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Cluster Workshop 2009-05-13. Space and Plasma Physics School of Electrical Engineering Royal Institute of Technology Stockholm Sweden. Small-scale plasmoids in the magnetosheath and the solar wind Tomas Karlsson, Nils Brenning, Georgios Spanopoulos. Cluster Workshop 2009-05-13. Introduction. - PowerPoint PPT Presentation
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Space and Plasma PhysicsSchool of Electrical Engineering
Royal Institute of TechnologyStockholmSweden
Cluster Workshop 2009-05-13
Small-scale plasmoids in the magnetosheath
and the solar windTomas Karlsson, Nils Brenning, Georgios Spanopoulos
Introduction
Cluster Workshop 2009-05-13
Reconnection Dominating process for
transfer of energy and plasma
Impulsive penetration Alternative/complementary
model proposed by Lemair ca 1976
Lemair, 1991
Introduction
Cluster Workshop 2009-05-13
Recent observations by Lundin et al. have revealed localized regions of magnetosheath plasma inside the magnetosphere
Lundin, 2003
Impulsive penetration
Geometry of penetrating elements unclear
Cluster Workshop 2009-05-13
Lemair, 1977
Lemair, 1991
Penetration mechanisms
Cluster Workshop 2009-05-13
Magnetic expulsion(followed by localized reconnection)
Self-polarizationEp = - v x B
Ma, 1991 Brenning, 2005
Three possibilities [Brenning et al .2005]
• B expulsion
∆B/B =100%
• Polarization
EP = -v0xB
• Rejection
Cluster Workshop 2009-05-13
0.1
0.01
10
100
TRANSITION
BOUNDARY 1
BOUNDARY 2
MAGNETIC EXPULSION
FORBIDDEN REGION
SELF POLA-RIZATION
SONG 1990
MISHIN 1986
ISHIZUKA 1982
LINDBERG 1978
kk
B
W
W
,ith
giwK
r
Methodology
Instruments
• EFW (S/C potential to get ne [Pedersen et al, 2001])
• CIS HIA (plasma bulk velocity)
• FGM (magnetic field data)
Cluster Workshop 2009-05-13
Calibration using WHISPER
310 2
U aU aen a e a e
021218, 030101, 030102, 030413
Cluster Workshop 2009-05-13
WH
ISP
ER
n e (
cm-3)
Uprobe (V)
a0 a1 a2 a3
8.5559 -7.6729 564.29 -0.94118
C.f. Escoubet et al., 1997, Pedersen et al., 2001
Methodology Event selection
• Main point is not to confuse plasmoids with double crossings of MP or BS
– No appreciable change in drift velocity, in particular no sign changes
– Keep to the ”middle” of the magetosheath– No ”nested structures”– Consider typical plasma density values:
MS ~ 10 cm-3
SW ~ 5 cm-3
MS (Lobe) < 1cm-3
• Other criteria
– All events over threshold ne/nBG > 1.5(boxcar avergage with T = 3600 s)
Cluster Workshop 2009-05-13
2002-12-23/24
Cluster Workshop 2009-05-13
021223overview
Density signatures associated with magnetic field variations
Cluster Workshop 2009-05-13
n e/
n e,B
Gn e
|B|
Bx
By
Bz
v xv y
v z
Methodology Analysis of 3D structure – scale sizes
1. Order according to minimum variance analysis (MVA) x’, y’ ;
• Planar = dn < 15 %
2. Move into plasma drift frame (HIA velocity)
'0, 0, 0' ' '
zB
x y z
v
x’y’
x’’ = x’ + vxty’’ = y’ + vytz’’ = z’ + vzt
Cluster Workshop 2009-05-13
Methodology Analysis of 3D structure – scale sizes
2. Move into plasma drift frame (cont’d)
ne(t)
Cluster Workshop 2009-05-13
x’’ (RE)
t (s)
ne (x’’)
Cluster Workshop 2009-05-13
n1 (x)
n2 (z)
n3 (y)
B
Distribution of angle between MVA normal and
average magnetic field
N
(n1,B)
Orientation: X-Y (GSE)
Cluster Workshop 2009-05-13
3. Get scale size along normal vector from MVA
4. Estimate scale sizes perpendicular to normal
ne(t)
ne(x)
Methodology Analysis of 3D structure – scale sizes
Cluster Workshop 2009-05-13
Estimation of scale sizes
1. Along x-direction: width of half maximum of ne
2. y and z: in effect only four measurement points
x
z
v
S/C 1
y
2002-12-23 (36 040 s)
Cluster Workshop 2009-05-13
Determination of scale sizesUse several different methods:
