On Resonant Interaction of Electrons with Falling-Tone Chorus Waves

2021 ◽  
Author(s):  
Ilya Kuzichev ◽  
Angel Rualdo Soto-Chavez
Keyword(s):  
Magnetic Field ◽  
Wave Field ◽  
Particle Dynamics ◽  
Wave Frequency ◽  
Spatial Inhomogeneity ◽  
Frequency Variation ◽  
Outer Radiation Belt ◽  
The Earth ◽  
Chorus Waves ◽  
Frequency Chirping

<p>Whistler-mode chorus waves are one of the most intense wave phenomena in the Earth’s inner magnetosphere. They are considered to be a major driver of the outer radiation belt dynamics, as they can efficiently scatter and energize electrons via resonant wave-particle interaction. These waves are observed as series of discrete coherent structures with rising or falling frequencies in the whistler frequency range (below local electron cyclotron frequency).</p><p>Such frequency variation results in a correction to the resonance Hamiltonian which describes particle dynamics in the given wave field. For a monochromatic wave, the effective potential in the resonance Hamiltonian consists of two terms. The first one corresponds to the nonlinear pendulum and describes the direct interaction of a particle with the wave. The second term accounts for plasma inhomogeneity, describing the effects of spatial gradients of plasma and wave parameters on the particle. Frequency chirping contributes to this effective inhomogeneity, producing a correction to this second term. The inhomogeneity term is of particular importance for the trapped particles that remain in resonance with the wave, this term defines their acceleration. And, as spatial inhomogeneity becomes zero at the equator (for dipole magnetic field), the wave frequency variation contribution might be the dominant one close to this region.</p><p>In this report, we present the results of test particle simulations of the electron dynamics in the field of a chirped wave. A general curvilinear relativistic code is developed to address the particle dynamics in the wave field, pre-determined from the simplified wave equations. We demonstrate that particle acceleration is affected by the competition between the effective inhomogeneity related to the wave frequency chirping and spatial inhomogeneity of the Earth’s magnetic field.</p><p>The work is supported by the National Science Foundation (NSF) grant No. 1502923. We would like to acknowledge high-performance computing support from Cheyenne (doi:10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory, sponsored by NSF</p>

The Plasmasphere During Major Geomagnetic Storms: Analysis Of Trapped Particles In The Outer Radiation Belt

2020 ◽  
Author(s):  
Jessy Matar ◽  
Benoit Hubert ◽  
Stan Cowley ◽  
Steve Milan ◽  
Zhonghua Yao ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Geomagnetic Field ◽  
Radiation Belt ◽  
Ring Current ◽  
Geomagnetic Storms ◽  
Outer Radiation Belt ◽  
Trapped Particles ◽  
The Earth ◽  
Field Lines

<p> The coupling between the Earth’s magnetic field and the interplanetary magnetic field (IMF) transported by the solar wind results in a cycle of magnetic field lines opening and closing generally known as the Dungey substorm cycle, mostly governed by the process of magnetic reconnection. The geomagnetic field lines can therefore have either a closed or an open topology, i.e. lower latitude field lines are closed (map from southern ionosphere to the northern), while higher latitude field lines are open (map from one polar ionosphere into interplanetary space). Closed field lines can trap electrically charged particles that bounce between mirror points located in the North and South hemispheres while drifting in longitude around the Earth, forming the plasmasphere, the radiation belts and the ring current. The outer boundary of the plasmasphere is the plasmapause. Its location is mostly driven by the interplay of the corotation electric field of ionospheric origin, and the convection electric field that results from the interaction between the IMF and the geomagnetic field. At times of prolonged intense coupling between these fields, the response of the magnetosphere becomes global and a geomagnetic storm develops. The ring current created by the motion of the trapped energetic particles intensifies and then decays as the storm abates. This study aims to find a possible relationship between the evolution of the trapped population and the process of magnetic reconnection during storm times. The EUV instrument on board the NASA-IMAGE spacecraft observed the distribution of the trapped helium ions (He+) in the plasmasphere. We consider several cases of intense geomagnetic storms observed by the IMAGE satellite. We identify the plasmapause location (Lpp) during those cases. We find a strong correlation between the Dst index and Lpp. The ring current and the trapped particles are expected to vary during storms. We use the Tsyganenko magnetic field model to map the electric potential between the Heppner-Maynard boundary (HMB) in the ionosphere and the magnetosphere and estimate the voltage and electric field in the vicinity of the plasmapause. The ionospheric electric field is deduced from the ionospheric convection velocity measured by the SuperDARN (SD) radar network at high latitudes. The tangential electric field component of the moving plasmapause boundary is estimated from IMAGE-EUV observations of the plasmasphere and is compared with expectations based on the SD data. We combine measurements of the trapped population from IMAGE-EUV and IMAGE-FUV observations of the aurora to better understand and quantify the variability of the Earth's outer radiation belt during strong storms. The auroral precipitation at ionospheric latitude is studied using FUV imaging and compared to the He+ response during the storms.</p>

scholarly journals The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth’s Magnetic Field

2020 ◽  
Author(s):  
Kun Li ◽  
Matthias Förster ◽  
Zhaojin Rong ◽  
Stein Haaland ◽  
Elena Kronberg ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spatial Inhomogeneity ◽  
Polar Cap ◽  
Polar Wind ◽  
The Earth ◽  
Polar Rain ◽  
Ionospheric Outflow ◽  
Low Energy Ions ◽  
The Magnetic Field ◽  
Positively Charged

<p>When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth’s polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the low-energy ions with a positively charged spacecraft. In this study, we found anti-correlation between ionospheric outflow and the strength of the Earth’s magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth’s magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels.</p>

scholarly journals Quasiadiabatic description of nonlinear particle dynamics in typical magnetotail configurations

2005 ◽  
Vol 12 (1) ◽  
pp. 101-115 ◽  
Author(s):  
D. L. Vainchtein ◽  
J. Büchner ◽  
A. I. Neishtadt ◽  
L. M. Zelenyi
Keyword(s):  
Magnetic Field ◽  
Characteristic Length ◽  
Neutral Line ◽  
Charged Particles ◽  
Particle Dynamics ◽  
Field Reversal ◽  
The Earth ◽  
Nonlinear Particle Dynamics ◽  
Small Parameters

Abstract. In the present paper we discuss the motion of charged particles in three different regions of the Earth magnetotail: in the region with magnetic field reversal and in the vicinities of neutral line of X- and O-types. The presence of small parameters (ratio of characteristic length scales in and perpendicular to the equatorial plane and the smallness of the electric field) allows us to introduce a hierarchy of motions and use methods of perturbation theory. We propose a parameter that plays the role of a measure of mixing in the system.

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