The BA Cloud!

Old Jun 25, 12, 1:42 pm
  #151  
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Oh, dear the things young people do!!


I note, dear BotB, you have not specifically mentioned one of my favourite terms [although you have alluded to it obliquely].

The adiabatic lapse rates which refer to the change in temperature of a parcel of air as it moves upwards (or downwards) without exchanging heat with its surroundings. The temperature change that occurs within the air parcel reflects the adjusting balance between potential energy and kinetic energy of the molecules of gas that comprise the moving air mass. There are two adiabatic rates:[6]
* Dry adiabatic lapse rate
* Moist (or saturated) adiabatic lapse rate
I just love the terminology, but for the life of me [even though I've done calculations based on it] I can't remember ever hearing it expressed in English!!

http://en.wikipedia.org/wiki/Lapse_rate
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Old Jun 25, 12, 2:07 pm
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Some from me.

CYYC/YYC-EGLL/LHR, over N. Canada.



EDDF/FRA-EGLL/LHR, coming over the Channel from the cockpit.

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Old Jun 25, 12, 2:24 pm
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Some land-based photos...





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Old Jun 25, 12, 2:26 pm
  #154  
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Old Jun 25, 12, 3:37 pm
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Originally Posted by BotB View Post
As dunk asked about why the fog only formed twice a year in Dubai I thought I would talk a bit about fog and how it forms which will hopefully help those thinking about it when trying to fly from an airport that is experiencing fog or trying to figure out when it will dissipate (which you can really only tell if you know how it formed in the first place)
Fascinating stuff. Thank you very much
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Old Jun 25, 12, 4:18 pm
  #156  
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Originally Posted by T8191 View Post
I note, dear BotB, you have not specifically mentioned one of my favourite terms [although you have alluded to it obliquely].

(BotB note: the term was adiabatic lapse rate...)

I just love the terminology, but for the life of me [even though I've done calculations based on it] I can't remember ever hearing it expressed in English!!
As stated before: I love a challenge T8191

I just hope we don't put off anyone with descriptions of technical terms...so for the advanced class today:

Lapse rates: as you point out there are two…a dry and a saturated adiabatic lapse rate.. so what are they and why are they of interest?

The adiabatic lapse rates (besides being a brilliant term to use in the pub)…is a way to follow the path any parcel of air would take as it rises in the atmosphere and follow how the physics would apply to that parcel of air.

What? I hear you say…

When you lift a parcel of air up in the atmosphere…it needs to be warmer than the surrounding air or it would not continue to rise

So, that particular parcel of air has a known temperature (when it started out), pressure (where we lifted it from) and dew point (moisture content of that parcel of air)….

When we lift this parcel of air (which is warmer than the surrounding air as mentioned) it rises…and because the pressure decreases as it rises the parcel expands…this requires energy…so we use up the energy in the parcel of air and this causes the temperature in the parcel to drop…but the temperature is still higher than the dew point (which remains constant as the amount of moisture in the parcel is still the same and the temperature has not dropped to that dew point level so the air is not saturated yet) so the rate that the parcel rises at is known as the 'dry' adiabatic lapse rate…or according to ICAO we lose about 9.8 degrees C / 1000 meters of ascent in a nice straight forward manner

Obviously, if the air in the parcel is still warmer than the surrounding air, it will continue to rise…once the temperature drops to the dew point, the air becomes saturated…this level where the air becomes saturated is called the convective condensation level (or CCL) and the rate that the parcel then continues to rise is different as the air is saturated and the energy needed to expand and cool now creates heat as well which warms up that parcel a bit at the same time it is cooling so it cools slower as it ascends further…so the rate of temperature lose with height is not as much as when it was dry…this is the saturated adiabatic lapse rate….

We use them to find out where cloud could develop and how thick that convective type cloud could be and what layers of cloud there could be…

This is all a fancy way of knowing how an air parcel will rise in the atmosphere…if it is saturated it rises and loses temperature at a different rate (slower) than when it is not saturated…

The lines of a tephigram show the rates of rise for any given starting temperature / dew point and pressure.

What is a tephigram?

http://en.wikipedia.org/wiki/Tephigram

A great bunch of lines on paper to help decide what is happening in the world according to the laws of physics!

A tephigram is a snap shot of the atmosphere looked at in cross section. (so you see the atmosphere from the ground up to the tropopause in a vertical line and can see where cloud will develop, what the winds are like, if there will be thunderstorms…

This is one of THE most useful tools a meteorologist has to understand what the atmosphere is doing right now…and then looking upstream to understand what is coming towards that location.

