The Role of Elevated Mixed Layers in Severe Weather

[PyroCu]

The equation of state is as follows: Pressure = (density) * (gas constant) * (temperature). So, colder air is more dense, assuming constant pressure. That's the key...pressure is not constant, especially in the vertical. And rocks definitely do not float...if there is less dense air below more dense air, it will overturn immediately. You'll see this condition in very limited circumstances (e.g., above a BBQ grill, a mirage in the desert, over a hood of a car on a hot day, etc.. Since the index of refraction changes when the density profile is inverted, you'll see that wavy appearance in the air immediately above these surfaces. As far as moisture goes, it is generally dealt with by using the virtual temperature, which is used in place of the temperature in the equation of state above. It's a small correction factor...the fundamental principle is still the same. So cold pools aloft, EMLs...the bottom line is that the atmosphere is in hydrostatic balance 99% of the time. Such features are not an exception. 

[ThompNickSon]

Dear PyroCu,

 

I am glad to have you state so baldly what I have always assumed, but never could quite get anybody else to assert, that if there is less dense air over more dense air, it will overturn immediately.  Nice to have that one in the bank.  However, I still wasn't clear, after I read your post, if you were agreeing or disagreeing with my notion that that a cold pool could only be less dense than warmer air below it by virtue of being moister.  (By "warmer" and "cool" of course, we are speaking of altitude-relative temperature).  n

[PyroCu]

If there is more dense air above less dense air, it will overturn immediately, yes.

 

We measure atmospheric water vapor in terms of grams per kilogram, and it doesn't exceed about 4% per unit volume even in a tropical environment. Whether the "cold pool" aloft is relatively moist or not is not of first order importance to understanding hydrostatic balance.     

[ThompNickSon]

Ok.  People keep banging that into my head and I think I am finally getting the point.  Water vapor does not make THAT much difference.  However, then, given that cool air is heavier that warm air, other things being equal, what keeps it up there? 

 

Perhaps this will help:  Boston is said to be under a "cold pool" at the present.  Here is a recent sounding from Chatham, south of Boston.  I assume the cold pool is the layer from 850 to 600 mb where the red dotted line exceeds the red solid one.  Before I read your comment I was inclined to explain the fact that it stays up there to the fact that the dewpoint is rising over that same range ... the air is getting moister with altitude ... a characteristic of EML's as well. 

 

The weather here, 70 miles west of Boston, is characterized by broken strato cumulus with some fractocumumulus below.  Can you help me see how this sounding relates to my clouds? 

 

[PyroCu]

Ok.  People keep banging that into my head and I think I am finally getting the point.  Water vapor does not make THAT much difference.  However, then, given that cool air is heavier that warm air, other things being equal, what keeps it up there? 

 

Perhaps this will help:  Boston is said to be under a "cold pool" at the present.  Here is a recent sounding from Chatham, south of Boston.  I assume the cold pool is the layer from 850 to 600 mb where the red dotted line exceeds the red solid one.  Before I read your comment I was inclined to explain the fact that it stays up there to the fact that the dewpoint is rising over that same range ... the air is getting moister with altitude ... a characteristic of EML's as well. 

 

The weather here, 70 miles west of Boston, is characterized by broken strato cumulus with some fractocumumulus below.  Can you help me see how this sounding relates to my clouds? 

 

The atmosphere is a fluid. What "keeps it up there" is hydrostatic balance. This is the vertical balance of forces between gravity - which points down toward the Earth, and the vertically directed pressure gradient force - which points up (from higher pressure near the surface to lower pressure aloft; see the y-axis on the sounding). If a volume of air is relatively heavy or light will be manifest as changes in atmospheric pressure to maintain hydrostatic balance, which is one reason why we analyze pressure on weather maps. Note that moisture does not need to be considered to explain this balance. 

 

Note also that a "cold pool" is a relative minimum in temperature as seen on a constant pressure (or constant height) chart. In other words, it's a temperature minimum in a horizontal or quasi-horizontal sense. The temperature through the troposphere typically decreases with height, so a "cold pool" isn't any different in that sense.  

