WHISTLER-TRIGGERED VLF EMISSIONS RECORDED AT JAMMU DURING DAY TIME

Whistler-triggered VLF emissions recorded at low latitude station Jammu (Geomagnetic latitude = 220 26/ N; L = 1.17) during day time period on 19th February 1999 at 14:35 hrs. IST. The recorded data have been analyzed. Based on whistler-triggered VLF emissions spectrum, the VLF waves propagate along the path with L – values lying between L = 4.4 and 4.38. During the observation period, magnetic activity was very high. Mostly these types of emissions recorded at mid latitudes. These whistler-triggered emission waves propagate along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal mode. Relative amplitude of whistlers waves is almost equal to relative amplitude of triggered emissions. The proposed generation mechanism explains through the dynamic spectra of the whistler-triggered emissions.

Parametric Interaction of VLF and ELF Waves in the Ionosphere

In this Chapter we analyze a non-linear parametric interaction between Very Low Frequency (VLF) and Extremely Low Frequency (ELF) waves in the ionosphere. We demonstrate that nonlinear parametric coupling between quasi-electrostatic Lower Oblique Resonance (LOR) and ELF waves significantly contributes to the VLF electromagnetic whistler wave spectrum. Analytical and numerical results are compared with experimental data obtained during active space experiments and satellite data. These data clearly show that presence of VLF waves in the region of plasmasphere boundary layer, where there are no injected due to substorm/storm activity energetic electrons with energies of tens keV can strongly affect the radiation belt boundary.

Heart rate variability in cross-country skiers with different baseline heart rate

У 83 мужчин из сборных Республики Коми по лыжным гонкам с помощью комплекса «Экосан-2007» проведен анализ вариабельности сердечного ритма (ВСР) в положении лежа и стоя (ортостатическая проба). Возраст спортсменов составлял от 18 до 30 лет. Для выявления особенностей ВСР у лиц с разной исходной частотой сердечных сокращений (ЧСС) добровольцы были разделены на две группы (группа 1 - ЧСС от 40 до 55 уд/мин, n=45; группа 2 - ЧСС 56-70 уд/мин, n=38). Исходная ЧСС была измерена в покое лежа. В положении лежа у спортсменов из группы 1 статистически значимо выше значения временных показателей (RMSSD, pNN50, SDNN), абсолютная мощность VLF-волн и ниже относительная мощность LF-волн, SI, LF/HF, чем у добровольцев из группы 2. При ортостазе у мужчин из обеих групп наблюдались однонаправленные сдвиги по большинству параметров ВСР. Однако у лыжников из группы 2 также выявлен статистически значимый рост значений абсолютной мощности LF- и VLF-волн. При анализе сдвигов параметров ВСР при ортостазе у лыжников группы 2 выявлены более выраженные снижения SDNN, TP, абсолютных значений HF-, LF- и VLF-волн, при этом рост ЧСС был более выраженным у лиц из группы 1. Установлено, что на вегетативную регуляцию ритма сердца в положении лежа у мужчин из группы 1, по сравнению с добровольцами из группы 2, большее влияние оказывает парасимпатическая нервная система, при этом роль более высоких уровней регуляции снижена. Аналогичные закономерности выявлены и при ортостазе. Heart rate variability (HRV) analysis was carried out in 83 men from the national teams of the Komi Republic in cross-country skiing using the Ecosan-2007 complex in the lying and standing positions (orthostatic test). The age of the athletes ranged from 18 to 30 years old. To identify the features of HRV in individuals with different heart rates, the volunteers were divided into two groups (group 1 - heart rate from 40 to 55 beats / min, n = 45; group 2 - heart rate 56-70 beats/min, n = 38). Baseline heart rate was measured at rest lying down. In the supine position, athletes from group 1 have statistically significantly higher values of time parameters (RMSSD, pNN50, SDNN), absolute power of VLF waves and lower relative power of LF waves, SI, LF/HF, than volunteers from group 2. With orthostasis in men from both groups, unidirectional shifts in most HRV parameters were observed. However, skiers from group 2 also showed a statistically significant increase in the absolute power of LF and VLF waves. When analyzing the shifts in HRV parameters during orthostasis in skiers of group 2, more pronounced decreases in SDNN, TP, absolute values of HF-, LF- and VLF-waves were revealed, while the increase in heart rate was more pronounced in persons from group 1. It was found that the autonomic regulation of the heart rate in the supine position in men from group 1, compared with volunteers from group 2, is more influenced by the parasympathetic nervous system, while the role of higher levels of regulation is reduced. Similar patterns were found in orthostasis.

A Review of Unusual VLF Bursty-Patches Observed in Northern Finland

Using numerical filtering techniques allowing to reduce noise from sferics, we are able to clearly study a new type of differently structured very low frequency (VLF) waves above f = 4 kHz at the ground station of Kannuslehto in northern Finland (KAN, MLAT=64.4°N, L=5.5). These emissions are intriguing since they are detected above the local equatorial electron gyrofrequency for the L-shell of Kannuslehto (fce ~ 5- 6 kHz). They are commonly observed at Kannuslehto, but have also been infrequently reported at other stations, sometimes under different names. Their possible common origin and manner of propagation is still under investigation. This paper unifies the nomenclature by regrouping all these waves detected at frequencies higher than the local equatorial 0.5 fce at the L-shell of observation under the name of VLF bursty-patches. We also give a review of the different characteristics of VLF bursty-patches observed by Kannuslehto, which at the moment, is the station with the highest observation rate. We will present recent observations between 2019 and 2021. While these waves have different spectral features, they appeared mostly composed of hiss bursts with durations of a few seconds to several minutes. They also show periodic features with varying periodicity and shape. They are sometimes characterized by single bursts covering very large frequency ranges of several kHz.

