Hi there. Can anyone explain to me what a "deformation zone"is in the context of mid-latitude cyclonic storms? I've asked this question of an EC meteorologist and Brett Anderson of AccuWeather, and have received responses from both. However the responses either referred to another site which was too complicated for me, or were too vague. A nice conceptual explanation in layman's terms would be appreciated, explaining what these zones are, why they're found where they are found, and why they frequently lead to extended periods of snow after a low pressure system has already passed (i.e. just what is the mechanism which is producing the lift which causes the precipitation to form).
Cheers -
Jim Patterson
Okay, that's a great question, Jim. I hope I can answer it to your satisfaction.
First off, I will say that deformation zones are patterns primarily found in the upper levels of the atmosphere. So think 500 mb, about 5 km off the surface.
Anyhow, the air flow at the upper levels can be pictured kind of like a river of air. But that river is always being pulled or pushed in different directions. So imagine a somewhat typical pattern of airflow at that level, from south to north. At the northern tip of this airflow, the pattern splits so some of the air goes east and some goes west. Picture what happens to the airflow in the middle. It gets torn apart and kind of mashed out, or deformed. The area where this happens is called a deformation zone. Here's an example, south of Nova Scotia. The area where the air is being torn apart is the deformation zone. Essentially what causes lift is the fact that because the air is being "torn" in all directions, there's a deficit of air, inducing flow from underneath--lift.
http://www.umanitoba.ca/faculties/enviro...ation.html
Hope this helps! If not, please let me know and I'll try again! :)
Oops, I forgot to explain where they usually happen. It's sort of where the upper level jet and mid-level jet work together. The upper level jet goes more or less from west to east, whereas the mid-level jet goes from south to north and then cuts west, at least sometimes. The airflow caught between is where the deformation occurs--it gets sort of torn apart.
Since we are sort of in in "meteorological phenomenon" discussion here I thought I would throw in my question.
What is a baroclinic zone, and a baroclinic leaf. I often read about these two things on the PASPC discussion, but don't understand what they are. I see you have a section on baroclinic leafs on the u of m wx central site, but I was still unclear as to what there are after looking at that satellite image. I think these have something to do with low pressure / forming low pressure. You very frequently read about baroclinic zones on the discussion as well, I think they have something to do with zones of cold and warm air, but that is as much as I know.
Since we are sort of in in "meteorological phenomenon" discussion here I thought I would throw in my question.
What is a baroclinic zone, and a baroclinic leaf. I often read about these two things on the PASPC discussion, but don't understand what they are. I see you have a section on baroclinic leafs on the u of m wx central site, but I was still unclear as to what there are after looking at that satellite image. I think these have something to do with low pressure / forming low pressure. You very frequently read about baroclinic zones on the discussion as well, I think they have something to do with zones of cold and warm air, but that is as much as I know.
Good question. A "baroclinic zone" is a front. It's just a fancy word for it.
A baroclinic leaf is something you've probably seen on a discussion from me, as I tend to write about them in the winter, as well as a few of my colleagues. <grin>
You're right in that it has to do with forming low pressure. It's a sign on satellite imagery that shows that cyclogenesis (low pressure system formation) is imminent or underway.
I thought I had had an example online, but apparently not. So here's a link to an image of a baroclinic leaf. It is the white part labeled "1" and the baroclinic leaf part goes from there to about where the arrow is between the 4s.
I didn't seem to get the link...is it over a word that I can't find?
Thanks Dave,
That makes things a lot clearer. Is the meteorologist's last name at the bottom of the discussion if he/she is the one who wrote it? Usually there are more than one name, and I sometimes see your last name.
Is the leaf usually on water vapour imagery, visible, infrared, etc? Speaking of water vapour imagery, what does it exactly show. I often hear discussions speaking of a wall of moisture moving, as evident of WV...does the WV image show moisture in all layers of the atmosphere, just upper, just lower? I often see supercells pop out of an area of the image that is supposed to be very dry, this seems contradictory.
Thanks for the explanations!
Thanks Dave,
That makes things a lot clearer. Is the meteorologist's last name at the bottom of the discussion if he/she is the one who wrote it? Usually there are more than one name, and I sometimes see your last name.
Is the leaf usually on water vapour imagery, visible, infrared, etc? Speaking of water vapour imagery, what does it exactly show. I often hear discussions speaking of a wall of moisture moving, as evident of WV...does the WV image show moisture in all layers of the atmosphere, just upper, just lower? I often see supercells pop out of an area of the image that is supposed to be very dry, this seems contradictory.
Thanks for the explanations!
You're welcome, Scott. (And to others on this board: if you have questions, ask away! I'll do my best to answer them, as will others here.)
The names at the end are **usually** the meteorologists' last names. Once in a while, a first name is used instead. "Victor" comes to mind. The FOCN45 is written jointly by the Winnipeg and Edmonton offices, so usually you'll see the name of a Winnipeg met and an Edmonton met on there.
The leaf is usually most evident on water vapour, but you can pick it out on any satellite image--visible, infrared.
WV imagery primarily shows the moisture in the layer approximately from 600 to 400 mb. This corresponds to the mid levels of the atmosphere, about 5 km above the surface. It's not so much for the moisture (although there is some use of that, which I'll get into shortly) but more for the placement of upper-level features. On a WV image you can readily pick out troughs and ridges, as well as vorticity centres (swirlies) and jet streaks.
The jet streak is where you usually see a relatively thin channel of drying on the WV image. This is indicative of drying, which is caused by the circulations around a jet streak. The air ahead of and to the left of the jet streak (known as the "left exit"), as well as behind and to the right ("right entrance"), is rising. To conserve mass, somewhere the air must be sinking. Often the vertical circulations are strong enough that very very dry stratospheric air is brought down into the troposphere, making the region much drier; hence the dryness on the WV imagery.
So when you see supercells pop out on what's supposedly dry, what you're seeing is the area where there is good "ventilation" aloft for the storm--there is enough upward motion to promote supercell (or any kind of thunderstorm) development. Further to that, though, dry air intrusions in mid levels of the atmosphere can intensify thunderstorms by steepening the lapse rates, making updrafts more vigorous.
To see moisture in the low levels, you need 3.9 micron infrared imagery (often called the fog channel) or visible imagery. And, of course, observation charts at the surface and up to about 850 mb.
Dave - thanks for the deformation zone information. It helped!
Jim Patterson