An extended discussion with a reader


Posted: 03 April 2009 Updated: whenever. See the main text of the essay for the usual caveats.


Recently, I had the following email exchanges with a reader of my essay What is a tornado? I thought it was a thoughtful and stimulating discussion so I'm sharing it here. It takes the form of a series of emails from Mr. Ben Bosher, with our responses - my contributions are in a different font. A light editing of these to correct typos has been done. I hope you will find this exchange as interesting and stimulating as I have. Mr. Bosher has agreed to having this exchange posted.

 

email and responses #1

Having read your essay entitled, "What is a Tornado?", and you being open to discussion of the topic, I wish to discuss the following points...

1) Damage, or the potential to cause damage, should not be a criterion used for defining a tornado. As you have said, "a tornado is a process". Thus only the process and it's purpose should be defined. Its purpose is to change some condition(s) of the atmosphere, not to be destructive. Damage is merely an unfortunate side-effect. Surely no one would see a tornado which caused no damage along a path on which damageable fauna and properties were located and say it was not a tornado. They would say it was a non-destructive tornado.

But a tornado's near-surface winds must be strong enough to have the POTENTIAL to cause damage. If those winds are below that threshold, then it should not be a tornado. There might be a near-surface vortex airflow, but if the winds have no potential to cause damage near the surface, then I'm pretty confident most scientists would agree that the vortex is NOT a tornado.

I was careful to point out that if there is nothing in the path of this vortex to be damaged, if its wind speeds have the potential to produce damage, it would still be a tornado.

As to a tornado's purpose ... no human being yet knows the "purpose" for tornadoes.

2) Whether or not it is in contact with a surface should not matter as that would require it to be of such an intensity (at least at the surface) as to be beyond some lower threshold. A tornado which does not "reach the surface" does not do so because there is nothing for it to do at that level which would fulfill its purpose.

Is it correct for me to infer from this that you believe that you KNOW the purpose for a tornado? If so, you apparently failed to specify that purpose. Without doing so, this comment is not useful in defining what a tornado is.

Also, have meteorologists determined if tornadoes ever actually touch the surface or do they only reach down to (or up from) a point close to it?

In principle, right directly at the surface (at a height of precisely zero), the windspeed must equal zero - hence, in this abstract sense, the tornado (i.e., the winds associated with the vortex) don't quite reach the surface - it must come VERY close, however. Those winds just above a height of exactly zero can become quite strong - strong enough to rip grass out of the ground, for instance, and cause soil particles to become airborne.

 

email and responses #2

But a tornado's near-surface winds must be strong enough to have the POTENTIAL to cause damage.

Why? Is it the tornado's purpose to damage things which may lie in its path?

The purpose of a tornado is irrelevant to the definition. Whatever its purpose might be, any meaningful definition of a tornado would surely require the vortex to be capable of damage, whatever might or might not be in its path.

If those winds are below that threshold, then it should not be a tornado.
 
That statement contradicts a portion of your own tentative definition.  That portion being, "This is without regard to"... "the intensity of the phenomenon beyond some lower threshold."

Not at all. The key phrase is that the intensity must equal or exceed a lower threshold, that being the point at which the winds have the potential to do damage.

There might be a near-surface vortex airflow, but if the winds have no potential to cause damage near the surface, then I'm pretty confident most scientists would agree that the vortex is NOT a tornado.

I agree, they would not.  However, most scientist once agreed that the Earth was flat but their consensus on that did not make it so.

I agree that scientific consensus isn't necessarily correct, but ... see my essay here:

http://www.flame.org/~cdoswell/How_science_works.html

If you choose to disagree with scientific consensus, you should offer up your alternatives and provide evidence for them. Disagreement is easy - confirmation of your alternative ideas requires effort. Your example is a case where the consensus changed when the evidence was irrefutable. But we're not discussing such a problem - OUR topic is a matter of definition. You can argue with the value of a definition, but definitions are neither right nor wrong. They are simply a way to classify things. Some classification systems might be more useful than others, but they can't be "proven" to be incorrect logically by the accumulation of evidence. In effect, a definition is a postulate. You can disagree with it but you can't show that it was "wrong" by some experiment.

In the case of my definition of a tornado, since you're not claiming to know the "purpose" of a tornado, you haven't provided any meaningful alternative way to define a tornado. You COULD propose that if we can determine the dynamical instability that results in intensification of the vortex, then any vortex that intensifies as a result of that instability could be argued to be "a tornado" ... but ... an infinitesimally weak vortex that does not intensify to finite intensity would NOT be a very satisfactory member of that class. Once an intensity level is mandated, then arbitariness becomes inevitable in the definition of the phenomenon.

