Optical measurements of precipitating relativistic electron microbursts during geomagnetic disturbance and pulsating aurora

Abstract. Using the NORSTAR riometer and CANOPUS magnetometer arrays we have investigated the modulation of high energy electron precipitation by ULF waves in the Pc5 frequency band. We conducted two separate studies of Pc5 activity in the riometers. The first is an independent survey of three riometer stations in the Churchill line (one at each sub-auroral, auroral, and typical polar cap boundary latitudes) in which we identified all riometer Pc5-band pulsations over 11 years. All had a corresponding magnetometer pulsation implying that a magnetic pulsation, is a necessary condition for a riometer pulsation (in the Pc5 Band). We find seasonal and latitude dependencies in the occurrence of riometer pulsations. By a factor of two, there are more riometer pulsations occurring in the fall-winter than the spring-summer. At higher latitudes there is a tendency towards noon pulsations during the spring-summer, suggesting that the criteria for riometer pulsations is affected by the dipole tilt. Our second study was based on the previous magnetometer study of Baker et al. (2003). Using the database of Pc5 activity from that study we were able to select the riometer Pc5 pulsations which adhere to the strict Pc5 definition in the magnetometer. We find that roughly 95% of the riometer pulsations occurred in the morning sector compared to 70% in the magnetometer. Given a magnetometer pulsation at Gillam in the morning sector, there is a 70% chance of there being a corresponding riometer pulsation. The morning sector probabilities at Rankin (geomagnetic (PACE) latitude 74°) and Pinawa (61°) are 3% and 5%, respectively. These statistics suggest there is a localized region in the pre-noon magnetosphere where Pc5 band ULF activity can modulate high energy electron precipitation. We also find that riometer pulsations display a Kp selection towards mid (i.e. 3–4) activity levels which mimics the product of the Kp dependence of high-energy electron fluxes on the dawn side (from CRRES) and all magnetic Pc5 activity. A superposed epoch analysis revealed that the elevated electron flux needed to produce a riometer pulsation is most likely provided by substorm injections on the nightside. We also find that the amplitude of modulated precipitation correlates well with the product of the background absorption and the magnetic pulsation amplitude, again leading to the idea that a riometer pulsation needs both favorable magnetospheric electron flux conditions and large enough magnetic Pc5 wave activity. We further separate our pulsations into field line resonances (FLRs), and non-field line resonances (non-FLRs), as identified in the Baker et al. (2003) survey. We find that FLRs are more efficient at modulating particle precipitation, and non-FLRs display an amplitude cutoff below which they do not interact with the high energy electron population. We conclude that the high energy electron precipitation associated with Pc5 pulsations is caused by pitch angle scattering (diffusion) rather than parallel acceleration. We suggest two future studies that are natural extensions of this one. Keywords. Energetic Particles/Precipitating; Wave-Particle Interactions; Auroral Phenomena

Statistical characteristics of medium-latitude VLF emissions (unstructured and structured): Local time dependence and the association with geomagnetic disturbances

Interplay between the Amplitudes of VLF Transmitter Signals and High-Energy Electron Precipitation during Geomagnetic Disturbances

High-energy electron precipitation in the high latitude regions enhances the ionization of the atmosphere, and subsequently increases the atmospheric conductivities and the vertical electric field of the atmosphere near the ground as well. The High-Energy Electron Flux (HEEF) data measured by the Fengyun-3 meteorological satellite are analyzed together with the data of near-surface atmospheric vertical electric field measured at the Russian Vostok Station. Three HEEF enhancements are identified and it is shown that when the HEEF increases to a certain level, the local atmospheric vertical electric field near the ground can increase substantially than usual. The response time of the electric field to HEEF enhancement is about 3.7 to 4 days.

It was shown recently that cyclotron instability in non-equilibrium plasma of a minimum-B electron cyclotron resonance ion source (ECRIS) causes perturbation of the extracted ion current and generation of strong bursts of bremsstrahlung emission, which limit the performance of the ion source. The present work is devoted to the dynamic regimes of plasma instability in ECRIS operated in pulsed mode. Instability develops in decaying plasma shortly after heating microwaves are switched off and manifests itself in the form of powerful pulses of electromagnetic emission associated with precipitation of high energy electrons. Time-resolved measurements of microwave emission bursts are presented. It was found that even in various gases (helium and oxygen were studied) and at different values of magnetic field and heating power, the dynamic spectra demonstrate common features: decreasing frequency within a single burst as well as from one burst to another.

The eastward electrojet in the dawn sector

Morphology of electron precipitation during auroral substorms

Modulated high frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low frequency (ELF)/very low frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency artificially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ∼ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval (Δf) of the discrete, multi-frequency waves. We find that there is a threshold value of Δf for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to Δf (proportional to the frequency components Nw) when Δf is below the threshold value but it remains unchanged with increasing Δf when Δf is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ‘effective frequency band’. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.

