Highest winds possible?

[Jason Harris]

I've seen claims regarding tornado strength that it's simply not possible to get much over 300 (OR 318 for max F5) mph with the OK city tornado being the strongest officially measured at 302 by radar. And do researchers actually believe that was the strongest ever or just the one measured with that sort of precision?
http://www.spc.noaa.gov/faq/tornado/

So, what makes it unlikely to get any higher than that and what would have to change about our atmosphere to allow for even higher wind speeds?

What are the physical limits on wind speed for hurricanes and tornados?

Also, with the EF scale ending at 290 (http://www.spc.noaa.gov/efscale/19.html), how are damage surveyors and NOAA and other agencies interested in researching severe weather going to determine
when tornados strike with winds over 290? Are F-ratings suggested in addition to EF ratings anymore in the research if not in the public statements? Are weather researchers continuing to press forward with wind measurements being ever more precise with radar and other tools beyond damage surveys?
Do scientists foresee a time when a tornado warning might actually say, "definitely get below ground for this one and stay there because this tornado is producing winds of at least 250 mph!"

Well, not exactly like that, but you get the idea. Thoughts? Revelations?

 

[Glen Romine]

I've seen claims regarding tornado strength that it's simply not possible to get much over 300 (OR 318 for max F5) mph with the OK city tornado being the strongest officially measured at 302 by radar. And do researchers actually believe that was the strongest ever or just the one measured with that sort of precision?
http://www.spc.noaa.gov/faq/tornado/

It is true that researchers have tried to determine maximum possible wind speeds for tornadoes, and the necessary dynamical force balances necessary to sustain such strong vortices. I'm not an expert on all of this work, but one source (Fiedler and Rotunno, 1986, JAS) suggested a top wind speed of around 110 m/s (246 mph). There is perhaps more recent work in this area with other possible numbers.

As for the DOW radar observation mentioned above, there are a long list of caveats to the value of that number. I don't know them all, but a few would include the time length of the sample (small scale turbulence added on to the mean vortex wind), sample size, the Doppler velocity measured is not of the actual wind but some rain/debris embedded in the wind, the height of the observation (well above the ground - and that is another area of work is trying to see how winds higher up equate to wind strength closer to the ground), etc...

So, what makes it unlikely to get any higher than that and what would have to change about our atmosphere to allow for even higher wind speeds?

As touched on above, there are dynamical limits, which get very technical to try and explain.

What are the physical limits on wind speed for hurricanes and tornados?

The dynamics of these two vortices are very different, as are their scale (which is part of the difference in force balance). Hurricanes are fundamentally heat engines, so the upper limits to their intensity is tied to the warmth of the oceans an the coolness of the upper troposphere in the tropics. Kerry Emanuel, I'm sure among others, has done some work on trying to estimate maximum possible intensity of hurricanes.

Also, with the EF scale ending at 200, how are damage surveyors and NOAA and other agencies interested in researching severe weather going to determine
when tornados strike with winds over 200? Are F-ratings suggested in addition to EF ratings anymore in the research if not in the public statements? Are weather researchers continuing to press forward with wind measurements being ever more precise with radar and other tools beyond damage surveys?
Do scientists foresee a time when a tornado warning might actually say, "definitely get below ground for this one and stay there because this tornado is producing winds of at least 250 mph!"

Well, not exactly like that, but you get the idea. Thoughts? Revelations?

The EF scale is very flexible, and could conceivably offer reliable damage indicators for winds exceeding 200 mph. Take a look here:

http://www.spc.noaa.gov/efscale/ef-scale.html

Of course, the EF scale is an evolving creature, updated as better estimates become possible. Plenty of folks in the wind engineering world that are actively working on such topics.

As for warnings suggesting getting below ground, that is fairly standard advice with any tornado to seek the safest possible shelter, and getting below ground can be a good start (though not entirely safe by itself).

 

[Jason Harris]

Thanks for the input Glen. I was a bit careless with the phrasing of my questions, and I also should have noted the EF 5 allows for an upper bound 290 wind possible with structural deformation of a significant high rise greater than 20 stories destruction.
http://www.spc.noaa.gov/efscale/19.html

I'll edit that for clarity. Also, I know getting underground (basement, etc.) is already mentioned in warnings, it was just the idea that a warning might eventually get precise about the actual wind estimates with the warning. I suppose though if a warning mentioned a lower end tornado speed the public might not take it seriously and the tornado could always strengthen. But maybe even that possibility of upper and lower intensity of a tornado one day might be forecast in advance too. . . .

