Hole Punch Clouds in Los Angeles
I’ve talked about distrails and hole punch clouds before, but I’ve actually never seen one myself until this morning, when I saw two side by side. It’s quite rare to have this kind of weather condition in Los Angeles. I took a couple of photos at around 7:30AM today, Aug 19th, 2007. Santa Monica ATIS reports the sky is clear now, but Van Nuys reports broken cloud at 18,000 feet and 28,000,which is probably where these are, given they look like they are precipitating ice in artificial cirrus uncinus. The cloud layer that the holes formed is cirrocumulus.
Cirrocumulus clouds contain both ice crystals, and supercooled water droplets. The introduction of the extra water from the jet exhaust causes a rapid increase in the rate of crystallization, and all the water turns to ice as the ice crystals get larger. This rapidly desaturates the air, which then pulls in moisture from the air around it, thus spreading the hole. The larger ice crystals then drift downwards (as virga), since they are heavier, resulting in the characteristic “V” or “wing” cross-section of the central cirrus uncinus cloud, which looks a bit like a bird or an angel, if you are imaginative enough.
I like this second one, since it clearly shows the central contrail from the plane that made the hole (look by the palm tree). It’s not quite as nice a regular hole as some you see though. That’s probably to do with the location, being so close to the airport the climb/descent rate won’t be so steep at altitude.
(note, the above images have been contrast enhanced and sharpened, the original of the top one can be found here, for reference).
Sunday 19 Aug 2007 | Uncinus | contrails