How many mesocyclones could exist in a supercell?

[Andrea Griffa]

Starting from this radar capture coming from the Greensburg Supercell of may 23th 08, I think we should discuss a little bit about the "common" definition of supercell:

A supercell is a thunderstorm that is characterized by the presence of a mesocylone: a deep, continuously-rotating updraft.

I think, as I saw it from the radar and I saw many times with my eyes, a supercell could contain more than one or two mesocylones.
First of all, often, if the supercell is cyclic you can see the occluded mesocylone and the new one forming. Anyway it can happen that you see other updrafts feeding the storm, especially if it has HP features.

Moreover it sounds a bit silly, to me, to think that an ypothetical supercell with a transverse diameter of 60-70 km is getting feeded by only one meso (for example the Paducha-Benjamin,tx supercell of may 13 2005 or the Greensburg supercell of may 4th 2007).

If you see this radar capture, you could see at least 3 different separate hooks that correspond with 3 rotating updrafts.

Any thoughts about that?

 

[Rob H]

It might be arguing semantics, but that definition doesn't explicitly state that there can only be one mesocyclone; just that a mesocyclone is present. I don't have time to dig into the archived level 2 velocity at work, but the Wikipedia image shows the "main" Greensburg meso with what I'm assuming is the occluded meso to the west:

I think it would be worth digging into whether those appendages really are caused by separate updrafts. A meso by definition is 2-10km in size, so it doesn't surprise me that this could feed a storm with reflectivity over a 60-70km range. The upper winds can really carry precip when you get in the 80kt+ jets. I've seen storms that have multiple tornado-producing updrafts, but eventually one updraft dominates and takes over. An interesting ancillary question is how strong of mesos/tornadoes can you have simultaneously in a storm and will one always be dominant?

 

[Patrick Marsh]

Ultimately, it depends on your definition of a thunderstorm. Is it a single updraft/downdraft pair? Is is a collection of updraft/downdraft pairs? Is it a system of updraft/downdraft pairs working in concert with one another? Once you answer this question, you can then answer the question posed.

 

[Andrea Griffa]

It might be arguing semantics, but that definition doesn't explicitly state that there can only be one mesocyclone; just that a mesocyclone is present. I don't have time to dig into the archived level 2 velocity at work, but the Wikipedia image shows the "main" Greensburg meso with what I'm assuming is the occluded meso to the west:

It could be Robert; at any rate if the definition says that it contains a mesocyclone, it seems that it should contain only one. By another point of view this defibition doesn't implicate that the phrase "it contains a mesocyclone" has necessary to exclude other mesocyclones or other updrafts; I mean the important thing is that contains at least a meso, no matter how many.

I think it would be worth digging into whether those appendages really are caused by separate updrafts.

I think so, as those are separate hooks and only a rotating updraft is able to wrap around precipitations in order to create a notch with an appendage like those.

 

[Andy Jackson]

Starting from this radar capture coming from the Greensburg Supercell of may 23th 08, I think we should discuss a little bit about the "common" definition of supercell:

I think, as I saw it from the radar and I saw many times with my eyes, a supercell could contain more than one or two mesocylones.
First of all, often, if the supercell is cyclic you can see the occluded mesocylone and the new one forming. Anyway it can happen that you see other updrafts feeding the storm, especially if it has HP features.

Moreover it sounds a bit silly, to me, to think that an ypothetical supercell with a transverse diameter of 60-70 km is getting feeded by only one meso (for example the Paducha-Benjamin,tx supercell of may 13 2005 or the Greensburg supercell of may 4th 2007).

If you see this radar capture, you could see at least 3 different separate hooks that correspond with 3 rotating updrafts.

Any thoughts about that?

Yeah, watch the radar loops they add some context to the discussion:
Greensburg

Velocity:
velocity

I'd say the meso or center of the storm remains constant after the storm organizes yet there are clearly different vortex signatures developing and merging with the center. This is the cyclic nature of supercells I believe correct me if I am wrong.

 

[Charles Kuster]

Ultimately, it depends on your definition of a thunderstorm. Is it a single updraft/downdraft pair? Is is a collection of updraft/downdraft pairs? Is it a system of updraft/downdraft pairs working in concert with one another?

I think Patrick stated it perfectly. For this question, I will assume that a thunderstorm/supercell can consist of a system of updraft/downdraft pairs working in concert. With this in mind, I would say that a supercell could have two (at max three) mesocyclones at a single moment in time. I would also say that this only applies if an occlusion is occurring. If you have two separate mature mesocyclones I would say that you are dealing with two separate supercells (perhaps two supercells merged at some time). One could argue then, that a supercell only consists of a single updraft/downdraft pair, but I have always considered the example below to be two updraft entities.

A supercell that occurred on June 15, 2009 in southern Nebraska comes to mind when I think about this question. This storm definitely had two separate mesocyclones at one time. The first meso began to occlude at 8:14pm CDT and I could see the start of a new mesocyclone at this time. About 6 minutes later the original meso finally produced a tornado while the second meso spun harmlessly to my north. The radar also clearly shows a double hook structure.

This shows 2 mesocyclones present at the same time. Meso #1 (hard to see, but is located at back left) produced the tornado. Pic taken at 8:25pm CDT and is looking WNW.

Corresponding radar image.

http://i36.tinypic.com/2s8hh0k.jpg (Initial formation of meso #2. Pic taken at 8:14pm CDT and is looking NNW.)
http://i47.tinypic.com/20a9ws8.jpg (Tornado associated with meso #1. Meso #2 was located to the north of my location at this time. Pic taken at 8:21pm CDT and is looking WNW.)

