Energization of particles in Saturn's inner magnetosphere: Monte Carlo simulation of stochastic electric field effects

Context.Our knowledge of energetic particles in Saturn's inner magnetosphere is based on observations made during the flybys of Pioneer 11, Voyager 1, Voyager 2, and recently by Cassini. The most important features of the energetic particle population in the inner Saturnian magnetosphere are: 1) the rings and the many large and small satellites inside this region reduce the population of particles whose energies are higher than 0.5 MeV to values of the order of 103 times less than would otherwise be present; 2) the sputtering and outgassing of the surfaces of the satellites injects particles into the system and by some physical process, particles of the resultant plasma are accelerated to energies of the order of tens of keV; 3) the radial distribution of very energetic protons Ep > tens of MeV exhibits three major peaks associated with rings and satellites; 4) a proton population Ep ~ 1 MeV lies outside the orbit of Enceladus; 5) a proton population Ep < 0.25 MeV has an apparent origin associated with Dione, Tethys, Enceladus, E-ring, Mimas, and G-ring; 6) a population of low-energy electrons is associated with the satellites. Aims.We propose a mechanism to explain the energetic particle population observed in Saturn's inner magnetosphere based on the stochastic behavior of the electric field. Methods.To simulate the stochastic electric field we employ a Monte Carlo Method taking into account the magnetic field fluctuations obtained from the observations made by Voyager 1 spacecraft. Results.Assuming different initial conditions, like the source of charged particles and the distribution function of their velocities, we find that particles injected with very low energies ranging from 0.104 eV to 0.526 keV can be accelerated to reach much higher energies ranging from 0.944 eV to 0.547 keV after a few seconds

Morphological characteristics of ionospheric E layer over El Cerrillo station, Mexico during magnetically quiet conditions

Se describe la región E de la ionosfera observada en la estación ionosférica de El Cerrillo, México bajo condiciones magneto tranquilas y para diferentes niveles de actividad solar. Se obtiene que su comportamiento es típico de una región en equilibrio fotoquímico y puede ser bien descrita a partir de la Teoría de Capa Simple de Chapman. Si se elimina la suposición de atmósfera isotérmica y se consideran gradientes de escala de altura constantes dH/dh==0.2, los valores del exponente N, encontrados por regresión lineal entre la frecuencia crítica y el ángulo cenital del Sol, son muy semejantes a los predichos por la teoría de Chapman. Sus máximos valores de frecuencia (concentración) se encuentran un poco después del mediodía local y dependen fuertemente del nivel de actividad solar. Bajo condiciones diurnas, foE se incrementa entre 7 y 10 veces, teniendo la máxima razón durante períodos de Baja Actividad Solar. Se observa una clara tendencia de incremento de foE con la actividad solar. doi: https://doi.org/10.22201/igeof.00167169p.1996.35.1.110

Dynamics of pick-up ions in collisionless velocity shears

We study the motion of charged particles in large-scale velocity shears that are produced in the interaction of magnetized plasma winds and plasma obstacles. The purpose of the analysis is to account for the observation of strongly energetic contaminant ions in the region of interaction of the solar wind with planetary/cometary non-magnetic ionospheric obstacles (Venus, Mars, comets). The convective electric field set up by the streaming plasma is incorporated to the equation of motion of ions born in a velocity shear. Neglecting collisions and the back reaction of the contaminant particles on the wind, the trajectories of the particles are computed as a function of the shear properties as well as of the mass of the ions and the magnetic field configuration. For a linear dependence of the wind velocity across the shear, the problem is solved analytically and we find that the particle velocity can have either a purely oscillatory behavior or grow exponentially with time depending on the value of a dimensionless parameter proportional to the product of the velocity gradient and the cyclotron frequency of the ion trajectories. In the latter case a strong acceleration of the contaminant ions can be achieved. Adopting magnetic field and flow properties appropriate for cometary and planetary environments, we explore the potential importance of the mechanism discussed to explain the presence of superthermal ions and filamentary structures in such regions