The Role of Elevated Mixed Layers in Severe Weather

[ThompNickSon]

EML's -- packets of  desert air that originate in the inter-mountain west -- are often invoked to explain severe weather as far away from the Rockies as New England.  For several months I have been puzzling how such dry (heavy, dense) air could maintain its coherence and altitude while passing the two thousand miles from ABQ to BDL.  To put the question in the least technical way possible:  Why wouldn't it fall down?  Looking at SKEW-T's I see that such parcels of air are fairly common in the East, manifesting themselves as a sharp rightward movement of the temperature line, and a very sharp, leftward movement of the dewpoint line at some point above the surface, with the two lines reconverging at higher altitudes to form a sort of tent-like pattern.  Over the last year, many intelligent and experienced people have contributed to this thread, and I am enormously grateful to them.  Their work is a great resource for anybody curious about layering in the atmosphere and its relation to severe weather. 

 

 

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[weatherwiz]

Absolutely!!!  I would discuss this with you all day.

 

First off, you should read these following papers by Michael Ekster and Peter Banacos on EML's.  When it comes to severe weather and SNE he is the man to go to.

 

http://www.erh.noaa.gov/btv/research/BanacosEML_waf.pdf

 

This paper is on the June 1st, 2011 event by Michael Ekster, Joe Dellicarpini, Eric Lyons, and Peter Banacos

 

http://www.erh.noaa.gov/box/papers/June_1_Sever_Weather_Analysis.pdf

[ThompNickSon]

Thanks for being so welcoming.  I will read the papers you attach,  but they are technical and it will take me some time.  In the meantime, could I check some assumptions with you?  I will paste in one of the SkewT's from the first paper so we have something to look at whie we talk.

 

I assume that it is universally true of all atmospheres that air density declines with altitude --that there is never (for long, anyway) a denser (heavier?) parcel sitting over a less-dense (lighter?) parcel.  So, as the baloon rises, and crosses over into the elevated mixed layer, the fact that the air has less water vapour in it (therefore, more dense for any particular millibar level) must be compensated by it's greater relative temperature (thereby, LESS dense for any particular millibar level). 

 

 

Is there any standard way to think about this tradeoff.  I note that in the above diagram, the air at 750 mb is about five degrees warmer than it "should" be at that altitude, but its dewpoint is 20-30 degrees lower.  I assume that if we were to take a  balloon filled with surface air at that altutude and suck 25 dewpoint-degrees-worth of moisture out of it, we would have to heat it by some number of degrees of temperature for it to continue to rise.  Does that number have a name?  Does it have to do with mixing ratio?  Could the question be put as follows:  how much would I have to raise the temperature of a parcel  for a given decrease in the mixing-ratio in order for the parcell to remain stable.  

 

Don't hesitate to correct my language.

 

Nick

[weatherwiz]

When it comes to the EML's it's very difficult for them to remain completely in tact further east than the Plains.  Even in the instances where EML's do make it to the east coast, often times, they aren't "true" EML's but more plumes of remaining EML air.  As you'll see once you get to reading the papers, there is a very distinct upper air pattern associated with the progression of the EML's from the Intermountain West to the East coast.

 

What you want to see is very strong ridging across the southeastern United States at the 700mb level with very strong anitcyclone curvature of the building ridge.  When the EML is entrained into this ridge, it makes it very difficult for the airmass to become "overturned" or mixed.  Atmospheric mixing in this process can only occur up to a certain height, usually to the base of where the EML begins, especially if the EML is strong.  You can measure strength of an EML by looking at the 850-500 or 700-500mb lapse rates.  Anything above 8-8.5 C/KM is considered quite strong.  The stronger the EML, the tougher it is to achieve mixing through this layer, unless you have some sort of forcing (like a strong cold front) working into the airmass.  

 

As for your question, " we would have to heat it by some number of degrees of temperature for it to continue to rise."  I believe what you're referring or referencing would be dry/moist adiabatic lapse rate.  I believe that as long as the lapse rate remain's dry adibatic that will work to prevent the airmass from become overturned and keep the integrity of the EML intact.  

[Amped]

EML stops storms from firing off tstorms until sufficient CAPE has built up. Without an EML, precip would be more widespread and less focused in intense discrete cells.

 

However, a strong low pressures still produce tornadoes in warm season even without an EML.Land falling TCs  are a good example of this. They don't produce the large cells and high radar returns seen on the plains, but they still produce weaker variety tornadoes.

[weatherwiz]

EML stops storms from firing off tstorms until sufficient CAPE has built up. Without an EML, precip would be more widespread and less focused in intense discrete cells.

However, a strong low pressures still produce tornadoes in warm season even without an EML.Land falling TCs are a good example of this. They don't produce the large cells and high radar returns seen on the plains, but they still produce weaker variety tornadoes.

Your first sentence isn't completely correct...you could have 8000 J of cape but if there is no sufficient lift to break through the cap nothing will pop.

Also I think the OP is referring to EML's and their role on stronger tornadoes and what it takes for EML's to survive their trip to the east coast

[ThompNickSon]

Your first sentence isn't completely correct...you could have 8000 J of cape but if there is no sufficient lift to break through the cap nothing will pop.

Also I think the OP is referring to EML's and their role on stronger tornadoes and what it takes for EML's to survive their trip to the east coast

 

Thanks, Amped.  WeatherWiz, has me exactly right.  ..

 

Here is where you all may have to be patient with me. An EML is a an example of a capping inversion, for sure, but it is a very strange one.  In a "norma"l inversion situation ... as, say with icestorms ... you get a warm moist layer overlaying a cold dry layer.   These situations tend to produce a very stratiform atmosphere. On a skew T, the dewpoint and temp line move together to the right.   Anything that would produce upward motion in teh atmosphere has to overcome two hurdles, the fact that the air above is moister (and therefore lighter) and the fact that the air is (warmer) and therefore lighter.  In an EML, these two factors work in the opposite directions.   The temperature line moves to the right, but the dewpoint line moves sharply to the left.  Now as I understand CAPE (and I am not sure I do), it is the  difference, integrated accross all levels of the atmosphere from the Lifted Condensation Level on up,  between between actual temperature at a given level and the temperature that would have to be at that level for a  parcel, moved from the surface, to be at rest.  If I am correct, then CAPE is at its strongest when the lower atmosphere is moist but the upper atmosphere is DRY.  Such a situation would not be a cap (i.e., would not restrain convection) unless the moist, lower, level is so much cooler than the dry capping layer that convection cannot cross the boundary between them.  .  It is the relation between these two variables that is so interesting to me.   .  . 

 

One of you made a comment that puzzled me,  Since I havent figured out how to go back to the original posts, once I have started a reply, I can't say which.  Sorry.  The comment seemed to imply that a steep lapse rate in the actual atmosphere suppressed convection.  On the contrary, it would seem to me that a steep lapse rate encourages convection.  The steeper the lapse rate , the more likely it is that a parcel warmed at the surface will continue to rise  Since colder dry air is always heavier than warmer dry air, isn't it the case that the dry adiabatic lapse rate is pretty much the steepest  a lapse rate can be.  Thus, the most ideal circumstance for convection is a source of heat and moisture at low levels, and dry air at higher levels.  How much of this do I have wrong? 

