Wave Normal Direction Research Articles

Group velocity of light in internal conical refraction.

We calculated the group velocity of light in internal conical refraction in a biaxial crystal as a function of the direction of the electric displacement vector, or the vibration direction, of its carrier wave. Our method represents group velocity through the electromagnetic fields of light, rather than its wave normal or ray direction. The travel time of a light pulse traversing a parallel plate biaxial crystal in internal conical refraction is found to vary as a sinusoidal function of twice the vibration angle of the light wave. Our method distinguishes the four directions of the two optic axes in monoclinic and triclinic crystals. Numerical examples are given for K N b O 3 at the wavelength of 400nm, and for S n 2 P 2 S 6 at the wavelength of 550nm.

Properties of Whistler Mode Waves in Earth's Plasmasphere and Plumes

AbstractWhistler mode wave properties inside the plasmasphere and plumes are systematically investigated using 5‐year data from Van Allen Probes. The occurrence and intensity of whistler mode waves in the plasmasphere and plumes exhibit dependences on magnetic local time, L, and AE. Based on the dependence of the wave normal angle and Poynting flux direction on L shell and normalized wave frequency to electron cyclotron frequency (fce), whistler mode waves are categorized into four types. Type I: ~0.5 fce with oblique wave normal angles mostly in plumes; Type II: 0.01–0.5 fce with small wave normal angles in the outer plasmasphere or inside plumes; Type III: <0.01 fce with oblique wave normal angles mostly within the plasmasphere or plumes; Type IV: 0.05–0.5 fce with oblique wave normal angles deep inside the plasmasphere. The Poynting fluxes of Type I and II waves are mostly directed away from the equator, suggesting local amplification, whereas the Poynting fluxes of Type III and IV are directed either away from or toward the equator, and may originate from other source regions. Whistler mode waves in plumes have relatively small wave normal angles with Poynting flux mostly directed away from the equator and are associated with high electron fluxes from ~30 keV to hundreds of keV, all of which support local amplification. Whistler mode wave amplitudes in plumes can be stronger than typical plasmaspheric hiss, particularly during active times. Our results provide critical insights into understanding whistler mode wave generation inside the plasmasphere and plumes.

Atmospheric gravity wave ray tracing: Ordinary and extraordinary waves

Calculation of internal gravity-wave ray paths in the atmosphere using a general three-dimensional ray tracing computer program is discussed. To initialize a ray-path calculation, it is necessary to specify the initial values for the components of the wave vector at the source so that the dispersion relation is satisfied. For acoustic waves, or for gravity waves in the absence of wind, there is no ambiguity in determining the magnitude of the wave vector once the frequency and direction of propagation (wave-normal direction) have been specified. For gravity waves with wind, however, it is necessary to solve a quartic equation to specify the magnitude of the wavenumber. Two of the roots of the quartic reduce to the usual solutions in the absence of wind, and we designate these roots as ‘ordinary waves.’ The two new roots (whose values approach infinity as the wind speed approaches zero), we designate as ‘extraordinary waves.’ A section contrasts the properties of the different gravity wave types.Comparison with some previously published examples of ray-path calculations of gravity waves shows that those previous examples were actually extraordinary waves, but their significance was not recognized at that time.In the absence of wind, gravity waves are restricted to a fan of propagation directions centered about horizontal propagation, but asymptotic gravity waves (in the Bousinesq approximation) have a fixed propagation direction for a given frequency. In the presence of a horizontal wind, however, the wave-normal direction is restricted to a fan of directions in the upwind direction, but not in the downwind direction. The ray direction for upwind propagation has no restrictions. A short review of gravity wave theory and the gravity wave dispersion relation is included.

