February 2017

February 2017

“We come in search of ice cream”

A fleet of flying saucers have descended on the beach at Torremolinos on the Costa del Sol, southern Spain. Clearly, alien beings are here in search of some winter sun.

Either that, or the atmospheric conditions on this day just happen to be perfect for Altocumulus lenticularis clouds to form. This is probably more likely. The wind is blowing from the northwest, which means it is flowing right over the Sierra de Mijas, a mountain range just inland from the coast. Whenever a steady wind flows over mountainous terrain, there is a good chance UFO-shaped lenticularis clouds can appear.

The atmospheric conditions need to be ‘stable’. This is to do with the way the air temperature varies with altitude. Stable conditions mean that an airflow kicked upwards by the mountains will sink back down again to where it started. Often, it will overshoot and and dip below the original ‘equilibrium’ altitude before floating back up again. Just like the ripples you see on a river downstream of some rocks, winds in stable conditions often flow in wave-like crests and troughs in the lee of mountain peaks. The air temperature cools at the crests of these invisible waves of air. This means that when there’s the right amount of moisture present, tiny droplets of water condense at the wave crest and these appear as disc-shaped clouds.

Conditions look good for lenticularis clouds as a steady northwesterly wind develops wavy paths in the lee of the Sierra de Mijas mountains, Spain. The pin shows where the Cloud of the Month was photographed.

The resulting flying-saucer shaped lenticularis clouds hover stationary in the wind so long as the airflow remains steady. Magical as this seems, it shouldn’t really surprise us. Aliens know, just as much as we do, you stay put when you find a parking space at the beach.

Altocumulus lenticularis clouds over La Carihuela, Torremolinos, Spain, spotted by Henrik Välimäki.

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