mesocyclone tornado Vs. non-mesocyclone tornado

The only discrepancy that I am trying to clear up, is whether or not a tornado can be born from a non-mesocyclone thunderstorm? A friends opinion was that anything non-mesocyclone born was to be categorized as landspout or gustnado. I figured that there have been atleast a few major tornados that were not "birthed" from mesocyclones.

Just a little confused about the "official" point of view. Especially since the distinction between landspout and tornado is usually quite obvious!

comments....?
 
I think that waterspouts that form in the FL Keys, would answer that question for you, but only to a small extent :), but at the same time, I'm open minded about this one, because I feel that some very weak tornadoes have indeed spawned from non-mesocyclonic thunderstorms, but I've not heard of any significant tornadoes being spawned from them :)

There is a good possibility that there has been an occasion or 2, where a significant tornado has spawned from a non-mesocyclonic storm and I would be interested to hear of anyone that knows of any tornadic events of this nature :)

I hope that in some small way or another, that this is of some help to you :)

Willie
 
It is really a question of semantics, but if you want to go by definitions your friend is wrong IMO.
Nonmesocyclone tornadoes are pretty common and they can become quite strong. They typically result from vortex stretching. Vorticity along boundaries can be ingested into an updraft and stretched creating a tornado (or landspout depending upon what you want to call it) due to the conservation of angular momentum. Steep low level lapse rates can also cause landspout type tornadoes through stretching. Misocyclones along boundaries in Colorado cause lots of landspout type tornadoes. I am sure a lot of other people can give you a better answer, but that is my shoot from the hip quick reply. Here is a link to one of Davie's papers on it.
http://www.nwas.org/ej/cardav/
 
It is really a question of semantics, but if you want to go by definitions your friend is wrong IMO.
Nonmesocyclone tornadoes are pretty common and they can become quite strong. They typically result from vortex stretching. Vorticity along boundaries can be ingested into an updraft and stretched creating a tornado (or landspout depending upon what you want to call it) due to the conservation of angular momentum. Steep low level lapse rates can also cause landspout type tornadoes through stretching. Misocyclones along boundaries in Colorado cause lots of landspout type tornadoes. I am sure a lot of other people can give you a better answer, but that is my shoot from the hip quick reply. Here is a link to one of Davie's papers on it.
http://www.nwas.org/ej/cardav/

This is not directly related, but using the same principle of vorticity stretching explains why cyclogenesis occurs east of the Rockies (or any major height change for that matter) and cyclolysis for a parcel with vorticity moving east into the Rockies. The best way to picture this is in the world of ice skating. When an ice skater is making circles and wrap their arms inward their tangental velocity increases. If the top of a parcel with some volume is held constant while it moves over the Rockies the bottom of the parcel will either be pushed upwards. If the pressure is kept constant, then the parcel will increase in width. When the volume is stretched in the vertical the width will decrease.

In thunderstorms if an area of vertical vorticity is turned upwards into the vertical and stretched (vertical becomes horizontal) the horizontal vorticity will increase. The same theory (streamline vorticity and stretching) has also been used to explain tornadogenesis in a weak mesocyclone in which the inflow has vertical vorticity.
 
A valid point was brought up about vorticity stretching being involved in both cases, so there's a related mechanism. Also, strong tornadoes *do* occur without a mesocyclone, there have been F3 landspouts and even firewhirls as well as strong tornadoes produced by mesovortices. Additionally, gustnadoes may evolve into a bona fide tornado.
 
I was under the understanding that the meteorological world has been referring to non-mesocyclone born nadors as landspouts. Nothing to do with intensity, just name.
 
Like I said in my earlier post, it is really a question of semantics. The AMS definition of a tornado (off the tornado faq page) is...
"a violently rotating column of air, pendant from a cumuliform cloud or underneath a cumuliform cloud, and often (but not always) visible as a funnel cloud."

There are a lot of people that have a lot of different opinions on exactly what constitutes a tornado, but IMO it doesn't matter whether a tornado is born from a parent mesocyclone or not if you want to go strictly by the definition. Both meet the criteria. I would call it a landspout too, but the reason I would specify it as a landspout is because of accuracy, due to the inherent weakness (in most cases) of landspouts vs. what a supercell tornado CAN do. Besides, if Davies is going to call them "tornadoes" then who am I to disagree.
 
Ah, this is always an interesting topic!

IMO, the landspout is redundent, as it is just a tornado, albeit not beneath a mesocyclone.

A tornado is a tornado, independant of what "type" of updraught is above it. Updraught rotation dynamically increases the strength of the updraught, and so would tend to favour stronger tornadoes beneath. However, some strong tornadoes have occurred which have not formed underneath mesocyclones.

A broader question should be "how important is thunderstorm rotation with tornadogenesis?" Obviously, quite a lot of tornadoes form beneath mesocyclones, and the atmosphere around the supercell is pretty rich in vorticity. But if mesocyclones were the main reason for tornadogenesis, then they shouldn't form elsewhere!
 
Ah, this is always an interesting topic!

IMO, the landspout is redundent, as it is just a tornado, albeit not beneath a mesocyclone.

A tornado is a tornado, independant of what "type" of updraught is above it. Updraught rotation dynamically increases the strength of the updraught, and so would tend to favour stronger tornadoes beneath. However, some strong tornadoes have occurred which have not formed underneath mesocyclones.

A broader question should be "how important is thunderstorm rotation with tornadogenesis?" Obviously, quite a lot of tornadoes form beneath mesocyclones, and the atmosphere around the supercell is pretty rich in vorticity. But if mesocyclones were the main reason for tornadogenesis, then they shouldn't form elsewhere!

