Probably very basic question...Dry adiabatic lapse rate vs. environmental lapse rate

[LongRoadBob]

Studying to retake the meteorology exam section.

Maybe this is a very basic thing I'm missing, I get how the lapse rates work, how the dry for instance at 3 deg. C / 1000 ft, while the environmental lapse rate is say 1 deg. C / 1000 ft, will be unstable. As the parcel of air rises it cools at 3 deg, while the surrounding air is only cooling at 1 deg, but the parcel started out warming which is why it rose. The parcel will keep rising, and it is unstable.

But the description for unstable is ELR > DALR or SALR

What I'm missing here is how is 1/1000 GREATER THAN 3/1000 or 1.5/1000 ?
Where is the "greater than" coming from? Maybe I'm punchy right now from study.
I tried checking on line (have found errors in this book) other sources but so far all point to the ELR > DALR as unstable, etc, but it must be obvious where the values are coming from?

I'm hung up on the DALR is a greater value, as is the temperature Of the parcel of air, until they meet.

 

[Cap'n Jack]

There was a guy here, Scott Dennstaedt, who knew this stuff well, but the "know-it alls" here ran him off the board. He runs https://www.avwxworkshops.com/
you may wish to check there.

I'll try to answer, but Scott knows this stuff and can explain it well.
In your example, the parcel of air is cooling "faster", at 3 °C/1000 feet than the surrounding air (1 °C/1000 feet) and so it will lose lift quickly as it matches the temperature of the surrounding air. If the environmental lapse rate is larger (more than 3 °C/1000 feet) than the dry lapse rate, the air is unstable. The air parcel cools at 3 °C/1000 feet, but the surrounding air is still colder (higher lapse rate) so it still has lift.

You also need to consider the moist environmental adiabatic lapse rate. If the environmental lapse rate is between the values for the moist and dry lapse rates, the air is conditionally unstable; it doesn't have a lot of lift.

I've left a fair bit out, but I hope it is useful to you.

 

[LongRoadBob]

Hey thanks, but at the moment I'm not up for being a member of that website.

What I'm really getting at, the example in the Pooleys book for example shows what I believe is an unstable example, where cumulus cloud is developed, so it fits the model that ELR > DALR and, after the air parcel gets saturated, ELR > SALR.

But in their example even ELR is given as 1 deg/1000 ft, where DALR is 3 deg. /1000 it is just that the parcel of air begins rising because it is heated up more than the surrounding air. Am I wrong in thinking that their example, even though cumulus, is unstable?

So the contradiction I can't figure out is how is 1/1000 in any way greater than 3/1000?

Seems like I'm just missing that part.

 

[midlifeflyer]

I'm really not the best at this, but...

The DALR and SALR refer to the parcel. ELR refers to the actual atmosphere. DALR is a "constant" 5.5F/1,000'; SALR is 3.3F.

The atmosphere is considered to be unstable if a rising parcel cools more slowly than the environmental lapse rate. Stable if the parcel cools more rapidly.

If the ELR is only 1 deg/1,000', the environmental rate of cooling is slower; the parcel is cooling more quickly (1 is less than 3). The parcel is cooler than the atmosphere and remains so, so it sinks and is stable.

 

[Cap'n Jack]

@LongRoadBob What is the moist adiabatic lapse rate in your example?

If the environmental lapse rate is between the values for the moist and dry adiabatic lapse rates, the air is conditionally unstable; it doesn't have a lot of lift. (and yes, I changed something in my original reply)

 

[DoubleD]

Studying to retake the meteorology exam section.

Maybe this is a very basic thing I'm missing, I get how the lapse rates work, how the dry for instance at 3 deg. C / 1000 ft, while the environmental lapse rate is say 1 deg. C / 1000 ft, will be unstable. As the parcel of air rises it cools at 3 deg, while the surrounding air is only cooling at 1 deg, but the parcel started out warming which is why it rose. The parcel will keep rising, and it is unstable.

But the description for unstable is ELR > DALR or SALR

What I'm missing here is how is 1/1000 GREATER THAN 3/1000 or 1.5/1000 ?
Where is the "greater than" coming from? Maybe I'm punchy right now from study.
I tried checking on line (have found errors in this book) other sources but so far all point to the ELR > DALR as unstable, etc, but it must be obvious where the values are coming from?

I'm hung up on the DALR is a greater value, as is the temperature Of the parcel of air, until they meet.

