|Elena Gibson captured this|
lenticularis cloud over Dublin.
The air was warm, the sky was a deep blue, dotted with just a few.......what are those spaceships from an alien invasion?
No, they were something called altocumulus standing lenticularis clouds, and Dublin got a rare treat, as these clouds usually form over or near mountains, and usually not over Dublin.
I've seen these clouds every once in awhile where I live in mountainous Vermont.
The clouds also usually form in the colder half of the year, not in the summer.
These beautiful clouds when the atmosphere is relatively stable. In other words, there aren't incredibly strong updrafts, the kind that makes thunderstorms.
The lenticular clouds form when fast moving air above us is forced to rise up and over a barrier, usually a mountain or mountain range that's perpendicular to the direction of the wind.
Picture a fast moving brook in which the water is forced up and over a rock protruding from the middle of the river.
|Lenticular clouds over Dublin, via @JoeyGartian on Twitter.|
The mountain the air is going up and over is like the rock in that stream, and there's a series of waves downstream in the air. These are called gravity waves.
When the air rises to form the peak of these gravity waves, the air cools and condenses, forming clouds.
Clouds always form when air rises, cools and condenses, so why do these clouds look so cool? It's because the strong winds sort of smooth out the clouds and shape them into something that's lens shaped, hence the name of the clouds.
|Looks like the Starship Enterprise is over Dublin|
From Twitter via B_Fitsimons.
These clouds tend to sit in one place, much like the waves you see downstream from that rock in the river.
The atmosphere must also have just the right amount of moisture in just the right layer, and winds must be just the right speed to form these clouds. That's why you don't see them everyday. In many places, like Dublin, they're quite rare.
Upwind from Dublin, there must be some hills or mountains that got these going. Or, there was a pocket of especially stable air that set the air rising up and over it. Maybe a weak warm front? I'm not sure.
Anyway, Dubliners enjoyed the show on a glorious June day.