Radial transport of radiation belt electrons due to stormtime Pc5 waves

During geomagnetic storms relativistic electron fluxes in the outer radiation belt exhibit dynamic variability over multiple orders of magnitude. This requires radial transport of electrons across their drift shells and implies violation of their third adiabatic invariant. Radial transport is induced by the interaction of the electron drift motion with electric and magnetic field fluctuations in the ULF frequency range. It was previously shown that solar-wind driven ULF waves have long azimuthal wave lengths and thus can violate the third invariant of trapped electrons in the process of resonant interaction with their gradient-curvature motion. However, the amplitude of solar-wind driven ULF waves rapidly decreases with decreasing <I>L</I>. It is therefore not clear what mechanisms are responsible for fast transport rates observed inside the geosynchronous orbit. In this paper we investigate wether stormtime Pc5 waves can contribute to this process. Stormtime Pc5s have short azimuthal wave lengths and therefore cannot exhibit resonance with the the electron drift motion. However we show that stormtime Pc5s can cause localized random scattering of electron drift motion that violates the third invariant. According to our results electron interaction with stormtime Pc5s can produce rapid radial transport even as low as <I>L</I>≃4. Numerical simulations show that electron transport can exhibit large deviations from radial diffusion. The diffusion approximation is not valid for individual storms but only applies to the statistically averaged response of the outer belt to stormtime Pc5 waves

Scaling in long term data sets of geomagnetic indices and solar wind ϵ as seen by WIND spacecraft

We study scaling in fluctuations of the geomagnetic indices (AE, AU, and AL) that provide a measure of magnetospheric activity and of the ε parameter which is a measure of the solar wind driver. Generalized structure function (GSF) analysis shows that fluctuations exhibit self-similar scaling up to about 1 hour for the AU index and about 2 hours for AL, AE and ε when the most extreme fluctuations over 10 standard deviations are excluded. The scaling exponents of the GSF are found to be similar for the three AE indices, and to differ significantly from that of ε. This is corroborated by direct comparison of their rescaled probability density functions

Science Objectives and Rationale for the Radiation Belt Storm Probes Mission

The NASA Radiation Belt Storm Probes (RBSP) mission addresses how populationsof high energy charged particles are created, vary, and evolve in space environments,and specifically within Earths magnetically trapped radiation belts. RBSP, with a nominallaunch date of August 2012, comprises two spacecraft making in situ measurements for atleast 2 years in nearly the same highly elliptical, low inclination orbits (1.1 5.8 RE, 10).The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every2.5 months, allowing separation of spatial from temporal effects over spatial scales rangingfrom 0.1 to 5 RE. The uniquely comprehensive suite of instruments, identical on the twospacecraft, measures all of the particle (electrons, ions, ion composition), fields (E and B),and wave distributions (dE and dB) that are needed to resolve the most critical science questions.Here we summarize the high level science objectives for the RBSP mission, providehistorical background on studies of Earth and planetary radiation belts, present examples ofthe most compelling scientific mysteries of the radiation belts, present the mission design ofthe RBSP mission that targets these mysteries and objectives, present the observation andmeasurement requirements for the mission, and introduce the instrumentation that will deliverthese measurements. This paper references and is followed by a number of companionpapers that describe the details of the RBSP mission, spacecraft, and instruments

Modeling Radiation Belt Electrons With Information Theory Informed Neural Networks

