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Atmospheric mechanics and thermodynamics

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Roger Critchlow-2

Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Nick Thompson

Re: Atmospheric mechanics and thermodynamics

Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks. One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [mailto:[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --

Carl Tollander

Re: Atmospheric mechanics and thermodynamics

What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Corn.

Out by Grand Island, everything is planted in corn, due to corn prices. Supported largely by irrigation from wells (the Platte River being a mile wide and inch deep, except when its not).   Right now, miles and miles and miles of dried up corn husks, because of the drought and the Ogallala Aquifer not being what it once was.   If corn future prices hit a certain level, it might become reasonable economically to turn on the pump anyway and you can end up with a very sudden humidity spike over a large area that was hours or minutes before, very very warm and dry.   When do you do that? After sunset, to minimize loss due to evaporation, since water is at a premium.

Or not. Speculative. Checkable.   Not quite sure what the model would be then....

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:

Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Carl Tollander

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Nick Thompson

Uneducated question.

I there any relationship between the heat burst question and wildfire weather dynamics? Yesterday there was a 20000 foot smoke monster above one of the local fires. We just see the outside of that.

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:

Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Steve Smith

Re: Atmospheric mechanics and thermodynamics

Carl-

Is 20,000 an official number?

My estimates of height were closer to 40000 from the relative scale of the Sangres (~5000 above local elevation) and the top of the cloud (about 8x as seen driving back from ABQ from the top of La Bajada).

- Steve

Uneducated question.

I there any relationship between the heat burst question and wildfire weather dynamics? Yesterday there was a 20000 foot smoke monster above one of the local fires. We just see the outside of that.

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Steve Smith

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Carl Tollander

What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Corn.

Reminds me vaguely of the punchline in a (Bruce Sterling?) short story about a US Weather Service computer churning on the question of how to redirect the path of tornados away from populated areas.

It's answer was to set up large mobile home parks in otherwise empty areas to draw the tornados to them.

- Steve

Out by Grand Island, everything is planted in corn, due to corn prices. Supported largely by irrigation from wells (the Platte River being a mile wide and inch deep, except when its not). Right now, miles and miles and miles of dried up corn husks, because of the drought and the Ogallala Aquifer not being what it once was. If corn future prices hit a certain level, it might become reasonable economically to turn on the pump anyway and you can end up with a very sudden humidity spike over a large area that was hours or minutes before, very very warm and dry. When do you do that? After sunset, to minimize loss due to evaporation, since water is at a premium.

Or not. Speculative. Checkable. Not quite sure what the model would be then....

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Carl Tollander

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Steve Smith

I read it on iciweb or nmfireinfo or something. Not at all surprised if it was much higher.

On 6/12/13 9:13 PM, Steve Smith wrote:

Carl-

Is 20,000 an official number?

My estimates of height were closer to 40000 from the relative scale of the Sangres (~5000 above local elevation) and the top of the cloud (about 8x as seen driving back from ABQ from the top of La Bajada).

- Steve
Uneducated question.

I there any relationship between the heat burst question and wildfire weather dynamics? Yesterday there was a 20000 foot smoke monster above one of the local fires. We just see the outside of that.

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Carl Tollander

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Steve Smith

Trailer parks create their own weather, if cities can.

On 6/12/13 9:19 PM, Steve Smith wrote:

What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Corn.

Reminds me vaguely of the punchline in a (Bruce Sterling?) short story about a US Weather Service computer churning on the question of how to redirect the path of tornados away from populated areas.

It's answer was to set up large mobile home parks in otherwise empty areas to draw the tornados to them.

- Steve
Out by Grand Island, everything is planted in corn, due to corn prices. Supported largely by irrigation from wells (the Platte River being a mile wide and inch deep, except when its not). Right now, miles and miles and miles of dried up corn husks, because of the drought and the Ogallala Aquifer not being what it once was. If corn future prices hit a certain level, it might become reasonable economically to turn on the pump anyway and you can end up with a very sudden humidity spike over a large area that was hours or minutes before, very very warm and dry. When do you do that? After sunset, to minimize loss due to evaporation, since water is at a premium.

Or not. Speculative. Checkable. Not quite sure what the model would be then....

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Nick Thompson

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Carl Tollander

What I don’t understand is why all that rising moist air doesn’t produce a shower.

Nick

From: Friam [mailto:[hidden email]] On Behalf Of Carl Tollander
Sent: Wednesday, June 12, 2013 10:10 PM
To: [hidden email]
Subject: Re: [FRIAM] Atmospheric mechanics and thermodynamics

On 6/12/13 1:31 PM, Nicholas Thompson wrote:

Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.
As this air cools it will become more dense,
NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Steve Smith

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Carl Tollander

On 6/12/13 9:29 PM, Carl Tollander wrote:

Trailer parks create their own weather, if cities can.

