Re: mass-conservative regridding

Got it! Thank you very much, Will!

Best,
Wenshan
------------------------------------------------------------------------------
Graduate Student Researcher
Earth System Science
University of California, Irvine

On Mon, Feb 17, 2014 at 1:39 PM, Will Hobbs <Will.Hobbs@utas.edu.au> wrote:

> Wenshan
>
> As a general rule (whether using NCL or some other language or tool), if
> you a looking at a variable where mass conservation is important you should
> NOT regrid; no regridding technique (at least none that I know of) will
> conserve mass. This is well known in oceanography, and is one of the
> reasons why e.g. CMIP5 data are released on each model's native grid rather
> than a common, regular lat/lon grid which would be much easier to work
> with.
>
> If mass conservation is important for your task (and it sounds like it
> is) then you need to plot and calculate on the data's native grid.
>
> Will
>
> From: Wenshan Wang <wenshanw@uci.edu>
> Date: Tuesday, 18 February 2014 7:49 AM
> To: Dennis Shea <shea@ucar.edu>
> Cc: ncl-talk <ncl-talk@ucar.edu>
> Subject: Re: mass-conservative regridding
>
> Hi Dennis,
>
> Thank you very much for the reply.
> But I am sorry I didn't quite get it.
> I mean I have a global emission data map. No matter the resolution is, the
> total emission should be the same, right?
> I am trying to regrid 1x1 degree fixed grid to 1.9x2.5 degree fixed grid.
> The total emission of 1x1 is about 70,000, but either using ESMF or area
> conservative remap, the total emission of 1.9x2.5 is no larger than 20,000.
> I guess it is because 99% grid points of my emission map are 0, the
> difference of average is not large.
>
> I found in ncl-talk that we can re-scale the regridded to map to match
> the original total emission, 70000. But it was an old message. So, right
> now, ESMF is the best we have, right?
>
> Thank you for your time and patience!
>
> Best,
> Wenshan
>
> ------------------------------------------------------------------------------
> Graduate Student Researcher
> Earth System Science
> University of California, Irvine
>
>
> On Sat, Feb 15, 2014 at 9:36 AM, Dennis Shea <shea@ucar.edu> wrote:
>
>> ESMF is as 'state of the art' as it gets.
>>
>> re: "The avg is good enough but the sum of all grids is quite off."
>>
>> This is rather obscure. The "sum of all grids" means nothing.
>> If you had 100 grid points an the other grid had 1000, the
>> sums would be different.
>>
>>
>>
>>
>>
>> On 2/13/14, 2:03 PM, Wenshan Wang wrote:
>>
>>> Hi all,
>>>
>>> I am now trying to regrid emission data, which asks for
>>> mass-conservative.
>>> I found a message talking about emission regridding about 6 years ago.
>>>
>>> I was wondering whether NCL has some new functions that can perform a
>>> mass-conservative regrid since then.
>>>
>>> I tried 'area_conserve_remap', 'area_hi2lores' and ESMF conservative
>>> method.
>>> The avg is good enough but the sum of all grids is quite off.
>>>
>>> Thank you!
>>>
>>> Best,
>>> Wenshan
>>> ------------------------------------------------------------
>>> ------------------
>>> Graduate Student Researcher
>>> Earth System Science
>>> University of California, Irvine
>>>
>>>
>>>
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>>>
>

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Received on Mon Feb 17 15:33:55 2014