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Whistler mode waves are a right-hand circularly polarized electromagnetic waves in the very low frequency (VLF) range, which can be excited and propagate in the region through the Earth's atmosphere to the magnetosphere. Typical examples of whistler mode waves include chorus, plasmaspheric hiss, lightning generated whistler (LGW), VLF waves ejected by ground transmitters. The whistler mode wave can interact with energetic electrons and plays an important role in both electron loss and acceleration in the magnetosphere.

The Earth's inner magnetosphere is populated by a host of high frequency plasma waves which, via wave-particle interactions, can shape the dynamics of the terrestrial radiation belts. One of these is an incoherent whistler-mode plasma wave commonly referred to as hiss. Hiss is nearly always present in the inner magnetosphere, acting to diffusively scatter electrons into the atmosphere. While hiss waves are often low amplitude, their persistence allows them to wear away at the radiation belts, carving out new slot regions over days to weeks.

Resonant wave-particle interactions with plasma waves (e.g. plasmaspheric hiss, whistler mode chorus, and electromagnetic ion cyclotron (EMIC) waves) are often cited as one of the main loss processes that drive the variability of electron fluxes in the Earth's radiation belts . The evolution of our understanding of the radiation belt electron precipitation, the driving mechanism for such events, and its relative impact on radiation belt particle fluxes has moved from single point measurements to the dawn of simultaneous multi-point measurements and conjunction studies. The BARREL mission, as a mission of opportunity to the Van Allen Probes mission, deployed an array of balloon borne detectors to observe radiation belt electron losses into the atmosphere. This mission offered extended periods of time in conjunction with Van Allen Probes and polar LEO orbiting satellites. Conjunction studies have been used to correlate observed plasma waves on Van Allen Probes with electron precipitation observed on BARREL and further constrained the spatial scale of electron precipitation [1-3]. These studies, in combination with theoretical modeling, have shown that the parameter space involved in wave-particle interaction extends beyond our measurements. Therefore, in order to further advance our understanding of these phenomena and their impact on the radiation belts we need to broaden the scope of our measurements and narrow the assumptions and undefined parameters that go into the theory.

The geomagnetic space environment is a natural laboratory for rich nonlinear plasma physics. The auroral zone ionosphere and magnetosphere of the Earth are replete with plasma waves and radiations. The energetic electrons precipitating to the auroral zone naturally excite various waves in the magnetosphere as well as in the ionosphere, which can be detected on the ground or by in situ spacecraft. Energetic electrons trapped in the dipolar field of the magnetosphere also excite naturally occurring plasma waves. One may use these radio emissions as an effective tool for diagnosing complicated plasma processes occurring in the natural environment. Among the most well-known electromagnetic radio emission processes in the tens to hundreds kHz frequency range is the terrestrial kilometric radiation (also known as the Auroral Kilometric Radiation or AKR for short) [1] , [2] . Terrestrial continuum radiation is also a well-known example [3] , [4] . Other types of naturally occurring auroral radio waves in the medium frequency range have also been identified. The hiss is a broadband emission below 1 MHz, medium frequency (MF) burst is a broadband emission at 1.5-4.5 MHz, and auroral roar, which is a narrowband emission near cyclotron harmonics [5] . Besides these nonlinear emission mechanisms may also be operating. For instance, recently it was proposed that a radiation emission mechanism similar to the plasma emission process, which is relevant for solar radio bursts, may be operative near the reconnection region [6] . The present paper will discuss kinetic theories of these radio emission processes that may be relevant to the naturally occurring radio emission phenomena in space plasma environment.

An ultrathin antenna of thickness nearly 100th of the wavelength is presented, which is capable of providing small-scale beam steering. The antenna is inspired by concepts used in high impedance surfaces (HISs) A linear array antenna comprised of periodic dogbone-shaped elements mounted on top of a grounded substrate with multiple feeds is analyzed to obtain beam scanning and large gain bandwidth, despite the ultrathin thickness. Beam steering is observed when one port at the time is excited among multiple ports distributed along the length of the array. When multiple ports are excited simultaneously, a significantly larger gain bandwidth is observed even from this ultra-low-profile configuration. A maximum gain of 5.7 dBi is achieved along with a 3 dB gain bandwidth over a wide frequency range from 19.2 GHz to 25.2 GHz (27%).

