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  Skew-T

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Topic:   Skew-T

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Thermit
Tech


Houston, TX
2733 posts, Jul 2000

posted 09-19-2000 08:42 PM     Click Here to See the Profile for Thermit   Visit Thermit's Homepage!   Edit/Delete Message   Reply w/Quote

This is the GOES Satellite Sounding Skew-T for Houston 9/19/2000.

It comes from the NOAA NESDIS page.

quote:

The GOES atmospheric temperature and moisture soundings are plotted on a 'SkewT-LogP' Chart. The chart's name reflects the parameters associated with the vertical and horizontal axes. Atmospheric pressure (in millibars) is plotted along the vertical axis using a logarithmic scale, which represents the variation of atmospheric pressure with height observed in the earth's atmosphere. Atmospheric temperature is increasing from left to right along the horizontal axis. The lines of constant temperature are 'skewed' from the lower left to the upper right of the chart. The GOES soundings use an initial estimate of the vertical temperature and moisture profile obtained for the AVN numerical forecast model .... The infrared radiation measured by the GOES sounder, for 18 different frequencies, is used to adjust the initial 'first guess' AVN profiles. Information of the magnitude and direction of these adjustments is useful for weather analysis and forecasting activities. For this reason, both the AVN 'first guess' sounding and the GOES satellite'adjusted' sounding. The darker red, solid line is the GOES atmospheric temperature as it varies with height, and the brighter red, solid line the AVN forecast temperature profile. The darker blue, dashed line is the GOES dewpoint temperature, and the lighter blue, dashed line the AVN forecast dewpoint temperature profile. The green line represents the temperature profile of a lifted parcel of low level air, based on the GOES data. The shaded in purple region denotes the area where that lifted parcel would be positively buoyant. In contrast, the area shaded in light blue signifies the area where the lifted parcel would be negatively buoyant. The thin black lines and numerical values along the right side of the chart represent 'gradient' wind estimates derived from the GOES sounding fields. Several stability, moisture and meteorological parameters derived from the GOES and AVN soundings are listed on the right-hand portion of the chart (described in detail below) Further to the right, the actual numerical data from the GOES derived temperature and moisture profiles is shown. Finally, since the GOES Soundings are not necessarily centered immediately at a given station location, directly underneath the position of the GOES Sounding, with respect to the station, is listed.

Here is more information on Skew-T interpretation.

I'd like to discuss how to read this chart and fully comprehend the factors that are relevant to contrail persistance.


To start off, if you follow the dark red line (temperature) up until it hits the 'skewd' -30C line it appears to be about 320 millibars, considering the logarithmic scale. Based on Lake Charles text soundings when the presure lowers to 300 millibars the altitude is around 9630-9640 meters. Convert to feet. For an altitude of 31594 feet.

In summary, air cools to -30C reaching ~32000 feet. Generally cold enough for contrail persistance.

But, is there a more accurate way to convert the millibars to altitude?

Next comes the moisture factor...

quote:

The dark blue dashed line represents the GOES dewpoint profile as a function of height. The dewpoint is the temperature at which condensation would occur as the air is cooled. Warmer dewpoint temperatures correspond to moister atmospheric conditions, and cooler dewpoints to dryer atmospheric conditions.

But how is this interpreted with respect to contrail persistance?

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theseeker
One moon circles

Damnit...I'm a doctor jim
3403 posts, Jul 2000

posted 09-24-2000 02:04 AM     Click Here to See the Profile for theseeker   Visit theseeker's Homepage!   Edit/Delete Message   Reply w/Quote
Sorry thermit ,I can tell you 'went to town' on this one, been procrastinating for this involves some work...

This will do nicely for RH and dewpoint :

Relative humidity is not an absolute measure of atmospheric water vapor content. It depends upon the temperature and shape of the surface. Other measures are mixing ratio, specific humidity, or dew point. Mixing ratio is the mass of water vapor per unit mass of dry air. Specific humidity is the mass of water vapor per unit mass of moist air. Dew point is the temperature to which moist air must be cooled, with pressure and mixing ratio held constant, in order for this air parcel to become "saturated." To get a "feel" for the difference between relative humidity and dew point, note that on July 21, 2000, Biloxi, Mississippi, reported a temperature of 97 F, a dew point of 84 F, but a relative humidity of 67%. The relative humidity doesn't sound terribly bad, does it? However, this is misleading. The temperature and dew point combined to give a heat index of 126 F!