z
ne
1. Extrapolate
z
ne
2. Half width of single event
z > w
w
z
ne
3. No signal on 1-3 S/C
z < S/C separation
x
ne
4. Cross correlation < thres.
z < S/C separation z
ne
5. Inconsistency
Cluster Workshop 2009-05-13
z > Max(S/C separation,w)
w
2002-12-23 (39 315 s)
Method 1a
Cluster Workshop 2009-05-13
Method 5
n e(x
)n e
(y)
n e(z
)
y (RE)
z (RE)
x (RE)
t (s)
1a + 5 =
Along B
z,B
y
x
2002-12-23 (36 740 s)
Method 2Cluster Workshop 2009-05-13
Scale sizes: x-yl y
(RE)
l y = l x
l y = 10 l x
Cluster Workshop 2009-05-13
lx (RE)
Scale sizes: x-zl z
(RE)
l z = l x
l z = 10 l x
lx (RE)Cluster Workshop 2009-05-13
Scale sizes: y-z
l z = l y
Cluster Workshop 2009-05-13
l z (R
E)
lx (RE)
Penetration parameters2
2,
,
20
00
,,
0
2
, 321eV2
, 50 nT2
( , , ), ( , , )
2.3
i e dk
i e i thi th
B
kk
B
i thi th
B
x y z x y z
i dgi
m n vW
m n vW T
BW B
W
W
W
W
w Min l l l Max l l l
m vr
eB
K
ExpulsionRejection
Self-polarization
kk
B
W
W
,ith
giwK
r
Cluster Workshop 2009-05-13
1.5
Conclusions I
• Plasmoids in MS often shaped like saucers or flattened flux tubes, with 0.1 RE < x < 14 RE
• Plasmoids orientated after bow shock/MP
• Parameters are such that magnetic expulsion will be likely mechanism for impulsive penetration, instead of self-polarization.
Cluster Workshop 2009-05-13
Dia- or paramagnetic?
Cluster Workshop 2009-05-13
t (s)
B (
nT)
n e (
cm-3)
2003-05-01
500 s
t (s)
B (
nT)
n e (
cm-3)
2002-12-23
500 s
B
Dia- or paramagnetic?
Cluster Workshop 2009-05-13
lx (RE)
B/B
(%
)
t (s) t (s)
t (s) t (s)
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
Cluster Workshop 2009-05-13
700 sSolar wind or magnetosheath?
SW
MSh
MSh
SW
700 s
t t
t t
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
n e (
cm-3)
B (
nT)
Cluster Workshop 2009-05-13
Dia- or paramagnetic?
Cluster Workshop 2009-05-13
lx (RE)
B/B
(%
)Magnetosheath
Solar wind
Dia- or paramagnetic?
Cluster Workshop 2009-05-13
t (s)
B/B
(%
)Magnetosheath
Solar wind
Conclusions II
• Smaller plasmoids – paramagnetic
• Larger plasmoids – diamagnetic
• Larger plasmoids found in the pristine solar wind. Compressed at bow shock?
• Smaller plasmoids are leakage of compressional waves from foreshock?
Cluster Workshop 2009-05-13
Cluster Workshop 2009-05-13
Thank you for your attention!
2002-12-23 (36 040 s)Signature of diamagnetic behaviour
1 2 3 4
Cluster Workshop 2009-05-13
2002-12-23 (36 040 s)
y
z
x
E and B1 2 3 4
1 2 3 4
1 2 3 4
x
Cluster Workshop 2009-05-13
2002-12-23 (36 040 s)
1 2 3 4
x
y
z
x
E and B
• Current sheets separate regions with different ne
• Current may be electron Hall current?
• Current sheet widths are of the order of 0.2 RE ≈ 2 rgi
• (rgi ≈ 800 km)
Cluster Workshop 2009-05-13
2002-12-23 (36 040 s)
2 2 3-1
9
2 2.1 10240 kms
12 10xz
y
E
B
-1
-30 0
36nT200 kms
(16 cm )A
i p p
Bv
n m m
Cluster Workshop 2009-05-13
2002-12-23 (36 040 s)
p, pB, pi , pi //
T
T//
B
ne
• Increased density and temperature (large-scale)
• Compensated by decrease in magnetic pressure (and perpendicular cooling at the highest densities?)
