Earth and Space Sciences, UCLA
MAGNETOTAIL TRNSIENTS
and their Role in Energetic Particle
Transport towards the Inner
Magnetosphere
A. Runov,
C. Gabrielse, S. Kiehas, J. Liu, S. Li, D. Turner, X.-Z. Zhou,
and V. Angelopoulos
IGPP/ESS UCLA
Thanks to THEMIS team
NASA Grants NAS5-0299, 1-LWSTRT11-0048, NNX13AE10G
NSF grant 1044495
Summer GEM workshop, June 17, 2013
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Outline

Introduction



“Average” Plasma Sheet, Dungey cycle time scale
Transient - a definition
Overview of magnetotail transients





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Bursty-bulk flows
Flow bursts and rapid flux transport events
Dipolarization fronts
Common characteristics
"Bubble" model as an "envelope" model for the transients
Origin: RX, kinetic interchange

3. Their role in particle energization and transport towards the inner
magnetosphere

4. Summary & Open Questions

5. Perspectives
Summer GEM workshop, June 17, 2013
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Introduction
The Magnetotail Plasma Sheet (PS)
Nominal PS geometry and the GSM (Geocentric
Solar Magnetospheric) Coordinate System
jmp
Z
dawn
jct
X
 PS thickness at X~-15 RE varies 3 – 10 RE;
 The current sheet with thickness of <1 – 3
RE is embedded into the PS;
 “Neutral sheet” is a region near min(|Bx|).
dusk
Y
Average quiet-time PS parameters
@ X=-19 - -13 RE
 The magnetotail PS is the major source N ~ 0.3 cm-3
<|B|> @ NS ~ 5 nT
of ring current and outer radiation belt
<Bz> @ NS ~ 3 nT
Ti ~ 5 keV
particle populations.
Te ~ 0.5 keV
<| j |> ~ 3 nA/m2
β = 2μ0nkT/B2 > 1 rLi = 1000 km
 Active PS often far from the average
di =c/ωpi= 400 km
 Transients: temporal large-amplitude
deviations from “nominal” parameters 
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Introduction
What is “Transient”
Definition of TRANSIENT
1
a : passing especially quickly into and out of
b : passing through or by a place with only a brief stay
2: affecting something or producing results beyond itself
http://www.merriam-webster.com
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Introduction:
Dungey Cycle Timescale
 What means “temporal”? Is there any “steady”
time scale?
 “Dungey Cycle” after Dungey (1961): “steady”
magnetospheric convection;
 “Dungey cycle timescale”: time from the opening
of the field lines at the dayside to the closing of
the field lines on the nightside.
 The Dungey cycle time in the Earth’s
magnetosphere is ~ 1 hr (Cowley, 1982)
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Transient Processes in the Active
Magnetotail
 Transient phenomena (transients) are
spatially and temporally localized
large-amplitude deviations from the
average parameters: BBFs, RFT,
transient dipolarizations, plasmoids &
flux ropes, FACs, high-energy particle
bursts, beamlets, etc…
 Time scale of transients varies from
seconds to several minutes (i.e. 0.001
– 0.1 of the Dungey cycle timescale).
Caution: spatial structures
In this tutorial:
• Bursty Bulk Flows (BBFs)
• Rapid Flux Transport (RFT) events
• Dipolarization Fronts (DF)
Summer GEM workshop, June 17, 2013
 Sharma et al., Ann. Geo. 2008:
A review of transient processes with
temporal scales of 10s – 10 min and
spatial scales of a few RE in the
magnetotail
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BBFs, Flow Bursts, & RFT
 BBF time scale: ~10 min
 Cross-tail extent ~2 RE.
 BBFs consist of a set of flow
bursts (FB) with time scale
~100 s
|V|>400 km/s
 Rapid flux transport events:
~100 s-long enhancements of
the convective electric field.
Angelopoulos et al., 1992
E>2.0 mV/m
Rapid Flux Transport, RFT
Schoedel et al., 2001
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RFTs in Reconnecting TCS
Bx
By
Bz
Vx<0
Ey
Vx>0
 C3 & C4: Impulsive behavior with
the characteristic time of 1 min.
Simultaneous peaks up to 7 mV/m
at C3 (Bx<0) and at C4 (Bx>0),
associated with local Bz peaks.
 Duration of a peak ~ 60 s
 Interval between peaks ~100 s
⇒ Micro loading-unloading
⇒ Birth of RFTs
Ey
Runov et al., JGR, 2008
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Dipolarization Fronts
 First reported by Russell &
McPherron (1973);
 Injection front (Moore et al., 1981)
 Earthward expanding current
disruption (Ohtani, 1998; Ohtani et
al., 1998)
 R. Nakamura et al, 2002: “DF”
 Sitnov et al., 2009: DF in PIC
 THEMIS observations:
•
•
•
•
•
Runov at al, 2009, Lyons et al., 2012
Summer GEM workshop, June 17, 2013
Sharp increase in Bz
Often preceded by a dip
Decrease in density
Embedded into earthward flow
Change in energy spectra
 A moving boundary between two
distinct plasma populations: the
intruding hot tenuous plasma and
the ambient plasma sheet.
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Dipolarization Fronts: Statistics
Runov et al., JGR, 2011
δBz
1320 x-ings
30
0
δN
Vx
δBz
20 nT
0
10 mV/m
0
Ey
δJi/Ji0
-120
δJe/Je0
-60
0
60
120
J.Liu et al., JGR, 2013
δN/N0
δTi/Ti0
δTe/Te0
 Readily detectable marker for the intruding
population; useful to organize statistics
(superposed epoch analysis).
Electric field pulse
Vx
60 s
δPth
DF
60 s
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Spatial Localization, Scale,
& Plasma Vortices

