Istituto di Fisica dello Spazio Interplanetario M.F. Marcucci SAIT Teramo 4-8 maggio 2008 Nuove...

Istituto di Fisica dello Spazio Interplanetario

M.F. Marcucci SAIT Teramo 4-8 maggio 2008

Nuove conoscenzeNuove conoscenze

sulla riconnessione magneticasulla riconnessione magnetica

dai dati della missione Cluster.dai dati della missione Cluster.

M.F. Marcucci



Outline

•Introduzione

• 3 esempi di osservazioni di Cluster durante la riconnessione

•Prospettive future



•La riconnessione magnetica converte rapidamente l’energia magnetica dei

plasmi spaziali in energia termica e cinetica.

•E’ un processo universale che si verifica in regioni di plasma diversissime per

valori di densità e temperatura.

•A tutt’oggi, domande fondamentali riguardanti questo processo non hanno

risposta.



Simulations show that resistive MHD gives elongated (system size) Sweet-Parker layer

and very low reconnection rates (Birn et al. 2001)

i AV V



Quando la riconnessione è di tipo Petschek il tasso di riconnessione raggiunge

valori confrontabili con quelli osservati

E’ fondamentale descrivere la struttura della regione di diffusione

e capire se a guidare il processo è la fisica in questa regione, o le

condizioni su grande scala.



The ESA cornerstone mission CLUSTER

Launched 2000 –Extended to 2009

Cluster is the first spacefleet flying in close

formation to study fundamental plasma

processes in three dimensions.

Cluster explores some of the most important

near-Earth regions. During 2004-2007

operated together with the ESA-CSNA

Double Star mission.

IFSI participated in the design and

development of the plasma analyzers in the

framework of an international collaboration.



~ 3000 km

Kinetic features of plasma near the X-point

Bavassano Cattaneo et al., 2006

11



~ 3000 km

Kinetic features of plasma near the X-point

350000 km

3500

00 k

m

Bavassano Cattaneo et al., 2006

Yokoyama, 2001



Retinò et al. 2005, Bavassano Cattaneo et al. 2006

Reconnection is continous while large scale conditions changes

C1 C3 C4

MP

E

Vn

Vt

ΔBΔVμρ

1



Retinò et al. 2005, Bavassano Cattaneo et al. 2006

Reconnection is continous while large scale conditions changes

C1 C3 C4

Spacecraft Separation 1000 kmTime Interval 4 hours



km8.0km40 km20

The Hall term enables fast reconnection also in collisionless plasma(Birn et al. 2001)

JJ

BJBVE

dt

d

enen pee 2

0

1P

11

Two component plasma full generalized Ohm’s law

Physics of the diffusion region



Adapted from Nakamura, 2005

Hall currents system quadrupolar out-of-plane magnetic field

Hall term signatures (Sonnerup 1979):



Cluster resolve the spatial

and temporal ambiguity

always present in the

single spacecraft

measurements and

observe unambiguously

the Hall term signature.

2D two fluid MHD numerical simulation of the diffusion region and Cluster configuration.

Spacecraft Separation 100 kmTime Interval 4 s

Hall magnetic field observations

Vaivads et al. 2004

22



Observation of an Elongated Electron Diffusion Region

Recently particle in cell simulations

show that the electron diffusion region

develops a distinct two-scale structure

along the outflow direction:

An out-of-plane current layer of length i

A super-Alfvenic outflow jet of electrons

extending 10s of i

Phan et al. 2007, Shay et al. 2007

33



Time Interval 15 s

Observation of an Elongated Electron Diffusion Region

Phan et al. 2007, Shay et al. 2007



How is reconnection initiated?– What triggers reconnection within a current sheet?

• What parameters control the spatial/temporal characteristicsof reconnection site?– How is a reconnection neutral line structured ?

• What are the consequences of reconnection?– How are ions and electrons energized as a consequence ofreconnection ?

It is important to note that reconnection is a multi-scale process

Unanswered Questions



Simultaneous 3D measurements on all

three scales

– electron, ion and fluid – are crucial.

This is the scope of

the Cross-Scale mission

Cross-Scale has been selected by

ESA's Space Science Advisory Panel to

proceed to the Assessment Phase

of Cosmic Vision 2015-2025

Istituto di Fisica dello Spazio Interplanetario M.F. Marcucci SAIT Teramo 4-8 maggio 2008 Nuove...

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