Storm Nomenclature

[Dan Chaffee]

Hi Mike, All;
(This is in response to the beginning of the thread regarding Hallam- Greensburg similarities, but it seems to warrant a new thread.) I think a clarification of storm nominclature might be in order.

I agree that Mike S's images are very good, certainly under the circumstances, but I would describe what they show differently.

(Mike Peregrine wrote)

One thing I noticed in Mike Scantlin's photos (which are exceptional from a structural perspective - and every other perspective), was that the mesocyclone appeared extremely well developed at the time the tornado was nearing Greensburg.

None of these images shows the mesocyclone. The very term refers to an area indicated by radar as the tight rotation(s) within the updraft that stretches and ultimitely forms the tornado. by this definition, you can't actually see a mesocyclone(See the NOAA definition for this term).
http://www.srh.noaa.gov/oun/severewx/glossary3.php

I think what you are refering to (and I understand the inclination) is the wrapping east flank, its base and its associated infow features. The fact that these features
curve cyclonicly, as do spiraling straitions under the base, does not mean they constitute a mesocyclone, alhough their presence is certainly symtomatic of its existance. Also, an updraft can look very similar from this image's vantage point and have more than one meso. I have never seen any evidence that the appearance of strictly these features can denote the size, strength, or maturity of a mesocyclone
itself at a given instant. The supercell can be cycling and between producing mesos and have all the spiraling straitions and inflow bands that these images show. Obviously if a violent, large tornado is in progress as this sure is, the meso must be in the mature phase.

It's tempting to think that if one is able to look up into the updraft's RFD occlusion, one is actually then seeing the mesocyclone. This is not consistant with the definition either, but it is certainly a more focused region for its containment. I suppose the closest thing
to direct visual evidence that may suggest at least the size at the lowest of a mesocyclone is seeing the wall cloud in motion, if there is one. However, in the first shot, we are barely able to see the faint
decrease in darkness at the lowest part of the base that indicates the RFD occlusion. We are looking NW to the SE flank and RFB. Sometimes it's possible to see the RFD occlusion dramtically from this quadrant of
a storm, but not in this image. Featurewise, if I were to describe what the first image shows I would say it shows a strongly arcing, softly striated east flank and low base, with a beaver's tail inflow cloud surmounted to the upper right by a shallow, cyclonicly curved mid-level inflow cloud deck. Aside from the wedge tornado, there is no conclusive indication of a wall cloud, although that may be what the lowest part
of the base is (it may simply look lower because it is further away than closest part of the base). There may be other ways of saying the same thing...

I think the most elucidating approach to considering and discussing storm morphology is to differentiate between topographical cloud structure and storm structure; they are not the same thing. Sorry if this is taken as being pendantic; I do feel that it is imperative that we are all on the same page regarding our abilities to discrimminate and interpret storm features (the WCMs are counting on us

Dan Chaffee

 

[Mike Peregrine]

I've always used the term 'mesocyclone' loosely ... and probably erroneously (no doubt). In fact, chasers in general use the term 'mesocyclone' to denote the area of visible rotation in a storm as set apart from inflow bands, rain-free base, downdraft, tornado, or other observable regions. The reason for this (I think) is that if we are strictly going by that NOAA definition, we don't have a good term to describe this visible field of rotation at times - other than wall cloud. And the thing is ... there are many times on a storm when the term 'wall cloud' just doesn't work very well. For some reason, when I hear the term 'wall cloud' all I can think of is a blocky chunk of cloud hanging under (connected to) the RFB. I've been on storms where you have a wall cloud - or maybe two wall clouds (one occluding and one new) that are connected by the same general field of rotation above them, as indicated by broad, rounded striations. Anyway ... there's no doubt I've been using the terminology incorrectly forever. I generally don't like the term 'wall cloud' because personally I feel like it's too generalized, overused by the public, and non-descript.

I DO think that if I'm describing what I'm seeing to a WCM, though, that they would interpret features I describe associated with a mesocylone as simply the broad area of discernable rotation in the right rear flank of the storm. At least I hope so, because that's what I've always done. I really doubt that they would enforce the textbook definitions while I'm calling in a report ... but at the same time I agree that it's good to try to overcome these bad habits as time goes on (yeah, good luck with that!).

 

[Willie Dines]

Forgive me for being somewhat blunt, but I'm going to get striaght to the point on this and these are just my own views on this.

If I'm out chasing, and there's the scenario of a tornado like the Greensburg Beast, I'm not going to be too worried about the correct classifications of parts of a storm, when calling in a report, time is of the essence and the sooner a warning goes out, the better chance people have of getting to safety, and so, the way I see it is, if I'm on the road, I'm going to say, if I got a supercell, meso, wall cloud, funnel, tornado, etc, I'm not going to waste time by going through all the politically correct definitions and terminology, not when people's lives may be at stake.

I realize that I may sound like I'm being a bit harsh in this view, but public safety comes first every time, being politically correct, comes later, when writing up a report or anything like that.

