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Ann. Geophys., 24, 153-162, 2006
www.ann-geophys.net/24/153/2006/
© European Geosciences Union 2006
Simultaneous observation of sporadic E with a rapid-run ionosonde and VHF coherent backscatter radar
T. Maruyama1, S. Saito1, M. Yamamoto2, and S. Fukao2
1National Inst. of Information and Communications Technology, 2-1 Nukuikita 4-chome, Koganei, Tokyo, 184-8795 Japan
2Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
Abstract. During the SEEK 2 rocket campaign, ionograms were recorded every minute at
the Yamagawa Radio Observatory at about 90km west of the region monitored
by a VHF (very high frequency) coherent backscatter radar. Sporadic E-layer
parameters, which include the critical (foEs) and blanketing (fbEs)
frequencies, the layer height (h'Es), and the width of the range spread of
sporadic E-traces, were compared with RTI (range-time-intensity) plots of
VHF quasi-periodic (QP) and continuous coherent backscatter echoes. A close
relationship was found between the appearance of QP echoes in the RTI plots
and the level of spatial inhomogeneity in sporadic E plasma, signified here
by the difference between foEs and fbEs. During QP echo events, foEs
increased while fbEs decreased, so that the difference foEs-fbEs was
enhanced, indicating the development of strong spatial structuring in
electron density within a sporadic E-layer. On the other hand, increases in
sporadic E range spreading also correlated with the occurrence of QP
echoes but the degree of correlation varied from event to event. Continuous
radar echoes were observed in association with low altitude sporadic
E-layers, located well below 100 km and at times as low as 90 km. During the
continuous echo events, both foEs and fbEs were less variable, and the
difference foEs-fbEs was small and not as dynamic as in the QP echoes. On
the other hand, the Es-layer spread intensified during continuous echoes,
which means that some patchiness or corrugation in those low altitude layers
is also necessary for the continuous backscatter echoes to take place.
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