A couple of observations made yesterday. We've had a huge run of very light tumble weed seed heads from grasses around work, and they've proved to be an excellent visual aid for lift as they are picked up easily, and there are thousands of them and are big enough to be seen clearly at a fair height (though I wouldn't go so far as to guess, but certainly 100's of meters up). Each is probably about 1 foot/30cm in diam.
1. First thermal was a very large (200m+ diam) slowly clockwise rotating and rising mass of air, in which there was a central core of very fast rotation and high vertical speed air. This was clearly visible from the grass pods. Across ground speed was moderate, and once the lift had passed on, everything fell out of the sky quite quickly.
2. Same conditions, day and near exact same path of 2nd thermal. A very large (200m+) mass of slowly counter clockwise rotating mass of air with no core, but with slower ground speed and less sink once it had passed on. Interestingly, neither thermal attracted bird attention despite the fact that there are large numbers of soaring birds around (raptors as well as others).
3. Same day, different thermal path, soaring raptor. The kestrel thermaled up from just above tree height to out of sight circling both directions freely in what appeared to be the same thermal.
4. I need to take my DLG to work so I can take advantage of these well defined and often big areas of lift