Statistical Properties of Plasmaspheric Hiss From Van Allen Probes Observations

AbstractVan Allen Probes observations are used to statistically investigate plasmaspheric hiss wave properties. This analysis shows that the wave normal direction of plasmaspheric hiss is predominantly field aligned at larger L shells, with a bimodal distribution, consisting of a near‐field aligned and a highly oblique component, becoming apparent at lower L shells. Investigation of this oblique population reveals that it is most prevalent at L < 3, frequencies with f/fce>0.01 (or f > 700 Hz), low geomagnetic activity levels, and between 1900 and 0900 magnetic local time. This structure is similar to that reported for oblique chorus waves in the equatorial region, perhaps suggesting a causal link between the two wave modes. Ray tracing results from HOTRAY confirm that it is feasible for these oblique chorus waves to be a source of the observed oblique plasmaspheric hiss population. The decrease in oblique plasmaspheric hiss occurrence rates during more elevated geomagnetic activity levels may be attributed to the increase in Landau resonant electrons causing oblique chorus waves to be more substantially damped outside of the plasmasphere. In turn, this restricts the amount of wave power that can access the plasmasphere and evolve into oblique plasmaspheric hiss. These results confirm that, despite the difference in location of this bimodal distribution compared to previous studies, a direct link between oblique equatorial chorus outside of the plasmasphere and oblique hiss at low L shells is plausible. As such, these results are in keeping with the existing theory of chorus as the source of plasmaspheric hiss.

New chorus wave properties near the equator from Van Allen Probes wave observations

AbstractThe chorus wave properties are evaluated using Van Allen Probes data in the Earth's equatorial magnetosphere. Two distinct modes of lower band chorus are identified: a quasi‐parallel mode and a quasi‐electrostatic mode, whose wave normal direction is close to the resonance cone. Statistical results indicate that the quasi‐electrostatic (quasi‐parallel) mode preferentially occurs during relatively quiet (disturbed) geomagnetic activity at lower (higher) L shells. Although the magnetic intensity of the quasi‐electrostatic mode is considerably weaker than the quasi‐parallel mode, their electric intensities are comparable. A newly identified feature of the quasi‐electrostatic mode is that its frequency peaks at higher values compared to the quasi‐parallel mode that exhibits a broad frequency spectrum. Moreover, upper band chorus wave normal directions vary between 0° and the resonance cone and become more parallel as geomagnetic activity increases. Our new findings suggest that chorus‐driven energetic electron dynamics needs a careful examination by considering the properties of these two distinct modes.

Statistics of whistler mode waves in the outer radiation belt: Cluster STAFF‐SA measurements

AbstractELF/VLF waves play a crucial role in the dynamics of the radiation belts and are partly responsible for the main losses and the acceleration of energetic electrons. Modeling wave‐particle interactions requires detailed information of wave amplitudes and wave normal distribution over L‐shells and over magnetic latitudes for different geomagnetic activity conditions. We performed a statistical study of ELF/VLF emissions using wave measurements in the whistler frequency range for 10 years (2001–2010) aboard Cluster spacecraft. We utilized data from the STAFF‐SA experiment, which spans the frequency range from 8 Hz to 4 kHz. We present distributions of wave magnetic and electric field amplitudes and wave normal directions as functions of magnetic latitude, magnetic local time, L‐shell, and geomagnetic activity. We show that wave normals are directed approximately along the background magnetic field (with the mean value of θ—the angle between the wave normal and the background magnetic field, about 10°–15°) in the vicinity of the geomagnetic equator. The distribution changes with magnetic latitude: Plasmaspheric hiss normal angles increase with latitude to quasi‐perpendicular direction at ∼35°–40° where hiss can be reflected; lower band chorus are observed as two wave populations: One population of wave normals tends toward the resonance cone and at latitudes of around 35°–45° wave normals become nearly perpendicular to the magnetic field; the other part remains quasi‐parallel at latitudes up to 30°. The observed angular distribution is significantly different from Gaussian, and the width of the distribution increases with latitude. Due to the rapid increase of θ, the wave mode becomes quasi‐electrostatic, and the corresponding electric field increases with latitude and has a maximum near 30°. The magnetic field amplitude of the chorus in the day sector has a minimum at the magnetic equator but increases rapidly with latitude with a local maximum near 12°–15°. The wave magnetic field maximum is observed in the night sector at L>7 during low geomagnetic activity (at L∼5 for Kp>3). Our results confirm the strong dependence of wave amplitude on geomagnetic activity found in earlier studies.

