problem by regridding subsets of the variable and stitching them together later. His situation was a little different because his variable was already naturally subsetted into individual files.

If your grid isn't too irregular, then a step-by-step method like this might work for you.

--Mary



On Tue, Jul 8, 2014 at 12:40 AM, Will Hobbs <Will.Hobbs@utas.edu.au<mailto:Will.Hobbs@utas.edu.au>> wrote:
Mary et al,

I am having problems running out of memory using the ESMF_regrid function. The problem is basically the same as reported last year by a user on March 19th, (Mary's reply is copied below), but I'm just checking to see if there was a resolution?

Many thanks

Will


From: Mary Haley <haley_at_nyahnyahspammersnyahnyah<mailto:haley_at_nyahnyahspammersnyahnyah?Subject=Re:%20ESMF%20regrid>>
Date: Tue Mar 19 2013 - 08:05:06 MDT

Hi Noel,

I see what the problem is, and I'm not sure yet how to fix it.

The issue is in order to do ESMF regridding, we need to write an intermediate NetCDF SCRIP file. This file will have two double variables of size grid_size, which is equal to nlat * nlon.

In your case:

   nlat/nlon = 16,800/43,200
   grid_size = nlat*lon = 725760000
   variable to be written to the file = 725760000*8 = 5,806,080,000 bytes

This is > 4 GB. This violates a NetCDF constraint that individual variables be less than 4 GB.

My first thought is that if you can create a NetCDF-4 file, then you won't be limited by this constraint. The problem is that the ESMF regridding tool we use appears to have a constraint that the intermediate NetCDF files be NetCDF-3 (classic or 64-bit offset) files, and not NetCDF-4.

I will check into this and get back to you.

--Mary

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Received on Tue Jul 08 11:18:29 2014