I'll have a go at explaining the relevant bits another time but these pages should keep you busy for some time T8191…

Tephigram plots for quite a few locations around the world updated several times a day…

Tephigrams provided by weatheronline

And this page tells you how to read a tephigram…so you can start to disect the atmosphere at any location in the world you choose and know what will happen to that parcel of air you raise up…

How to use a tephigram

Better than any video game I tell you…Here you can create your own world of clouds and thunderstorms, lightning, rain, etc…

Back in the day...you had to send this weather balloon up and then plot the data by hand and then analyse the chart...nowadays...I tell ya...they have it easy...the bloomin' computer does all this whiz bang stuff...

Last edited by BotB; Jun 25, 12 at 4:27 pm Reason: Add some manly 'back in the day' humour...
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Old Jun 25, 12, 4:52 pm
  #157  
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Originally Posted by Heathrow Tower View Post
Some from me.

CYYC/YYC-EGLL/LHR, over N. Canada.



EDDF/FRA-EGLL/LHR, coming over the Channel from the cockpit.

Welcome to the thread and thanks for contributing these excellent photos Heathrow Tower!

The first picture shows some Stratocumulus I believe and the long line of cloud is a weak weather front showing the boundary between two air masses! I am guessing but it looks like the front is moving from right to left in the picture and if this is a warm front then the colder air mass is the clear air to the left of that wall of cloud...and the air behind the wall of cloud is warmer in nature. (might only be a few degrees)...No idea of the moisture content of the two air masses but I would again guess the air in front is moist as there is some convective cloud around...but not a lot given that the temperature is not that warm and there is not that much topographical areas to cause lift here...Also the tops of the clouds are cut off very evenly...so to go back to the adiabatic lapse rates...these cloud tops are exactly where the surrounding air is at the same temperature as the parcels of air that have been lifted to create this cloud and why the cloud does not extend any higher!

The second photo (again a brilliant photo ) shows some great Altostratus that is being highlighted by longer wavelength red spectrum light from the Sun...as you are higher up in the atmosphere while flying you see more red long wavelength radiation (or to use a friendlier term...sunshine) that is not being scattered out by the usually much more prevalent shorter wavelength blue spectrum light...that we see at the ground...this is further strengthened by the fact that the Sun is not high in the atmosphere here (its rising or setting) so there is more of the blue light being scattered in the air and allowing the red spectrum to reach your eye...
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Old Jun 25, 12, 5:04 pm
  #158  
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Originally Posted by Heathrow Tower View Post
Some land-based photos...





Again, some very nice, exotic cloud photos...so thank you!

The first one is showing some very low based ACC (Altocumulus Castellanus forming that incredibly is also turbulent in the downward flow as well...so the cloud is developing in both directions...this can be seen in the Mammatus that are formed / forming on the bottom...Not seen this before at mid levels so a new lesson for me...thank you! Not particularly good to fly through that air at that time (especially in smaller aircraft...)

The next photo shows some great Cumulus and Virga (precipitation that does not reach the ground)...the air is hot and moist at elevation but is dry as a popcorn [email protected] at lower levels...so the precipitation and energy get soaked up by the atmosphere as it falls downward...until the air is moist enough to allow the precipitation to reach the ground.

And finally the third photo...simply brilliant.

I have no idea how this formed like this...but very, very nice to look at and try to analyse...

You've set the bar mighty high Heathrow Tower...

Thanks for the great pics, a real pleasure to view.
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Old Jun 25, 12, 10:42 pm
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Lots of different things going on in the sky over where I am tonight. I took this about 10 minutes ago - the iPhone doesn't really do it justice:


Sadly not taken from a BA (or any) plane, but on the plus side that is the view from my living room!
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Old Jun 26, 12, 12:14 am
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Thank you BotB.

Some more!



The following one was taken 10 minutes or so after the one in my post above.
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Old Jun 26, 12, 3:20 am
  #161  
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Originally Posted by BotB View Post
As stated before: I love a challenge T8191

I just hope we don't put off anyone with descriptions of technical terms...so for the advanced class today:
..
Back in the day...you had to send this weather balloon up and then plot the data by hand and then analyse the chart...nowadays...I tell ya...they have it easy...the bloomin' computer does all this whiz bang stuff...
Thank you very much!! Several grey cells have gone "Ah, yes, of course!" and a few others twitched at hearing 'tephigram'. I'm sure I used to know something about the latter, and having read the links I'm even more convinced

Sadly all those bits of learning expired from lack of use over the following >5 decades
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Old Jun 26, 12, 5:29 am
  #162  
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Originally Posted by wind-blownmind View Post
Lots of different things going on in the sky over where I am tonight. I took this about 10 minutes ago - the iPhone doesn't really do it justice:


Sadly not taken from a BA (or any) plane, but on the plus side that is the view from my living room!
Thanks for contributing wind-blownmind

Nice picture...had to think about this one for a while...looks can appear deceptive!

