Last Monday was the first day of February.
It was a cold, clear day and people all felt that the good weather heralded the first day of spring. Let’s be clear…spring does not officially start until 1st March. In fact, let’s be even clearer, spring does not start until the first summer migrants begin to appear which is usually on or about St Patrick’s Day (17th March).
That evening, news broke of several very rare sightings across Ireland. I have written several blogs in the past few weeks about rare sightings in Ireland…those gulls and that lovely little Siberian Chiffchaff. However, the sightings that were causing such excitement were not birds at all. No, in fact it was clouds that was causing the excitement!
Yes, you read that correctly…I am writing about clouds, or, to be more precise, a phenomenon known as nacreous (or polar stratospheric) clouds.
Nacreous clouds apparently form in the winter polar stratosphere, a layer of our atmosphere from 15,000 to 25,000m in altitude. The stratosphere is generally very dry and so cloud formation is rare, but it seems that the recent storms (and we have had lots so far) may have driven moisture high into the atmosphere. Nacreous clouds will also only form when the temperature in the stratosphere is below -78°C, which turns any moisture in the air into super-cooled liquid or ice crystals. Such temperatures generally only occur in the winter at high latitudes…these clouds are rarely seen as far south as Ireland.
During the hours of dawn or dusk, when the sun is between 1° and 6° below the horizon, the first or last rays of the day illuminate these high altitude clouds from below. This light is then refracted by the ice crystals in the clouds, producing the shimmering rainbow effect.
‘Wow! They look amazing,’ I thought to myself.
I have been interested in weather since childhood and I don’t think I had ever heard of nacreous clouds before (never mind seen them).
Early on Tuesday 2nd Feb, I was setting off to a school to share my passion for birds with the birdwatchers of the future. It was a lovely morning. I looked up and there they were…my very own ‘rainbow clouds’ over our house. These light, wispy clouds shimmered with the colours of the rainbow…the colours faded and shimmered again.
I stood watching these beautiful clouds with Hazel (who was happy to be dragged from her jet-lag induced sleep) as they passed over us. The photo above does not do justice to their beauty…it is a shot taken with my phone. However, it might just capture a little of their shape and form.
I was even happy to be able to show them to a whole school of children who were entranced by the rainbow clouds. It was funny to hear one child point me out to her mother at the school gate at the end of the day…
‘That’s the Cloudman,’ she said.
I smiled…it sure makes a change from being called ‘The Birdman’!