Caleb Routt
EF1
- Joined
- Jul 2, 2014
- Messages
- 50
So what exactly causes a tornado and a mesocyclone to sort of "link up" and become one rotating mass? Birmingham Alabama April 27, 2011 being just one example
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Wall Cloud on ground
- Thread starter Caleb Routt
- Start date
Skip Talbot
EF5
Can you expand a little on what you mean? I'm assuming from your title, "Wall Cloud on ground" and "tornado and a mesocyclone link up" that you're wondering how and why some very large tornadoes may appear to be extensions of larger, more broad circulations that normally remain aloft (like the mesocyclone).
First of all, it might be helpful to try and sort out some terminology and definitions, and others with a better understanding of the dynamics can try to help me out here. A "wall cloud on the ground" is not necessarily a tornado. A rotating wall cloud in contact with the ground doesn't have to be one either. You need a violent, circulating wind field on the surface to call something a tornado. So we should keep in mind that there is this distinction between types of clouds like condensation funnels and wall clouds, and the winds that make up a tornado.
There are different scales of rotation in supercells. Beginning the mesocyclone as the largest and broadest, to the tornado cyclone, which may be associated more on the level of a wall cloud, the tornado and then its subvortices. These different scales and levels of circulations may each have some influence at ground level in different situations, and potentially, each of them could be defined as a tornado if they're strong enough and in contact with the ground. A few examples: the noodly, multi vortex tornadoes that don't wedge out are what we'd normally identify as subvortices inside of a tornado. It may be that the tornado scale circulation didn't wrap up or intensify enough to become a tornado, so these smaller vortices are what we would identify as the actual tornado.
A size up from the tornado, if there is a ground dragging wall cloud that is associated with a damaging circulation, we'd call that a tornado, even though this circulation is usually larger than and above the circulations of what we'd normally call a tornado. Examples of this might be your Birmingham example (I'd have to look at that one more but it seems about right), El Reno 2013, and sw of Conger, MN on June 17, 2010. Baroclinic aspects, like pressure and temperature differences, of the storm probably determine how a wall cloud/tornado cyclone acts as a large tornado. I suspect that the main contributor is the RFD, more specifically you need an unusually large RFD that gets entrained by and powers the low level circulation. Storms in environments with both strong to extreme instability and large storm relative helicity seem to produce very large RFD circulations that are labeled as large tornadoes. These storms are often, but not always, massive HPs.
I guess it's possible for the mesocyclone of the updraft tower to be a tornado too. I'm imagining a supercell in high terrain where the updraft tower is basically dragging across the ground and the circulating winds in the meso are doing damage.
To answer your question, I think in some cases you're seeing circulations that could still be identified as mesocyclones or tornado cyclones that are essentially acting as tornadoes (a damaging circulation at ground level). It's also possible that the tornado is just getting so large that it's difficult to distinguish it from its parent circulation. The culprit behind both of these scenarios appears to be massively large RFDs and baroclinic properties that put these circulations near or at ground level.
First of all, it might be helpful to try and sort out some terminology and definitions, and others with a better understanding of the dynamics can try to help me out here. A "wall cloud on the ground" is not necessarily a tornado. A rotating wall cloud in contact with the ground doesn't have to be one either. You need a violent, circulating wind field on the surface to call something a tornado. So we should keep in mind that there is this distinction between types of clouds like condensation funnels and wall clouds, and the winds that make up a tornado.
There are different scales of rotation in supercells. Beginning the mesocyclone as the largest and broadest, to the tornado cyclone, which may be associated more on the level of a wall cloud, the tornado and then its subvortices. These different scales and levels of circulations may each have some influence at ground level in different situations, and potentially, each of them could be defined as a tornado if they're strong enough and in contact with the ground. A few examples: the noodly, multi vortex tornadoes that don't wedge out are what we'd normally identify as subvortices inside of a tornado. It may be that the tornado scale circulation didn't wrap up or intensify enough to become a tornado, so these smaller vortices are what we would identify as the actual tornado.
A size up from the tornado, if there is a ground dragging wall cloud that is associated with a damaging circulation, we'd call that a tornado, even though this circulation is usually larger than and above the circulations of what we'd normally call a tornado. Examples of this might be your Birmingham example (I'd have to look at that one more but it seems about right), El Reno 2013, and sw of Conger, MN on June 17, 2010. Baroclinic aspects, like pressure and temperature differences, of the storm probably determine how a wall cloud/tornado cyclone acts as a large tornado. I suspect that the main contributor is the RFD, more specifically you need an unusually large RFD that gets entrained by and powers the low level circulation. Storms in environments with both strong to extreme instability and large storm relative helicity seem to produce very large RFD circulations that are labeled as large tornadoes. These storms are often, but not always, massive HPs.
I guess it's possible for the mesocyclone of the updraft tower to be a tornado too. I'm imagining a supercell in high terrain where the updraft tower is basically dragging across the ground and the circulating winds in the meso are doing damage.
