MESSENGER – BepiColombo Workshop, Nov. 2-5, 2010
Direct Measurements of the Poynting Flux
Associated with Convection Electric Fields
Toshi Nishimura12, Larry Lyons1, Takashi Kikuchi2,
John Wygant3, Yuji Tsuji2, Tomoaki Hori2, Sigeru Fujita4,
and Takashi Tanaka5
1. University of California, Los Angeles, USA
2. Nagoya University, Japan
3. University of Minnesota, USA
4. Meteorological College, Japan
5. Kyushu University, Uapan
 Spatial distribution of
large-scale electric fields
CRRES
Akebono
mV/m
Ey
• Recent spacecraft
observations provided
wide spatial coverage.
• Enhanced electric field in
the dusk-premidnight inner
magnetosphere
[Rowland and Wygant, 1998]
2
[Nishimura et al., 2007]
The enhanced electric field (SAPS) Subauroral polarization streams (SAPS)
is closely related to low
conductance in the subauroral
ionosphere.
E
If we find a similar feature in the
Mercury magnetosphere…
Strong indication of the M-I(S) coupling
[Goldstein et al., 2006]
Simultaneous observation in the ionosphere and magnetosphere
Ionosphere
Equator
MLAT [deg]
[Nishimura et al., 2008]
Agreement of electric fields in the ionosphere and magnetosphere,
indicating mapping of electric fields along field lines toward the inner
magnetosphere.
e.g., ΣP~0.9-3.3 mho [Ohtani et al., 1996]
E [mV/m], ∆B [nT]
If the corresponding magnetic field perturbations are observed (though
not easy near the equator), ionospheric conductance can be estimated
remotely (B/E=-µ0ΣP) [Smiddy et al., 1980]
3
 Response on the southward turning of the IMF Bz
Plasma flow (SuperDARN)
Dayside
(1225 MLT)
[Goldstein et al., 2005; Murakami et al., 2007]
Convection electric fields in the
ionosphere and magnetosphere change
quickly associated with solar wind and
IMF variations.
Nightside
(2050 MLT)
[Ruohoniemi and Greenwald, 1998]
• Rapid communication between the
ionosphere and magnetosphere.
• The response will be much slower if
insulated.
4
 Transmission of electric fields toward the magnetosphere
Electrostatic
mapping
Dungey cycle (convection)
[Mozer, 1970]
[Dungey, 1961]
FAC (Alfven wave)
Fast mode
E
E
[Wing et al., 2002]
[Kikuchi, 2005]
Electrostatic mapping along field lines is widely adopted to deduce electric
field distributions which are required for ring current and MHD simulations
[e.g., Jordanova et al., 2006; Tanaka, 2003]. However, transmission paths of
electromagnetic energies (Directions of the Poynting flux) should be
determined to understand evolution of convection electric fields.
Purpose
• Quasi-spatial distribution of large-scale electric fields in
relation to particle structure
• Time evolution of large-scale electric fields associated with
IMF southward turning, SW pressure change and substorm
onset
Poynting flux associated with convection electric field
changes
• Expected features in the Mercury magnetosphere
6
IMF Bz [nT]
 Quasi-spatial structure during a magnetic storm
CRRES
Southward IMF
E [mV/m]
Ey Ez
The enhanced electric field is confined
earthward of the electron plasma
sheet (SAPS-type feature).
E [keV] log(Ne [/cm3]) ∆B [nT]
Intense electric field
BΦ Bz
Ring current
OPP
Large E on low Σ field line
Small E on high Σ field line
IPP
High density
cold plasma
Plasmasheet
electron
no data
UT[hr]
L
MLT
3
13
5
14.8
6.2
15.5
6.8
16.2
The outer plasmapause (plume edge)
corresponds to the earthward edge of
the plasmasheet
Bz decrease occurs associated with
the electric field enhancement:
Acceleration of ring current
particles by the electric field
 Response of the electric field to southward turning
10
CRRES orbit
Shifted: 2 min
X [RE]
5
4
2
0
-2
250
∆H
[nT]
Ey
Pdyn
[mV/m] [nPa]
IMF Bz
[nT]
Southward turning
0
0
-5
-10
10
Anchorage
JHall=∑HallE┴
60.9 MLAT
∆B=μ0JHall/2
5
0
-5
Y [RE]
IMF southward turning
• Enhancement of the ionospheric electric field
• Enhancement of the electric field in the inner
magnetosphere
Simultaneous
(<1 min)
8
-10
 Sudden commencement
IMF
[nT]
Solar wind and SYM-H
January 13, 2004
Preliminary
Main impulse (MI)
Impulse (PI)
Dawn-dusk E
Dusk-dawn E
Pdyn
[nPa]
21 MLT
SYM-H
[nT]
8 MLT
Sudden
commencement
9
Electric and magnetic field data
measured by Cluster
PI at SLZ
Preliminary
Impulse (PI)
Main impulse (MI)
B-BT02
[nT]
Cluster C1 13 Jan. 2004
E
[mV/m]
E
Poynting flux
(Compressional wave)
Cluster
Dusk-dawn electric fields began to intensify 20 sec
before the main impulse reached the spacecraft.
It indicates existence of an energy transmission process
other than the propagation across the magnetosphere.