Auroral Emission Radio Observer (AERO) is a NASA H-TIDeS-funded 3U CubeSat mission with the main objective of observing Earth's radio aurora. AERO will conduct a three-month mission in polar orbit to measure the direction of arrival, frequency spectra, and occurrence rates of radio frequency emissions from Earth's aurora. AERO will also advance the technology readiness level (TRL) of its vector sensor payload. The vector sensor (VS) has six mutually orthogonal loop and dipole antennas that detect all six electromagnetic wave components. VS technology allows for direction of arrival calculations of signal sources with a single antenna in a compact space. To facilitate testing and performance studies of the VS payload, we have created an end-to-end simulation of the AERO data collection system that is designed to simulate and process synthetic voltage data from the VS. The VS simulator includes the following elements: modelling the spacecraft orbit, simulating auroral signals, and implementing real-time signal processing. A precise prediction of spacecraft orbit is created using AGI's Systems Tool Kit (STK), constrained to altitudes of 450 to 550 km and a noon/midnight polar orbit with a target local time of midnight. This model is used to generate the position of the spacecraft at a given time in the mission life. Simulated auroral radio point signals with various polarizations, intensities, and frequency spectra are used to simulate four major types of auroral radio emissions: Auroral Kilometric Radiation, Medium Frequency Burst, Auroral Hiss, and Auroral Roar. Stationary, grouped, and banded point sources are all explored as possible emission types. In addition to the spacecraft location and orientation, these point sources are superimposed with expected ambient radio noise and then split into a six-channel VS simulator which produces voltage time series data. The voltage signals are then put through a signal processing chain implemented on a field programmable gate array (FPGA). Implementing the FPGA results in a prototyped system that receives data in real-time as it is passing through the auroral zone which is simulated from the VS simulator. It executes signal processing calculations in parallel at the same moment that data is coming in from the VS. The AERO CubeSat's anticipated launch date is January 2022 and will perform the first localizations of Earth's auroral emissions. Ultimately, this end-to-end simulator will allow for the testing of advanced signal processing algorithms for the VS and assist in data analysis for the AERO CubeSat mission.

Hiss is the name given to the collection of incoherent whistler-mode waves that populate the near-Earth region in and around the plasmasphere, a cold plasma torus about Earth. Hiss waves scatter electrons in pitch angle over a broad energy range, often causing them to be lost from the inner magnetosphere and deposited into the upper atmosphere. The persistent electron scattering and loss driven by hiss waves is important to the dynamics of the inner magnetosphere and radiation belts. These waves determine the shape of the Earthward edge of the radiation belts and are largely responsible for the formation of the gap between electron radiation belts (the slot region).

Wabs. Plasmaspheric hiss constitutes one of the main components of the waves, but lightning and VLF ground transmitters also make important contributions to the wave population. Benchmark models for each of these types of waves, pre-VAP but post-CRRES, were given by Abel and Thorne [1998]. Much work on refining these estimates has been done since then, using wave measurements from VAP as well as Cluster, THEMIS, and others. (The bulk of these observations have been equatorial, though informed by ray tracing.) The effects of very low frequency hiss, highly oblique whistlers, and magnetosonic (MS) waves have come to be recognized as significant. MS waves particularly come into consideration in discussions of butterfly pitch angle distributions. Of greater global significance is the presence or absence of MeV electrons at L

International audience; We present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22–14 magnetic local time (MLT) the boundary between plasmaspheric hiss and chorus moves to lower values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200 to 500 Hz frequency band during active conditions, 400

Whistler mode waves play an important role in space weather dynamics. Plasmaspheric hiss and chorus are types of whistler mode waves prevalent in the magnetosphere. The source location of whistler mode wave energy has been a topic of research for nearly half a century. We present results of warm plasma whistler mode raytracing considering three source locations at $L=2$, 3.8 and 5 in the magnetosphere. Comparison of simulation results with frequency normalized observations from the Van Allen Probes spacecraft suggest that sources within the plasmasphere (L∼2) provide a significant contribution to the observed whistler mode wave power distribution.

