Weather Conditions Analysis

[Dinga]

Guys,

 

I would like to share some conditions experienced on Sun for comment by the more knowledgeable among us :-) & appreciate some comments on what you guys see as happening in relation to the Wx Balloon Data attached (wx balloon data is Perth Airport).

 

Locations: 55nm East of Perth (Wheatbelt)

 

Elevation 1000'

 

Time: ~0600-0830 Local

 

On the ground it was ~8kts 010/125

 

Noticeably cool from ground to ~1300' AGL and moderately turbulent with strong wind (I never checked the strength at that level).

 

Between ~1300-1500AGL same but there were very small pockets and wafts of warm air mixing with the cool air. But still as turbulent.

 

>1500'AGL a sudden transition to warm air and silky smooth flying. At 1500+ & all the way to 3500 (didn't test any higher) it was just hands off flying but with 15/20kts of wind still from the original direction.

 

I'm with the whole inversion layer thing but would still love to hear any comments from other habitual wx analysers.

 

The main thing I am looking to understand is why so much turbulence? It wasn't thermals as that hadn't kicked in and if it was wind why such turbulent wind and not more laminar flow? In general terrain around me was generally flat.

 

Anyway, just throwing it out there for some discussion.

 

 

 

[facthunter]

The notable thing is the temp RISE with altitude increase in the lower levels. Normally the temp lowers adiabatically with height gain at around 2 degree s C /1,000 feet of altitude change. ( the standard lapse rate approx.) There is an aberration for some reason which will affect mixing of the different layers. Lapse rate affects stability . That's not a complete answer, I know. Nev

 

 

[Nobody]

A good explanation is in one of the classic gliding texts (eg Meterology for Glider pilots by Wallington or the one by Reichman but the exact name escapes me) but my explanation is:

 

There are a few concepts to understand:

 

1. Air that is less dense than air around it will rise. This is the well known phrase "hot air rises" expanded a bit to take into account humidity.
    
    
   
2. Air doesn't mix very well with the air around it. That is a pocket of hot (or cold) air will stay together as a "clump", it does not become the same temperature as the air around it for a long time.
    
    
   
3. When you compress air it gets hotter, and when you lower its pressure its temperature gets colder. The pressure in the atmosphere changes at a reasonably well known rate. The pressure change equivalent to a change of height of 1000 feet is 3 degrees at the heights we typically fly.
    
    
   
4. Something is stable if it returns to its previous condition after a disturbance. If there is nothing returning the thing to its original condition it is unstable.
    
    
   

 

 

Now imagine that you had the power to just move bits of the atmosphere around at your will. Imagine that you could take a chunk of the air from the surface at the time and location that the trace was taken and move it up to 1000 feet. The air temperature at the surface in that trace is 17 degrees. Now in raising by 1000 feet the temperature of that parcel of air will drop by 3 degrees to 14 degrees. But in looking at the trace the temperature of the surrounding air is 12.5 degrees at this level. So this parcel is now hotter than the surrounding air and so it will continue rising. At this level in the atmosphere the air is unstable. If it is disturbed and moves upwards then is will continue to rise. The reverse is also true. A parcel of air at 1000 feet is 12.5 degrees. If it somehow is moved to the surface it will gain 3 degrees because it is compressed. It will now be 15.5 degrees. But the air at the surface is 17 degrees and so the parcel of air being moved down is colder than the air around it and so it is more dense and wants to sink to the bottom. We have looked at it over a 1000 differential, but it happen over a smaller scale and that starts off the process. A little bit of wind over the surface and something will rise a little bit and then because it is less dense than its surrounds it will keep going.

 

The unstable atmosphere (having a temperature reduction greater than 3 degrees per 1000) will be constantly trying to resolve the buoyancy imbalance constantly inverting itself. It will be turbulent and bumpy. Often it will lead to thunderstorms if it is unstable to a high height.

 

What is interesting in the trace you posted is that is is capped by an inversion. Imagine doing the same thing but taking the parcel of air from 1200 feet up to 2200 feet. The air, when at 1200 feet would be 12.5 degrees, but when raised up to 2200 feet with have cooled to 9.5 degrees. On the day you posted the trace for the surrounding air at this height is 16 degrees. The parcel we have moved up is now colder that the surrounding air and it will settle back down to original height. In reality when the air is in this condition there is very little vertical movement and the flying is smooth.

 

The dark green lines on the trace represent a reduction of 3 degrees per 1000 feet increase in height. Where the ambient temperature reduces by more than this ( ie the blue line is flatter than the dark green lines) then the air will be unstable and the flying bumpy. The graph shows this was the case below about 1300 and this aligns well with what you experienced.

 

Moisture (cloud formation) complicates things a bit.....

 

 

[Head in the clouds]

A good explanation is in one of the classic gliding texts (eg Meterology for Glider pilots by Wallington or the one by Reichman but the exact name escapes me) but my explanation is: ...

Yes, three times World Gliding Champion Helmut Reichmann's books are pure gold for anyone wanting to really understand the medium in which we fly.

 

'Cross-Country Soaring' (ISBN 1-883813-01-8) and 'Flying Sailplanes - a Practical Training Manual' (ASIN B0006E1VSK). I cannot recommend them more highly, both are available on Amazon and elsewhere, a great investment in your pastime. Additionally they'll help you very significantly cut the cost of your flying. When flying your powered plane cross-country, if you employ the methods used by sailplane pilots you can easily reduce your fuel burn by 20% and get there faster ... so the books will more than pay for themselves over time - and you'll enjoy the flights more as well.