10
Poynting flux
PI at SLZ
Cluster C1 13 Jan. 2004
MI
B-BT02
[nT]
PI
Poynting flux
(Alfven wave)
Poynting
flux
[mW/m2]
E
[mV/m]
High
pressure
solar wind
Poynting flux
(Compressional wave)
P||
Upward
P┴east
Downward
P┴radial
The Poynting flux in the PI phase was directed upward and fieldaligned (Alfven mode), different from compressional waves.
11
 Response to IMF southward
turning in the inner
magnetosphere
[nT]
[nPa]
[mW/m2]
C1
S||,
[nT]
[mW/m2]
[mW/m2]
Pdyn
MGD H
PC3
PC2
PC1
IMF
Cluster C1-4 Poynting flux 11 May 2003
C2
C4
E┴ C3
Ez unavailable
for C4
The field-aligned
component is directed
upward.
[RE]
[RE]
[RE]
[RE]
[deg]
[deg]
[deg]
[deg]
[deg]
S||, R1 FAC
 Poynting flux in the MHD simulation during an SC
T = 0 min (quiet)
T = 2 min (shock arrival)
Z
X
-10
(down)
T = 4 min
0
10 (up)
T = 6 min
13
 In the Mercury magnetosphere (with the ionosphere),
FAC (Alfven wave)
[Hashimoto et al., 2002; Kikuchi, 2005]
• Region-1 FACs and electric field in the SW-M interaction
• Quick response of ionospheric convection (Incompressible)
• Alfven wave toward the magnetosphere
• Response of magnetospheric convection
14
 In the Mercury magnetosphere (without the ionosphere),
FAC (Alfven wave)
[Hashimoto et al., 2002; Kikuchi, 2005]
• Charge distribution on the dayside high-latitude ground will change.
• Effects on the magnetospheric electric field would be negligible
unless the ground charging is huge.
15
AU AL
E [mV/m]
March 14, 1991
SYM-H
[nT]
AU AL
[nT]
 Response of large-scale electric fields to substorm onset
UT[hr]
L
MLT
Ey Ez
4.2
20
5.5
21
6.2
21.5
6.8
22
UT [hour]
• Substorm onset at 10:25 UT
• CRRES measurements in the premidnight sector where
SAPS are frequently observed in the conjugated
ionosphere
16
∆H [nT]
KAK 1 sec
High latitudes
CRRES ∆H [nT]
E [mV/m] Mid latitudes
∆H [nT]
 Onset timing of the electric field
The onset of the electric field
enhancement occurs
simultaneous with the substorm
onset.
Pi2
The magnetospheric convection
in the premidnight is strongly
controlled by substorms in
addition to storms.
Negative bay
Positive bay
•Acceleration of ring current ions
•Plasmapause erosion
Convection
enhancement
Er
Equator, ~4.5 RE
UT [hour]
17
Ne [/cm3] E [mV/m]
 Response of the ring current, plasmapause and plasmasheet
2
• Electric field enhancement
around the plasmapause: SAPS
CRRES March 14, 1991
-Ecor
Er EΦ
0
-2
103
102
• Enhancement of ring current
ions
PP
• The outer edge corresponds to
the inner edge of the plasmasheet.
101 Plasmasphere
Pe [nPa] Pi [nPa]
100
101
electron
• The plasmapause corresponds to
the inner edge of the plasmasheet.
100
100
10-1
10-2
UT[hr]
L
MLT
Plasmasheet
ion
4.2
20
5.5
21
6.2
21.5
6.8
22
• The plasmapause location
deviates from the stagnation point.
→ Plasmapause erosion
Substorm as a consequence of the M-I coupling
Midnight meridian
70◦
N
1. Poleward
boundary
intensification
(PBI)
2. Equatorward
motion of the
north-south
(NS) arc
60◦
W
E
S
Onset
Earthward
flow
RX
3. NS arc reaching the
equator portion of the
4. Breakup
oval
[Nishimura et al. 2010]
Substorm onset is triggered in the M-I coupled convection system.
Summary
mV/m
 Quasi-spatial distribution of large-scale
electric fields during storms and substorms
X [RE]
Enhanced electric field confined earthward of
the electron plasma sheet.
Ey
E-field observations can be used to determine
if the ionosphere that significantly affects M-I
coupling exists.
Y [RE]
 Time evolution of large-scale electric
fields associated with IMF southward
turning and substorm onset
Nearly simultaneous response in the inner
magnetosphere, leading to quick
enhancement of the ring current flux
Field-aligned Poynting flux suggesting
energy exchange between M-I by Alfven
waves
[nT]
[nPa]
[mV/m]
[mV/m]
[mV/m]
[mV/m]
IMF
Pdyn
△EEDI, C2
△EEFW, C4
△EEDI, C3
△EEDI. C1
Cluster C1-4 Electric field 11 May 2003
 Response to IMF southward
turning
The inner three spacecraft
measured electric field changes
almost simultaneously (<30 sec):
Quick response of large-scale
electric fields
Cluster C1-4 Magnetic field 11 May 2003
[nT]
IMF
[nT]
[nT]
[nT]
[nT]
Pdyn [nPa]
△BC2
△BC4
△BC1
[RE]
[RE]
[RE]
[RE]
[deg]
[deg]
[deg]
[deg]
[deg]
△BC3
[nT]
[nPa]
[mV/m]
[mV/m]
[mV/m]
[mV/m]
IMF
Pdyn
△EEDI, C2
△EEFW, C4
△EEDI, C3
△EEDI. C1
Cluster C1-4 Electric field 11 May 2003
[RE]
[RE]
[RE]
[RE]
[deg]
[deg]
[deg]
[deg]
[deg]