Spring-Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall-Effect

E. L. Macotela; M. Clilverd; T. Renkwitz; J. Chau; J. Manninen; D. Banyś

doi:10.1029/2021GL094581

Spring-Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall-Effect

E. L. Macotela, M. Clilverd, T. Renkwitz, J. Chau, J. Manninen, D. Banyś

Research output: Contribution to journal › Article › peer-review

5 Citations (SciVal)

Abstract

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.

Original language	English
Article number	e2021GL094581
Number of pages	10
Journal	Geophysical Research Letters
Volume	48
Issue number	16
Early online date	30 Jul 2021
DOIs	https://doi.org/10.1029/2021GL094581
Publication status	Published - 10 Aug 2021

Bibliographical note

Funding Information:
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.

Publisher Copyright:
© 2021. The Authors.

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. 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.

Keywords

D-region
mesospheric temperature
semidiurnal solar tide
VLF propagation
VLF signal absorption

ASJC Scopus subject areas

Geophysics
General Earth and Planetary Sciences

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10.1029/2021GL094581Licence: CC BY-NC-ND

Cite this

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title = "Spring-Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall-Effect",

abstract = "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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AU - Chau, J.

AU - Manninen, J.

AU - Banyś, D.

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PY - 2021/8/10

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N2 - 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.

AB - 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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Spring-Fall Asymmetry in VLF Amplitudes Recorded in the North Atlantic Region: The Fall-Effect

Abstract

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Funding

Keywords

ASJC Scopus subject areas

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