 

[Andrea Griffa]

I found this interesting article about multiple mesocyclone supercell:

http://cat.inist.fr/?aModele=afficheN&cpsidt=2383492

Pulsating downdrafts periodically invigorate the storm and the gust front never occludes, thus allowing the main updraft to persist for a prolonged period of time. The storm's intensity is also maintained by frequent updraft mergers.

 

[Andrea Griffa]

I've got another supercell example with multiple mesocylones. The supercell was the huge Benjamin-Crowell, Tx HP supercell of may 13 2005.

I remember differents updrafts feeding the supercell and a main huge meso.

Here are some pics and the radar images.

 

[Paul Knightley]

I would imagine that quite a few 'supercells' are actually somewhat multicellular at times - the thunderstorm spectrum which is often quoted as going from single cell through multicell to supercell is rather misleading, IMO, as I've seen many supercells which have multicellular characteristics at times, especially those towards the HP end of the spectrum. The simple fact is, I believe, that the term 'supercell' describes quite well the behaviour of updraughts with mesocyclones, but perhaps is not such a good term for describing the thunderstorm as a whole.

 

[William Reid]

I suspect that most healthy Great Plains supercells are typically characterized by two or three (and sometimes more) low-level mesos in various stages of maturity. I think of the supercell as the broad "mother" (or "mothership"), which spawns (or would it be more accurate to say: "is sustained by"??) these mesos.

It might be helpful to make a comparison of cyclonic circulations at larger and smaller scales. A long-wave trough gives rise to individual short waves or "vort maxes" and individual surface low pressure systems. A tornado gives rise to individual "suction-spot" vorticies. A tornado cyclone is sometimes associated with more than one tornado at the same time. It follows that a broadly rotating "supercell" would be home to more than one smaller "meso" circulations.

Now, getting back to the definition of a supercell offered here:

"A supercell is a thunderstorm that is characterized by the presence of a mesocylone: a deep, continuously-rotating updraft."

I would quibble with the first five words! California is privy to plenty of supercells, though weak for the most part compared to those on the Plains. Many of our supercells are low-topped and entirely without thunder, even many of the tornadic supercells. So, a supercell is not necessarily a thunderstorm.

William Reid
Westlake Village, CA

 

[Scott Olson]

I agree that 3 is certainly possible with the most agreeable definitions of what a mesocyclone is and what a thunderstorm is. Whether two new mesocyclones, two occluding or some combination herein. Whether 4 or 5 or more is possible, would probably need to be studied and may need DOW data to identify. Of course, this number changes as you change the definition of mesocyclone/thunderstorm. There are also mesovorticies and misocyclones, which do share some characteristics.

 

[Greg McLaughlin]

I witnessed 4 simutaneous mesocyclones on a supercell in Kansas on September 15th. Each meso was in a different stage of its life cycle, however each meso had persistent rotation and rfd cuts. I have never seen anything like this before, however I am confident in what I saw.

 

[ChristianTerry]

I have never seen a tornado, but in May 2000, while I was living in Dallas, I saw at least two mesos on different parts of the storm.

 

[Greg McLaughlin]

Adding to my previous post, the supercell on Sept 15th was riding along an outflow boundary. It is my belief because of the storm's interaction with this boundary it was able to develop four mesocyclones simutaneously. Like I said before, each meso had it's own rfd cut and inflow bands. The cluster of low-level mesocyclones arced from west to north to east with a void to the south due to the main rfd gust front wrapping into and under the main updraft.

What was interesting in this case was the western low-level meso in the group produced the first tornado. This was somewhat of a surprise to me as I originally thought the meso had occluded to the point it was completely cut off from the moist inflow.

About 10-15 minutes after the first tornado, the meso to the east became the dominant meso as it had the clear path to the moist air to the south and east. This meso quickly tightened and produced periodic, brief, multi-vortex tornadoes over about a 10 minute period.

This event definitely deserves a graphic illustration, and I plan to render one soon.

Also, when it comes to how many mesocyclones a supercell can have, I suggest reading this article on an event in Texas: http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469(1997)054%3C2387%3ATNSONT%3E2.0.CO%3B2

While this is considered a non-supercell event, it still illustrates how a thunderstorm can generate several organized vorticies (in this case non-supercell tornadoes) at once. Hypothetically, I believe a supercell would be capable of producing as many low-level mesocyclones and tornadoes given the right conditions.

 

[Jeff Duda]

I
It might be helpful to make a comparison of cyclonic circulations at larger and smaller scales. A long-wave trough gives rise to individual short waves or "vort maxes" and individual surface low pressure systems. A tornado gives rise to individual "suction-spot" vorticies. A tornado cyclone is sometimes associated with more than one tornado at the same time. It follows that a broadly rotating "supercell" would be home to more than one smaller "meso" circulations.

Amen to that. See:

"Big whirls have little whirls,
That feed on their velocity;
And little whirls have lesser whirls,
And so on to viscosity."

Now, getting back to the definition of a supercell offered here:

"A supercell is a thunderstorm that is characterized by the presence of a mesocylone: a deep, continuously-rotating updraft."

I would quibble with the first five words! California is privy to plenty of supercells, though weak for the most part compared to those on the Plains. Many of our supercells are low-topped and entirely without thunder, even many of the tornadic supercells. So, a supercell is not necessarily a thunderstorm.

I would suspect a satisfactory edit of that definition would be to substitute "moist convective updraft" for "thunderstorm". You need the gravitational instability to get the twisting and strecthing to produce the rotation, but some storms are not tall enough to get above the freezing level, get charge separation, and result in lighting/thunder. But certainly, such short storms can rotate.