Influence of geomagnetic perturbation on resonant gravitational wave   detector
  The level of background signals in modern cryogenic resonant mass gravitational wave antenna is discussed caused by (a) the geomagnetic field pulsations and (b) an atmosferic of very low frequency band, generated by a lightning flash. The analysis of our results show that the signals of this origin will generally exceed the signals from the gravitational wave sources. To suppress these artifacts in such gravitational antenna, it is necessary to use the magnetometer included as anti-coincidence protection and a system of magnetic screens. 
Peter Vorob'ev (BINP), Valeri Ianovski and Igor Okunev (PNPI)