Last night I turned off the CER ACs, that were again producing the 13.1 Hz broad comb in DARM (we had shut these down before: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=73430), for two hours to see if the frequency would be changed when I turned them back on. It did, but by this morning the AC peak had drifted back to 13.1 Hz and was again producing peaks in DARM. I think we can run with these three of six shut off - we will monitor the temperature today and leave them off if there are no problems. The figure shows the spectra associated with the 2 or 3 Mpc improvement, even at these very high microseisms.

16:47 UTC off

17:03 on

17: 18 off