Based on measurements of magnetospheric electron fluxes with energies > 2 MeV in geostationary orbits, solar wind (SW) velocity, and geomagnetic activity for the period 1995–2023, a catalog of electron flux enhancements (with fluence exceeding 108 particles∙cm−2∙st−1∙day−1) has been compiled. For the events of this catalog, interplanetary disturbances have been determined, after which high-energy electron fluxes (HEEF) begin to increase, and their solar sources have been established. It is found that in 97.2 per cent of cases, one of the solar sources of interplanetary disturbances that led to electron flux increases were high-speed streams from coronal holes (HSSs from CHs), in particular only HSSs from CHs were observed in 52.5 per cent of events, and in the remaining cases, HSSs from CHs were observed together with coronal mass ejections (CMEs) after solar flares and/or filaments disappearance. The average behavior of the HEEF, SW velocity and geomagnetic activity indices for events associated with the arrival of an HSS from CH to the Earth is obtained. It is shown that electron flux enhancements events associated with interplanetary disturbances from HSSs from CHs and from CMEs differ in duration and maximum electron fluence.

The paper is concerned with the dynamic regimes of cyclotron instabilities in non-equilibrium plasma of a minimum-B electron cyclotron resonance ion source operated in pulsed mode. The instability appears in decaying ion source plasma shortly (1–10 ms) after switching off the microwave radiation of the klystron, and manifests itself in the form of powerful pulses of electromagnetic emission associated with precipitation of high-energy electrons along the magnetic field lines. Recently it was shown that this plasma instability causes perturbations of the extracted ion current, which limits the performance of the ion source and generates strong bursts of bremsstrahlung emission. In this article we present time-resolved diagnostics of electromagnetic emission bursts related to cyclotron instability in the decaying plasma. The temporal resolution is sufficient to study the fine structure of the dynamic spectra of the electromagnetic emission at different operating regimes of the ion source. It was found that at different values of magnetic field and heating power the dynamic spectra demonstrate common features: Decreasing frequency from burst to burst and an always falling tone during a single burst of instability. The analysis has shown that the instability is driven by the resonant interaction of hot electrons, distributed between the electron cyclotron resonance (ECR) zone and the trap center, with slow extraordinary wave propagation quasi-parallel with respect to the external magnetic field.

The aim of the study was to identify the impact of natural (geomagnetic disturbances), socioeconomic and man-made factors on mortality from cardiovascular diseases (CVD) in Northwestern Russia. Data from 9057 CVD deaths in Kirovsk town (Kola Peninsula, 67.6 N, 33.7 E) were analyzed with respect to seasons of the year from 1948 to 2010. Total male CVD deaths showed three significant peaks in May, September and winter. The May maximum was dominant for all males, except for the oldest age (≥70 years) group and seemed to be caused by emotional and physical effects of increased hormones in spring. Total female CVD deaths showed two significant maxima in autumn and winter and one insignificant spring peak. Seasonal distribution of the moderate (50<Ap<100 nT) magnetic had a bimodal pattern with spring and autumn peaks. This bimodal pattern of seasonal variation is also present in the female and male oldest age (≥70 years) groups. Multi-Taper-Method (MTM) spectral analysis revealed periods of ~9-10 years, ~4.7 years and ~2.3 years at confidence level of ≥90%. These periods seem to coincide with the main cycles of variations of the aa-index of geomagnetic activity. There is no significant association of air pollution and CVD mortality at the region.

The mechanism for the formation of the polar wall of the main ionospheric dip in the electron density in the ionospheric F region has been studied. The dynamics of this wall has also been studied. A model has been developed for the precipitation of high-energy electrons in the auroral oval. This model works at an arbitrary level of geomagnetic activity. A theoretical model of the high-latitude ionosphere is used to calculate the electron density at the maximum of the F2 layer for Kp=0 and 5. As the geomagnetic activity increases to Kp=5, the polar wall of the dip shifts about 7° toward the equator. This shift is confirmed by experimental data. The model describes the experimentally established fact that the changes which occur in the gradient of the electron density at the polar wall of the dip upon a change in the level of geomagnetic activity are small. The results of the model-based calculations are compared with data from the network of vertical radiosonde stations. A qualitative and quantitative agreement is demonstrated.

The interaction of artificial and natural electron beams with the ionosphere and magnetosphere has been observed to give rise to a rich variety of phenomena. Most of the work on this topic has concentrated on the interaction of a beam with the ambient thermal plasma, on plasma wave generation near a beam source, etc. Relatively little attention has been paid to the effects of a beam on the distant magnetosphere, and on high energy particles. This paper will discuss two observations in which an electron beam apparently stimulated the precipitation of high energy electrons from the deep magnetosphere. These observations were made by the UH Group in conjunction with two active magnetospheric experiments, the first Araks experiment on January 26, 1975 (Roeder et al., 1980 (paper 1)) and the Trigger experiment on February 11, 1977. (Bering, et al., 1980 (paper 2)). In both cases, the data were obtained from rocket-boosted, parachute-borne X ray bremsstrahlung detectors which were initially deployed of an altitude of 80 km near the foot of the flux tubes affected by each experiment.

Spectra of high energy electron precipitation and atmospheric ionization rates retrieval from balloon measurements.

High-energy electron fluxes derived from EISCAT electron density profiles