Auroral Boundaries:
Finding Them in Data and Models
Gang Lu
High Altitude Observatory
National Center for Atmospheric Research
Joint CEDAR/GEM Workshop, Santa Fe, June 29, 2005
Outline
• Plasma Convection & Convection Reversal Boundary (CRB)
• Plasma Boundary Layers & Auroral Boundaries
• Auroral Boundaries from High Frequency (HF) Radar
Measurements
• Auroral Boundaries from Incoherent Scatter (IS) Radar
Measurements
• Auroral Boundaries in Global MHD Models
• Advanced Modular Incoherent Scatter Radar (AMISR)
Dipole Magnetic Field
Distorted Magnetic Field
Magnetic Reconnection
& Circulation
x
Noon-Midnight Meridional Plane
Magnetospheric
Topology & Plasma
Convection
CRB and OCB
do not always coincide
Equatorial Plane
Open-Closed
Boundary
(OCB)
Flow lines
Dawn
60°
Noon
Bow Shock
Magnetopause
High-Latitude
Ionosphere
Midnight
Solar
wind
Dusk
Noon-Midnight Meridional Plane
Magnetospheric
Topology & Plasma
Convection
Solar
wind
High-Latitude
Ionosphere
Equatorial Plane
Dawn
Flow lines
60°
Midnight
Auroral
Oval
Noon
Bow Shock
Dusk
Ion Drifts Measured by DMSP Satellites
CRB
Southward
IMF Bz
Northward
IMF Bz
CRB
Ion Drifts Measured by Sondrestrom IS Radar
CRB
(Clauer & Ridley, JGR, 1995)
Ion Drifts Measured by SuperDARN HF Radars
CRB
Convection Patterns Derived from SuperDARN
Northward Bz
Southward Bz
Convection Patterns Derived from AMIE
(Lu et al., JGR, 1994)
Morphology of Plasma Boundary Layers
Radiation Belt
Mantle
Cusp
Boundary
Plasma Sheet
(BPS)
w
Bo
Mantle
k
oc
Sh
Cusp
Magnetopause
Plasmasphere
Central Plasma Sheet
(CPS)
Morphology of Plasma Boundary Layers in 3D
Ma
gne
top
aus
e
Cu r
r en
t
y
ar
d
un
Bo
e
ud )
t
i
t
La LLBL
w
(
Lo yer
a
L
(after Kivelson & Russell, 1995)
Auroral Precipitation Boundaries from DMSP Satellites
(Newell & Meng, GRL, 1988)
Relationship Between Auroral Precipitation & Convection
Mantle
Cusp
LLBL
BPS
CPS
Subvisual
Bz < 0
By < 0
Bz > 0
By < 0
Bz < 0
By > 0
Bz > 0
By > 0
Polar Rain
(Newell et al, JGR, 2004)
Relationship Between Auroral Precipitation & Convection
Mantle
Cusp
LLBL
BPS
CPS
Subvis
Bz < 0
By < 0
Bz > 0
By < 0
Bz < 0
By > 0
Bz > 0
By > 0
Polar Rain
(Newell et al, JGR, 2004)
Auroral Boundaries – A Global View
POLAR-VIS
Polar UVI
Jan. 9, 1997 (LBHL)
(Brittnacher et al, JGR, 1999)
0749:16
0651:27
0759:32
Time
Time
0534:47
0719:40
GW Km2 x 106
IMAGE FUV
0839:24
Polar Cap Area
Precipitation Power
05:00
06:00
07:00
08:00
09:00
10:00
(Mende et al, JGR, 2003)
Auroral Boundaries from HF Radar Measurements
Width (m/s)
Geo. Latitude
Spectral Width (m/s)
(Milan et al, 1999)
Intensity (kR)
MSP @ 6300Ă
Geo. Latitude
- the dayside Cusp
Number of Events
• A sharp latitudinal gradient in the
Doppler spectral width has been
associated with:
(Baker et al, JGR, 1995)
(Milan et al, Ann. Geophys.,1999)
Auroral Boundaries from HF Radar Measurements
• A sharp latitudinal gradient in the
Doppler spectral width has been
associated with:
- the dayside Cusp
- the boundary between the CPS and
the BPS
- the LLBL
- the open-closed boundary
Based on 6 HF radars between
October 1996 – May 1997
(Villain et al, Ann. Geophys., 2002)
Auroral Boundaries from HF Radar Measurements
• A sharp latitudinal gradient in the
Doppler spectral width has been
associated with:
- the dayside Cusp
- the boundary between the CPS and
