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Ann. Geophys., 24, 1411-1418, 2006
www.ann-geophys.net/24/1411/2006/
© European Geosciences Union 2006
Eastward traverse of equatorial plasma plumes observed with the Equatorial Atmosphere Radar in Indonesia
S. Fukao1, T. Yokoyama1,*, T. Tayama1,**, M. Yamamoto1, T. Maruyama2, and S. Saito2
1Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan
2National Institute of Information and Communications Technology, Tokyo, Japan
*now at: Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi, Japan
**now at: NTT Data Co. Ltd., Tokyo, Japan
Abstract. The zonal structure of radar backscatter plumes
associated with Equatorial Spread F (ESF), probably
modulated by atmospheric gravity waves, has been investigated
with the Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia
(0.20° S, 100.32° E; dip latitude 10.1° S)
and the FM-CW ionospheric sounders on the same magnetic meridian as the EAR.
The occurrence locations and zonal distances of the ESF plumes
were determined with multi-beam observations with the EAR.
The ESF plumes drifted eastward
while keeping distances of several hundred to a thousand kilometers.
Comparing the occurrence of the plumes and
the F-layer uplift measured by the FM-CW sounders,
plumes were initiated within the scanned area around sunset
only, when the F-layer altitude rapidly increased.
Therefore, the PreReversal Enhancement (PRE) is considered as
having a zonal variation with the scales mentioned above,
and this variation causes day-to-day variability, which has
been studied for a long time. Modulation of the underlying
E-region conductivity by gravity waves,
which causes inhomogeneous sporadic-E layers, for example,
is a likely mechanism to determine the scale of the PRE.
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