First Sprites observed by the new global network supported at Piñon Flat by HPWREN

By Toby Whitley (T.Whitley @ bath.ac.uk) and Martin Füllekrug, University of Bath, England

During the summer of 2009 work began on installing a four-station global network to study sprites with sites at Piñon Flat in California, Sutherland in South Africa, Canberra in Australia and Eskdalemuir in Scotland.

Piñon Flat

Sutherland, South Africa

Canberra, Australia

Eskdalemuir, Scotland

While all sites in this new state of the art four-station global network are not yet fully connected, three stations, including the first one based at Piñon Flat, were recording data simultaneously with optical observations of sprites in Southern Europe. Sprites are Transient Luminous Events (TLEs), which occur at heights between 55 and 80km above large thunderstorms. Sprites are triggered by intense, positive, cloud to ground lightning discharges having a significant continuing current and follow them with a time delay of ~1-100 ms.

The electromagnetic sprite signatures recorded by the network can be seen below and show the waveform seen at each station. The waveform has a double peak, the first peak is caused by the triggering lightning strike and the second peak is caused by the sprite. Interestingly, with these sprites occurring over Europe, only a single peak is seen at the Australian site due to dispersion effects and attenuation, but it is seen twice. The first waveform comes along the shorter great circle path in the positive direction for the magnetic coil sensors, and then the slightly delayed waveform along the longer great circle path and the negative direction for the coils so inverted.

An unusual and particularly spectacular sprite and corresponding electromagnetic signatures recorded on the 2nd of September 2009 at three of the global network sites. The first peak is the causative lightning and the second peak is the sprite.

A second sprite and corresponding electromagnetic signatures recorded on the 2nd of September 2009.

The sites in these recordings are at Canberra in Australia supported by Geoscience Australia, the Sutherland Observatory in South Africa supported by the South African Astronomical Observatory group and Piñon Flat in California supported by UCSD and HPWREN

Piñon Flat, United States (UCSD)