Radio Science

Automatic whistler detection: Operational results from New Zealand



[1] Lightning-generated “whistlers,” the strongly dispersed radio wave pulses that have propagated along the Earth's magnetic field from one hemisphere of the Earth to the other, have long been regarded as inexpensive and effective tools for plasmasphere diagnosis. The Eötvös University Automatic Whistler Detector (AWD) system has been operating in Dunedin, New Zealand, since mid-May 2005. Here we report on the first 530 days of near-continuous AWD operation. In this time period the AWD system detected 92,528 individual whistler events containing 236,019 whistler traces. This equates to a whistler event rate of 0.12 min−1 and a whistler trace rate of 0.31 min−1. Despite the conjugate lightning rate for Dunedin being a factor of ∼1500 lower than that for Hungary, the AWD-reported whistler rate from Dunedin was only ∼3 times lower. Dunedin whistler rates are high, hundreds of times higher than estimated from the conjugate lightning activity, showing that conjugate lightning activity levels are not a good predictor of whistler rates. Dunedin-observed whistlers are most common during the daytime, in stark contrast with earlier findings and general expectations. We suggest that North American lightning may be the principal source of Dunedin whistlers. The Dunedin-based AWD has detected a large number of whistlers over a wide range of L shells, with a sufficiently small false trigger rate (∼58%) to allow rapid processing of the data. Dunedin observations may soon provide a valuable near-continuous plasmaspheric measurement stream after the planned upgrade of the existing AWD to an automatic analyzer and AWD system.