An empirical model of radiation belt relativistic electrons (μ = 560–875 MeV G−1 and I = 0.088–0.14 RE G0.5) with average energy ∼1.3 MeV is developed. The model inputs solar wind parameters (velocity, density, interplanetary magnetic field (IMF) |B|, Bz, and By), magnetospheric state parameters (SYM-H and AL), and L*. The model outputs the radiation belt electron phase space density (PSD). The model is operational from L* = 3 to 6.5. The model is constructed with neural networks assisted by information theory. Information theory is used to select the most effective and relevant solar wind and magnetospheric input parameters plus their lag times based on their information transfer to the PSD. Based on the test set, the model prediction efficiency (PE) increases with increasing L*, ranging from −0.043 at L* = 3 to 0.76 at L* = 6.5. The model PE is near 0 at L* = 3–4 because at this L* range, the solar wind and magnetospheric parameters transfer little information to the PSD. Using solar wind observations at L1 and magnetospheric index (AL and SYM-H) models solely driven by solar wind, the radiation belt model can be used to forecast PSD 30–60 min ahead. This baseline model can potentially complement a class of empirical models that input data from low earth orbit (LEO)

Scaling and a Fokker-Planck model for fluctuations in geomagnetic indices and comparison with solar wind as seen by Wind and ACE

The evolution of magnetospheric indices on temporal scales shorter than that of substorms is characterized by bursty, intermittent events that may arise from turbulence intrinsic to the magnetosphere or that may reflect solar wind-magnetosphere coupling. This leads to a generic problem of distinguishing between the features of the system and those of the driver. We quantify scaling properties of short-term (up to few hours) fluctuations in the geomagnetic indices AL and AU during solar minimum and maximum, along with the parameter that is a measure of the solar wind driver. We find that self-similar statistics provide a good approximation for the observed scaling properties of fluctuations in the geomagnetic indices, regardless of the solar activity level, and in the parameter at solar maximum. This self-similarity persists for fluctuations on timescales at least up to about 1–2 hours. The scaling exponent of AU index fluctuations show dependence on the solar cycle, and the trend follows that found in the scaling of fluctuations in . The values of their corresponding scaling exponents, however, are always distinct. Fluctuations in the AL index are insensitive to the solar cycle, as well as being distinct from those in the parameter. This approximate self-similar scaling leads to a Fokker-Planck model which, we show, captures the probability density function of fluctuations and provides a stochastic dynamical equation (Langevin equation) for time series of the geomagnetic indices

Effect of EMIC waves on relativistic and ultrarelativistic electron populations: Ground-based and Van Allen Probes observations

Abstract We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of \u3e0.7 MeV electrons nor reductions in Van Allen Probe 90° pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90°. For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultrarelativistic (~2-8 MeV) electron loss but which is confined to pitch angles below around 45° and not affecting the core distribution. Key Points EMIC wave activity is not associated with precipitation of MeV electrons EMIC waves do not deplete the ultra-relativistic belt down to 90° EMIC waves cause loss of low pitch angle electrons with energies ~2-8 MeV

Energetic, relativistic and ultra-relativistic electrons: Comparison of long-term VERB code simulations with Van Allen Probes measurements

In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (\u3e100 keV), relativistic (~0.5–1 MeV), and ultrarelativistic (\u3e2 MeV) electrons. One year of relativistic electron measurements (μ = 700 MeV/G) from 1 October 2012 to 1 October 2013 are well reproduced by the simulation during varying levels of geomagnetic activity. However, for ultrarelativistic energies (μ = 3500 MeV/G), the VERB code simulation overestimates electron fluxes and phase space density. These results indicate that an additional loss mechanism is operational and efficient for these high energies. The most likely mechanism for explaining the observed loss at ultrarelativistic energies is scattering by the electromagnetic ion cyclotron waves

The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales

Artificial Intelligence to Enhance Mission Science Output for In-situ Observations: Dealing with the Sparse Data Challenge

In the Earth's magnetosphere, there are fewer than a dozen dedicated probes beyond low-Earth orbit making in-situ observations at any given time. As a result, we poorly understand its global structure and evolution, the mechanisms of its main activity processes, magnetic storms, and substorms. New Artificial Intelligence (AI) methods, including machine learning, data mining, and data assimilation, as well as new AI-enabled missions will need to be developed to meet this Sparse Data challenge.Comment: 4 pages, 1 figure; Heliophysics 2050 White Pape