Explore the vast range of titles available.

Plasmaspheric hiss plays an important role in radiation belt electron dynamics, and its excitation and propagation have long attracted attention. During a substorm, Van Allen Probe B observed the disappearance of plasmaspheric hiss at the magnetic dip, which was driven by the injection of energetic protons. The perpendicular (to the magnetic field) components of both the wave vector and Poynting vector were directed mainly radially outward. We analyzed the event from two perspectives: excitation and propagation. The growth rate of plasmaspheric hiss remained below the threshold both inside and outside the dip, indicating that the waves were not locally excited. Regarding propagation, theoretical calculations suggest that the observed whistler‐mode hiss waves were reflected by the magnetic dip in a broad frequency range. Our results indicate the important role that the magnetic structures play in the propagation of plasmaspheric hiss.

Plasmaspheric plume hiss plays a crucial role in shaping Earth's electron radiation belts and influencing magnetosphere–ionosphere energy coupling. However, its generation mechanism remains contested between cyclic‐linear and localized‐nonlinear models. By analyzing over 64,000 high‐resolution plume hiss wave segments from the Van Allen Probes (1 January 2013–31 July 2019), we identify a distinct frequency dependence in their latitudinal distributions of directionality and amplitude. For high‐frequency hiss, bidirectional propagation is sharply confined near the magnetic equator, beyond which poleward‐propagating waves overwhelmingly dominate, and the wave amplitude increases obviously with latitude. These signatures are consistent with a rapid, single‐pass, equatorially confined, nonlinear amplification process. In contrast, low‐frequency hiss exhibits a high prevalence and wide latitudinal extension of bidirectional propagation, with relatively smooth amplitude variations. This pattern supports a generation scenario involving slower growth, potentially linear or nonlinear, that is coupled with wave bounce motion along magnetic field lines.

The plasmapause is the outer boundary of the plasmasphere and plays a crucial role in the propagation of plasma waves. We statistically investigate the relationship between the distribution of banded hiss and plasmapause locations. Wave power distributions of banded hiss are analyzed in terms of two ways: (a) the distance away from the plasmapause (ΔL) and (b) the equatorial distance away from the Earth. Statistical results show both bands of banded hiss have larger wave powers and occurrence rates near the plasmapause. The frequencies of two banded hiss waves both decrease discernably with increasing L‐shell at most magnetic local time sectors and geomagnetic activities, but remain nearly constant with increasing ΔL. The highly consistent distribution suggests both bands may be generated in the plume region. The correlation between banded hiss waves and plasmapause locations sheds new light on the generation mechanisms of banded hiss waves. Plain Language Summary Plasmaspheric hiss is a whistler‐mode emission with a broad frequency range from ∼20 Hz to several kHz. The wave is generally observed inside the dayside plasmasphere and plumes. Hiss wave powers are modulated by the combining effect of many parameters such as L (the distance of observation away from the Earth), MLT (magnetic local time), geomagnetic activities, and plasmapause locations. Owing to the difference in electron density inside and outside the plasmapause, the chorus may be damped when propagating into the plasmasphere, and hiss waves in the plasmasphere can be reflected when they propagate near the plasmapause. Recently, A new banded structure of hiss has been reported with a lower band below ∼100 Hz and an upper band above ∼200 Hz. Using ∼7 years measurements of Van Allen Probes, we statistically investigate the distribution of banded hiss wave power with respect to the plasmapause location. The L, MLT, and geomagnetic activities are also considered. Our results suggest that banded hiss wave power shows a strong correlation with the location of plasmapause. Banded hiss waves closer to the plasmapause show larger powers. Plasmapause‐sorted banded hiss wave power can be used to better understand the generation and propagation mechanisms of banded hiss. Key Points The intensity distributions of banded hiss with plasmapause locations at different MLTs under various geomagnetic levels are investigated In statistics, the frequencies of two banded hiss waves decrease discernably with increasing L, but remain nearly constant with ΔL Banded hiss waves with larger amplitudes usually occur close to the plasmapause, implying both bands may be generated in the plume