I'm not an expert and have probably forgotten half of what I once knew. But first, let's agree on some numbers:

DALR= 3 degC/1000'
SALR= 1.1-2.8 degC/1000' (It varies because cooler air at higher altitude contains less water)
ELR = 2 degC/1000 (This is an average and can vary a lot, which is a major reason air can be stable or not)
Convergence Rate = 1.5 degC/1000' (this is the rate at which dew point and DALR converge with altitude. In other words, DP decreases with altitude but not as fast as DALR decreases. This is the basis of those written test question about estimating cloud bases from the Temp/DP spread.) These numbers are from the "Pilot's Handbook of Aeronautical Knowledge".

Note that your sequence ELR>SALR or DALR is not correct. Also keep in mind that ELR varies widely from the average of 2 deg.

Now, when an unsaturated parcel of air is lifted, it cools at the DALR. When the DP and ambient temperature converge, water begins to condense, releasing a huge amount of heat per gram or pound of water. At this point, if the parcel is warmer than the ambient temperature, it will continue to rise, and cool at the SALR. (The release of heat of condensation is the reason SALR is less than DALR). Sufficient moisture to continue the release of heat through condensation combined with an ACTUAL (not average) ELR greater than the WALR results in instability (cumulus clouds, thunderstorms, hurricanes, etc.).

I hope this helps. It's all thermodynamics.

 

[LongRoadBob]

I'm not an expert and have probably forgotten half of what I once knew. But first, let's agree on some numbers:

DALR= 3 degC/1000'
SALR= 1.1-2.8 degC/1000' (It varies because cooler air at higher altitude contains less water)
ELR = 2 degC/1000 (This is an average and can vary a lot, which is a major reason air can be stable or not)
Convergence Rate = 1.5 degC/1000' (this is the rate at which dew point and DALR converge with altitude. In other words, DP decreases with altitude but not as fast as DALR decreases. This is the basis of those written test question about estimating cloud bases from the Temp/DP spread.) These numbers are from the "Pilot's Handbook of Aeronautical Knowledge".

Note that your sequence ELR>SALR or DALR is not correct. Also keep in mind that ELR varies widely from the average of 2 deg.

Now, when an unsaturated parcel of air is lifted, it cools at the DALR. When the DP and ambient temperature converge, water begins to condense, releasing a huge amount of heat per gram or pound of water. At this point, if the parcel is warmer than the ambient temperature, it will continue to rise, and cool at the SALR. (The release of heat of condensation is the reason SALR is less than DALR). Sufficient moisture to continue the release of heat through condensation combined with an ACTUAL (not average) ELR greater than the WALR results in instability (cumulus clouds, thunderstorms, hurricanes, etc.).

I hope this helps. It's all thermodynamics.

Thanks, and to the others too. I think I can be more clear simply by showing what the book says. There is a real chance the book is wrong (typo, mistake). I have found other mistakes in this book, though the book is well written and has great illustrations, I contacted the publisher to check, and they agreed that the two I mention were mistakes and are corrected in the next edition. I'm just not sure here.

They write:

Unstable: (ELR > DALR or SALR) a parcel of air continues to move vertically after being displaced from its original position. This results in cumuli form clouds which may continue to develop up to high altitudes.

Neutral: (ELR = DALR or SALR) a parcel of air remains in the position it was vertically displaced to. This usually results in stratiform clouds.

Stable: (ELR < DALR or SALR) a parcel of air returns back to the position it was displaced from. This results in stratiform clouds or fog formation

I think they juxtaposed greater than and less than signs. Equal makes sense. "Unstable" I think should be ELR < DALR. And "Stable" should be ELR > DALR...

This is what we all are pretty much saying, right?

Maybe it is not that important, as I can plot the difference, as we all say here too, if the parcel is STILL at higher temperature than the env. It will continue rising. If it matches it will stop, if it is lower will sink. Also the dew point is in ther, and if it rises after saturation clouds form...

But also, there is the start point. If a parcel of air above a cleared land area has a temp of +17 and the environment around (say forest) has +12, EVEN though the ELR is smaller than the DALR, because of the start temp diff it will rise, and after a point will match the env. So the thing makes no sense to me, since it is the temperature that is the main thing?

 

[Clark1961]

I hope this helps. It's all thermogodamics.

FTFY

 

[iamtheari]

Thanks, and to the others too. I think I can be more clear simply by showing what the book says. There is a real chance the book is wrong (typo, mistake). I have found other mistakes in this book, though the book is well written and has great illustrations, I contacted the publisher to check, and they agreed that the two I mention were mistakes and are corrected in the next edition. I'm just not sure here.

They write:

Unstable: (ELR > DALR or SALR) a parcel of air continues to move vertically after being displaced from its original position. This results in cumuli form clouds which may continue to develop up to high altitudes.

