questions for Hart diagrams, symmetric, asymmetric and convective pattern cyclones

[DanieleItalyRm]

Hello friends,
I'm preparing a scheme that contains the type of cyclones (extratropical, tropical, subtropical, possible convective pattern, symmetric warm core, asymmetric warm core, etc). I want to create an easy-to-understand scheme of cyclone classification for the public. Unfortunately, in some European countries even some meteorologists do the in errors and are linked to old paradigms over cyclonic classification.
Often the European public, not abitue at tropical cyclone analysis, confuses on convective eyes and low clouds eyes, and The classification of some cyclones is often confused, especially for those tropical cyclones that develop outside the tropic by tropical transition, such as Grace, Pablo, and some Mediterranean systems. For this reason, I would like to include all the possible scenarios

These are my doubts:

1. A symmetric warm core surely will produce symmetric convection? for symmetric should the convective "ring'' necessarily be closed (fig.1 TC typeB)? I have seen some tropical T3-T4 cyclones with non-closed, hooked rings, only partly convective (fig.1 TC typeA), but I imagine we can still talk about symmetric warm-core cyclone with symmetric convection, right?

2. An asymmetric warm core it's surely a subtropical cyclone? I have noticed tropical cyclones that with strong shear have asymmetric convection; the convective nucleus is moved from the center, and the vortex of low clouds remains uncovered just outside (fig.1 TC typeD). Can this type of tropical cyclones be defined as asymmetric warm core with asymmetric convection?

3. In Hart's diagrams a tropical cyclone should fall in moderate to deep warm core for to be considered tropical? if the system fall in "shallow warm core" is definitely subtropical (fig.2)? I thought that in the Hart diagram shallow, moderate and deep it was based on system pressure, but if the system is 995hpa maybe it should be towards moderate, or I don't understand something?

4.Do you think in conclusion that my scheme is correct? (it's just a sketch yet). Im Sorry for these many questions, Thanks

Fig1.


Fig2.

[AJC3]

Daniele, I mostly agree with your assessments, though are points of contention I have. The problem here is trying to compartmentalize cyclones when they exist on two different spectrums (warm core-cold core, and frontal-non-frontal) and in three spatial dimensions.

First, as we have discussed previously, I agree with your thinking with respect to depth of the warm core being the primary determinant of a subtropical versus subtropical cyclone. In my mind, the transition of some symmetric Azores lows, MEDSEA lows, and in rarer cases, Kona lows (near Hawai'i) are the best examples of this line of thinking. I often refer to these cyclones as baroclincally initiated or "BI", an acronym I first saw used by another well known meteorologist, Dave Tolleris, of Wxrisk.com

I don't think a sheared asymmetric warm core cyclone always constitutes "subtropical" (some may disagree with me here). Even though the jet stream is a thermal wind, and therefore, by definition, baroclinic, the shear layer varies in both height and layer thickness (not to mention magnitude). Sometimes it's shallow/upper tropospheric, sometimes shallow/mid tropospheric, and sometimes deep/mid-upper tropospheric. The latter of these results in a more deeply tilted (in the vertical [z]) warm core, and often more severe spatial (in the horizontal [x/y]) displacement of the convection/warm core. Consequently, these cyclones have more argument to be called "subtropical" (IMO). However, I have seen hurricanes which become severely sheared which I would not at all describe as "subtropical hurricanes" as their 3D vortices/warm cores, while not vertically well-aligned, remain vertically well-defined through a deep layer.

When in comes to degree of tilt/displacement being the main determinant of "tropicality" vs. "subtropicality" of a cyclone, the most common examples I can think of is T-wave interaction with either the mid-Atlantic TUTT, a TUTT low (one which fractures off of the TUTT), or a TUTT-type low (one whose vorticity doesn't originate, at least in part, from the TUTT). The asymmetry and convective displacement in these cyclones is very apparent, as is the frequent lack of a well-defined vortex/warm core. Since the incipient disturbance is a tropical wave, and jet-forced ascent (upper level divergence) makes a significant contribution to convective development, I refer to these types of systems as baroclincally enhanced, or "BE" (another DT term), rather than "BI".

Since the degrees of baroclinic and warm core processes vary with each cyclone (or system), it naturally becomes difficult to classify these systems. It's a very, very subjective thing. I can tell you those in the met field often disagree on what constitutes a tropical vs a sub-, extra-, or post- tropical cyclone. Obviously, it's the subject of frequent disagreements on this forum.

This may be a bit of a hot take, but I often wonder if the colloquial terms "tropical" and "subtropical" should be abandoned. Both are misnomers as they refer more to the location of the genesis rather than the structure of the cyclone itself. While the terminology I prefer to use works within academia, it's more technical. And going to a more unfamiliar and more complex categorization (much like abandoning the Saffir-Simpson hurricane scale/SSHS) would surely lead to confusion among the general public. YOMV

Also, since this seems to be a sticking point for some with regards to being able to classify a warm core cyclone of moderate depth as truly "tropical", the 28C/80F temperature threshold REALLY needs to be de-emphasized, if not outright ignored, outside of the MDR, since it assumes a convective lapse rate typical of the deep tropics, which in turn is dependent on the environmental mid- (or upper-, depending upon who you ask) tropospheric temperature. Since these temperatures decrease as latitude increases, so does the SST threshold for warm core formation/maintenance. We have discussed this aspect many times in the past as well.

I'll have to re-read these rambling thoughts tomorrow and see if they form a coherent post. LOL