the BPS
- the LLBL
- the open-closed boundary
• Advantage:
The broad radar coverage allows to
image the auroral boundaries
continuously and globally
Cusp Boundary
Auroral Boundary
• Limitation:
The high spectral width can be
observed both on closed and open
regions (e.g., Lester et al., Ann. Geophys.,
2001; Woodfield et al., Ann. Geophys.,
2002; Andre et al., Ann. Geophys., 2002)
(Villain et al, Ann. Geophys., 2002)
3x104 cm-3
Electron Density
• Advantage:
- not affected by “blackouts”
- able to observe several important
plasma parameters (e.g., Ne, Ti,
Te, Vi) simultaneously
• Limitation:
- limited availability of IS radars
- expensive to operate
(de la Beaujardiere et al, JGR, 1991)
Invariant Latitude (degree)
Intensity [R]
- the dayside Cusp
- the nightside auroral poleward
boundary
Ne [103 cm-3]
• Ti and/or Te, and the E-region
electron density have been
used to identify:
Altitude (km)
Auroral Boundaries from IS Radar Measurements
(Blanchard et al, JGR, 1996)
Auroral & Open-closed Boundaries in Global MHD Models
UCLA-GGCM Code
Energy flux for diffuse e-
Energy flux for discrete e-
Lyon-Fedder-Mobarry Code
NH energy flux
Electric Potential
Electric potential
SH energy flux
Field-aligned current
Field-aligned current
(Courtesy of Jimmy Raeder)
(Fedder et al, JGR, 1995)
Why should we care about auroral boundaries?
¾Observations of auroral boundaries can be used to
remotely monitor magnetospheric processes (e.g.,
reconnection rate), and to validate large-scale
magnetospheric models
¾Auroral boundaries may be used as a dynamical
coordinate system to better organize some physical
parameters (e.g., Poynting flux, ion upflow/outflow)
Auroral Boundaries – Dynamic Coordinates
Ion Outflow (ILAT/MLT Coordinates)
Ion Outflow (Dynamic Coordinates)
Oxygen
60°
18
60°
Poleward
Boundary
18
Equatorward
Boundary
00
(Andersson et al, JGR, 2004)
Hydrogen
Why should we care about auroral boundaries?
¾Observations of auroral boundaries can be used to
remotely monitor magnetospheric processes (e.g.,
reconnection rate), and to validate large-scale
magnetospheric models
¾Auroral boundaries may be used as a dynamical
coordinate system to better organize some physical
parameters (e.g., Poynting flux, ion upflow/outflow)
¾Auroral precipitation and ionospheric plasma convection
represent two of the major magnetospheric forcings on
the ionosphere and thermosphere dynamics and
electrodynamics (they are the two primary upper boundary
inputs of GCMs)
¾Let’s not forget about the ionospheric feedback effects
AMISR
Advanced
Modular
Incoherent
Scatter
Radar
384 Panels, 12,288 AEUs
3 DAQ Systems
3 Scaffold Support Structures
(Courtesy of Craig Heinselman)
Plasma Parameter Maps
1500 PULSES
Altitude (km)
800
0
-400
0
400
Ground Distance (km)
(Courtesy of Craig Heinselman)
V7-6 END
AMISR Ion Velocity Estimation
ALTITUDE (km)
160
140
120
100
Vector Scale
:3000 ms–1
3 positions, 3 km & 3 m intervals
E-FIELD (V m–1)
0.10
0
E East
E North
–0.10
3 positions, 3 m intervals
10:00
11:00
TIME (UT)
12:00
(Courtesy of Craig Heinselman)
v12
AMISR Coverage – Global Context
A Great Observatory:
• ISRs
• SuperDARN
• Optical Instruments
(MSPs & All-sky imagers)
• Distributed Arrays of
Small Instruments (DASI)
+ Satellites
(Courtesy of Craig Heinselman)
v21B