[Wrf-users] cu_physics for dx = 7km

[Jonas Kaufmann]

Hello Thomas,

yes, I think I have to test the CU scheme in my use case - but maybe some
other users were facing the same problem, too. In my current test case and
for my optimization it looks like running without a CU scheme might be
better.

Thank you for your hint regarding the PBL scheme. I am looking to optimize
for 10m above ground winds, for this I am using the YSU scheme
(bl_pbl_scheme = 1). I am still testing with topo_wind = 1 enabled. Does
anyone have experience with this use case or maybe a hint for a better
configuration?


Best regards,

Jonas

On Wed, Jun 29, 2016 at 1:31 AM, Thomas Kloetzke <t.kloetzke at uq.edu.au>
wrote:

> Hi Jonas,
>
>
>
> indeed, between 3 km (or 4 km) and 10 km it is a bit hard to find out what
> suits best.
>
>
>
> I was running WRF for a simulation of an observed tropical cyclone (for
> reproduction) and my domains were 10 km and 3.3 km (following the 1:3 grid
> ratio). For the outer domain, I always used a cumulus scheme, for the inner
> domain I tried both cumulus scheme on and off and there were only tiny
> differences regarding track and intensity. But this may differ from case to
> case.
>
>
>
> From my personal point of view, there is no thumb rule saying: You have to
> use a CU scheme or not for resolutions below 10 km. As I said before, this
> can be different depending what are you trying to simulate. I would
> recommend to try both, first leave the CU scheme on for the 4 km domain,
> second, turn it off and compare the results. From this sort of simulation
> you will learn much more about the behaviour of the CU scheme and it’ll
> help you to evaluate which parameterisation might fit better.
>
>
>
> Which pressure levels do you use for your wind forecasts? For low-level
> winds, the choice of the planetary boundary layer scheme will be important
> as well.
>
>
>
> Hope this helps. I am happy to discuss more about that, as I am in the
> learning process as well and I think many people might be interested in
> sharing some experiences as well.
>
>
>
> Regards,
>
> Thomas
>
>
>
> *From:* wrf-users-bounces at ucar.edu [mailto:wrf-users-bounces at ucar.edu] *On
> Behalf Of *Jonas Kaufmann
> *Sent:* Wednesday, 29 June 2016 6:09 AM
> *To:* wrf-users at ucar.edu
> *Subject:* [Wrf-users] cu_physics for dx = 7km
>
>
>
> Hello,
>
>
>
> I have set up a domain over Europe with 7km resolution. My main focus is
> to generate wind forecasts with this domain.
>
>
>
> I am comparing outputs between different physics settings, and there is
> one thing with Cumulus schemes that I do not understand at the moment. I
> have found presentations online that said that below 4km resolution you
> probably won't need a cumulus scheme, between 4km and 10km it is not sure
> and above 10km you need a cumulus scheme. However I have also found that
> the Grell 3D scheme (cu_physics = 5) is also supported for resolutions
> below 10km.
>
>
>
> Now I am not sure how to proceed with this. Can you give a recommendation
> when to use the Grell 3D scheme vs. not using a Cumulus scheme for my use
> case?
>
>
>
>
>
> Thank you for your help!
>
>
>
> Best regards,
>
>
>
> Jonas
>
>
>
>
>
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