reply to post by PlanetXisHERE
Do contrails sometimes persist and spread out?
Yes, see the Encyclopædia Britannica article on vapour trails (contrails):
Contrail, streamer of cloud sometimes observed behind an airplane flying in clear, cold, humid air. It forms upon condensation of the water vapour
produced by the combustion of fuel in the airplane engines. When the ambient relative humidity is high, the resulting ice-crystal plume may last for
several hours. The trail may be distorted by the winds, and sometimes it spreads outwards to form a layer of cirrus cloud.
vapour trail. (2007). In Encyclopædia Britannica.Retrieved May 4, 2007,from Encyclopædia Britannica Online:
(The above quote is from the current EB. However, a Google books search dates the inclusion on the EB back to 1993)
Are spreading contrails a relatively new thing?
No, it has been exactly the same for decades, the only change has been the size of jet engines (producing bigger contrails), engine technology
(burning fuel more efficiently in high bypass jet engines creates cooler exhaust which is more likely to condense before it mixes with the surrounding
air) and the amount of air traffic (producing more contrails). Spreading contrails have been mentioned consistently through the history of aviation,
including in the popular press. Like Sports Illustrated , Nov 6th 1989:
Now, late in the afternoon, the hatchery explored and the fishing over for the day, Crooks points to the sky. Blue all day, it has now turned hazy.
“Contrails,” he says. “The haze is caused by aircraft contrails that have gotten spread out till they cover the sky. This is a major air route
from the East Coast to the West.”
For scientific discussion, see, for example, all these articles on contrails. In particular the one titled “Airborne Observations of Contrail
Effects on the Thermal Radiation Budget“, from 1970:
The spreading of jet contrails into extensive cirrus sheets is a familiar sight. Often, when persistent contrails exist from 25,000 to 40,000 ft,
several long contrails increase in number and gradually merge into an almost solid interlaced sheet.
Contrail development and spreading begins in the morning hours with the start of heavy jet traffic and may extend from horizon to horizon as the air
traffic peaks. Fig. 1 is a typical example of midmorning contrails that occured on 17 December 1969 northwest of Boulder. By midafternoon, sky
conditions had developed into those shown in Fig. 2 an almost solid contrail sheet reported to average 500 m in depth.
Source - contrailscience.com...
If the humidity is high (greater than that needed for ice condensation to occur), the contrail will be persistent. Newly formed
ice particles will continue to grow in size by taking water from
the surrounding atmosphere. The resulting line-shaped contrail
extends for large distances behind an aircraft (See Figures 2 and
3). Persistent contrails can last for hours while growing to several kilometers in width and 200 to 400 meters in height.
Contrails spread because of air turbulence created by the passage of aircraft, differences in wind speed along the flight track,
and possibly through effects of solar heating.
Source - www.faa.gov...