 

Please, others who join this thread, look at the earlier posts.  We are trying to build a common understanding, here, and some of the points you might be tempted to raise will have been raised and settled in earlier posts. 

 

Thanks, all,

 

N

[weatherwiz]

Your description of the EML is absolutely correct.  As you stated, on skew-t soundings, once you get to a certain level of the atmosphere you see the temp line quickly jolt to the right with the dewpoint quickly jolting to the left up to a certain level and then the atmosphere becomes cooler again and more moist.  I believe a previous question of yours was, how/why does this stay in tact.  Well, when EML's remain associated along the southern edge of the westerlies (Sub-tropical jet for instance), this will prevent deep atmospheric mixing from occurring.  Since EML's are pockets of very warm/dry air that exist in the upper portion of the lower atmosphere to middle portion of the atmosphere, let's use 800-600 mb as a reference point, you don't want the airmass in this level to be mixed.  Once the atmosphere becomes mixed here, it cools the airmass and also allows for moisture to increase aloft and decrease at the surface, thus weakening the integrity of the EML.  

 

As far as Cape goes, you're right in how it's measured.  That was a nice simple explanation.  Cape is at it's strongest when the surface is hot/moist, along with the lower levels of the atmosphere and the air in the mid levels of the atmosphere are much colder/drier, as you stated.  However, there could still be a cap in this situation b/c if the low levels are very warm, then the convective temperature could be rather high and you would need a strong source of lift to overcome that.  One thing to watch out for is if the mid levels are quite dry and you have strong atmospheric mixing in place, the result would be for drier air to work down to the lower levels and to the surface, lowering dewpoints and Cape values.  Having an EML in place, however, prevents this process from occurring.  

 

Steep lapse rates can certainly enhance the potential for convection as a steep lapse rate environment indicates a great deal of temperature decrease with height so this would allow for a parcel of air to not only rise but rapidly rise.  However, if lift there is no source of lift and you have a strong presence of capping in place, steep lapse rates alone won't do you any good.  

[ThompNickSon]

SORRY TO BE IN CAPS, HERE.  i CAN'T GET THE INTERFACE TO GIVE ME COLORS TO DISTINGUISH MY TEXT FROM YOURS. SO CAPS IT HAS TO BE.  NOT SHOUTING.  NOT EVEN RAISING MY VOICE. NOTE ABSENSE OF EXCLAMATION POINTS. 

 

Your description of the EML is absolutely correct.  As you stated, on skew-t soundings, once you get to a certain level of the atmosphere you see the temp line quickly jolt to the right with the dewpoint quickly jolting to the left up to a certain level and then the atmosphere becomes cooler again and more moist.

 

THIS CONVERSATION IS TRULY SATISFYING TO ME BECAUSE WE ARE NAILING SOME THINGS DOWN.

 

 

 I believe a previous question of yours was, how/why does this stay in tact.

 

YES THAT IS EXACTLY MY PROBLEM. 

 

Well, when EML's remain associated along the southern edge of the westerlies (Sub-tropical jet for instance), this will prevent deep atmospheric mixing from occurring.

 

OK, BUT WHY?  (I KNOW; I SOUND LIKE A THREE-YEAR OLD)  

 

Since EML's are pockets of very warm/dry air that exist in the upper portion of the lower atmosphere to middle portion of the atmosphere, let's use 800-600 mb as a reference point, you don't want the airmass in this level to be mixed.  Once the atmosphere becomes mixed here, it cools the airmass and also allows for moisture to increase aloft and decrease at the surface, thus weakening the integrity of the EML.  

 

I WISH I HAD A MORE PRECISE SENSE OF WHAT IS MEANT BY A "MIXED LAYER" .  A KIND MAN OUT OF THE FORT DODGE, ks, NOAA OFFICE REMINDED ME AT SOME POINT THAT EML'S, EVEN THOUGH THEY PREVENT MIXING, ARE THEMSELVES MIXED.  HIS EVIDENCE WAS THE PRESENSE OF HIGH BASED CUMULUS AT THE TOP OF THE EML.  ALTHOUGH THERE IS VERY LITTLE WATER VAPOR IN AN EML, WHAT WATER VAPOR THERE IS POOLS AT THE TOP OF THE LAYER AND WE GET FAIRWEATHER CLOUD FORMATION.  THUS EML'S ARE MIXED WITH RESPECT TO TEMPERATURE BUT NOT WITH RESPECT TO WATER VAPOUR CONTENT.  ALL THE WATER IS AT THE TOP.

 

 

 

As far as Cape goes, you're right in how it's measured.  That was a nice simple explanation.  Cape is at it's strongest when the surface is hot/moist, along with the lower levels of the atmosphere and the air in the mid levels of the atmosphere are much colder/drier, as you stated.  However, there could still be a cap in this situation b/c if the low levels are very warm, then the convective temperature could be rather high and you would need a strong source of lift to overcome that.  One thing to watch out for is if the mid levels are quite dry and you have strong atmospheric mixing in place, the result would be for drier air to work down to the lower levels and to the surface, lowering dewpoints and Cape values.  Having an EML in place, however, prevents this process from occurring.  

 

I WANT TO MAKE SURE YOU UNDERSTAND MY THOUGHT -- ILL-CONCEIVED OR NOT -- ABOUT "AMBAVLENT" ATMOSPHERES.  WE ==>ARE<==CLEAR  ABOUT SITUATIONS IN WHICH WARM, MOST AIR OVER RUNS COOL DRY AIR.  sUCH ATMOSPHERES ARE HIGHLY STABLE.  BUT WHAT ABOUT SITUATIONS IN WHICH WARM, DRY AIR OVER RUNS COOL, MOIST AIR.  NOW WE AREN'T SO SURE, RIGHT?  WE NEED TO KNOW, HOW MOIST AND HOW COOL.  aND HOW WARM AND HOW DRY.  AND INDEED, WITH AMBIVALENT ATMOSPHERES, WHICH AIR MASS IS LIGHTER AND WHICH HEAVIER COULD DEPEND ON TIME OF DAY, AS THE SUN SHINING ON THE EARTH HEATS AND MOISTENS THE BOUNDARY LAYER.  DO YOU SEE WHAT i MEAN BY "AMBAVALENT".  AM I CORRECT THAT THE TECHNICAL TERM FOR SUCH AN ATMOSPHERE IS "CONDITIONALLY UNSTABLE"?

 

Steep lapse rates can certainly enhance the potential for convection as a steep lapse rate environment indicates a great deal of temperature decrease with height so this would allow for a parcel of air to not only rise but rapidly rise.  However, if lift there is no source of lift and you have a strong presence of capping in place, steep lapse rates alone won't do you any good.