 

On the sounding, where the temperature and dewpoint come together are typically levels associated with clouds, since the environment is at/near saturation. So, on the CHH sounding this is the case very near the ground and there is also a moist layer between 750-675mb.  

[calm_days]

Long water vapor animation from 6-16 and 6-17

 

Yes, the most recent severe weather outbreak does seem to have a logical explanation in hydrostatic balance, as far as hydrostatic balance can explain abnormal and extreme adjustments in the atmosphere layers.  In this case the hydrostatic balance of the large clockwise flow in the pacific seems to have been connected with the severe outbreak.  I'm certain there is clearer analysis to be gained from the deeper levels of data available to professionals; and this satellite data itself is thanks to many forum members for helping to identify a source of satellite imagery of this event that was not scrambled by some sort of error.  

 

The atmosphere is a fluid. What "keeps it up there" is hydrostatic balance. This is the vertical balance of forces between gravity - which points down toward the Earth, and the vertically directed pressure gradient force - which points up (from higher pressure near the surface to lower pressure aloft; see the y-axis on the sounding). If a volume of air is relatively heavy or light will be manifest as changes in atmospheric pressure to maintain hydrostatic balance, which is one reason why we analyze pressure on weather maps. Note that moisture does not need to be considered to explain this balance.

[ThompNickSon]

Thanks again, Calm Days, for another stunning WV loop.  If you learn anything that connects the vigorous anticyclonic flow in the pacific with the severe weather in the US, please post it. 

 

I have not had time to do my homework about hydrostatic balance, so the following may not be worth an answer.  But just in case:  I like to think in terms of potential temperature.  So when I speak of warm air, it is air at any altitude which, if it were brought down to the surface, would be warm.  Or, to put it another way, air that is relatively warm, relative to the mean temperature of air at the same altitude.  Similarly with "dense" or "heavy" air.  So, from my point of view the following question comes to mind:  How is saying that something is caused by hydrostatic balancing different from saying that something is caused by the fact that things that have a greater potential density tend to fall, and things that have a lesser potential density tend to rise.  So the mystery is how do things ever get out of hydrostatic balance in the first place.  Now we know "hot pools" form at the surface.  that's the whole story of heating at the surface building up under a cap.  But how do cold pools form in higher levels of the atmosphere?  I am in correspondence with a very kind professional meteorologist who gave me a brief and technical description about how cold core lows form cold pools.  Unfortunately, I did not understand it.  But, by analogy with the "hot pools" that form below a cap, I would be tempted by a theory that, say, dry warm air  brought to the top of the atmosphere by the process of convection and wringing out of its moisture, if it stays there long enough, radiates enough heat to become "heavy" , and then, "falls", giving us the snow flurries for which the NE can be famous in the winter.  But then I would need something analogous to a cap, to keep it from mixing down as it warmed cooled (!-nst).   All of this is, of course,mere madness, but I haven't had time to work out a sane version.

 

All the best,

 

N

[PyroCu]

Long water vapor animation from 6-16 and 6-17

 

Yes, the most recent severe weather outbreak does seem to have a logical explanation in hydrostatic balance, as far as hydrostatic balance can explain abnormal and extreme adjustments in the atmosphere layers.  In this case the hydrostatic balance of the large clockwise flow in the pacific seems to have been connected with the severe outbreak.  I'm certain there is clearer analysis to be gained from the deeper levels of data available to professionals; and this satellite data itself is thanks to many forum members for helping to identify a source of satellite imagery of this event that was not scrambled by some sort of error.  

 

Hydrostatic balance is an equilibrium condition. The point being that cold pools or EMLs don't simply fall down because there is a vertical balance of forces (which was the question that had been posed). Hydrostatic balance doesn't describe severe weather, in which there are small-scale departures from this equilibrium state due to buoyancy. With convective motions, you'll see air motions on the order of 1-10 m/s with updrafts and downdrafts.  

