Cluster Workshop 2009-05-13

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


Reconnection Dominating process for

transfer of energy and plasma

Impulsive penetration Alternative/complementary

model proposed by Lemair ca 1976

Lemair, 1991

Introduction


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


Lemair, 1977

Lemair, 1991

Penetration mechanisms


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


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)


Calibration using WHISPER

310 2

U aU aen a e a e

021218, 030101, 030102, 030413


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)


2002-12-23/24


021223overview

Density signatures associated with magnetic field variations


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



2. Move into plasma drift frame (cont’d)

ne(t)


x’’ (RE)

t (s)

ne (x’’)


n1 (x)

n2 (z)

n3 (y)

B

Distribution of angle between MVA normal and

average magnetic field

N

(n1,B)

Orientation: X-Y (GSE)


3. Get scale size along normal vector from MVA

4. Estimate scale sizes perpendicular to normal

ne(t)

ne(x)



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)


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


z > Max(S/C separation,w)

w

2002-12-23 (39 315 s)

Method 1a


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


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


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


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.


Dia- or paramagnetic?


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



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)


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)




lx (RE)

B/B

(%

)Magnetosheath

Solar wind



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?



Thank you for your attention!

2002-12-23 (36 040 s)Signature of diamagnetic behaviour

1 2 3 4


2002-12-23 (36 040 s)

y

z

x

E and B1 2 3 4

1 2 3 4

1 2 3 4

x


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)


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


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?


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?


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?


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)



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)


Methodology Event selection

SW excursion MSph/MS excursion


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


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


Ang

le b

etw

een

B a

nd

max

imum

var

iatio

n

Angle between B and medium variation


2002-12-23 (36 040 s)

Method 1a


Method y = 1

Method z = -1


Along B

Method y = -1

Method z = 1


B in MVA coordinates, corrected according to direction of B

Bx (min. var. direction)

By (~ max. var. direction)

Bz (~ background B direction)


Method y = -1

Method z = 1

~3.5 RE in z-direction

Inconsistency in y-direction


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


Orientation: X-Z (GSE)


Orientation: Y-Z (GSE)


Max density


Velocity dependence?

ne

ne – ne,BG


Orientation and velocity


Orientation and magnetic field


Cluster Workshop 2009-05-13

Documents

Transcript of Cluster Workshop 2009-05-13