Maximum occurrence rate at
-15<X<-8 RE 0<YGSM<5 RE
-- similar to RX localization (e.g. Nagai et al.,
2013);

Cross-tail extent,~ 2 RE -- similar to BBFs’
(e.g., Nakamura et al., 2004)

Vortical plasma flow around the front head
~1 RE
J.Liu et al., JGR, 2013
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DF Origin:
Impulsive (transient) RX or/and Interchange
Transient RX, Semenov et al., 1984
Bz
E*
Kinetic interchange
(ballooning)
Pritchett & Coroniti, 2010
Kiehas et al., 2009
Pritchett & Coroniti, 2011
•Timing of THEMIS observations suggests RX:
PIC simulations of TRX,
Sitnov et al, 2009
Summer GEM workshop, June 17, 2013
Angelopoulos et al., Science, 2008;
Oka et al., GRL, 2011;Runov et al., JGR, 2012
•Contra-example: Panov et al., JGR, 2012
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Summary I: “Plasma Bubble“ is
an ‘envelope ‘model for the transients
 Magnetotail transients inter-relationship:
 BBF (~10 min) consists of individual
flow bursts with the time scale of 100 s;
 Flow bursts (FB) or rapid flux transfer
(RFT) events are a dipolarized, density
depleted flux tubes – “plasma bubbles”
(see e.g., Wolf et al, 2009 for review)
generated by reconnection pulses;
 Dipolarization front (DF) is a gyro-scale
boundary (magnetopause) separating
the depleted flux tube from the ambient
plasma sheet.
Pembroke et al., JGR, 2012
 Time scales of the magnetotail transients vary within 1 to a few 100 s
 The transients’ cross-tail extent is of 1 – 3 RE (<1 hr MLT)
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Why Do We Care?
 Q: What large-scale uniform dawn-dusk electric field is to transport 10 –
30 keV electrons @~12 RE at midnight to the Van Allen Probes orbit?
Dipole B-field
Uniform E-field
Edd = 0.5 mV/m
10 keV
Initial energy: 20 keV
30 keV
Dipole B-field
Uniform E-field
Edd = 5.0 mV/m
10 keV
Initial energy: 20 keV
30 keV
 A: ~5 mV/m ~ 10 times larger than the typical one.
 Corresponds to the cross-polar-cap potential (30 RE) of 900 kV! Oops!
Gabrielse et al., JGR, 2012
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Localized Electric Field Pulse
δBz
Ey
10 mV/m
 Localized electromagnetic pulse
(e.g., Li et al, 1998; Sarris et al., 2002;
Zaharia et al., 2004, Gabrielse et al., 2012) ;
 Burst particle transport on top of slow
convection in the global dawn-dusk E-field
 Seed population for the outer RB
Summer GEM workshop, June 17, 2013
Gabrielse et al., JGR, 2012
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High Energy Electron Transport:
A Seed Population for RB
E=-VxB
Dawnwarddrifting HE
After Birn et al., 2013, SSR electrons
100 keV
100 keV
10 keV
Summer GEM workshop, June 17, 2013
Electrons
(E>30 keV)
Runov et al., 2013, JGR
