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Ann. Geophys., 23, 2307-2318, 2005
www.ann-geophys.net/23/2307/2005/
© European Geosciences Union 2005
Radar observations of field-aligned plasma irregularities in the SEEK-2 campaign
S. Saito1, M. Yamamoto2, S. Fukao2, M. Marumoto2, and R. T. Tsunoda3
1National Institute of Information and Communication Technology, Nukui-Kita 4-2-1, Koganei, Tokyo 184-8795, Japan
2Research Institute of Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
3SRI International, Menlo Park, California, USA
Abstract. During the Sporadic E Experiment over Kyushu 2 (SEEK-2) campaign,
field-aligned irregularities (FAIs) associated with midlatitude sporadic-E
(Es) layers
were observed with
two backscatter radars, the Lower Thermosphere Profiler Radar (LTPR) and
the Frequency Agile Radar (FAR), which were located 40 km apart in Tanegashima,
Japan.
We conducted observations of FAI echoes
from 31 July to 24 August 2002, and the radar data were used to
determine launch timing of two sounding rockets on 3 August 2002.
Our comparison of echoes obtained by the LTPR and the FAR revealed that
echoes often appeared at the FAR about 10min earlier than they did at
the LTPR and were well correlated.
This indicates that echoing regions drift with a southward velocity component
that maintains the spatial shape.
Interferometry observations that were conducted with the LTPR from
3 to 8 August 2002, revealed that the quasi-periodic (QP)
striations in the Range-Time-Intensity (RTI) plots were due to the apparent motion
of echoing regions across the radar beam including both main and side lobes.
In most cases, the echo moved to the east-southeast at an almost
constant altitude of 100–110 km, which was along the locus of
perpendicularity of the radar line-of-sight to the geomagnetic
field line.
We found that
the QP pattern on the RTI plot reflects the horizontal structure and motion
of the (Es layer,
and that echoing regions seemed to be in one-dimensionally
elongated shapes or in chains of patches.
Neutral wind velocities from 75 to 105 km altitude were simultaneously
derived with meteor echoes
from the LTPR.
This is the first time-continuous simultaneous observation
FAIs and neutral wind with interferometry measurements.
Assuming that the echoing regions were drifting with an ambient
neutral wind, we found that the echoing region was aligned
east-northeast-west-southwest in eight out of ten QP echo events during
the SEEK-2 campaign.
A range rate was negative (positive), when a frontal structure
of echoing regions elongated east-northeast-west-southwest drifts
with southward (northward) neutral wind.
Keywords. Ionosphere-atmosphere interactions; Ionospheric
irregularities; Plasma waves and instabilities
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