 

AM I CORRECT THAT ANY INSERTION OF MOISTURE INTO AN ATMOSPHERE WITH STEEP LAPSE RATES WILL PRODUCE CONVECTION?  THE INTRODUCED  PACKET OF WATER VAPOUR WILL RISE LIKE A BALLOON TO THE TOP OF THE Eml?  SO THE CAP IS ACTUALLY AT THE BOTTOM OF THE EML, PRESUMABLY AT THE INTERFACE BETWEEN THE EML AND THE LAYER JUST BELOW IT.  

 

BUT IF THE EML IS ACTUALLY HEAVIER THAN THE LAYER BELOW IT, I STILL CAN'T SEE WHY IT WOULD NOT DISPLACE IT.  SO i WON'T OVER-COMMIT TO ONE THEORY, I HAVE TRIED TO DEVISE A ===>LIST<=== OF THEORIES, FROM THE MOST PLAUSIBLE TO THE LEAST PLAUSIBLE, TO EXPLAIN WHY THIS DOES HAPPEN.

 

THEORY 1.  iT DOESN'T HAPPEN BECAUSE IT NEVER GETS A CHANCE TO.  THE EML IS MAINTAINED BY THE FACT THAT IT ALWAYS OVERLAYS A DRYER COOLER LAYER, UNTIL IT IS ADVECTED INTO THE SITUATION IN WHICH IT CAUSES SEVERE WEATHER.  tHIS MIGHT EXPLAIN WHY A HIGHPRESSURE AREA OVER THE SE CONUS EXPLAINS HOW EML'S GET TO HARTFORD, BUT ONLY IF THE HIGH OVER THE SE IS OF CONTINENTAL (COOL, DRY) ORIGIN.  i DON'T THINK THE BERMUDA HIGH WOULD DO. 

 

THEORY TWO.  CALL THIS THE HIGH SPEED ON A BUMPY ROAD THEORY.  THE EML IN THE JET STREAM IS LIKE A CAR MOVING AT HIGH SPEED ON A BUMPY ROAD.  EVEN THOUGH IT IS HEAVIER THAN THE LAYER BELOW, IT IS MOVING TOO FAST TO SINK INTO IT.  i AM NOT SURE HOW THIS WORKS.  ARE EML'S THE SORT OF THINGS THAT CAN BOUNCE?  PEOPLE TELL ME THAT AIRMASSES ARE MUCH MORE LIKE BRICKS THAN ONE WOUD SUPPOSE.

 

THEORY THREE:  THE RATCHET OR BOTTLE-NECK THEORY.  INVERT A BOTTLE WITH A THIN ENOUGH NECK AND, EVEN THOUGH THE WATER  IN THE BOTTLE WANTS TO DRAIN OUT, IT WONT.  i AM NOT SURE WHY THIS IS, BUT IT HAS SOMETHING TO DO WITH THE FACT THAT THE TWO FLUIDS, THE AIR AND THE WATER CANNOT GET BY ONE AOTHER IN THE NARROW NECK OF THE BOTTLE.  IN THIS MODEL, I GUESS A REGION OF HIGH ==>'CIN"<==  PLAYS THE ROLE OF THE BOTTLENECK.   NOW, IF CAPE IS HARD TO UNDERSTAND, CIN IS EVEN HARDER FOR ME. A REGION OF HIGH CIN IS A REGION IN WHICH  ANY PARCELTHAT IS MOVED UPWARD AND COOLED ADIABATICALLY WILL ARRIVE AT A REGION THAT IS SO MUCH LIGHTER THAT IT WILL TEND TO RETURN TO ITS PREVIOUS LEVEL.  BUT HERE i NEED FURTHER SCHOOLING, BECAUSE IT WOULD SEEM TO ME THAT ANY LAYER THAT IS LIGHT ENOUGH TO PREVENT PARCELS FROM BELOW GETTING INTO THE EML WOULD BE LIGHT ENOUGH TO RISE THROUGH THE EML ITSELF.  fOR THIS THEORY TO BE CORRECT, IT MUST BE POSSIBLE TO HAVE THREE LAYERS, WITH THE MIDDLE ON LIGHT ENOUGH TO RESTRAIN CONVECTION FROM BELOW, BUT NOT SO LIGHT AS TO CONVECT IT SELF THROUGH THE LAYER THAT LIES OVER IT. HAVING A HARD TIME GETTING MY MIND AROUND THAT. 

 

THEORY FOUR:  THE SKY HOOK THEORY.  ONE COMMENTATOR TOLD ME EARLY ON IN THIS INQUIRY (I THINK IT WAS HABY) THAT I HAD TO TAKE PRESSURE EFFECTS INTO ACCOUNT.  i DON'T UNDERSTAND THIS AT ALL, AND SO HAVE A TENDANCY TO SATARIZE IT MY IMAGINATION HAS GENERATED A LOW PRESSURE AREA THAT GRABS HOLD OF THE EML FROM THE TOP AND CARRIES IT AROUND.  LIKE ALL THINGS I DON'T UNDERSTAND, I DON'T LIKE IT, BUT I FEEL I SHOULD SAVE A PLACE FOR IT. 

 

tHANKS FOR YOUR PATIENCE WITH MY CAPS.  PERHAPS YOU CAN INSTRUCT ME IN HOW TO INSERT COMMENTS IN A MESSAGE IN THIS INTERFACE. 

 

ALL THE BEST,

 

N

[weatherwiz]

 With EML's the cap is typically quite strong, so this ensures that the low level moisture remains below the inversion.  As for why atmospheric isn't all that strong?  This may not be 100% correct but when EML's are along the southern edge of the westerlies, typically this is the area of strongest mid level ridging.  When under a strong ridge mixing is not usually all that deep.  For example, in the summer time say in SNE, when we have our hottest days when under the core of the ridging, atmospheric mixing just isn't very deep...it's very shallow.  As for the meteorological reason why I'm not sure if I know the answer to that.  As for the rest of your post, I'm not really sure if I'm understanding what you're trying to ask.

 

As for learning how to quote someone.  If you're posting via computer or ipad, under a person's post there will be a quote box.  All you have to do is hit this quote box under the post you want to quote and in the reply box, you'll see the quoted post.  Just make sure you're typing outside of the quoted box or it will look all funky. 

[ThompNickSon]

Let's put our heads together concerning why there might be less mixing in high pressure areas.  Air rises in low pressure areas and the rising air has to go somewhere, so it is "parked" in high pressure areas.  Since it keeps being inroduced at the top, it must descend.  This descent, is no doubt helped by the fact that air is stripped of its moisture on it's way up.  It is dry, and to that extent, heavier.  But it also must be warm, for the same reasonn.  So, contrary to our High Desert Source theory, it seems to me that high pressure areas, particularlarly the subtropical highs (including the bermuda  -- I know I am contradicting something I said earlier -- would be a natural source of EML's.  In fact, I have always assumed that we have the causality a bit backwards when we talk about the intermountain west.  They are dry in part because the mountains strip away the lower, cooler, moister layers of the subtropical atmosphere, giving admission to the mountains only to the warmer, dryer layer on top ...

