Do you know what a blue thermal day is? It's a day of invisible thermals. I didn't know that until yesterday—which was one.
Normally, of course, thermals bubble up over the landscape and grow cumulus clouds as they go, so you can see where they are. On a blue thermal day, there's not a single cumulus growing or dying; no clouds at all. Just invisibly rising air.
I spent this blue thermal day getting lightly sunburned walking around Orford Ness with a student who's working on this place for her dissertation. It was warm enough that the nuclear testing pagodas wobbled in the haze coming off the beach, and the water-flashes in the grazing marsh were packed with dunlins stopping off to refuel with muddy invertebrates on their way north. By midday they were all gone.
Of course I didn't bring a camera, so I can't show you what Orford Ness looks like in white sunlight on a blue thermal day, but here are some from last autumn, when Orford is full of mist-nets and bird-ringers and tired migrant passerines. Orford Ness is one of the strangest places in the whole of East Anglia, which (along with the Forest of Dean) is one of the strangest places in the whole of Britain. Click on the pictures to make them bigger...