Correction to “A statistical study of the propagation characteristics of whistler waves observed by Cluster”

, 2011), the incorrect reference frame (i.e., ISR2) was used to analyze the data. In Figure 2, a statistical analysis of the distribution of wave-normal angles as a function of latitude was presented. The results were obtained using data from the STAFF-SA instrument from the Cluster Active Archive (CAA), by assuming that the data was in the ISR2 coordinate system as written in the data description [Cornilleau-Wehrlin et al., 1997; Cornilleau-Wehrlin and STAFF Team, 2011]. Unfortunately , recently it became evident that the true reference frame system of STAFF-SA data in the CAA is the SR2 (Spin Reference 2) coordinate system, which differs from the ISR2 (inverted SR2) by the inverted signs of the Y and Z axes. We have re-analyzed all of the data in the correct reference frame (i.e., SR2). The results of the new analysis are presented in Figure 1. In the present correction we describe the newly-obtained results and discuss how they impact the discussion in our original paper. [2] Identification of the error only recently became possible when the data of the STAFF-SC instrument in the burst mode, namely, waveforms with a sampling rate of 450 samples per second (that were obtained on January 26, 2001) became available in the CAA. Making use of this data, we performed cross-calibration tests between the STAFF-SC waveforms and the STAFF-SA spectrum matrices. For the comparison, we used observations from a whistler wave that had a frequency of 100 Hz (0.15 of the local f ce). For both STAFF-CA and STAFF-SA we determined that the wave had a circular polarization. The wave-normals determined from the STAFF-SA and STAFF-SC had different signs for the Y and Z components. The vector rotation with respect to the background magnetic field was right-handed from the STAFF-SC (as expected for whistler waves), but left-handed from the STAFF-SA. Since the coordinate system of the STAFF-SC has been verified using FGM data, the results unambiguously demonstrate that the true coordinate system of the STAFF-SA data in the CAA is SR2, not ISR2. The STAFF team, after verification , has confirmed that STAFF Spectral Matrix (SM) and Power Spectral Density (PSD) data at CAA are in SR2 reference frame and not in ISR2 as previously written by mistake (N. Cornilleau-Wehrlin, personal communication, 2012). The CAA documentation has now been modified accordingly by the STAFF team. [3] The corrected probability distribution functions (PDF) of the whistler wave-normal direction q (relative to the background B

Modeling the properties of plasmaspheric hiss: 1. Dependence on chorus wave emission

There is increasing evidence that plasmaspheric hiss is formed by the evolution of a portion of chorus waves that are excited in the plasmatrough and propagate into the plasmasphere. Comparison between the statistical spatial distributions of these two emissions in the morning sector during active times from THEMIS over ∼3 years shows that the two emissions have comparable peak intensities but are distinct in their spatial distributions. We present a modeling study of the hiss spectrum, based on ray tracing, by taking the observed chorus source region as an input in the magnetosphere, which contains cold and suprathermal electrons. Our modeling results show that we are able to reproduce the main features of typical hiss, including the frequency spectrum, wave normal angle and spatial distribution. However, the simulated hiss intensity is weaker (∼15 dB less) than the observed intensity, which suggests some modest internal amplification inside the plasmasphere. The responses of hiss to variations in the spatial distribution, wave normal angle distribution and frequency distribution of the source chorus are examined. We find that the majority of hiss formation is due to a small portion of chorus emission originating within ∼3 RE from the plasmapause, with wave normal directions pointing toward the Earth at an angle of 30°–60°, and over a frequency range of 0.1–0.3 fce. If the chorus power is made to increase closer to the plasmapause, the hiss intensity and the peak frequency also increases, which roughly mimics active geomagnetic conditions. Variations of the chorus source distribution do not significantly affect the wave normal angle distribution and frequency distribution of hiss, but does impact the absolute intensity of the resulting hiss.

Asymmetric V-shaped streaks recorded on board DEMETER satellite above powerful thunderstorms

[1] We report here observations of both symmetric and asymmetric forms of V-shaped streaks on VLF spectrograms recorded on board the DEMETER satellite. Recent investigations have shown that V-shaped streaks are associated with intense and numerous 0+ whistlers generated in the VLF range by active thunderstorms. To understand the origin of the different spectral forms of the V-shaped events, a systematic survey of these phenomena is performed by means of a visual inspection of the VLF spectrograms covering more than 5 years of DEMETER observations. Asymmetric events are more frequently observed over high-latitude regions. The influence of the magnetic field inclination on the observed asymmetry is investigated. First, a full wave method is used to compute, at the lower ionospheric boundary, the electromagnetic pattern that is due to a streak of lightning. This allows us to show a small asymmetry especially for high frequencies (f > 10 kHz). Then, cold plasma dispersive properties are used to determine the characteristics of the waves propagating from the mesosphere to the satellite altitude. We find that, at the plasma cutoff altitude, the propagation is more efficient for waves having wave-normal directions parallel, or quasi parallel, to the Earth's magnetic field direction. Finally, a detailed analysis of an asymmetric V-shaped event is performed. The precise localization of the lightning associated with the V-shaped event is provided by the METEORAGE network. A relationship between the local inclination of the magnetic field above active thunderstorms and the asymmetry of the V-shaped event is pointed out for this particular event.

