Relative humidity difference between persistent and non-persistent contrails

[Lisa P]

If I read your info correctly, the flight in question was HX16 from Gold Coast to Cairns (Airbus A330-343) that passed over Noosa Heads at 40,000 ft. This is higher than 200 hPa, so temperature could be even lower than -53°C. Perhaps, it was just cold enough for the formation of a short contrail even in dry ambient air. In a more humid air, the contrail would last longer and be longer as well. Other conditions being equal, for RHi below 100%, there would be a correlations between relative humidity and the contrail length/duration. Non-persistent contrails can be quite long. A one minute contrail will extend for nine miles behind the plane that flies with the speed of one mile in about seven seconds.

Could you recall how long was the non-persistent contrail that you saw?

Going by my memory the contrail was about 4 or so plane lengths maybe longer. My attention to detail and memory recall is pretty bad probably because my head is filled with daydreams.
To my surprise (not as rare as I imagined) I had 2 more non-persistent contrails today which I took video of on my old phone and wrote the flight down straight away. No time yet to upload them.

This is where I got the weather info and I was aware the reading was 120km or more away and almost 2 hours out.
This is where I got the 12200 feet is 200hPa from, first I have heard of hPa being used for height above ground.
http://weather.uwyo.edu/cgi-bin/sounding?region=pac&TYPE=TEXT:LIST&YEAR=2016&MONTH=01&FROM=0900&TO=0900&STNM=94578

Would this site be better to use it seems more difficult to use/understand
http://earth.nullschool.net/#2016/0...aphic=-207.53,-26.97,3000/loc=153.093,-26.589

p.s. HX16 was the flight I thought would have been the one as I couldn't track it immediately.

 

[Trailspotter]

Going by my memory the contrail was about 4 or so plane lengths maybe longer. My attention to detail and memory recall is pretty bad probably because my head is filled with daydreams.

Yes, I thought the trail would be rather short at this low humidity. I guess that at the altitudes above 40,000 ft a very low temperature (below -50°C) alone is sufficient for the contrail formation and that all commercial planes flying at these altitudes would make a contrail. I do not know this for sure, but this hypothesis can be readily tested.

This is where I got the weather info and I was aware the reading was 120km or more away and almost 2 hours out.
This is where I got the 12200 feet metres is 200hPa from, first I have heard of hPa being used for height above ground.
http://weather.uwyo.edu/cgi-bin/sounding?region=pac&TYPE=TEXT:LIST&YEAR=2016&MONTH=01&FROM=0900&TO=0900&STNM=94578

I've looked for the relationship between the altitude and atmospheric pressure for average atmosphere, but, I guess, in Summer and closer to the Equator, the actual value of pressure will be greater than average for the same altitude.

Would this site be better to use it seems more difficult to use/understand
http://earth.nullschool.net/#2016/0...aphic=-207.53,-26.97,3000/loc=153.093,-26.589

I always use this site to check the forecasted values of RH and wind speed and direction at contrail altitudes (250 hPa). I did it for your example as well to see whether there was an agreement with the sounding data.