Two curvilinear radiating elements (loop and spiral) are placed above a circular HIS ground plane. It is shown through simulations and measurements that in addition to the bandwidth enhancement compared to a rectangular HIS ground plane, the gain increases by an additional 3 dB when a circular HIS is used instead of the conventional HISs due to the radial phase profile.

This paper presents an accurate and efficient algorithm for multidimensional harmonic retrieval (MHR) problems. The new algorithm improves the previously addressed hierarchical signal separation (HISS) technique by using more robust constrained filtering instead of the projection matrices in the signal separation process. Thereby, the new algorithm not only requires lower complexity, but it can provide even superior performance, especially in low signal-to-noise ratio (SNR) scenarios. Moreover, the pairing of the estimated parameters is automatically achieved without extra overhead. While the new algorithm, as HISS, calls for low complexity as only one-dimensional (1-D) parameters are estimated in each stage, it, as shown in the simulations, provides competing performance compared with the main state-of-the-art works.

The optimal control problem is studied for a class of hybrid dynamical systems (HDS), namely, hybrid impulsive and switching systems (HISS). Then the minimum principle of HISS is given, and then is proved by needle-shaped variational method and matrix-structured cost functional. Based on this main result, a class of linear HISS is illustrated and the optimal control algorithm is given. Moreover, the cases of pure impulsive systems and pure switched systems are discussed in this paper.

Plasmaspheric hiss emissions, which are typically observed inside the plasmasphere, are known to play an important role in controlling the overall structure and dynamics of the Earth's radiation belts through pitch angle scattering. Although the characteristics of hiss have been studied using previous satellite data, the statistical results need further improvement due to the limited frequency coverage and resolution of previous satellites, and the difficulty of differentiating hiss from other types of emissions in the inner magnetosphere. Moreover, despite its recognized importance, the generation of plasmaspheric hiss has been a topic of intense debate for over four decades since its discovery.

Chorus and hiss-like emissions in the VLF band (several hundred Hz to 10 kHz) are the most common and intense whistler mode waves in the inner magnetosphere. Though frequency spectra of chorus waves having rising tone frequencies are different from those of hiss-like emissions, their wave amplitude and propagation characteristics are similar [1]. A recent simulation study shows that geomagnetic field gradient along a field line near the equatorial plane plays an important role in the generation of hiss-like emissions and chorus emissions [2]. When the geomagnetic field gradient varies to more gradual one, a threshold amplitude for triggering chorus emissions becomes smaller in the nonlinear wave growth theory. Then, multiple chorus emissions are frequently generated, and hiss-like emissions are produced by merging these chorus emissions in frequency spectra. We observed a high correlation between luminosity of a pulsating aurora (PA) and intensities of grouped chorus and hiss-like emissions on 7 February 2013 at Athabasca (L=4.3) in Canada. In this event, the periodic PA luminosity disappeared when the chorus emissions changed to hiss-like emissions. For this event, variations of the geomagnetic field gradient near the equator were estimated by using the Tsyganenko model [3]. The estimated geomagnetic field gradient became more gradual when the hiss-like emissions were observed. It is consistent with the nonlinear wave growth theory of the generation process of hiss-like emissions. Also, these observation results suggest a close relationship between periods of PA and hiss-like emissions. In this presentation, we will discuss the importance of the effect of geomagnetic field gradient on periods of PA and hiss-like emissions.

