Naive questions - input and output grib frequency

Forum dedicated to older versions of EMS package (WRFEMS v3.2, v3.1 or older). Support is user-to-user based, so please help others if you can.
pattim
Posts: 158
Joined: Sun Jun 24, 2012 8:42 pm
Location: Los Angeles, CA, USA

Re: Naive questions

Post by pattim » Sun Jul 01, 2012 6:22 pm

meteoadriatic wrote: Yes you can do global WRF run. But you will need plenty of computing resources. I don't see any practical use of that when GFS forecasts are freely available for feeding regional domains with BC.

P.S. When NMM-B model becomes ready for linux/public use, global runs might become bit more popular, but still lot of computing resources will be needed.
I have found that 5 x 5 degree runs, say in GISS ModelE, don't take all that much time on my Phenom II x6 workstation. That's why I chose that resolution. I thought NMM-B was already released (NEWR EMS)?
meteoadriatic wrote:
pattim wrote:I think I saw in the docs that EMS linearly interpolates the coarse-resolution BC time steps to the time steps it needs.
Where is time interpolation of the BC's done?
Nowhere!
I think this is becoming clearer - part of my background is in CFD - but in NWP, you *only* care about the future - so there is no data for time interpolation! Still, that seems an ill-posed problem unless you assume that the synoptic flows (i.e., the BC's of a grid) stay constant during any given EMS run.

This may be the main benefit of my global model approach - when nesting from a global domain, EMS automatically time-interpolates the boundaries because it "knows" how the synoptic flows change with time. Of course, this introduces errors from knowledge of the synoptic flows, and that's why the global domain (at least) would need to be nudged.

meteoadriatic
Posts: 1543
Joined: Wed Aug 19, 2009 10:05 am

Re: Naive questions

Post by meteoadriatic » Sun Jul 01, 2012 6:28 pm

pattim wrote:
meteoadriatic wrote: Yes you can do global WRF run. But you will need plenty of computing resources. I don't see any practical use of that when GFS forecasts are freely available for feeding regional domains with BC.

P.S. When NMM-B model becomes ready for linux/public use, global runs might become bit more popular, but still lot of computing resources will be needed.
I have found that 5 x 5 degree runs, say in GISS ModelE, don't take all that much time on my Phenom II x6 workstation. That's why I chose that resolution. I thought NMM-B was already released (NEWR EMS)?
Not yet but we hope it will be soon.

pattim wrote:
meteoadriatic wrote:
pattim wrote:I think I saw in the docs that EMS linearly interpolates the coarse-resolution BC time steps to the time steps it needs.
Where is time interpolation of the BC's done?
Nowhere!
I think this is becoming clearer - part of my background is in CFD - but in NWP, you *only* care about the future - so there is no data for time interpolation! Still, that seems an ill-posed problem unless you assume that the synoptic flows (i.e., the BC's of a grid) stay constant during any given EMS run.

This may be the main benefit of my global model approach - when nesting from a global domain, EMS automatically time-interpolates the boundaries because it "knows" how the synoptic flows change with time. Of course, this introduces errors from knowledge of the synoptic flows, and that's why the global domain (at least) would need to be nudged.
I must correct myself here. In fact I don't know if some kind of BC interpolation happens during WRF runtime (while model is integrating between it's timesteps) or not! It could be investigated if needed. But it doesn't make any practical difference for users if that interpolation is done or not, really. Either way, we need to feed model with as frequent BC data as we can get.

pattim
Posts: 158
Joined: Sun Jun 24, 2012 8:42 pm
Location: Los Angeles, CA, USA

Re: Naive questions

Post by pattim » Sun Jul 01, 2012 8:41 pm

meteoadriatic wrote:
pattim wrote: This may be the main benefit of my global model approach - when nesting from a global domain, EMS automatically time-interpolates the boundaries because it "knows" how the synoptic flows change with time. Of course, this introduces errors from knowledge of the synoptic flows, and that's why the global domain (at least) would need to be nudged.
I must correct myself here. In fact I don't know if some kind of BC interpolation happens during WRF runtime (while model is integrating between it's timesteps) or not! It could be investigated if needed. But it doesn't make any practical difference for users if that interpolation is done or not, really. Either way, we need to feed model with as frequent BC data as we can get.
I think it would be impossible to interpolate forward in time, although you can try to predict based on past trends, at least until a shock or cusp are encountered. So I guess I should follow
http://strc.comet.ucar.edu/software/new ... pter05.pdf
...and try to create and run a nested global domain. I think I recall that nest BCs are interpolated in both time and space. Do you know of an online step-by-step for a nested EMS run? There are SO MANY options on the run scripts that my head will be swimming for weeks!

Patricia

PS: Now we need to get the ClimateInABox people to be like Robert and publish a statically-linked model code suite! So many people have SO MUCH trouble getting everything linked! It took me a month to get ModelE running so I shudder at getting GEOS-5 running, which is the ultimate need. Maybe if the CESM folks would make their code easier to install, that might also be an option.

PPS: ...and if enough people installed EMS, it could be migrated to BOINC!

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