I was careful to point out that if there is nothing in the path of this vortex to be damaged, if its wind speeds have the potential to produce damage, it would still be a tornado.  

Yes, you did.  However, causing damage is something it may have the potential to DO but could never be one of a set of characteristics which define what it IS.  Damage, when it occurs, is merely an unfortunate side-effect of the tornadic process.

Sorry, but you continue to miss the point. I'm not saying that damage is necessary - I'm talking about the CAPABILITY to do damage. Indeed, damage is an unfortunate side-effect, but I've been careful to avoid saying that damage is necessary in the definition. Otherwise, tornadoes that do no damage would not be tornadoes, which is an unacceptable version of any reasonable definition.

Is it correct for me to infer from this that you believe that you KNOW the purpose for a tornado?  If so, you apparently failed to specify that purpose. 

Of this much I am certain... it is to right some atmospheric imbalance not to destroy flora, fauna, Humans and their properties.  If there existed nothing on the surface of the Earth for a tornado to potentially damage, the tornado would still be the same.  Thus, the potential to cause damage, is irrelavant to defining what a tornado IS.

Your logic here continues to be flawed in the same way. I agree that the existence of this vortex is to respond to some atmospheric "imbalance" - at the moment, science has no clear ideas regarding the nature of that imbalance. However, a weak vortex in response to a weak imbalance would not generally be considered to be a tornado. The imbalance must reach a point where the growth rate of the disturbance intensity becomes large in response. A weak vortex would not satisfy that requirement. Are you aware of normal mode instability theory?

Also, I repeat as in my previous e-mail to you, that a tornado should not have to reach near-surface level in order to be a tornado. If one does not reach that level it is simply because there was nothing for it to do at that level to fulfill its purpose.

Nonsense. It's perfectly acceptable to restrict our definition to those vortices that attain some threshold intensity near the surface. Non-tornadic convective vortices that fail to produce potentially damaging winds near the surface (although they may do so aloft) happen frequently. Despite the likelihood that they also likely have some similar "purpose" to a tornado, they simply fail to meet a threshold intensity near the surface.

You apparently object to the imposition of arbitrary thresholds. I understand that and even sympathize with it to a certain extent. But arbitrary thresholds are imposed all the time in science. So long as we understand their arbitrary nature, it isn't much of an issue. When we are talking about quantitative differences and not dynamical differences, thresholds are inevitable.

When we understand the physical instability that results in intense vortices, we still will have to deal with quantitative thresholds. Are you familiar with baroclinic instability theory? We understand the "purpose" of extratropical cyclones (ETCs) to a significant degree, but not every center of cyclonic relative vorticity on the synoptic scale would be considered an ETC. If substantial growth in intensity of the vortex occurs as a result of various forms of instability, *then* the storm qualifies as an ETC.

What's your background? Your questions and notions are interesting, even if we continue to disagree about my definition.

 

email and responses #3

What I have been saying is ... the capability to do damage is not a characteristic which clarifies what a tornado with that capability IS.  Such would be appropriate for an essay on "What are the Capabilities of a Tornado?"  However, it is obvious, both from the title and content of your essay, that you seek a definition which would make it possible to better determine which atmospheric vortices should properly be classified as tornadoes.

That's true.

It is possible for a tornado to form, travel at near-surface level along its path and then dissipate, in an environment insufficient during its lifetime to ever bring it to such intensity that it would be capable of doing damage even to the most easily damageable of objects in its path.  Such a tornado would, no doubt, be at the extreme weak end of the spectrum and thus also of the most extreme rarity.  Nonetheless, such a tornadic event IS possible but by your definition it would not be a tornado.  However, it should definitely be identified as tornado.

I think we're going to have to agree to disagree about this. A vortex incapable of doing damage would not be considered a tornado by virtually anyone in the field. It might be called a "proto-tornado" or an "incipient tornado" but without intensifying to the point where it begins to be capable of doing damage, the processes leading to its development are too weak to be worth considering. How would we observe such a vortex? By what means would we even know it was present? If such things are possible, and I can't deny the logical possibility of such, they might be very numerous but of no significance and predominantly undetectable.

The other thing I have been saying is ... the vortex should not have to span the distance between the base of a deep convective cloud (or some level within it) and the near-surface level in order to be a tornado.  Whether or not it can "reach the ground" is also irrelevant to what it IS.

Again, I think we're going to have to agree to disagree, here. The ability of an intense vortex to reach the surface is a critical part of why we study them in the first place. If "tornadoes" NEVER did damage at the surface, then they would be mostly an intellectual curiosity, like mammatus cloud formations. There would be little reason to support the scientific research if they had such little impact.

A tornado should be considered as ... any vortex occurring in association with a deep convective cloud due to the process(es) taking place within such a cloud and its near environment.
 
