[RegCNET] RegCM Ensemble run
Solmon Fabien
fsolmon at ictp.it
Tue May 7 09:07:33 CEST 2013
Hello
In my experience, whatever the perturbation it will propagates fast : I
got the "same" internal variability (IV )coherent pattern whether I used
temperature / humidity perturbation in BC or e.g. radiative field
perturbation in the euro domain .
A question that I had was about applying the perturbation during the
whole run via BC OR just as an initial conditions (i.e. starting with a
different date) : I heard some people claiming that IV should be
evaluated by initial perturbation only vs continuous perturbation. I
think in my case I did not see big difference between the 2 methods( but
it was a quick test) and do not have any strong opinion about that ,
but maybe somebody in the regcnet does !
For info right now the perturbation option is applied every time the
model reads ICBC ( evry 6 hours all along the run)
Fabien
On 05/07/2013 01:23 AM, Travis O'Brien wrote:
> Hi James,
>
> That is a detail that we probably should have noted in our paper. The
> decision to perturb humidity was arbitrary.
>
> I think that it would be reasonable to perturb any or all of the
> boundary condition (BC) fields by some small amount. In our case, we
> used humidity because it was the first field that we decided to
> perturb when trying to demonstrate that sensitivity experiments can
> produce large and coherent precipitation anomalies that are nothing
> more than 'model noise'. The humidity perturbation experiments
> demonstrated this thoroughly, so we never went beyond perturbing
> humidity in our study.
>
> I'm not sure I have great advice for how to choose which field(s) to
> perturb. Since we were trying to demonstrate that RegCM is quite
> sensitive to boundary conditions, it served well to perturb only one
> BC field by a tiny amount. However, we had no a priori reason for
> choosing humidity. In retrospect though, I wonder if it might be a
> better choice to perturb all the BC fields by a small amount if you're
> trying to sample the range of model states that can result from a
> given set of (uncertain) boundary conditions. Then the problem would
> be to decide how large the perturbation should be for each BC
> field--this likely depends on the field and on the estimated
> uncertainty in the boundary conditions being used for the simulation.
> As far as I'm aware, this isn't something that has been rigorously
> studied.
>
> Cheers,
> -Travis-
>
> Travis O'Brien
> Lawrence Berkeley National Lab
> http://esd.lbl.gov/about/staff/travisobrien/
> <http://esd.lbl.gov/about/staff/travisobrien/index.html>
> (510) 495-8047
>
>
> On Mon, May 6, 2013 at 3:39 PM, James Ciarlo`
> <james.ciarlo at physics.org <mailto:james.ciarlo at physics.org>> wrote:
>
> Is there a reason why you chose to perturb only humidity and not
> temperature and or surface pressure for instance?
>
>
> On 3 May 2013 17:31, James Ciarlo` <james.ciarlo at physics.org
> <mailto:james.ciarlo at physics.org>> wrote:
>
> That is actually very helpful. Thanks :)
>
>
> On 3 May 2013 16:16, Travis O'Brien <travis.obrien at gmail.com
> <mailto:travis.obrien at gmail.com>> wrote:
>
> Hi James,
>
> The ensemble_run flag is one of the parameters that
> activates the ensembling system. This is a relatively new
> feature that is described in the latest version of the
> RegCM UserGuide
> <http://gforge.ictp.it/gf/download/docmanfileversion/54/973/UserGuide.pdf>,
> Section 6.1.7.
>
> When the ensembling system is activated, one or more of
> the boundary condition fields are perturbed by a small
> fraction each time they are read in. For example, the
> following settings would use the ensembling strategy of
> O'Brien et al. (2011)
> <http://dx.doi.org/10.1007/s00382-010-0900-5>, which is
> the main reference that describes the details of the
> ensembling method:
>
> &globdatparam
>
> ensemble_run = .true.
>
> /
>
> &perturbparam
>
> lperturb_q = .true.
>
> perturb_frac_q = 0.001d0
>
> /
>
>
> With these settings turned on, each time you run regcm,
> the output will be slightly different. So to create an
> ensemble of simulations, you might run RegCM five times,
> and each time change the parameter dirout to output.1,
> output.2, output.3, output.4, output.5, etc.
>
> I hope this helps, and please let me know if I can clarify
> anything.
>
> Kind Regards,
> -Travis-
>
> --
> Travis O'Brien
> Lawrence Berkeley National Lab
> http://esd.lbl.gov/about/staff/travisobrien/
> <http://esd.lbl.gov/about/staff/travisobrien/index.html>
> (510) 495-8047 <tel:%28510%29%20495-8047>
>
>
>
>
>
>
> On Fri, May 3, 2013 at 2:51 AM, James Ciarlo`
> <james.ciarlo at physics.org
> <mailto:james.ciarlo at physics.org>> wrote:
>
> Dear RegCNET,
>
> I am interested in running an ensemble expleriment
> with RegCM4. My intention was to choose different
> settings for the different simulations.
>
> I have noticed the setting: ensemble_run = .false.,in
> the globdatparam. This obviously needs to be set to
> true, but since I have never done an ensemble run
> before with RegCM4 I was wondering if there was
> anything I needed to know.
>
> Regards,
> James
>
> _______________________________________________
> RegCNET mailing list
> RegCNET at lists.ictp.it <mailto:RegCNET at lists.ictp.it>
> https://lists.ictp.it/mailman/listinfo.cgi/regcnet
>
>
>
>
>
>
>
> _______________________________________________
> RegCNET mailing list
> RegCNET at lists.ictp.it
> https://lists.ictp.it/mailman/listinfo.cgi/regcnet
--
---------------------------------------------------
Fabien Solmon
Research Scientist
+39 040 2240206 (office) | Earth System Physics
+39 040 2240449 (fax) | ICTP (UNESCO-IAEA)
esp.ictp.it | Strada Costiera 11
| 34014 Trieste, Italy
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.ictp.it/pipermail/regcnet/attachments/20130507/8e21dc27/attachment.htm>
More information about the RegCNET
mailing list