 |
 |
Contrail Motion
Name: Craig
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Last weekend was a beautiful and clear sunny day. I was
facing south, and observed a jet contrail flying from the south to
the north. What struck me was how there was NO upper atmosphere wind
to disturb the trail and it completed a full line across the sky
(south to north). But, I noticed that over time, the line was moving
east (relative to us the observers). Showing off to my kids, I
explained that we were witnessing the rotation of the earth! But, as
I pondered my answer it was critically flawed: the jet's contrail
was moving from the west to the east -- OPPOSITE of what would be
expected if the earth was turning underneath the fixed atmosphere.
PLUS, the atmosphere itself must be rotating along with the earth. I
do not see how it could be upper atmosphere wind, because the
contrail stayed intact the entire length of the sky for over 30
minutes. Other flights came and they created a series of these
"meridians" across the sky. WHAT in the world is going on to produce
this? It is like the upper atmosphere was rotating FASTER than the
earth in order for the contrail to move easterly. Thank you so much
for giving this your thinking.
Replies:
My guess is that the contrails were being pushed by a gentle, non-turbulent
wind AT THE HEIGHT of the jet planes (25,000 to 35,000 feet). Those winds can
be very different from the wind speed and direction at ground level. At that
altitude the air could very possibly be moving in the same direction as the
Earth's rotation, but faster. If you measure the angle change of the contrail
vs. time and using a little trigonometry you might be able to estimate the speed
of the air in the upper atmosphere.
Vince Calder
Craig,
The contrails were moving from west to east because
of westerly winds at the altitude where the planes
were flying. Even at that altitude, the atmosphere
is well tied to the Earth's surface and does not slip
as the Earth turns. It is very likely that
the planes were flying in the lower part of the stratosphere,
where the air temperature increases with height;
this atmospheric condition leads to little turbulence,
resulting in the contrails remaining straight for a long
period of time. I have observed the same thing many times.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
Click here to return to the Weather Archives
| |
Update: June 2012
|
|
