Download presentation
Presentation is loading. Please wait.
Published byStewart Perry Modified over 9 years ago
1
Kinetic Effects in the Magnetosphere Richard E Denton Dartmouth College
2
What Do We Mean by Kinetic Effects? Related to kinetic theory, but more general Kinetic theory is a description of a plasma using a phase space distribution In a phase space distribution, there is assumed to be a smooth distribution of particles with respect to spatial position and velocity
3
Examples of Kinetic Effects Hall reconnection Meandering orbits in reconnection Particle drifts around the earth separating ions from electrons Drift shell splitting Cusp bifurcation of trapped populations Curvature scattering Drift resonant acceleration of particles from fast mode fronts
4
Hall Reconnection [Birn et al., JGR, 2001]
5
Invariants
6
Adiabatic Particle Drifts [from Emilia Kilpuna from ?]
7
Meandering Orbits of Unmagnetized Electrons Can Support the Out of Plane Reconnection Electric Field [Hesse, Space Sci. Rev., 2011]
8
Separation of Particle Populations [Thorne, GRL, 2010]
9
So What Do I Mean by Kinetic Effects? In the broadest sense, effects that cannot be described by single fluid MHD In a more narrow sense, effects that cannot be described by fluid equations In the most narrow sense, effects that occur because of a distribution of particles in velocity space
10
WAVES Wave phenomenon strongly depend on kinetic effects and have a large influence on important particle distributions
11
Classification of Waves Waves are categorized by frequency or the process that generated them Ultra Low Frequency (ULF) have a frequency range of roughly 1 mHz to about 3 Hz (magnetospheric definition) The Pc (pulsation continuous) classes are –Pc 5, 1-7 mHz –Pc 4, 7-22 mHz –Pc 3, 22-100 mHz –Pc 2, 0.1-0.2 Hz –Pc 1, 0.2-5 Hz ELF about 3 Hz to 3 kHz (magnetospheric definition) VLF 3 to 30 kHz
12
ULF Waves Mostly MHD waves (not Pc 1) - aspects of these waves can be described by MHD equations Ion scale – the ions are able to oscillate at these frequencies (electron stick with the ions to maintain quasi-neutrality) Pc 4-5 – often associated with fundamental or 2 nd harmonic of the Alfven wave eigenmode along field lines –may be externally driven by fast mode waves related to oscillations of the magnetopause or internally driven by the particle population Pc 2-4 – often associated with higher harmonics of the Alfven wave eigenmodes driven by external waves Pc 1-2 – often associated with electromagnetic ion cyclotron waves (EMIC) driven by the ion velocity distribution (much of the talk will focus on these) –Frequency near the proton gyrofrequency
13
VLF Waves 3 to 30 kHz High frequency waves are associated with electrons – only the electrons are able to oscillate at these frequencies Includes plasma waves (Langmuir oscillations) and whistler chorus waves
14
ELF Waves 3 Hz to 3 kHz Range in between proton gyrofrequency and electron gyrofrequency Includes waves at harmonics of the proton gyrofrequency, at the lower hybrid frequency, and in a broad range of whistler waves Includes whistler “hiss” waves
15
KINETIC DRIVING OF WAVES Waves grow due to an instability resulting from inhomogeneity. Some waves, such as the lower hybrid drift wave and the drift Alfven ballooning mode (Pc 4-5), can be driven by spatial inhomogeneity. Here we consider velocity space instabilities.
