June 24, 2010
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.
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
Piñon Flat, United States (UCSD)
Canberra, Australia (Geoscience Australia)
Graham Heinson (Adelaide University)
Sutherland, South Africa (SAAO)
Eskdalemuir, Scotland (BGS)