Resonant scattering of plasma sheet electrons by whistler‐mode chorus: Contribution to diffuse auroral precipitation

A quantitative analysis is presented of the resonant scattering of plasma sheet electrons (∼100 eV–20 keV) at L = 6 due to resonant interactions with whistler‐mode chorus. Using wave parameters modeled from observations under geomagnetically disturbed conditions, it is demonstrated that the rate of pitch angle scattering can exceed the level of strong diffusion over a broad energy range (200 eV–10 keV) containing the bulk of the injected plasma sheet population. Scattering by chorus appears to be more effective than previous analyses of resonant interaction with electrostatic electron cyclotron waves. Chorus scattering is therefore a major contributor to the origin of the diffuse aurora and should also control the MLT distribution of injected plasma sheet electrons. The rates of scattering are sensitive to the distributions of wave power with respect to wave normal direction and wave frequency spectrum. Upper‐band chorus (ω/Ωe > 0.5) is the dominant scattering process for electrons below ≈5 keV while lower‐band chorus (0.1 ≤ ω/Ωe ≤ 0.5) is more effective at higher energies especially near the loss cone.

Crack distributions which account for a given seismic anisotropy

SUMMARY The effect of microfractures or small-scale inclusions within Earth structures may be measured seismically. Wavespeeds, as a function of wave-normal direction, lead to effective or mean elastic parameters and the difference between these and the values for unfractured material is related to parameters for the size, distribution and internal conditions of the cracks or inclusions. Thus it appears that measurement of the seismic wavespeeds for a sequence of different propagation directions can lead to information about fractures or inclusions within the rock, even though the scale-size of this microstructure may be very small compared with a wavelength. However, the crack parameters are continuous functions of orientation and the elastic parameters for the material provide values for only 21 independent quantities. This is enough to describe the crack distribution in terms of spherical surface harmonics up to fourth order only. The relationship between the effective elastic parameters and t he crack distribution is accurate to second order in the number density which limits the applications to materials where the contribution of microfractures is less than 10 per cent. The relationships referred to above show that inherent material anisotropy is equivalent to a distribution of (hypothetical) cracks embedded in an isotropic material. It then follows that the effect of microfractures in an anisotropic solid may be calculated by imposing both systems of cracks (real and hypothetical) on an isotropic matrix, for which solutions are known.

Analysis methods for multi-component wave measurements on board the DEMETER spacecraft

We describe analysis methods to estimate parameters of electromagnetic waves based on the multi-component measurements of the DEMETER spacecraft. Using the fact that the wave magnetic field is perpendicular to the wave vector, the wave normal direction can be estimated by different methods. We use these plane-wave estimates to interpret measurements of the observed wave emissions. For instance, we use the recently developed singular value decomposition (SVD) technique. The results of the plane-wave analysis have an advantage that they often allow a straightforward interpretation. These different methods have been successfully tested with the data of previous spacecraft. All these methods are also implemented in the analysis tools designed for the analysis of the DEMETER wave measurements. We show the first results of these analysis techniques for different types of wave emissions observed on board DEMETER. Obliquely propagating right-hand polarized electromagnetic waves at a few hundreds of Hz are usually connected with a multi-ion mode structure below the local proton cyclotron frequency and with a sharp lower cutoff of left-hand polarized waves, as well as with right-hand polarized waves tunelling below the multi-ion cross-over frequency. Electron and proton whistlers are also very frequently observed on DEMETER. An unusual narrow-band emission at 140 Hz (well below the local proton cyclotron frequency) serves us as another case for a detailed analysis. We find that these waves are right-hand polarized and obliquely propagating. Using this example case, we also present analysis methods to estimate continuous distribution of wave energy density as a function of wave vector directions. These techniques of wave distribution function (WDF) analysis need both wave and particle measurements. In the analyzed case, two different methods of WDF analysis give similar results consistent with the results of the plane-wave techniques. To identify the source region we use the backward ray-tracing method. The wave normal direction obtained by the analysis of multi-component data is used for a simulation of wave propagation from the point of measurement. By this procedure, we obtain an inverse trajectory of the wave ray. We can thus follow the ray path back to the anticipated source region which is in our case located a few degrees of latitude to the South from the spacecraft position.

