Dan Chaffee
Hi Mike, All;
(This is in response to the beginning of the thread regarding Hallam- Greensburg similarities, but it seems to warrant a new thread.) I think a clarification of storm nominclature might be in order.
I agree that Mike S's images are very good, certainly under the circumstances, but I would describe what they show differently.
(Mike Peregrine wrote)
None of these images shows the mesocyclone. The very term refers to an area indicated by radar as the tight rotation(s) within the updraft that stretches and ultimitely forms the tornado. by this definition, you can't actually see a mesocyclone(See the NOAA definition for this term).
http://www.srh.noaa.gov/oun/severewx/glossary3.php
I think what you are refering to (and I understand the inclination) is the wrapping east flank, its base and its associated infow features. The fact that these features
curve cyclonicly, as do spiraling straitions under the base, does not mean they constitute a mesocyclone, alhough their presence is certainly symtomatic of its existance. Also, an updraft can look very similar from this image's vantage point and have more than one meso. I have never seen any evidence that the appearance of strictly these features can denote the size, strength, or maturity of a mesocyclone
itself at a given instant. The supercell can be cycling and between producing mesos and have all the spiraling straitions and inflow bands that these images show. Obviously if a violent, large tornado is in progress as this sure is, the meso must be in the mature phase.
It's tempting to think that if one is able to look up into the updraft's RFD occlusion, one is actually then seeing the mesocyclone. This is not consistant with the definition either, but it is certainly a more focused region for its containment. I suppose the closest thing
to direct visual evidence that may suggest at least the size at the lowest of a mesocyclone is seeing the wall cloud in motion, if there is one. However, in the first shot, we are barely able to see the faint
decrease in darkness at the lowest part of the base that indicates the RFD occlusion. We are looking NW to the SE flank and RFB. Sometimes it's possible to see the RFD occlusion dramtically from this quadrant of
a storm, but not in this image. Featurewise, if I were to describe what the first image shows I would say it shows a strongly arcing, softly striated east flank and low base, with a beaver's tail inflow cloud surmounted to the upper right by a shallow, cyclonicly curved mid-level inflow cloud deck. Aside from the wedge tornado, there is no conclusive indication of a wall cloud, although that may be what the lowest part
of the base is (it may simply look lower because it is further away than closest part of the base). There may be other ways of saying the same thing...
I think the most elucidating approach to considering and discussing storm morphology is to differentiate between topographical cloud structure and storm structure; they are not the same thing. Sorry if this is taken as being pendantic; I do feel that it is imperative that we are all on the same page regarding our abilities to discrimminate and interpret storm features (the WCMs are counting on us
Dan Chaffee
(This is in response to the beginning of the thread regarding Hallam- Greensburg similarities, but it seems to warrant a new thread.) I think a clarification of storm nominclature might be in order.
I agree that Mike S's images are very good, certainly under the circumstances, but I would describe what they show differently.
(Mike Peregrine wrote)
One thing I noticed in Mike Scantlin's photos (which are exceptional from a structural perspective - and every other perspective), was that the mesocyclone appeared extremely well developed at the time the tornado was nearing Greensburg.
None of these images shows the mesocyclone. The very term refers to an area indicated by radar as the tight rotation(s) within the updraft that stretches and ultimitely forms the tornado. by this definition, you can't actually see a mesocyclone(See the NOAA definition for this term).
http://www.srh.noaa.gov/oun/severewx/glossary3.php
I think what you are refering to (and I understand the inclination) is the wrapping east flank, its base and its associated infow features. The fact that these features
curve cyclonicly, as do spiraling straitions under the base, does not mean they constitute a mesocyclone, alhough their presence is certainly symtomatic of its existance. Also, an updraft can look very similar from this image's vantage point and have more than one meso. I have never seen any evidence that the appearance of strictly these features can denote the size, strength, or maturity of a mesocyclone
itself at a given instant. The supercell can be cycling and between producing mesos and have all the spiraling straitions and inflow bands that these images show. Obviously if a violent, large tornado is in progress as this sure is, the meso must be in the mature phase.
It's tempting to think that if one is able to look up into the updraft's RFD occlusion, one is actually then seeing the mesocyclone. This is not consistant with the definition either, but it is certainly a more focused region for its containment. I suppose the closest thing
to direct visual evidence that may suggest at least the size at the lowest of a mesocyclone is seeing the wall cloud in motion, if there is one. However, in the first shot, we are barely able to see the faint
decrease in darkness at the lowest part of the base that indicates the RFD occlusion. We are looking NW to the SE flank and RFB. Sometimes it's possible to see the RFD occlusion dramtically from this quadrant of
a storm, but not in this image. Featurewise, if I were to describe what the first image shows I would say it shows a strongly arcing, softly striated east flank and low base, with a beaver's tail inflow cloud surmounted to the upper right by a shallow, cyclonicly curved mid-level inflow cloud deck. Aside from the wedge tornado, there is no conclusive indication of a wall cloud, although that may be what the lowest part
of the base is (it may simply look lower because it is further away than closest part of the base). There may be other ways of saying the same thing...
I think the most elucidating approach to considering and discussing storm morphology is to differentiate between topographical cloud structure and storm structure; they are not the same thing. Sorry if this is taken as being pendantic; I do feel that it is imperative that we are all on the same page regarding our abilities to discrimminate and interpret storm features (the WCMs are counting on us

Dan Chaffee
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