The system science development of local time dependent 40 keV electron flux models for geostationary orbit

At Geosynchronous Earth Orbit (GEO), the radiation belt/ring current electron fluxes with energies up to several hundred keV, can vary widely in Magnetic Local Time (MLT). This study aims to develop Nonlinear AutoRegressive eXogenous (NARX) models using system science techniques, which account for the spatial variation in MLT. This is difficult for system science techniques, since there is sparse data availability of the electron fluxes at different MLT. To solve this problem the data are binned from GOES 13, 14, and 15 by MLT, and a separate NARX model is deduced for each bin using solar wind variables as the inputs to the model. These models are then conjugated into one spatiotemporal forecast. The model performance statistics for each model varies in MLT with a Prediction Efficiency (PE) between 47% and 75% and a correlation coefficient (CC) between 51.3% and 78.9% for the period from 1 March 2013 to 31 December 2017

Forecast of the energetic electron environment of the radiation belts

Different modeling methodologies possess different strengths and weakness. For instance, data based models may provide superior accuracy but have a limited spatial coverage while physics based models may provide lower accuracy but provide greater spatial coverage. This study investigates the coupling of a data based model of the electron fluxes at geostationary orbit (GEO) with a numerical model of the radiation belt region to improve the resulting forecasts/pastcasts of electron fluxes over the whole radiation belt region. In particular, two coupling methods are investigated. The first assumes an average value for L* for GEO, namely urn:x-wiley:15427390:media:swe21428:swe21428-math-0001 = 6.2. The second uses a value of L* that varies with geomagnetic activity, quantified using the Kp index. As the terrestrial magnetic field responds to variations in geomagnetic activity, the value of L* will vary for a specific location. In this coupling method, the value of L* is calculated using the Kp driven Tsyganenko 89c magnetic field model for field line tracing. It is shown that this addition can result in changes in the initialization of the parameters at the Versatile Electron Radiation Belt model outer boundary. Model outputs are compared to Van Allen Probes MagEIS measurements of the electron fluxes in the inner magnetosphere for the March 2015 geomagnetic storm. It is found that the fixed urn:x-wiley:15427390:media:swe21428:swe21428-math-0002 coupling method produces a more realistic forecast

Interactions between energetic electrons and realistic whistler mode waves in the Jovian magnetosphere

The role of plasma waves in shaping the intense Jovian radiation belts is not well understood. In this study we use a realistic wave model based on an extensive survey from the Plasma Wave Investigation on the Galileo spacecraft to calculate the effect of pitch angle and energy diffusion on Jovian energetic electrons due to upper and lower band chorus. Two Earth-based models, the Full Diffusion Code and the Versatile Electron Radiation Belt code, are adapted to the case of the Jovian magnetosphere and used to resolve the interaction between chorus and electrons at L = 10. We also present a study of the sensitivity to the latitudinal wave coverage and initial electron distribution. Our analysis shows that the contribution to the electron dynamics from upper band chorus is almost negligible compared to that from lower band chorus. For 100 keV electrons, we observe that diffusion leads to redistribution of particles toward lower pitch angles with some particle loss, which could indicate that radial diffusion or interchange instabilities are important. For energies above >500 keV, an initial electron distribution based on observations is only weakly affected by chorus waves. Ideally, we would require the initial electron phase space density before transport takes place to assess the importance of wave acceleration, but this is not available. It is clear from this study that the shape of the electron phase space density and the latitudinal extent of the waves are important for both electron acceleration and loss

Rapid electron acceleration in low density regions of Saturn's radiation belt by whistler mode chorus waves

Electron acceleration at Saturn due to whistler mode chorus waves has previously been assumed to be ineffective; new data closer to the planet shows it can be very rapid (factor of 104 flux increase at 1 MeV in 10 days compared to factor of 2). A full survey of chorus waves at Saturn is combined with an improved plasma density model to show that where the plasma frequency falls below the gyrofrequency additional strong resonances are observed favoring electron acceleration. This results in strong chorus acceleration between approximately 2.5 RS and 5.5 RS outside which adiabatic transport may dominate. Strong pitch angle dependence results in butterfly pitch angle distributions that flatten over a few days at 100s keV, tens of days at MeV energies which may explain observations of butterfly distributions of MeV electrons near L=3. Including cross terms in the simulations increases the tendency towards butterfly distributions

