Cumulonimbus visualized in GRLevel2 AE

[Dan Doleiden]

Hi everyone,

Here is (what I believe to be) a cumulonimbus incus in both (poorly) photographed and GR2AE views. I took the picture during August 2005 in Carbon County, PA. I was about 26 miles NW of the cloud as indicated by radar. The pics should be clickable for larger views.


camera 122 by custom981, on Flickr

Volume rendered:


kdix_20050803_2259 by custom981, on Flickr

Played around with the alpha table settings a bit:


kdix_20050803_2246 by custom981, on Flickr

Some other activity that day. The cloud pictured above is in the bottom right area:

<a href="http://www.flickr.com/photos/60275451@N06/5505537724/" title="kdix_20050803_2246# by custom981, on Flickr"><img src="http://farm6.static.flickr.com/5251/5505537724_7bf6fb0643_z.jpg" width="640" height="378" alt="kdix_20050803_2246#" /></a>

I have a few basic questions that I'd appreciate help with:

1. Is this actually a cumulonimbus incus or am I way off? I believe it is because it demonstrates a classic anvil top and appears to have reached a layer of stratospheric stability.

2. Is the anvil in this particular cloud formed by high-level winds, the tropopause or both? I understand that the height of the tropopause varies by latitude. (I'm at about 45 degrees N). I would guess that both are factors. You can see whisps being blown off the front of the anvil by what I would guess are high level winds.

3. Am I correct in assuming that the area of 40+ dBZ reflectivity protruding upwards is an updraft and that the green areas towards the bottom show rear and front flank downdrafts?

I'm an undergraduate student at Penn State. I've been considering our meteorology program for a few weeks now and have been trying to get my feet wet in the field before visiting the department next month. I've always had an interest but never really pursued it until lately. Everything I know (or think I know) is from reading posts here, hunting around the NOAA site and a few other sources. Input is always appreciated!

Thanks,



Dan

 

[Jeff Duda]

Dan,
If you are already using the 3-D volume rendering tool on GR2AE I'm curious as to why you aren't already in the meteorology program at PSU! Your interest level sounds very high, so I would strongly suggest joining the program. There are at least two faculty members that are pretty into severe weather research, including Paul Markowski and Yvette Richardson.

Regarding the topic itself, I've actually never heard an anvil referred to as "incus" so I've already learned something new today. For your comment (1), yes, you are right on. Good job on being able to expose the anvils using the volume renderer. I'm guessing that teal/blue color is in the 5-18 dBZ range to have been able to see that (given the paucity of falling hydrometeors from the anvil region).

Regarding (2), you are right again (it's both). Parcels that make up an updraft tend to reach their equilibrium level (or level of neutral stability) very near the tropopause then settle there after some oscillations (you can see the first part of the first period of oscillation as the overshooting top). Continued upward motion helps push the previous parcels outward thus causing the anvil to form, but it is usually the presence of wind shear at the tropopause that causes the anvil to shift preferentially towards one side of the storm (usually downstream). If there was no shear between the top of the updraft and the equilibrium level, the anvil would be more or less perfectly circular in shape with the updraft at the center of the anvil.

Regarding (3), I'm not an expert on radar meteorology so I suppose someone else could give a better explanation, but higher reflectivities could suggest both an updraft and a downdraft. The second picture shows the structure of these storms the best. These storms are ordinary cells since they are stacked vertically (there is little or no shear to tilt the storm). The particular storm in the image appears to be in the mature stage where the precipitation is reaching peak intensity (the higher dBZ near the bottom of the storm is probably the downdraft beginning to undercut or take over the updraft). In general, the higher the reflectivity the larger the drops OR the more drops there are in the pulse volume (thus heavier precipitation, in a general sense). Also, ordinary cells don't really have parts named "forward flank downdraft" and "rear flank downdraft", as their engine is basically one vertical column of rapidly moving air (whether it is up or down).

Hope this helps.

 

[Greg Higgins]

Can you share your color table for the volume explorer in the 1st picture? Thank you!

 

[Dan Doleiden]

Hey Jeff,

Thanks for the reply! I'm looking forward to having a look around the department up there and might bring these renders along in case I'm able to meet any of the professors. I found the cumulonimbus species descriptions here. I haven't really been able to find a solid reference to those names anywhere online besides Wikipedia...

I was surprised that the cloud structure can be defined as well as it is on GR2AE. You're right, the color table I was using plots approximately 5-18 dBZ as a teal color. You mention the paucity of falling hydrometeors falling from the anvil - would we normally only see them fall from that region in a supercell as pictured below?

Thanks for the clarification on RFD/FFD not being applicable here. I have a lot to learn about storm structure in general. This helped clarify:

Dan,
If you are already using the 3-D volume rendering tool on GR2AE I'm curious as to why you aren't already in the meteorology program at PSU! Your interest level sounds very high, so I would strongly suggest joining the program. There are at least two faculty members that are pretty into severe weather research, including Paul Markowski and Yvette Richardson.

Regarding the topic itself, I've actually never heard an anvil referred to as "incus" so I've already learned something new today. For your comment (1), yes, you are right on. Good job on being able to expose the anvils using the volume renderer. I'm guessing that teal/blue color is in the 5-18 dBZ range to have been able to see that (given the paucity of falling hydrometeors from the anvil region).