Storm-Time Features of the Ionospheric ELF/VLF Waves and Energetic Electron Fluxes Revealed by the China Seismo-Electromagnetic Satellite

This study reports the temporal and spatial distributions of the extremely/very low frequency (ELF/VLF) wave activities and the energetic electron fluxes in the ionosphere during an intense storm (geomagnetic activity index Dst of approximately −174 nT) that occurred on 26 August 2018, based on the observations by a set of detectors onboard the China Seismo-Electromagnetic Satellite (CSES). A good correlation of the ionospheric ELF/VLF wave activities with energetic electron precipitations during the various storm evolution phases was revealed. The strongest ELF/VLF emissions at a broad frequency band extending up to 20 kHz occurred from the near-end main phase to the early recovery phase of the storm, while the wave activities mainly appeared at the frequency range below 6 kHz during other phases. Variations in the precipitating fluxes were also spotted in correspondence with changing geomagnetic activity, with the max values primarily appearing outside of the plasmapause during active conditions. The energetic electrons at energies below 1.5 MeV got strong enhancements during the whole storm time on both the day and night side. Examinations of the half-orbit data showed that under the quiet condition, the CSES was able to depict the outer/inner radiation belt as well as the slot region well, whereas under disturbed conditions, such regions became less sharply defined. The regions poleward from geomagnetic latitudes over 50° were found to host the most robust electron precipitation regardless of the quiet or active conditions, and in the equatorward regions below 30°, flux enhancements were mainly observed during storm time and only occasionally in quiet time. The nightside ionosphere also showed remarkable temporal variability along with the storm evolution process but with relatively weaker wave activities and similar level of fluxes enhancement compared to the ones in the dayside ionosphere. The ELF/VLF whistler-mode waves recorded by the CSES mainly included structure-less VLF waves, structured VLF quasi-periodic emissions, and structure-less ELF hiss waves. A wave vector analysis showed that during storm time, these ELF/VLF whistler-mode waves obliquely propagated, mostly likely from the radiation belt toward the Earth direction. We suggest that energetic electrons in the high latitude ionosphere are most likely transported from the outer radiation belt as a consequence of their interactions with ELF/VLF waves.

Lightning‐Generated Whistler Amplitudes Measured by the Van Allen Probes

<p>This talk will show a statistical analysis of both electric and magnetic field wave amplitudes of very low frequency lightning‐generated whistlers (LGWs) based on the equivalent of 11.5 years of observations made by the Van Allen Probes. We complement this analysis with data from the ground‐based World Wide Lightning Location Network (WWLLN) to explore differences between satellite and ground‐based measurements. We will discuss how LGW mean amplitudes were generally found to be low compared with other whistler mode waves even though there exists extreme events (1 out of 5,000) that can reach 100 pT and contribute strongly to the mean power below L = 2. We will reveal a region of low wave amplitude existing below L=2 thanks to the denser dayside ionosphere, which prevents the intense equatorial lightning VLF waves from propagating through it. Below L = 1.5 at all MLT, LGW amplitudes are found to be weak while the ground‐level lightning activity is maximal. This suggests a difficulty of lightning VLF waves to penetrate / propagate / remain at low L‐shells, certainly due at least to the denser ionosphere during daytime. On the contrary, the mean LGW magnetic power (or RMS) remains nearly constant with respect to L‐shell. We will explain that this is due to strong to extreme LGWs that dominate the wave mean power to the point of compensating the decay of LGW occurrence at low L‐shell. Even though extreme LGW were found to be very powerful, particularly at low L and during night, the mean electric/magnetic power remains low compared with other whistler waves. This implies that LGW resonant effects on electrons are consequently long‐term effects that contribute to “age” trapped inner belt electron populations.</p>

A Novel Method to Identify the Physical Mechanism and Source Region of ELF/VLF Waves Generated by Beat-Wave Modulation Using Preheating Technique

One of the most important effects of ionospheric heating by HF (high-frequency) waves is the generation of ELF/VLF (extremely low-frequency/very low-frequency) waves by modulated heating. An important limitation of amplitude modulation (AM) is its dependence on ionospheric electrojet, which means to achieve better modulation effect, some strict spatio-temporal conditions must be met. To solve this problem, some possible methods have been proposed including beat-wave (BW) modulation. However, due to the controversy of its mechanism and the source region of the stimulated ELF/VLF waves, it is not clear whether it is an electrojet-independent method or not, which has become one of the hot topics in recent years. In this paper, we found that the effect of preheating on modulation efficiency of BW based on different theories is the opposite. We suppose the opposite character of the influence and effect on the efficiency of BW in D region and F region as a base for a novel method to identify the physical mechanism and source region of BW. This method can be feasible to solve the controversy of BW. The feasibility of this method is verified by simulation results in the paper.