Elasticity of magnesite and dolomite from a genetic algorithm for inverting Brillouin spectroscopy measurements

A hybrid numerical scheme that simultaneously retrieves single-crystal elastic constants, C ij , and wave-normal directions is applied to determine the elasticity of natural samples of both magnesite and dolomite, as measured by Brillouin spectroscopy at ambient conditions. The scheme incorporates the genetic algorithm (GA) as a global searching tool and a final local linearization to overcome the intrinsic difficulty of fitting non-linear Christoffel's equation. To compensate for the stochastic nature of GA, especially when the misfit function of the problem manifests highly rugged topography in the model space, the procedure was repeated for multi-runs. This is to assure that the best solution is captured by examining the statistics among the runs that yield the fittest solutions. The resultant elastic constants C 11, C 12, C 13, C 14, C 33 and C 44 are, respectively, 260.3(2.6), 82.9(4.5), 59.6(3.1), (−)20.1(1.3), 153.7(4.1) and 59.7(1.4) GPa for magnesite. For dolomite, C 11, C 12, C 13, C 14, C 15, C 33 and C 44 are, respectively, 204.1(2.2), 68.5(3.4), 45.8(4.4), 20.6(1.3), 6.7(1.5), 97.4(5.3) and 39.1(1.5) GPa. Unfortunately, the results for dolomite are statistically non-unique in the numerical calculation. The above data were adopted because the cleavage plane of dolomite was used in the experiment. The results for both magnesite and dolomite are compatible with those determined earlier by ultrasonic methods. It is anticipated that the new method developed in the present study should be applicable to less symmetric crystals, since there are no particular assumptions on the crystal symmetry embedded within the scheme.

Characteristics of magnetospherically reflected chorus waves observed by CLUSTER

Abstract. Chorus emissions are often observed by the STAFF spectrum analyser on board the 4 satellites of CLUSTER. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the propagation characteristic of these chorus waves. Measurements of the parallel component of the Poynting vector around the magnetic equator indicate that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it has also been observed that lower intensity waves propagate toward the equator at the same frequency. Using the wave normal directions of these waves, a ray tracing study has shown that the waves have suffered a Lower Hybrid Resonance (LHR) reflection at low altitudes and now return to the equator at a different location with a lower intensity. The paper presents other similar events when WBD data are simultaneously recorded. The WBD experiment provides a much better time resolution and allows one to check the structure of the returning waves. It is observed that these waves have still a high degree of polarization, even if they started to lose the coherent structure of the chorus elements. They reach the equator with a small wave normal angle which is more efficient for a further amplification. It is explained that these emissions could be a source of hiss.

Determination of plasmaspheric electron density profile by a stochastic approach

The determination of plasmaspheric electron density profiles has been attempted using a stochastic approach, using Omega signals observed on the Akebono satellite. Since the wave normal directions and delay times of Omega signals can be theoretically calculated by ray tracing under an appropriate electron density model, the density profile can be estimated by fitting the calculated directions and times to the observed values. In the present paper, we introduce a flexible model and a novel algorithm in the fitting method, taking into account the stochastic factors of the density distribution and wave propagation. The stochastic representations of directions and times enable us to separately estimate the effects of the ionosphere and the plasmasphere. The validity of the proposed method is examined using observational data collected during the recovery phase of a magnetic storm. In another example, an estimation of the asymmetry of the plasmasphere is attempted.

Magnetospherically reflected chorus waves revealed by ray tracing with CLUSTER data

