Transcript Physics 1301: Lecture 1 - Home Page

Multi-Scale Coupling and Auroral Dynamics:
Reporter Review
Bob Lysak, University of Minnesota, USA
Purpose of the review: to examine the consequences of smallscale auroral processes on large-scale dynamics, and the
coupling of different plasma regions with each other.
Significant advances in the last 2 years, due to new and
continuing observations from FAST, Akebono, IMAGE, Polar,
and Cluster as well as ground observations, theory, and
numerical modeling.
Over 200 papers published in this area since the 2001 IAGA
meeting.
Outline of the Talk
Optical aurora and relation to plasma parameters
Electrostatic acceleration and time-independent coupling
Time-dependent coupling by Alfvén waves
Alfvénic particle acceleration
Ion acceleration and outflow
Nonlinear plasma waves: Electron and ion phase space holes
Coupling between aurora and outer magnetospheric processes
Optical Auroral Features and Plasma
Processes
Conjugacy of auroras:
 First simultaneous images of aurora with one camera, showing 40 min
MLT eastward displacement (Frank and Sigwarth, 2003).
 Conjugate observations of spirals, consistent with Hallinan theory, rotation
opposite to KH instability (Partamies et al., 2001).
 Latitude displacements of up to 5° due to IMF (Vorobjev et al., 2001)
Comparison with particle data
 FAST data compared with images from UVI (Peria et al., 2001) and
IMAGE (Mende et al., 2002, 2003) show poleward arcs associated with
wave-accelerated electrons, equatorward with inverted V’s
 Coordinated images for dynamic auroras, such as poleward moving
auroral forms (Kozlovsky and Kangas, 2002; Drury et al., 2003) and black
aurora (Peticolas et al., 2002)
Multi-spectral imaging
 Use of multiple wavelengths to determine precipitation
characteristics (Semeter et al., 2001; Janhunen, 2001; Galand et al.,
2002)
Northern and Southern Aurora
First simultaneous images
of both auroral ovals
Displacement of auroral
features by MLT of 40
minutes, with southern
aurora displaced to the
east.
Frank and Sigwarth, JGR,
2003.
Crossing of “Double Oval” with FAST
and IMAGE (Mende et al. 2003)
IMAGE
11:20
11:26
LBH
Lyman α
135.6 (OI)
IMAGE images of double oval compared with
FAST (arrows give time of images)
Seasonal effects on aurora
Plasma density in auroral
acceleration region larger in
summer than in winter
(Johnson et al., 2001, 2003)
Winter
Dark
Summer
Light
Polar cap densities also show
strong seasonal asymmetry
(Laakso et al., 2002)
Auroral activity dependent
on solar wind dynamic
pressure more for southward
IMF and winter (Shue et al.,
2002)
N Hemis,
4-6 RE
S Hemis,
2 RE
Three Regions of Auroral Acceleration
Illustration of three regions of auroral acceleration: downward current regions,
upward current regions, and the region near the polar cap boundary of Alfvénic
acceleration (Courtesy C. Carlson, from Auroral Plasma Physics, International
Space Science Institute, 2003)
Electrostatic Coupling and Acceleration
of Auroral Electrons (Observations)
Direct measurements of parallel electric fields
 Upward current region:
FAST shows large E|| (~ 100 mV/m) at lower edge of
auroral density cavity (Ergun et al., 2002)
parallel electric fields of 25-300 mV/m seen on Polar;
scale sizes 10’s of km based on potential of energized
particles (Hull et al., 2003)
 Downward current region
Strong E|| (up to 1 V/m), consistent with oblique double
layer model (Ergun et al., 2001; Andersson et al., 2002)
In both current regions, observation of E|| has been
supported by in situ particle acceleration as well as
double probe measurement.
Large Upward Parallel Electric Fields
from FAST and Polar
← FAST data
showing
large E|| at
boundaries
of auroral
cavity
(Ergun et
al., 2002)
→ Polar data
showing E||
associated
with
electron
and ion
acceleration
(Hull et al.,
2003)
Downward Parallel Electric Fields From
FAST
Observation of large
downward field in region of
strong turbulence (Ergun et
al., 2001)
Downward E|| and particle data,
together with inferred trajectory of
spacecraft with respect to potential
(Andersson et al., 2002)
Auroral Current-Voltage Relation
Old subject (e.g., Knight, 1973), but new interest, especially due to
observations in downward current region
Borovsky and Bonnell (2001) consider linear Knight relation (j = KΦ)
including dipole mapping with different constants in up and down
current regions
Rönnmark (2002) considered case when source population varies so
that quasi-neutrality is satisfied (with fixed ion density profile), found j
~ Φ1/2.
Boström (2003) considered general description of current carried by
various types of distributions, found Knight-type relations, but
variations in details.
