Max has finally come forward with his "evidence" that RH levels at cruising altitude are too low to form contrails: Thus;
https://www.facebook.com/photo.php?...t=a.10151300810995396.524896.685100395&type=1
As expected Max has no idea about what Relative Humidity actually is.
The definition:
Relative humidity is the ratio of the
partial pressure of water vapor in an air-water mixture to the saturated
vapor pressure of water at a
prescribed temperature.
The key words there are "prescribed temperature".
For those unfamiliar with RH, air can hold water as invisible water vapor. The warmer the temperature, the more water vapor can be held in any given parcel of air. The amount of water vapor in the air, compared to the maximum it can theoretically hold is called RH and is expressed as a percentage.
At 100% RH the air is saturated with water vapor, and condensation into visible water begins. (this also explains the gap in contrails behind aircraft engines, as hot exhaust air rapidly cools, the water vapor contains reaches saturation levels and condenses to form the contrail.)
Max, has failed to take into account that cabin air is at least 70C warmer than the outside air, so the same air coming from the outside, with say 50% RH, will have a much lower RH inside the cabin as soon as it warms up. That is what the R in stands for. The same cubic metre of air could have an RH of 60% outside the aircraft; then have an RH of 5% inside and after it is expelled and rapidly drops 70C, will go back to its former 60% plus whatever moisture it picked up from the people in the cabin. (this also explains why in some photos, small contrails can be seen from air conditioning outflow valves positioned at the back of aircraft.)
Some people think that the prescribed temperature is the temp of the air. ( I used to). The RH, as seen from the definition above is actually based on the temperature of the water itself, which undoubtedly has implications for contrail formation.
In the link provided, an old newspaper article is featured. This is an example of poor research as Max has homed in on a quote that says that contrails only form in a narrow band. (most days this is probably true). Max is trying to make an issue of the amount of contrails seen above his house in France, which is at the crossroads of some of the busiest air routes in Europe. Reading the rest of the article confirms everything about contrails, however Max ignores that bit.
http://news.google.com/newspapers?nid=1243&dat=19550422&id=eK9YAAAAIBAJ&sjid=WfcDAAAAIBAJ&pg=2904,5247238