• No electron data available (at present at least)
• AW at the end of the pressure gradient.
AW?
Cluster Workshop 2009-05-13
2002-12-23 (36 740 s)
p, pB, pi , pi //
T
T//
B
ne
• Similar properties to prevoius case.
• What will the electron temperature signature be? A cooling to keep the pressure constant???
• Or is this plasmoid expanding?
Cluster Workshop 2009-05-13
Signature of diamagnetic behaviour and self-polarization.
2002-12-23 – Lion roars
10.00 10.10 10.20 10.30 10.40 10.50
Data provided by Ondrej Santolik
• Lion roars are associated with anisotropies in electron distribution in magnetosheath.
• ’Type A’ (30 % occurence rate) associated with dip in magnetic field (Zhang et al., 1998).Cluster Workshop 2009-05-13
2002-12-23
• The lion roars are there all the time (we are in MS!), but become more intense at plasmoids, and frequency decreases.
• Direction of the Poynting flux varies from centre to edges. Can this effect the electron temperatures?
Cluster Workshop 2009-05-13
Conclusions III
• Excess thermal pressure balanced by diamagnetic effect.
• Diamagnetic effect associated with thick current sheets at the plasmoid density gradients.
• Plasmoids are associated with Type A lion roars. (Propagation direction varies with position in plasmoid)
Cluster Workshop 2009-05-13
Cluster Workshop 2009-05-13
Thank you for your attention (again)!
Extra material
B in MVA coordinates, corrected according to direction of B
Bx (min. var. direction)
By (~ max. var. direction)
Bz (~ background B direction)
Cluster Workshop 2009-05-13
Methodology Event selection
SW excursion MSph/MS excursion
Cluster Workshop 2009-05-13
n e(S
/C 1
)n e
/ n e
,BG
n ev x
v yv z
n en e
/ n
e,B
G
Methodology II. Event selection
mag
neto
shea
th
mag
neto
sphe
revwave
vMS
A magnetopause boundary wave could give a similar signature in density, but…
vwave = vMS ??
v = const around the disturbance ???
nMsph < 1 cm-3
vMsph
Cluster Workshop 2009-05-13
Calibration using WHISPER
Time interval a0 a1 a2 a3
021213 - 030506 8.5559 -0.13033 564.29 -1.0625
310 2
U aU aen a e a e
Cluster Workshop 2009-05-13
Ang
le b
etw
een
B a
nd
max
imum
var
iatio
n
Angle between B and medium variation
Cluster Workshop 2009-05-13
2002-12-23 (36 040 s)
Method 1a
Cluster Workshop 2009-05-13
Method y = 1
Method z = -1
Cluster Workshop 2009-05-13
Along B
Method y = -1
Method z = 1
Cluster Workshop 2009-05-13
B in MVA coordinates, corrected according to direction of B
Bx (min. var. direction)
By (~ max. var. direction)
Bz (~ background B direction)
Cluster Workshop 2009-05-13
Method y = -1
Method z = 1
~3.5 RE in z-direction
Inconsistency in y-direction
Cluster Workshop 2009-05-13
2002-12-23 (49 315 s)
Method 4Cluster Workshop 2009-05-13
Plasma densities
ne /ne,BG (cm-3)
N
ne,max (cm-3)
N
Cluster Workshop 2009-05-13
Orientation: X-Z (GSE)
Cluster Workshop 2009-05-13
Orientation: Y-Z (GSE)
Cluster Workshop 2009-05-13
Max density
Cluster Workshop 2009-05-13
Velocity dependence?
ne
ne – ne,BG
Cluster Workshop 2009-05-13
Cluster Workshop 2009-05-13
Orientation and velocity
Cluster Workshop 2009-05-13
Orientation and magnetic field
Cluster Workshop 2009-05-13
Orientation and velocity
Cluster Workshop 2009-05-13
Orientation and magnetic field
Cluster Workshop 2009-05-13
Orientation and velocity
Cluster Workshop 2009-05-13
Orientation and magnetic field
Cluster Workshop 2009-05-13