LIGO Document T2000634-v1

Intersite Magnetic Signals from Lightning

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T - Technical notes
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Comparison of LEMI Omicron triggers with Vaisala's GLD360 data set is used to establish the detection of lighting by the LEMIs, primarily in North America. Coincident millisecond scale transients in LHO and LLO LEMI magnetometer signals occur at a rate of about 1000-2000 events per hour and reach up to at least 900 Hz. Roughly 50% of the LEMI coincidences are also coincident with Vaisala-identified lightning strokes. Of the Vaisala-identified strokes in North America, 1.6% are coincident with LHO-LLO LEMI coincidences. For Vaisala-identified lightning strokes outside North America, there are almost no LEMI coincidences. Coincident Vaisala-identified strokes slightly favor ground-to-cloud transmission. Coincident LEMI signals tend to favor higher frequencies. These lightning signals are consistent with being responsible for the observed high-frequency magnetic coherence between LHO and LLO. Including magnetometer signals from Virgo highlights higher current lightning at higher SNR. Three-site coincidences still emphasize lightning signals in North America, but also make clear regions of sensitivity in South America and the Northern Mediterranean. Comparing coincidences with normal lightning to signals coincident with observed gigantic jets suggest that these jets do not pose any more of a problem than the strongest lightning signals.
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