The energetic electron population measured by multiple low-altitude POES satellites is used to infer whistlermode wave amplitudes using a physics-based inversion technique. We validate this technique by quantitatively analyzing a conjunction event between the Van Allen Probes and POES, and find that the inferred hiss wave amplitudes from POES electron measurements agree remarkably well with directly measured hiss waves amplitudes. We also use this technique to construct the global distribution of chorus wave intensity with extensive coverage over a broad L-MLT region during the 8–9 October 2012 storm and demonstrate that the inferred chorus wave amplitudes agree well with conjugate measurements of chorus wave amplitudes from the Van Allen Probes. The evolution of the whistler-mode wave intensity inferred from low-altitude electron measurements can provide real-time global estimates of the wave intensity, which cannot be obtained from in-situ wave measurements by equatorial satellites alone, but are crucial in quantifying radiation belt electron dynamics.

AKEBONO (EXOS-D) has been continuously operated for more than 25 years since 1989 to observe particles and plasma waves in the auroral region and the plasmasphere of the Earth. It covers altitude region from 300 km to about 10,000 km with an inclination of 75 degree. Analyses of large amounts of data obtained by AKEBONO enable us to study comprehensively how the magnetosphere varies temporally and spatially. The WBA (Wide Band Analyzer) is one of subsystems of the VLF instruments onboard AKEBONO. It measures 1 component of electric or magnetic analogue waveform in the frequency band of 50 Hz–15 kHz. Typical waves such as chorus, hiss and whistler were frequently observed by the WBA. Data obtained by the WBA for more than 25 years are originally recorded as analogue waveform format in the magnetic audio tapes. Data conversion from analogue to digital is now being carried out and the converted data are stored in our computer storage as digital WAVE format.

Plasmaspheric hiss is an incoherent, broadband electromagnetic whistler-mode emission, preferentially and steadily observed inside high-density plasmasphere and storm-time plasmaspheric plume [1-2]. The frequency of plasmaspheric hiss typically ranges between ∼200 Hz and 2 kHz, with peak wave power in a few 100s Hz. It has been recently proposed [3] that the dominant source of this emission is coherent chorus waves generated outside the plasmasphere. Subsequent ray tracing simulations [4] by tracing million rays of chorus waves reproduced a realistically spatial and spectral distribution of plasmaspheric hiss [Figure 1], showing the spatial confinement of plasmaspheric hiss emission within the plasmapause, and the typical frequency range from 200 Hz and 2 kHz with peak intensity around 500–700 Hz. It is worth pointing out that there is little hiss emission below 200 Hz in the simulation, indicating the chorus-as-embryonic-source mechanism does not work for such low frequency because chorus waves at those frequencies cannot propagate inward into the plasmasphere without substantial attenuations.

The reflection characteristics of a circularly symmetric high impedance surface, with a circular substrate in a cartesian coordinate system, is studied and compared with that of the rectangular HIS with straight strips. The operational bandwidth of the circular and rectangular HISs are obtained and compared together.

For most cases, the reflection phase diagram of a curved High Impedance Surface (HIS) is independent of the curvature. However, the surface waves generated on HISs, due to their periodic geometry, distorts their reflection characteristics within specific frequency intervals. In those intervals, the reflection phase changes as a function of radius of curvature and size of the HIS. These effects are not observed for the flat cases because of the lower radiation resistance of the surface waves.

Summary form only given. Earth's auroral ionosphere emits several types of spontaneous emissions, including auroral hiss, medium frequency burst, and roar. Auroral roar occurs at harmonics of the electron cyclotron frequency. The most commonly observed harmonic is 2fce, first reported in the 1970's. Since the 1990's, the 3fce harmonic has also been regularly observed from ground level. These emissions both favor pre-midnight magnetic local times and require darkness for observation at ground-level. Significant evidence has accumulated that they result from mode conversion of upper hybrid waves excited where the upper hybrid frequency matches the cyclotron harmonic. Satellite and rocket observations of the 2fce emission support that mechanism. Recently, two papers report observations of 4fce and 5fce emissions in Svalbard and in Antarctica. These higher harmonic emissions also favor pre-midnight magnetic local times but require sunlit ionosphere for observation. For all harmonics observed so far, the frequency scales linearly with the strength of the geomagnetic field at the observing station. Combining data from multiple stations allows estimation of source altitudes. Observations of the harmonics at a given station also provides a method for remotely sensing the ionospheric density.

