# Downdraft CAPE -- How to do it

1. Apr 13, 2015

### limiqt

Hi everyone.

I was wondering if someone could show me how to calculate the downdraft convective available potential energy (dcape) using the NCEP reanalysis. I will appreciate any assistance.

Thanks,

Lim

2. Apr 13, 2015

### davenn

Hi Lim
welcome to PF

see if this helps :)
from http://glossary.ametsoc.org/wiki/Downdraft_convective_available_potential_energy

downdraft convective available potential energy
(Abbreviated http://glossary.ametsoc.org/w/index.php?title=DCAPE&action=edit&redlink=1 [Broken].) The maximum energy available to a descending parcel, according to parcel theory.

On a http://glossary.ametsoc.org/w/index.php?title=Thermodynamic_diagram&action=edit&redlink=1 [Broken] this is called negative area, and can be seen as the region between the descending parcel process curve and the environmental sounding, from the parcel's level of free sink to some lower level, usually the surface. Its quantitative definition is

where αp and αe are the specific volumes of the parcel and its environment, respectively, and ps and pf are the surface pressure and the pressure of the level of free sink, respectively.

I'm not a maths man so don't ask me to work it out for you

Last edited by a moderator: May 7, 2017
3. Apr 13, 2015

### DaveC426913

Aw. From the thread title, I thought this was going to be about someone making an actual flying cape.

4. Apr 13, 2015

### davenn

LOL no such luck

being a storm chaser I actively keep close tabs on CAPE and LI ( lifted index) and a few other factors found on Skew-T diagrams

Dave