Lower Band Chorus Research Articles

Efficient diffuse auroral electron scattering by electrostatic electron cyclotron harmonic waves in the outer magnetosphere: A detailed case study

This paper is a companion to a paper by Liang et al. (2011) which reports a causal connection between the intensification of electrostatic ECH waves and the postmidnight diffuse auroral activity in the absence of whistler mode chorus waves at L = 11.5 on the basis of simultaneous observations from THEMIS spacecraft and NORSTAR optical instruments during 8–9 UT on February 5, 2009. In this paper, we use the THEMIS particle and wave measurements together with the magnetically conjugate auroral observations for this event to illustrate an example where electrostatic electron cyclotron harmonic (ECH) waves are the main contributor to the diffuse auroral precipitation. We use the wave and particle data to perform a comprehensive theoretical and numerical analysis of ECH wave driven resonant scattering rates. We find that the observed ECH wave activity can cause intense pitch angle scattering of plasma sheet electrons between 100 eV and 5 keV at a rate of >10−4 s−1 for equatorial pitch angles αeq < 30°. The scattering approaches the strong diffusion limit in the realistic ambient magnetic field to produce efficient precipitation loss of <∼5 keV electrons on a timescale of a few hours or less. Using the electron differential energy flux inside the loss cone estimated based upon the energy‐dependent efficiency of ECH wave scattering for an 8‐s interval with high resolution wave data available, the auroral electron transport model developed by Lummerzheim (1987) produced an intensity of ∼2.3 kR for the green‐line diffuse aurora. Separately, Maxwellian fitting to the electron differential flux spectrum produced a green‐line auroral intensity of ∼2.6 kR. This is in good agreement with the ∼2.4 kR green‐line auroral intensity observed simultaneously at the magnetic foot point (as inferred using the event‐adaptive model of Kubyshkina et al. (2009, 2011)) of the location where the in situ observations were obtained. Our results support the scenario that enhanced ECH emissions in the central plasma sheet (CPS) can be an important or even dominant driver of diffuse auroral precipitation in the outer magnetosphere. This paper is an important compliment to recent work that has shown lower band and upper band chorus to be mainly responsible for the occurrences of diffuse aurora in the inner magnetosphere.

Global distribution of wave amplitudes and wave normal angles of chorus waves using THEMIS wave observations

[1] The global distribution of chorus wave amplitudes and their wave normal angles is investigated using high-resolution wave spectra and waveform data from THEMIS for lower-band and upper-band chorus separately. Statistical results show that large amplitude chorus (>300 pT) occurs predominantly from premidnight to postdawn and is preferentially observed at lower L shells (<8) near the magnetic equator. However, strong or moderate chorus extends further into the afternoon sector and to higher L shells. For lower-band chorus, strong waves (>50 pT) tend to have wave normal angles of <20° and their wave normal angles become even smaller with increasing wave amplitudes. For modest waves, the wave normal angles are distributed over a broad range with a major peak at <20° and a secondary peak at 60°–80°. Wave normal angles of lower-band chorus are generally smaller on the dayside than on the nightside possibly due to the more uniform and more compressed magnetic field configuration on the dayside. Lower-band chorus becomes more oblique with increasing latitude on the dayside, whereas on the nightside the probability of observing oblique chorus decreases at higher latitudes. Compared to lower-band chorus, the properties of upper-band chorus are somewhat different. Upper-band chorus is considerably weaker in magnetic wave amplitudes, shows tighter confinement to the magnetic equator (<10°), and occurs at smaller L shells (<8). Furthermore, wave normal angles of upper-band chorus are generally larger than those of lower-band chorus, but the occurrence rate still peaks at wave normal angles of <20°, particularly for strong upper-band chorus.

Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions

[1] A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of ∼5000 km diameter for corresponding azimuthally elongated patches with ∼100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.