Neutral: (ELR = DALR or SALR) a parcel of air remains in the position it was vertically displaced to. This usually results in stratiform clouds.

Stable: (ELR < DALR or SALR) a parcel of air returns back to the position it was displaced from. This results in stratiform clouds or fog formation

I think they juxtaposed greater than and less than signs. Equal makes sense. "Unstable" I think should be ELR < DALR. And "Stable" should be ELR > DALR...

This is what we all are pretty much saying, right?

Maybe it is not that important, as I can plot the difference, as we all say here too, if the parcel is STILL at higher temperature than the env. It will continue rising. If it matches it will stop, if it is lower will sink. Also the dew point is in ther, and if it rises after saturation clouds form...

But also, there is the start point. If a parcel of air above a cleared land area has a temp of +17 and the environment around (say forest) has +12, EVEN though the ELR is smaller than the DALR, because of the start temp diff it will rise, and after a point will match the env. So the thing makes no sense to me, since it is the temperature that is the main thing?

They have it right. A high environmental lapse rate results in unstable air. Here is a thought experiment:

Think about what the lapse rates mean and what causes air to rise relative to other air.

The environmental lapse rate is the lapse rate of the actual atmosphere, and it is very unlikely to be constant. It can in fact vary from a negative to positive, vice versa, or just all over the charts. Look at a Skew-T/Log-P sounding plot sometime to see an example of the real-world lapse "rate" through the atmosphere. But don't get into that too deep until you're ready. It's kind of a rabbit hole to Wonderland. For now, assume that the environmental lapse rate is a simple, constant figure.

The dry and moist adiabatic lapse rates are the rates at which a particular parcel of air will cool as it rises through the atmosphere, if it actually rises through the atmosphere. If I take a bucket of dry air from 5,000 MSL to 6,000 MSL, and do nothing else to it, it will lose 3 degrees celsius as a result of adiabatic cooling because 3C/1,000ft is the dry adiabatic lapse rate.

Warm air rises. The warmer it is relative to the surrounding air, the more lifting force there will be.

Stable air is happy where it is. Or at least it will be happy when it gets to its rightful place in the atmosphere. Imagine that the environmental lapse is 1C/1,000ft. If the temperature at sea level is 10C, then at 5,000 MSL it will be 5C. Now introduce a bucket of 15C dry air at sea level. It is warmer than the surrounding air, so it will rise, and it will cool adiabatically 3C/1,000ft on its way. At 5,000 MSL our bucket of air will have cooled to 0C. But it will not make it to 5,000 MSL because the surrounding air and the parcel we are following will be the same temperature at a lower altitude (namely 2,500 MSL where the parcel and surrounding air are both 7.5C so neither one wants to rise above the other). When they are the same temperature, neither our bucket of air nor the surrounding air will rise above the other. Stable air -> ELR < DALR

Unstable air is not happy where it is and it is never going to be happy. Imagine the same sea level conditions as above (10C at sea level and a 15C bucket of dry air being introduced), but an environmental lapse rate of 4C/1,000ft. At 5,000 MSL the atmosphere will be -10C while the bucket we put into the atmosphere will be 0C, which is still warmer than the surrounding air so it will continue to rise. Unstable air -> ELR > DALR

You might ask where the bucket of warm air comes from in the first place. The answer is that the sun heats the ground, which heats the air near the ground, which then starts to rise through the atmosphere. How forcefully and how far it will rise depend on the conditions of the surrounding air.

 

[midlifeflyer]

This is better than me:I don't know if this will help or not - it's a link to my playlist containing the two part video I used to learn how to decipher a Skew-T (I edited it for the guy who did the presentation). Part 1 is mostly theoretical and might be helpful. Weather in the Vertical

BTW, I think where some people get confused (I sure did - that's why I like pretty pictures instead of threory!) is lapse rate vs temperature, since they are opposite. A higher lapse rate means a faster rate of cooling, IOW lower temperatures. So, an environmental lapse rate which is higher than the ALRs produces temperatures which are lower than the parcel's

 

[LongRoadBob]

They have it right. A high environmental lapse rate results in unstable air. Here is a thought experiment:

Think about what the lapse rates mean and what causes air to rise relative to other air.

The environmental lapse rate is the lapse rate of the actual atmosphere, and it is very unlikely to be constant. It can in fact vary from a negative to positive, vice versa, or just all over the charts. Look at a Skew-T/Log-P sounding plot sometime to see an example of the real-world lapse "rate" through the atmosphere. But don't get into that too deep until you're ready. It's kind of a rabbit hole to Wonderland. For now, assume that the environmental lapse rate is a simple, constant figure.

