Though I appreciate seeing the old and familiar, when I venture outside on frosty mornings, I usually see at least three unexpected things. Three unexpected things before breakfast. A few days ago, the frost at first appeared more hoary than curvy, but when I peered over the top of a black SUV, I saw ice curves in the shape of an eye. Just for fun, I put an image of it next to a mirror-reversed copy, to give the following composite.

Call it the eyes of frost. Like me, you've probably seen curvy growth before, even if it didn't take the form of an eye. But let's venture into the eye of frost and notice something new: straight-segmented web-like growth.

I've never seen that before, and I never expected it.

Notice that the boundaries of the straight growth are parallel with the six prismatic faces of the larger crystals that stick up. So it seems that these web-segments grew from the vapor phase, not from a liquid film. Growth in liquid water does not produce prismatic faces, at least I've neither seen nor heard of it happening; for example, notice how the perimeter of the ice star in "They came from out of the tub" compares to that on any of Mark's snow crystals: the former are smooth and rounded, the latter straight. Moreover, curvy blades form when ice grows in a liquid at a surface. So, what I think happened is this. The car had a thin coating of liquid water that froze. But freezing wasn't uniform (it almost never is); rather, thin curving blades of ice formed. When an ice blade grows through the film, it forms a surface for ice to deposit from the vapor. Probably much of this vapor initially comes from evaporating liquid next to the blade, drying out the nearby film and preventing ice from growing there. Two such blades of opposite curvature formed the outline of the eye, and the interior film evaporated. But the dry car surface (as well as the ice blades) was still cold enough for net vapor deposition. So, from the ice blades, some crystals grew inward into the eye's interior, staying next to the cold surface. It's just a guess, though. I wish I could have had a time lapse microscopy set up for things like this.

Frost on a car roof differs from that on the hood. For one thing, the roof probably gets colder due to it having a greater 'view' of the clear night sky. Down on the warmer hood of the same car, I saw these little islands of columns - like towers of a tall castle surrounded by a huge moat.

Amazing how clean and dry it is around the columns. The ice-free moat around the towers may be a bit similar to the interior of the eye. I'll guess that the original water film that condensed here was thinner than that on the roof. In isolated spots, ice nucleated on some small, unseen particle. If the surface temperature was about -4 to -8 degrees C, which is consistent with the air temperature I measured of about 1-2 degrees, and the ice was oriented to grow as a column off the surface, then a column, or column-cluster would shoot up off the surface, as observed. If the film was thin enough, growth of ice in the water film surrounding the towers would be relatively slow. The growing tower would have sucked water out of the vapor, causing the film to dry up near the towers. Ice that nucleated further away may have spread through the liquid film, but stopped at the dry moat. Once again, I can only guess. If the roof was a degree or two colder, then the hoar would no longer be columnar. Such growth agrees with what I saw. It is consistent anyway.

-JN