This manuscript utilizes the global survey of electron precipitation due to chorus and hiss waves based on waves and electron flux measurements made by Van Allen Probes. To analyze the loss‐cone precipitation presented in these papers, we compared electron energy fluxes and their mean energies entering the ionospheric altitudes on the global scale based on UCLA Full Diffusion (UCLA code) and NASA SuperThermal ElecTrons codes and reveal the role of magnetosphere‐ionosphere‐atmosphere (MIA) energy interplay in the formation these values. This information is used for calculation of height‐integrated ionospheric conductance in the presence of both hiss and chorus waves activities involving in electron precipitation of energy fluxes. MIA coupling phenomena increases Pederson and Hall conductance up to factors of 2–2.3 and 1.7–1.9, correspondingly. Plain Language Summary Whistler‐mode chorus and hiss waves are two major modes of electromagnetic plasma waves in the Earth's inner magnetosphere. These waves play the major role in the pitch angle scattering of electrons in Earth's magnetosphere, provide the major precipitating energy input to the ionosphere, lead to diffuse aurora and enhance the energy fluxes into the ionosphere. The contribution of these waves in the calculation of height‐integrated ionospheric conductance is non‐linear and requires specific treatment of their total energy fluxes and their mean energies when considering the MIA energy interplay with participation of two magnetically conjugate northern and southern hemispheres. We combine the simulation techniques of magnetospheric precipitation and MIA coupling codes to quantify the wave‐driven precipitation and impacts on ionospheric conductance. Our study demonstrates the enhanced electron precipitation impacts due to chorus and hiss waves when the MIA coupling processes are considered, compared to the previous modeling results which only consider the energy input from the magnetosphere to the ionosphere. Key Points UCLA and NASA SuperThermal ElecTrons codes in the estimation of loss‐cone electron precipitation The role of MIA energy interplay in the calculation of height‐integrated ionospheric conductance Height‐integrated ionospheric conductance in the presence of both hiss and chorus waves

We present a novel method to quantify the event‐specific spatial evolution of plasmaspheric hiss wave power using a Drift‐Diffusion model. Constrained by Polar Operational Environmental Satellites/Meteorological Operational Satellites data, the model simulates low‐altitude electron distributions, accounting for azimuthal drift, pitch‐angle diffusion, and atmospheric backscatter. Applying to an event on 15 October 2016, the model quantifies the spatial evolution of hiss waves at L = 3.9, which contributes to the steady decay of electron flux observed by Van Allen Probes (VAPs). The model reproduces local‐time dependent features and shows excellent agreement with hiss wave power observed by VAPs. The model shows increased wave power and spatial spread following increased activities in the AL‐index, consistent with previous statistical results. The model also suggests the presence of “low”‐frequency hiss, which was undetected by VAPs, likely masked by instrument noise. This is the first time low‐altitude measurements are used to quantify event‐specific wave distributions which include both diffusion and drift effects. Plain Language Summary We present a novel method to estimate the location and strength of plasmaspheric hiss waves in the Earth's magnetosphere during specific events. These waves play a critical role in shaping the dynamics of Earth's radiation belts by scattering energetic electrons into the atmosphere. However, directly measuring these waves everywhere in the magnetosphere is unfeasible given the inherent limited coverage of satellites. Our approach uses a Drift‐Diffusion model, a physics‐based simulation on how electrons behave in the presence of these waves, and through iteratively best‐fitting model to observations from Polar Operational Environmental Satellites/Meteorological Operational Satellites, we can quantify the free parameters in the model, such as wave power and its location. The model shows remarkable agreement with hiss wave observations from Van Allen Probes (VAPs) during an event on 15 October 2016. It also shows how the waves intensify and spread following increases in AL‐index activity, consistent with past statistical studies. The model also suggests the presence of “low”‐frequency hiss waves, though they were not detected by VAPs, likely due to instrument noise. This method provides a powerful tool to study wave activity in areas where direct measurements are unavailable. Key Points A novel method using a Drift‐Diffusion model constrained by Polar Operational Environmental Satellites/Meteorological Operational Satellites data estimates the event‐specific spatial evolution of wave power The model reveals increase in hiss wave power and spatial spread during high AL activity, consistent with previous statistical results The model suggests the presence of low‐frequency hiss waves during the event, though they were not observed by Van Allen Probes

