Monday, August 08, 2011
Sharp shadows, contrail dictaphone
This morning the sunlight had a special quality. All vertical shadows were exceedingly sharp, bringing out some details of brickwork and windows that I hadn't seen before. If I had to put a name on the effect, I'd call it vertical polarization, though I don't know if that's possible.
Thinking about that, I started looking closely at the clouds to see if there was something Polaroidish about them. Hard to tell.
But in the process of examining the clouds closely, I noticed something else.
All the clouds were clearly formed from jet contrails, in a pattern of fairly regular stripes. This didn't make sense, because I know there's only one jet path in that direction, not several widely spaced parallel paths. (Widely spaced parallel paths couldn't all lead to the same airport anyway!) In fact, a jet was running along that one path as I watched, so I could spot it definitely.
The first part of the contrail was clear, then it blurred out; and each line of clouds to the left was unquestionably formed by an even more blurred remainder of an earlier contrail.
Finally I got the picture. Jets run along the same path toward the airport at regular intervals. After each jet passes, the contrail blurs out, and simultaneously the prevailing upper-level wind carries all the earlier and fuzzier contrails steadily toward the left. It's like recording an old dictaphone cylinder. More accurate but more strained metaphor: It's like plowing a field by running the tractor north and south in one line, with long pauses between runs, while slowly and steadily towing the whole field to the west... in a strong wind that smears each furrow after it's plowed. (Told you it was strained!)
[Artistic note: The animation is speeded up, which is necessary and good. It also has too much vertical movement, which isn't so good. The streaks should be vertically stationary, moving only toward the left. I couldn't think of a nice way to make that happen within the Poser mechanism.] ¶ 11:45 AM
Thinking about that, I started looking closely at the clouds to see if there was something Polaroidish about them. Hard to tell.
But in the process of examining the clouds closely, I noticed something else.
All the clouds were clearly formed from jet contrails, in a pattern of fairly regular stripes. This didn't make sense, because I know there's only one jet path in that direction, not several widely spaced parallel paths. (Widely spaced parallel paths couldn't all lead to the same airport anyway!) In fact, a jet was running along that one path as I watched, so I could spot it definitely.
The first part of the contrail was clear, then it blurred out; and each line of clouds to the left was unquestionably formed by an even more blurred remainder of an earlier contrail.
Finally I got the picture. Jets run along the same path toward the airport at regular intervals. After each jet passes, the contrail blurs out, and simultaneously the prevailing upper-level wind carries all the earlier and fuzzier contrails steadily toward the left. It's like recording an old dictaphone cylinder. More accurate but more strained metaphor: It's like plowing a field by running the tractor north and south in one line, with long pauses between runs, while slowly and steadily towing the whole field to the west... in a strong wind that smears each furrow after it's plowed. (Told you it was strained!)
[Artistic note: The animation is speeded up, which is necessary and good. It also has too much vertical movement, which isn't so good. The streaks should be vertically stationary, moving only toward the left. I couldn't think of a nice way to make that happen within the Poser mechanism.] ¶ 11:45 AM