[PyroCu]

Thanks again, Calm Days, for another stunning WV loop.  If you learn anything that connects the vigorous anticyclonic flow in the pacific with the severe weather in the US, please post it. 

 

I have not had time to do my homework about hydrostatic balance, so the following may not be worth an answer.  But just in case:  I like to think in terms of potential temperature.  So when I speak of warm air, it is air at any altitude which, if it were brought down to the surface, would be warm.  Or, to put it another way, air that is relatively warm, relative to the mean temperature of air at the same altitude.  Similarly with "dense" or "heavy" air.  So, from my point of view the following question comes to mind:  How is saying that something is caused by hydrostatic balancing different from saying that something is caused by the fact that things that have a greater potential density tend to fall, and things that have a lesser potential density tend to rise.  So the mystery is how do things ever get out of hydrostatic balance in the first place.  Now we know "hot pools" form at the surface.  that's the whole story of heating at the surface building up under a cap.  But how do cold pools form in higher levels of the atmosphere?  I am in correspondence with a very kind professional meteorologist who gave me a brief and technical description about how cold core lows form cold pools.  Unfortunately, I did not understand it.  But, by analogy with the "hot pools" that form below a cap, I would be tempted by a theory that, say, dry warm air  brought to the top of the atmosphere by the process of convection and wringing out of its moisture, if it stays there long enough, radiates enough heat to become "heavy" , and then, "falls", giving us the snow flurries for which the NE can be famous in the winter.  But then I would need something analogous to a cap, to keep it from mixing down as it warmed.   All of this is, of course,mere madness, but I haven't had time to work out a sane version.

 

All the best,

 

N

 

The word "potential" implies that air would have a particular temperature or density if it were displayed dry adiabatically to a different pressure level. 1000mb is the level typically used as a reference. The point remains that density has to decrease as you go up in the atmosphere. A cold pool aloft simply isn't "heavier" than the air beneath it. Pressure is due to the weight of all the air above a particular point. So, if you are at the ground (say around 1000mb at sea-level), there is more weight of the air above than there would be at 700mb, or 500mb because there is less depth of atmosphere as one goes upward.

 

Another point is that temperature typically decreases as you go upward in the troposphere. A "cold pool" refers to a relative minimum in temperature in a quasi-horizontal sense. Temperature may decrease more rapidly with height with a cold pool (i.e., steeper lapse rates), but temperature still typically deceases on average as you go upward from the surface through the troposphere. So, obviously there is a general state of balance with colder air aloft...otherwise the atmosphere would be "falling down" everywhere! 

 

Hydrostatic balance is an excellent assumption. Consider that for synoptic systems (highs and lows, as they might appear on a weather map), vertical motions are typically on the order of cm/s. This is a very small deviation from the vertical force balance, but is still enough to create important weather. Consider that horizontal motions in the atmosphere are typically on the order of 10 ms-1. That is a difference of 3-4 orders of magnitude. Where more appreciable vertical motions exist due to convection (on the order of ms-1), it tends to be over small areas and are a result of strong buoyant forces due to radiative and diabatic processes. A cold pool aloft might cover hundreds of miles. Individual thunderstorm updrafts are much smaller than this. So, we can't really equate strong vertical motion associated with thunderstorms to the larger-scale processes you are interested in.  

 

A cold pool aloft arises - in part - from sustained synoptic-scale vertical ascent. We often see them in association with slow-moving low pressure systems aloft. As warm air rises it expands and cools, again, because the pressure is decreasing aloft. This can create a relative minimum in temperature over a certain area and it may persist for days as cut-off lows gradually weaken. 

 

You’re asking good questions, but keep in mind that these are topics covered in undergraduate thermodynamic courses for atmospheric science majors, which are rooted in calculus and physics. If explanations seem unsatisfactory, it is because they can be difficult to arrive at intuitively without that type of theoretical background. 

[ThompNickSon]

Dear PyroCu,

 

Many, many thanks for your post.  I will respond to the technical points in a minute, but here I want to make a broader point, inspired by your last comment.

