Tuesday, October 12, 2010

Contrails!

Here is a marvelous picture from the NASA MODIS satellite showing conditions this afternoon over the Northwest (you can see the Columbia River directly below). There are some high cirrus and cirrostratus, but what caught my eye was the extraordinary show of jet contrails (click on the image for a better view).

Contrails occur because composition in jet engines produces water vapor and small particles. The water vapor is injected into the very cold upper atmosphere, where the vapor rapidly condenses into small water droplets or ice crystals. Particles produced by combustion can help this condensation process.

Contrails are promoted by an atmosphere close to saturation--so that is why contrails are particularly evident on days with cirrus or cirrostratus around (indicating upward motion and air at or close to saturation). Below is this afternoon radiosonde sounding (balloon-launched weather instruments) at Salem, Oregon, temperature is red and dewpoint is dashed blue. Above 500 mb (roughly 18,000 ft), the temperature and dewpoint are relatively close, indicating an atmosphere close to saturation.


Several times of year I get emails from people claiming that contrails are really chemtrails, which have been injected into the atmosphere by some dark government conspiracy. Obviously complete nonsense, and my attempts to point out the weaknesses of chemtrail theories rarely convince them. It is similar to those folks who feel that Elvis is still alive--you can't convince them otherwise.

11 comments:

Brad said...

Wait! You mean Elvis is dead???

Lisa said...

I was wondering why there were so many pretty, fluffy contrails yesterday. Thanks for the explanation. Chemtrails: snort. Trying to disabuse conspiracy theorists is useless, ike pouring water over a rock: it looks wet, but isn't absorbing anything.

Blake said...

I found some of the images from yesterday fascinating.

In the afternoon, there were four distinct 'hooks' on the left side of the 1km vis image. It's not often you see such an obvious pattern like this.

I assume they are international flights that turn and head towards SeaTac. If anyone has other theories, I'd love to hear them!

Here is the sequence.

One: http://www.atmos.washington.edu/images/vis1km/201010122130.gif

Two: http://www.atmos.washington.edu/images/vis1km/201010122200.gif

Three:
http://www.atmos.washington.edu/images/vis1km/201010122215.gif

Four: http://www.atmos.washington.edu/images/vis1km/201010122245.gif

bob said...

Cliff,
'A suggestion and a question....
I would like to see your ideas on the "9/11 Experiment" were we had zero contrails in the atmosphere for three days. Also, I would appreciate your tips on acquiring MODIS imagery. I have read their FAQs, tried different browsers and settings, and still see only white boxes where thumbnails go. Thanks for covering our daily upper atmosphere modification due to jet air travel!

Betsy said...

Wait, Elvis ISN'T alive? First I've heard.

trav said...

So... are you saying Elvis isn't alive? :-)

geri said...

elvis is dead?

Sail on MIke said...

What? Elvis isn't still alive?

Blake said...

Looks like the comment editor truncated the image names. Here they are again in case anyone is interested.

1. 201010122130.gif
2. 201010122200.gif
3. 201010122215.gif
4. 201010122245.gif

Patrick said...

Blake - I'm actually leaning towards a 787 or 747-800 test flight doing counterclockwise circles over the Pacific. In the third and fourth pictures you can see faint lines on the north and east sides. The contrailing is stronger on the SW side so it like multiple hooks instead of an eastward blowing spiral.

Dan B said...

Good call Patrick. Most likely this flight: http://flightaware.com/live/flight/BOE3/history/20101012/1930Z/KBFI/KBFI

Neat how the aircraft flys the same pattern over the earth while the airmass flows eastward.