[ncl-talk] Computation of baroclinity in TC environments

[Prashanth Bhalachandran]

Thank you, George and Dennis. As George said, casually using the function
without completely understanding what it was intended for and whether it is
applicable, would mislead interpretations. That is exactly what I wanted to
avoid. The above emails have certainly pointed me in a direction where I
can learn more about the topic and its applicability to the problem I am
trying to address.

Thank you.
Prashanth

On Fri, Feb 9, 2018 at 10:52 AM, George Vandenberghe <
george.vandenberghe at noaa.gov> wrote:

> 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/~tipp
> ett/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> 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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>
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-- 
Kind Regards,
Prashanth

Email : prashanth.bhalachandran at gmail.com; Phone : +91 9962187100 ; Skype :
viscousprash
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