I assume this was taken in the greater Vancouver area? (those hills can't be London )

Nice view of the sky from your window

To the picture:

At first I thought this was some instability and almost Mammatus showing but after a more thorough examination I see there are two distinct layers of cloud there and the way the light is shining through makes it look like one layer in places...

So there is some Altocumulus at the lower level which in the top half of the picture here is also showing the Floccus sub species (so upwards motion where the cloud is and downward motion in a ring around that cloud ...making a dotted canvas...)

Above this quite thin AC Floccus layer we have some Cirrostratus and the lighting is rather strange so shows very luminous and makes it appear that there is only one layer in places...

I love the picture and the lighting contrasts between colours, very nice.

Thanks for sharing. Hope you do find a new job that does allow you to travel more and get some good cloud pics for the thread!
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Old Jun 26, 12, 6:02 am
  #163  
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Originally Posted by Heathrow Tower View Post
Thank you BotB.

Some more!



The following one was taken 10 minutes or so after the one in my post above.
great stuff thanks.

The first picture is interesting (but not for the usual reasons of it looking dramatic rather...)

Although there are mountains in the background here which cause a lot of upward lift and convergence (along with the associated increase in speed of the wind)...the clouds are not being affected...so this tells me that the winds aloft here are quite low and very friendly conditions with a stable atmosphere. If the winds were moderate on the ground then the winds aloft would be much stronger due to this channelling and the predominant Altocumulus we see here at the higher level would be changed in shape to lenticular clouds...

So the atmosphere is stable and there is also very little moisture available as we can also see the 'flat' Altocumulus in the picture is not developing any further...

We do see some Cumulus cloud in the picture (in the upper right hand side about 4/5 of the way over and 4/5 of the way up in this photo)...which has developed from the convective cycles and heating of the ground from the Sun...but there atmosphere just doesn't have enough moisture nor enough instability to develop into any serious cloud that can cause turbulence or precipitation.

The second picture...again, really interesting but unfortunately I can't explain what is going on...maybe it would help to know where this was taken and if there is Ocean or large source of water to the left of that mountain range?

I can't for the life of me explain why the cloud edge is so sudden on the left hand side just where the mountain range is (unless the flow is left to right) but this cloud has some convective characteristics while also showing some great vertical extent which would not be the case if it was just some cloud being formed as it passes over the mountain...so the cloud is thick and has been around before passing over the mountain but there is some winds 'scouring' the underside of the cloud causing some of the shapes here...but why it ends so abruptly is unknown (unless it is also the cloud associated with a frontal passage)...did the winds change direction shortly thereafter? (by 45 degrees or more?)

Maybe more details will help...a good one to stew over...thanks for a good challenge!
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Old Jun 26, 12, 7:47 am
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I was trying to see how much you could surmise merely from the pictures!

Both were taken in Yellowstone, September 2010, on the same day. The two pictures of the same cloud formation were taken shortly after a 20 minute long snow shower, which came towards the end of a rather hot and sunny day.

The temperature dropped from mid 20s to about 5 degrees shortly before it started snowing.
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Old Jun 26, 12, 9:07 am
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Ah, that does help...in one way at least...

Yellowstone...and Colorado weather...some very interesting and strange weather there!

So the cloud in your photo was definitely a TCU (towering Cumulus or CB cloud then as they are the only ones to provide a snow shower and some of the cloud details in your photo...but I could't say that without your additional info

Not a frontal cloud then, just some local bizarre effect that produced those interesting clouds.

I forgot to mention that you can see two concentric halos in your second photo...this in itself is quite unusual! the outer ring almost is strong enough to make a Sun dog. I have taken a screenshot and applied two quick circles to show what I mean...They are not exactly in the right place but you get the idea...


Concentric Sun rings by BA_pics, on Flickr

Again, great photo and a good challenge...you got the better of me on this one...I look forward to more when you get the chance!

BTW, how did I do on the other ones you posted? (in case you have any thoughts or notes on those conditions as well?) Will keep me honest if nothing else!
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