 

 

The word "potential" implies that air would have a particular temperature or density if it were displayed dry adiabatically to a different pressure level. 1000mb is the level typically used as a reference. ....[LONG DELETION]

 

"... keep in mind that these are topics covered in undergraduate thermodynamic courses for atmospheric science majors, which are rooted in calculus and physics. If explanations seem unsatisfactory, it is because they can be difficult to arrive at intuitively without that type of theoretical background. 

I taught a technical subject for many years but I grew up in a publisher's family, so I used to tell my undergraduates that "they couldn't really say they understand something until they could explain it to their roommates."   If you have some freshman meteorologists you would like to sick on me, I am all for it.  As a retired person I deeply miss those sorts of interactions with students who are struggling to master a field; so, seriously, if anybody wants to pass on to me some students the project of getting an old dumb guy to understand hydrostatics, I would be grateful to them. 

 

Now I DON'T want to turn this thread (which has brought together so many good, thoughtful, patient comments) into a thread on philosophy of science, but I genuinely am curious about what it is to UNDERSTAND something.  I think that understanding something is not just being able to work the equations.  Before you understand something you have to have a workable MODEL of it.  Models, formal and informal, are everywhere in meteorology and they interact in all sorts of interesting ways, because meteorologists, perhaps even more then doctors, are experts who have to make themselves understood by The Public. "Pool" is already a model; "cap" is a model.    When you suspend a pool overhead, you violate the model of a pool (cf Fukishima).  The modeler may or may not intend those violations, but s/he has to deal with them. 

 

In my experience, the lack of an adequate model can lead smart people into error.  I think you will see some of that in  our discussion here on EML's  where there is confusion between a dry line and a cold front.  That leads the writer to assign to the dryline both the role of a cold front (undercutting, lifting) and the role of a warm front (capping)  and miss the singularly important point that it is the warm air (potentially warm, remember) running out ahead of the dry line at mid-altitudes that makes the plains states' atmospheres so dangerous.  The dry line IS a warm front, of sorts, although, admittedly, a very strange one.

 

Thanks again,

 

N

[ThompNickSon]

Dear PyroCu,

 

To avoid me being confused, let's always insert the word "potentially" to modify any parameter where we are referring to the properties of a packet of air relative to its surroundings (or how it would feel if it were brought down to us)  and the word "actually" to refer to how it would feel to us if we were taken up there with it.  So, for instance, the air at high altitudes, ahead of a warm front is actually cold, but potentially warm.  We agree that its potential warmth is what determines its behavior, right?   So I am going edit your message below in accordance with these understandings.  You follow along and see if I got it right.  My additions are in red.  Readers should be aware that PyroCu had nothing to do with the red bits. 

 

The word "potential" implies that air would have a particular temperature or density if it were displayed dry adiabatically to a different pressure level. 1000mb is the level typically used as a reference.  ....

 

Another point is that actual temperature typically decreases as you go upward in the troposphere. A "potentially cold pool" refers to a relative minimum in temperature in a quasi-horizontal sense. Actual Temperature may decrease more rapidly with height within a potentially cold pool (i.e., steeper lapse rates), but actual temperature still typically deceases on average as you go upward from the surface through the troposphere. So, obviously there is a general state of balance with actually colder air aloft...otherwise the atmosphere would be "falling down" everywhere! 

 

Am I correct so far? PyroCu continues: 

 

A potentially cold pool aloft arises - in part - from sustained synoptic-scale vertical ascent. We often see them in association with slow-moving low pressure systems aloft. As potentially warm air rises it actually expands and actually cools, again, because the pressure is decreasing aloft. This can create a relative (!!!) minimum in temperature over a certain area and it may persist for days as cut-off lows gradually weaken. 

 

Do you see my problem?  A cold pool is potentially cold (or relatively cold, as you put it).  But how do you get a potentially  cold pool, by raising air that is potentially warm to a high altitude?   I see how you get air that is actually cold, but not how you get air that is potentially cold. 

