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C.A.P.E. - Convective Available Potential Energy (Method for storm calcs)

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ArbitraryNumbers

ArbitraryNumbers

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I don't know if this has been used before by any calcers besides me, but recently I've come across Convective Available Potential Energy, which essentially measures the instability through the depth of the astmosphere and environment that a storm happens in. If I'm not mistaken, it should be applicable for thunderstorms, tornadoes, and the like.

"Weak Instability" refers to a CAPE value of less than 1 kj/kg, "Moderate Instability" means 1 to 2.5 kj/kg, and "Strong Instability" yields 2.5 to 4 kj/kg.

Some facts:

  • An EF5 tornado tore through Greensburg, Kansas in 2007 when the CAPE reached 5.5 kj/kg.
  • Two hours prior to the 1999 Oklahoma Tornado Outbreak, CAPE reached 5.89 kj/kg.
  • The 1997 Central Texas Tornado Outbreak occurred with 7 kj/kg.
  • The 1990 Plainfield tornado had an envorinment yielding 8 kj/kg.
Sources:

I feel like this could be used for calcing the yield of a thunderstorm or a tornado, but I don't know if one should apply the CAPE to the mass of the total air in the environment or the mass of the storm.
 
You can inform the other calc group members about this thread via their message walls if you wish.
 
I'm guessing that this is the energy per mass of cloud, it sound fine but I need to ask: what's the density of clouds? People here use no much above of 1 kg/m^3, but looking at internet it doesn't surpass 0.005 kg/m^3
 
Man, if we downgrade from 1.003 kg/m^3 to 0.005 kg/m^3 pretty much all the cloud calcs are completely obliterated.

Edit: Yeah I just some quick searches and found two sources citing half a gram per cubic meter. Where is our source to get 1.003 kg/m^3?
 
Perhaps Darkanine should be informed about this thread. He tends to perform weather calculations.

It would also be useful if we had an official instruction page for these types of calcs.
 
Unite My Rice said:
So you're suggesting we switch from our current methods to judging by instability?
Click to expand...
I don't think AN is suggesting a switch, but an alternative method to be available. I believe he used the method for storms without a proper timeframe.
 
Darkanine is right. I'm not suggesting a switch, but a new method to be available when needed.

The question here is whether the mass refers to all of the air in the environment, or the mass of the storm cloud.

Also, I'm all for a page suggesting various different methods for storm calculations.
 
This isn't a good metric, since the correlation between CAPE and the resulting winds are too weak, CAPE values are typically not consistent throughout different heights and typically fictional sotrm creating uses very different methods then real life.

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Limitations[edit]​

As with most parameters used in meteorology, there are some caveats to keep in mind. One of which is what CAPE represents physically and in what instances CAPE can be used. One example where the more common method for determining CAPE might start to break down is in the presence of Tropical Cyclones (e.x. Tropical Depressions, Tropical Storms, Hurricanes).[7] [8]

The more common method of determining CAPE can break down near Tropical Cyclones because CAPE assumes that liquid water is lost instantaneously during condensation. This process is thus irreversible upon adiabatic descent. This process is not realistic for Tropical Cyclones (TC for short). To make the process more realistic for Tropical Cyclones is to use Reversible CAPE (RCAPE for short). RCAPE assumes the opposite extreme to the standard convention of CAPE and is that no liquid water will be lost during the process. This new process gives parcels a greater density related to water loading.

RCAPE is calculated using the same formula as CAPE, the difference in the formula being in the virtual temperature. In this new formulation, we replace the parcel saturation mixing ratio (which leads to the condensation and vanishing of liquid water) with the parcel water content. This slight change can drastically change the values we get through the integration."

An exerpt from wikipedia.
 
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