Contrail Critical Temperature Calculator and Contrail Diagnosis
This calculator will calculate the Contrail Critical Temperature for Flight Levels 360 and 380.
It will indicate if, on the basis of the sounding data acquired, contrails will be formed, and what their characteristics will be; short lived or persistent.
The sounding data is obtained from a database at University of Wyoming. These good people conveniently
collect upperair data from all over the world.
Instructions
Select the station and date (in UTC) and Submit Inquiry (or use data for any other station obtained from the University of Wyoming site).
See notes below about UTC or if you are having trouble on the first day of a month.
A new browser window will be launched containing a listing of the sounding.
In that browser, Right-click, Select All, Right-click, Copy.
Back here, Click in the TextArea, Right-click, Paste.
Click on the "Calculate Contrail Critical Temperature ..." button.
TextArea for Upperair Data
Contrail Analysis
This diagnosis was made using the following criteria: (on the basis of the sounding data)
If the environment temperature is below the Contrail Critical Temperature (CCT), contrails will be formed; otherwise, not.
If the air is supersaturated with respect to ice, any contrails that are formed will be persistent.
It's as simple as that.
"Stuve" Atmospheric Thermodynamic Diagram
... with the Critical Temperature trace for the formation of contrails added between 500hPa and 100hPa.
(This only works for the stations in the options of the form above... 3 stations in NZ and 3 in Australia.)
click here to load the chart
What does this mean?
The "Stuve" Atmospheric Thermodynamic Diagram is a graph of the ambient air temperature (right) and the
dew point temperature plotted against a function of the air pressure in the atmosphere, which in this graph more or less corresponds to height.
The blue line between 500 and 100 hPa traces the Critical Temperature for the formation of contrails.
If the ambient air temperature (the black line one on the right)
is colder than this temperature at any level (i.e., to the left of the Critical Temperature), then contrails will be formed at that level.
Further, if the relative humidity of air in the contrail region is high enough that the air is supersaturated with respect to ice,
then the contrails will be persistent.
It's as simple as that. It is these two ideas that the simplistic official explanations of the "chemtrails" are ineffectively trying to convey.
Notes:
All meteorological data is stored in Univeral Time Coordinates (UTC).
New Zealand is 12 (or 13) hours ahead of UTC, so midday local time is 00:00 hours UTC on the same date.
For New Zealand stations, the Wyoming site stores the "midday" (0000 UTC) data against 2100 UTC on the previous day, and "midnight" (1200 UTC) data against 0900 UTC.
For midday on 4 Jan, you need to select From 04/12Z and To 05/00Z.
This may present a bit of a problem when you want data for 2008 Jan 01/00Z because there is only one specification for month.
This will work: Select Year=2007, Month=Dec, From=31/12Z, To=01/00Z.
The correct settings to get the latest data are preselected, though you may need to make a small adjustment to the selection.
If you happen to get more than one sounding back from University of Wyoming, only the first one will be processed.
To process the second one, just delete the first one from the TextArea, making sure that the station name is on the first line.
The present generation of radiosonde sensing equipment has trouble measuring RH at low temperatures, and this results in what is known as the "dry bias".
To take into account that there may be more moisture present that is reported in this data, the contrail diagnosis is shown as
'Contrails (? persistent)' if 5% more RH would result in the air being supersaturated with respect to ice.
If a chart from the calendar pages is compared with one of these from Paraparaumu at the same time, there will be a difference in the CCT trace
when the RH is high. This is because the calendar charts have a correction applied for the "dry bias" and these do not.
Future developments
Depending on feedback from users of this utility, I may consider implementing these or other suggestions.
User chooses the flight levels, and more of them
Find and draw the flight levels of the lower and upper boundaries of the contrail layer
Credits
The calculations made by this utility are based on the work of Mark L. Schrader (Air Weather Service, Scott Air Force Base, Illinois)
in his paper Calculations of Aircraft Contrail Formation Critical Temperatures.
Created: 04-Jan-2008 21:00 NZDT
Last modified: 09-Feb-2008 22:58:52 NZDT