Plasmaspheric hiss waves play a key role in scattering energetic electrons and are often modeled in the inner magnetosphere using empirical hiss power maps parameterized by L shell. In this study, we compare the dependence of hiss power on both L shell (2 ≤ L ≤ 6) and the ratio of electron plasma frequency to electron gyrofrequency (ωpe/Ωce) using observations from the Van Allen Probes. The statistical comparison spans a wide range of magnetic local times, frequency bands, and substorm activity levels. Hiss power shows a stronger correlation with ωpe/Ωce than with L shell, especially at low frequencies and during periods of enhanced substorm activity. These results indicate that ωpe/Ωce is a more physically meaningful parameter for describing plasmaspheric hiss and should be considered in radiation belt modeling. Plain Language Summary Plasmaspheric hiss waves are a type of electromagnetic wave in the inner magnetosphere, named for the hiss sound when converted to audio. These waves are mainly found in the plasmasphere and play a critical role in regulating the radiation belts. By scattering high‐energy electrons through wave‐particle interactions, plasmaspheric hiss contributes to the loss of electrons to the atmosphere and the formation of the slot region, a low‐radiation zone between the inner and outer belts. In this study, we use observations from NASA's Van Allen Probes to investigate how hiss wave intensity varies with both L shell and local plasma conditions. In particular, we examine the ratio of electron plasma frequency to electron gyrofrequency, which reflects electron density and magnetic field strength. Our analysis shows that hiss wave power is more strongly related to the frequency ratio than to the L shell, especially at lower frequencies and during enhanced substorm activity. These results hold significant implications, challenging the adequacy of current magnetospheric models that primarily consider radial distance as their fundamental organizing parameter. Key Points The first statistical comparison of hiss wave power dependence on L shell and ωpe/Ωce is performed Hiss wave power correlates more strongly with ωpe/Ωce than with L shell or ne The ωpe/Ωce dependence is strongest at low frequencies and during enhanced substorm activity

Plasmaspheric hiss waves are important to shape the Earth’s electron radiation belt. These waves are commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. However, this hypothesis has not been experimentally confirmed yet, because of the challenging observational requirements in terms of location and timing. With wave and particle measurements from five magnetospheric satellites and detailed modeling, we present the first report of long lifetime (∼42 s) hiss rays in the substorm‐disturbed plasmasphere. The low‐frequency hiss waves are found to originate from the middle piece of the plasmaspheric plume, bounce between two hemispheres, and eventually drift into the plasmaspheric core. These hiss rays can travel through ∼3 hr magnetic local time and ∼4 magnetic shell. Such a long‐time and large‐scale permeation of hiss rays could benefit from the ducting process by plasmaspheric field‐aligned density irregularities. Plain Language Summary Earth’s plasmasphere is populated by a type of whistler‐mode wave named plasmaspheric hiss which is able to shape the electron radiation belt. Hiss waves were commonly envisioned to have a long lifetime which allows them to permeate the global plasmasphere from a spatially restricted source. Although there have been numerous studies on the source of plasmaspheric hiss waves, the hypothesis regarding their long lifetime remains not experimentally confirmed yet because of the challenging observational requirements in terms of location and timing. On the basis of wave and particle measurements from five magnetospheric satellites covering the entire plasmasphere and detailed modeling, we show that the hiss rays can survive at least 42 s in the plasmasphere disturbed by substorms. Within the survival period, these hiss rays migrated from the middle piece of the plasmaspheric plume to the plasmaspheric core, whose path lengths reached 25 Earth radii. Such a long‐time and large‐scale permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core could benefit from the ducting process by plasmaspheric field‐aligned density irregularities. Key Points Low‐frequency hiss waves were excited by energetic electrons inside the dayside plasmaspheric plume following substorms Low‐frequency hiss rays survived at least 42 s, allowing themselves to migrate from the plasmaspheric plume to the plasmaspheric core Plasmaspheric density ducts facilitated the permeation of hiss rays from the plasmaspheric plume to the plasmaspheric core

