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- Belova, Evgenia, et al.
(author)
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High-speed echoes in the polar winter mesosphere: Infrasound as a probable cause
- 2023
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 72:8, s. 3181-3201
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Journal article (peer-reviewed)abstract
- We considered three events on 4 November 2015, 22 December 2016, and 12 November 2018, when the signals travelling in the polar winter mesosphere with high horizontal velocities above 300 m/s were measured by the atmospheric radar ESRAD (Chilson et al., 1999) located at Esrange, near Kiruna in northern Sweden. We proposed four mechanisms of generation of such special cases of polar mesosphere echoes, e.g. high-speed PMWE, that involve microbaroms, i.e. infrasound waves at 0.1 - 0.35 Hz frequencies created by ocean swell. These mechanisms are (i) generation of viscous waves, (ii) generation of thermal waves, (iii) direct contributions of infrasound, and (iv) generation of secondary waves at sound dissipation. These processes necessarily accompany sound propagation in inhomogeneous, thermally conducting and viscous fluid (air). The four models were theoretically analysed and their efficiency was estimated. The infrasound measurements at the IS37 station (Gibbons et al., 2019) located about 170 km north-west from the ESRAD radar, modelled maps of the microbarom sources, infrasound propagation conditions and ionospheric conditions for these three PMWE events support the proposed models. Infrasound-generated thermal waves are suggested to be the most probable specific cause of the observed high-speed, high-aspect-ratio PMWE events. However, absence of in-situ infrasound and plasma measurements did not allow us to quantify contributions of individual physical mechanisms to the fast-travelling echoes generation.
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| 2. |
- Belova, Evgenia, et al.
(author)
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Polar Mesosphere Winter Echoes and their relation to infrasound
- 2020
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Conference paper (peer-reviewed)abstract
- Polar Mesosphere Winter Echoes (PMWE) are radar echoes that originate from the mesosphere at 50-80 km altitude and are observed with VHF radars during equinox and winter seasons. Strong PMWE are relatively rare phenomena, in most cases they are observed when the lower ionosphere displays high ionisation. Interpretations of observational results concerning PMWE are controversial and the origin of the echoes is still under debate. Especially intriguing is that in some cases of strong PMWE, the measured horizontal speeds of the radar reflecting structures can exceed 300 m/s. Radar reflection (scattering) by infrasound waves at frequencies below about 2 Hz was suggested in order to explain these observations. We will give recent examples of PMWE events of high horizontal speed as observed with the 52 MHz MST radar (ESRAD) located at Esrange (68°N, 21ºE) in northern Sweden. Together with this we will analyse infrasound measurements made at ground-based stations near Kiruna (67.5°N, 20.13ºE) and at the infrasound station IS37 (69°N, 18ºE) in Norway during these events. We discuss prospective relations between PMWE and the microbaroms that are generated by ocean swell in the North Atlantic.
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