 

At the risk of driving everybody nuts, allow me to pursue for a moment the cold pool "model".  A pool, to be a pool, has to be restrained by an impervious medium of some sort.  So, pursing that idea, what could be the medium that contains the cold pool?  Now, a mature extra tropical cyclone, as you make clear, generates energy by advecting potentially warm, moist, air over potentially cooler, dryer air.  In so doing, it wrings the moisture out of it making it potentially even warmer.  Since a mature low is a spiral, in wraps this air around itself.  So we have a circle of warm, dry air up there?  Could that be the container of the pool, in some sense.  Or:  here's another thought.  Does the fall of moisture out the layer that is wrung out carry so much heat out of the advected air that it becomes potentially cold?  It would have to carry away not only the realized latent heat  of the wrung out moisture, but also the original potential heat that existed in teh airmass at the beginning of the process.

 

Ok.  Bad idea!  Forget the "cold pool" model.  Let's work with a wash-basin model, for a minute.  When I stir the water in the washbasin, the water level falls in the center of the whirlpool.  That happens even without pulling the plug out of the basin. ILet's say that an extra tropical cyclone works that way.    Because (unlike a hurricane) it is cyclonic all the way up, it's center is evacuated at high levels of the atmosphere and therefore "cold".   OK, now I am in trouble.  Is it potentially cold or just actually cold.  If we returned the packet to 1000mb, it would not be cold, so it it's not;  But if we returned the entire circulation to the surface, it would still be evacuated, and therefore would prove to be potentially cold..  But not by comparison with an average airmass spinning at the same speed.  

 

Ok.  Another bad idea.  

 

Well, anyway.  Thanks for helping me think about it.   

[thewxmann]

BTW, for a sexy elevated mixed layer, the OAX sounding from 06/18 0Z (the day of the Coleridge tornado) is a classic. Nearly dry adiabatic lapse rates in the layer and nice inversion at the bottom. The steep lapse rates contributed to over 6000 J/kg of SBCAPE!

[ThompNickSon]

thanks, the wxman,

 

Here for others to see is that skewT.  It would be fabulous if some of you wise folks could comment on other features of this sounding.  0000Z is about 7 am in Iowa, right?   The second image is the same station 12 hrs later.   The cap has increased.  Again, love to hear some wise comment on that.   Thanks, all.  N.

 

 

 

[thewxmann]

No, 0Z is around 7 PM. The subsequent 12Z sounding would be at 7 AM.

[ThompNickSon]

Sorry, I went backwards.  So, the two soundings I posted were for 7pm on the 17th and 7am on 18th?  The tornado, according to news reports, was on the ground a 9pm.  Hard to imagine anything scarier than a nighttime tornado. 

 

N

[PyroCu]

Well, I believe a discussion of potential temperature and related variables can only be useful through a solid understanding of the relevant equations. In my view, there is little to be gained by having a specific discussion about application of theoretical concepts in meteorology without that foundation.

 

There are many good reads on the elevated mixed layer, and interested individuals should start with those scientific papers as published by the American Meteorological Society and elsewhere. It's perfectly okay if there are parts that aren't fully understood. Even experienced meteorologists with multiple degrees may be unfamiliar with certain methods used to achieve some results. That can serve as an opportunity to investigate things further. 

 

For a weather enthusiast, just getting a qualitative understanding of the abstract and conclusions can be a helpful and exciting way to expand one's knowledge. I think specific questions are easier to answer if they come directly from the scientific literature or from a specific weather event. As an example, the Banacos and Ekster (2010) paper includes an annotated sounding (their Figure 1) and accompanying discussion that would likely be helpful in answering questions about features shown in the Omaha soundings above, which does include a "textbook" EML. There is a link to that paper here if you are interested: http://www.erh.noaa.gov/btv/research/BanacosEML_waf.pdf . 

[ThompNickSon]

PyroCu,

 

Thanks, as always, for your well thought out response.