Diffuse auroral scattering by whistler mode chorus waves: Dependence on wave normal angle distribution

[1] Using the statistical CRRES measurements of the electric field intensities of lower band chorus (LBC) and upper band chorus (UBC) around L = 6 under geomagnetically moderate conditions, we evaluate the variations in modeled magnetic field spectral intensity and the resultant changes in resonant scattering rates of plasma sheet electrons caused by different choices of the wave normal distribution. UBC scattering rates inferred from electric field measurements show a common trend of decreasing scattering with increasing peak wave normal angle, θm, for the plasma sheet electrons at all resonant pitch angles. This trend is mainly due to the lower power of magnetic field as derived from the electric field measurements for oblique waves. The LBC resonant diffusion inferred from electric field measurements shows a considerable increase in scattering rates with increasing θm for ∼1 keV electrons at all resonant pitch angles and for 3–30 keV electrons over certain ranges of pitch angles, which is contrary to the decrease in wave magnetic field amplitude and results mainly from the decrease in resonant energy and redistribution of the majority of wave power at large wave normal angles for increased peak wave normal angle. LBC-induced scattering rates of 3–10 keV electrons decrease with increasing θm at low pitch angles, consistent with the decrease in wave magnetic field amplitude when θm increases. Our investigation demonstrates that the knowledge of the wave normal distribution of LBC and UBC is essential for an accurate quantification of the net resonant scattering rates and loss timescales of the plasma sheet electrons for an improved global simulation of diffuse auroral precipitation and the evolution of plasma sheet electron pitch angle distribution if only measurements of wave electric field intensity are available. In contrast, the diffuse auroral scattering rates calculated from magnetic field measurements are much less sensitive to the assumption on wave normal angle distribution. While UBC scattering with constant magnetic field power is roughly insensitive to the assumed wave normal distribution, LBC scattering with constant magnetic field power becomes more dependent on the assumed wave normal angle distribution, especially for ∼1 keV electrons.

Cluster observations of whistler mode ducts and banded chorus

[1] Bell et al. (2009) proposed that the source region for banded chorus consists of whistler mode ducts of depleted electron density (Ne) for upper band (UB) chorus for all wave normal angles (θ) and ducts of either enhanced or depleted Ne for lower band (LB) chorus for small θ and θ near or greater than the Gendrin angle, respectively. This paper provides support for this model using new high resolution (17 km) Ne observations from the Cluster WHISPER and EFW instruments. Data is examined from January 20, 2004, when strong banded chorus was observed over 3000 km of the Cluster 2 orbit, ending at the magnetic equator. Previous analysis of LB chorus on this day indicated the wave normal angles were larger than the Gendrin angle. Using the Ne data, we show that the LB chorus is generated within depletion ducts in the source region and that the half-width of these ducts (∼70 km) is comparable to the transverse scale (∼100 km) of the chorus source region. Making use of the fact that the group velocity of the LB chorus waves has a significant cross-L component, we show that the source region extends over 500 km near the magnetic equator.

A Three-Dimensional Ray Tracing Study on Whistler-Mode Chorus During Geomagnetic Activities

A three-dimensional ray tracing study of a whistler-mode chorus is conducted for different geomagnetic activities by using a global core plasma density model. For the upper-band chorus, the initial azimuthal wave angle affects slightly the projection of ray trajectories onto the plane , but controls the longitudinal propagation. The trajectory of the upper-band chorus is strongly associated with the plasmapause and the magnetic local time (MLT) of chorus source region. For the high geomagnetic activity, the chorus trajectory moves inward together with the plasmapause. In the bulge region, the plasmapause extends outward, while the chorus trajectory moves outward together with the plasmapause. For moderately or high geomagnetic activity, the lower-band chorus suffers low hybrid resonance (LHR) reflection before it reaches the plasmapause, leading to a weak correlation with the geomagnetic activity and magnetic local time of the chorus source region. For low geomagnetic activity, the lower-band chorus may be reflected firstly at the plasmapause instead of suffering LHR reflection, exhibiting a propagation characteristic similar to that of the upper-band chorus. The results provide a new insight into the propagation characteristics of the chorus for different geomagnetic activities and contribute to further understanding of the acceleration of energetic electron by a chorus wave.

Typical properties of rising and falling tone chorus waves

[1] Chorus waves, which have received intense attention recently due to their significant role in radiation belt electron dynamics, frequently exhibit rising and falling tones. Lower-band chorus waves, observed using THEMIS wave burst data, are analyzed to obtain the typical properties of either class of chorus emissions. Our results show that rising tones are more likely to be quasi field-aligned, whereas falling tones are typically very oblique, close to the resonance cone. Furthermore, rising tones occur significantly more often than falling tones, and magnetic amplitudes of rising tones are generally much larger than those of falling tones. We also show the preferential regions of rising and falling tones dependent on MLT and magnetic latitude. Our new findings suggest that two separate mechanisms may be responsible for the generation and nonlinear evolution of rising and falling tone chorus.

