[Wrf-users] Is it a must to run wrf with a nest

[afwande juliet]

Thanks all for this

On Jul 27, 2016 1:55 AM, <mmkamal at uwaterloo.ca> wrote:

> Hi there,
>
> I would like to offer the following seven points (the first two copied
> from "WRF Advanced Usage and Best Practices" lecture note):
>
> 1) Nestng is probably needed if your target resolution is much less than
> your analysis resolution.
>
> 2) Outer domain grid size could be 1/3 analysis (or boundary data)
> resolution.
>
> 3) In your case, analysis data set's horizontal resolution is 83 km.
> Therefore, according to suggestion 2, you can set your outermost domain's
> grid spacing (83/3= ~ 27 km). Following a 1:3 parent:daughter grid ration,
> your second domain's resolution would be 9 km; 3rd domain's grid spacing
> would be 3 km and 4th domain's grid spacing would be 1 km.
>
> 4) WRF run times depends on multiple factors, including grid spacing,
> integration time steps, choice of physical parameterization schemes (e.g.,
> Morrison double moment microphysics schemes takes nearly 15% more computing
> time than WRF single moment six class microphysics scheme), the number of
> grid points WRF needs to integrate (i.e., if you have 200 grid boxes along
> east-west, 175 north-south, and 28 vertical layers then WRF needs to
> integrate 200*175*28 = XXXXXXX points. For second nest, the number of grid
> points would be: 3*(east-west grid box number * north-south gridbox number
> * vertical layers number). For 2nd nest number of grid points would be:
> 9*(east-west grid box number * north-south gridbox number * vertical layers
> number). Now, you can imagine how many grid points you need to integrate
> for each successive nest. Model integration time will follow nearly the
> same trend. Nest will take approximately four times higher CPU time than
> parent domain.
>
> 5) Now, depending on your computing resources (which is not too much) you
> can consider only one nest. In that case your highest resolution domain
> would be 9km (if you set your outer domain grid spacing 27 km).
>
> 6) You can set more than one nest if you set a small domain area for nest
> compared to parent domain. You can not set larger domain area for outermost
> domain if you would like to use more than one nest.
>
> 7) So, while running WRF model, one should follow the famous proverb "cut
> your coat according to your cloth".
>
>
> Cheers,
> Kamal
>
>
>
>
>
> Quoting afwande juliet <afwandej965 at gmail.com>:
>
> Thanks guys for this useful piece of information. I have 32cpus and 2
>> nodes. I am testing many convective schemes over East Africa. If I got you
>> right, if my data is at 83km, then the outer nest should be between 5-3
>> times less, that means the inner nest will be about 9.33km if ratio 1.3 is
>> considered. My confusion is 9km is too expensive to run than 28 or 32km.
>> For my case do I set the domain such that the inner nest is 28km or
>> what??.
>> This is because the if outer nest is 32km then inner must be 10.5km there
>> about which is too expensive.
>>
>>
>> On Jul 25, 2016 9:05 PM, "Mike Dvorak" <mike at sailtactics.com> wrote:
>>
>> Hi there,
>>>
>>> You typically don't have to start with your first domain at the same
>>> resolution of the input dataset. I would start out with something on the
>>> order of 3 to 5 times smaller in delta x and y. So if your input data is
>>> 83
>>> km, your WRF parent (first) domain could be roughly between 28 to 16 km.
>>>
>>> You might run some sensitivity experiments to see how well the model
>>> matches observations by going directly to 16 km. The results might be
>>> good
>>> enough for your purposes and would save you having to run that extra
>>> domain. Removing parent domains does *not* often make a huge difference
>>> in wallclock time because the inner nests run multiple timesteps for each
>>> time the parent domains runs.
>>>
>>> Best of luck with your experiment.
>>>
>>> Cheers,
>>> Mike
>>>
>>> On 07/24/2016 09:34 AM, afwande juliet wrote:
>>>
>>> Dear users
>>> I am running wrf using era interim which is at 83km resolution. I am
>>> downscaling to about 16KM nest
>>> It's very slow. I even deactivated the parent domain so that I only get
>>> output from nest to reduce runtime but still takes 84hrs to run 3months
>>> simulation which is too slow.
>>>
>>> What would be the danger if I run without nest to reduce runtime
>>>
>>> Would there be any mismatch between the driving data and the model
>>>
>>>
>>> _______________________________________________
>>> Wrf-users mailing listWrf-users at ucar.eduhttp://
>>> mailman.ucar.edu/mailman/listinfo/wrf-users
>>>
>>>
>>> --
>>> [image: Sail Tactics logo]
>>> Mike Dvorak, PhD
>>> Founder
>>> Sail Tactics, LLC
>>> Corpus Christi, TX
>>> +1 650-454-5243
>>> http://sailtactics.com
>>>
>>> _______________________________________________
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>>>
>>>
>>>
>>
>
>
>
>
>
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