 

If the Banacos paper is the one I am thinking of, I think I have already gone through it a couple of times.  It is splendid.  However,  time for me to look through it again.  If there are other resources that can be reached on the internet for free or nearly free, please let me know.  I know about the NOAA tutorials, and Haby's material, but probably naive beyond that.

 

I am kind of bending my own thread, here, so feel free to ignore what follows.

 

snip ----------------------------------------------------------------------------------------------------------------------------------------------snip

 

Obviously, fluency with the equations is important, but haven't you known students who are fluent with the equations but lack any grasp of what is going on?  I once talked to to a commercial pilot about the weather.  I suddenly realized during the conversation that he conceived of the atmosphere in terms of routes and rules, but didn't really grasp the three-dimensionality of it.  He didn't have -- to use the language I used above -- adequate "model" of the atmosphere.  Now, I should have been more careful in my use of that term, because I gather, for meteorologists, "model' means, in effect, a very large set of inter-related equations.  That's not the use I intended.  In many sciences, and in philosophy of science, "model" often refers to a thing or process that you understand well that you  bring to bear on a situation you don't understand so well   "Cold Front" and "Warm Front" are "models" originally borrowed, presumably, from military science.   Now, I gather that many meteorologists feel that "models" in my sense are scientificly frivolous, and they should be used -- if ever -- only for communication with the public.  But many good scientists and philosophers of science argue that such "model"s are unavoidable in scientific thought, that inexplicit "models" have their dangers, and that it is best to make one's "models" explicit.  It is this conception of scientific thought that you see working as I try to understand EML's and Cold Pools.

 

end snip ------------------------------------------------------------------------------------------------------------------------------------------ end snip

 

No need to respond to the above.  I am enormously grateful for the help you have given me so far, and we don't need to talk about "meta-science."

 

All the best,

 

N

[PyroCu]

Good discussion. Three quick points: 

 

(1) Available science papers on the EML: 

 

American Meteorological Society (AMS) Journal articles more than 3-years old are open access (i.e., free) and are available at the following URL: http://journals.ametsoc.org/. So, if you wanted to read some of the seminal papers concerning the EML, you can search for elevated mixed layer and get a list of all the relevant papers, read the abstracts, and download the full PDFs if you wish. A good one with regard to Northeast severe weather is Farrell and Carlson (1989), which reviews the 31 May 1985 severe weather outbreak. Here is the link to that one: http://journals.ametsoc.org/doi/abs/10.1175/1520-0493%281989%29117%3C0857%3AEFTROT%3E2.0.CO%3B2. Of course, there is a reference list at the end of each paper, which can lead to further reading. So, that is one way to gain scientific knowledge on different topics in meteorology, including the EML. Of course, there are many people here that can answer questions should they arise, or you can always e-mail the corresponding author to ask questions.   

 

(2) Mathematical fluency vs. forecasting: 

 

You are correct, there are folks who are mathematically fluent how haven't a clue how to forecast, because they don't really have a feel for it or much experience applying their knowledge in that way. The opposite is also true; there are individuals that have a great feel for the data and good empirical knowledge/"rules of thumb" who are among the best forecasters, yet don't have the theoretical knowledge. This is true of many disciplines, of course. You might have an expert in music theory that can't play, or a Jimi Hendrix who could flat out PLAY but didn't read music. 

 

So the point with respect to the EML and cold pool discussion is not attempting to take the thermodynamic theory into a purely qualitative realm, because it gets confusing and isn't necessarily intuitive without analyzing the equations simultaneously, or at least having that foundation to work from.  

 

(3) Mathematical vs. conceptual models: 

 

The non-mathematical models you speak of are called conceptual models, and remain an integral part of meteorology and form an important basis for how we visualize atmospheric processes. I'm not sure about "military science", but the Bergen School of Meteorology led by Vilhelm Bjerknes developed conceptual models of cold and warm fronts and the Norwegian Cyclone Model, which was done near the time of World War I. The term "front" was taken from the battlefield and applied to the emerging conceptual model being developed to analyze mid-latitude weather systems at that time.  