 

Does any of this make sense?  I will try to state my earlier idea more clearly.

 

N

[weatherwiz]

Let's put our heads together concerning why there might be less mixing in high pressure areas.  Air rises in low pressure areas and the rising air has to go somewhere, so it is "parked" in high pressure areas.  Since it keeps being inroduced at the top, it must descend.  This descent, is no doubt helped by the fact that air is stripped of its moisture on it's way up.  It is dry, and to that extent, heavier.  But it also must be warm, for the same reasonn.  So, contrary to our High Desert Source theory, it seems to me that high pressure areas, particularlarly the subtropical highs (including the bermuda  -- I know I am contradicting something I said earlier -- would be a natural source of EML's.  In fact, I have always assumed that we have the causality a bit backwards when we talk about the intermountain west.  They are dry in part because the mountains strip away the lower, cooler, moister layers of the subtropical atmosphere, giving admission to the mountains only to the warmer, dryer layer on top ...

 

Does any of this make sense?  I will try to state my earlier idea more clearly.

 

N

 

I think I understand a bit better.  Is this still reflecting back on to some of your original questions of why do EML's develop over the Intermountain west region of the US and why/how they can survive to the east coast at times?  You're still looking for some sound answers to these questions, correct?  

[ThompNickSon]

I think I am fairly clear about why New Mexico (for instance) is dry.  (1) it is at subtropical latitude, and there fore under the descending return flow from the inter tropical convergence zone a lot of the year.  It is dry for the same reason the Arabia is dry.  (2) it is west of an N-S running mountain range.  There is a dry belt running from N to S all the way from  Mexico to Alaska.  So, New Mexico, which lies at the intersection of these two effects, is dry.  So, I am more concerned about how these patches of warm DRY air retain their altitude. 

 

Of the four theories I offered, I presently favor theory 1, which states that an EML is maintained at altitude because it never passes over a less dense atmosphere until it reaches the place where it is going to called upon to explain severe weather.    I think the first article you sent me supports that theory with its trajectory analyses, but it is so technical and i am so dumb I cannot be sure.   If I am correct, then scooting around the northern flank of a highpressure area might provide the support for a relatively heavy airmass to remain aloft, assuming that the high is oozing cold dense air at its base.  But why, you ask, would a high pressure area be cold, if they originate as pools of moisture-stripped air? Well, given that they are cloudless, they support a lot of outbound radiation during winter nights, and they don't get that much back, particularly at high latitudes.  Thus, the typical structure of canadian origin high is warm dry air aloft and cold dry air (very dense) below.  So, the idea of an EML being held aloft as it skirts the dense lower flanks of a Polar Continental High, really appeals to me.  But my mind is open both to the bottle neck theory and to the High-speed-driving-on-rough-road theory.  (If anybody is joining this correspondence at this point, better read the previous post, or you will be SURE I have lost my mind.)

 

Please, anybody reading this, correct any or all of its errors.

 

N

[Amped]

Your first sentence isn't completely correct...you could have 8000 J of cape but if there is no sufficient lift to break through the cap nothing will pop.

Also I think the OP is referring to EML's and their role on stronger tornadoes and what it takes for EML's to survive their trip to the east coast

 

Thanks wiz, I forgot to mention that. Yes, EML can be too strong.

[weatherwiz]

I think I am fairly clear about why New Mexico (for instance) is dry.  (1) it is at subtropical latitude, and there fore under the descending return flow from the inter tropical convergence zone a lot of the year.  It is dry for the same reason the Arabia is dry.  (2) it is west of an N-S running mountain range.  There is a dry belt running from N to S all the way from  Mexico to Alaska.  So, New Mexico, which lies at the intersection of these two effects, is dry.  So, I am more concerned about how these patches of warm DRY air retain their altitude. 

 

Of the four theories I offered, I presently favor theory 1, which states that an EML is maintained at altitude because it never passes over a less dense atmosphere until it reaches the place where it is going to called upon to explain severe weather.    I think the first article you sent me supports that theory with its trajectory analyses, but it is so technical and i am so dumb I cannot be sure.   If I am correct, then scooting around the northern flank of a highpressure area might provide the support for a relatively heavy airmass to remain aloft, assuming that the high is oozing cold dense air at its base.  But why, you ask, would a high pressure area be cold, if they originate as pools of moisture-stripped air? Well, given that they are cloudless, they support a lot of outbound radiation during winter nights, and they don't get that much back, particularly at high latitudes.  Thus, the typical structure of canadian origin high is warm dry air aloft and cold dry air (very dense) below.  So, the idea of an EML being held aloft as it skirts the dense lower flanks of a Polar Continental High, really appeals to me.  But my mind is open both to the bottle neck theory and to the High-speed-driving-on-rough-road theory.  (If anybody is joining this correspondence at this point, better read the previous post, or you will be SURE I have lost my mind.)

 

Please, anybody reading this, correct any or all of its errors.

 

N

 

Here is another website you should check out on EML's

 

http://bangladeshtornadoes.org/EML/emlpage.html

 

Here is also a sample sounding of an EML from that page:

 

So to answer your first question, as to why they are able to retain their altitude let's look at the sounding.  At around 800mb you can start to see the temperature line quickly jolt to the right and increase up to around 750mb or so while the dewpoint line quickly jolts to the left and decreases to about 700mb or so.  From about 700mb to 500mb you have rapid cooling with temperatures aloft (leading to very steep mid-level lapse rates) and increasing moisture.  

 

To further explain what I will say I have taken the image from above and placed it into paint.net and highlighted the area I am referring to in blue.

 

 

When looking at this skew-t let's imagine we are looking at it in 3D or even 4D and not 2D like these graphics are given to us as the atmosphere as you know is not 2D.  Let's take a look at the bottom layer, where the temp line jolts right and dewpoint line jolts left.  At this level the airmass is becoming much warmer and a great deal drier than the air below it.  Let's think of this like filling a glass with water and then putting oil in it.  What's going to happen?  The oil is going to remain on the top of the water no matter what, even if you shake it.  

 

Originally, the EML's remain in tact b/c there is no atmospheric process occurring to violently shake this airmass and allow it to mix, that is no secondary factors such as convection, strong forcing, strong lift, etc.  The strong capping in place at about 800mb where the EML begins, prevents the dry/warm air in this level from mixing with the more cool (relative to the airmass) and more moist air below it.  Since this airmass is warmer, the air parcels below it can't continue rising, therefore, they remain below the EML.  

