[Wrf-users] Wrf-users Digest, Vol 145, Issue 14
Ian Dragaud
iandragaud at lamma.ufrj.br
Thu Sep 8 08:36:46 MDT 2016
Jose,
I calculate the sigma levels heights (m) using the wrfout variables of
perturbation geopotential (PH) and base-state geopotential, through the
equation ((PH+PHB) / 9,8). The result gives the heights above the sea
level. To calculate the heights above the ground, I subtracted the first
level height from the above levels heights.
Best regards,
Ian Dragaud
Federal University of Rio de Janeiro
2016-09-06 20:21 GMT-03:00 <wrf-users-request at ucar.edu>:
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> 1. Re: Question about levels in wrf (Brandt Maxwell - NOAA Federal)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 6 Sep 2016 16:12:09 -0700
> From: Brandt Maxwell - NOAA Federal <brandt.maxwell at noaa.gov>
> Subject: Re: [Wrf-users] Question about levels in wrf
> To: Jose Augusto Paix?o Veiga <veiga.uea at gmail.com>
> Cc: "wrf-users at ucar.edu" <wrf-users at ucar.edu>
> Message-ID:
> <CAAwUs94aEOoQm6M7b+LQpxrusLqNQuj3iE9DEYKas1XdnKE4
> iw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Jose,
>
> The model sigma levels are there to distribute your model levels between
> the model top and the surface. Since pressure will vary at the surface,
> both horizontally and temporally, then the sigma value of 1 will be your
> surface level (versus the model top, with the sigma value of 0, which will
> usually be a fixed pressure). Your first model level (or any other sigma
> level) above the surface should have a pressure of (model top) +
> (sigma)*(surface pressure - model top). Thus, if you have a model top of
> 50 mb, a surface pressure of 1000 mb, and a first sigma value above the
> surface of 0.995, then the pressure of that sigma level should be 50 +
> 0.995 * (1000 - 50) = 995.25 mb (and from there you can calculate the
> height, which would be a little less than 50 meters). It should be pretty
> easy to get 8 or more levels below 1 km in a model, though obviously be
> careful to not have any sudden changes in distance between sigma levels (so
> something like 0.970, 0.964, 0.933 would be bad).
>
> Later...
> Brandt
>
>
>
>
> On Tue, Sep 6, 2016 at 3:05 PM, Jose Augusto Paix?o Veiga <
> veiga.uea at gmail.com> wrote:
>
> > Brandt,
> >
> > based on your explanations (if I not loose anything), I can't choose the
> > first model level, since the WRF do it during the course of run (based on
> > the initial and boundary conditions). If it is true, why is there an
> option
> > to set the model sigma levels?
> >
> > I want to set a run (in non-hydrostatic mode) with 8 or more levels
> > between surface and 1 km of altitude to "better resolve" PBL processes
> (you
> > already show me how to do that). But, I'd like the first model level
> start
> > at 50 meters of altitude. In this case, what should I do?
> >
> > My advanced apologises for any mistake or problem of interpretation from
> > your explanation on this issue.
> >
> > Thanks
> >
> >
> >
> > Jos? Augusto P. Veiga
> > CREA n.: 24161
> >
> > ======================================
> > Universidade do Estado do Amazonas
> > Departamento de Meteorologia
> > Escola Superior de Tecnologia (EST)
> > ======================================
> > Av. Darcy Vargas, 1200, Manaus-AM Brasil
> > Work phone: (92) 3878 4317, Ramal 4317
> > Skype: veiga_j.a.p.
> > ======================================
> > CV: http://lattes.cnpq.br/4027612512091565
> > Site: https://scientificmet.wordpress.com
> > ======================================
> >
> >
> >
> >
> > On Tue, Sep 6, 2016 at 5:21 PM, Brandt Maxwell - NOAA Federal <
> > brandt.maxwell at noaa.gov> wrote:
> >
> >> Jose,
> >>
> >> WRF can be run either hydrostatically or (preferred)
> >> non-hydrostatically. Any pressures at the corresponding
> heights/pressures,
> >> including at the surface, should be determined by the WRF (based on
> intial
> >> and boundary conditions). Some people use an ideal/standard atmosphere
> >> experimentally as input to the WRF (perhaps they add an anomaly of some
> >> sort to specificially study the resulting effect), though this is far
> >> different from using real data, which is almost always substantially
> >> different from the standard atmosphere.
> >>
> >> Later...
> >> Brandt
> >>
> >>
> >> On Tue, Sep 6, 2016 at 1:04 PM, Jose Augusto Paix?o Veiga <
> >> veiga.uea at gmail.com> wrote:
> >>
> >>> Hi Brandt Naxwell,
> >>>
> >>> thank you very much for all your very clear explanations.