The dry and moist adiabatic lapse rates are the rates at which a particular parcel of air will cool as it rises through the atmosphere, if it actually rises through the atmosphere. If I take a bucket of dry air from 5,000 MSL to 6,000 MSL, and do nothing else to it, it will lose 3 degrees celsius as a result of adiabatic cooling because 3C/1,000ft is the dry adiabatic lapse rate.

Warm air rises. The warmer it is relative to the surrounding air, the more lifting force there will be.

Stable air is happy where it is. Or at least it will be happy when it gets to its rightful place in the atmosphere. Imagine that the environmental lapse is 1C/1,000ft. If the temperature at sea level is 10C, then at 5,000 MSL it will be 5C. Now introduce a bucket of 15C dry air at sea level. It is warmer than the surrounding air, so it will rise, and it will cool adiabatically 3C/1,000ft on its way. At 5,000 MSL our bucket of air will have cooled to 0C. But it will not make it to 5,000 MSL because the surrounding air and the parcel we are following will be the same temperature at a lower altitude (namely 2,500 MSL where the parcel and surrounding air are both 7.5C so neither one wants to rise above the other). When they are the same temperature, neither our bucket of air nor the surrounding air will rise above the other. Stable air -> ELR < DALR

Unstable air is not happy where it is and it is never going to be happy. Imagine the same sea level conditions as above (10C at sea level and a 15C bucket of dry air being introduced), but an environmental lapse rate of 4C/1,000ft. At 5,000 MSL the atmosphere will be -10C while the bucket we put into the atmosphere will be 0C, which is still warmer than the surrounding air so it will continue to rise. Unstable air -> ELR > DALR

You might ask where the bucket of warm air comes from in the first place. The answer is that the sun heats the ground, which heats the air near the ground, which then starts to rise through the atmosphere. How forcefully and how far it will rise depend on the conditions of the surrounding air.

Yes, thanks. It makes sense. All you wrote up to the comparison equation always made sense to me, and I understood it the way you describe, but at the risk of exposing myself as a blockhead I still am not there.

I understand it that...

As long as the ELR is greater than the DALR (or after dewpoint, the SALR) the parcel will not "catch up" to the environment.
it will be unstable and keep rising. If they are equal, nothing happens, the parcel is just like the environment, etc,

Part of what messed me up, there is as you say, an imbalance to start with...

But also, I think the figure in the book, though showing an illustration is showing the formation of a cumulus cloud, it is not unstable except that it IS UNTIL the parcel of air catches up to the env. Did that make sense?

For one thing the book mentions Unstable often produces cumuli form clouds. Same section they show a forest with + 12 and an ELR 1 deg/1000 right next to a parcel of air over a plains...where DALR 3 deg. /1000 ft and is warmed to +17.

So the parcel is staring out warmer, even though ELR < DALR it isn't stable. The air rises. Because of temp difference. That is what kicks it off.

They give a dewpoint of +11 so at that point the parcel is at 2000 ft, is +11 degrees, while the env is at +10 deg, and a cloud forms.

The parcel is saturated at this point but still ELR < SALR ( 1/1000 < 1.5/1000) since temp hasn't caught up it still rises but more slowly. At 3000 ft, env = +9 and parcel = +9.5...so still rises...isn't this unstable?

At 4000 they both are at +8 Deg... And become stable? And at this point, the rules work.

I'm almost there, but I can't not see this as (as you pointed out, in real life it varies much more but here they are using constant ELR) that throughout the parcel of airs vertical journey, ELR is always less than either DALR or SALR, Yet it is unstable until 4000 ft, and only then does the rule enter into it and it is stable.The illustration is of a cumulus cloud.

I really appreciate your help here, and everyone's. This may be just the way I'm looking at it.

It seems like we are breaking the rule until we get to 4000 where the temperatures meet and then follow them. Is what I describe a stable cumulus? Seems unstable when it is created, but I just don't know where I'm off track here.

 

[iamtheari]

As long as the ELR is greater than the DALR (or after dewpoint, the SALR) the parcel will not "catch up" to the environment.
it will be unstable and keep rising. If they are equal, nothing happens, the parcel is just like the environment, etc,

The parcel and environment can have the same lapse rate but different temperature, which means that air will still move. Imagine if it were a foot race. Even if you go the same speed as your opponent, if he starts out 100m in front of you he will still win the race. The person who is behind has to run faster than the opponent in order to catch up.

