The influence of geomagnetic perturbation on a resonant gravitational wave detector

Modern cryogenic resonant mass gravitational wave antenna backgrounds are discussed. Two possible sources are considered: (a) geomagnetic field pulsation and (b) atmospheric pulses of low frequency generated by thunderstorms. It is shown that these backgrounds can exceed the signals from the gravitational wave sources. To suppress them an anti-coincidence magnetometer and a system of magnetic screens are proposed.