A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space

Martinez-Calderon, Claudia; Manninen, J.; Manninen, J.; Turunen, T.

doi:10.1186/s40623-021-01516-y

Cited by 8 publications

(21 citation statements)

References 26 publications

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“…Figure 2b shows multiple VLF bursty-patches between 6 and 8 kHz observed on 9 January 2017 from 07:00 to 07:30 UT. These might correspond to the "S-shaped" emissions described in Martinez-Calderon et al (2021). However, in this study, the characteristic "S" shape was not clearly visible in all cases.…”

Section: Emission Typecontrasting

confidence: 67%

“…These might correspond to the “S‐shaped” emissions described in Martinez‐Calderon et al. (2021). However, in this study, the characteristic “S” shape was not clearly visible in all cases.…”

Section: Selection Criteriasupporting

confidence: 56%

“…This means that it is unlikely that the waves traveled long distances in the waveguide, as otherwise they would have been damped and their intensities would be much lower. Cases observed by Martinez-Calderon et al (2021) found that the signals were detected at KAN as arriving from all directions. This can only be explained if the waves arrived from directly above the KAN receiver, that is, along the KAN field line at L = 5.5.…”

Section: General Resultsmentioning

confidence: 99%

“…Previous studies of VLF bursty‐patches observed at KAN show that they had right‐handed polarization, suggesting that KAN detects these waves directly after their exit from the ionosphere (Manninen et al., 2021; Martinez‐Calderon et al., 2015a, 2021; Ozaki et al., 2008). In addition, bursty‐patches have shown to be very strong with usual wave intensities at least two orders of magnitudes greater than the background.…”

Section: Occurrence Ratesmentioning

confidence: 95%

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Statistics of Unusual Naturally Occurring VLF Radio Emissions Termed Bursty‐Patches Observed at Kannuslehto, Finland

Martinez-Calderon

Manninen

et al. 2023

JGR Space Physics

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We report the results from a statistical study of a new type of naturally occurring, but differently structured very low frequency (VLF) radio waves called “VLF bursty‐patches.” Their main characteristic is that they are detected at frequencies above the electron gyrofrequency (fce) in the equatorial plane for the L‐shell of observation. Here we use the data from the station of Kannuslehto, Finland (KAN, MLAT = 64.4°N, L = 5.5) with fce ∼ 5–6 kHz where VLF bursty‐patches are commonly detected on at least 43% of its campaign days. We analyzed all available data for 2017 (∼8 months) separating the observations by spectral type, periodicity, number of bursts, observed frequency, and accompanying usual VLF emissions at lower frequencies (f < 6 kHz). We found that the overall highest occurrence rate is in the morning sector (05–12 MLT) correlating with general VLF occurrence rate at KAN (07–13 MLT, MLT = UT + 1.5 hr). Grouping usual VLF emissions and bursty‐patches showing similar spectral features, suggests that both groups are being generated by the same mechanisms (e.g., temperature anisotropy magnetospheric plasma distribution). However, unlike the situation for usual VLF emissions, the daily occurrence of bursty‐patches did not show a clear relationship with AE index. Superposed epoch analysis of magnetic components from the Sodankylä magnetometer (∼45 km from KAN) shows that VLF bursty‐patches are detected when the horizontal component of the magnetic field shows minimum variations. This suggests that propagation to the ground of bursty‐patches is conditioned to localized low variations of magnetic activity.

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Section: Emission Typecontrasting

confidence: 67%

Section: Selection Criteriasupporting

confidence: 56%

Section: General Resultsmentioning

confidence: 99%

Section: Occurrence Ratesmentioning

confidence: 95%

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Statistics of Unusual Naturally Occurring VLF Radio Emissions Termed Bursty‐Patches Observed at Kannuslehto, Finland

Martinez-Calderon

Manninen

et al. 2023

JGR Space Physics

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“…The roles of wave-particle interactions have been studied for decades. Whistler-mode waves play important roles in scattering energetic electrons into the loss cone in the magnetosphere as well as the acceleration of radiation belt electrons [e.g., Baker, 2021;Martinez-Calderon et al, 2021]. Nonlinear wave-particle interactions between whistler-mode chorus emissions and energetic electrons have been intensively studied from the point of view of the wave generation process as well as the acceleration/scattering of energetic electrons [Omura et al, 2008[Omura et al, , 2009Katoh et al, 2018;Kitahara and Katoh, 2019;Omura, 2021;Nunn, 2021;Foster et al, 2021;Liu et al, 2021].…”

Section: Introductionmentioning

confidence: 99%

Effect of the mirror force on the collision rate due to energetic electron precipitation: Monte Carlo simulations

Katoh

Rosendahl

Ogawa

et al. 2022

Preprint

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We study the effect of the mirror force on the collision rate due to the energetic electron precipitation into the ionosphere. We develop a simulation code for the motion of energetic electrons with the mirror force to solve the variation of the pitch angle of electrons during their precipitation. In this code, a module computing the collision between precipitating energetic electrons and neutral gas using the Monte Carlo method is employed. By combining the developed modules, altitude profiles of the collision rate due to energetic electron precipitation in the keV energy range are investigated, and the effect of the mirror force acting on precipitating electrons is examined. The simulation results show that the influence of the mirror force on the altitude profile of the collision rate is significant for electrons with a high initial pitch angle, corresponding to the pitch angle close to the loss cone. The effect of the mirror force results in the broadening of the altitude profile of the collision upward due to the reflection of mirroring electrons. Simulation results for energetic electrons with kinetic energies above 100 keV show that a secondary peak near the mirror point is formed in the altitude profile of the collision rate. The formation of the secondary peak can be explained by the stagnation of electrons around the mirror point. The relatively long duration staying in neutral gas results in the increase of the collision rate around the mirror point, against the smaller collision cross-section in the higher energy range. Simulation results reveal that the maximum collision rate in the altitude range lower than 100 km becomes one order of magnitude smaller if electrons in the kinetic energy range larger than tens of keV precipitate with the pitch angle close to the loss cone. The results of the present study emphasize the importance of the mirror force for the precise modeling of ionospheric response due to the energetic electron precipitation.

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Unexpected VLF Bursty-Patches Above 5 kHz: A Review of Long-Duration VLF Series Observed at Kannuslehto, Northern Finland

et al. 2022

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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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A review of unusual VLF bursty-patches observed in Northern Finland for Earth, Planets and Space

Cited by 8 publications

References 26 publications

Statistics of Unusual Naturally Occurring VLF Radio Emissions Termed Bursty‐Patches Observed at Kannuslehto, Finland

Statistics of Unusual Naturally Occurring VLF Radio Emissions Termed Bursty‐Patches Observed at Kannuslehto, Finland

Effect of the mirror force on the collision rate due to energetic electron precipitation: Monte Carlo simulations

Unexpected VLF Bursty-Patches Above 5 kHz: A Review of Long-Duration VLF Series Observed at Kannuslehto, Northern Finland

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