New contributions on VLF radio wave perturbations measured at high-latitudes
Abstract The Earth-ionosphere system behaves as a waveguide for the propagation of very low frequency (VLF) radio waves. If in this system the electrical conductivity of its boundaries is disturbed, the propagation of VLF waves is also disrupted, which is observed as phase and amplitude variations o...
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ftunivoulu:oai:oulu.fi:isbn978-952-62-2570-8 2023-07-30T04:05:50+02:00 New contributions on VLF radio wave perturbations measured at high-latitudes Macotela Cruz, E. L. (Edith Liliana) Manninen, J. (Jyrki) Turunen, T. (Tauno) 2020-04-15 application/pdf http://urn.fi/urn:isbn:9789526225708 eng eng University of Oulu info:eu-repo/semantics/altIdentifier/pissn/1456-3673 info:eu-repo/semantics/openAccess © University of Oulu, 2020 D-region forcing factors VLF emissions VLF propagation ionospheric disturbances ozone shadowing D-alueen pakotustekijät VLF-emissiot VLF-leviäminen ionosfäärin häiriöt otsonivarjostus info:eu-repo/semantics/doctoralThesis info:eu-repo/semantics/publishedVersion 2020 ftunivoulu 2023-07-08T19:57:20Z Abstract The Earth-ionosphere system behaves as a waveguide for the propagation of very low frequency (VLF) radio waves. If in this system the electrical conductivity of its boundaries is disturbed, the propagation of VLF waves is also disrupted, which is observed as phase and amplitude variations of VLF waves with respect to their quiescent levels. There is a diversity of physical phenomena that are able to alter significantly the conductivity of the upper boundary. These phenomena can have their origin at the Earth (e.g., lightning), in the solar system (e.g., solar flares) or even much farther away (e.g., galactic gamma-ray bursts). The aim of this thesis is to study short- and long-term VLF variations measured in Northern Finland (at the Sodankylä Geophysical Observatory) and their associations to different phenomena. The main results are as follows: [i] The minimum energy a solar flare should have in order to produce ionospheric disturbances depends on the solar cycle. This energy is understood as the ionospheric sensitivity and for daytime conditions its value lies in the range (1–12) × 10⁻⁷ J/m². [ii] The semiannual oscillation that appears in VLF measurements was determined to be related to geomagnetic activity variations. At the same time, it was found that the 27-day solar rotation oscillation is dominant during the declining phase of the solar cycle. [iii] The main characteristics of the observed VLF sunrise phase perturbation are derived from the shadowing of short wavelength solar UV radiation due to stratospheric ozone absorption when the Sun rises. [iv] VLF emissions with banded structure were observed in the 16–39 kHz frequency range, which are frequencies not usually used for the study of whistler mode VLF emissions coming from the magnetosphere. All these results are important since the VLF signals are related to variations of electron density in the ionospheric D-region, and thus have been used to identify the processes that influence the behavior of the upper atmosphere. The mentioned results ... Doctoral or Postdoctoral Thesis Northern Finland Sodankylä Jultika - University of Oulu repository Sodankylä ENVELOPE(26.600,26.600,67.417,67.417) |
institution |
Open Polar |
collection |
Jultika - University of Oulu repository |
op_collection_id |
ftunivoulu |
language |
English |
topic |
D-region forcing factors VLF emissions VLF propagation ionospheric disturbances ozone shadowing D-alueen pakotustekijät VLF-emissiot VLF-leviäminen ionosfäärin häiriöt otsonivarjostus |
spellingShingle |
D-region forcing factors VLF emissions VLF propagation ionospheric disturbances ozone shadowing D-alueen pakotustekijät VLF-emissiot VLF-leviäminen ionosfäärin häiriöt otsonivarjostus Macotela Cruz, E. L. (Edith Liliana) New contributions on VLF radio wave perturbations measured at high-latitudes |
topic_facet |
D-region forcing factors VLF emissions VLF propagation ionospheric disturbances ozone shadowing D-alueen pakotustekijät VLF-emissiot VLF-leviäminen ionosfäärin häiriöt otsonivarjostus |
description |
Abstract The Earth-ionosphere system behaves as a waveguide for the propagation of very low frequency (VLF) radio waves. If in this system the electrical conductivity of its boundaries is disturbed, the propagation of VLF waves is also disrupted, which is observed as phase and amplitude variations of VLF waves with respect to their quiescent levels. There is a diversity of physical phenomena that are able to alter significantly the conductivity of the upper boundary. These phenomena can have their origin at the Earth (e.g., lightning), in the solar system (e.g., solar flares) or even much farther away (e.g., galactic gamma-ray bursts). The aim of this thesis is to study short- and long-term VLF variations measured in Northern Finland (at the Sodankylä Geophysical Observatory) and their associations to different phenomena. The main results are as follows: [i] The minimum energy a solar flare should have in order to produce ionospheric disturbances depends on the solar cycle. This energy is understood as the ionospheric sensitivity and for daytime conditions its value lies in the range (1–12) × 10⁻⁷ J/m². [ii] The semiannual oscillation that appears in VLF measurements was determined to be related to geomagnetic activity variations. At the same time, it was found that the 27-day solar rotation oscillation is dominant during the declining phase of the solar cycle. [iii] The main characteristics of the observed VLF sunrise phase perturbation are derived from the shadowing of short wavelength solar UV radiation due to stratospheric ozone absorption when the Sun rises. [iv] VLF emissions with banded structure were observed in the 16–39 kHz frequency range, which are frequencies not usually used for the study of whistler mode VLF emissions coming from the magnetosphere. All these results are important since the VLF signals are related to variations of electron density in the ionospheric D-region, and thus have been used to identify the processes that influence the behavior of the upper atmosphere. The mentioned results ... |
author2 |
Manninen, J. (Jyrki) Turunen, T. (Tauno) |
format |
Doctoral or Postdoctoral Thesis |
author |
Macotela Cruz, E. L. (Edith Liliana) |
author_facet |
Macotela Cruz, E. L. (Edith Liliana) |
author_sort |
Macotela Cruz, E. L. (Edith Liliana) |
title |
New contributions on VLF radio wave perturbations measured at high-latitudes |
title_short |
New contributions on VLF radio wave perturbations measured at high-latitudes |
title_full |
New contributions on VLF radio wave perturbations measured at high-latitudes |
title_fullStr |
New contributions on VLF radio wave perturbations measured at high-latitudes |
title_full_unstemmed |
New contributions on VLF radio wave perturbations measured at high-latitudes |
title_sort |
new contributions on vlf radio wave perturbations measured at high-latitudes |
publisher |
University of Oulu |
publishDate |
2020 |
url |
http://urn.fi/urn:isbn:9789526225708 |
long_lat |
ENVELOPE(26.600,26.600,67.417,67.417) |
geographic |
Sodankylä |
geographic_facet |
Sodankylä |
genre |
Northern Finland Sodankylä |
genre_facet |
Northern Finland Sodankylä |
op_relation |
info:eu-repo/semantics/altIdentifier/pissn/1456-3673 |
op_rights |
info:eu-repo/semantics/openAccess © University of Oulu, 2020 |
_version_ |
1772818103788371968 |