I have seen it(adds) moist and cold enough at 28k to produce trails .....unfortunately if there are no cumulus around it is hard to judge cloud height , some trails form expand and fall , and look like their on top of you but really are way up there.

Cloud types :

Water droplet cloud :

Molocules of water floating around in the air as a vapor bounce around occasionally hitting each other . The warmer the air is the more they move , some stick, most don't = blue skies.

Put in more molocules and reduce the temp to increase RH and you get more and more collisions.If the RH is 100% or more with respect to liquid water, then more will stick. If there is aerosol, dust, or soot or something these molocules will stick together easier and more rapidly and form a water droplet (cloud).

Ice cloud :

Solid water is the state in which the molocules are required to have a particular arrangemnet typically based on some hexagonal structure.Just like the vapor (water cloud) needed some nucleus to from a droplet ,ice needs some nucleus that has a similar structure to the ice crystaline pattern.If one of these ice nuclei touches the droplet, it will immediately freeze.If the temp is less than -40 ,the movement in the water molocules is so small that as soon as a few of the molocules in the water droplet randomly arrange in the crystaline pattern the bonds between the molocules are stronger than the movment and the ice develops all by itself from the droplet.

As configured a jet flying through such conditions would inject lots of water vapor mixing with the air moistening and warming the air, it rises slightly and cools greatly increasing the RH. So the planes exhaust makes cloud formation possible in otherwise clear air.....

sleepy and out of beer.....

********************************************

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theseeker
One moon circles

Damnit...I'm a doctor jim
3403 posts, Jul 2000

posted 09-24-2000 11:09 PM     Click Here to See the Profile for theseeker   Visit theseeker's Homepage!   Edit/Delete Message   Reply w/Quote
Did that overload your circuts thermit ?

Look at this:
http://virga.sfsu.edu/gif/jetstream_pac_init_00.gif

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Thermit
Tech


Houston, TX
2733 posts, Jul 2000

posted 09-25-2000 10:20 AM     Click Here to See the Profile for Thermit   Visit Thermit's Homepage!   Edit/Delete Message   Reply w/Quote
Thanks Seeker,
No didn't overload, but I'm still not sure how to interpret the moisture information in the Chart to see if contrail persistence is expected or not. Will have to study this more...

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SuzieB
New Member


4 posts, Sep 2000

posted 09-25-2000 01:57 PM     Click Here to See the Profile for SuzieB     Edit/Delete Message   Reply w/Quote
Question: I admit that I'm going to show my ignorance here, but is there really a connection between weather and -trails? This was fascinating reading. I believe I'm going to start recording weather conditions too when I'm observing -trails. I've got a blinding headache right now from the low pressure system dragging a cold front through Alabama. See ya'll tomorrow. Ive got a date with headache medicine right now.

------------------

SuzieB

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Thermit
Tech


Houston, TX
2733 posts, Jul 2000

posted 09-25-2000 03:03 PM     Click Here to See the Profile for Thermit   Visit Thermit's Homepage!   Edit/Delete Message   Reply w/Quote
SuzieB,

Contrails are definately associated with weather. They require certain parameters to be persistant. Therefore, if you can show a pattern of Trails persisting outside of those parameters, then it indicates that there are Trails that aren't limited by the typical atmospheric requirements. This would be evidence of Chemtrails.

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Thermit
Tech


Houston, TX
2733 posts, Jul 2000

posted 09-25-2000 05:47 PM     Click Here to See the Profile for Thermit   Visit Thermit's Homepage!   Edit/Delete Message   Reply w/Quote
Here is the Skew-T for 9/25, another chart I'm interested in...


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Thermit
Tech


Houston, TX
2733 posts, Jul 2000

posted 10-04-2000 12:08 AM     Click Here to See the Profile for Thermit   Visit Thermit's Homepage!   Edit/Delete Message   Reply w/Quote
From the Climate Change Research Center

quote:

FORECASTING CONDENSATION TRAILS (CONTRAILS)

Method

- If forecasting clear-scattered conditions at cirrus levels, draw in 40 % RH line.

- If forecasting cloud deck in vicinity of tropopause, or broken-overcast clouds at cirrus levels, draw in 70 % RH line.

- Using temperature profile, forecast contrails to the left of the 40 % or 70 % RH line, depending on cloud forecast.

- Label contrail area boundaries in millibars.




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