Acceleration of electrons by whistler-mode hiss waves at Saturn

Plasmaspheric hiss waves at the Earth are well known for causing losses of electrons from the radiation belts through wave particle interactions. At Saturn, however, we show that the different plasma density environment leads to acceleration of the electrons rather than loss. The ratio of plasma frequency to electron gyrofrequency frequently falls below one creating conditions for hiss to accelerate electrons. The location of hiss at high latitudes ( > 25°) coincides very well with this region of very low density. The interaction between electrons and hiss only occurs at these higher latitudes, therefore the acceleration is limited to mid to low pitch angles leading to butterfly pitch angle distributions. The hiss is typically an order of magnitude stronger than chorus at Saturn and the resulting acceleration is rapid, approaching steady state in one day at 0.4 MeV at L=7 and the effect is stronger with increasing L-shell

The ELFIN mission

The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or heretoforth simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (∼93∘ inclination), nearly circular, low-Earth (∼450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (Torbit ∼ 90 min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50 keV to 5 MeV electrons with Δ E/E 1 MeV. This broad energy range of precipitation indicates that multiple waves are providing scattering concurrently. Many observed events show significant backscattered fluxes, which in the past were hard to resolve by equatorial spacecraft or non-pitch-angle-resolving ionospheric missions. These observations suggest that the ionosphere plays a significant role in modifying magnetospheric electron fluxes and wave-particle interactions. Routine data captures starting in February 2020 and lasting for at least another year, approximately the remainder of the mission lifetime, are expected to provide a very rich dataset to address questions even beyond the primary mission science objective.Published versio

Acceleration mechanism responsible for the formation of the new radiation belt during the 2003 Halloween solar storm

Observations of the relativistic electron flux increases during the first days of November, 2003 are compared to model simulations of two leading mechanisms for electron acceleration. It is demonstrated that radial diffusion driven by ULF waves cannot explain the formation of the new radiation belt in the slot region and instead predicts a decay of fluxes during the recovery phase of the October 31st storm. Compression of the plasmasphere during the main phases of the storm created preferential conditions for local acceleration during interactions with VLF chorus. Local acceleration of electrons at L = 3 is modelled with a 2-D pitch-angle, energy diffusion code. We show that the energy diffusion driven by whistler mode waves can explain the gradual build up of fluxes to energies exceeding 3 MeV in a new radiation belt which is formed in the slot region normally devoid of high energy electrons

Mechanisms for the acceleration of radiation belt electrons

During the declining phase of the solar cycle fast solar wind streams produce corotating interaction regions (CIRs) that drive moderate geomagnetic storms. These storms often have an unusually long recovery phase and produce high fluxes of relativistic electrons. Here we investigate the physical mechanisms responsible for accelerating electrons to relativistic energies inside the outer radiation belt. We review the most important electron acceleration and loss mechanisms, and present global simulations that combine radial diffusion with acceleration and loss by whistler mode chorus waves. We show that acceleration by chorus waves alone can increase the -MeV electron phase space density between 4.5 < L < 6.5 by up to three orders of magnitude. When radial diffusion and wave acceleration are included accelerated electrons are transported both inwards and outwards and increase the phase space density by a factor of 10 between 3.5 < L < 7. At lower energies of similar to 0.1 to a few hundred keV, chorus waves cause electron precipitation that enhances inward radial diffusion. We conclude that chorus wave acceleration and loss play a major role in the dynamics of the outer radiation belt. We suggest that during the declining phase of the solar cycle Alfvenic wave activity in the fast solar wind provides continuous inward transport of similar to 1-100 keV electrons inside the magnetosphere which maintains whistler mode wave power long enough to accelerate electrons up to similar to MeV energies, and drives radial diffusion to fill up the entire outer radiation belt