Willie

 

[Mike Hollingshead]

Guess we need a new term for what looks like a meso. I say we call those cases, mooso. It just seems funny this comes up on a storm that had 197 knots of shear at the time of the images. I think if a crack can be something you step over, as well as something you smoke, a meso should be able to be what a chaser views visually as well as the definition of it on radar.

Just ignore me.

 

[Shane Adams]

If Mike S's top image doesn't show a mesocyclone....then in 11 years of chasing, I've never seen one.

I'm sure there's a half dozen degreed dudes reading this, just salivating and waiting to pounce into an anal, paragraphs-long explanation of how we're all technically-wrong regarding our interpertation of mesocyclones/supercell structure.

I don't care what it says in the dictionary...a wedding cake is a meso.

But while we're being technically-accurate (or experimental anyway), I've read more than once that often-times the mesocyclone is actually in a decaying phase (collapsing) as a strong tornado develops......so the assertion that the meso is "obviously in the mature stage" just because a powerful tornado is happening, isn't gospel.

Just food for thought...

 

[Greg Stumpf]

Pouncing on Shane!!!

The mesocyclone is properly defined as a thunderstorm scale-vortex. You measure a component of the mesocyclone using a radar. You see evidence of it in cloud structure.

The mesocyclone is not defined as a rotating updraft, nor is it defined visually by cloud. The mesocyclone circulation extends beyond the boundaries of cloud, and consists of three-dimensional air motions...updraft, downdraft, sidedrafts, etc. The vortex can be open, closed, tilted, have varying "diameters" at different heights, twist, turn, spiral, and even be multiple-vortex.

That said, I don't really care if someone looks at an upside-down wedding cake updraft and calls it a meso. In fact, I use the term "low-level mesocyclone" (a smaller and more intense vortex) to describe the visual pre-tornadic phase of a supercell - occlussion downdraft having completely encircled a portion of an updraft, with violent upward motion in the center of the cloud base.

 

[Paul Knightley]

Is this argument not the same as looking at a satellite picture, and saying "that's a mid-latitude cyclone", or "that's a hurricane"? Technically, they are the cloud features associated with those systems, but they are not actually the system per se.

Meso-scale has its own classification as size, as we all know - the term "mesocyclone" should really mean a cyclone on the scale of 1-100km. However, it's really been "pinched" to solely describe rotation within thunderstorms.

If you can't "see" a mesocyclone as such, then you can't really "see" a mid-latitude depression on a satellite picture.

 

[Mikey Gribble]

Are we seriously having this discussion? I say mesocyclone all the time. What else are we supposed to call it? I have heard virtually (no pun intended David W.) every serious chaser on here call it a mesocyclone at one time or another. We aren't the NWS and we aren't watching radar when we are talking about first hand visual accounts. I think everybody is forgetting that the purpose of language is to communicate thoughts and ideas. Nobody is getting confused when you call the storm scale rotation in the updraft a "mesocyclone". It's not like the readers at home are saying "what the hell is that, you can't see a mesocyclone in person".
If we must have a new name, I am going to throw this out there for everybody to kick around and maybe if people like it we can adopt it. How about we call it the "kundis" (pronounced koondis with a strong U).
Example - "Ohh, there's a kundis!" or "Hey Mike, that's a nice kundis"

 

[Shane Adams]

Pouncing on Shane!!!



The mesocyclone circulation extends beyond the boundaries of cloud, and consists of three-dimensional air motions...updraft, downdraft, sidedrafts, etc. The vortex can be open, closed, tilted, have varying "diameters" at different heights, twist, turn, spiral, and even be multiple-vortex.

That is awesome....I never realized it could have such a "loose" form sometimes...I always assumed it was a "standard" vertical column. That's pretty fascinating to try and visualize. Makes it easier to understand how you get those wacky, serpentine tornadoes sometimes, like the '86 MN copter video.

 

[Mike Peregrine]

That is probably one of the better descriptions I've ever heard ... and it's also likely going to affect the way I visualize what's going on in the rear flank of a storm. Would be cool to even be able to see some 3D modeling of some of these processes.

 

[Mikey Gribble]

On the same note as Shane, that is pretty fascinating. Something that seems so organized and disorganized at the same time. I had never thought of mesocyclones being as unique and one of a kind as different tornadoes, but it makes absolute sense.
Kind of off topic, but they used to have that computer simulation of a supercell on U. of Illinois site before. It was pretty cool to get to see the storm going from a tower to an organized supercell. It really helps you to visualize/grasp how these things work. It would be awesome to get to see the same kind of simulation with different mesocyclones with tracers.

 

[Terrence Cook]

I would agree that mesocyclone's are highly visible in some storms and my avatar is proof that you can visually observe and document Meso characteristics. That is pretty interesting explanation Greg, makes me think of when I hear you guys refer to a meso as "on the ground" because of how low it is in apperance, imagine the overall coverage of a meso such as that.

 

[Paul Knightley]

Yes, good description - it's like any area of low pressure - it can be organised, but at the same time, appear more disorganised, due to complex interactions.

I also like to think about mesocyclones seperately from tornadoes - I know tornadoes do form beneaths mesocyclones, but much of the time, mesocyclones do not have tornadoes below.