Supercells seem to produce the vast majority of intense tornadoes, but it's not clear what percentage of all tornadoes are produced by supercells. The importance of the mesocyclone to intense tornadoes is probably a result of impact of the mesocyclone on the distribution of vertical velocity and vertical vorticity around the storm.

Supercells usually have stronger low-level updrafts than other storms in similar thermodynamic profiles owing to pressure perturbation effects with the mesocyclone. It's not completely clear how environmental factors modulate tornadogenesis in supercells, though we've got lots of climatological evidence that favors moist environments (possibly related to buoyancy characteristics of RFD) with strong low-level shear (stronger mesocyclone closer to the ground which enhances low-level stretching?). Other factors, such as cloud drop/particle distribution, may explain some of the variability not captured by the other parameters.

All you really need for a tornado is a sufficient updraft (may not be particularly strong) and some source of vertical vorticity for the updraft to concentrate and stretch. I think the bigger problem with tornadoes is how we perceive them. Almost all of us have a different picture in our mind when we hear the word "tornado". However, not all tornadoes are created equal, and simply knowing of a "tornado" doesn't say much for the actual threat to life and property.

Rich T.
 
Thanks for the reply Rich - I agree that the supercell/mesocyclone is the bearer of most of the stronger/violent tornadoes - I think this may have skewed research (at least, in the past) towards these events, logically because these cause the most damage.

Coming from the UK where (thankfully) we only very rarely see intense tornadoes (but frequently have damaging tornadoes), research has been skewed towards non-supercell tornadoes (although quite a few may be associated with supercells!). The trouble we have is with the lack of Doppler radar information, no real "season", and little chance to chase storms because of too much traffic and too much moisture (most of ours seem to be rain-wrapped). However, this is off-topic!


I have wondered whether it is the presence of a supercell per se, or just a strong low-level mesocyclone, which helps the tornado formation process...is it possible to have a strong low-level mesocyclone in the absence of mid-level rotation?
 
I had always thought this was impossible due to their position at the gust front. How would it happen? What kind of sustained updraft would be available to make it possible?

What if a "gustnado" (horrible term - use eddy-whirlwind instead!) forms along the leading edge of the RFD, and then gets spun-up?
 
Landspout - [Slang], a tornado that does not arise from organized storm-scale rotation and therefore is not associated with a wall cloud (visually) or a mesocyclone (on radar). Landspouts typically are observed beneath Cbs or towering cumulus clouds (often as no more than a dust whirl), and essentially are the land-based equivalents of waterspouts.

That is the NWS NOAA definition of a landspout, it has been for some time now.
Their has definitely been a few very damaging Landspouts throughout the years. Particularly those that hit populated areas. I think the common consensus is that landspouts are just weak, this is not true. You do not want to be around one when it hits.
 
What if a "gustnado" (horrible term - use eddy-whirlwind instead!) forms along the leading edge of the RFD, and then gets spun-up?

I always thought that GUSTnadoes - by their very name - only formed on the leading edge of a gust front. That is how they are characterized - as ground-level eddies that form on the leading edge of outflow from a thunderstorm. Given this description - I don't think that true gustnadoes can be confused with vortices that form on an RFD boundary but I don't know how to categorize the latter, either.

I guess my problem is that for gustnadoes to form they have to be on a gust front - and if they are on a gust front that precludes any tornadic/tornado possibilities as the parent storm has probably already been undercut and is a big windy mess.

Landspouts and waterspouts must fall under the heading of tornadoes according to the NWS definition of the term because they are underneath a cumuliform cloud. As this is the only "official" definition of the word TORnado - there is a pretty large catchment area for what is considered a tornado.

Therein lies one of our problems in defining these phenomena. Due to the official definition being so broad, there is a necessity to "split up" what is considered a tornado into many smaller categories - hence landspout, waterspout, tornado, non-mesocyclonic tornado, non-supercell tornado etc. etc. I think so far the handiest category for me has proved to be tornado vs. non-mesocyclonic tornado - as both can be and have been formed by tornadic supercells.

KL
 
Do you think, though, that research should try to find out how a tornado actually develops beneath an updraught, but in the first instance, put the type of updraught to one side - there must be a chance that the actual process of getting tornadogenesis to occur is the same, whatever the nature of the updraught above (i.e. conservation of angular momentum, etc). Although the type of updraught is probably very important for many aspects of a tornado's character, the actual formation might be the same.

Just a thought anyway!

p.s. on a personal note, I think the word 'tornado' should suffice...it is the same phenomenon, whatever the type of updraught, and whatever surface it moves over.
 
i always understood gustnadoes to be along any thunderstorm-wind gust, whether rfd, gust front, or anything else. it doesnt have to be a gust front to be a gust does it? just my peices of copper.
 
Much of the reason for this taxonomy is to help the forecasters responsible for issuing warnings to better understand the physical processes behind the formation and maintenance of the vortex. If I'm sitting at a radar desk and I hear a chaser say "tornado" - my first question is whether the chaser is seeing a classic supercell tornado with RFD, clear slot, under a large updraft base, etc., or is it a "landspout" along a flanking line towering cumulus, or a spin up on surging outflow ("gustnado"). The answer will make a big difference on whether I'm worried about a violent, long-track tornado or something weaker and more transient.
 
That's a fair point Kevin - I'm just thinking that in the wider view of why tornadoes form, there may well be some connection between the various modes.
 
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