In-situ observations of magnetic reconnection in solar system plasma

In-situ observations of magnetic reconnection in solar system plasmaWhat can we export to other astrophysical environments?

Alessandro Retinò, R. Nakamura and W. BaumjohannSpace Research Institute, Austrian Academy of Sciences, Graz, Austria

A. VaivadsSwedish Institute of Space Physics, Uppsala, Sweden

D. Sundkvist and F. S. Mozer Space Sciences Laboratory, University of California, Berkeley, USA

F. SahraouiLaboratory of Physics of Plasmas, CNRS, Paris, France

MFPO conference - Krakow 2010 [email protected]

Motivation

Magnetic reconnection: basics, importance, universality

Collisionless reconnection in near-Earth space

In-situ observations of turbulent reconnection:

• first evidence

• energy dissipation

• particle acceleration

Possible comparisons with other astrophysical environments:

• heating of the solar corona

• cosmic ray acceleration

Summary

Outline

2MFPO conference - Krakow 2010 [email protected]

Motivation


Magnetic forms produce activity and violence in the otherwiseserene thermal degradation of the cosmic landscape [E.N. Parker]

Magnetized plasma ubiquitous in the universe

Key processes in magnetized plasma: dynamo, reconnection, MHD instabilities ,...

In-situ observations required to understand the basic physics

Synergy between in-situ & remote observations important

[ESA/SOHO-EIT in EUV][NASA/HBT in UV] [NASA/HBT-FCO in UV]

Violation of the frozen-in condition

4

Frozen-in

E' =E+VxB=0

E||=0

[ Paschmann, Nature, 2006]

Reconnection: basics

No frozen-in

E' =E+VxB=J/

E||≠0

( conductivity in the diffusion region)


5

[Vaivads et al., Space Sci. Rev., 2006]

Breaking of frozen-in condition ->->local topology change ->

->large-scale:

reconfiguration of magnetic fields

energy conversion/dissipation:• plasma acceleration (Alfvénic)• plasma heating • particle acceleration

plasma transport

Reconnection: importance

E'

E'

E' is the reconnection rate


Laboratory plasma [Intrator et al., Nature Physics, 2009]

near - Earth space[Paschmann et. Al, Nature, 1979]

[Hones et al., Geophy. Res. Lett., 1984][Phan et al., Nature, 2006]

[Retinò et. al, Nature Physics, 2007]

also observed at Mercury, Mars & Saturn

Solar corona [Yokoyama et. al., ApJ Lett., 2001]

6

Reconnection: universality

mfp ~ 1 A. U.

collisionless plasma

In-situ vs remote observations


LAB NEAR-EARTH SUNASTRO

Direct measur. of E & B yes yes (high res) no no

Direct measur. of f(v) no yes (high res) no no

Imaging no no yes (high res) yes

Boundary conditions controlled natural natural natural

Repeatability yes no no no

Number of objects a few one onemany

direct mesurements of E, B and f(v) required to resolve the basic physics of reconnection!

near-Earth space best laboratory (so far)

comparison with remote observations important

Near-Earth observations: Cluster spacecraft


ESA cornerstone mission

first 4 spacecraft mission !

distinguish temporal/spatial variations

measurement of 3D quantities: J=(1/μ0) xB,

B = 0, EJ, ...

tetrahedrical configuration with changeable spacecraft separation 100-10000 km -> measurements at different scales

4 sets of 11 identical instruments to measure:

magnetic field

electric field

thermal particle distribution functions

suprathermal particle distribution functions

FGM magnetometer

http://sci.esa.int/science-e/www/area/index.cfm?fareaid=8

Collisionless reconnection

MHD anomalous

conductivity ?

Hall electron

pressure ?

electron

inertia ?

Three scales:

MHD ( >> i) 103 – 104 km

ion ( ~ i ) 50-500 km

electron ( ~ e) 1-10 km

[NASA/MMS]

large-scalelaminar current sheet

(e.g. magnetotail)

Reconnection rateReconnection first proposed by Giovanelli [Nature, 1946] to explain solar flares

Sweet-Parker reconnection:

rate ~ (Rm)-1/2 ~ ()-1/2 depends on resistivity -> SLOW (flare ~100s)

Collisionless reconnection:

rate ~ 0.1 independent on resistivity -> FAST !!!

