Contrails

David Duda

Hampton University/NASA LaRC

Outline

• Introduction – What are contrails?

• Making a cloud  (how contrails form)

• Why do we study contrails?

• S’COOL and contrails

• Contrail cousins

Introduction

• Contrails are 

CLOUDS

that form in the wake of
aircraft.

• Contrail is a shortened

name for condensation
trails.

• Also known as vapor

trails, jet trails,
“chemtrails”

Contrails have been around for a

long time!

• They were first

described in the
scientific literature in
1919.

• During WWII,

contrails sometimes
littered the skies
during aerial combat.

Making A Cloud

Clouds form when water vapor in the air
condenses into visible water droplets or ice
crystals.

Condensation can occur in two ways:

1. Increase the water content in the air.
2. Cool the air to reach the dew point.

Making A Cloud (Part 2)

Nearly all contrails form by the 

mixing

 of

the colder, drier atmosphere with the
warmer, wetter jet exhaust 

(mixing cloud).

Mixing clouds

• Mixing clouds form

because the ability of air
to ‘hold’ water vapor
increases rapidly with
temperature.

• Like contrails, the cloud

that forms on your breath
during a cold day is a
mixing cloud.

Nearly all contrails are mixing clouds

Most contrails that you see in the sky form
at high altitudes (above 26,000 ft) and at
very cold temperatures (less than -40

°

F).

Why Do We Study Contrails?

Contrails cause detection and visibility
problems for military aircraft.

When the upper
atmosphere is
moist enough,
the contrails
continue to grow.

Under these
conditions, the
contrails become

persistent.

We currently
estimate that
contrails add
an additional
0.5 to 5
percent
warming to the
greenhouse gas
effect.

Persistent
contrails
occasionally
cover large
areas.

 Like cirrus
clouds,
contrails
likely
contribute to
global
warming.

Air traffic and persistent contrail coverage will
continue to increase.

By 2050, the warming due to contrails may be 2.5
to 25 percent of the current greenhouse gas warming.

S’COOL and Contrails

Our estimates
of the
climatic
effects of
persistent
contrails are
still
uncertain.

We still have
trouble
estimating
contrail
coverage.

Most contrails are still smaller than the
resolution of most satellites.

Using inventories of commercial aircraft flight data
and satellite data, we are learning more about the
growth and coverage of contrails under different
atmospheric conditions.  Surface observations from
S’COOL would improve our studies.

Contrail Cousins

Unconventional Contrails

(clouds, but not mixing clouds)

Contrails (not!)

This B-52 is producing smoke!

Skywriting planes also
produce smoke.  Often
the smoke is from a type
of cooking oil!

Inverse contrails (distrails)

Aircraft sometimes make holes in clouds!