|
|
 |
|
|
Ann. Geophys., 23, 2231-2237, 2005
www.ann-geophys.net/23/2231/2005/
© European Geosciences Union 2005
Optical observations geomagnetically conjugate to sprite-producing lightning discharges
R. A. Marshall1, U. S. Inan1, T. Neubert2, A. Hughes3, G. Sátori4, J. Bór4, A. Collier3, and T. H. Allin5
1STARLab, Stanford University, Stanford, CA, USA
2Danish Space Research Institute, Copenhagen, Denmark
3University of KwaZulu-Natal, Durban, South Africa
4Geodetic and Geophysical Research Institute, Sopron, Hungary
5Danish Technical University, Lyngby, Denmark
Abstract. Theoretical studies have predicted that large positive
cloud-to-ground discharges can trigger a runaway avalanche process
of relativistic electrons, forming a geomagnetically trapped
electron beam. The beam may undergo pitch angle and energy
scattering during its traverse of the Earth's magnetosphere, with
a small percentage of electrons remaining in the loss cone and
precipitating in the magnetically conjugate atmosphere. In
particular, N2 1P and N2+1N optical emissions are
expected to be observable. In July and August 2003, an attempt
was made to detect these optical emissions, called "conjugate
sprites", in correlation with sprite observations in Europe near
 . Sprite observations were made from the
Observatoire du Pic du Midi (OMP) in the French Pyrenées, and
VLF receivers were installed in Europe to detect causative sferics
and ionospheric disturbances associated with sprites. In the
Southern Hemisphere conjugate region, the Wide-angle Array for
Sprite Photometry (WASP) was deployed at the South African
Astronomical Observatory (SAAO), near Sutherland, South Africa, to
observe optical emissions with a field-of-view magnetically
conjugate to the Northern Hemisphere observing region.
Observations at OMP revealed over 130 documented sprites, with
WASP observations covering the conjugate region successfully for
30 of these events. However, no incidences of optical emissions in
the conjugate hemisphere were found. Analysis of the conjugate
optical data from SAAO, along with ELF energy measurements from
Palmer Station, Antarctica, and charge-moment analysis, show that
the lightning events during the course of this experiment likely
had insufficient intensity to create a relativistic beam.
Keywords. Ionosphere (Ionsophere-magnetosphere interactions;
Ionospheric disturbances; Instruments and techniques)
Full Article in PDF (1390 KB) |
|
|