Chorus-driven resonant scattering of diffuse auroral electrons in nondipolar magnetic fields

[1] We perform a comprehensive analysis of resonant scattering of diffuse auroral electrons by oblique nightside chorus emissions present along a field line with an equatorial crossing of 6 RE at 00:00 MLT, using various nondipolar Tsyganenko magnetic field models. Bounce-averaged quasi-linear diffusion coefficients are evaluated for both moderately and actively disturbed geomagnetic conditions using the T89, T96, and T01s models. The results indicate that inclusion of nondipolar magnetic field leads to significant changes in bounce-averaged rates of both pitch angle and momentum diffusion for 200 eV to 10 keV plasma sheet electrons. Compared to the results using a dipole field, the rates of pitch angle diffusion obtained using the Tsyganenko models are enhanced at all resonant pitch angles for 200 eV electrons. In contrast, for 500 eV to 10 keV electrons the rates of pitch angle scattering are enhanced at intermediate and/or high pitch angles but tend to be considerably lower near the loss cone, thus reducing the precipitation loss compared to that in a dipole field. Upper band chorus acts as the dominant cause for scattering loss of 200 eV to 2 keV electrons, while lower band chorus scattering prevails for 5–10 keV electrons, consistent with the results using the dipole model. The first-order cyclotron resonance and the Landau resonance are mainly responsible for the net scattering rates of plasma sheet electrons by oblique chorus waves and also primarily account for the differences in bounce-averaged diffusion coefficients introduced by the use of Tsyganenko models. As the geomagnetic activity increases, the differences in scattering rates compared to the dipole results increase accordingly. Nonnegligible differences also occur particularly at high pitch angles for the diffusion rates between the Tsyganenko models, showing an increase with geomagnetic activity level and a dependence on the discrepancy between the Tsyganenko model fields. The strong dependence of bounce-averaged quasi-linear scattering rates on the adopted global magnetic field model and geomagnetic activity level demonstrates that realistic magnetic field models should be incorporated into future modeling efforts to accurately quantify the role of magnetospheric chorus in driving the diffuse auroral precipitation and the formation of electron pancake distributions.

Resonant scattering of plasma sheet electrons leading to diffuse auroral precipitation: 2. Evaluation for whistler mode chorus waves

[1] Using the statistical wave power spectral profiles obtained from CRRES wave data within the 0000–0600 MLT sector under different levels of geomagnetic activity and a modeled latitudinal variation of wave normal angle distribution, we examine quantitatively the effects of lower band and upper band chorus on resonant diffusion of plasma sheet electrons for diffuse auroral precipitation in the inner magnetosphere. Whistler mode chorus-induced resonant scattering of plasma sheet electrons is geomagnetic activity dependent, varying from above the strong diffusion limit (timescale of an hour) during active times (AE* > 300 nT) with peak wave amplitudes of >50 pT to weak scattering (timescale of a day) during quiet conditions (AE* ∼2 keV) plasma sheet electrons in the inner magnetosphere. Efficient scattering by the combination of active time lower band and upper band chorus can cover a wide energy range from ∼100 eV to >100 keV and a broad interval of equatorial pitch angle, thereby accounting for the formation of observed electron pancake distribution. Decreased chorus scattering during less disturbed times can also modify the magnetic local time distribution of plasma sheet electrons. Compared to the effects of chorus waves, electron cyclotron harmonic wave-induced resonant diffusion coefficients are at least 1 order of magnitude smaller and are negligible under any geomagnetic condition, indicating that chorus waves act as the major contributor dominantly responsible for diffuse auroral precipitation in the inner magnetosphere. Chorus-driven momentum diffusion and mixed diffusion are also important. Lower band and upper band chorus can cause strong momentum diffusion of plasma sheet electrons in the energy ranges of ∼500 eV to ∼2 keV and ∼2 keV to ∼3 keV, respectively, which can significantly result in energization of the electrons and attenuation of the waves.