 

[mike scantlin]

I'm going to go ahead and say that what you are thinking is nearly impossible. For a radar to actually know ground wind speed in a tornado, it would have to be instantaneous data and even then, it would only see so low. Theres only so far you can advance, you know? With so many details and ever changing microscale conditions, I believe we are nearing the ceiling as far as short-term tornado forecasting goes. Do you get what I'm trying to say?

 

[Jason Harris]

Gotcha on the impossibility of that precise forecasting, largely speculative for future technological advances. Would be great to still hear more about this:

--

What are the physical limits on wind speed for hurricanes and tornados?

 

[Glen Romine]

Would be great to still hear more about this:

--

What are the physical limits on wind speed for hurricanes and tornados?

Jason,

I offered a reference (and number) above for tornadoes (~246 mph). Here is a link to that work which you can read for yourself:

http://ams.allenpress.com/archive/1520-0469/43/21/pdf/i1520-0469-43-21-2328.pdf

I also noted that hurricane intensity was limited by the difference in sea surface temperature, tropopause temperature and efficiency of the hurricane as a heat engine. I suggested looking into work by Kerry Emanuel. I'll specifically provide the following reference point to learn more:

http://wind.mit.edu/~emanuel/holem/holem.html

Choosing realistically observed values, you end up in the vicinity of ~ 220 mph, though this would only be possible in the warm western Pacific waters and under optimal conditions. Most hurricanes don't come close to what is believed to be optimal efficiency. The most intense storm on record was in the 190 mph wind range, so the upper range of around 220 seems reasonable based on modern atmospheric state possibilities.

 

[Jason Harris]

Thanks for following up with the links to those specific sources Glen, I'll check it out.

 

[Jason Harris]

Hello Glen,


I read through the tornado article, and I have a few questions to help clarify it for someone of my very limited knowledge of physics.

#1 Might one say that basically the tornado's intensity past a certain point causes an imbalance that cuts off its energy supply? On page 11 end of section 4: "thus, one would expect the maximum disparity between upstream and downstream conditions to occur when the vortex breakdown is positioned just above the surface [. . ] When the vortex breakdown is in this position, any attempts to make supercritical end-wall cortex more intense leads to a disparity in upstream and downstream conditions which cannot be matched. This will ultimately cause the vortex breakdown to descend to the lower surface and the supercritical flow vanishes." So, might one glean from this that a tornado can't exceed a certain intensity because it loses its energy source in the process?

#2 What exactly is the definition of an "end-wall vortex" as opposed to a "vortex aloft"?

#3 What exactly is a "vortex breakdown" and where are some pics of that? The article alludes to some pics being available where one can see this in some tornados.

#4 What are the general tendencies of wind speeds before, during, and after a "vortex breakdown"?

 

[Glen Romine]

Hello Glen,
I read through the tornado article, and I have a few questions to help clarify it for someone of my very limited knowledge of physics.

Jason, google could probably help you more than me in digging deeper on this topic, but there seems to be some confusion in your interpretation of vortex breakdown. With a strongly swirling flow, like a tornado or dust devil, where the vortex ends at the ground, the speed of the winds whirling around the vortex is controlled by the ability of that swirling flow to evacuate air out of the center (friction at the ground forces air to converge toward the central axis of the swirling flow - if not removed the vortex would not be sustained). So, along the center axis of the swirling flow - you would expect to find an updraft evacuating air, and the stronger this updraft, the faster the air can swirl. At the center of this swirling flow, the air pressure is much lower than outside the vortex (centrifugal force balanced with pressure gradient force), and to have an updraft maintained in the central core of the vortex, the vertical gradient in perturbation pressure must point upward. If the lowest pressure in the vortex was closer to the ground - which can happen if the flow is swirling faster near the ground than aloft (e.g., as can develop with supercritical flow), the vertical perturbation pressure along the central axis of the swirling flow can be downward directed, leading to a downdraft developing toward the point in the vortex where the flow is swirling most rapidly. This downdraft poking down the central axis of the vortex leads to vortex breakdown, and subcritical flow. Interesting things can still happen in subcritical flow - such as suction vortices where the flow can again well exceed the thermodynamic limits (the latter is bound by the maximum possible updraft strength, which in the atmosphere is limited maximum possible buoyancy).

Perhaps others will want to chime in on some of your other questions.