DEMETER is a low orbiting satellite (660 km) which was operating for more than six years to study ionospheric perturbations in relation with seismic and anthropogenic activities. For this purpose, it recorded wave and plasma parameters all around the Earth (except in the auroral zones) at two different local times (10.30 and 22.30 LT). This paper will present an overview of the electromagnetic waves observed during sustained magnetic activity, and then enhanced by a wave-particle interaction. Many different waves have been observed. It includes: — strange MLR (Magnetospheric Line Radiation) which have frequency lines close to the PLHR (Power Line Harmonic Radiation) at the harmonics of 50 (60) Hz but which are drifting in frequency, — waves such as hiss, chorus, QP (Quasi Periodic) emissions, triggered emissions, EMIC (ElectroMagnetic Ion Cyclotron) waves in the equatorial region, — emissions at the lower hybrid frequency, and — specific waves recorded during very intense magnetic activities or in particular regions (SAA, sub-auroral zones).

The electromagnetic equations of qyrotropic waves in the general form have been examined. The analysis shows that attenuation of one of modes tends to zero in the perpendicular direction to the magnetic field while along this direction the attenuation is finite. Basing on this feature it was supposed that low frequency electromagnetic fluctuations tend to expand along the magnetic field. It forms in the ionosphere long areas with invariable direction of the electric field and current and weakly variable magnitude of these parameters. This assumption was checked by numerical solving of the direct problem of electromagnetic fluctuation evolution.

Radiation belt particle acceleration and loss is intimately connected to wave-particle interactions. To measure these interactions, NASA will launch the two-satellite Radiation Belt Storm Probes (RBSP) mission in 2012. The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) investigation on RBSP is an integrated set of instruments consisting of DC magnetic field measurements from DC to 30 Hz and AC electric and magnetic fields from 10Hz to 400 kHz. Examples of key wave science such as VLF hiss, magnetosonic equatorial noise, electromagnetic ion cyclotron waves, and chorus are presented along with the mission and instrument complement.

Holographic information storage systems (HISS) have been a good candidate for a volumetric recording technology due to their large storage capacities and high transfer rates. Recently, revival of activity in HISS has resulted from the dramatic developments in systems, such as laser technology, spatial light modulators (SLM) and complementary metal-oxide semiconductor (CMOS) image sensors. Holographic Versatile Disc (HVD) system using Collinear Technology, a new technology for HISS, is proposed and demonstrated by OPTWARE Corporation. This technology can produce a small, practical HISS more easily than conventional 2-axis holography.

The global optimal control problem with free system terminal states is proposed for the hybrid impulsive and switching systems (HISS). Towards the problem mentioned above, the necessary condition of the above problem, the HISS' minimum principle, is given. In the process of proving the above theorem, the Ekeland's variational principle and the matrix cost functional formulation are utilized. Based on the main result, a special linear HISS is illustrated and the optimal control algorithm is presented.

Towards a special class of hybrid systems, the hybrid systems with impulses and switches, a global optimal control problem with free system terminal states is proposed in this paper. Based on this problem, the necessary condition is studied, and then the HISS' minimum principle is obtained. In the proof of the above theorem, the general variational methods and matrix cost functional formulations are employed. In the end of the paper, a special linear HISS is illustrated and the optimal control is obtained by calculation.

In this paper several kinds of high impedance surfaces (HISs) such as mushroom, Jerusalem cross-shaped HIS, spiral-shaped HIS and meander line-based HIS are analyzed. The sensitivity of reflection phases with respect to incident angles for TE and TM-polarized wave are compared. A meander line-based HIS has the least sensitivity to variation of the incident angles and operates at lower resonant frequency. The simulations show that the designed meander line based-HIS has a bandgap region between 4.83 to 6.82 GHz for TE and TM surface waves.

