Plasma transfer event seen by Cluster

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Abstract
A plasma transfer event (PTE) was observed by Cluster C3 on 8 March, 2003, beginning at 0707 UT. For over a minute CIS saw, inside the magnetopause, a burst of solar wind plasma with a density up to 0.8 cm -3 , a factor of 4 higher than was observed before and after. PEACE showed field aligned fluxes at energies up to 500 eV. At higher energies from 1 to 40 keV the fluxes had a pancake distribution indicating closed field lines surrounding the event. The electric field was observed by EFW to vary between -5 and 5 mV/m. WHISPER recorded strong plasma oscillations mostly in two bursts coincident with intense fluxes recorded by PEACE. The other s/c C1, C2, and C4 were in the magnetosheath; the data were used by Sonnerup et al. (32) as evidence for a flux transfer event (FTE), a major question but a separate issue from the PTE. 1. Physics of the Magnetopause
PLASMA TRANSFER EVENT SEEN BY CLUSTER
Walter J. Heikkila
(1)
, Patrick Canu
(2)
, Iannis Dandouras
(3)
, Wayne Keith
(4)
, and Yuri Khotyaintsev
(5)
(1)
University of Texas at Dallas, Box 830688, Richardson, TX, 75083, USA; heikkila@utdallas.edu
(2)
CETP/CNRS/UVSQ, 10 Avenue de l’Europe, 78140 Velizy, France; Patrick.Canu@cetp.ipsl.fr
(3)
Centre d’Etude Spatiale des Rayonnements, 31028 Toulouse, France; Iannis.Dandouras@cesr.fr
(4)
Angelo State University, ASU Station #10904, San Angelo, TX 76909, USA; wayne.keith@angelo.edu
(5)
Swedish Institute of Space Physics, Box 537, SE-75121, Uppsala, Sweden; yuri@irfu.se
ABSTRACT
A plasma transfer event (PTE) was observed by Cluster
C3 on 8 March, 2003, beginning at 0707 UT. For over a
minute CIS saw, inside the magnetopause, a burst of
solar wind plasma with a density up to 0.8 cm
-3
, a factor
of 4 higher than was observed before and after. PEACE
showed field aligned fluxes at energies up to 500 eV. At
higher energies from 1 to 40 keV the fluxes had a
pancake distribution indicating closed field lines
surrounding the event. The electric field was observed
by EFW to vary between -5 and 5 mV/m. WHISPER
recorded strong plasma oscillations mostly in two bursts
coincident with intense fluxes recorded by PEACE. The
other s/c C1, C2, and C4 were in the magnetosheath; the
data were used by Sonnerup et al. [32] as evidence for a
flux transfer event (FTE), a major question but a
separate issue from the PTE.
1. Physics of the Magnetopause
The interaction of the solar wind with the dayside
magnetopause introduces plasma particles across this
boundary. These particles, SW ions and electrons, carry
their momentum and energy with them, perhaps
modified in the interaction process, into the low latitude
boundary layer (LLBL). Two processes were proposed
in the same year 1961 for this interaction, magnetic
reconnection by Dungey [7] and viscous interaction by
Axford and Hines [2]. The first quickly became the
preferred explanation as it was apparently able to
explain several key features of geomagnetic activity as
noted by Sonnerup et al. [31]; this was especially true
after the process of a flux transfer event (FTE) was
suggested by Russell and Elphic [27] thought to be
time-dependent reconnection. The second, viscous
interaction, is a result of the massive tailward plasma
flow in the low latitude boundary layer (LLBL),
suggested by Cole also in 1961 [5], discovered later by
Hones et al. [14]. The concept of a plasma transfer event
[13, 19] is essential for the efficient transport of SW
plasma across the magnetopause into the LLBL on
closed field lines.
The Cluster quartet of spacecraft witnessed an
event on March 8, 2003 after 0707 UT that is highly
relevant to this important question. That was discussed
in the recent article “Anatomy of a flux transfer event
seen by Cluster” by Sonnerup et al. [2004]. We present
data analysis of a plasma transfer event (PTE) on C3 for
the same event.
2. Anatomy of a Flux Transfer Event (FTE)
Fig 1 displays some relevant data from all s/c for 20 m;
the region marked FTE2 from 0707-0709 was discussed
in Sonnerup et al. [32], also here but only C3. Their
paper is an example of superb usage of the Cluster data
for one event, as shown dramatically by their Figure 2.
The FTE was observed near the northern cusp; the GSE
location was approximately (7.1, 2.5, 7.4) R
E
with the
spacecraft separations being about 5000 km.
