University of Oulu

Manninen, J., Kleimenova, N.G., Martinez-Calderon, C. et al. Unexpected VLF Bursty-Patches Above 5 kHz: A Review of Long-Duration VLF Series Observed at Kannuslehto, Northern Finland. Surv Geophys 44, 555–581 (2023).

Unexpected VLF bursty-patches above 5 kHz : a review of long-duration VLF series observed at Kannuslehto, Northern Finland

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Author: Manninen, J.1; Kleimenova, N. G.2,3; Martinez-Calderon, C.4;
Organizations: 1Sodankylä Geophysical Observatory, University of Oulu, 99600, Sodankylä, Finland
2Schmidt Institute of Physics of the Earth RAN, Moscow, 123995, Russia
3Space Research Institute RAN, Moscow, Russia
4Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, 4648601, Japan
5Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAN, Moscow, 142191, Russia
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.5 MB)
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Language: English
Published: Springer Nature, 2023
Publish Date: 2023-05-26


Unexpected short patches of natural VLF emissions at f > 5 kHz have been observed at the ground station of Kannuslehto (KAN, L ~ 5.5) in Northern Finland. In contrast with usual VLF emissions (e.g., chorus, hiss, and quasiperiodic emissions) these high-frequency bursty-patches are observed at frequencies higher than half of the equatorial electron gyro-frequency of the L shell of KAN. Moreover, most of these waves reached frequencies above the local equatorial electron gyrofrequency at L = 5.5. Thus, they cannot be attributed to the classical theory of electron-cyclotron interaction. We present a review of VLF bursty-patches at KAN during winters 2011–2021. These emissions have rarely been observed as they are usually hidden by sferics originating from lightning discharges. Therefore, a special numeric filtering technique was used to reduce noise from sferics. VLF bursty-patches typically occur as sequences of short right-hand polarized bursts separated by a few minutes and lasting several hours. Here, we discuss the spectral structure of long-lasting bursty-patches (6 + hours) and the properties of individual patches. We established two categories: (1) “triggered-like” hiss-like bursts at f ~ 4–7 kHz with a very abrupt onset and detected under quiet geomagnetic conditions, and (2) “dash-like” emissions at f > 6 kHz that resemble narrowband hiss and observed under moderate activity. Even though VLF bursty-patches in winters 2011–2021 were observed under weak or slightly disturbed magnetic activity, their annual cyclical occurrence was similar to variations in solar activity. The nature of these VLF patches has not been established yet, but they appear to be generated at L shells lower than that of KAN. Their exact generation region and propagation behavior remain unknown, with further theoretical and experimental research being required.

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Series: Surveys in geophysics
ISSN: 0169-3298
ISSN-E: 1573-0956
ISSN-L: 0169-3298
Volume: 44
Issue: 2
Pages: 555 - 581
DOI: 10.1007/s10712-022-09741-0
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
114 Physical sciences
Funding: Open Access funding provided by University of Oulu including Oulu University Hospital. This study was funded by the Academy of Finland (Research Council for Natural Sciences and Engineering, grant number 308501).
Academy of Finland Grant Number: 308501
Detailed Information: 308501 (Academy of Finland Funding decision)
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