But also, I think the figure in the book, though showing an illustration is showing the formation of a cumulus cloud, it is not unstable except that it IS UNTIL the parcel of air catches up to the env. Did that make sense?

Cumulus clouds form when unstable air rises and cools (adiabatically) until it is saturated (dewpoint equals temperature). That's why you can estimate the elevation of the base of a cumulus cloud based on the temperature-dewpoint spread at the surface and the rate that temperature and dewpoint converge as the air moves up through the atmosphere. The air already must have some lifting force in order to go up and turn into a cloud. That can be from thermal lifting or mechanical lifting such as a wind over a mountain ridge. The lapse rate of the environment is not a constant, so at some point above the base of the cumulus cloud the air runs out of lifting force, which becomes the top of the cloud. That is why you can usually assume the air is smooth (stable) above cumulus clouds. If the air were still unstable at that altitude, the cloud would continue building upward into a towering cumulus or cumulonimbus.

For one thing the book mentions Unstable often produces cumuli form clouds. Same section they show a forest with + 12 and an ELR 1 deg/1000 right next to a parcel of air over a plains...where DALR 3 deg. /1000 ft and is warmed to +17.

There will be a lifting force, and as long as the earth keeps heating the air will keep rising. I think this might play into the conditionally stable thing. That is, the air will rise but it will be capped out somewhere when its own lapse rate catches up with the environmental lapse rate. This is where my LACK of expertise comes into play, as I pretty much wrote everything I understand about the atmosphere in my earlier post!

 

[mtnflyr]

now i remember why i didnt do that great on the weather portion.

 

[F01LA]

Here's a practical question: How possible is it to reliably predict turbulence (or lack thereof) from the Skew-T plot?

 

[iamtheari]

Here's a practical question: How possible is it to reliably predict turbulence (or lack thereof) from the Skew-T plot?

 

[F01LA]

Pretty much a crapshoot then? Let me rephrase.. is it helpful at all to glance at the Skew-T to say something like "Oh, better stay below 7000' for smoother air today" or "Looks like it's gonna be a rodeo anywhere below 15,000, better tighten those belts."?

I've found low AIRMETs to be overly pessimistic and to "cry wolf" too often. There's also the turbulence forecast here which looks promising:

http://aviationweather.gov/gfa

I don't worry about turbulence, but my passengers do sometimes. It would be helpful to know more.

 

[iamtheari]

Pretty much a crapshoot then? Let me rephrase.. is it helpful at all to glance at the Skew-T to say something like "Oh, better stay below 7000' for smoother air today" or "Looks like it's gonna be a rodeo anywhere below 15,000, better tighten those belts."?

I've found low AIRMETs to be overly pessimistic and to "cry wolf" too often. There's also the turbulence forecast here which looks promising:

http://aviationweather.gov/gfa

I don't worry about turbulence, but my passengers do sometimes. It would be helpful to know more.

Actually I have really good luck finding the cloud tops and smooth air using Skew-T charts. But I am too much of a novice to know if I have just had beginner’s luck or actually know what I’m doing.

On the Skew-T chart as found through rucsoundings, altitudes where the bright red temperature line (environmental lapse rate) is sloped to the right of the brownish dry adiabatic lapse rate curves are stable, altitudes where temperature is sloped left of the blue moist adiabatic lapse rate curves are unstable, and in between those two the air is conditionally stable.

One thing about trying a new weather briefing tool like this is that it is free to try. Give it a shot and see how it turns out for you. Maybe you’ll have the same luck as I have so far.

 

[midlifeflyer]

now i remember why i didnt do that great on the weather portion.

The US does not go that deeply into weather theory for pilot certification. Note LongRoadBob's location.

 

[midlifeflyer]

Actually I have really good luck finding the cloud tops and smooth air using Skew-T charts. But I am too much of a novice to know if I have just had beginner’s luck or actually know what I’m doing.

Cloud tops is one of the simple items. I’ve had the same luck as you. Convective actuvity a little more complex. But as Scott is fond of saying, the Skew-T is only one of a number of tools to develop the full picture.

 

[dmspilot]

Maybe this is a very basic thing I'm missing, I get how the lapse rates work, how the dry for instance at 3 deg. C / 1000 ft, while the environmental lapse rate is say 1 deg. C / 1000 ft, will be unstable. As the parcel of air rises it cools at 3 deg, while the surrounding air is only cooling at 1 deg, but the parcel started out warming which is why it rose. The parcel will keep rising, and it is unstable.

You have that backward. If at sea level the temperature is 15°C, and the environmental lapse rate is 1°C, then at 1,000 feet, the temperature is 14°C. Your dry parcel of air which is going to cool at a rate of 3°C will now be 12°C when it is lifted to 1,000 feet. It is now colder and denser than the surrounding air, thus it will sink. The air is stable.