Fig. 1. Records of Cl, C2, C4 from the magnetosphere, MP,
and two flux transfer events. C3 was in the magnetosphere
throughout; C3 at FTE2 is treated here.
_________________________________________________________________
Proceedings Cluster and Double Star Symposium – 5
th
Anniversary of Cluster in Space,
Noordwijk, The Netherlands, 19 - 23 September 2005 (ESA SP-598, January 2006)
1
Data from Cluster (all 4 spacecraft) were used to
study the structure of the FTE. Immediately before and
after the event C3 was located mainly in the
magnetosphere whereas the other three spacecraft were
measuring magnetosheath-like conditions. In the event
itself, all spacecraft recorded a pronounced maximum in
field magnitude. A peak in number density accompanied
by a minimum in temperature was seen by C3.
The speed of the structure relative to the spacecraft
was determined as the deHoffmann-Teller (HT) frame
velocity. The frame velocity V
HT
relative to the
spacecraft was obtained from a least squares procedure.
In this frame the plasma flow is as nearly field aligned
as the velocities and magnetic fields, measured during
the event, permit. The proper frame of the FTE structure
slides along the magnetopause past the observing
spacecraft. Additionally, it shares the inward/outward
motion of the magnetopause. They find that the velocity
revealed by Cluster is well anchored to the HT high
speed flow at (-234, 51, 166) km/s, anti-sunward,
duskward and poleward. The flux rope has a strong core
field “which must have been created by component
merging at some site equatorward of Cluster. The
absence of reconnection signatures implies that, by the
time the FTE reaches Cluster, it is nearly a fossil
structure.” They suggest that the average reconnection
electric field for this FTE must have been at least as
large as 0.18 mV/m.
3. Observations of a Plasma Transfer Event (PTE)
In the limited amount of space in this preliminary report
we show only data in the next 4 figures.
3.1 CIS ion data
Figure 2 displays the ion data obtained by the CIS
experiment as described by Rème et al. [27], obtained
onboard spacecraft C3 between 07:07 and 07:09 UT.
The top five panels give the energy-time ion
spectrograms from the HIA sensor (no mass
discrimination), for ions arriving in the 90° x 180°
sector with a field-of-view pointing in the sun, dusk,
tail, and dawn direction respectively, and then the
omnidirectional ion flux. The following four panels
show the omnidirectional ion flux measured by the
CODIF sensor, separately for H
+
, He
++
, He
+
and O
+
ions. All spectrogram units are in particle energy flux
(keV cm
-2
s
-1
sr
-1
keV
-1
). The density values are given
in the bottom two panels, for the HIA sensor (no mass
discrimination) and the CODIF sensor (separately for
H
+
, He
++
, He
+
and O
+
ions). The PTE associated burst of
plasma is clearly seen in the data. The density, during
the event, increases by a factor of 4, and the presence of
He
++
ions confirms its solar wind origin.
Fig. 2: C3 observed a burst of SW plasma for over 1 minute.
The first 4 show the spectrograms in different directions.
Observation of He
++
confirms it’s identity as the solar wind.
The increase in density is up to a factor of 4.
3.2 PEACE electron data
Electron measurements were obtained by the Plasma
Electron And Current Experiment. PEACE consists of
two sensors with hemispherical electrostatic analyzers,
each with a 180field of view radially outwards and
perpendicular to the spin plane. Together, the sensors
cover an energy range from 0.6 eV up to 26 keV over
twelve polar sectors after Johnstone et al. [15]. The data
shown were taken by the High Energy Electron
Analyzer (HEEA) sensor on Cluster-3, covering the
energy range from 34 eV to 22 keV. Pitch angle
distributions were determined on-board at one spin
resolution. Thirteen pitch-angle bins and 30 energy
steps are telemetered in this mode, which were reduced
to the 10 energy bins shown in Figure 3. Full-resolution
pitch-angle data is retained within each energy bin,
going from 0 degrees at the top of each panel to 180
degrees at the bottom. The bottom panel labeled “Flow
AZ” shows the spin angle traveled between the start of
the spin and the sensor aperture facing the magnetic
field direction.
2
Fig. 3. PEACE electron data divided into 10 channels with the
center energy indicted on the left. Each channel is divided into
pitch angle with 0
0
at the top, 180
0
at the bottom. The electron
counting rate at the highest energies maximizes near 90
0
,
indicating trapping on closed field lines surrounding the event.
