Soundings -  Page 2
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diagram
Look at this new graph
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It shows yet another type of presentation that is available on the internet 
(Uni Wyoming)
In fact, this is a Skew-T and is very like the demonstration charts seen earlier but with minor variations.
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The sounding is the midnight one on what was arguably "the day of the year" when many big flights were achieved
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Points to note: 
Very strong inversion at 850 mbs thus convection limited to about 5,000 feet
An inversion is when the temperature increases with height - more usually it decreases
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At 850 mbs the air is very dry (the left dewpoint line is well separated from the right environmental line)
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Winds are light at all levels, but near coasts, sea breezes need to be considered 
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Not shown on this Skew-T, but using information from other sources, cooler air between 850 and 800 mbs was expected to move in from the west during the day raising the depth of convection.  That was taken into account when making the forecast for 15th August
Sea Breeze rule of thumb
Deep penetration inland only likely if total depth of convection, including cumulus tops, is between 3,500 and 10,000 feet. Less or greater depth  will probably mean any sea breezes confined to very near the coast.
So with light winds and appropriate depth of convection on 15th August, sea breezes were forecast to move well inland.  See the separate tutorial on sea breezes


Adiabatic Lapse Rates
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Two final lines on this chart.
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dagram
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Straight lines (arrowed in black) run diagonally up at 45 from the bottom right to the top left.
These are the Dry Adiabatic Lapse Rate (DALR) lines.
Adiabatic means no external heat added nor taken away
from the air mass.
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A rising parcel of air cools (because it expands) at the DALR until such time as it becomes saturated.
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DALR can be taken as being about 3C per 1,000 feet.
So a thermal which leaves the surface with a temperature of 20C will have cooled to 14C by the time it has reached 2,000 feet.
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When the thermal rises far enough and cools sufficiently for condensation to occur, cloud forms.  Condensation takes place if the air continues to rise, and latent heat is given out by the condensation process.  Thus the temperature in the cloudy thermal falls off rather more slowly than it does in a dry thermal.
At low levels, this can be taken to be roughly 1C per 1,000 feet.
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These Saturated Adiabatic Lapse Rates lines (SALR) are curved and indicated by the blue arrows spacer
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NOTE : Air behaves either as being dry or saturated.  It is not a gradual process of change between one state and the other .


Now we should know what all the various lines mean.
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So how do we use them?
 
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Let's recap.
diagram
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The red ELR line starts from about the 1000 mb level.
Now using those red temperature lines that go diagonally upwards to the right, it can be seen that the ELR reaches the surface at about 15C
Just to the right of this point, there is a black DALR  lines (they go diagonally up to the left) which intercepts the 1000 mb surface at about 16C
So if the surface temperature reaches 16C, then a bubble of air (being warmer than the environment) will rise as a thermal and follow that DALR line (temperature decreasing by 3C every 1,000 feet as it does so).
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Eventually, that thermal reaches the red ELR line at about 850 mbs (5,000 feet) and if it were somehow able to rise above that point, would in fact be cooler than the environment.  This cannot happen, (ignoring orographic effects) so where this particular DALR line from a surface temperature of 17C reaches the environmental line, the air stops rising, and this marks the top of the thermal.


 
Possible limitations of this simplistic interpretation are given below.
diagram
diagram
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These are rather "coarse" forecast soundings and don't always model the profiles in great detail. 
Above left is an enlargement of part of the larger diagram.  It might simply show that at 15C, there is a dry adiabatic to around 850 mbs
But it might hide an early morning inversion as shown in the middle picture.
The right hand diagram shows that 15C is needed as trigger to "break the inversion".
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Some of the more detailed soundings such as those from Dr.Jack and Meteoblue deal with these lower levels rather better, but still have their limitations.
In this illustration, formation of cumulus has deliberately been ignored as a simplification.  That will be considered later.
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