 

[mtnflyr]

The US does not go that deeply into weather theory for pilot certification. Note LongRoadBob's location.

Thank you...I was reading all this thinking man my test wasn’t this in depth.

 

[LongRoadBob]

You have that backward. If at sea level the temperature is 15°C, and the environmental lapse rate is 1°C, then at 1,000 feet, the temperature is 14°C. Your dry parcel of air which is going to cool at a rate of 3°C will now be 12°C when it is lifted to 1,000 feet. It is now colder and denser than the surrounding air, thus it will sink. The air is stable.

I believe I wrote in that example the parcel of air starting at +17 degrees, and the envorinment at +12 degrees.
With 3 degrees DALR and ELR of 1 deg /1000 ft.

 

[dmspilot]

I believe I wrote in that example the parcel of air starting at +17 degrees, and the envorinment at +12 degrees.
With 3 degrees DALR and ELR of 1 deg /1000 ft.

So at 3,000 feet the parcel is 8° and the surrounding air is 9°. It's not going to keep rising. It's stable.

 

[LongRoadBob]

So at 3,000 feet the parcel is 8° and the surrounding air is 9°. It's not going to keep rising. It's stable.

One degree is not enough to cause more rise? The book shows a cloud formed in this situation beginning at 2000 feet (saturated, at the dewpoint for the parcel of air) and continuing past 3000 (parcel of air now is just 9.5, since now using SALR past 2000 and temp of surrounding shown as 9 degrees) on up to a top at 4000 ft. where both surrounding air and parcel are at 8 degrees.

It's just what they show as an example. Theoretical. But I'm seeing that maybe I'm mixed up about stable vs. unstable. I saw this as "unstable" because it formed a cumulus cloud, and that also was in the example for typical Unstable cloud type. Since at no point is ELR > DALR or SALR in the example, it actually fits the description of "stable" except...the cloud type formed. This is what drives me nuts about meteorology...I'm now thinking this is a stable air mass, but that the heat difference between env. and parcel is the whole story. It is stable.

Again, thanks.

 

[luvflyin]

Well that pretty much puts to rest the concept that this was a very 'basic' question

 

[LongRoadBob]

Well that pretty much puts to rest the concept that this was a very 'basic' question

Well...I'm not changing the subject line now

I still think it is kinda basic, but I'm just having a hard time getting the whole picture.

 

[Ben]

I didn't know what either of these things were. Am I supposed to know this stuff?? Oh man!

reminds me of this video:

 

[dmspilot]

One degree is not enough to cause more rise?

As I said the parcel would be 8° and the surrounding air 9°. Why would it rise? It is denser.

 

[Clark1961]

Well...I'm not changing the subject line now

I still think it is kinda basic, but I'm just having a hard time getting the whole picture.

Maybe adjust the antenna?

 

[Skyrys62]

I didn't know what either of these things were. Am I supposed to know this stuff?? Oh man!

reminds me of this video:

What the Retroencabulator probably looks like today:

 

[LongRoadBob]

Maybe adjust the antenna?

I tried kicking it (me)...helped a lot!

I got it now. That illustration was definitely showing just cloud formation due to heating. But all the discussion here helped a LOT for me to feel I have a good grasp now on the adiabatic lapse rate.

Next up: Føhn Corialis effect...

Just kidding. I'm done, stick a fork in me.

 

[denverpilot]

But the description for unstable is ELR > DALR or SALR

What I'm missing here is how is 1/1000 GREATER THAN 3/1000 or 1.5/1000 ?
Where is the "greater than" coming from? Maybe I'm punchy right now from study.
I tried checking on line (have found errors in this book) other sources but so far all point to the ELR > DALR as unstable, etc, but it must be obvious where the values are coming from?

I may see what you got tripped up on. Don’t compare the two mathematically as fractions, compare what the air the ELR number describes DOES when you release it into an atmosphere made up of the other standard air. (DALR or SALR)

If you have a parcel of air that wants to cool 1 degree per 1000’, and we know the dry adiabatic lapse rate (a constant) is 3 degrees per thousand feet, let’s push it upward somehow / release it / let it go and see what happens...

Assuming some sort of lift... we have to lift it in their thought process. (Or in real life something has to lift it...) We don’t care how for this determination of stability... any of the four ways to lift air is fine.

We release it 1000’ up, so it cools 1 degree. The air surrounding it cooled 3. The parcel is a LOT warmer than the “normal” air around it. To reach equilibrium it MUST KEEP going up and cool and expand some more. It wants to go up.

