Statistical characteristics of ionospheric hiss waves

In this study, we use the observations of electromagnetic waves by DEMETER satellite to investigate propagation characteristics of low altitude ionospheric hiss. In an event study, intense hiss wave power is concentrated over a narrow frequency band with a central frequency that decreases as latitude decreases, which coincides to the variation of local proton cyclotron frequency fCH. The wave propagates obliquely to the background magnetic field and equatorward from high latitude region. We use about 6 years' observations to statistically study the dependence of ionospheric hiss wave power on location, local time, geomagnetic activity and season. The results demonstrate that the ionospheric hiss power is stronger on the dayside, under higher geomagnetic activity, in local summer and confined near the region where the local fCH is equal to the wave frequency. To explain the concentration of wave power, a ray tracing simulation is performed and reproduced the wave propagation process

Source of the low-altitude hiss in the ionosphere

We analyze the propagation properties of low-altitude hiss emission in the ionosphere observed by DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions). There exist two types of low-altitude hiss: type I emission at high latitude is characterized by vertically downward propagation and broadband spectra, while type II emission at low latitude is featured with equatorward propagation and a narrower frequency band above ∼fcH+. Our ray tracing simulation demonstrates that both types of the low-altitude hiss at different latitude are connected and they originate from plasmaspheric hiss and in part chorus emission. Type I emission represents magnetospheric whistler emission that accesses the ionosphere. Equatorward propagation associated with type II emission is a consequence of wave trapping mechanisms in the ionosphere. Two different wave trapping mechanisms are identified to explain the equatorial propagation of Type II emission; one is associated with the proximity of wave frequency and local proton cyclotron frequency, while the other occurs near the ionospheric density peak

Seismo-ionospheric anomalies in ionospheric TEC and plasma density before the 17 July 2006 M 7.7 south of Java earthquake

Abstract. In this paper, we report significant evidence for preseismic ionospheric anomalies in total electron content (TEC) of the global ionosphere map (GIM) and plasma density appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. After distinguishing other anomalies related to the geomagnetic activities, we found a temporal precursor around the epicenter on day 2 before the earthquake (15 July 2006), which agrees well with the spatial variations in latitude–longitude–time (LLT) maps. Meanwhile, the sequences of latitude–time–TEC (LTT) plots reveal that the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator in the daytime from day 2 before the earthquake. This anomalous asymmetric structure disappears after the earthquake. To further confirm these anomalies, we studied the plasma data from DEMETER satellite in the earthquake preparation zone (2046.4 km in radius) during the period from day 45 before to day 10 after the earthquake, and also found that the densities of both electron and total ion in the daytime significantly increase on day 2 before the earthquake. Very interestingly, O+ density increases significantly and H+ density decreases, while He+ remains relatively stable. These results indicate that there exists a distinct preseismic signal (preseismic ionospheric anomaly) over the epicenter

Possible Lithosphere-Atmosphere-Ionosphere Coupling effects prior to the 2018 Mw = 7.5 Indonesia earthquake from seismic, atmospheric and ionospheric data

In this study, we analyse Lithosphere Atmosphere Ionosphere Coupling (LAIC) effects to identify some phenomena that could, possibly, be linked to the preparation phase of the MW=7.5 earthquake occurred in Indonesia on September 28th, 2018, by investigating the eight months preceding the seismic event. First, we find a seismic acceleration that started two months before the mainshock. Then, studying some physical properties of the atmosphere (skin temperature, total column water vapor and aerosol optical thickness), we find two increases of atmospheric anomalies about 6 and 3.7 months before the mainshock, and the latter one is very promising as a candidate for seismic-related phenomena. Furthermore, we investigate ionospheric disturbances, by analysing the Swarm and, for the first time, China Seismo-Electromagnetic Satellite (CSES), magnetic and electron density data during quiet geomagnetic time. From different techniques, we find interesting anomalies concentrated around 2.7 months before the mainshock. On August 19th, 2018, Swarm and CSES showed an enhancement of the electron density during night time. We critically discuss the possibility that such phenomenon can be a possible pre-seismic-induced ionospheric effect. Finally, we performed a cumulative analysis using all detected anomalies, as a test case for a possible chain of physical phenomena that could happen before the earthquake occurrence. With this study, we support the usefulness to collect and store large Earth ground and satellite observational dataset that in the future could be useful to monitor in real time the seismic zones to anticipate earthquakes, although nowadays, there is no evidence about useful prediction capabilities.Published1040972A. Fisica dell'alta atmosferaJCR Journa