By that definition, the vortices associated with mesocyclones, tornado cyclones, suction vortices, satellite vortices, flanking line tornadoes, landspouts, waterspouts and funnel clouds should all be considered tornadic vortices.  Gustnadoes I'm still not certain about.  Dust devils, definitely not.

Once we have a clear understanding of what role tornadoes play in the atmosphere (the "purpose" for tornadoes), then we can move toward a more dynamical definition, along the lines you're suggesting. But I'm confident we will continue to have more or less arbitrary additional criteria, in order to confine our scientific attention to those phenomena that are detectable and are intense enough to have societal impact.

As for my background, I am self-taught in meteorology.  From libraries and the internet, I have studied everything I could find pertaining to meteorology in general and severe weather phenomena in particular.  For the past 23 years, I have studied to the fullest extent as many severe weather events in my local area as my time and resources would allow (this includes questioning witnesses).

So I'm assuming you're unfamiliar with linear and nonlinear dynamics, including various instability theories and normal modes. I'm not denigrating the effort you've made for 23 years, but when you lack certain elements in your background, it makes certain types of reasoning useless in our interaction.

 

email and responses #4

I think we're going to have to agree to disagree about this.
 
I understand not everyone sees things from the same point of view.  Of course, we can agree to disagree. =)
 
A vortex incapable of doing damage would not be considered a tornado by virtually anyone in the field.
 
I agree, they would not consider it as such.
 
It might be called a "proto-tornado" or an "incipient tornado" but without intensifying to the point where it begins to be capable of doing damage, the processes leading to its development are too weak to be worth considering.
 
All things are worth considering, and studying to the fullest extent.  The reason(s) why such a "tornado" never intensified to the point where it begins to be capable of doing damage might reveal something important.  Who knows what light knowledge from a seemingly insignificant thing might shed on a thing of great significance? Such has happened many times in the past.
 
It is an unwise leader (meteorologist) who does not consider the advice (knowledge) of  "lessers" (to use one of your terms, "proto-tornadoes") in matters of great importance (tornadic events).  -  Modified Old Chinese Saying
 
How would we observe such a vortex?  By what means would we even know it was present?
 
Such a vortex, at present, would of course be difficult to detect and study but then so were such things as atoms, microscopic organisms, and even mesocyclones many years ago.
 
If such things are possible, and I can't deny the logical possibility of such, they might be very numerous but of no significance and predominantly undetectable.

One possible significance could be in the combining of two or more of them.  Such as when two tornadic vortices combine. Another could be in why they fail to acheive damage potential intensity.
 
Some future technological advancement could make it possible to detect and study them.
 
Again, I think we're going to have to agree to disagree, here.
 
Of course. =)
 
The ability of an intense vortex to reach the surface is a critical part of why we study them in the first place.  If "tornadoes" NEVER did damage at the surface, then they would be mostly an intellectual curiosity, like mammatus cloud formations.
 
I'm saying some tornadoes could lack damage potential, not all tornadoes.  I'm also saying the potential to cause damage or lack of that potential is not a characteristic of what a thing IS. It is a capability some tornadoes may have but others may not.
 
There would be little reason to support the scientific research if they had such little impact.

There would be, perhaps, little "urgent" reason to study such tornadoes since they would never cause damage or take lives. However, study of such harmlessly weak tornadoes may somehow reveal some important clues about the ones with damage potential.  Again, who knows what light knowledge of even an insignificant thing might shed on a thing of great significance?
 
Once we have a clear understanding of what role tornadoes play in the atmosphere (the "purpose" for tornadoes), then we can move toward a more dynamical definition, along the lines you're suggesting.
 
I'm going to place my bet on something very similar to the following:
 
The purpose of a tornado is that of its parent deep convective cloud (of which it is merely a small part thus its purpose is one and the same).  That purpose (being the same for all storm modes*) is to restore such a degree of atmospheric stability locally as is within the capability of its parent DCC.  The tornado itself being indicative of both a more intense, better organized DCC and a need for the DCC to pursue its purpose below its base down to some lower level (at times even to near-surface level).
 
Sometimes, a thing is far more simple than some of us choose to believe.
 
*Different storm modes are the result of instability variations in the pre-storm, and on-going storm, local environments.
 
But I'm confident we will continue to have more or less arbitrary additional criteria, in order to confine our scientific attention to those phenomena that are detectable and are intense enough to have societal impact.

We will. At least for the time being.
 
So I'm assuming you're unfamiliar with linear and nonlinear dynamics, including various instability theories and normal modes.  I'm not denigrating the effort you've made for 23 years, but when you lack certain elements in your background, it makes certain types of reasoning useless in our interaction.

I am familiar with them.  However, I tend to have a bit of an uncommon/unusual view of things.