[ncl-talk] CAPE computation in NCL: more info on (1) entrainment, (2) adiabatic, (3) environment, (4) computation process, and (5) choice of the parcel with maximum CAPE for mCAPE

[Bill Ladwig]

Hi Maxine,

You can check out the source code here:

https://github.com/NCAR/ncl/blob/master/ni/src/lib/nfpfort/rip_cape.f

There are plenty of comments to go with the code, so hopefully it will
answer a lot of your questions.

Regards,

Bill

On Wed, May 9, 2018 at 7:21 PM, Maxime Colin <m.colin at unsw.edu.au> wrote:

> Dear community,
>
>
> To understand the ins and outs of the CAPE computed by NCL's
> wrf_user_getvar out of my WRF simulations, I would like to have a reliable
> source of information on this computation. Note that I use NCL v6.4.0.
>
>
> For example:
>
> - Is it the buoyancy of non-entraining and adiabatic parcels? Or does it
> take into account entrainment and non-adiabatic transformations?
>
> - Would anybody know by any chance if the "environment" that is considered
> by the code to compute CAPE is actually the same column as the one from
> which the parcel was raised, or it is the neighbouring columns?
>
>
> I can read some basic but useful information on the NCL website (
> https://www.ncl.ucar.edu/Document/Functions/Built-in/wrf_cape_2d.shtml).
> There is also some info on the RIP code from the UCAR website (
> http://www2.mmm.ucar.edu/mm5/documents/ripug_V4.html). Are these sources
> accurate?
> wrf_cape_2d - CISL's NCAR Command Language (NCL)
> <https://www.ncl.ucar.edu/Document/Functions/Built-in/wrf_cape_2d.shtml>
> www.ncl.ucar.edu
> NCL Home > Documentation > Functions > WRF, RIP wrf_cape_2d. Computes
> maximum convective available potential energy (CAPE), maximum convective
> inhibition (CIN), lifted condensation level (LCL), and level of free
> convection (LFC).
> There seems to be a disagreement between these 2 sources at least: the NCL
> website claims that the mCAPE is computed from the parcel with maximum
> Theta_e (equivalent potential temperature, I assume) but the RIP User guide
> on the UCAR webiste says mCAPE is computed from the parcel with maximum q_e
> (water vapour mixing ratio, I assume). This is quite different, no? Does
> anyone know what is actually used in NCL v.6.4.0.
>
>
> Other related questions:
>
> - What does the average over 500m depth, used to define a parcel, mean for
> air that is very close to the surface (say first model level at 15m)?
>
> - Is it accurate that mCAPE is calculated as the CAPE of the parcel with
> maximum of q_e (or theta_e) only over the lowest 3km of the column? (that
> should not be too restrictive I think)
>
>
> Thank you for those who have already investigated this in more details and
> who are happy to share their knowledge.
>
>
> All the best,
>
>
> Maxime.
>
>
> Maxime Colin
> ---------------------------------------------
> PhD candidate
> Climate Change Research Centre & ARC Centre of Excellence for Climate System Science, UNSW, Australia
> and Laboratoire de Météorologie Dynamique, UPMC, France
> http://www.ccrc.unsw.edu.au/ccrc-team/students/maxime-colin
> http://www.climatescience.org.au/staff/profile/mcolin
> ---------------------------------------------
> +61 (0)421 620 779    /    +33 (0)6 25 57 81 93
> m.colin at unsw.edu.au    /     colinmaxime at hotmail.fr <https://www.normalesup.org/phare/squirrelmail/src/compose.php?send_to=maxime.colin%40normalesup.org>
>
>
>
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