Geomagnetically trapped electrons are removed from the radiation belts by pitch-angle scattering with plasma waves. Much theoretical and experimental evidence supports the argument that VLF whistlers, plasmaspheric hiss, chorus, and ground-based transmitters contribute to this removal. However, there is considerable uncertainty about which class of waves is most important in the various regions of the magnetosphere. A better knowledge of the wave fields throughout the magnetosphere is needed for a complete assessment of the electron-wave interaction process.

We present in this paper a number of powerful innovations we have recently developed for the printing of applique antennas, HISs, and similar devices. These innovations pertain specifically to very low temperature direct-write printing and include (1) the capability for printing highly conductive metal directly onto microwave laminate without damage to the laminate, and (2) printing multilayered structures composed of metal and low-loss dielectric layers. With these capabilities, for example, we have printed planar conductive antennas directly onto multilayered HISs, which themselves were printed directly onto standard microwave laminate.

Propagation of short electromagnetic pulse in ionosphere was discussed in (Gutman, 1999, Gutman et al., 2001 and Gutman, 2002). Qualification of previous articles is contained in this article.

It is accepted to consider low frequency noise as radio interference. Actually it is a very useful means for diagnosis of the medium in which it is excited and propagated. The results of research of low frequency emissions (0.1-20.0 kHz) obtained from the "Intercosmos" satellite data have shown that the low frequency emissions bear information on parameters of the environment: about variations of energy particle fluxes in the area where the noise is excited, about parameters (density and temperature) of plasma in which it is propagated, about level of disturbance and turbulence of plasma, and about geomagnetic and solar activity level.

The paper describes the analysis of how variations of an impulse field going through the ionosphere influence the nonlinear processes in the plasma. It is concluded that the initial electromagnetic field significantly decreases as the impulse propagates through the ionosphere. That significantly reduces the number of effective collisions between electrons and neutral particles.

Todays sensor systems provide adequate information for automatic control systems and reliable alarm detection systems, but they do not provide enough information to make human supervision superfluous. Any plant needs human supervision, some round the clock, some just every few days. This increases the costs of plant operation dramatically, especially for plants far away from the next central station or even offshore plants. To reduce these costs, Siemens I&S has developed a system called HISS, the Human Interface Supervision System. The idea of this system is to replace human supervision by an automatic system that has human abilities and that supervises the plant round the clock. The first prototype of this system, installed at a plant of BEB, the biggest German gas producer, has got video cameras, microphones and a gas detection system to emulate the human senses watching, listening, and smelling. The sensor information is processed by an intelligent logic, that is able to combine, to compare and to learn, just like a human being. HISS Logic includes the combination, comparing and learning of the data. The results can be viewed either on site on the server PC or remote on any client PC that is connected to the selected transmission network. HISS Logic is described in the paper.

MR signals can be acquired with high spatial and spectral resolution so that each pixel is represented by a high-resolution proton spectrum of water and fat. The spectra can be analyzed to produce images with improved contrast, anatomic accuracy, and sensitivity to contrast media uptake, compared to conventional MR imaging. Analysis of high spectral and spatial resolution (HiSS) MR datasets must take the complex structure of water and fat proton signals in vivo into account. This complexity can greatly increase the information content of HiSS MR images when appropriate data analysis methods are used. We evaluate two methods that effectively increase spectral resolution of HiSS data and, thus, improve image contrast, signal-to-noise ratio, and edge delineation. We describe methods that reduce artifacts due to truncation of the free induction decay, identify maxima of complex proton signals associated with each image voxel, and generate images derived from pure absorption spectra of the water resonance. We demonstrate improvements in image quality obtained with these methods and use them to distinguish between metastatic and non-metastatic rodent tumors based on numerical measures of image texture. Related approaches may significantly improve sensitivity and specificity of clinical MRI.