The summary pages for the X,Y, and Z PEM magnetic noise channels show a change in magnetic noise at EY between 14 July 2017 (Firg. 1) and 15 July 2017 (Fig. 2) characterized by a peak at about 30 Hz and higher broadband noise below the peak. Five minute spectra with start times spaced 10 minutes apart are shown in Fig, 3, again for the Z direction. The starting time is 15 July 2017 00:00:00 UTC (red) with subsequent times 00:10:00 (gold), 00:20:00 (green), 00:30:00 (purple), and 00:40:00 (blue). From Fig. 4, the peak at about 30 Hz starts to appear around 00:20 UTC on 15 July (about 17:20 PDT on 14 July). The full transition is shown for X,Y, and Z several hours apart in Fig. 4 where the elevated broadband noise increase is also seen. In Fig. 4, the two times shown are 14 July 10:00:00 UTC (red, green, blue) and 15 July 20:00:00 UTC (purple, gray, gold). 

The time of this transition appears to correspond with PEM injections at EY carried out by Robert Schofield and Pep Covas to identify noise produced by thirsty ravens (see alog 37630). Alog 37523 indicates that the injections began on 14 July at 22:37 UTC and continued for about 2 hours.

Recent Bruco scans (see, e.g., the one on 19 July in alog 37614 do not show any indication that this excess noise correlates with h(t).