[ThompNickSon]

Thanks, again, PyroCu, 

 

Another very informative post. I will get into the AMS material straightaway.

 

Thanks also for the term, "conceptual model."  Has anybody written about "Conceptual Models in Meteorology"?  How they work?  Advantages and hazards? 

 

N

 

N

[calm_days]

I'm trying to find more complete reports/journal articles about the results of this research as it seems like it will contain a lot of information that will augment what understanding we are exploring about convection and pooling. 

 

http://geo.arc.nasa.gov/

Stratosphere-Troposphere exchange project outline

 

http://geo.arc.nasa.gov 2

Additional processes mentioned including;

 

*horizontal transport mechanisms within the lower stratosphere and between stratosphere and troposphere

*mechanistic modeling using linear gravity wave models / air parcel trajectory calculations

 

Even this may be important; although somewhat less directly connected to EMLs than the above information, the high desert areas you have mentioned still receive a lot of air traffic. 

It was interesting to notice in southern California for example, for about a year I had seen only straight flight paths and straight contrails, and this winter in January or February many flight paths began to curve over the same regions; the curved areas of the contrail tending to remain as clouds of that shape.

This may be happening in other regions too but I am not there to find out.

 

http://geo.arc.nasa.gov/sge/jskiles/fliers/all_flier_prose/cirrusclouds_jensen/cirrusclouds_jensen.html

 

 

[calm_days]

Tropical Composition, Cloud, and Climate Coupling

 

Here is a fairly recent complete research article that, while it doesn't directly mention EMLs, it does seem to pertain to this subject and related subjects in many ways. 

 

This recent spring and early summer convective behavior over CONUS have been more tropical; it could be that the hydrostatic properties that were once more specific to the tropics have been delocalized by changes in moisture balance.

 

I will read through and try to find details that are the most connected. 

[calm_days]

 

A current water vapor image, in this case it seems that the dry area in the far western pacific is like a stone in a river and everything has had to flow around it, causing feedback effects across the pacific and then over the US. 

 

Which one caused which: as per the above article it is also possible that if changes in the troposphere-stratosphere exchange happen on a large scale in one place, it would, as information in this topic is suggesting, affect the hydrostatic balance elsewhere. 

 

If you learn anything that connects the vigorous anticyclonic flow in the pacific with the severe weather in the US, please post it.

 

[ThompNickSon]

we are awaiting relieving thunderstorms in western massachusetts.  Having a hard time getting them started.  Here is the skew T from Albany, this morning.  Is this a "doubly capped" atmosphere?  http://www.spc.noaa.gov/exper/soundings/14072312_OBS/ALB.gif

 

N

[ThompNickSon]

I wonder if some body could help me visualize the geometry of this situation.  Attached  is the progged map

 

 

, . And here is the relevant synoptic discussion:

 

ALL MODELS INDICATE A JET MAX OF 80 KT AT 300 MB PASSING OVER NJ
WHICH PLACES SOUTHERN NEW ENGLAND IN THE LEFT FRONT QUADRANT... A
POSITION FAVORABLE FOR RISING MOTION. IN ADDITION...AN ELEVATED
MIXED LAYER WILL BE PRESENT WITH 500-700 MB LAPSE RATES AROUND
7C/KM. THUS...WITH THE WARM FRONT APPROACHING...THE BAND OF
THUNDERSTORMS THAT WILL BE APPROACHING THE BERKSHIRES AROUND
DAYBREAK SHOULD CONTINUE TO PROGRESS EASTWARD...ESPECIALLY OVER
SOUTHERN NH AND NORTHERN MA...PERHAPS EXITING THE REGION AROUND
NOON OR 1 PM. LOW LEVEL WIND FIELDS WILL BE STRENGTHENING DURING
THE MORNING...TO 30-40 KT AT 5000 FT...AND THIS MEANS THAT ANY
REMAINING STORMS COULD PRODUCE STRONG TO POTENTIALLY DAMAGING
WINDS BEFORE EXITING NORTHEAST MA.