 

Cross-Country Soaring was written first and is for more advanced flyers, Flying Sailplanes is aimed more at the beginner. They're both wonderfully written because Prof Dr Reichmann was an accomplished teacher, among several other talents.

 

 

[Dinga]

Hi Guys,

 

Thanks for the comments so far, and certainly for the book recommendations I'll be seeking them out.

 

Great explanation Nobody thanks for the effort on this, I am re-reading it still just getting my head around it.

 

Since flying Microlights I've never been so wrapped up in what the damn weather is doing, flying fixed wing previously there seemed to be far less to be concerned with (or maybe I was just more naive back then:smile:)

 

Anyway thanks again.

 

 

[kasper]

Hi Guys,Thanks for the comments so far, and certainly for the book recommendations I'll be seeking them out.

 

Great explanation Nobody thanks for the effort on this, I am re-reading it still just getting my head around it.

 

Since flying Microlights I've never been so wrapped up in what the damn weather is doing, flying fixed wing previously there seemed to be far less to be concerned with (or maybe I was just more naive back then:smile:)

 

Anyway thanks again.

Yep, When you have 12-15 square metres of wing actually 'live' in your hands when flying you really want to know what the winds are doing ... 3 hours of being bashed about is something I can do every now and then but i like to know its going to happen so I can decide IF i want to sit on the ground for a couple of hours to get less bashed.

 

 

[facthunter]

Like Sailing. Might be challenging but you get sick of the effort just to stay safe on a wave. Particularly with a catamaran. Sometimes the air is so smooth you could cut it with a knife. Not a ripple. When it's really rough I think of what the wing spars are putting up with. Nev

 

 

[Dinga]

Yep, When you have 12-15 square metres of wing actually 'live' in your hands when flying you really want to know what the winds are doing ... 3 hours of being bashed about is something I can do every now and then but i like to know its going to happen so I can decide IF i want to sit on the ground for a couple of hours to get less bashed.

Agreed, and because I am little OCD and Black or White, I find it frustrating when I think I've picked the weather aloft from the forecast only to find that in fact its quite different. Then when this happens I 'have' to know why, what caused it and what was actually happening in the air at that time to cause the turbulence or other condition, frustrating very frustrating

 

Like Sailing. Might be challenging but you get sick of the effort just to stay safe on a wave. Particularly with a catamaran. Sometimes the air is so smooth you could cut it with a knife. Not a ripple. When it's really rough I think of what the wing spars are putting up with.Nev

lol, yes Nev, I have a friend with a 50' Cat that I sail with sometimes and I must say I'd rather be picking that than the flying weather. Its not the structure that I get concerned with I think its just because when you are hanging on to the control frame you are literally feeling every movement of the pod relative to the wing unlike in a GA aircraft. Cant say I ever concerned myself with turbulent weather in GA even when it was quite bad. ah well, its would be boring if it was easy .

 

Here's a thought. The Wx Balloon Data was based at Perth AP so more or less sea level (not sure exactly) however I was flying 130kms East at Aerodrome Elevation of 1000' so when looking at the data and relating it to say my AP level of 1000' would the 0 altitude on the data graph still relate to me or would it be the 1000' line which is the elevation of where I was flying at the time. Certainly the ground temperature at the airfield was nearer the 17C mark as shown at 0 Graph Altitude.

 

 

[Nobody]

Here's a thought. The Wx Balloon Data was based at Perth AP so more or less sea level (not sure exactly) however I was flying 130kms East at Aerodrome Elevation of 1000' so when looking at the data and relating it to say my AP level of 1000' would the 0 altitude on the data graph still relate to me or would it be the 1000' line which is the elevation of where I was flying at the time. Certainly the ground temperature at the airfield was nearer the 17C mark as shown at 0 Graph Altitude.

This is not really an easy question to answer however it is very likely that the temperature profile in atmosphere early in the morning has more to do with proximity to the surface than the absolute altitude. Ie would would probably find that the general shape was similar. What is important is the rate of change with altitude, if the air temperature drops by more than 3 degrees for every 1000 foot gained it will be unstable. If doesn't matter is it is 25 or 15 degrees.

 

 

[Blueadventures]

Yes, three times World Gliding Champion Helmut Reichmann's books are pure gold for anyone wanting to really understand the medium in which we fly.'Cross-Country Soaring' (ISBN 1-883813-01-8) and 'Flying Sailplanes - a Practical Training Manual' (ASIN B0006E1VSK). I cannot recommend them more highly, both are available on Amazon and elsewhere, a great investment in your pastime. Additionally they'll help you very significantly cut the cost of your flying. When flying your powered plane cross-country, if you employ the methods used by sailplane pilots you can easily reduce your fuel burn by 20% and get there faster ... so the books will more than pay for themselves over time - and you'll enjoy the flights more as well.

 

Cross-Country Soaring was written first and is for more advanced flyers, Flying Sailplanes is aimed more at the beginner. They're both wonderfully written because Prof Dr Reichmann was an accomplished teacher, among several other talents.

Hi HIC The books by Bernard Ecky are well written. Have you read them? I know he wrote a 3rd revision. I've got versions 1 & 2. On the hot days with plenty of clouds I try and pick the decaying cloud shodow indicators on the ground to stay in the nicer air. And some time ago flying with mates to Temora we were able to get into the lift bands of the cloud streets and reduce our fuel burn. Can't get it all the time but nice when things go our way. Cheers and how's your build progressing.