Post on 13-Mar-2022
National Aeronautics and Space Administration
www.nasa.gov
Contrail Identification Chart and Formation GuideContrails are clouds formed when water vapor condenses and freezes around small particles (aerosols) that exist in aircraft exhaust. Some of that water vapor comes from the air around the plane, and some is added by the exhaust of the aircraft. Clouds are the largest variable controlling Earth's atmospheric temperature and climate. Any change in global cloud cover may contribute to long-term changes in Earth's climate. Contrails, especially persistent contrails, represent a human-caused increase in the Earth's cloudiness, and are likely to be affecting climate and ultimately our natural resources. Scientists today are trying to learn more about the longevity of persistent contrails and how much they may affect the climate in the future.
�e X-axis (horizontal axis) represents the temperature and the Y-axis (vertical axis) represents
the amount of moisture in the atmosphere.
1. Hot, moist gas from plane. 2(=F Formation of contrail). As it mixes with the air,
the exhaust cools to the condensation curve. 3. Water drops freeze to ice crystals.
4. Water drops would evaporate, but ice persists. 5(=D Dissipation of contrail). Ice sublimates,
and the contrail dissipates.
Contrail Education Website: http://asd-www.larc.nasa.gov/GLOBE/ Contrail Prediction Website: http://asd-www.larc.nasa.gov/GLOBE/resources/activities
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
B
NoCloud
Cloud
A
1
3
4
2=F
5=D
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
If you crossthe curve . . . Contrail!
Set
ting
up C
ontr
ail C
ondi
tions
Gra
ph
The
Mix
ing
Pro
cess
Sta
rts
at B
and
Mo
ves
Tow
ard
A
1
4
�e shaded area shows where condensation (gas to liquid) occurs. Because it is cold where
airplanes fly, any water drops freeze into ice crystals (liquid to solid). �e hatched area
shows where ice will persist. In the white area, ice will sublimate (solid to gas). �e reverse process (gas to solid) does not occur in the
atmosphere.
NoCloud
Cloud
CondensationCurve
SublimationCurve
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
Whe
re W
ater
Cha
nges
Sta
te
2
�e cloudless atmosphere at high altitude is generallycold and dry (point A). Aircraft exhaust is hot and
moist (point B).
NoCloud
Cloud
B
ACold,dry air in upperatmosphere
Hot,moist air
fromplane
exhaust
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
Typi
cal S
tart
ing
Poi
nts,
A a
nd B
3
When point A2 is such that the straight line betweenpoints B and A2 crosses further into the condensation
area, and A2 is closer to the sublimation curve, alonger lasting, or persistent, contrail forms between
points F and D.
When point A3 is in the hatched area(moister air), theaddition of warm, moist airplane exhaust leads to apersistent, possibly spreading, contrail since the ice
particles created at point F will not sublimate atpoint A3.
�e exhaust from the airplane mixes with the air from the atmosphere, along the straight line between
points B and A1. A contrail forms at point F and persists to point D. When the straight line between
points A1 and B barely crosses into the condensation curve, a short-lived contrail is formed.
Con
trai
ls in
Moi
ster
Air
P
ersi
sten
t Spr
eadi
ng C
ontr
ails
Sho
rt-l
ived
Per
sist
ent
Per
sist
ent
Sp
read
ing
B
A1No
Cloud
Cloud
Colder, dry air in upperatmosphere A2
D
F
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
Cold, moister
air in upperatmosphere
BF
A1No
Cloud
Cloud
A3
Temperature
Moi
stur
e
Cold Hot
Dry
C
on
tra
ils i
n D
ry A
ir
Sh
ort
-Liv
ed
Co
ntr
ails
Co
ntr
ails
in
Co
lde
r A
ir
Pe
rsis
ten
t C
on
tra
ils
Hot, moist air from plane
exhaust
Hot, moist air from plane
exhaust
Hot, moist air from plane
exhaust
B
A1No
Cloud
Cloud
Cold, dry air in upperatmosphere
D
F
Temperature
Mo
istu
re
Cold
Moist
Dry
Hot
A contrail that forms and disappears as the plane movesalong. Although its length remains about constant it maybe very short, or it may span a large fraction of the sky.
Generally it is very thin.
A thin contrail that remains in the sky after the plane hasdisappeared. �ese contrails are not much wider than the
short-lived contrails and are thinner than 1 fingerheld at arm’s length.
A thick contrail that remains in the sky after the planehas disappeared. �ese are wider than 1 finger held at
arm’s length. �ese contrails can grow to resemblenatural cirrus clouds.
5
6
7
Moist