J. Kissel, for B. Lantz and J. Harms

There's been some interesting discussions on the DetChar mailing list about seasonal variation of ground motion around the world's network of gravitational wave observatories. Two things (of many) that have come out of it that might be of particular interest to LHO:
- Jan Harm's data set from 2009/2010 T1500224, showing what I'm calling "meta" ASDs showing the percentile ASDs for each month over a year. 
- Brian Lantz has used that data, shown it in a slightly different way which can be found in SEI aLOG 766.

More data is to come. 

Why do we care? It's merely to call attention to the fact that for the active isolation feed-back,
(a) We shouldn't expect a "one (blend filter / sensor correction) filter fixes all" solution for both LHO and LLO.
(b) Seasonal variations of the secondary microseismic may explain why we've needed to work harder at the microseism this past winter (i.e. use the 45 [mHz] DeRosa, LLO blend) and now we're doing just fine with a 90 [mHz] blend everywhere.