...
Also decided to clean the radiometers while I was there, since I could imagine a film of dust on the SPN1, though the tissue didn't come away dirty. There were spider webs around. At most, the change of either Rsw.in or Rsw.global was 3 W/m2 -- not enough to explain the large differences we've seen.
Cleaning done about 15:30, though I was standing near the radiometers starting about 15:15. 