> >>>
> >>> It seems that, considering an ideal atmosphere we can inclusively from
> >>> the hydrostatic equation set the model first level. I mean ... from the
> >>> equation p(z) = po exp(-z/H), where H = RT/g0, z is given in km, and
> po =
> >>> 101300,0 Pa (atmospheric pressure at surface), we can compute a
> pressure
> >>> value related to any height and include it in the model. Is it correct?
> >>>
> >>>
> >>> Thank you again.
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>> Jos? Augusto P. Veiga
> >>> CREA n.: 24161
> >>>
> >>> ======================================
> >>> Universidade do Estado do Amazonas
> >>> Departamento de Meteorologia
> >>> Escola Superior de Tecnologia (EST)
> >>> ======================================
> >>> Av. Darcy Vargas, 1200, Manaus-AM Brasil
> >>> Work phone: (92) 3878 4317, Ramal 4317
> >>> Skype: veiga_j.a.p.
> >>> ======================================
> >>> CV: http://lattes.cnpq.br/4027612512091565
> >>> Site: https://scientificmet.wordpress.com
> >>> ======================================
> >>>
> >>>
> >>>
> >>>
> >>> On Tue, Sep 6, 2016 at 3:06 PM, Brandt Maxwell - NOAA Federal <
> >>> brandt.maxwell at noaa.gov> wrote:
> >>>
> >>>> Jose,
> >>>>
> >>>> First of all, I think these should be sigma levels, even though
> they're
> >>>> called eta levels in WRF. The sigma levels are based on pressure, so
> one
> >>>> can calculate approximately how many levels would be below the
> pressure
> >>>> found at 1 km above the surface (though not this will vary based on
> surface
> >>>> elevation, temperature in the layer, among other things).
> >>>>
> >>>> If you have a surface (for simplicity sake) of 1010 mb and a top of 10
> >>>> mb (many of us will have a lower top), then 0,001 in the sigma
> coordinates
> >>>> would equate to about 1 mb. 1 km above the surface would be around
> 900 mb
> >>>> given the above surface pressure, so you can approximate anything
> between
> >>>> sigma levels of .890 and 1.000 to be below 1 km (you can use a
> standard
> >>>> atmosphere calculator to see how things like temperature can affect
> this).
> >>>> If your model top is really low, like 100 mb, then your 1 km sigma
> level
> >>>> would be more like .880.
> >>>>
> >>>> Later...
> >>>> Brandt Maxwell
> >>>> National Weather Service/San Diego
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> On Sun, Sep 4, 2016 at 4:03 PM, Jose Augusto Paix?o Veiga <
> >>>> veiga.uea at gmail.com> wrote:
> >>>>
> >>>>> Dear all,
> >>>>>
> >>>>> I am using the following eta levels in my runs with WRF (38 in this
> >>>>> case).
> >>>>>
> >>>>>
> >>>>>
> >>>>> *eta_levels = 1.000, 0.995, 0.990, 0.985,
> >>>>> 0.980, *
> >>>>>
> >>>>> * 0.970, 0.960, 0.950, 0.940,
> >>>>> 0.930, *
> >>>>>
> >>>>> * 0.920, 0.910, 0.900, 0.880,
> >>>>> 0.860, *
> >>>>>
> >>>>> * 0.830, 0.800, 0.770, 0.740,
> >>>>> 0.710, *
> >>>>>
> >>>>> * 0.680, 0.640, 0.600, 0.560,
> >>>>> 0.520, *
> >>>>>
> >>>>> * 0.480, 0.440, 0.400, 0.360,
> >>>>> 0.320, *
> >>>>>
> >>>>> * 0.280, 0.240, 0.200, 0.160,
> >>>>> 0.120, *
> >>>>>
> >>>>> * 0.080, 0.040, 0.000*
> >>>>>
> >>>>>
> >>>>>
> >>>>> However, I would like to know how many levels, in this example, are
> >>>>> included (a) in the first km and (b) how can I identify the eta level
> >>>>> representing the first km?
> >>>>>
> >>>>> I really appreciate any comment on this issue.
> >>>>>
> >>>>> Thanks.
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> Jos? Augusto P. Veiga
> >>>>> CREA n.: 24161
> >>>>>
> >>>>> ======================================
> >>>>> Universidade do Estado do Amazonas
> >>>>> Departamento de Meteorologia
> >>>>> Escola Superior de Tecnologia (EST)
> >>>>> ======================================
> >>>>> Av. Darcy Vargas, 1200, Manaus-AM Brasil
> >>>>> Work phone: (92) 3878 4317, Ramal 4317
> >>>>> Skype: veiga_j.a.p.
> >>>>> ======================================
> >>>>> CV: http://lattes.cnpq.br/4027612512091565
> >>>>> Site: https://scientificmet.wordpress.com
> >>>>> ======================================
> >>>>>
> >>>>>
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> Wrf-users mailing list
> >>>>> Wrf-users at ucar.edu
> >>>>> http://mailman.ucar.edu/mailman/listinfo/wrf-users
> >>>>>
> >>>>>
> >>>>
> >>>
> >>
> >
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