Evolution of electron pitch angle distributions following injection from the plasma sheet

[1] The temporal evolution of the phase space density of plasma sheet electrons (100 eV–30 keV) injected into the nightside at L = 6 during moderate geomagnetic activity is investigated using a quasi-linear diffusion formulation. Scattering in energy and pitch angle during interactions with both whistler mode chorus waves and electron cyclotron harmonic waves are included using an improved wave model recently obtained using CRRES spacecraft data. We compare our simulation results with observations from the THEMIS spacecraft and demonstrate that the formation of the observed electron pitch angle distributions is mainly due to resonant interactions with a combination of upper and lower band chorus waves. The pancake distributions at low energies (E < 2 keV), the flattened pitch angle distributions at medium energies (between 2–3 keV), and the distributions with enhanced pitch angle anisotropy at high energies (E > 3 keV) are explained using the banded chorus wave structure with a power minimum at half the electron cyclotron frequency. Results of the current work can be used to model the dynamical evolution and resultant global distribution of plasma sheet electrons.

Path-integrated gain of whistler-mode chorus in the magnetosphere by a kappa distribution

The path-integrated gain of whistler-mode chorus is evaluated by the incorporation of a kappa distribution of energetic electrons and a realistic field-aligned density model of background electrons. Variations of temperature anisotropy and number density of energetic electrons along the magnetic latitude are derived based on the conservation of the first adiabatic invariant. Numerical simulation shows that a lower-band chorus has a much higher path-integrated gain than an upper-band chorus under the same conditions. During propagation towards higher latitudes, chorus waves grow to large amplitudes in the early stage but ultimately attenuate due to wave damping. The path-integrated gain is higher with the initial wave vector pointing toward lower L shells than toward higher L shells. Moreover, the energetic electron population has a significant influence on the path-integrated gain, and the wave gain is larger as the temperature anisotropy or the density of energetic electrons is enhanced. This result provides further understanding of the chorus wave propagation characteristics in space plasmas.

The source region and its characteristic of pulsating aurora based on the Reimei observations

[1] Using image and particle data sets obtained from observations by the Reimei satellite, we carried out time-of-flight (TOF) analysis for 29 pulsating aurora events to understand the precise properties of pulsating auroras and the possible generation process. While the sources identified using a standard TOF model were distributed almost continuously from magnetic latitudes 50° to −20°, the sources identified using a different TOF model that takes into account whistler mode wave propagation were confined to the equatorial region up to about 15°. The latter source distribution agrees with previous statistical studies of whistler mode chorus waves. In addition, the cold plasma density of the source region and the wave frequency can be estimated from the latter TOF analysis. The estimated cold plasma densities and wave frequencies normalized by the equatorial cyclotron frequency ranged in 0.20–21.7 cm−3 and 0.22–0.65, respectively. The estimated wave frequency showed clear dependence on the invariant latitudes of the pulsating aurora source region and increased up to the frequency range of the upper band chorus as the distance from the Earth decreased (up to about 5–6 RE). These results suggest that both lower and upper band chorus wave contribute to the electron scattering of pulsating auroras, which depends on the radial distance of the source region.

A parametric study on the diffuse auroral precipitation by resonant interaction with whistler mode chorus

The diffuse aurora is generally believed to be the result of ∼keV electron precipitation from the magnetosphere, which presents an important sink of magnetospheric particles, a primary high‐latitude ionospheric energy source, and a strong magnetosphere‐ionosphere coupling mechanism. Resonant scattering of the plasma sheet electrons by electron cyclotron harmonic and whistler mode chorus waves is suggested to be responsible for the diffuse auroral precipitation. The dependence of quasi‐linear diffusion rates and consequent diffuse auroral precipitation on the spatial position L, normal angle, and frequency distribution of both upper‐band chorus (UBC) and lower‐band chorus (LBC) is investigated in detail. Whistler mode chorus waves are found to be more effective in the production of diffuse aurora at larger L shells. The normal angle and frequency distribution of UBC can significantly affect the diffusion rates for ∼keV electrons and the consequent diffuse aurora precipitation. Numerical results show that the strong diffusion limit for ∼keV electrons can be reached up to large pitch angles closer to 90°, and the diffuse auroral precipitation can be remarkably enhanced when the UBC waves possessing a relatively larger normal angle range or centering higher in the band. In contrast, the diffusion rates and diffuse auroral precipitation of electrons with energies Ek &lt; 2 keV are largely independent of the normal angle and frequency distribution of LBC waves. Enhanced precipitations of ∼5 keV electrons are found to occur when the LBC waves centering higher in the band. The current results suggest that the significant variability of wave characteristics and the variation with spatial position should be taken into account in order to identify the dominant mechanism for diffuse aurora.