16
Types of Velocity Space Instabilities Two stream velocity distribution, or beam velocity distribution, or bump on tail velocity distribution Temperature anisotropy
17
DISPERSION SURFACES Fluid theory describes wave dispersion surfaces, but kinetic calculations show that these surfaces can be altered by the finite temperature of the plasma
18
Electromagnetic Ion Cyclotron Waves in H+, e- Plasma [See Andre, Dispersion Surfaces, 1985]
19
H+, He+, e- Plasma
20
H+, He+, O+, e- Plasma
21
Group Velocity
22
Kinetic Effects Alter the He Dispersion Surface ehkim@pppl.gov [Denton et al., JGR, 2014]
23
Kinetic Effect on Ion Bernstein Dispersion Surface [Denton et al., JGR, 2010]
24
jWhamp available from me (redenton@dartmouth.edu)
25
jWhamp Output And output files with detailed field and particle species information
26
SIMULATIONS ELECTROMAGNETIC ION CYCLOTRON WAVES (EMIC) Fluid theory and kinetic dispersion codes can give valuable information about waves, but ultimately observed waves result from nonlinear growth, which is usually best modeled by simulations
27
General Wave Properties Electromagnetic (dB as well as dE) < cp Driven by properties of the ion (normally proton) velocity distribution function, temperature anisotropy T > T // or possibly a loss cone distribution function Waves driven near magnetic equator where h// is large Resonance particles see Doppler shifted wave frequency that matches the proton gyrofrequency For parallel propagation ( kB 0), the waves are left hand polarized, but they become linearly polarized at large kB Heavy ions make a difference since they alter the wave dispersion surfaces
28
Causes of EMIC Waves Waves driven by compressions (ephemeral waves) or by replenishment of anisotropic ring current H+ (driven waves) Drift shell splitting Stagna -tion P dyn
29
Hybrid Code Description Self-consistent hybrid code simulation of electromagnetic ion cyclotron waves Full dynamics particle ions and/or electrons, inertialess fluid electrons to bring about charge neutrality Dipole coordinates Can have reflecting conductor boundary conditions, but here we are damping waves at the boundaries Initialize particle distribution from anisotropic MHD equilibrium Waves driven by hot protons with T /T // 2 near the magnetic equator Hot protons, cold H+, cold He+, and cold O+ Some runs include a plasmapause for cold species
30
Hybrid Code Description – New Features Now making full scale runs at geostationary orbit with realistic parameters Can make particles relativistic –Evolve u = v = p/m 0 rather than v – 2 = 1 + u 2 /c 2 –du/dt = F Lorentz /m 0 –dx/dt = u/ Can remove precipitating particles –Mark time of precipitating particles (and stop evolving) if sin 2 = u 2 /u 2 < B b /( L 0 3 *sqrt( 4 – 3/L ) ) when particles cross the ionospheric boundary (otherwise reflect them) Simple 1D Matlab hybrid code available (not this one) – email redenton@dartmouth.edu
31
Normalized Equations
32
Geometry
33
A h sqrt( h// ) From Anisotropic MHD Code
34
Finding equilibrium
35
Evolution of EMIC Wave Fields
36
Evolution of kB
37
Spectra Observed in plume (data courtesy Brian Fraser) Simulation in plasmasphere (different time and location)
38
2D Ellipticity-Power Color Map
39
Wave Power on Curvilinear Grid at Different Times ( He+, 0.5% O+)
40
Wave Power Development and Poynting Vector
41
Effect of O+ Concentration on Wave Development
42
O+ Heating
43
Effect of Gradients – Coherence Length [Hu and Denton, 2009] q
44
Effect of Plasmapause
45
Heavy Ion Composition [Craven et al., JGR, 1997] [Denton et al., JGR, 2011]
46
L Profiles of Plasma Parameters From Vania’s Jordanova’s Simulation of 9 June 2001 EMIC Event Cold Compo- sition Constant Cold Compo- sition Variable
47
Simulations with low O+ and large O+ in trough
48
Frequencies WHAMP Simulation
49
Effect of Waves on Ring Current H+
50
Run with Realistic Parameters and Full Scale Size
51
Pitch Angle Distribution Functions Now integrate over v, and define normalized pitch angle distribution function for bi- Maxwellian with R T = T /T //
52
Pitch Angle Distribution Functions for Run t=0, q<0.2 t=2000, q<0.2 t=2000, precipitated
53
Precipitation of Ring Current H+
54
Precipitation (loss) to Ionosphere of Radiation Belt Electrons
55
Wave Power
56
Fields
57
Wave Proper- ties
58
Probability of Precipi- tation in 1 s
59
Probability Versus Pitch Angle and Energy
60
Diffusion Coefficients
61
Conclusions Kinetic effects usually refer to effects arising from a distribution of particle velocities. In the broadest sense, a multifluid description could be considered to be kinetic. Kinetic effects give rise to different evolution for different particle populations, either differences due to a difference in species (westward versus eastward drift), or differences due to different velocities (drift shell splitting) Kinetic effects influence processes such as magnetic reconnection Kinetic effects alter wave properties Kinetic effects cause waves to grow and these waves affect different parts of the velocity distribution differently
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.