To answer your question, I think in some cases you're seeing circulations that could still be identified as mesocyclones or tornado cyclones that are essentially acting as tornadoes (a damaging circulation at ground level). It's also possible that the tornado is just getting so large that it's difficult to distinguish it from its parent circulation. The culprit behind both of these scenarios appears to be massively large RFDs and baroclinic properties that put these circulations near or at ground level.
Caleb Routt
EF1
- Joined
- Jul 2, 2014
- Messages
- 50
Okay so basicly what happens is if the RFD has a lot of moisture and the tornado is really strong there is a big amount of moisture around the vortex? I do know when a tornado gets to be really strong centripcal force pushes the walls of the tornado outward. I just saw some place I cant really remember where but it stated that if the tornado the tornado cyclone and mesocyclone become one rotating mas then the entire rotat
I think this is a great discussion and one of those topics that generally hasn't been fully discussed on this forum yet. Granted, I have not actually done a search for this topic on the forum, so I could very well be wrong.
Once again, Skip pretty much covered it as far as my knowledge base extends. Generally I can only agree and perhaps offer my opinion by stating it slightly differently than him. Perhaps some of the true experts like Jeff Snyder will see this and offer a more in-depth or more accurate explanation.
I think a case like El Reno 2013 shows that all of these features (from mesocyclone to sub-tornadic suction vortex) exist on a continuum of spatiotemporal scales such that there may not always be a clear distinction between them - i.e., different circulations may obtain length and time scales more characteristic of other types of circulations (e.g., a tornado approaching the size of a mesocyclone). We, as scientists, have not yet sampled enough cases to be 100% confident that there is a meaningful difference between suction vortices, a main tornado, a tornado cyclone, and a ground-hugging & damaging "mid-level" mesocyclone. We just don't have the data for an empircal analysis, and as far as I'm aware (limited awareness) no one is running modeling studies focusing on the distinction between these phenomena.
I'm a reductionist, meaning I tend to simplify complex objects and ideas by reducing them to progressively more fundamental notions, eventually arriving at the root level explanation. In that regard, I think the AMS definition of a tornado (repeated below) is the best place to start. The word "violently" was added by me - although it does appear in the definition from other sources (like the NWS).
Granted, this definition remains subjective (how "violent" is "violently"? How "often" is "often"? Is that detail even important?), and that hinders using it as the base level. However, I think it offers enough objectivity to be useful. In my opinion, if there is a column of air (not necessarily perfectly perpendicular to the average Earth gravity force vector - i.e., "vertical") attached to a cloud that contains significant vertical motion and development on the convective or tornado scale that is rotating fast enough to produce winds that cause damage to common surface objects like trees, homes, street signs etc, then it's all the same thing - a tornado. Are there dynamically-based differences between suction vortices and mesocyclones? Most certainly. But is that significant in regards to classification? That I'm not so sure of. Both features can cause damage and are harmful to human beings (who always seem to be seeking ways to classify things). However, they are the result of different processes.
TLDR: IDK, I'm just making an educated guess.
Once again, Skip pretty much covered it as far as my knowledge base extends. Generally I can only agree and perhaps offer my opinion by stating it slightly differently than him. Perhaps some of the true experts like Jeff Snyder will see this and offer a more in-depth or more accurate explanation.
I think a case like El Reno 2013 shows that all of these features (from mesocyclone to sub-tornadic suction vortex) exist on a continuum of spatiotemporal scales such that there may not always be a clear distinction between them - i.e., different circulations may obtain length and time scales more characteristic of other types of circulations (e.g., a tornado approaching the size of a mesocyclone). We, as scientists, have not yet sampled enough cases to be 100% confident that there is a meaningful difference between suction vortices, a main tornado, a tornado cyclone, and a ground-hugging & damaging "mid-level" mesocyclone. We just don't have the data for an empircal analysis, and as far as I'm aware (limited awareness) no one is running modeling studies focusing on the distinction between these phenomena.
I'm a reductionist, meaning I tend to simplify complex objects and ideas by reducing them to progressively more fundamental notions, eventually arriving at the root level explanation. In that regard, I think the AMS definition of a tornado (repeated below) is the best place to start. The word "violently" was added by me - although it does appear in the definition from other sources (like the NWS).
AMS glossary said:
Granted, this definition remains subjective (how "violent" is "violently"? How "often" is "often"? Is that detail even important?), and that hinders using it as the base level. However, I think it offers enough objectivity to be useful. In my opinion, if there is a column of air (not necessarily perfectly perpendicular to the average Earth gravity force vector - i.e., "vertical") attached to a cloud that contains significant vertical motion and development on the convective or tornado scale that is rotating fast enough to produce winds that cause damage to common surface objects like trees, homes, street signs etc, then it's all the same thing - a tornado. Are there dynamically-based differences between suction vortices and mesocyclones? Most certainly. But is that significant in regards to classification? That I'm not so sure of. Both features can cause damage and are harmful to human beings (who always seem to be seeking ways to classify things). However, they are the result of different processes.
TLDR: IDK, I'm just making an educated guess.
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