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Ann. Geophys., 18, 1182-1196, 2000
www.ann-geophys.net/18/1182/2000/
© European Geosciences Union 2000
More evidence for a planetary wave link with midlatitude E region coherent backscatter and sporadic E layers
M. Voiculescu1, C. Haldoupis2, D. Pancheva3, M. Ignat4, K. Schlegel5, and S. Shalimov6
1Physics Department, University of Galati, Galati, Romania
2Physics Department, University of Crete, Iraklion, Crete, Greece
3The Department of Physics, University of Wales, Aberystwyth, Wales, UK
4Physics Department, University of Iasi, Iasi, Romania
5Max-Planck Institut fur Aeronomie, Katlenburg-Lindau, Germany
6Institute of Physics of the Earth, Moscow, Russia
Abstract. Measurements of midlatitude E region
coherent backscatter obtained during four summers with SESCAT, a 50 MHz Doppler
system operating in Crete, Greece, and concurrent ionosonde recordings from the
same ionospheric volume obtained with a CADI for one of these summers, are used
to analyse the long-term variability in echo and Es
occurrence. Echo and Es layer occurrences, computed in percent
of time over a 12-h nighttime interval, take the form of time sequences. Linear
power spectrum analysis shows that there are dominant spectral peaks in the
range of 2–9 days, the most commonly observed periods appearing in two
preferential bands, of 2–3 days and 4–7 days. No connection with geomagnetic
activity was found. The characteristics of these periodicities compare well with
similar properties of planetary waves, which suggests the possibility that
planetary waves are responsible for the observed long-term periodicities. These
findings indicate also a likely close relation between planetary wave (PW)
activity and the well known but not well understood seasonal Es
dependence. To test the PW postulation, we used simultaneous neutral wind data
from the mesopause region around 95 km, measured from Collm, Germany. Direct
comparison of the long-term periodicities in echo and Es layer
occurrence with those in the neutral wind show some reasonable agreement. This
new evidence, although not fully conclusive, is the first direct indication in
favour of a planetary wave role on the unstable midlatitude E region
ionosphere. Our results suggest that planetary waves observation is a viable
option and a new element into the physics of midlatitude Es
layers that needs to be considered and investigated.
Key words: Ionosphere (ionosphere irregularities;
mid-latitude ionosphere) – Meteorology and atmospheric dynamics (waves and
tides)
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