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Descending Reflectivity Core

Some formal publications pertinent to DRCs:

Rasmussen, Erik N., Jerry M. Straka, Matthew S. Gilmore, Robert Davies-Jones, 2006: A preliminary survey of rear-flank descending reflectivity cores in supercell storms. Wea. Forecasting, 21, 923–938.

Kennedy, Aaron, Jerry M. Straka, Erik N. Rasmussen, 2007: A statistical study of the association of DRCs with supercells and tornadoes. Wea. Forecasting, 22, 1191–1199.

Byko, Z., P. Markowski, Y. Richardson, J. Wurman, and E. Adlerman, 2009: Descending reflectivity cores in supercell thunderstorms observed by mobile radars and in a high-resolution numerical simulation. Wea. Forecasting, 24, 155–186.
 
So the 'gist' is they're searching for the signature of a descending rain curtain (possibly pulling lines of vorticity from mid levels to lower down), and attempting to tie it to tornado production?
 
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Did someone specifically mention the DRC? In Karen Kosiba's presentation, her slide summarizing "Precursors to tornadogenesis" had a bullet point that said "Descending Reflectivity (not shown)". I asked about it in the follow-up, and mentioned it in the Bar & Grill ChaserCon thread because I had not heard of it and it seemed significant to me. I also discovered Aaron's unfinished pages on the DRC. This quote grabbed me...
Found a page on
the subject that says: "This has changed with the release of Gibson
Ridge Level 2 Analyst Edition software (GR2AE). Taking advantage of
the graphics processing unit on video cards, GR2AE is capable of
rendering 3-D volume scans of storms in real-time."
Click to expand...
.

I emailed Mike Gibson to ask about recommended specs of the graphics card to take advantage of that and his opinion of the significance of the DRC. I noted that he
mentions (and demonstrates) this ability on the following page:
http://www.grlevelx.com/<wbr>gr2analyst/volume_renderer.htm
He was nice enough to give me a thoughful response, which I'll pass along here:
DRCs are a somewhat confusing topic because there appear to be two different
physical processes involved:

1) A true descending reflectivity core, where something is falling (big
drops, hail, etc.). While they're typically near the hook echo, they're not
centered on a rotation core. You can see these in many supercells and they
have various shapes.

2) A "vortex hole" or "reflectivity tube" coincident with a rotation core,
due to the centrifuging of targets (rain, hail, etc) out of the core. These
are the significant ones because they indicate very strong rotation in a
cell. In GR2AE you can locate a VH in the reflectivity and then compare its
location to peaks in GR2AE's Normalized Rotation product (NROT).

I'm not a meteorologist, so these are just my opinions based on looking at
many tornadic storms in the volume explorer. I highly recommend reading Les
Lemon's paper on "vortex holes" and the Greensburg tornado.

As for graphics cards, any card with Shader Model 2.0 or higher support will
work. If you're going to use GR2AE's Volume Explorer much of the time, I
recommend getting a card in the $75-100 range. I just installed an AMD 5750
card (~$100) and it gives excellent performance. I believe that an AMD 5670
card ($75) will perform well, too.
Click to expand...
I don't know how many case studies have been done so far on DRCs. It seems that they need to be within a specific "donut-shaped" range from a radar site for the scans to reach the correct heights of the storm to see the phenom. I have the gut feeling that a whole new round of research on DRCs will take place as the WSR-88D Weather Radar upgrades with Dual Polarization capability are installed and operational. That should provide a whole new high-res look at the DRC.

I think the subject is fascinating and have just begun to read up on the subject. It seems that anyone who already has GR2AE could have a lot of fun looking for storms in the data archives on which to do their own research in looking for this feature.

EDIT: The Lemon paper that Mike Gibson refers to was co-authored by ST Member Mike Umscheid, so perhaps he can shed a bit more light. For those interested, the paper is here.
 
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I would urge everyone interested in this to review their tornado footage to see whether they can see rain curtains 'appearing' seconds or even a few minutes before a tornado develops, in the region of the RFD.
 
DRC... an individual emailed me about my research. Unfortunately, I managed to lose the email. If you see this, please resend the email and I'd be happy to respond. Was it you Darren? My mind is fried right now.

Another paper I wrote on a visual observation of a DRC: http://www.ejssm.org/ojs/index.php/ejssm/article/view/16

During V2, I believe I saw a few more (non-tornadic storms). One of these days, I'll go back and look at the radar data to confirm.

To summarize the research, DRCs are common... they occur with and without tornadoes. When they do occur with tornadoes, they have limited applications for the warning decision process. Many tornadoes occured within minutes +/- of it reaching the lowest elevation tilt (level 2). Might be hard to see them on L3. That said, there are some future avenues of research. It might be possible to discriminate between types of DRCS (which way they descend, where they originate, etc.). In the small sample I had, there seemed to be a preference to those that were tornadic. Finally, DRCs might be more interesting as a clue for the dynamic processes involved with tornadogenesis (or failed genesis for that matter).

Some day I'll get around to revamping my research page. With a kid on the way and a dissertation in the works... low on the totem poll :)
 
Paul Knightley said:
I would urge everyone interested in this to review their tornado footage to see whether they can see rain curtains 'appearing' seconds or even a few minutes before a tornado develops, in the region of the RFD.
Click to expand...

This happened on (amongst other dates) with the 6/13/07 supercell and tornadoes near Orienta, OK. I'll include my YouTube video below -- skip ahead to the 6:00 min mark to see what looks like a DRC. I think I even mention that it looks like a descending reflectivity core, noting that the "blob" of precip rapidly descends to the ground (i.e. it does not appear to "wrap around" like usual). A tornado develops shortly after this precip "blob" hits the ground, though, as Aaron noted (and he'd know as well as anyone considering his research into this topic!), there are quite a few DRCs that aren't associated with tornadogenesis. Additionally, the first several tornadoes did not appear to be coincident or preceded by DRCs (visually, at least).

Watch video >
 
What direction are we looking there, Jeff? Is the DRC just west of where the tornado forms?

Those of you that have Tim Marshall's 2004 chase DVD (I just picked mine up at ChaserCon)...
I've only gotten to watch the start of it, but there is what appears to be a DRC preceding the very first tornado on the DVD. It is not a big dump like Jeff's (above) but more pencil-like area of precip. to the direct west of where the tornado forms. Tim comments on the precip when it appears. (This would have been two years before the first paper on DRCs was published).
 
Darren Addy said:
What direction are we looking there, Jeff? Is the DRC just west of where the tornado forms?
Click to expand...

Yes, that highway runs east-west, and I'm looking to the west. The precip dumps rapidly descends and hits the ground west of the low-level mesocyclone. A pencil-thin funnel develops only a few seconds after the most opaque part of this hits the ground, and it's important not to forget that "correlation != causation".
 
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