Sunset Virga

As I’ve said many times, sometimes Sky Lights is just about pretty pictures, and that’s the case this week. I was lucky to get this photo as the display only lasted a few minutes. I’d stepped out on the deck to check the sunset — a daily ritual often rewarded with eye candy. There was no time to set up a tripod, so I just grabbed my camera and shot at full auto. The camera decided on f/5.6, 1/60 sec, ISO-400.

What you’re seeing here is virga illuminated by the red-filtered light of a sunset. This happens fairly often over Lake Pleasant, around 10 miles west of me just beyond those silhouetted mountains. It’s the low humidity of the air here in the Southwest that makes virga so common. The meteorological conditions for producing rain are being met at higher altitudes, but as the precipitation falls through drier warmer air below it re-evaporates and returns to its invisible gaseous state.

Interestingly, even though the water has returned to its vapor state, the density of the air doesn’t change much and it continues “falling” as a cool humid downdraft. If you happen to be standing under it, you won’t get wet but you’ll feel a cool humid breeze sweep over you like a mini-microburst.

So unless you didn’t already know about virga, or red sunsets, or microbursts, and had to follow those links, there’s not much science in this week’s post. Otherwise, rest your brain and enjoy the pretty picture.

Next Week in Sky Lights ⇒ Why Rockets Use Stages

Q&A: Rocket Exhaust Trails at High Altitude
Q&A: Why Rockets Use Stages