 

Now as these EML's progress eastward through the Plains they obviously are leaving their home environment and start encountering weather systems, cold fronts, low pressures, etc.  These EML's lead to extreme instability and now that you have lift present explosive t'storms are able to develop.  This lift is also strong enough to pop through this capping inversion and once this process occurs, the air is finally able to become mixed and the EML slowly begins to lose it's integrity.  

 

Now, with this said how is it possible for EML's to sustain to the east coast?  I did previously state this before but I will go back into it.  Like I previously mentioned, you want a building ridge at the 700mb level across the Southeastern US...not just a building ridge but a rather strong ridge.  As this ridge builds and strengthens across the south, the return flow in the mid levels actually begins to come from the intermountain west region.  Also, at the same time you want a trough to work into the northern tier of the country, this shows that 1) you have a potent system working in from Canada and 2) well you're going to have an increased pressure gradient so the jet stream here will be much stronger...this second point is key here b/c a stronger flow means that drier/warmer mid level air which originates from the intermountain west region can now get "sucked into" the the crest of the ridge and now your EML can not only sustain itself but it may also regain it's integrity thanks to warmer/drier air aloft advecting in.

[ThompNickSon]

Brilliant! Thanks for this thoughtful and elegantly illustrated post.  It should go into somebody's FAQ on EML's

 

I have a little time, and I want to focus on one part of it.  You wrote:

 

When looking at this skew-t let's imagine we are looking at it in 3D or even 4D and not 2D like these graphics are given to us as the atmosphere as you know is not 2D.  Let's take a look at the bottom layer, where the temp line jolts right and dewpoint line jolts left.  At this level the airmass is becoming much warmer and a great deal drier than the air below it.  Let's think of this like filling a glass with water and then putting oil in it.  What's going to happen?  The oil is going to remain on the top of the water no matter what, even if you shake it.

 

With this paragraph, you implicitly answer one of the questions I have been ham-handedly trying to articulate.  It is the case ... it MUST be the case ..., that each level of the atmosphere is less dense than the level just below it.  Right?  It is never the case that a denser level over-lies a less dense level.  OK.  So.  That being the case ,the jolt to the right and the jolt to the left must be such that the relatively small increase in temperature MORE THAN COMPENSATES FOR the relatively large decrease in dewpoint.  Am I ok, so far? 

 

Where can I learn more about that trade-off?  Where is there a "constant density" table or chart which has lines of constant density as a function of airmass dewpoint and airmass temperature?  Or does the fact that I can ask such a dumb question reveal my total lack of understanding of thermodynamics? 

 

Ok.  Let's imagine that there is such a chart and table.  Now, for a dryer airmass to lie atop a moister one, it must be the case that its greater warmth is sufficient to compensate for its lesser moisture.  That might be true in the morning before diurnal heating begins, and become not true later in the day as the sun's action on the boundary layer makes it warmer.  So:  knowing the temperature characteristics of the overlying warm, dry layer, we should be able to calculate the increase in the temperature of the top of the boundary layer sufficent to break into EML   I suspect that the Storm Prediction Lab makes that calculation every day, but I don't know what it is called, how to look for the table.  I am guessing that one of the numbers on a standard SKEW-T actually is the number I am looking for. 

 

Thanks for your patience and help in clarifying my question.

 

Nick

[ThompNickSon]

I happen to be in Houston at the moment where there has been a prediction of severe weather tomorrow.  The factors included in earlier discussions include a vigorous jetstream overhead in advance of an Arizona trough, lower level advection of moist air off the gulf, and a cap.  I think they said .... but perhaps I remember in correctly .... that the cap was a layer of very dry air.  Flew here from ABQ this afternoon in a 737 ... very bumpy ... high cirrus layer and two layers of small cumulus much lower down..  Pursuant to the severe prediction, I went lookiong for an EML to the west of HOU.  This is the midland TX skew T for 4pm, about the time I flew over it. There is indeed a cap, but the atmosphere aloft is WET, isn't it?  Where the dickens would a layer of such wet air have come from over Midland TX.   Please have a look at the Skew-T and tell me where I am going wrong. Also, hard to see how one wouold get severe Wx out of this sounding.

 

sorry, everybody.  I tried to paste in the Midland TX skew T for Friday 20th  at 4pm and it wouldn't paste.    The wet and dry lines hug each other all the way up to 500mb.  Together, they start out at about 50 degrees, move straight up to around 1km, and then move horizontally to the right for about 15 degrees centigrade, and then almost vertically together up to 500mb.  

 

Here is the link from Unisys.

 

http://weather.unisys.com/upper_air/skew/ua_sound.php?type=no&city=kmaf&region=sp&t=-12

 

but you may have to adjust the time to see the plot I am talking about.  

 

 

 

 

 

N

 

.  

[thewxmann]

EML's -- packets of , desert air that originate in the intermountain west -- are often invoked to explain severe weather as far away from the Rockies as New England.  For several months I have been puzzling how such dry (heavy, dense) air could maintain its coherence and altitude while passing the two thousand miles from ABQ to BDL.  To put the question in the least technical way possible:  Why wouldn't it fall down?  Looking at SKEW-T's I see that such parcels of air are fairly common in the East, manifesting themselves as a sharp rightward movement of the temperature line, and a very sharp, leftward movement of the dewpoint line at some point above the surface, with the two lines reconverging at higher altitudes to form a sort of tent-like pattern.  I would love to get a discussion going on EML's and/or skewT's  in general.  Any takers?

 

To answer this question: actually, elevated mixed layers are actually less dense than low-level moist layers, because they are warmer and reside at higher heights/lower pressures. (From the ideal gas law, density is proportional to pressure and inversely proportional to temperature.) 

 

EML's are not cold; they form when the sun strongly heats up elevated terrain such that lapse rates are dry-adiabatic. These layers of hot dry-adiabatic air are advected horizontally towards the eastern portions of the U.S.

 

Think of it as oil sitting on top of water. At equilibrium, an EML will remain elevated. However, a disruption of equilibrium in the form of vertical mixing (coming from deep moist convection, solar heating, forced vertical ascent of parcels) will disrupt the layer. 

[thewxmann]

Thanks, Amped.  WeatherWiz, has me exactly right.  ..

 

Here is where you all may have to be patient with me. An EML is a an example of a capping inversion, for sure, but it is a very strange one.  In a "norma"l inversion situation ... as, say with icestorms ... you get a warm moist layer overlaying a cold dry layer.   These situations tend to produce a very stratiform atmosphere. On a skew T, the dewpoint and temp line move together to the right.   Anything that would produce upward motion in teh atmosphere has to overcome two hurdles, the fact that the air above is moister (and therefore lighter) and the fact that the air is (warmer) and therefore lighter.  In an EML, these two factors work in the opposite directions.   The temperature line moves to the right, but the dewpoint line moves sharply to the left.  Now as I understand CAPE (and I am not sure I do), it is the  difference, integrated accross all levels of the atmosphere from the Lifted Condensation Level on up,  between between actual temperature at a given level and the temperature that would have to be at that level for a  parcel, moved from the surface, to be at rest.  If I am correct, then CAPE is at its strongest when the lower atmosphere is moist but the upper atmosphere is DRY.  Such a situation would not be a cap (i.e., would not restrain convection) unless the moist, lower, level is so much cooler than the dry capping layer that convection cannot cross the boundary between them.  .  It is the relation between these two variables that is so interesting to me.   .  . 

