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