Divided Mesocyclone

[John Hudson]

I have recently been taking a closer look at a paper submitted back in 1979 (Lemon and Doswell), Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis. It is a fascinating read, especially with regard to the hypothesis of the divided mesocyclone structure.

Some conclusions in this paper are consistent with those reached by Fujita, including the hypothesis that the strongest tornadoes actually occur during the collapse phase of the supercell, after dissipation of BWER and decrease in updraft intensity.

I wanted to see if there had been any follow-up study with regard to this paper, and if there was any new evidence to support or disprove the idea of the formation of a divided mesocyclone structure prior to tornadogenesis.

If anyone could shed some light on this, I would really appreciate it.


John

 

[Martin North]

PDF of the article here if anyone wishes to read it.

 

[John Cameron]

Wow...I thought this subject would get a lot of responses considering the body of scientists who frequent this board.

I'm fascinated with the subject of the Doswell Lemon paper and however many times I read it (or try to read it) I have a difficult time drawing a mental picture of all that's happening during the evolution of the supercell and what is causing the separation of the meso from the primary updraft.

Gosh it wasn't until I saw a lecture from Lemon that I realized that the upwind component of the velocity couplet is in fact RFD or some evidence of it.

The reason I searched ST for discussion of the Lemon/Doswell paper is to see if someone has a "for dummies" version where the scientific jargon isn't so dense.

So is there a "Severe Thunderstorm Evolution and Mesocyclone Structure as Related to Tornadogenesis for Dummies"?

 

[Glen Romine]

John, the Lemon and Doswell paper is quite remarkable, particularly given how little was known at the time, such that much of the basic premise of their work remains valid today. Some of the details have been revised in the last three decades, of course. Still, much remains unknown regarding the structure, behavior and evolution of supercell storms, in particular how they manage to sometimes produce tornadoes. It is very difficult to measure all of the needed details on the spatial and temporal scales needed to follow what goes on, and we still lack tools able to do this well. Improvements have been made in storm observations, particularly with radars, but we still miss what is happening very near the surface and places where there isn't any precip or other particles, and often have incomplete observations and for only a small portion of the storm. High resolution computer models can give details everywhere, but these are only approximations to how the real atmosphere works and we don't know how important the finer details are in the end result without better observations to verify models against. The VORTEX2 field campaign aims to try and get the best set of storm observations to date, though this will only be on a small sample of storms from the Central Plains and still will be imperfect observations. Still, as with the last VORTEX project it will likely lead to new insights.

 

[John Cameron]

Glen,
Thank you for the response

 

[Paul Knightley]

Re: the collapsing storm & tornadogenesis. Recent work using Doppler radar, etc, has shown some correlation between a descending reflectivity core (DRC) at the back side of the storm, and rapid tornadogenesis a short time later. I would urge chasers this year to see if they can document the rapid appearence of precip shafts in the RFD, especially when tornadogenesis happens a very short time later.

These shafts should not be confused with the precip which may already be present.

 

[John Cameron]

Re: the collapsing storm & tornadogenesis. Recent work using Doppler radar, etc, has shown some correlation between a descending reflectivity core (DRC) at the back side of the storm, and rapid tornadogenesis a short time later. I would urge chasers this year to see if they can document the rapid appearence of precip shafts in the RFD, especially when tornadogenesis happens a very short time later.

These shafts should not be confused with the precip which may already be present.

Would the DRC appear as an appendage at the rear flank or, if there is already a 'hook', and intensification or swelling of the hook?

 

[John Cameron]

Another thought...
I think it was Don Burgess who noted an overall weakening of the Wichita Falls storm as the 4/10/79 tornado was developing. Of course, the radar data from this event is less than spectacular. But, Burgess suggests this storm, from a precip standpoint, was not at it's strongest when it produced a tornado that stayed on the ground for 47 miles (Fujita et al).

 

[Paul Knightley]

Have a look here, John:

http://ams.confex.com/ams/pdfpapers/115153.pdf

Also, if you search for Descending Reflectivity Cores online, and in Google Scholar, you might throw up a few more.

cheers,

Paul.

 

[John Cameron]

Have a look here, John:

http://ams.confex.com/ams/pdfpapers/115153.pdf

Also, if you search for Descending Reflectivity Cores online, and in Google Scholar, you might throw up a few more.

cheers,

Paul.

Thank you Paul, I appreciate that!

 

[John Hudson]

Gee, I thought this thread flatlined a long time ago. Thanks to everyone for their interest, and replies.

I suppose it's kind of obscure research, but my interest was piqued after reading about Fujita's reports, and how he explained a possible connection between tornadogenesis and a weakening storm core (IE: dome collapse).

Paul, many thanks for the link to the paper on descending reflectivity cores. I'm looking forward to reading that.


John
VE4 JTH