 

Not sure where really to start with this paragraph, but I will respond to the last part. First off, high instability is achieved when the lower levels are warm, and the upper levels are cold, because the parcels originating from the lower levels have buoyancy if given a push up. A slight agitation from equilibrium will push the parcels to free convection (this is akin to the physics concept of an unstable equilibrium point). Simple as that.

 

There is a correlation between that aforementioned unstable state and the state where the upper atmosphere is dry. If the upper atmosphere were wet, diabatic heating from latent heat released from condensation warms up the upper atmosphere, and instability is decreased. 

 

One of you made a comment that puzzled me,  Since I havent figured out how to go back to the original posts, once I have started a reply, I can't say which.  Sorry.  The comment seemed to imply that a steep lapse rate in the actual atmosphere suppressed convection.  On the contrary, it would seem to me that a steep lapse rate encourages convection.  The steeper the lapse rate , the more likely it is that a parcel warmed at the surface will continue to rise  Since colder dry air is always heavier than warmer dry air, isn't it the case that the dry adiabatic lapse rate is pretty much the steepest  a lapse rate can be.  Thus, the most ideal circumstance for convection is a source of heat and moisture at low levels, and dry air at higher levels.  How much of this do I have wrong? 

 

The EML suppresses convection not because of its dry-adiabaticness, but because it's less dense than the air below it. If you place a block of water in a pool of oil, the water will sink. Similarly, air below the EML will not freely rise through the EML because once it hits its base it will immediately sink back down. 

 

Please, others who join this thread, look at the earlier posts.  We are trying to build a common understanding, here, and some of the points you might be tempted to raise will have been raised and settled in earlier posts. 

 

Thanks, all,

 

N

 

See comments above bolded.

[thewxmann]

Brilliant! Thanks for this thoughtful and elegantly illustrated post.  It should go into somebody's FAQ on EML's

 

I have a little time, and I want to focus on one part of it.  You wrote:

 

When looking at this skew-t let's imagine we are looking at it in 3D or even 4D and not 2D like these graphics are given to us as the atmosphere as you know is not 2D.  Let's take a look at the bottom layer, where the temp line jolts right and dewpoint line jolts left.  At this level the airmass is becoming much warmer and a great deal drier than the air below it.  Let's think of this like filling a glass with water and then putting oil in it.  What's going to happen?  The oil is going to remain on the top of the water no matter what, even if you shake it.

 

With this paragraph, you implicitly answer one of the questions I have been ham-handedly trying to articulate.  It is the case ... it MUST be the case ..., that each level of the atmosphere is less dense than the level just below it.  Right?  It is never the case that a denser level over-lies a less dense level.  OK.  So.  That being the case ,the jolt to the right and the jolt to the left must be such that the relatively small increase in temperature MORE THAN COMPENSATES FOR the relatively large decrease in dewpoint.  Am I ok, so far? 

 

Where can I learn more about that trade-off?  Where is there a "constant density" table or chart which has lines of constant density as a function of airmass dewpoint and airmass temperature?  Or does the fact that I can ask such a dumb question reveal my total lack of understanding of thermodynamics? 

 

Ok.  Let's imagine that there is such a chart and table.  Now, for a dryer airmass to lie atop a moister one, it must be the case that its greater warmth is sufficient to compensate for its lesser moisture.  That might be true in the morning before diurnal heating begins, and become not true later in the day as the sun's action on the boundary layer makes it warmer.  So:  knowing the temperature characteristics of the overlying warm, dry layer, we should be able to calculate the increase in the temperature of the top of the boundary layer sufficent to break into EML   I suspect that the Storm Prediction Lab makes that calculation every day, but I don't know what it is called, how to look for the table.  I am guessing that one of the numbers on a standard SKEW-T actually is the number I am looking for. 

 

Thanks for your patience and help in clarifying my question.

 

Nick

 

p = rho*R*T

 

rho = sum(rho_i * M_i), 

 

where M_i are the number/mass fractions of each molecular component of the atmosphere.

 

So the equations are simple. But really, the computations aren't necessary.

 

The saturation mixing ratios - the most water vapor that air can hold - at sensible atmospheric temperatures are on the order of 10 g/kg (or 1 part in 1 hundred). So density is much more strongly governed by pressure and temperature changes.

[thewxmann]

I happen to be in Houston at the moment where there has been a prediction of severe weather tomorrow.  The factors included in earlier discussions include a vigorous jetstream overhead in advance of an Arizona trough, lower level advection of moist air off the gulf, and a cap.  I think they said .... but perhaps I remember in correctly .... that the cap was a layer of very dry air.  Flew here from ABQ this afternoon in a 737 ... very bumpy ... high cirrus layer and two layers of small cumulus much lower down..  Pursuant to the severe prediction, I went lookiong for an EML to the west of HOU.  This is the midland TX skew T for 4pm, about the time I flew over it.   There is indeed a cap, but the atmosphere aloft is WET, isn't it?  Where the dickens would a layer of such wet air have come from over Midland TX.   Please have a look at the Skew-T and tell me where I am going wrong. Also, hard to see how one wouold get severe Wx out of this sounding.

 

N

 

.  

 

If you look at the 500mb-700mb wind vectors, you can see that the EML is actually originating from the Sierra Madres in Mexico. Check out the MMTC sounding.

 

But yeah, it's not the best example of an EML we got here. 

[thewxmann]

P.S. didn't mean to steal your thunder Paul -- just trying to put it in another perspective here. You explained it just fine.

[weatherwiz]

P.S. didn't mean to steal your thunder Paul -- just trying to put it in another perspective here. You explained it just fine.

 

Steal my thunder...nonsense!  It's great to have some further perspective in here and at the time I was really hoping this would blossom into a further discussion as well.  

 

Great perspective by you though and you explained several things which I wasn't sure how and completely didn't understand!

[ThompNickSon]

Thanks for your response.  I still have some questions.  I hope that, in my confusion, I don't seem too pigheaded.

 

To answer this question: actually, elevated mixed layers are actually less dense than low-level moist layers, because they are warmer and reside at higher heights/lower pressures. (From the ideal gas law, density is proportional to pressure and inversely proportional to temperature.) 

 

The language is so difficult, here.  Of course the density of overlying air is less than the density of underlying air because there is less pressure on it.  But we are not really talking about absolute density here, but relative density: whether the parcel is more or less bouyant than the parcels around it, right?  So pressure divides out.  The fundamental question that is driving my inquiry is how relatively  hot DRY air cana be more bouyant than relatively mild, moist air. 

