A. Vaivads, M. AndrA. Vaivads, M. Andréé, S. Buchert, N. Cornilleau-Wehrlin, , S. Buchert, N. Cornilleau-Wehrlin, A. Eriksson, A. Fazakerley, Y. Khotyaintsev, B. Lavraud, A. Eriksson, A. Fazakerley, Y. Khotyaintsev, B. Lavraud,

C. Mouikis, T. Phan, B. N. Rogers, J.-E. WahlundC. Mouikis, T. Phan, B. N. Rogers, J.-E. Wahlund

STAMMS WorkshopOrleans, France, 2003

The magnetopause on electron The magnetopause on electron scalesscales

Current layers and waves

slide 2

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Outline

Small scale current sheets at the magnetopause Comparison to numerical simulations Lower hybrid drift waves and whistlers Comparison to laboratory observations Particle diffusion Summary

Why small scales?

What is their structure? What is their role?

May affect large scale phenomena Decoupling of particles from field lines often on small scales. Efficient energy conversion from electromagnetic to kinetic energy often on small scales

Waves They transport energy and particles, heat particles, they also can be used as remote or local sensing tools of plasma.

slide 3

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Scales

Parameter Magnetosheath Magnetosphere

B,n,Te,Ti 30nT, 10cm-3, 150eV, 1keV

30nT, 1cm-3, 1keV, 10keV

Gyroradius H+ 150km, e- 1.4 km H+ 480km, e- 3.5km

Inertial length H+ 72km, e- 1.7km H+ 230km, e- 5.3km

Gyrofequency H+ 0.46Hz, e- 840Hz H+ 0.46Hz, e- 840Hz

Lower hybrid 20Hz 20Hz

Small spatial scales between ion and electron scales and smaller

a few tens of km and below

slide 4

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

High latitude, northern hemisphere MP crossing

100km Cluster separation s/c in burst mode

slide 5

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

There is a narrow current sheet (yellow)

Parallel current within the current sheet is in opposite direction to magnet-opause current

Significant differences among s/c in E and B.

slide 6

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Generalized Ohms law and Cluster

jjpE

jjpBjBvE

t

t

d

d

2e

2e

ne

m

ne

1ne

m

ne

1)(

ne

1

II

At spin resolution •B 3D[FGM], E [EFW,EDI], n [CIS, PEACE, WHISPER], pe [PEACE], v [CIS], j [PEACE+CIS, curlometer]

At high time resolution (5 S/s and higher)•B 3D[FGM,STAFF], E [EFW,EDI], sometimes n [WBD]•n satellite potential [EFW]•j [curlometer, planar current sheet assumption]•Te

•v

slide 7

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Narrow current sheet (~20km, 5-10 e,e) in both jperp and jII

Jump in magnetic field magnitude coincides with density gradient

E~j x B Electron pressure

gradient not important In addition to gradient,

the electron beam carrying parallel current can be a source of free energy for wave generation

slide 8

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

p1039 14-May-2003 23:02:33

s/c4a) s/c1 s/c2 s/c3

s/c4. vMP

=105 [-0.76 -0.35 -0.54] km/s GSE, Te=150eV. E low pass filtered at 30 HzN - normal to MP, towards MSh, L - closest to the mean direction of B, M=LxN. dt= [0 0.19 0.72 -0.17] s.

1

2

3

4

5

s/c 1b)

s/c1

, E

[m

V/m

]

-40

-20

0

20EjxB/ne- T

e d

x n/n

s/c 2c)

s/c2

, E

[m

V/m

]

-40

-20

0

20EjxB/ne- T

e d

x n/n

s/c 3d)

s/c3

, E

[m

V/m

]

-40

-20

0

20EjxB/ne- T

e d

x n/n

s/c 4e)

06-Feb-2002

s/c4

, E

[m

V/m

]

08:11:56 08:11:57 08:11:58 08:11:59 08:12:00

-40

-20

0

20EjxB/ne- T

e d

x n/n

E~j x B Potential drop across the

current sheet of a few hundred V

slide 9

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Numerical simulations of reconnection

Two fluid simulations of reconnection with a guide field

No electron pressure and partial time derivative included

Width of separatrix is a few times electron inertial length

Electric field is strong along the whole separatrix

E ~j x B, in most of the system

[Rogers]

slide 10

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Waves strongest in the narrow current sheet (gradient in n and B)

Broad band spectra in E and B

Spectral peaks in E and B close to fLH ’LHD’

Spectral peaks in E and B at ~100 Hz, ’whistlers’

Strong Poynting flux associated to both ’whistlers’ and ’LHD’

Waves generated by gradients or electron beams?

E

B

S

slide 11

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

EFW internal burst

In internal burst separate signal for every probe available (9000 S/s)

Cross-correlation gives phase speed in the spin plane

slide 12

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

slide 13

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Laboratory observations [Carter et al. 2002]

Reconnection is driven by increasing the magnetic flux around Flux cores

Lower hybrid drift waves near the low- edge

LHD waves have low coherence and have no clear correlation with reconnection rate

Analysis of magnetic field fluctuations and narrow current sheets in progress

MRX – magnetic reconnection experiment

slide 14

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

LHD waves in laboratory vs. space

Laboratory

Space

Broadband, fmax ~ fLH

~ e

Strongest at low- edge Low coherence Fast growth rate & damping The propagation direction vDe along MP

emax ~ 5% Te ?

The next step is to compare magnetic field observations (current sheets, whistlers) in laboratory and space.

slide 15

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Particle diffusion, effective collision frequency

In the diffusion approximation diffusion coefficient is given by

j

jj

n

nD

v

The effective collision frequency is given by [Carter et al. 2002]

jyjyjj

jeff nE

Vmn

qv

,

Fluctuation correlations can be estimated using analytical estimates of density fluctuations if the electric field fluctuation spectrum is known.

EFW instrument allows simultaneous estimate of the density and electric field fluctuations under assumption that fluctuations in spacecraft potential can be interpreted as density variations

slide 16

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

xy

xy

08:11:57.0 .5 08:11:58.0 .5 1

1.5

2

2.5

06-Feb-2002

NV

ps [

cm-3

]

-20

0

20

s/c4, filter [15 40] Hz

E [

mV

/m]

DS

-0.2

0

0.2dn

[cm

- 3]

-50

0

50

E [

mV

/m]

DS

-1

0

1

2

3x 10

9

D=

<nv

>/

<n>

[m

2/s

]

slide 17

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Narrow strong current sheets (width 5-10 e,e , j~1-5A/m2) at the magnetospheric side of the magnetopause

Coincides with density gradients, strong E fields and wave activity E~jxB, electron pressure gradients are not important Similarities with separatrixes in numerical simulations of reconnection LHD waves similar to those in lab-experiments of reconnection Narrow regions of whistler emission within the current sheet. Diffusion across the current sheets, D~ 109 m2/s, outside D<108 m2/s.

Continue comparisons with 3D numerical simulations Identify reconnection events where Cluster are at small separation and

close to the diffusion region (poster by Yuri Khotyaintsev) Look for the events where measurements of EII are possible

Summary

Future

slide 18

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Other event

EE

BB

SS||||

2001-03-02

slide 19

Swedish Institute of Space Physics

Uppsala

STAMMS, Orleans15 May 2003

Aurora vs Magnetopause

Aurora mainly ion scale phenomena but can have scales down to electron scales Auroral field lines – strong parallel current sheets, particle acceleration, different

plasma waves, often boundary phenomena (PSBL) Infering EII from measurements of Eperp

There are many similarities but are physics similar? cause vs. effect