Ehh, read the link I included in my previous post. More specificly the part about the "hydrologic cycle".
A cloud is a visible aggregate of tiny water droplets and/or ice crystals suspended in the atmosphere and can exist in a variety of shapes and
sizes.
Condensation generally occurs in the atmosphere when warm air rises, cools and looses its capacity to hold water vapor. As a result, excess
water vapor condenses to form cloud droplets. The upward motions that generate clouds can be produced by convection in unstable air, convergence
associated with cyclones, lifting of air by fronts and lifting over elevated topography such as mountains.
As you can see... clouds are formed by water (in one of it's 3 states) in the upper atmosphere. With that in mind...
Contrails form through the injection of water vapor into the atmosphere by exhaust fumes from a jet engine. If the surrounding air is cold
enough, a state of saturation is attained and ice crystals develop, producing a contrail.
As you can now also see... contrails are formed by water vapor in the upper atmosphere as well. Clouds, and Contrails
are the same, and
are comparable to one another because
both are a byproduct of water in the atmosphere. Contrails are most compared to "cirrus
clouds".
Cirrus Clouds: The most common form of high-level clouds are thin and often wispy cirrus clouds. Typically found at heights greater than 20,000
feet (6,000 meters), cirrus clouds are composed of ice crystals that originate from the freezing of supercooled water droplets. Cirrus generally occur
in fair weather and point in the direction of air movement at their elevation.
Source:
ww2010.atmos.uiuc.edu...(Gh)/wwhlpr/cirrus.rxml?hret=/guides/mtr/cld/cldtyp/oth/cntrl.rxml
As you can also see... cirrus clouds
point in the direction of air movement at their elevation; which once again explanes the sometimes "sheet
cloud" look of a contrail.
My only real concern about contrails is what Thomas Crowne brought up earlier... fumes from jet fuel released into the air (if its true that jet
engines do release said fumes). I'm certain the fumes don't make it down to our level, but even so, that
has to have a detrimental effect on
the environment. That has nothing to do with gov't plots to poison you though... merely just loose regulations by the DOT when it comes to plane
emissions. Surely
they're not out to get you too...
[edited to fix typo]
[edit on 6/15/05 by microcosm]