Numerical simulations [Birn, JGR, 2001] Spacecraft data

[Mozer et. al., Phys. Rev. Lett., 2002][Vaivads et al., Phys. Rev. Lett., 2004][Retinò et al., Nature Physics, 2007]

Turbulent reconnection: importantfor astrophysical plasma?

Turbulence and reconnection ubiquitous in the universe: turbulent reconnection should be common in astrophysical plasmas

Turbulent configuration could increase the reconnection rate wrt laminar case: faster reconnection

Turbulent reconnection could be important for energy dissipation

Larger electric fields and small-scale irregularities could enhance particle acceleration


Turbulent reconnection

[Matthaeus, Phy. Fluids, 1986]

B

Small-scale laminarcurrent sheet

in turbulent plasma Turbulent current sheet

[adopted from Lazarian & Vishniac,1999]

Turbulence in laminar current sheets

[Bale et al. 2002, Vaivads et al., 2004, Retinò et al., 2006]

Which configuration ?


In-situ evidence of turbulent reconnection

13

cartoon of current sheet formation in turbulent plasma

(contours are magnetic field lines)

[Retinò et al., Nature Physics,2007]also in solar wind [Gosling et al., ApJ,, 2007]

volume-filling current sheets

reconnecting current sheets

energetic ions

First evidence !

Small-scale laminar current sheet in turbulent plasma

14

single spacecraft four spacecraft (assumptions: planarity & stationarity)

SC separation ~ 100 km

turbulence ?

turbulent current sheet ?

R ~ 0.1 (fast rec)


Energy dissipation

15

Alfvenic turbulence (E/B ~Va)

E&B Kolmogorov-like

[ Sundkvist et al., PRL,2007]

Turbulence properties

Intermittency

Gaussian

ii

measured dissipation rate <EJ> comparable with that expected from waves

around ion gyrofrequency: turbulent reconnection in volume-

filling current sheets can be important energy dissipation mechanism !

[ Servidio et al., Phy. Plasma, 2010]

Large number of reconnection regions

Particle acceleration

16

suprathermal ions

B

First order Fermi acceleration during fast reconnection in turbulent current sheet [Lazarian et al., 2010]

Particle acceleration in small-scale current sheet in turbulent plasma [Dmitruk & Matthaeus, JGR, 2006]

No clear evidence (so far) of particle acceleration from in-situ data !

Comparison with other astrophysical plasma

17

[Vaivads et al., Plasma Phys. Contr. Fus., 2009]

Can we directly export resultsfrom in-situ observationsto other astrophysical environments?

Caution is needed: (most)solar

system plasma are:

fully ionized

mainly H+, e-

not relativistic (Va<<c)

collisionless


Possible comparisons (TBD)

18

The magnetic carpet on the Sun

[From SOHO/SOI http://soi.stanford.edu]

Heating of the solarchromosphere/corona:small-scale reconnection events[Shibata et. al, Science, 2007]

Cosmic ray acceleration:

Giant radio galaxies[Kronberg et al., Ap. J. Lett., 2004]

Anomalous cosmic rays (5-100 MeV/nucleon) [Lazarian et. al, ApJ, 2009; Drake et al., ApJ, 2010]


Reconnection universal energy conversion/dissipation process

In-situ observations required to resolve the basic physics

Fast collisionless reconnection is observed in-situ in the solar system e.g. in near-Earth space

First experimental evidence of turbulent reconnection obtained in near-Earth space. Turbulent reconnection important for energy dissipation and (possibly) for particle acceleration.

Results from in-situ observations may be exported to distant astrophysical environments but much caution is needed. Crucial first to understand differencies and similarities between environments.

Possible examples for turbulent reconnection: heating of solar corona and cosmic ray acceleration

19

Summary


Documents

In-situ observations of magnetic reconnection in solar system plasma