Regarding (2), you are right again (it's both). Parcels that make up an updraft tend to reach their equilibrium level (or level of neutral stability) very near the tropopause then settle there after some oscillations (you can see the first part of the first period of oscillation as the overshooting top). Continued upward motion helps push the previous parcels outward thus causing the anvil to form, but it is usually the presence of wind shear at the tropopause that causes the anvil to shift preferentially towards one side of the storm (usually downstream). If there was no shear between the top of the updraft and the equilibrium level, the anvil would be more or less perfectly circular in shape with the updraft at the center of the anvil.

Regarding (3), I'm not an expert on radar meteorology so I suppose someone else could give a better explanation, but higher reflectivities could suggest both an updraft and a downdraft. The second picture shows the structure of these storms the best. These storms are ordinary cells since they are stacked vertically (there is little or no shear to tilt the storm). The particular storm in the image appears to be in the mature stage where the precipitation is reaching peak intensity (the higher dBZ near the bottom of the storm is probably the downdraft beginning to undercut or take over the updraft). In general, the higher the reflectivity the larger the drops OR the more drops there are in the pulse volume (thus heavier precipitation, in a general sense). Also, ordinary cells don't really have parts named "forward flank downdraft" and "rear flank downdraft", as their engine is basically one vertical column of rapidly moving air (whether it is up or down).

Hope this helps.

 

[Dan Doleiden]

Can you share your color table for the volume explorer in the 1st picture? Thank you!

Sure, let me find a link to it. I'll edit this post when I have the link.

Edit: I couldn't find the pallet on GRLevelX stuff where I originally downloaded it from. It's called "stormwatchnc2". I was just using the default alpha table setting in the picture you mentioned. I uploaded the .pal file here - hope that's okay since it was originally free. Rapidshare will try to trick you into a premium account - just tell it no thanks.

 

[Greg Higgins]

Thank you for posting! Easily downloaded!

 

[Jeff Duda]

I was surprised that the cloud structure can be defined as well as it is on GR2AE. You're right, the color table I was using plots approximately 5-18 dBZ as a teal color. You mention the paucity of falling hydrometeors falling from the anvil - would we normally only see them fall from that region in a supercell as pictured below?

Well...to some extent there will be some precipitation falling from the anvil region of a supercell and of MCSs (it's part of what causes the structure of MCSs to be what it is), but not so much for an ordinary cell. THere will be hydrometeors that fall from the anvil due to being thrown out of the updraft, caught by the higher jet-level winds, and then falling back down through the anvil. Precipitation from the anvil region of MCSs is a completely different story that I won't get into here.

 

[Dan Doleiden]

Well...to some extent there will be some precipitation falling from the anvil region of a supercell and of MCSs (it's part of what causes the structure of MCSs to be what it is), but not so much for an ordinary cell. THere will be hydrometeors that fall from the anvil due to being thrown out of the updraft, caught by the higher jet-level winds, and then falling back down through the anvil. Precipitation from the anvil region of MCSs is a completely different story that I won't get into here.

Ahh okay. It's starting to click for me now. I checked out some of your storm chasing pics - neat stuff!

 

[Jared Farrer]

Thats an amazing comparison! I usually always plot higher dbz when rendering severe weather structure in GR2AE. I am sorta surprised it was able to outline general cloud structure using small profiles. But not too surprised. It just seems pretty clear when compared to an actual image. Might be neat to go back and do that for some older chase days!

 

[Dan Doleiden]

Thats an amazing comparison! I usually always plot higher dbz when rendering severe weather structure in GR2AE. I am sorta surprised it was able to outline general cloud structure using small profiles. But not too surprised. It just seems pretty clear when compared to an actual image. Might be neat to go back and do that for some older chase days!

It can really show some cool details with a little tweaking. I've been giving the NCDC archive a workout!

 

[Dan Hildebrand]

I'm curious. Is the GRL2A cell the same one that was photographed? If so then that was from 5 years ago! How did you get that data, because i'm definitely wanting to go back and investigate some old storms!

 

[Jeff Duda]

You can get archived Level 2 and Level 3 data from NCDC: http://www.ncdc.noaa.gov/nexradinv/

 

[Dan Doleiden]

I'm curious. Is the GRL2A cell the same one that was photographed? If so then that was from 5 years ago! How did you get that data, because i'm definitely wanting to go back and investigate some old storms!

Yes it is. As Jeff mentioned above, the NCDC archive has excellent archives since the mid 1990s I believe.

 

[Dustin Janise]

How do you get the downloaded volume tables into GR2Analyst? I'm still unsure of hoe to do that.

 

[Dan Doleiden]

I found these in my old pictures on a backup hard drive. If the EXIF data is correct (and it may not be) they were taken on [date] at approximately 11:00 AM EDT, area code 18066. Sorry about the poor quality - these are from before I was into photography as a hobby. This was literally in my back yard.

I don't like to just ask what something is without making an educated guess first so I'll give it a shot: it didn't exhibit visible rotation when I observed it, but based on outward appearance I think there is a small mesocyclone present, most visible in the third frame. Could the downward protrusion be the beginning of a tornado? I can't really guess any further based on what I know so far, I really need to order Storm Structure 101!


Edit: I'm a dope. Listed the modified date instead of the created date. Will fix asap.