Wave normal angles of magnetospheric chorus emissions observed on the Polar spacecraft

Using data from the High Frequency Waveform Receiver on board the Polar spacecraft, 1,765 and 993 wave normal angles have been analyzed for 13 orbits containing upper band magnetospheric chorus emissions and 15 orbits containing lower band emissions, respectively. The purpose of this study is to characterize the distribution of the polar wave normal angle, θ, for chorus emissions as a function of magnetic latitude, λ. Understanding wave normal angles is an important step in evaluating resonant wave‐particle interactions. For upper band chorus, wave normal angles tend to remain at or rise toward the resonance cone angle for low latitudes and midlatitudes but move away from the resonance cone angle at higher latitudes. For lower band chorus, wave normal angles with values θ &lt; 20° have the highest probability of occurrence in the latitude range of 10°–50°. Just off the equator, 10° ≤ λ &lt; 25°, there exists a secondary occurrence peak in the range of 50° ≤ θ &lt; 70°. The probability of observing these higher wave normal angles decreases with increasing latitude. The time‐averaged Poynting flux, S, is much larger for lower band chorus waves, which have a mean value of 8.5 × 10−8 W/m2, than for upper band chorus waves, which have a mean value of 1.4 × 10−9 W/m2. S is fairly evenly distributed about its median value, 3.1 × 10−10 W/m2, for all wave normal angles for upper band chorus but deceases as θ increases for lower band chorus.

Oblique lower band chorus waves: Time shifts between discrete elements observed by the Cluster spacecraft

We report observations of remarkable frequency differences and time shifts between the corresponding elements of lower band chorus recorded by the four Cluster spacecraft at low magnetic latitudes on 20 January 2004. The Poynting flux measurements made by the Spatio‐Temporal Analysis of Field Fluctuations (STAFF) instrument confirm that the chorus source is located in the magnetic equatorial plane. Surprisingly, the spacecraft located closer to the equator systematically received the corresponding chorus elements later than the spacecraft located at higher magnetic latitudes. Owing to the orbit, the spacecraft located closer to the equator were at lower L shells. The time shifts and frequency differences depended almost linearly on the perpendicular distance between the various spacecraft. Analysis of data from both the wideband data and STAFF instruments shows that chorus emissions were generated with highly oblique angles of propagation. We discuss several properties of the chorus source that could lead to these observations. We show that the sources moving across the magnetic field lines are reasonably consistent with these observations. We propose that the transverse motion of the chorus sources is a consequence of a feedback between the oblique waves and counter streaming electrons during nonlinear cyclotron interactions, and we provide an estimate of the transverse velocity of the source.

Evolution of electron pitch angle distribution due to interactions with whistler mode chorus following substorm injections

During substorms, pitch angle distribution (PAD) of freshly injected plasma sheet electrons can develop into the typical pancake distribution from the nearly isotropic distribution, which has previously been suggested as the result of resonant scattering driven by electrostatic cyclotron harmonic (ECH) and whistler mode waves in the equatorial regions. In this paper, using the two‐dimensional bounce‐averaged Fokker‐Planck equation, we present a quantitative analysis of the electrons PAD evolution at L = 6 due to interactions with upper (ω/∣Ωe∣ &gt; 0.5) and lower (ω/∣Ωe∣ &lt; 0.5) band chorus based on the observed wave characteristics during substorms. It is found that the upper band chorus can efficiently scatter the electrons with energies 0.1–2 keV into loss cone and drive the electrons with energies above 2 keV toward loss cone. The lower band chorus can only cause precipitation loss of the electrons with energies above 1 keV by resonant scattering. The PADs of electrons with energies above 0.1 keV can develop into the pancake‐shaped distributions due to the combined resonant scattering by upper and lower band chorus, and the pancake index PI, defined as the flux ratio between 90° and 70°, can reach 6 after 5 hours since substorm injections. The PI variation timescale and amplitude are consistent with previous statistical results. The numerical results suggest that the resonant scattering of electrons by the whistler mode chorus waves can be a substantial mechanism responsible for the formation of a pancake distribution outside L = 6. Besides, the rapid precipitation of electrons (∼keV) driven by resonant scattering of chorus waves may also be responsible for the diffuse aurora.

