Abstract
Abstract In this paper we presented two typical global 6-day planetary wave oscillations occurring in sporadic E layers. By analyzing the f o E s time series observed from several ionosonde stations on the basis of the methods suggested by Haldoupis and Pancheva (2002), we computed estimates for the PW propagation direction, zonal wave number and phase velocity. We obtained results that the 6-day PW, with zonal wave number about 1, propagates westward, which are in agreement with those reported from radar and satellite neutral wind MLT measurements. The results provide experimental evidence for a close relationship between PWs and midlatitude E s. In addition, the study proves the validity of E s observations measured routinely and rather reliably with a dense global network of digital ionosondes used as an alternative means of studying large-scale neutral atmospheric dynamics in the MLT region.
Highlights
The main factor involved in midlatitude sporadic E (E s ) formation is vertical neutral wind shears, associated with tides and/or gravity waves, which can compress the long-living metallic ions into a thin layer
We obtained results that the 6-day planetary waves (PWs), with zonal wave number about 1, propagates westward, which are in agreement with those reported from radar and satellite neutral wind MLT measurements
We have reported two experimental cases in this study and found that planetary waves play a profound role in sporadic E layers
Summary
The main factor involved in midlatitude sporadic E (E s ) formation is vertical neutral wind shears, associated with tides and/or gravity waves, which can compress the long-living metallic ions into a thin layer (e.g., see review articles by Whitehead, 1989; Mathews, 1998). Tsunoda et al (1998) and Voiculescu et al (1999) were the first to give evidence for planetary wave effects on midlatitide backscatter and the sporadic E layer occurrence. Voiculescu et al (2000) analyzed measurements of midlatitude E region coherent backscatter obtained during four summers with SESCAT E SCATter experiment), a 50 MHz Doppler radar system operating in Crete, Greece, concurrent ionosonde recordings from the same ionospheric volume obtained with a CADI (Canadian Advanced Digital Ionosonde) for one of these summers and simultaneous neural wind data from the mesopause region around 95 km, measured in Germany
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