At lower energies the data show intense electron bursts in the
PTE.
3.3 WHISPER plasma emissions
Figure 4 illustrates the emissions observed up to 40 kHz
by WHISPER [Pickett et al., 26] on the four spacecraft
during the FTE2 event identified in Figure 1. The
differences in the signatures observed between C1, C2,
C4, in the magnetosheath and C3 in the magnetosphere
are evident. The faint emissions close to 30-35 kHz is
the local plasma frequency, corresponding to a local
density of ~10-15 e/cc for C1, C2, C4. The bursty
broadband emissions observed at low frequencies are
also common in this region and due to solitary potential
structures [23]. In the magnetosphere, C3 is detecting a
lower density plasma, identified here by the low
frequency cut-off of the continuum radiation at 8 kHz
(Ne ~ 0.8 e/cc). The signatures associated with the
boundary of the PTE are very strong bursts, up to ~1
mV/m, of upper hybrid emissions, which are probably
triggered by the low energy field aligned beams
observed by the PEACE instruments (see figure 3).
Intense broadband emissions, more than two order of
magnitude above background, possibly triggered by the
counterstreaming electron beams reported from Peace
data are observed when C3 penetrates in the PTE.
Fig 4. Plasma emissions from C1, C2, and C4 are quite
different from those observed by C3. The latter shows intense
bands on either side of the PTE.
Fig. 5. Panels from top to bottom show: negative of the
spacecraft potential, magnetic field, high resolution electric
field from one boom pair, angle between the spacecraft spin
plane and the magnetic field, spin resolution electric field (the
z-component electric field is calculated assuming E.B=0, the
dash-dot lines are components of VxB from CIS HIA).
3
3.4 EFW data
Figure 5 presents electric field measurements during the
interval 07:07--07:09 UT after Gustafsson et al. [9]. The
upper panel shows negative of the spacecraft potential
which indicates a density/temperature change around
07:07:10--07:08:00. Middle panel shows a simultaneous
enhancenet of wave activity in a frequency range
between 0.25 to 10 Hz. One should note that the electric
field presented is coming from only one probe pair, and
thus represents an incomplete measurement of the
electric field. The last panel shows spin resolution
electric field measured by the EFW and CIS HIA. One
can see a clear bipolar signature in Ey between 07:07:10
and 07:08:00, where Ey is changing from negative to
positive in the middle of the structure at 07:07:40 UT.
4. The concept of a plasma transfer event
There is no question about the reality of a plasma
transfer event (PTE); observations come from a variety
of sources beginning with the rocket results of Carlson
and Torbert [4] (see the reviews by Lundin [19],
Lemaire and Roth [16, 17], Heikkila [13], and Lundin et
al. [20]). The concept of PTE is not as well known as
the FTE so we describe it here, however briefly.
It is very important that we pay close attention to
the reference frame; we use 2 frames called the
laboratory frame and the reconnection frame.
Conservation of momentum and energy of the entire
system is the goal. Maxwell’s equations are an
expression of Helmholtz's theorem for the two fields E
and B. Poynting’s Theorem (obtained directly from
Maxwell’s equations) allows one to see essential
differences between the various processes on the
interaction of solar wind plasma at the magnetopause:
0
1
vol surf
d d
E J E B S
(1)
2 2
0
0
2 2
vol
E B
d
t
(2)
This is a cause and effect relationship regarding energy.
The cause (source of energy, a dynamo with
0
E J ,
terms on the right) indicates that the plasma yields its
energy to the electromagnetic field; the effect
(dissipation with
0
E J , term to the left) is the
electrical load. In either case, a source of energy is
required (
0
E J ), in the same current circuit, to
provide for the reconnection load (
0
E J ).
In the case of magnetic reconnection (eq. 1),
Poynting flux originates from some external source, a
dynamo somewhere else in the current circuit.
Equivalently, a Poynting flux carries this energy, but
this too comes from this dynamo [13]. The Dungey
model of the magnetosphere has a dynamo with
0
E J over the lobe magnetopause by Cowley [6];
it is not clear where the dynamo for the FTE is located.
Three dimensions are required for a realistic
considering of local effects (eq. 2). The relevant terms
occur only in the volume integrals of Poynting's
theorem, expressing changes in electric and magnetic
energy densities. Because of time limitations energy
cannot travel super-Alfvénically; the relevant volume
must be closely confined. This is quite different from
the steady state. There are two complementary
processes: (1) the polarization electric field, which does
not depend on the movement of the magnetopause itself,
and (2) the inductive electric field due to magnetopause
erosion, which does.