Observations of discrete magnetosonic waves off the magnetic equator

Fast mode magnetosonic waves are typically confined close to the magnetic equator and exhibit harmonic structures at multiples of the local, equatorial proton cyclotron frequency. We report observations of magnetosonic waves well off the equator at geomagnetic latitudes from −16.5°to −17.9° and L shell ~2.7–4.6. The observed waves exhibit discrete spectral structures with multiple frequency spacings. The predominant frequency spacings are ~6 and 9 Hz, neither of which is equal to the local proton cyclotron frequency. Backward ray tracing simulations show that the feature of multiple frequency spacings is caused by propagation from two spatially narrow equatorial source regions located at L ≈ 4.2 and 3.7. The equatorial proton cyclotron frequencies at those two locations match the two observed frequency spacings. Our analysis provides the first observations of the harmonic nature of magnetosonic waves well away from the equatorial region and suggests that the propagation from multiple equatorial sources contributes to these off-equatorial magnetosonic emissions with varying frequency spacings

A multi-parametric and multi-layer study to investigate the largest 2022 Hunga Tonga–Hunga Ha’apai eruptions

On 20 December 2021, after six quiet years, the Hunga Tonga-Hunga Ha'apai volcano erupted abruptly. Then, on 15 January 2022, the largest eruption produced a plume well registered from satellites and destroyed the volcanic cone previously formed in 2015, connecting the two islands. We applied a multi-parametric and multi-layer study to investigate all the possible pre-eruption signals and effects of this volcanic activity in the lithosphere, atmosphere, and ionosphere. We focused our attention on: (a) seismological features considering the eruption in terms of an earthquake with equivalent energy released in the lithosphere; (b) atmospheric parameters, such as skin and air temperature, outgoing longwave radiation (OLR), cloud cover, relative humidity from climatological datasets; (c) varying magnetic field and electron density observed by ground magnetometers and satellites, even if the event was in the recovery phase of an intense geomagnetic storm. We found different precursors of this unique event in the lithosphere, as well as the effects due to the propagation of acoustic gravity and pressure waves and magnetic and electromagnetic coupling in the form of signals detected by ground stations and satellite data. All these parameters and their detailed investigation confirm the lithosphere-atmosphere-ionosphere coupling (LAIC) models introduced for natural hazards such as volcano eruptions and earthquakes

Gamma-Ray Burst observations by the high-energy charged particle detector on board the CSES-01 satellite between 2019 and 2021

In this paper we report the detection of five strong Gamma-Ray Bursts (GRBs) by the High-Energy Particle Detector (HEPD-01) mounted on board the China Seismo-Electromagnetic Satellite (CSES-01), operational since 2018 on a Sun-synchronous polar orbit at a $\sim$ 507 km altitude and 97$^\circ$ inclination. HEPD-01 was designed to detect high-energy electrons in the energy range 3 - 100 MeV, protons in the range 30 - 300 MeV, and light nuclei in the range 30 - 300 MeV/n. Nonetheless, Monte Carlo simulations have shown HEPD-01 is sensitive to gamma-ray photons in the energy range 300 keV - 50 MeV, even if with a moderate effective area above $\sim$ 5 MeV. A dedicated time correlation analysis between GRBs reported in literature and signals from a set of HEPD-01 trigger configuration masks has confirmed the anticipated detector sensitivity to high-energy photons. A comparison between the simultaneous time profiles of HEPD-01 electron fluxes and photons from GRB190114C, GRB190305A, GRB190928A, GRB200826B and GRB211211A has shown a remarkable similarity, in spite of the different energy ranges. The high-energy response, with peak sensitivity at about 2 MeV, and moderate effective area of the detector in the actual flight configuration explain why these five GRBs, characterised by a fluence above $\sim$ 3 $\times$ 10$^{-5}$ erg cm$^{-2}$ in the energy interval 300 keV - 50 MeV, have been detected.Comment: Accepted for publication in The Astrophysical Journal (ApJ