Contrail Grids are not Chemtrail Grids

One very popular photo amongst the “chemtrail” theorists is this one from NASA:

This enhanced infrared image from NASA's Terra satellite shows a widespread outbreak of contrails over the southeastern United States during the morning of January 29, 2004. Satellite data are critical for studying the effects of contrails. The crisscrossing white lines are contrails that form from planes flying in different directions at different altitudes. Each contrail spreads and moves with the wind. Contrails often form over large areas during winter and spring. CREDIT: NASA

The image is quite striking, showing a very large number of contrails over an area five hundred miles wide. It’s an infrared image which has been enhanced specifically to bring out the contrails. This image has been used by NASA a few times:

http://www.nasa.gov/centers/langley/news/releases/2004/04-140.html

http://earthobservatory.nasa.gov/IOTD/view.php?id=4435

http://mynasadata.larc.nasa.gov/preview_lesson.php?&passid=83

It’s actually a small part of a much larger image. It was cropped and enhanced to just show the areas of contrail activity. Here’s the full image:

The full infrared image

You can already start to see that the contrails are confined to a band of cloud, they stop abruptly where the clouds also stop. It’s a bit less dramatic in the original infra-red image. You get an even better view of the overall situation in the true-color satellite photo:

True Color Satellite Image. Note these are all from the same photo.

Looks a lot less dramatic now. But still it’s an unusually large amount of persistent contrails. Something you only get with some rather specific weather conditions. Of course you get conditions like this every day, somewhere in the US. It’s just unusual to have such a wide area.

The above image is available at full 250m/pixel resolution. It’s a 17MB jpg file, here. Quite a spectacular image, with some dramatic “grids” when you zoom in.

Full resolution image of contrails over Florida. Look at the direction they are streaking in to see the wind direction

We can tell which way wind is blowing for a particular cloud by seeing what streaks it leaves behind. This is particularly true for ice clouds – as the older crystals grow large enough they precipitate out and sink to air that is generally slower moving (wind speeds generally increase at you get higher, and decrease as you get lower). This is also what produces the distinctive Cirrus Uncinus clouds, which are basically the same thing, except from a smaller individual cloud, not a long thin cloud.

From the 1963 book "A Colour Guide to Clouds", this diagram shows how decreasing wind speeds cause precipitation from an ice cloud to spread out as it falls.

We can see this pattern of wind pretty consistently when we look at the weather aloft for Jacksonville Florida. This is from Jan 30th 2011, so at the same time of year.

Winds aloft over Florida. This shows that contrails will be blown to the east at 100 mph, and as they precipitate ice it will be spread over the sky.

If you look at the contrails just to the upper left of the center, you can see the streaks point more or less a bit south of west. So we’ve got an westerly wind blowing. The contrails are moving, probably pretty fast (over 100 mph) towards the East, and out into the Atlantic. We can see this even clearer if we enhance the contrast on those contrails over the ocean:

You can see how far the contrails have moved. Probably twice as far as the length of the tail they leave.

The lake in the bottom left is Lake George in Florida. It’s about ten miles long. We can see that some of the older contrail tails are around 30 miles long, and that the contrails to the East have longer tails. All of this suggests that the contrails were formed a long way from where they ended up, possibly more than 100 miles away.  If a contrail were to persist today for two hours, then with the 122 mph winds at 34,000 feet, it would move 244 miles away from where the plane originally flew.

With all this information is very easy to see how the grid patterns form. Planes flying either over Florida to other destination, or flying to and from the cites of Southern Florida, will leave trails in this large mass of moist cold air. These trails will successively be blown to the east at 122mph, leaving the long smears of clouds across the sky, while new planes flay along similar routes, leaving trails parallel to the firs trails. These continue to be blown to the east, and after a couple of hours of the right weather conditions, and perfectly normal air traffic, we get the impressive looking images we see above.

Unfortunately in the chemtrail community, this impressive and informative image has taken on a life of its own, co-opted to suggest the pattern of spraying is deliberate. Here’s an example of the reasoning given:

The "chemtrail" interpretation of the image. Note that "lines connecting cities" is the exact opposite of what we would expect to see.

They indicate the positions of some nearby cities, and say that because the lines don’t connect the cities, then it must be a deliberate grid. Of course “lines connecting cities” is the LAST thing we would expect to see in a satellite photo of contrails. Firstly, as we see above, the contrails are moving sideways at 100 mph, so they will not end up positioned on the line between the cities, but instead tens or hundreds of miles away, but parallel to that route.

I wrote a simulator to demonstrate this:
http://contrailscience.com/contrail-simulations/

Secondly, and this is a frequently missed point. Planes don’t leave contrails near the airports they land at or take off from. They don’t because they are too low. Only when a plane reaches cruising altitude will it typically be cold enough for persistent contrails to form.

Thirdly, as you can see from the larger images, the regions of moist cold air are concentrated in bands. It’s actually quite rare for a contrail to form and persist for the entire length of a flight (at cruising altitude). You are going to see the contrails broken up, and only in some areas, as the plane moves in and out of various regions of air.

So, an impressive image. But what it’s really indicative of is the weather conditions on that day, and the sheer volume of traffic we can get in a few hours over that region of the US. Check out this video to see 24 hours of flights: