For those of you new to gliding, the time lapse video below demonstrates quite nicely how cumulus are formed. As the morning progresses and the sun heats up the ground, the occasional bubbles of rising air over Booker become a constant stream to keep the clouds refreshed with water vapour. Notice the thermals over Didcot power station (bottom left) have started much earlier due to that heat source. You can also see how the rising air spills outwards at the top of the thermal causing sink at the edges of the cumulus. The video spans the time 10.30 to 12.00 BST or 9.30 to 11.00 GMT or "Sun Time".