Thanks for the comments reef and Stormmad26.
I note from the trouble-shooting section of the Vantage console manual that they suggest that unusually "high" solar sensor readings could be caused by the presence of high, thin cirrus. As a general meteorological question, any idea of the physical mechanism behind such a phenomenon?
One supplementary question I had, specific to the Vantage, concerns the time-stamp in the data records. Each stored data value is supposed to be the average readout over the requested interval (1 min.... 30 mins). The answer may be buried in the documentation - apologies if so - but does anyone know whether, for example, a data record time-stamped 08:01 with a 1 min archive interval will be the averaged data from
08:00:00 --> 08:01:00
08:00:30 --> 08:01:30 or
08:01:00 --> 08:02:00
Comparing the data displayed on the console with the archived data, I have my doubts that it's any of them! Also what is the sensor readout frequency (ie readings per time interval not electromagnetic!) - does it vary from sensor to sensor? Just wondering what it means when the manual says the console displays the "current" value.
Cheers