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Temperature traces James Cooper

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Temperature traces James Cooper Powered By Docstoc
					Temperature trace
    F 160
www.jamescooper.com.au
       Gliding
       Articles
The temperature trace looks
       complicated.
Let’s look at what all the lines are.
                              The pink lines are
                              lines of constant
                              temperature.




                                0 Degrees
Lines of constant pressure
                         As a guide
                         100 mb
                         per 3000 ft
   The graph does not use °C
• The graph uses mill bars
• On this basis we can see the pressure at
  sea level.
Why do constant temperature lines
         not go vertical.
• Because this reduces the amount of paper
  that the graph takes up.
• The next diagram will explain this.
Dry Adiabat




This is the rate
that a bubble of
air cools if
raised through
the atmosphere.
    Air cools at 3° -per 1000 ft
• If the dry lines of constant temperature
  were vertical the dry adiabat lines would
  be very laid back and consume a lot of
  paper.
Saturated Adiabat
                    Saturated
                    Adiabat.



                     The rate of
                     cooling for
                     a bubble of
                     saturated
                     air.
                     About
                     1.1°C per
                     1000 ft
Mixing Lines   These lines
               indicate how
               the moisture
               in a bubble of
               air changes
               as it mixes
               with the
               surrounding
               air as it rises
Let’s look at some traces
 There are two red lines
What can we see from
 and generally 2 blue
this trace.
 lines.
The red lines are the last
trace.
The right line indicates
the air temperature with
height.
The left line indicates
the due point.
The height that
the balloon has
been released

The air is moist
were the due point
comes close to the
temperature trace.
Indicating there
may be upper level
cloud

We are interested
in the lower levels
There are 3 Grey
lines drawn by the
met office that help
us
The lower right line
shows what would
happen to a bubble
of air that is heated
to the maximum
temp for the day.
25°C in this case.

All things being
normal it would rise
till it met the
inversion at 800mb
(6000ft)
On this day the grey
line on the left,
running parallel with
the mixing lines,
meets the grey line on
the right running
parallel with the dry
adiabat. They meet to
the right of the
temperature trace.

At the point these
meet the humidity
will reach 100% and
thus cloud will form.
Now we have a cloud the
cooling rate follows the
saturated adiabat.
Until it reaches the
inversion.

 You can see the
 thickness of the cloud
 about 2000ft
 The top of the thermal
 6000ft

  If the temperature
  rose you could
  see that the cloud
  base will rise.
  But the cloud will
  get thinner.
Let’s look at another day
You can see the morning
inversion

Thermals will top 3000ft
until the temperature gets
to about 30°
With 38 degrees
thermals will go to
about 10,000 ft but
because the mixing
lines meet the dry
adiabat to the left of
the temperature there
will not be cloud.

What if the
temperature were to
be a few degrees
hotter.
We have assumed
that the
temperatures we
take are from the
point where the
balloon is released
32° in this case

If we were at a
higher altitude say
700ft

We would only need
to get a temperature
of 28° on the
assumption that the
inversion is no
different from the
trace inland.
What happens
here?
                   Wind
• I have not shown on this chart the wind.
• This is shown by bars up the side of the
  chart indicating wind direction and strength
  with height they are quite self explanatory
    So what can we see from the
              chart?
• The shape of the inversion and thus the amount
  of heating requited for it to be broken.
• The depth of the inversion, can we go cross
  country before it is broken.
• The temperature that the inversion will be
  broken.
• The height that the thermals will reach
• If cloud will form
• The base and depth of cloud if it were to form
For an article you can download
• www.jamescooper.com.au
• Go to the gliding links and articles
         To get the temp trace
•   www.bom.gov.au
•   Click Aviation Users
•   Sport Aviation
•   Vertical temperature and wind profiles
•   User name bomw0007
•   Password aviation
•   Click on the area on the map

				
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posted:11/13/2011
language:English
pages:26