Timmer Aurora Intercept

[Jeff Duda]

I'd love to see the results from the CLOVER work...I'd love to see what kind of vertical velocities they were measuring in concert with the horizontal winds.

 

[John Peters]

Since this topic reminded me, figured I'd might as well bring it up here. I found/find it interesting that in their intercept, they mention measuring 138.8 mph winds. Given the logistics that I recall, and by watching their video as well as reliving the experience through mine; it appears to be fairly obvious to the untrained eye that their intercept occurred while the tornado was still much weaker than it was about to become. That being said, the tornado was only estimated to have winds between 111 & 135 mph at its peak (per Hastings Damage Survey). Before you start with the yeah buts, I realize the rating is based per the damage caused by the tornado; that being said, in this case I feel the tornado hit the house while at, or very near its peak strength, and IMO it was certainly stronger when it hit the house, than it was earlier on when it hit the TVN vehicle. This has me wondering, first and foremost is the TVN vehicle accurate in measuring wind speed? If so, doesn't this raise some serious questions about how well the "estimated wind speeds" of the EF scale match the actual wind speeds occurring inside tornadoes? Also at what point will damage surveryers begin to look past the fact that there might be no "damage indicators" and when available, rate tornadoes by the actual measuerd wind speeds from inside the vortex?

you create inconsistencies in the tornado database here, since a very very small fraction of tornadoes will every have direct interior wind measurements. With regard to damage indicators, nearly every tornado will produce them to some degree, and one can maintain a certain degree of database consistency.

 

[Dustin Wilcox]

you create inconsistencies in the tornado database here, since a very very small fraction of tornadoes will every have direct interior wind measurements. With regard to damage indicators, nearly every tornado will produce them to some degree, and one can maintain a certain degree of database consistency.

I don't see how it would exaggerate the vast current inconsistencies much at all. Say 1 in 50 tornadoes is sampled by a supported instrument, and that instrument recorded a strength equivalent to an EF-3 tornado, meanwhile the lack of "damage indicators" only allows the tornado to be rated EF-0; I don't see how going ahead and giving the tornado a rating of EF-3, based on good solid data creates inconsistencies, in fact, I'd say it's just the opposite and if anything eliminates inconsistencies; though given the small percentage, not enough to help matters any. That being said, I understand it is by no means a reliable overall tornado strength database, but serves more as a reliable tornado damage database. As it is, I still question the EF wind strength estimates of at least the Aurora tornado; my initial post was more geared towards not necessarily the idea that tornadoes should be ratted based on measured winds speed, (Though IMO not a bad Idea) but more the question of, to what degree are the scientist/engineers behind the formation of the EF scale going to look outside the lab and begin to use some of the solid field data to take a more serious look at what wind speeds are required to do what sort of damage, and better perfect using damage indicators to estimate wind speed. I'm guessing with all this new Data coming in over the next couple years, and more and more tornado cores being sampled, by 2012 we'll have the EEF scale...

 

[joel ewing]

Don't know if anybody's still reading this thread, but I'd like to weigh in. On the Aurora event, my chase partner Doren Berge and I were no more than 35 yards or so from the original spinup. FWIW, if you're interested in seeing this on you tube, keyword Aurora and Doren Berge. Reed and I were hop-scotching each other a time or two jockeying into positions during this time. When the initial spinup started, it truly appeared to me that it was no stronger than one of the millions of dust devils we get out here in the So. Ariz. deserts annually. But it didn't take long for that spinup to "amp up" very quickly. On YouTube, you'll see me looking at it, and then going "uhhh ohhhh"....as I could see it was really ratcheting up. I figured Doren and I were poked, being as close as we were. Anyhow, Reed maneuvered himself into dead center of that spinup...and claims the 139mph. Not knocking him, and fyi, I've defended him in S.T. many times (although I think he's RUINED every great video he's put out by his screaming) but I was surprised at the mph reading he got. Hard to believe, really. But I'm going to stand by him once again. I DO think that perhaps the Aurora nader was stronger than the rating it was given...at least for part of it's lifecycle. To kick 17 railroad cars off a moving train...that's some kind of wind.