In this case, I think the conceit was that the computer found the *strong correlation* between tornado damage reports and trailer parks (since that is where the threshold for damage is lower than conventional homes).

On 6/12/13 9:19 PM, Steve Smith wrote:
What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Corn.

Reminds me vaguely of the punchline in a (Bruce Sterling?) short story about a US Weather Service computer churning on the question of how to redirect the path of tornados away from populated areas.

It's answer was to set up large mobile home parks in otherwise empty areas to draw the tornados to them.

- Steve
Out by Grand Island, everything is planted in corn, due to corn prices. Supported largely by irrigation from wells (the Platte River being a mile wide and inch deep, except when its not). Right now, miles and miles and miles of dried up corn husks, because of the drought and the Ogallala Aquifer not being what it once was. If corn future prices hit a certain level, it might become reasonable economically to turn on the pump anyway and you can end up with a very sudden humidity spike over a large area that was hours or minutes before, very very warm and dry. When do you do that? After sunset, to minimize loss due to evaporation, since water is at a premium.

Or not. Speculative. Checkable. Not quite sure what the model would be then....

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com

Carl Tollander

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Nick Thompson

Re; smoke monster, it's like seeing inside a tornado. We don't know.

OTOH, if it was moist, maybe there wouldn't have been a fire?

We may be conflating questions, here. Was originally just trying to see if one or the other model was any simpler.

On 6/12/13 9:32 PM, Nicholas Thompson wrote:

What I don’t understand is why all that rising moist air doesn’t produce a shower.

Nick

From: Friam [[hidden email]] On Behalf Of Carl Tollander
Sent: Wednesday, June 12, 2013 10:10 PM
To: [hidden email]
Subject: Re: [FRIAM] Atmospheric mechanics and thermodynamics

Uneducated question.

I there any relationship between the heat burst question and wildfire weather dynamics? Yesterday there was a 20000 foot smoke monster above one of the local fires. We just see the outside of that.

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

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Carl Tollander

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Steve Smith

There's a lot more corn area than there are trailer park area. Also still not convinced interacting microclimates aren't relevant. The corn thing could indeed produce showers, maybe. But it's nightime so maybe it did. Nobody said anything about the humidity going up or down as the temperature blasted.

On 6/12/13 9:38 PM, Steve Smith wrote:

On 6/12/13 9:29 PM, Carl Tollander wrote:

Trailer parks create their own weather, if cities can.

In this case, I think the conceit was that the computer found the *strong correlation* between tornado damage reports and trailer parks (since that is where the threshold for damage is lower than conventional homes).
On 6/12/13 9:19 PM, Steve Smith wrote:
What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Corn.

Reminds me vaguely of the punchline in a (Bruce Sterling?) short story about a US Weather Service computer churning on the question of how to redirect the path of tornados away from populated areas.

It's answer was to set up large mobile home parks in otherwise empty areas to draw the tornados to them.

- Steve
Out by Grand Island, everything is planted in corn, due to corn prices. Supported largely by irrigation from wells (the Platte River being a mile wide and inch deep, except when its not). Right now, miles and miles and miles of dried up corn husks, because of the drought and the Ogallala Aquifer not being what it once was. If corn future prices hit a certain level, it might become reasonable economically to turn on the pump anyway and you can end up with a very sudden humidity spike over a large area that was hours or minutes before, very very warm and dry. When do you do that? After sunset, to minimize loss due to evaporation, since water is at a premium.

Or not. Speculative. Checkable. Not quite sure what the model would be then....

C.

On 6/12/13 1:31 PM, Nicholas Thompson wrote:
Dear Fans of Elevated Mixing Layers,

I have several questions about the account of the heat burst (reproduced below). But first, let’s develop a bench language between us that will help us avoid confusion. Let’s call air that is warmer than average for its altitude “Warm” and air that is colder than average for its altitude, “Cold.” And let’s call “Moist”, air that has a high content of water vapor and distinguish it from air that is accompanied by lots of liquid or frozen water which we will call, “water burdened.”. The capital letters in each case will remind us that Warm air may not be cozy and Dry air may have a lot of moisture with it. Thus, air can have a temperature many degrees below zero and still be Warm and can be Dry, even though it is mixed with many tons of water.

Ok, so now for the problems:

A heat burst is caused when a shower or thunderstorm weakens over a layer of dry air. As the last of the precipitation from the weakening shower or thunderstorm falls through the layer of dry air NSTèNote that the explanation as written does not make use of the fact that this falling precipitation will impart downward momentum to any air if falls through. çNST, the precipitation begins evaporating thus causing the air to cool.

