University of Oulu

Macotela, E. L., Clilverd, M., Renkwitz, T., Chau, J., Manninen, J., & Banyś, D. (2021). Spring-fall asymmetry in VLF amplitudes recorded in the North Atlantic region: The fall-effect. Geophysical Research Letters, 48, e2021GL094581.

Spring-fall asymmetry in VLF amplitudes recorded in the North Atlantic region : the fall-effect

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Author: Macotela, E. L.1,2; Clilverd, M.3; Renkwitz, T.2;
Organizations: 1Faculty of Mathematics and Natural Sciences, University of Rostock, Rostock, Germany
2Leibniz-Institute of Atmospheric Physics, University of Rostock, Kuehlungsborn, Germany
3British Antarctic Survey, UKRI-NERC, Cambridge, UK
4Sodanklä Geophysical Observatory, University of Oulu, Sodankyla, Finland
5Institute for Solar-Terrestrial Physics, German Aerospace Center, Neustrelitz, Germany
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.8 MB)
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Language: English
Published: American Geophysical Union, 2021
Publish Date: 2021-10-14


A spring-fall asymmetry is observed in daytime amplitude values of very low frequency (VLF) radio wave signals propagating over the North Atlantic during 2011–2019. We explore the processes behind this asymmetry by comparing against mesospheric mean temperatures and the semidiurnal solar tide (S2) in mesospheric winds. The solar radiation influence on VLF subionospheric propagation was removed from the daytime VLF amplitude values, isolating the fall-effect. Similarly, the symmetric background level was removed from mesospheric mean temperatures undertaking comparable analysis. During fall, all three analyzed parameters experience significant deviation from their background levels. The VLF amplitude variation during spring is explained by the seasonal variation in solar illumination conditions, while the fall-effect can be interpreted as a mean zonal wind reversal associated with both a S2 enhancement, and temperature reductions. Decreases in temperature can produce decreases in collision frequency, reducing VLF signal absorption, driving the observed VLF asymmetry.

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Series: Geophysical research letters
ISSN: 0094-8276
ISSN-E: 1944-8007
ISSN-L: 0094-8276
Volume: 48
Issue: 16
Article number: e2021GL094581
DOI: 10.1029/2021GL094581
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: This work is supported by "AMELIE - Analysis of the MEsosphere and Lower Ionosphere fall Effect" (DLR project D/921/67286532). The authors thank Alexander Kozlovsky for providing his insights for this research work, in particular for looking mesospheric temperature data. MAC would like to acknowledge support from the UK Research and Innovation (UKRI-NERC) through National Capability Space Weather Observatory funding (NC-SS SWO). Open access funding enabled and organized by Projekt DEAL.
Copyright information: © 2021. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.