 

[John Peters]

I don't see how it would exaggerate the vast current inconsistencies much at all. Say 1 in 50 tornadoes is sampled by a supported instrument, and that instrument recorded a strength equivalent to an EF-3 tornado, meanwhile the lack of "damage indicators" only allows the tornado to be rated EF-0; I don't see how going ahead and giving the tornado a rating of EF-3, based on good solid data creates inconsistencies, in fact, I'd say it's just the opposite and if anything eliminates inconsistencies; though given the small percentage, not enough to help matters any. That being said, I understand it is by no means a reliable overall tornado strength database, but serves more as a reliable tornado damage database. As it is, I still question the EF wind strength estimates of at least the Aurora tornado; my initial post was more geared towards not necessarily the idea that tornadoes should be ratted based on measured winds speed, (Though IMO not a bad Idea) but more the question of, to what degree are the scientist/engineers behind the formation of the EF scale going to look outside the lab and begin to use some of the solid field data to take a more serious look at what wind speeds are required to do what sort of damage, and better perfect using damage indicators to estimate wind speed. I'm guessing with all this new Data coming in over the next couple years, and more and more tornado cores being sampled, by 2012 we'll have the EEF scale...

You bring up a good point - in certain situations where there is question, and wind speed measurements, use the wind speed measurements to aid in the overall assessment.

 

[Jason Foster]

OK...seems to be a few reasons for the doubt on the wind speed, but not sure who's thinking what.

Are we questioning whether Reed's instruments reported correctly and Reed is telling the truth,

Or, that Reed is exaggerating the speed reading (I would guess for self-promotion), and that he never saw those speeds at all?

 

[Jeff Duda]

Are we questioning whether Reed's instruments reported correctly and Reed is telling the truth,

Or, that Reed is exaggerating the speed reading (I would guess for self-promotion), and that he never saw those speeds at all?

I don't know about others, but I don't doubt that the anemometer they had indeed read 138 mph. What I question is the representativeness of that reading. Was the anemometer high enough to be out of the slipstream of the vehicle? If not, then the winds measured by the anemometer would've been artificially accelerated by the forcing of the air over the car.

 

[Jason Foster]

I don't know about others, but I don't doubt that the anemometer they had indeed read 138 mph. What I question is the representativeness of that reading. Was the anemometer high enough to be out of the slipstream of the vehicle? If not, then the winds measured by the anemometer would've been artificially accelerated by the forcing of the air over the car.

I'm not an expert in fluid dynamics and aerodynamics, but my experiences in hurricanes has been that at anything more than 90mph, the wind is only affected at most about 2 or 4 feet above the vehicle. Granted the SRV is a little more 'ramp' shaped....I still think the anemometer is high enough for accurate reading in regard to your theory.

 

[Jeff Duda]

Well, the reason I say that is by looking at the SRV (there's a good picture of it with the anemometer here), and at the Straka et al. (1996) article that describes the mobile mesonet stations used in VORTEX, specifically sections 2.c.2.i and 2.c.2.iv (including figs. 2 and 3), which mention putting anemometers at 3 m above ground (a little less than 2 m above the roof of the car) for obtaining accurate, effective wind measurements. Looking at the SRV, I'm pretty sure those distances are not met. Also mentioned in the Straka article, however, are that when moved forward a little bit, an anemometer height of 2-3 m (it's probably 2 m AGL on the SRV) is sufficient. However, I don't think the anemometer is far enough forward to meet that criterion.

Here's a link to that article: http://ams.allenpress.com/archive/1520-0426/13/5/pdf/i1520-0426-13-5-921.pdf

 

[Jason Foster]

I think I got the TIV and SRV confused...thanks for the photo Jeff....yeah...way too low to avoid corrupt wind readings.