Ergun et al. (2002) consider more local situation and found double
layer solution with realistic populations.
A gallery of currentvoltage relations
(Boström, 2003)
Response of plasma to
parallel potential drops
depends on form of particle
distribution at top of field
lines. Figure gives a variety
of distributions, with
voltage as a function of
current at right.
Alfvénic Coupling:
Observations
E
New Cluster observations show timevariations in auroral electric fields
and currents between passage of 4
spacecraft (Marklund et al., 2001)
J||
Alfvén wave Poynting flux correlated
with aurora and with electron energy
flux (Keiling et al., 2002, 2003)
Vsc
Observations consistent with field
line resonance found (Milan et al.,
2001)
Laboratory experiments confirm
kinetic Alfvén wave dispersion
relation (Kletzing et al., 2003)
Alfvénic Coupling: Theory and Modeling
Effects of parallel resistivity on small-scale structures (~ 1 km)
emphasized: enhanced damping of ionospheric resonator
(Lessard and Knutsen, 2001)
Energy budget of field line resonance with anomalous resistivity
included shows maximum dissipation at intermediate scales (~ 10
km) (Streltsov and Lotko, 2003)
Role of E|| in reflection of Alfvén waves trapped in ionospheric
Alfvén resonator emphasized (Pilipenko et al., 2002)
Model coupling the ionosphere to outer magnetosphere
developed showing role of auroral acceleration in modifying tail
pressure (Blixt and Vogt, 2002)
Effects of ionospheric Joule heating on production of tall auroral
rays modeled (Otto et al., 2003)
Alfvénic Coupling: Feedback Instability
Great deal of new work on ionospheric feedback: selfconsistent conductivity variations due to Alfvén wave
currents
 Compressible effects included in theory: effect not critical to
instability (O. Pokhotelov et al., 2001)
 Energetics of the instability considered: supported by
reduction of ionospheric Joule heating (Lysak and Song,
2002)
 New modeling of field line resonances including ionospheric
conductivity variations (D. Pokhotelov et al., 2002a,b;
Prakash et al., 2003)
Alfvén Feedback Modeling
Seasonal asymmetry between winter (top)
and summer (bottom) ionospheres:
feedback instability stronger in winter
(Pokhotelov et al., 2002)
Simultaneous excitation of
feedback in ionospheric
resonator (upper band
near 0.1 Hz) and for field
line resonance (lower
band at 0.01 Hz)
(Pokhotelov et al., 2003)
Alfvénic Acceleration of Electrons
In addition to “classical” quasi-static electron acceleration,
recent observations and theories have emphasized timedependent acceleration, giving broad energy distribution
and narrowly field-aligned pitch angles
 Akebono shows field-aligned electrons on edge of auroral
acceleration region (Miyake et al., 2001)
 Freja observations show field-aligned
distributions with energy dispersion:
particles arrive before wave, accelerated
above spacecraft (Andersson et al., 2002)
 Polar observations see field-aligned
acceleration of electrons at ~ 4 RE at
plasma sheet boundary layer (Wygant et al.,
2002)
FAST observations and modeling of
Alfvénic acceleration
Chaston et al. (2002ab, 2003abc) has looked at fieldaligned electrons and done test particle models to compare
with data.
FAST data showing fieldaligned bursts (Chaston et al.,
2002a)
Simulated (left column) and
observed (right) energy-pitch
angle distributions (Chaston
et al., 2002b)
Kinetic Theory of Alfvén Waves
New work has emphasized kinetic effects on Alfvén waves:
Tikhonchuk and Rankin (2002) developed kinetic theory of field
line resonances, found enhancement of E|| due to bouncing
electrons
Wright et al. (2002) and Wright and Hood (2003) emphasized
nonlinear convective term in two-fluid and kinetic models.
Lysak and Song (2003a,b) considered nonlocal kinetic theory in
ionospheric resonator, also found enhancement of E|| and strong
absorption near IAR resonances.