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Interaction with Ambient Ions:
Localized Pressure Build-up
Y, RE
X, RE
Plasma bubble
Compressed plasma
Earthward-streaming accelerated ions
S.Li et al., JGR, 2011
Summer GEM workshop, June 17, 2013
J.Yang et al., JGR, 2011, 2012
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Interaction with ions in PS & PSBL
Observations and Modeling
X-Z. Zhou et al., 2012, JGR
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Interaction with Ions in PS & PSBL
“Statistics”
• Select simultaneous observations of
PSBL and plasma sheet;
• In 16 of 18 selected events the PSBL
beam was followed with 1 – 2 minutes
delay by earthward flow and
dipolarization front in the PS.
The PSBL beams are closely related
to BBFs and dipolarization fronts in
CPS (Baumjohann, 1988; Angelopoulos et
al., 1993; Lennartsson et al., 2001, 2009).
X-Z. Zhou et al., 2012, JGR
Summer GEM workshop, June 17, 2013
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Summary II
Open Questions
 The magnetotail transients (FB/RFT/DF) are spatially localized earthwardpropagating electric field pulses that
 provide burst transport of energetic particles towards the inner
magnetosphere on a top of the slow global convection;
 bring energetic (~100 keV) particles towards smaller L-shells, providing the
seed population for the outer radiation belt.
 DFs create localized pressure enhancements in the near-Earth PS and ion
beams in PSBL ahead of them  FAC generation, waves
 Open Questions

How do 1-100 s time scale, spatially localized transients form large-scale
injections, global dipolarizations, SCW? (Substorm onset FG, TIMI FG)

FB/DF rarely reach GEO (<30%) - How and where to their kinetic and
electromagnetic energy is converted? (TIMI FG)

What determines spatial localization (premidnight) and characteristic time of
reconnection pulses (100 s)? What are relative roles of RX and
interchange? How do they (inter-)connected? (RX FG)
Summer GEM workshop, June 17, 2013
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Perspectives
 The NASA Van Allen Probe
mission was launched on
August 30, 2012.
 THEMIS/Van Allen campaigns
are planned
 THEMIS/ARTEMIS/MMS
alignments at solar max:
ideal for PS studies
2010-04-10 00:00:00
FY 14/15
Z
MMS Phase2 or 1/3
P3
P4
X
P4
P3
P2
RBSP
LOS GEO
P1
Y
X or -X
P5
MMS
P5
A tetrahedron within a tetrahedron
Summer GEM workshop, June 17, 2013
MMS
FY 15/16
New adventures are waiting!
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Dipolarization Front Structure
Δt  Vt  Δx = ∫Vt dt
Runov et al., JGR, 2011
Summer GEM workshop, June 17, 2013
TCS ~1RLI
10 s
103 km
10 s
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