In this study, we statistically analyze the wave properties of plasmaspheric hiss using data from the Van Allen Probes. The magnetic power spectral densities of hiss waves exhibit dependence on magnetic local time, geomagnetic activity, and the L$L$ ‐shell. Based on variations in wave properties—including normal angle, electromagnetic planarity, and the net Poynting flux direction Rs$\\left({R}_{s}\\right)$ —with L$L$ ‐shell and normalized frequency (the ratio of wave frequency to electron cyclotron frequency), hiss waves are categorized into four distinct regions. Waves with frequencies above 0.1fce$0.1{f}_{ce}$exhibit characteristics of locally generated plasmaspheric hiss. Furthermore, the statistical distribution of suprathermal electron fluxes shows that the upper energy of injected energetic electrons matches well with the minimum resonant energy corresponding to the lower frequency of locally generated hiss. This study identifies locally generated hiss waves, which are well supported by the electron distributions. Plain Language Summary Whistler‐mode plasmaspheric hiss waves occur in near‐Earth space and are named for their distinct hiss‐like sound. These waves primarily exist in dense plasma regions and play a critical role in electron loss of Earth's radiation belts, particularly by scattering high‐energy electrons. Plasmaspheric hiss waves are crucial for understanding Earth's radiation belt dynamics, though their potential generation mechanisms remain under active investigation. In this study, we used data from the Van Allen Probes to analyze how wave properties depend on the L$L$shell and normalized frequency, identifying regions of locally generated plasmaspheric hiss. We also incorporated statistical data on electron distributions to confirm that hiss waves above approximately 0.1 times the electron cyclotron frequency at large L$L$shells are locally generated. This study validates the mechanism of local generation and provides insights to support future research on the origins of plasmaspheric hiss. Key Points The locally generated hiss waves are identified based on the wave properties The suprathermal electron features in the plasmasphere are statistically analyzed The distributions of suprathermal electrons and corresponding growth rates well support the local generation of identified hiss

Plasmaspheric hiss, a whistler‐mode emission confined in the high‐density plasmasphere, is of great interest to the space community attributed to its important role in inner magnetospheric dynamics. Their frequency‐time structures provide crucial evidence for understanding the wave origin. In this work, based on ∼7‐year Van Allen Probes data, we statistically studied the frequency‐drifting plasmaspheric hiss characterized by an increasing lower cutoff frequency over a timescale exceeding 1 hr. Frequency‐drifting hiss waves predominantly occur at 3 < L < 6 from predawn to noon during geomagnetic active times. Observations and theoretical analyses suggest the frequency‐drifting hiss could result from the local excitation inside the plasmasphere by energy‐dispersive injected electrons. This unique feature of plasmaspheric hiss waves serves, to a certain extent, as an “identifier” for discerning the wave origins and as a “marker” facilitating the link between hiss waves across a broad spatial range. Plain Language Summary Inside the plasmasphere, a cold and dense plasma region surrounding the Earth, plasmaspheric hiss is a frequently observed electromagnetic wave. Through wave‐particle interactions, plasmaspheric hiss plays a critical role in controlling the geospace environment. Since their discovery in the 1960s, there have been intense debates regarding the generation mechanisms of plasmaspheric hiss. Fortunately, the frequency‐time structure of plasmaspheric hiss provides valuable evidence to understand the wave origin. In this work, on the basis of long‐term observations from Van Allen Probes, we statistically investigate the frequency‐drifting plasmaspheric hiss characterized by an increasing lower cutoff frequency over a timescale exceeding 1 hr. Our analyses indicate this frequency‐drifting feature could be used to some extent to identify the origin of hiss waves. Key Points We investigate the frequency‐drifting plasmaspheric hiss characterized by an increasing lower cutoff over a timescale exceeding 1 hr Frequency‐drifting hiss waves predominantly occur at 3 < L < 6 from predawn to noon during geomagnetic active times The frequency‐drifting feature could result from the local excitation by energy‐dependent dispersive injection of hot electrons

Hiss waves play a critical role in shaping Earth's radiation belts and mediating magnetosphere‐ionosphere energy transfer. Intense hiss emissions are frequently generated within dynamic plasmaspheric plumes through linear and nonlinear wave‐particle interactions. However, the contribution of plume hiss to the spatial distribution of hiss throughout the plasmasphere is not yet well quantified. In this study, we perform ray‐tracing simulations to investigate the global propagation of plume hiss under varying plume morphologies, including different widths and levels of density lumpiness. We find that most hiss power is confined near the local time sector of the plume. Narrower plumes with embedded density ducts significantly enhance earthward wave guidance into the plasmaspheric core, compared to wide, smooth plumes. Furthermore, a subset of rays guided azimuthally along the plasmapause can serve as seed waves for intense dayside hiss. Our results highlight the role of plume hiss in shaping the global‐scale distribution of hiss waves.