Lemaire and Roth [16, 17] used electric energy of
the plasma, i.e. plasma in motion, in a process they
called impulsive penetration (IP). This was based on the
pioneering work by Schmidt [29, 30], and the results of
laboratory experiments by Baker and Hammel [3].
Heikkila [11, 12] used a different process, that of
tapping magnetic energy with the induction electric
field; he used the term plasma transfer event (PTE) after
Carlson and Torbert [4], Lundin and Evans [18], Woch
and Lundin [33]. The changing δB due to a perturbation
current δJ is a change in the state of interconnection
(the obvious term magnetic reconnection is reserved for
the very different process suggested by Dungey [7],
Owen and Cowley [22], Sonnerup et al., [32] and many
others).
There is also polarization of the plasma in a PTE.
Both processes (IP and PTE) play key roles [13];
tapping both electric and magnetic energy is involved in
getting SW plasma through the MP.
4.1 Fundamentals
To begin at the beginning, we note that the electric field
has 2 sources, charge separation and induction. For this
reason it is better to use the E,J paradigm rather than the
B,V discussed by Parker[23]; with the B,V there is only
one electric field, the convection electric field:
other terms
E V B (3)
The only source of a magnetic field is a current J
by Ampere’s law; therefore, to study changes in the
magnetic field we should consider perturbation electric
currents J, the source of B. A changing current will
create an induction electric field, by Lenz’s law. We
focus on the electric field directly, noting that the total
field E is
/
es ind
t
E E E A (4)
has both the electrostatic and induction components.
The plasma response to the imposition of the induced
electric field
/
ind
t
E A leads to the creation of
an electrostatic field
es
E , at least when
conductivities are not zero.
4
A PTE is three-dimensional object, 2-D to show the
magnetic topology (x-z plane in GSM coordinates), and
another set to show localization involving curl E (x-y
plane). These two types of field have different
topological characteristics, one being solenoidal with
0
ind
E using the Coulomb gauge discussed
extensively by Morse and Feshbach [21], the other
being irrotational (conservative) with zero curl,
0
es
E Consequently, they can never cancel each
other; the most the plasma can do is to redistribute the
field while maintaining the curl.
It is instructive to express the induction electric
field in integral form:
/
mag
circuit
emf d d dt
E l
(5)
where
mag
is the magnetic flux through the circuit
used for the integration. It is only by this emf that we
can tap stored magnetic energy.
Fig. 6. (a) The unperturbed magnetopause current is shown on
left; this is the frame used in reconnection theories where the
reconnection electric field is shown embedded (supposedly
due to anomalous resistivity along the X-line in the magnetic
field topology in the normal plane). PTE assumes a different
approach, that of a localized meander of the MP current on the
right This is associated with an induction electric in the frame
of the unperturbed MP current. (b) The perturbation current
by itself.
4.2 Localized pressure pulse
The inferred immediate cause of a plasma transfer event
is a localized pressure pulse from the magnetosheath, an
inward push by solar wind plasma associated with
erosion found by Aubry et al. [1]. The pressure pulse is
likely to be in some small region, not extending to
infinity in the y-direction (Fig. 6).
Only the induction electric field is shown in Fig. 6;
the plasma response through charge separation (creating
an electrostatic field) is treated in next three
subsections. On the left is the undisturbed
magnetopause current J(t
0
) before the pressure pulse; on
the right is the condition after the first strike (the
tangential velocity is assumed to vanish here; its effect
will be discussed in Fig. 9). The total current
perturbation δJ is shown in Figure 6 at the bottom; it is
this change in current which induces a voltage (by
Lenz's law):
0
4
ind
d
t r
A J
E (6)
where A is expanded to show the dependence on the
time rate of the current. The field is in the reference
frame of the undisturbed current on the left, the
laboratory frame, everywhere opposing the perturbation
(note the negative sign) This induction electric field
causes the earthward flow of both magnetosheath and
magnetospheric plasma in step with the moving
magnetopause.
Fig. 7. In this view it is assumed that the frame of reference is
fixed to the magnetopause in the center, as in reconnection
models. The magnetopause is moving sunward, top and
bottom in view of the localized perturbation. If there is a
normal component of the magnetic field through the current
sheet E
ind
can polarize the plasma, causing an electrostatic
field tangential to the MP, reversing as indicated. We see that
this E
es
will drive the SW plasma into the current sheet
.