Abstract. This paper is related to the propagation characteristics of a chorus emission recorded simultaneously by the 4 satellites of the CLUSTER mission on 29 October 2001 between 01:00 and 05:00 UT. During this day, the spacecraft (SC) 1, 2, and 4 are relatively close to each other but SC3 has been delayed by half an hour. We use the data recorded aboard CLUSTER by the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the wave normal directions relative to the Earth’s magnetic field. This calculation is done for the 4 satellites at different times and different frequencies and allows us to check the directions of these waves. Measurements around the magnetic equator show that the parallel component of the Poynting vector changes its sign when the satellites cross the equator region. It indicates that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it is also observed on SC1, SC2, and SC4 that lower intensity waves propagate toward the equator simultaneously with the SC3 intense chorus waves propagating away from the equator. Both waves are at the same frequency. Using the wave normal directions of these waves, a ray tracing study shows that the waves observed by SC1, SC2, and SC4 cross the equatorial plane at the same location as the waves observed by SC3. SC3 which is 30 minutes late observes the waves that originate first from the equator; meanwhile, SC1, SC2, and SC4 observe the same waves that have suffered a Lower Hybrid Resonance (LHR) reflection at low altitudes (based on the ray tracing analysis) and now return to the equator at a different location with a lower intensity. Similar phenomenon is observed when all SC are on the other side of the equator. The intensity ratio between magnetic waves coming directly from the equator and waves returning to the equator is between 0.005 and 0.01, which is in agreement with previously published theoretical calculation of the growth rates with the particle distribution seen by GEOS.Key words. Magnetospheric physics (plasma waves and instabilities) – Ionosphere (wave propagation) – Radio science (magnetospheric physics)

Large meteoroid detection using the global International Monitoring System infrasound system

We will review the subject of infrasound from large bolides (large meteor-fireballs) entering the atmosphere at hypersonic speeds and their expected rate of detection by the 60 infrasonic arrays of the global IMS network (International Monitoring System). This will include the details of the generation of a quasiline source blast wave and its subsequent decay for near-continuum flow conditions. We will also discuss new highly refined models of bolide ablation and fragmentation and of known compositional types and their effect on sound and light production. In addition, we will consider the effects of refraction of the waves by the middle atmospheric and tropospheric thermodynamic sound speed and horizontal wind profiles in a range-independent atmosphere so that the characteristic velocity and wave normal directions radiated at the source are conserved during the propagation. Next, we will discuss the detection of the signals and their interpretation in terms of plane wave arrivals regarding the 3-D source location (latitude, longitude, height), the source energy level, etc. Finally, we will use the infrasound data from bolides to estimate the expected steady-state global influx rate, including formal errors, as a function of their observed source energy. Infrasound from recent large events will also be examined.

Theory of spatial dispersion of dielectric and magnetic constants in magnetic uniaxial gyrotropic crystals

The theory of spatial dispersion of dielectric and magnetic constants of magnetic uniaxial crystals based on generalized Maxwell’s equations D = eE = (e + inγ E = −ns × H and B = μH = (μ + inδ)H = ns × E with spatial dispersion parameters γ and δ is considered. Generalized Fresnel’s and polarization equations for the obtained vectors E, D, H, and B are analyzed for the wave normal direction s ⊥ C (where C is the optic axis of a crystal). The possibility of the existence of a third natural wave in a crystal is proved.

Determination of global plasmaspheric electron density profile by tomographic approach using omega signals and ray tracing

It has been necessary requirements to determine the global electron density distribution in the plasmasphere with time resolutions, of less than a day. We have provided solutions to this requirement using the wave normal directions, delay time of Omega signals and the in situ electron density observed on-board the Japanese satellite Akebono (Sawada et al., Journal of Geophysical Research 98(11) (1993) 267, Kimura et al., Advance Space Research 15(2) (1995) 103, Advance Space Research 18(6) (1996) 279, Journal of Atmospheric and Solar-Terrestrial Physics 59 (1997) 1569). The present paper is intended to review our earlier studies.

Propagation characteristics of auroral kilometric radiation observed by the MEMO experiment on Interball 2

The MEMO experiment is a part of the Interball 2 wave consortium. It is connected to a total of six electric and nine magnetic independent sensors. It provides waveforms associated with the measurement of two to five components in the three frequency bands: ELF (5–1000 Hz), VLF (1–20 kHz), and LF (20–250 kHz). Waveforms of three magnetic components and one electric component recorded during observations of auroral kilometric radiation (AKR) allow a detailed study of the characteristics of these emissions. In particular, the wave normal directions of AKR relative to the Earth's magnetic field are determined using several methods: the classical methods based on the plane wave approximation [Means, 1972] and the wave distribution function method which represents the evaluation of the wave energy density distribution with respect to the angular frequency and the wave normal direction(s). One event is fully analyzed in this paper. It is shown that AKR propagates with a polarization quasi‐circular (ellipticity value ∼ 0.9), a right polarization (i.e., R‐X mode), and wave normals weakly oblique (∼30°).