Lacunosus

I went birding, and all I saw was lacunosus—but what spectacular lacunosus it was.

Lacunosus occurs in thin clouds when bubbles of buoyant dry air from below the cloud rise and poke holes in the cloud. I have shown pictures of this before, but today’s sighting was, if anything, more spectacular.

When seen (which is not all that often), it usually appears in unsteady wave clouds. When formed from a thin layer of moisture in the atmosphere, a wave cloud does not sit at the lifting-condensation level. As a result, when the amplitude of the wave decreases, the sinking air warms by compression. But, the temperature in the cloud increases more slowly (warms at the moist-adiabatic lapse rate) than the temperature of the air below (warms at the dry-adiabatic lapse rate). The result is that bubbles of the warmer dry air from below rise and punch holes through the cooler cloud.

This is the physical understanding of what happenings, but the transient patterns that emerge are clearly worth the price of admission.

I show three pictures from this morning, and as this was happening in the vicinity of the Sun, the final image actually shows a touch of iridescence. Granted that this iridescence isn’t quite as spectacular as that seen a few weeks ago, but with such a sighting, who is complaining?

The lacunosus formed and vanished within perhaps five minutes. That is actually a much longer viewing interval than is afforded by most of the birds I see.