4.3 Motion of the magnetopause
A localized induction electric field, E
ind
= - A/t, is
forced upon the plasma, not an electrostatic field. It is
entirely local, opposed to the current perturbation. This
solenoidal feature is consistent with the inward motion
of the magnetopause as in Fig. 7. Here it is assumed that
the frame of reference is fixed to the magnetopause in
the center, as in reconnection models.
5
Let’s assume that the perturbation is very wide so
that the electric field E
es
shown becomes quite small and
can be neglected. The induction has a tangential
component at each side the perturbation, which reverses
as in Fig. 6, so the plasma on both sides of the MP is
moving to the left, in step with the MP.
Now let’s bring in a narrower perturbation as
shown in Fig. 7. With a localized perturbation the
magnetopause at the top and bottom is moving sunward
in our frame of reference; now the induction electric
field is here. It has a component normal to the
magnetopause at the edges of the perturbation, with
opposite polarities. We need to consider 2 cases
regarding B
n
.
If B
n
= 0 the plasma cannot respond by charge
separation as shown by + and signs, no electrostatic
field is created; E
es
is zero. It should be noted that the
induction has a normal component at each side the
perturbation, which reverses as in Fig. 6, and we recover
the previous case.
However, if there is a normal component of the
magnetic field through the current sheet E
ind
can
polarize the plasma along B
n
causing an electrostatic
field tangential to the MP, reversing as indicated. We
see that this E
es
will drive the SW plasma into the
current sheet, in the reconnection frame. This is contrary
to the views of Owen and Cowley [22].
4.4 Response of the plasma: B
n
= 0
To return to the laboratory frame Fig. 6, the electric
field shown is not the actual electric field observed on a
satellite, or even in the magnetopause frame (the
reconnection frame). The plasma response is hindered
by the magnetic field if B
n
vanishes. Because B
z
is the
dominant component of the magnetic field on either side
of the magnetopause (at least for high as well as low
shears), the very low Pedersen conductivity σ
1
~ 0 for a
collisionless plasma in the tangential y direction limits
polarization of charge in that direction. The induction
electric field alone is the field that determines the
motion of the plasma over the bumpy surface, a velocity
that is everywhere tangential to the local magnetopause
[24, 25].
4.5 Response of the plasma: B
n
is finite
The plasma response changes dramatically with an open
magnetosphere. In this case, a rotational discontinuity
will be present, with a finite B
n
. Electron and ion
mobilities are high along the magnetic field. Now we
can use the very large direct conductivity σ
0
; the plasma
can polarize along the magnetic field lines as shown in
Figure 7, top and bottom, in different senses, causing an
electrostatic field tangential to the MP, reversing as
indicated. Thus we see that this E
es
will drive the SW
plasma into the current sheet. On the other side, since
both B and E reverse, the electric drift E B will be
also earthward. A PTE is produced.
Fig. 8. If B
n
is finite, then plasma can polarize in response to
the induction electric field. Any reduction in the net E
||
(top
and bottom) in an arbitrary closed contour involves
enhancement of the perpendicular component at least
somewhere around the chosen contour, otherwise the curl
(emf) would be affected. The tangential component of the
induction field will be enhanced by the plasma.
This is elaborated further by Fig. 8, Fig. 6(b) but
showing the plasma response by creating an
electrostatic field. Because it has no curl, an
electrostatic field can have no effect on the curl, or
electromotive force, of the induction field. Any
reduction in the net E
||
in an arbitrary closed contour
involves enhancement of the perpendicular component
at least somewhere around the chosen contour,
otherwise the curl (emf) would be affected. Whatever
the distribution of the secondary field E
||
es
, the resultant
field has to remain finite and large enough to make the
line integral finite and equal to dФ
M
/dt by eq. 6 [12].
The result of a cancellation, or even a partial
cancellation, is a tangential (to the MP) electrostatic
field E
p
es
directed oppositely on the two sides of the
localized current meander, enhancing the induction
component. In the frame of the moving MP this extra E
(= E
tan
to MP) will cause a finite V
n
through the MP,
exactly as found in the high shear case of Phan et al.
[24], and Phan and Paschmann [25]. A finite B
n
is
crucial to the analysis of a PTE. (see Figure 8)
4.6 Tangential motion
It is essential to include the tangential motion (to the
magnetopause) to understand the effects of a PTE upon
the physics of the magnetosphere. In the magnetosheath
all the SW plasma is moving anti-sunward, even super-
Alfvénically toward the flanks. Whatever plasma
penetrates through the MP must face conditions in a
new medium. The two black arrows are meant to denote
the tailward motion of the plasma, higher in the MS,
lower in the low latitude boundary layer (LLBL). For
6
example, this difference makes it possible to have
multiple injection events in the LLBL due to successive
blasts from the magnetosheath as observed by Carlson
and Torbert [4] and Woch and Lundin [33].