 

The warm front is to the south roughly parallel to teh mason dixon line.  A trough is to the west.  I cannot make a picture of how a warmfront and a eml relate.  Presumably there is warm most air over NE;  but presumably also, there is warm DRY air.  Can anybody else make a picture out of this?

 

N

[calm_days]

168 hour satellite loop

 

I am not certain this imagery will help with the specific question, but, it does show several days of cyclogenesis/water vapor and air interactions;

which may help you figure out more about what keeps the EML type of airmass together and when, where, and why during the path of the systems involved in this event this and related EMLs could have developed.

[Wx4cast]

Here is a link to more on EML's and NEUS severe weather...

http://www.spc.noaa.gov/publications/hurlbut/ne-svr.pdf

[ThompNickSon]

Ok.  So you guys have convinced me that Hot Dry Pools (EML's) can overlie Warm Wet Pools  because you have demonstrated to me that moisture is not as important factor in determining the bouyancy of air as is temperature.  But you have yet to explain to me how Cold Dry Pools can overlie Warm Wet ones.  So, here is a case in point.  I am Western MA and I am told there is a dramatic cold pool aloft.  The weather is showery with alternations of sunny weather, popup showers, and alto stratus blow off, presumably from the showers. 

 

Here is the morning skew T from Albany, just west of us.  (If I can manage to post the darn thing.)  I will try to post the afternoon one when its circulated.

 

 

Notice that the potential temperature of that overlying airmass is 10 degrees  C colder than that of the air mass below it. Why  don't they flipover. 

 

Does anybody know of a chart that shows lines of equal buoyancy for different temperature and dewpoint combinations.  I suppose there would have to be a different one of those for every millibar level  Oh, gosh!  I really don't know what I am talking

about here, do I?

 

[sigh]

 

N

[calm_days]

 

Something as far as the hydrostatic balance and seemingly the region suggested to have a lot to do with some EMLs (Near-pacific high deserts), there has been, maybe it is like this each year but it looks new to me, two continuous spaces of drier air in the northern hemisphere.  The Eurasian-African dry area is very visible in the animation below.  The behavior of them that i find noteworthy in this topic is how persistent they are and how often it seems that upper level lows and related atmospheric turnover cannot seem to make these areas change.  I think that as autumn progresses or by winter, these should change, but otherwise it will bear paying attention.

 

(15 day animation - it doesn't take too long to load considering)

http://www.atmos.washington.edu/~ovens/wxloop.cgi?wv_moll+/15d

 

This was a rare time when there was a temporary image replacement from a satellite with a different scale of moisture to brightness, so that the interior of the dry section could actually be seen. 

 

 

For the second one, this type of image swapping happens for about two frames every 24 hours on the global water vapor images that i can access.  If there was a better source i would be less confused about what makes these areas so persistent and similar. 

[calm_days]

An update to the above:

 

The dry areas have begun to mix again throughout the month of October.

The satellite imagery switch was apparently each day at 2100 UT and this ended after September; see this animation:

 

late Sept - mid October 2100 UT global water vapor

 

I am not certain but now that the satellite imagery is remaining from one source, there are signs of why the satellite images were swapping at 2100 UT , although i am not sure what it is; a pro met may know.    It is two wide areas of dimmed readout in the water vapor that are travelling slowly east over the Eurasian continent (one that is a bit harder to see and more diagonal) and over the Eurasian continent and southern oceans (a long vertical shape). 

 

October composite 2100 UT global water vapor

 

It seems like a satellite anomaly but fairly organic in nature; I can understand why this would lead to initially trying to replace the frame.  What is always present to create this visual phenomenon at 2100 UT?  I am considering making a separate topic but for now it is just an extra subject that was found while observing EMLs.  It isn't meant to take any precedence over any new updates from ThompNickSon and others. 

 

 

 

 

[calm_days]

 

The shadowing is about the size of whatever this quite different satellite anomaly was several years ago (2010); but I'm not sure what this would be.