That’s “unstable”. It wants to keep moving upward after we lift it.

Air with an ELR 1 released into standard DALR of 3.

Unstable parcel of air. 1 < 3.

(If it’s easier, don’t make it into fractions of 1/1000 < 3/1000 in your head and try comparing fractions. Just use the number of degrees. I think that is what you did when tired.)

Now let’s take a parcel that wants to cool at 3 degrees per 1000’.

Standard air. Released into standard air. But lifted.

Release it. It is the same temperature 1000’ up as the surrounding air. It doesn’t want to rise or fall any faster than the surrounding air. Stable. It’s just going to sit there. No up, no down. It’s happy.

ELR 3 = DALR 3. Stable. Nothing happening.

Now let’s take a parcel that wants to cool 5 degrees per 1000’.

Whatever lifting mechanism lifts it. Release it.

1000’ up this parcel is now 2 degrees colder than the surrounding air. It wants to sink back down, compress and warm up. It will try to move downward until it finds an equal temperature with the surrounding air.

That’s also stable. It wants to return downward to equilibrium when lifted. ELR 5 > DALR 3... stable.

Remember there’s multiple ways to lift a parcel of air, but the lapse rate comparison is measuring to see if the air wants to keep rising once it starts moving.

If you lift unstable air, it wants to keep going. If you lift stable air, it wants to stop after you stop lifting it, or return to where it started.

That’s the stability number comparison. If ELR > than DALR that air wants to keep going up when released.

(I left out SALR for simplicity but same thing. Now if you want the next thing to think about try an ELR of 2 degrees. Hmm.. ELR < DALR so the parcel is unstable until... it reaches dew point... now ELR > SALR...)

Now on to turbulence and Skew-T...

Turbulent air can be caused by a whole bunch of stuff, that doesn’t necessarily have anything to do with the lapse rate...

Example: Orographic lifting and falling as a pressure (wind) system slams into an immovable object like a mountain range. Rocks in a stream.

So not ALL sorts of turbulence can be seen in a Skew-T, no. Definitely not. You can’t see a mountain range standing in the way of tight isobars on a Skew-T. Wrong tool for that.

(Isobars drawn on a topographical map is the right tool for visualizing that turbulence... or at least the setup for massive mechanical turbulence...)

But sometimes hints on your ride quality CAN be seen in a Skew-T.

For example, a temperature inversion. Cold air trapped underneath warmer air is by definition, not mixing. It’s stuck under there waiting for something to mix it up a little and cause it to get back to equilibrium (ELR), and that only happens in very stable air...

So... no mixing, no vertical movement, your ride is probably going to be very good ... below the inversion point.

And you can see an inversion on a Skew-T.

Of course you might get freezing rain if warm air is precipitating into cold air below it too... but that’s a different use of the Skew-T!

Fun stuff.

There was a guy here, Scott Dennstaedt, who knew this stuff well, but the "know-it alls" here ran him off the board. He runs https://www.avwxworkshops.com/
you may wish to check there.

I hadn’t seen any of that or heard it from Scott, I thought he just got REALLY busy when he went to work for ForeFlight? I’m not even sure he’s had much time to run as many workshops as in the past.

But he’s definitely very good at taking his meteorology knowledge and applying it to Aviation and dumbing it down for pilots.

 

[Cap'n Jack]

<SNIP>

I hadn’t seen any of that or heard it from Scott, I thought he just got REALLY busy when he went to work for ForeFlight? I’m not even sure he’s had much time to run as many workshops as in the past.

But he’s definitely very good at taking his meteorology knowledge and applying it to Aviation and dumbing it down for pilots.

This was some time ago, before he got involved with FF. He is a classy person, and didn't leave with a big fan-fare. Look at the "getting rid of fat" thread....people disagreeing with a biochemist PhD. The board is better than it used to be.

 

[LongRoadBob]

I may see what you got tripped up on. Don’t compare the two mathematically as fractions, compare what the air the ELR number describes DOES when you release it into an atmosphere made up of the other standard air. (DALR or SALR)

If you have a parcel of air that wants to cool 1 degree per 1000’, and we know the dry adiabatic lapse rate (a constant) is 3 degrees per thousand feet, let’s push it upward somehow / release it / let it go and see what happens...

Assuming some sort of lift... we have to lift it in their thought process. (Or in real life something has to lift it...) We don’t care how for this determination of stability... any of the four ways to lift air is fine.