Fig. 9. In the magnetosheath all the SW plasma is moving
anti-sunward, even super-Alfvénically toward the flanks.
Whatever plasma penetrates through the MP must face
conditions in a new medium. The two black arrows are meant
to denote the tailward motion of the plasma, higher in the MS,
lower in the low latitude boundary layer (LLBL).
5. A plasma transfer event seen by Cluster
This process was seen by C3 as shown by Fig. 2.
CIS/CODIF data showing penetration of solar wind
plasma lasting for over 1 minute at the time of the event
just described. The presence of He
++
, and the similar
shape of H
+
profile, verifies this identification of SW
plasma. The plasma density is increased, quadrupled in
the middle, for over one minute, in a burst of plasma
entering through the magnetopause.
PEACE electron data show several aspects in
agreement with a PTE. (1) The pitch angle distribution
for the higher energy channels has a maximum near 90
0
,
indicating field lines are closed on either side. (2) In the
heart of the PTE these fluxes are greatly reduced but
still showing some maximum at 90
0
. Since B
n
is small
compared to the magnetic field on the either side
(magnetosheath and LLBL) their will be some trapping
along B
n
in the current layer. This result may indicate
open magnetic field lines, a firm requirement for the
PTE process. (3) At lower energies intense fluxes are
observed, with a maximum at 0
0
at 0730 and 180
0
at
0742. Taking note of the speed of the disturbance [32],
this is consistent with a vertical dimension in Fig. 8 of
3,500 km(0.5 R
E
) forJ.
WHISPER instrument showed two bursts of plasma
emissions at the beginning and end of the PTE. It is
likely that these bursts coincided with parallel
component of the induction electric field as shown in
Fig. 8. These bursts probably produced the emissions.
EFW instrument also showed the bursty structure.
The DC electric field showed that the sense reversed in
E
y
; it was strong in magnitude (~5 v/km). Fig. 8
includes a possible trajectory of C3 through the PTE.
6. Discussion
After many years of research on the interaction process
of solar wind plasma at the magnetopause the big
question is still the details of the processes involved.
There are two problems that we need to confront.
6.1 Diversion of the magnetosheath flow
The diversion of the magnetosheath flow around the
magnetospheric obstacle (the magnetopause) involves
more than 90% of the solar wind intercepted by the bow
shock, about 10
28
ions/s. This is a major problem that
Sonnerup et al. [32]have faced.
However, they should not have included C3 in their
analysis. With C3 left out they would be released from
at least three difficulties.
(a) The fit would be better; as they said, “This
relatively low value [of the correlation
coefficient] is a consequence of the fact that C1
and C3 separately gave somewhat different
V
HT
vectors”;
(b) The velocities for C3 were supersonic,
violating the conditions of their analysis;
(c) The temperature minimum on C3 at FTE2 is
quite visible in Fig. 1. The reconnection
process requires dissipation with E·J > 0,
implying a temperature maximum.
6.2 Penetration of some SW plasma into the LLBL
The temperature minimum follows from the action of
the dynamo, with E·J < 0 on the right in Fig. 8; the
plasma is losing, not gaining, energy [12]. This process
is supported by the electric field observations in Fig. 5:
E
y
reverses as opposed to being constant as assumed in
the reconnection model.
Some SW plasma (less than 10%) does penetrate
through the magnetopause into the magnetosphere
(LLBL), about 10
27
ions/s deduced by Eastman [7]. This
does happen quickly, in a few seconds with individual
events.
The PTE is a likely candidate. The electrostatic
field E
es
(Fig. 7) will drive the SW plasma into the
current sheet. On the other side, since both B and E
reverse, the electric drift E B will be also tailward.
Particles go wherever the local electric and magnetic
fields direct them; they have no time to check whether
they are on open B or not. From open field lines in the
MP current sheet the particles go to closed field lines in
the low latitude boundary layer.
Another order of magnitude (or even more) is
involved for the plasma source of the plasma sheet, 10
26
to 10
25
ions/s. This minute fraction, 10
2
to 10
3
, is
responsible for all the glorious auroral displays!
Acknowledgment
It is a pleasure to work with Cluster, and the Cluster
team! (WJH).
7
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8
This research hasn't been cited in any other publications.
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