An empirical model of equatorial electron density in the magnetosphere has been developed, covering the range 2.25 < L < 8. Although the model is primarily intended for application to the local time interval ∼00–15 MLT and to situations in which global magnetic conditions have been slowly varying or relatively steady in the preceding ∼20 hours, a way to extend the model to the 15‐24 MLT period is also described. The principal data sources for the model were (1) electron density profiles deduced from sweep frequency receiver (SFR) radio measurements made along near‐equatorial ISEE 1 satellite orbits and (2) previously published results from whistlers. The model describes, in piecewise fashion, the “saturated” plasmasphere, the region of steep plasmapause gradients, and the plasma trough. Within the plasmasphere the model profile can be expressed as logne = Σxi, where x1 = −0.3145L+3.9043 is the principal or “reference” term, and additional terms account for (1) a solar cycle variation with a peak at solar maximum, (2) an annual variation with a December maximum, and (3) a semiannual variation with equinoctial maxima. The location of the inner edge of the plasmapause (outer limit of the plasmasphere) Lppi is specified, with some qualifications, as Lppi = 5.6 ‐ 0.46Kpmax, where Kpmax is the maximum Kp value in the preceding 24 hours. The plasmapause density profile is described as logne =logne(Lppi) − (L ‐ Lppi)/Δpp, where Δpp is the scale width of the plasmapause, or distance in L value over which the density drops by an order of magnitude. For modeling purposes, Δpp is suggested to be ∼0.1 (∼600 km) at night and to increase across the dayside, but values no greater than ∼ Δpp=0.025 (∼150 km), the limiting spatial resolution of the ISEE SFR, have been observed. The inner part of the plasma trough, prior to significant refilling, is described as ne = ne(Lppo) × (L/Lppo)−4.5, where Lppo is the outer limit of the plasmapause segment. The model includes the effects of a factor‐of‐order ∼5 diurnal variation in electron density in the plasma trough region, as well as a relatively abrupt transition near dusk from day to night trough levels. It also includes an approach at large L values to a limiting low density of ∼1 el cm−3. (It is possible that the trough levels in the model are a factor of 5‐10 higher than trough levels in some nightside regions during the early phases of substorms.) ISEE data indicate that for those profiles on which one or more plasmapause decreases can be identified, the mean radius of the innermost plasmapause varies only slightly with magnetic local time, exhibiting a slight bulge near 18 MLT (dusk/dawn difference ΔL...

[1] Electron acceleration inside the Earth's magnetosphere is required to explain increases in the $MeV radiation belt electron flux during magnetically disturbed periods. Recent studies show that electron acceleration by whistler mode chorus waves becomes most efficient just outside the plasmapause, near L = 4.5, where peaks in the electron phase space density are observed. We present CRRES data on the spatial distribution of chorus emissions during active conditions. The wave data are used to calculate the pitch angle and energy diffusion rates in three magnetic local time (MLT) sectors and to obtain a timescale for acceleration. We show that chorus emissions in the prenoon sector accelerate electrons most efficiently at latitudes above 15°for equatorial pitch angles between 20°a nd 60°. As electrons drift around the Earth, they are scattered to large pitch angles and further accelerated by chorus on the nightside in the equatorial region. The timescale to accelerate electrons by whistler mode chorus and increase the flux at 1 MeV by an order of magnitude is approximately 1 day, in agreement with satellite observations during the recovery phase of storms. During wave acceleration the electrons undergo many drift orbits and the resulting pitch angle distributions are energy-dependent. Chorus scattering should produce pitch angle distributions that are either flat-topped or butterfly-shaped. The results provide strong support for the wave acceleration theory.

Abstract.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

[1] Electromagnetic ion cyclotron (EMIC) waves which propagate at frequencies below the proton gyrofrequency can undergo cyclotron resonant interactions with relativistic electrons in the outer radiation belt and cause pitch-angle scattering and electron loss to the atmosphere. Typical storm-time wave amplitudes of 1-10 nT cause strong diffusion scattering which may lead to significant relativistic electron loss at energies above the minimum energy for resonance, E min . A statistical analysis of over 800 EMIC wave events observed on the CRRES spacecraft is performed to establish whether scattering can occur at geophysically interesting energies ( 2 MeV). While E min is well above 2 MeV for the majority of these events, it can fall below 2 MeV in localized regions of high plasma density and/or low magnetic field ( f pe /f ce,eq > 10) for wave frequencies just below the hydrogen or helium ion gyrofrequencies. These lower energy scattering events, which are mainly associated with resonant L-mode waves, are found within the magnetic local time range 1300 < MLT < 1800 for L > 4.5. The average wave spectral intensity of these events (4-5 nT 2 /Hz) is sufficient to cause strong diffusion scattering. The spatial confinement of these events, together with the limited set of these waves that resonate with 2 MeVelectrons, suggest that these electrons are only subject to strong scattering over a small fraction of their drift orbit. Consequently, drift-averaged scattering lifetimes are expected to lie in the range of several hours to a day. EMIC wave scattering should therefore significantly affect relativistic electron dynamics during a storm. The waves that resonate with the $MeV electrons are produced by low-energy ($keV) ring current protons, which are expected to be injected into the inner magnetosphere during enhanced convection events. INDEX TERMS: 2730Magnetospheric Physics: Magnetosphere-inner; 2772 Magnetospheric Physics: Plasma waves and instabilities; 7867 Space Plasma Physics: Wave/particle interactions; 2716 Magnetospheric Physics: Energetic particles, precipitating; KEYWORDS: EMIC waves, relativistic electrons, wave/particle interaction, outer radiation belt Citation: Meredith, N. P., R. M. Thorne, R. B. Horne, D. Summers, B. J. Fraser, and R. R. Anderson, Statistical analysis of relativistic electron energies for cyclotron resonance with EMIC waves observed on CRRES,

[1] We analyze wave and particle data from the CRRES satellite to determine the variability of plasmaspheric hiss (0.1 < f < 2 kHz) with respect to substorm activity as measured by AE*, defined as the maximum value of the AE index in the previous 3 hours. The study is relevant to modeling the acceleration and loss of relativistic electrons during storms and understanding the origin of the waves. The plasmaspheric hiss amplitudes depend on spatial location and susbtorm activity, with the largest waves being observed during high levels of substorm activity. Our survey of the global distribution of hiss indicates a strong day-night asymmetry with two distinct latitudinal zones of peak wave activity primarily on the dayside. Equatorial hiss (jl m j < 15°) is strongest during active conditions (AE* > 500 nT), with an average amplitude of 40 ± 1 pT observed in the region 2 < L < 4 from 0600 to 2100 MLT. Midlatitude (jl m j > 15°) hiss is strongest during active conditions with an average amplitude of 47 ± 2 pT in the region 2 < L < 4 from 0800 to 1800 MLT but extending out beyond L = 6 from 1200 to 1500 MLT. Equatorial hiss at 600 Hz has minimum cyclotron resonant energies ranging from $20 keV at L = 6 to $1 MeV at L = 2, whereas midlatitude hiss at 600 Hz has minimum resonant energies ranging from $50 keV at L = 6 to $2 MeV at L = 2. The enhanced equatorial and midlatitude hiss emissions are associated with electron flux enhancements in the energy range of tens to hundreds of keV, suggesting that these electrons are the most likely source of plasmaspheric hiss. The enhanced levels of plasmaspheric hiss during substorm activity will lead to increased pitch-angle scattering of energetic electrons and may play an important role in relativistic electron dynamics during storms.