We release it 1000’ up, so it cools 1 degree. The air surrounding it cooled 3. The parcel is a LOT warmer than the “normal” air around it. To reach equilibrium it MUST KEEP going up and cool and expand some more. It wants to go up.

That’s “unstable”. It wants to keep moving upward after we lift it.

Air with an ELR 1 released into standard DALR of 3.

Unstable parcel of air. 1 < 3.

(If it’s easier, don’t make it into fractions of 1/1000 < 3/1000 in your head and try comparing fractions. Just use the number of degrees. I think that is what you did when tired.)

Now let’s take a parcel that wants to cool at 3 degrees per 1000’.

Standard air. Released into standard air. But lifted.

Release it. It is the same temperature 1000’ up as the surrounding air. It doesn’t want to rise or fall any faster than the surrounding air. Stable. It’s just going to sit there. No up, no down. It’s happy.

ELR 3 = DALR 3. Stable. Nothing happening.

Now let’s take a parcel that wants to cool 5 degrees per 1000’.

Whatever lifting mechanism lifts it. Release it.

1000’ up this parcel is now 2 degrees colder than the surrounding air. It wants to sink back down, compress and warm up. It will try to move downward until it finds an equal temperature with the surrounding air.

That’s also stable. It wants to return downward to equilibrium when lifted. ELR 5 > DALR 3... stable.

Remember there’s multiple ways to lift a parcel of air, but the lapse rate comparison is measuring to see if the air wants to keep rising once it starts moving.

If you lift unstable air, it wants to keep going. If you lift stable air, it wants to stop after you stop lifting it, or return to where it started.

That’s the stability number comparison. If ELR > than DALR that air wants to keep going up when released.

(I left out SALR for simplicity but same thing. Now if you want the next thing to think about try an ELR of 2 degrees. Hmm.. ELR < DALR so the parcel is unstable until... it reaches dew point... now ELR > SALR...)

Now on to turbulence and Skew-T...

Turbulent air can be caused by a whole bunch of stuff, that doesn’t necessarily have anything to do with the lapse rate...

Example: Orographic lifting and falling as a pressure (wind) system slams into an immovable object like a mountain range. Rocks in a stream.

So not ALL sorts of turbulence can be seen in a Skew-T, no. Definitely not. You can’t see a mountain range standing in the way of tight isobars on a Skew-T. Wrong tool for that.

(Isobars drawn on a topographical map is the right tool for visualizing that turbulence... or at least the setup for massive mechanical turbulence...)

But sometimes hints on your ride quality CAN be seen in a Skew-T.

For example, a temperature inversion. Cold air trapped underneath warmer air is by definition, not mixing. It’s stuck under there waiting for something to mix it up a little and cause it to get back to equilibrium (ELR), and that only happens in very stable air...

So... no mixing, no vertical movement, your ride is probably going to be very good ... below the inversion point.

And you can see an inversion on a Skew-T.

Of course you might get freezing rain if warm air is precipitating into cold air below it too... but that’s a different use of the Skew-T!

Fun stuff.



I hadn’t seen any of that or heard it from Scott, I thought he just got REALLY busy when he went to work for ForeFlight? I’m not even sure he’s had much time to run as many workshops as in the past.

But he’s definitely very good at taking his meteorology knowledge and applying it to Aviation and dumbing it down for pilots.

Thanks very much for taking the time to go into this. I realized a few days ago the illustration that was messing me up was actually not meant to show the lapse rate effect, but the warming of a parcel of air by heat, of course, still the lapse rates are at work, but I wasn't seeing that in fact it did not break the "rules" but followed them after the heating of the parcel.

And yes, definitely am looking just at lapse degrees not fraction. I feel like I have it now but your reply here confirmed, and even better some of the extra points you make I found very useful as far as what it actually means for a pilot flying into it. After all, that is really a main reason for knowing this. Often the books will explain what is happening technically, but give short shrift to what it MEANS to a pilot, how to assess the situation in regards your aircraft. Or else they mention it slightly, but a student gets too focused on getting the math right, and the answers to questions one is likely to get on the exam.

I mean, or think, unstable air often will produce then a cumuliform type cloud, where stable air would be often more stratus. Starting to try and put things together. Like before starting learning to fly I never got why flying over clouds was often less turbulent than under, but I see it is because under is unstable and mixing, and over indicates most likely the point where it is stable and even. The main difficulty I think in meteorology is putting it all together with so many factors. im just getting a little bit of a better feeling about it. Have been drawing the illustrations from my book, which helps me a LOT to get deeper into what is being shown, and I'm getting pretty good at drawing clouds now
And noticing the smaller details in all the information shown in these.

So specially thanks for the extra insights too!