As this air cools it will become more dense,

NSTè Hold on, here. Evaporation will also cause the air to become less dense because it is becoming more Moist. I am not sure how trade off between these two variables works. I would love to see a table with temp on the x axis, water vapor on the y axis and density on the z axis. In fact, I would like to see a family of such tables for different levels of the atmosphere. çNST eventually more dense when compared to the surrounding warmer air and as a result, begins descending to the surface at a high rate of speed. Eventually, all of the precipitation within the descending air evaporates. NSTè So, now we have a Cool, Moist falling airmass. This sort of thing happens all the time in thunderstorms and is called a “downburst”. çNST At this point the air is completely dry NSTèNo. Wrong. The most that can be said is that all the water in it has evaporated. This does not make it Dry. In fact, it makes it Moist. çNST and because no more evaporation can occur, the air can no longer cool. The air however continues to descend toward the surface due to the momentum it has already acquired. As dry air descends through the atmosphere, compression due to increasing atmospheric pressure causes the air to warm. NSTè Well, I suppose. But we still have Moist air, don’t we? As it descends, it’s relative humidity will fall, but the amount of water vapor in the packet will not decrease because the packet is falling. çNST It is important to note that the density of this air is now going to begin decreasing because of the increasing temperature. However, because the descending air already has a great deal of momentum carrying it to the surface, the increase in temperature and resultant decrease in density does little to slow the descending air. So, the dry air continues to descend, all the while warming more and more due to the aforementioned compressional heating. Eventually, this descending air reaches the surface and the momentum, which was moving downward towards the surface, is now moving horizontally along the surface in all different directions, thus resulting in a strong wind! In addition, the intrusion of the very warm and very dry airmass from aloft, will cause the temperature at the surface to increase very quickly, and the dewpoint at the surface to decrease very quickly. Acquiring all the needed ingredients for a heat burst can be difficult, thus making the development and observance of a heat burst rare. NSTè We all know there was an elevated mixing level (layer of very Warm, Dry air) over running Moister Cooler air moving up from the Gulf. If we could find a way to get that layer down to the surface, then we would have explained the heatburst. The only think I can think of is that the falling mass of ice and water and the mass of falling air it took with it actually drives the EML through to the surface, but does not itself reach the ground. Ugh. More skyhooks.   One feature of this explanation that puzzles me is the fact that the heat burst lasts as long as it does. A typical down burst last for a few minutes at most. Why does this warm air which (ex hypothesi) is less dense than the air it has penetrated not “bounce”.

Also, I am wondering if a falling mass of ice and water can reach the ground but set up a downward momentum in the column over it that will continue to drag air down to the surface for some time after the moisture is out of the picture.

These heat bursts seem a lot like Chinooks. A Chinook is also an exceptionally hot and dry wind. They occur when a Cool Wet airmass is driven over a high mountain range. The increase in altitude of the air squeezes out all the moisture and when the airmass comes down the other side of the mountain range it is hot and dry. What we need to explain heat bursts perhaps is to discover something out there on the flatlands to perform the function of the mountain range.

Nick

From: Friam [[hidden email]] On Behalf Of Roger Critchlow
Sent: Tuesday, June 11, 2013 2:26 PM
To: The Friday Morning Applied Complexity Coffee Group
Subject: [FRIAM] Atmospheric mechanics and thermodynamics

I was highly amused to read the description of how a heat burst happens here:

  http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/06/11/stunning-late-night-heat-burst-in-nebraska-99-degrees-at-5-am/

because it invokes the momentum of an atmospheric packet, something that I don't think any of our weather discussions has ever brought into our explanations.

Also note how the explanation proceeds as a logical-causal fait accompli, there is no physics or math involved in the explanation, just a narration of a sequence of physical causes.

-- rec --
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
to unsubscribe http://redfish.com/mailman/listinfo/friam_redfish.com
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Meets Fridays 9a-11:30 at cafe at St. John's College
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Arlo Barnes

Re: Atmospheric mechanics and thermodynamics

In reply to this post by Steve Smith

In this case, I think the conceit was that the computer found the *strong correlation* between tornado damage reports and trailer parks (since that is where the threshold for damage is lower than conventional homes).

Populated areas might have been defined for the computer as 'areas with a population density above a certain threshold' to eliminate the extra load of having the computer calculate a path that also avoids that one hermit out in the middle of nowhere, the programmers being concerned mostly with cities and suburbs. The computer's solution? Eliminate "populated areas" by spreading the local population out evenly over the ground, using RV trailers as the method by which such widespread housing could be comparatively quickly/easily/cheaply established. Boom - problem solved!
That might be overanalyzing the humour, though. :P
-Arlo James Barnes

Steve Smith

Re: Atmospheric mechanics and thermodynamics

Arlo -
> ... The computer's solution? Eliminate "populated areas" by spreading
> the local population out evenly over the ground, using RV trailers as
> the method by which such widespread housing could be comparatively
> quickly/easily/cheaply established. Boom - problem solved!
> That might be overanalyzing the humour, though. :P
This is FRIAM... there is little chance of overanalyzing *anything*!

Carry on,
- Steve

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