  Schumann resonance transients which propagate around the globe can
potentially generate a correlated background in widely separated gravitational
wave detectors. We show that due to the distribution of lightning hotspots
around the globe these transients have characteristic time lags, and this
feature can be useful to further suppress such a background, especially in
searches of the stochastic gravitational-wave background. A brief review of the
corresponding literature on Schumann resonances and lightnings is also given.