Génot et al. (2001) performed electromagnetic particle
simulations with Alfvén wave
fields; found formation of
localized electric fields in
density cavities
Ion Outflows
Recent work has emphasized
correlations with external
parameters and auroral arcs
Akebono shows good correlations with
solar F10.7, solar wind dynamic
pressure, solar wind E, and magnetic
fluctuations (Cully et al., 2003)
However, short-scale (5 minute) AE
fluctuations do not correlate with ion
outflow (Peterson et al., 2002)
Outflow (ions/m2s)
Direct response of ions to solar wind
pressure pulse seen by IMAGE
(Fuselier et al., 2002)
AE
More ion outflow
Ion outflow found to correlate well
with auroral forms (Wilson et al.,
2001)
Outflows follow convective motions
of arcs (Kistler et al., 2002) and
concentrate on arc boundaries
(Stevenson et al., 2001)
Modeling:
Solid: O+ ouflow; dashed:
LBH luminosity
Dynamic fluid/kinetic hybrid model of ion transport shows transverse
heating, “pressure cooker” effect of downward E|| (Wu et al., 2002)
3-d electrostatic PIC simulations show electron beam excitation of low
frequency (LH) waves, producing ion heating (Singh et al., 2001)
Global modeling shows heavy ion outflow mass-loads the outer
magnetosphere, lowering polar cap potential (Winglee et al., 2002)
Nonlinear Plasma Waves: Electron Holes
Electron holes form as a result of
beam-plasma interaction (Newman et
al., 2002)
Polar observations show width
increases with amplitude (Cattell et
al., 2001)
Consistent with allowed regions in
BGK models (Chen and Parks, 2002)
Perp width
3-d hole structures stable (Jovanovic
et al., 2002; Roth et al.,
2002) especially
when strongly
magnetized (Singh
et al., 2001)
Amplitude
Electron Holes as Source of VLF saucers
VLF saucers well-known for many
years (James, 1976); new FAST data
shows association with electron
holes (Ergun et al., 2001)
Theoretical model shows electrons
on trapped orbits in hole can radiate
VLF (Berthomier et al., 2002)
Simulations show that whistler mode
wave packets can be radiated from
holes (Singh,
2002)
Nonlinear Plasma Waves: Ion Holes
Ion holes observed
by Polar between
H+ and O+ velocities,
with larger
amplitudes for holes
near H+ speed
(Dombeck et al., 2001), supporting
ion-ion two-stream mechanism.
Ion holes observed by FAST show
acceleration of electrons by hole
potential (McFadden et al., 2003)
Outer magnetospheric coupling: shocks
and pressure pulses
Interplanetary shock
produces anti-sunward
propagating auroras
(Zhou et al., 2003)
Solar wind pressure
pulses increase auroral
oval width and
decreases polar cap
area (Boudouridis et
al., 2003)
WIND observations
IMAGE UV images
Southward turning of IMF leads to equatorward expansion of
auroral oval, propagating anti-sunward at convection speed
(McWilliams et al., 2001)
Outer magnetospheric coupling:
expansion phase onset
Onset arc forms a few minutes before
onset, rather than being long-lasting
growth phase arc (Lyons et al., 2002)
Pseudo-breakup associated with
localized current system in postmidnight oval (Partamies et al., 2003).
Two types of auroral development
during onset: arc “jumping” to higher
latitudes (associated with
reconnection); general expansion of
bright patch in all directions
(development of instability)
(Kornilova et al., 2003)
Outer magnetospheric coupling: bursty
bulk flows (BBF) and polar boundary
intensifications (PBI)
Comparison of MSP and All-sky
cameras show north-south extent of
aurora associated with PBI (Zesta et
al., 2002)
PBI/BBF associated with large-scale
ULF wave power in the tail (Lyons et
al., 2002). Association with Pi2
packets also seen (Sutcliffe and
Lyons, 2002)
BBF is diverted azimuthally in inner
magnetosphere, as seen from
equatorward extension of PBI
(Kauristie et al., 2003)
Series of PBI’s moving equatorward
in late expansion phase indicate series
of BBF’s (Sandholt et al., 2002)
Summary
Auroral plasma physics remains a quickly developing
field combining aspects of microscropic plasma
physics, MHD waves and energy flows, ionospheric
structure and chemistry, optical observations, etc.
Importance of parallel electric fields has been well
established; evolution and structure of the auroral
acceleration region remain important questions.
Auroral features are a diagnostic of both the local
plasma conditions and the outer magnetospheric
conditions along the field lines.
Combination of in situ plasma measurements and
optical features in the aurora are providing a wealth of
new information.
Some outstanding questions
Development and evolution of parallel potential drops
and their relation to external conditions is still not well
understood: our suspicion is that Alfvenic processes
pre-condition auroral field lines to form quasi-static
potentials (see, e.g., Song and Lysak, 2001).
Relation of ion outflows to driving forces (e.g.,
Poynting flux into auroral zone) is still not clear; role
of these ions in magnetospheric dynamics is still
speculative.
Formation of narrow (< 1 km) auroral forms remains a
mystery; probably due to interactions between the
acceleration region and the ionosphere.
Role of ionospheric processes (ionization,
recombination, heating, chemistry) on auroral
formation is just beginning to be investigated
For further information…
Special section of JGR-Space Physics, “Causes of the
Aurora” published in April, 2003.
New monograph Auroral Plasma Physics by team of >
30 authors published by International Space Science
Institute (Kluwer, 2003).
Set of 219 articles published in 2001-2003 period
were compiled for this review: list will be available at
http://ham.space.umn.edu/spacephys/~bob after this
meeting (as will this presentation).