 

EML's are not cold; they form when the sun strongly heats up elevated terrain such that lapse rates are dry-adiabatic. These layers of hot dry-adiabatic air are advected horizontally towards the eastern portions of the U.S.

 

I hope I never said, even in my worst confusion, that EML's were COLD.  They are, for their altitude, very warm.  But they are DRY.  (I am also -- as a side line -- curious about the boyancy of "cold pools" that follow along behind surface lows at high altitudes, but we can save that inquiry for another thread.)   

 

Think of it as oil sitting on top of water. At equilibrium, an EML will remain elevated. However, a disruption of equilibrium in the form of vertical mixing (coming from deep moist convection, solar heating, forced vertical ascent of parcels) will disrupt the layer. 

 

This how I think about it, so we are good.  I am having a hard time mastering this interface so allow me to include here some comments on other relevant postings.

 

The saturation mixing ratios - the most water vapor that air can hold - at sensible atmospheric temperatures are on the order of 10 g/kg (or 1 part in 1 hundred). So density is much more strongly governed by pressure and temperature changes.

 

I am a bit too math-challenged for the equasions in the first part of this post, but these two sentences are absolutely clear to me and are a big help.  I understand them as follows:  Because the capacity of air to carry water as a vapour is so limited, the effect of adding water vapour to air is much more limited than the effect of heating it.  So, to get back to my basic question, here, an EML doesnt sink because it takes a lot of watervapour below it to overcome the bouyancy imposed by its [relative] warmth. 

 

Let me use this space to add a something I think I learned from an exchange with somebody at the Severe Storms Lab.  (Caveat:  I may have misunderstood.)  Condensed water does impose a drag on the air it is in.  If I have understood this correctly, a layer of saturated mild air over run by a warmer dryer layer, might stay put in part because of the weigfht of the fog it is carrying   This would imply that when fog "burns" off, the air is rendered more bouyant for two reasons, the increased water vapor and the decreased water "burden". 

 

Finally, I made a change in the post I made earlier to correct the fact that the skewT I tried to paste in didn't go. 

 

Thanks for your patience, everybody.  Your patience in explaining something that has puzzled me for years are greately appreciated. 

 

N

 

 

 

[thewxmann]

The language is so difficult, here.  Of course the density of overlying air is less than the density of underlying air because there is less pressure on it.  But we are not really talking about absolute density here, but relative density: whether the parcel is more or less bouyant than the parcels around it, right?  So pressure divides out.  The fundamental question that is driving my inquiry is how relatively  hot DRY air cana be more bouyant than relatively mild, moist air.

 

Not sure what you mean here by relative density. Soundings measure ambient temperature - its measurements are representative of the state of the all the air parcels around it. 

 

To your fundamental question, it depends on the temperature profile of the atmospheric column. The question about buoyancy is always: if a parcel is nudged from equilibrium, in an adiabatic process, what is its affinity to rise? Hot dry air usually doesn't have much affinity to rise because, in an adiabatic lifting process, its temperature decreases with height dry-adiabatically. The environmental temperature usually does not. Pretty quickly, the hot dry air parcel will cool so fast that it's cooler than the environment, at which point the hot dry parcel sinks.

 

For moist parcels, when they reach saturation, latent heat released from condensation offsets the adiabatic cooling. Hence moist parcels, when they reach saturation, rise at the moist-adiabatic lapse rate rather than the dry-adiabatic lapse rate. In severe weather situations, it's critical that the environmental lapse rate is steeper than the moist adiabatic lapse rate.

 

This is a really simplified version of everything but hopefully it clears some stuff up. EML's are layers of environment/ambient air. Parcels that are lifted are buoyant/not buoyant depending on their state after an adiabatic process relative to the state of the environment/ambient air.

 

 

 

I hope I never said, even in my worst confusion, that EML's were COLD.  They are, for their altitude, very warm.  But they are DRY.  (I am also -- as a side line -- curious about the boyancy of "cold pools" that follow along behind surface lows at high altitudes, but we can save that inquiry for another thread.)  

 

Cold pools are negatively buoyant. They sink. They are denser because they are colder. Anyway that term is reserved for convective cold pools left behind from thunderstorms.

 

 

I am a bit too math-challenged for the equasions in the first part of this post, but these two sentences are absolutely clear to me and are a big help.  I understand them as follows:  Because the capacity of air to carry water as a vapour is so limited, the effect of adding water vapour to air is much more limited than the effect of heating it.  So, to get back to my basic question, here, an EML doesnt sink because it takes a lot of watervapour below it to overcome the bouyancy imposed by its [relative] warmth. 

 

Let me use this space to add a something I think I learned from an exchange with somebody at the Severe Storms Lab.  (Caveat:  I may have misunderstood.)  Condensed water does impose a drag on the air it is in.  If I have understood this correctly, a layer of saturated mild air over run by a warmer dryer layer, might stay put in part because of the weigfht of the fog it is carrying   This would imply that when fog "burns" off, the air is rendered more bouyant for two reasons, the increased water vapor and the decreased water "burden".

 

 

I'm not sure what you're conveying, but yes... I think. If only advection were acting on EML's they can last for a very long time. For instance the SAL that travels from the Sahara to Florida at least once per year is an elevated mixed layer. But yes, temperature is the key. Density drops as temperature rises.

 

I'm not sure what you mean by the second paragraph. (Sorry, I know I keep saying that in my responses!) Could you please clarify?

[ThompNickSon]

Wxmann,

 

Squall line just went through Galveston Bay.  No tornadoes here.  not even much thunder.  The Lake Charles LA shows a nice EML, however, so things may get more interesting further east.  To your questions:

 

Not sure what you mean here by relative density

 

Struggling with the language, here.  "Altitude-relative density"  If two parcels, at the same level of he atmosphere, have different "altitude-relative densities", The one with the lesser "altitude-relative density" will move upward, and the other will move downward.

 

 

Cold pools are negatively buoyant. They sink. They are denser because they are colder. Anyway that term is reserved for convective cold pools left behind from thunderstorms.

 

I think there is another context in which this term is used.  Cold pools also form behind "cold core" lows (i.e., non tropical low pressure systems) and account for the instability of the atmosphere in the days after snowstorms in the NE. 

 

I'm not sure what you mean by the second paragraph. (Sorry, I know I keep saying that in my responses!) Could you please clarify?

 

I am trying to get settled in my mind all the reasons that a warm moist layer might be confined by a hot dry layer above, given that, all other things being equal, dry air is heavier than moist air.  (By moist, I mean having a lot of water vapour ... near saturated)  Heat is obviously the most important reason, and that was made more clear by the person (perhaps you, I have lost track) who pointed out that while heat affects the whole of a parcel, water vapour effects only a relatively small portion of it.  Thanks for that. Another possible reason I wanted to consider was the "burden" of condensed water in the moist air. below  This was a new idea to me, and I wondered if anybody following this thread had heard of it. 