Parameterization of radiation belt electron loss timescales due to interactions with chorus waves

Wave‐particle interactions lead to the loss of relativistic electrons from the outer radiation belt on timescales ranging from hours to weeks. For a fixed value of chorus wave amplitudes pitch‐angle diffusion coefficients are computed for a range of energies and L, and are related to the loss rates of radiation belt electrons. By analyzing the dependence of the loss rates on L‐value and energy we find functional dependencies for the lifetime of the radiation belt electrons. Parameters of the functional dependences are obtained using a linear regression technique. To create parameterizations of loss rate as a function of geomagnetic indices, we also analyzed the statistical data from day‐side lower band chorus observations in the range of geomagnetic latitudes from 20° to 30°. The combined parameterizations of the wave amplitudes and scattering rates indicate that electron loss due to chorus waves strongly depends on energy and geomagnetic activity. During storm‐time conditions the lifetimes of relativistic electrons, in the heart of the outer zone are on the order of a day and are on the scale of hours at lower energies. Pitch‐angle scattering by chorus waves thus plays an important role in radiation belt dynamics. The developed parameterizations may be used in particle tracing codes and radial diffusion codes. The limitations of the parameterization, effect of scattering by other waves, and local acceleration processes are also discussed.

Propagation of whistler-mode chorus to low altitudes: divergent ray trajectories and ground accessibility

Abstract. We investigate the ray trajectories of nonductedly propagating lower-band chorus waves with respect to their initial angle θ0, between the wave vector and ambient magnetic field. Although we consider a wide range of initial angles θ0, in order to be consistent with recent satellite observations, we pay special attention to the intervals of initial angles θ0, for which the waves propagate along the field lines in the source region, i.e. we mainly focus on waves generated with &amp;amp;theta0 within an interval close to 0° and on waves generated within an interval close to the Gendrin angle. We demonstrate that the ray trajectories of waves generated within an interval close to the Gendrin angle with a wave vector directed towards the lower L-shells (to the Earth) significantly diverge at the frequencies typical for the lower-band chorus. Some of these diverging trajectories reach the topside ionosphere having θ close to 0°; thus, a part of the energy may leak to the ground at higher altitudes where the field lines have a nearly vertical direction. The waves generated with different initial angles are reflected. A small variation of the initial wave normal angle thus very dramatically changes the behaviour of the resulting ray. Although our approach is rather theoretical, based on the ray tracing simulation, we show that the initial angle θ0 of the waves reaching the ionosphere (possibly ground) is surprisingly close - differs just by several degrees from the initial angles which fits the observation of magnetospherically reflected chorus revealed by CLUSTER satellites. We also mention observations of diverging trajectories on low altitude satellites.

Substorm dependence of chorus amplitudes: Implications for the acceleration of electrons to relativistic energies

Intense interest currently exists in determining the roles played by various wave‐particle interactions in the acceleration of electrons to relativistic energies during/following geomagnetic storms. Here we present a survey of wave data from the CRRES Plasma Wave Experiment for lower band (0.1–0.5fce) and upper band (0.5–1.0fce) chorus, fce being the electron gyrofrequency, to assess whether these waves could play an important role in the acceleration of a seed population of electrons to relativistic energies during and following geomagnetic storms. Outside of the plasmapause the chorus emissions are largely substorm‐dependent, and all chorus emissions are enhanced when substorm activity is enhanced. The equatorial chorus (|λm| &lt; 15°) is strongest in the lower band during active conditions (AE &gt; 300 nT) with average amplitudes typically &gt;0.5 mV m−1 predominantly in the region 3 &lt; L &lt; 7, between 2300 and 1300 magnetic local time (MLT). This is consistent with electron injection near midnight and subsequent drift around dawn to the dayside. The high‐latitude chorus (|λm &gt; 15°) is strongest in the lower band during active conditions, with average amplitudes typically &gt;0.5 mV m−1 in the region 3 &lt; L &lt; 7 over a range of local times on the dayside, principally in the range 0600–1500 MLT, consistent with wave generation in the horns of the magnetosphere. An inner population of weak, substorm‐independent emissions with average amplitudes generally &lt;0.2 mV m−1 are seen in both bands largely inside L = 4 on the nightside during quiet (AE &lt; 100 nT) and moderate (100 nT &lt; AE &lt; 300 nT) conditions. These emissions lie inside the plasmapause and are attributed to signals from lightning and ground‐based VLF transmitters. We conclude that the significant increases in chorus amplitudes seen outside of the plasmapause during substorms support the theory of electron acceleration by whistler mode chorus in that region. The results suggest that electron acceleration by whistle mode chorus during/following geomagnetic storms can only be effective when there are periods of prolonged substorm activity following the main phase of the geomagnetic storm.