[1] Pitch angle and energy diffusion rates for scattering by whistler-mode chorus waves are proportional to the wave magnetic field intensity and are strongly dependent on the frequency distribution of the waves and to the ratio between the electron plasma frequency (f(pe)) and the electron gyrofrequency (f(ce)). Relativistic electrons interact most readily with lower-band chorus (0.1 300 nT). Enhanced waves in these regions could play a major role in electron acceleration to relativistic energies during periods of prolonged substorm activity.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003GL017698

Favored regions for chorus‐driven electron acceleration to relativistic energies in the Earth's outer radiation belt

[1] Energetic electrons are deposited into the atmosphere from Earth's inner magnetosphere, resulting in the production of odd nitrogen (NOx). During polar night, NOx can be transported to low altitudes, where it can destroy ozone, affecting the atmospheric radiation balance. Since the flux of energetic electrons trapped in the magnetosphere is related to solar activity, the precipitation of these electrons into Earth's atmosphere provides a link between solar variability and changes in atmospheric chemistry which may affect Earth's climate. To determine the global distribution of the precipitating flux, we have built a statistical model binned by auroral electrojet (AE) index, magnetic local time (MLT), and L shell of E > 30 keV precipitating electrons from the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA Polar Orbiting Environmental Satellites (POES) low-altitude satellites NOAA-15, NOAA-16, NOAA-17, and NOAA-18. We show that the precipitating flux increases with geomagnetic activity, suggesting that the flux is related to substorm activity. The precipitating fluxes maximize during active conditions where they are primarily seen outside of the plasmapause on the dawnside. The global distribution of the precipitating flux of E > 30 keV electrons is well-correlated with the global distribution of lower-band chorus waves as observed by the plasma wave experiment onboard the Combined Release and Radiation Effects Satellite (CRRES) satellite. In addition, the electron precipitation occurs where the pitch angle diffusion coefficient due to resonant interaction between electrons and whistler mode chorus waves is high, as calculated using the pitch angle and energy diffusion of ions and electrons (PADIE) code. Our results suggest that lower-band chorus is very important for scattering >30 keV electrons from Earth's inner magnetosphere into the atmosphere.

/pdf/origin-of-energetic-electron-precipitation-30-kev-into-the-25vjko0obl.pdf

Origin of energetic electron precipitation >30 keV into the atmosphere

Gyroresonant wave-particle interactions with electromagnetic ion cyclotron (EMIC) waves are a potentially important loss process for relativistic electrons in the Earth's radiation belts. Here we perform a statistical analysis of the EMIC waves observed by the Combined Release and Radiation Effects Satellite (CRRES) to determine the global morphology and spectral properties of the waves and to help assess their role in radiation belt dynamics. Helium band EMIC waves, with intensities, Bw2, greater than 0.1 nT2, are most prevalent during active conditions (AE> 300 nT), from 4 0.1nT2 reported on here will contribute to relativistic electron loss in the Earth's radiation belts and should be included in radiation belt models.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JA020064

Global morphology and spectral properties of EMIC waves derived from CRRES observations

Electromagnetic Ion Cyclotron (EMIC) waves cause electron loss in the radiation belts by resonating with high-energy electrons at energies greater than about 500 keV. However, their effectiveness has not been fully quantified. Here we determine the effectiveness of EMIC waves by using wave data from the fluxgate magnetometer on CRRES to calculate bounce-averaged pitch angle and energy diffusion rates for L*=3.5–7 for five levels of Kp between 12 and 18 MLT. To determine the electron loss, EMIC diffusion rates were included in the British Antarctic Survey Radiation Belt Model together with whistler mode chorus, plasmaspheric hiss, and radial diffusion. By simulating a 100 day period in 1990, we show that EMIC waves caused a significant reduction in the electron flux for energies greater than 2 MeV but only for pitch angles lower than about 60°. The simulations show that the distribution of electrons left behind in space looks like a pancake distribution. Since EMIC waves cannot remove electrons at all pitch angles even at 30 MeV, our results suggest that EMIC waves are unlikely to set an upper limit on the energy of the flux of radiation belt electrons.

Electron losses from the radiation belts caused by EMIC waves

[1] The origin of the diffuse aurora has been a source of controversy for many years. More recently, the question has taken a new significance in view of the associated changes in atmospheric chemistry which may affect the middle atmosphere. Here, we use CRRES data to assess the importance of upper band chorus and electron cyclotron harmonic (ECH) waves in the production of the diffuse aurora. Both wave modes increase with increasing geomagnetic activity, suggesting they are related to periods of enhanced convection and/or substorm activity. They are confined to the near-equatorial region, which excludes the prenoon sector from the wave survey. During active conditions, intense ECH waves and upper band chorus, with amplitudes exceeding 1 mV m−1, are observed in the region 4 < L< 7 from 2100 to 0600 MLT approximately 20% and 6% of the time, respectively. This suggests that both wave modes can put electrons on strong diffusion, but only during active conditions and not at all local times. Scattering rates fall below the strong diffusion limit at other times when the wave amplitudes are weaker. Fluxes of low energy electrons (100 eV < E < 30 keV) also increase with increasing geomagnetic activity in approximately the same region of geospace as the waves, suggesting that these electrons are responsible for the generation of the waves. The patterns of the upper band chorus, ECH waves, and low-energy electrons are similar to the global morphology of the diffuse aurora, suggesting that both wave modes play significant roles in the production of the diffuse aurora.

/pdf/survey-of-upper-band-chorus-and-ech-waves-implications-for-35ior0kui3.pdf

Survey of upper band chorus and ECH waves: Implications for the diffuse aurora

A quantitative model of the magnetospheric magnetic field and associated procedures for accurately cataloging charged-particle data out to and beyond geosynchronous orbit is developed. The magnetic field model incorporates all major magnetospheric current systems and is valid for all tilt angles; i.e., angles of incidence of the solar wind on the dipole axis. The model accurately represents the total magnetospheric magnetic field for conditions of low magnetic activity and to a geocentric distance of 15 earth radii or to the magnetopause. A new (B, I) coordinate system is developed to organize charged-particle data more accurately. The electric field produced by the daily varying tilt angle is computed.

K.A. Pfitzer

Papers

Magnetospheric magnetic field modeling. Annual scientific report