Mapping the Inside of a Tornado-Particularly Severe Ones

[Saul Trabal]

I have seen computer models of developing severe thunderstorms. Has anyone tried the following: doing a radar measurement of, let's say an F4 or F5, and using the measurements, creating a 3-D computer animation so one could get an idea of how the winds operated inside the vortex.

 

[Michael P. Morris]

Josh Wurman and Howie Bluestein did lots of measurements like that on the May 3, 1999 Moore tornado. There are also countless computer simulations and numerical models that deal with tornadogenesis.

 

[Robin Tanamachi]

Lou Wicker recently completed a microscale model of tornadogenesis based on the conditions around the 24 June 2003 Manchester, SD tornado. The resultant animation was featured on the NOVA special a few months ago. I believe he has a journal article forthcoming.

 

[Glen Romine]

Originally posted by Robin Tanamachi
Lou Wicker recently completed a microscale model of tornadogenesis based on the conditions around the 24 June 2003 Manchester, SD tornado. The resultant animation was featured on the NOVA special a few months ago. I believe he has a journal article forthcoming.

Actually, there will be no journal article on this work - we've found too many hurdles to make it over to get this work publishable to justify the end result - too many easier projects to get publications with. A similar work may get published eventually - but probably by Matt Gilmore as lead. Even the study by Lou mentioned was at relatively coarse resolution (100 m)- too much so to talk about tornado dynamics - but appropriate for looking at tornadogenesis. In numerical modelling - the tornadogenesis mode almost always follows something akin to the dynamic pipe effect genesis - why we don't really understand yet why other modes in supercells generally aren't well simulated. Further, noone has yet really simulated both the supercell and the tornado using reasonable dynamics. The equations sets appropriate for describing the dynamics within a tornadic circulation are more complex than those used to simulate the parent supercell - but there are folks working to advance this. Lewellen & Lewellen probably have the best numeric model of a tornado circulation, at ~ 5 meter resolution, but they don't model the parent cell - so that aspect is a major weakness.

Glen

 

[Thomas Loades]

THe April National Geoegraphic has some illustrations of modelling of (I think) airflow in a tornado — although I think that might have been the UIUC model by Lou Wicker.

 

[Glen Romine]

Originally posted by Thomas Loades
THe April National Geoegraphic has some illustrations of modelling of (I think) airflow in a tornado — although I think that might have been the UIUC model by Lou Wicker.

There are two animation sequences shown - one of a tornado vortice producing supercell simulation - where the perturbation pressure is given by the isosurface and radar reflectivity is shown on the contour map at the bottom. This is from a simulation led by Lou, the second animation is from simulations by Lewellen though, and that one shows just a tornado flow.

Glen

 

[Robin Tanamachi]

I am also working on using ground-based velocity track display software to reconstruct a tornado wind field from W-band radar scans. I'll be presenting a poster on it at the SLS conference.

 

[Shane Adams]

Originally posted by Robin Tanamachi
I am also working on using ground-based velocity track display software to reconstruct a tornado wind field from W-band radar scans. I'll be presenting a poster on it at the SLS conference.

I'm curious as to the calibrations you use when compiling this data, since ground-based velocity readings are taken with a grain (318mph on 5-3-99)

 

[Robin Tanamachi]

I was not involved with the calibration or testing of the mobile W-band radar since it was built at the U. of Massachusetts. Bluestein and Pazmany published a paper on the engineering of the radar itself in BAMS in (I think) 1999. The AMS Journals website is down right now or I could get you an exact reference.

I operate on the assumption that the data I work with is true, or at least true enough to be useful (which is what really matters). Obviously, you always have to take the velocity measurements with a grain of salt. As with any Doppler velocity data, it could be contaminated by a lack of scatterers (i.e. in the torando's eye) or a really big scatterer (like a bird) that biases the power spectra in each pixel. I tried to account for this by threshholding the velocity data on low reflectivity (-18 dBZ or less) and manually editing out a few pixels of obviously bad data. After those filters had been applied, there were still enough points with a velocity of 50 m/s or greater left in the tornado that I believed those velocities were real. (Tornado threshold velocity is 35 m/s, and we know for a fact that there was a tornado in the sector.) GBVTD analysis showed that those velocities existed all the way around the tornado funnel during its mature stage.

I hope that answers your question. Radar meteorology is a much more inexact science than we'd like to admit, but it's still immensely useful!