[ncl-talk] Computation of baroclinity in TC environments

[George Vandenberghe]

Where the concept is relevant  (with an enormous number of caveats, yes) 
is to answer the fundamental question, will TC interaction with 
baroclinicity, induce transition to a growing or stable baroclinic 
system (often observed) or will the TC perturbation just damp out (also 
often observed) with a theoretically expected but hard to actually point 
out, increase in baroclinic available potential energy for some future 
perturbation to extract.

I am obviously not an expert either (and my M.S is 31 years stale)  and 
I did sleep at home last night, not in a Holiday Inn Express but I think 
it is a tractable forecast and theoretical modeling problem, again with 
the caveats mentioned below.

Casually plugging this into a program without understanding the concepts 
is worrisome, also agreed.

Thanks everyone for the response!

On 02/09/2018 10:25 AM, Dennis Shea wrote:
> I am not really knowledgeable about Eady Growth Rate (EGR) so  I asked 
> a person and got the following response:
> --------
> Hi Dennis,
>
> Ha!  When I google Eady growth rate, the first thing that comes up is 
> your NCL function and the second thing that comes up are some class 
> notes that I wrote when I taught a course.  Apparently we are the 
> state of knowledge on Eady growth rate, which is slightly concerning.
>
> Erm, for [1] I don't think the Eady model is intended to tell you 
> something about tropical cyclone environments. It's really intended to 
> describe the growth of mid-latitude eddies.  Since it's formulated on 
> an f-plane, I don't think it's really appropriate for use in tropical 
> environments.  That being said, the eady growth rate really is just a 
> measure of baroclinicity so it might be fine to determine what the 
> baroclinicity is in their tropical cyclone environments.
>
> For [2b] I'd say no too.  But I don't think using equivalent potential 
> temperature would work either.  I think you'd have to include a 
> diabatic heating term in the thermodynamic equation that's being 
> solved to account for the release of heat associated with the 
> convergence of moisture and precipitation that accompanies the growing 
> wave.  WIth my expert googling skils, I came across this... 
> https://iri.columbia.edu/~tippett/pubs/moist.pdf 
> <https://iri.columbia.edu/%7Etippett/pubs/moist.pdf>
>
> For [2a] I don't really know the answer.  But I'm also not sure how 
> you would measure the real world growth rates.  The eady model is 
> intended to describe the growth of the normal modes and I think you 
> could compare the predictions with a normal mode calculation using the 
> real world basic state but I'm not sure how you would actually measure 
> the growth rates of the real world.  I also think it might give you a 
> dimensionless growth rate which tells you what scales dominate by 
> growing fastest, but I'm not sure to what extent it is something that 
> can be compared with the real world. In short, I don't really know.
> -----------
> HTH
> D
>
> On Wed, Feb 7, 2018 at 10:56 AM, George Vandenberghe 
> <george.vandenberghe at noaa.gov <mailto:george.vandenberghe at noaa.gov>> 
> wrote:
>
>     On 02/07/2018 12:47 PM, Prashanth Bhalachandran wrote:
>
>         Hello all,
>         I want to compare the baroclinity of two tropical cyclone
>         environments. What is the best way to do this using NCL?
>
>         I did some digging and found a function to calculate Eady
>         growth rate in v6.4 . I have never used it thus far, so I want
>         to know what the options are.
>
>         Thank you,
>         Prashanth
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>
>     Okay this is tangential to the topic but VERY INTERESTING in its
>     own right.  How well do the observed growth rates
>
>     for (presumably large scale because small length scale damps)
>     compare with the theoretical Eady growth rates
>
>     and (something I should know but don't) do Eady growth rates
>     incorporate the effect of moisture on stratification?
>
>
>
>
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