[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
>
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-- 
---------------------------------------------------
Fabien Solmon
Research Scientist
+39 040 2240206 (office) | Earth System Physics
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