 

Please don't apologize for my lack of clarity.  I am a writer by temperament and an experimental psychologist/ethologist by training (got my degree right there in Berkeley, in fact) so I really don't have the physics background necessary to be a qualified participant in my own thread.  But grew up in MA with the hurricanes, blizzards, and the tornado of the 50's and have studied weather in an informal way all my life, so I am pretty highly motivated.  I even wrote a book about it 40 years ago, believe it or not.  For 0.01$ plus shipping, you could have your own copy.

 

http://www.amazon.com/The-Weather-Wise-Gardener-Understanding-Predicting/dp/087857428X/ref=sr_1_1?ie=UTF8&qid=1387662492&sr=8-1&keywords=Calvin+Simonds+Weather

 

Calvin Simonds is a pseudonym.

 

All the best,

 

N

 

Not sure what you mean here by relative density. Soundings measure ambient temperature - its measurements are representative of the state of the all the air parcels around it.  

 

To your fundamental question, it depends on the temperature profile of the atmospheric column. The question about buoyancy is always: if a parcel is nudged from equilibrium, in an adiabatic process, what is its affinity to rise? Hot dry air usually doesn't have much affinity to rise because, in an adiabatic lifting process, its temperature decreases with height dry-adiabatically. The environmental temperature usually does not. Pretty quickly, the hot dry air parcel will cool so fast that it's cooler than the environment, at which point the hot dry parcel sinks.

 

For moist parcels, when they reach saturation, latent heat released from condensation offsets the adiabatic cooling. Hence moist parcels, when they reach saturation, rise at the moist-adiabatic lapse rate rather than the dry-adiabatic lapse rate. In severe weather situations, it's critical that the environmental lapse rate is steeper than the moist adiabatic lapse rate.

 

This is a really simplified version of everything but hopefully it clears some stuff up. EML's are layers of environment/ambient air. Parcels that are lifted are buoyant/not buoyant depending on their state after an adiabatic process relative to the state of the environment/ambient air.

 

 

 

 

Cold pools are negatively buoyant. They sink. They are denser because they are colder. Anyway that term is reserved for convective cold pools left behind from thunderstorms.

 

 

 

I'm not sure what you're conveying, but yes... I think. If only advection were acting on EML's they can last for a very long time. For instance the SAL that travels from the Sahara to Florida at least once per year is an elevated mixed layer. But yes, temperature is the key. Density drops as temperature rises.

 

I'm not sure what you mean by the second paragraph. (Sorry, I know I keep saying that in my responses!) Could you please clarify?

[thewxmann]

Wxmann,

 

Squall line just went through Galveston Bay.  No tornadoes here.  not even much thunder.  The Lake Charles LA shows a nice EML, however, so things may get more interesting further east.  To your questions:

 

Not sure what you mean here by relative density

 

Struggling with the language, here.  "Altitude-relative density"  If two parcels, at the same level of he atmosphere, have different "altitude-relative densities", The one with the lesser "altitude-relative density" will move upward, and the other will move downward.

 

I've never heard of the term "altitude-relative density". As far as I know the key variables of gases are the ones that go into the ideal gas law and maybe some thermodynamic equations, none of which involve "height". Also for all intensive purposes the acceleration due to gravity is constant with height in the troposphere.

 

Maybe you're referring to the density of a parcel relative to the density of the surrounding air at a given height?  But in a sounding we assume the sampled temperature/moisture is true for all the air over small spatial/temporal scales.

 

 

 

I am trying to get settled in my mind all the reasons that a warm moist layer might be confined by a hot dry layer above, given that, all other things being equal, dry air is heavier than moist air.  (By moist, I mean having a lot of water vapour ... near saturated)  Heat is obviously the most important reason, and that was made more clear by the person (perhaps you, I have lost track) who pointed out that while heat affects the whole of a parcel, water vapour effects only a relatively small portion of it.  Thanks for that. Another possible reason I wanted to consider was the "burden" of condensed water in the moist air. below  This was a new idea to me, and I wondered if anybody following this thread had heard of it. 

 

I am a writer by temperament and an experimental psychologist/ethologist by training (got my degree right there in Berkeley, in fact)

 

Glad to clear things up! I don't know if there's any burden from condensed water. I think it might reduce updraft acceleration a bit. Not sure, a degreed met would have to comment on this.

 

And I got my physics degree at Berkeley. Go Bears!

[ThompNickSon]

This must be frustrating to you.  The only physics I had was from Edward Teller (Physics 10).  I don't remember a thing. 

 

Maybe you're referring to the density of a parcel relative to the density of the surrounding air at a given height?  But in a sounding we assume the sampled temperature/moisture is true for all the air over small spatial/temporal scales.

 

The reason you never heard of altitude relative density is that I made it up.  I think I was going for "bouyancy".  So, I am thinking of the density that a given parcel would have if it were raised to an altitude where conditions warmer, wettter, cooler, dryer, etc. than the parcel would be when it go there.  

 

Anyway, you have certainly done your duty by the non-physicists of the world today, and I should let you get back to serious work.

 

All the best,

 

N

[thewxmann]

This must be frustrating to you.  The only physics I had was from Edward Teller (Physics 10).  I don't remember a thing. 

 

Maybe you're referring to the density of a parcel relative to the density of the surrounding air at a given height?  But in a sounding we assume the sampled temperature/moisture is true for all the air over small spatial/temporal scales.

 

The reason you never heard of altitude relative density is that I made it up.  I think I was going for "bouyancy".  So, I am thinking of the density that a given parcel would have if it were raised to an altitude where conditions warmer, wettter, cooler, dryer, etc. than the parcel would be when it go there.  

 

Anyway, you have certainly done your duty by the non-physicists of the world today, and I should let you get back to serious work.

 

All the best,

 

N

 

Lol wut. It wasn't frustrating at all. I had fun thinking of your question in a physical manner. I enjoyed this back and forth discussion. 

 

Doing my duty to non-physicists? Serious work? lol. If I didn't think this discussion was worthwhile, I would've stopped posting long ago.

 

If I asked you a psychology question, and you answered it and specified you were a psych major, I'd be really appreciative.

[ThompNickSon]

Dear Wxmann, and anybody else who is following,

 

I have been working on the meted tutorial and discovered an interesting parameter, virtual temperature.

 

The virtual temperature (T_v) is the temperature at which dry air would have the same density as the moist air, at a given pressure. In other words, two air samples with the same virtual temperature have the same density, regardless of their actual temperature or relative humidity.

 

the diagram below dramatizes how small a difference in temperature is required to compensate for a substantail difference in dewpoint.  Notice in the example the depoint depression is 19 degrees, but the difference in temp is only two degrees.  This goes a long way toward helping me understand the "shape" of an EML on a Skew T.  In other words, for  a dry layer to remain bouyant over a moist layer, it only has to be a little warmer. 

 

 

 

The tutorial can be found at

 

http://www.meted.ucar.edu/mesoprim/skewt/tv.htm

under the heading, virtual temperature. 

 

N