Estudo observacional da reconexão magnética na magnetosfera terrestre

Bolsista da Bolsa PCIDGE/CEA/INPE

Daiki Koga

Supervisor :

Dr. Walter Demetrio Gonzalez Alarcon

Plasmas

99% do espaço observável são plasmas.

SDO

eters simultaneously at large number of points in thereconnection region !Yamada, 2001". By contrast, aspace satellite provides data only at a few selectedpoints. Dedicated laboratory experiments quantitativelycross-check theoretically proposed physics mechanismsand models and provide a bridge between space obser-vations and theoretical ideas !Sweet, 1958". Recent sig-nificant progresses in data acquisition technologies hasallowed detailed magnetic field structures of reconnec-tion regions to be measured by space satellites and inlaboratory experiments. Figure 5 presents contours ofconstant flux which was deduced from experimentallymeasured data using magnetic probes located at mul-tiple !30" locations in the reconnection region of themagnetic reconnection experiment !MRX" !Yamada etal., 1997a; Yamada, 1999a".

The primary objectives of this review are to highlightthe recent progress in understanding magnetic reconnec-tion and to illuminate key physics mechanisms for fastreconnection. One of the most important questions hasbeen why reconnection occurs much faster than pre-dicted by classical MHD theory. During the past tenyears, notable progress in understanding the physics ofthis fast reconnection has been made through numericalsimulations, observations from satellites, and dedicatedlaboratory plasma experiments. Extensive theoreticaland experimental work has established that two-fluid ef-fects, resulting from the fundamentally different behav-ior of ions and electrons, are important within the criti-cal layer where reconnection occurs. The two-fluideffects are considered to influence the rate at which re-connection occurs in the magnetosphere, stellar flares,and laboratory plasmas. Dedicated laboratory experi-ments and magnetospheric satellite measurements showstrikingly similar data in the profiles of magnetic fieldand electrostatic and magnetic fluctuations. Recent im-provements in the understanding of reconnection on theinvestigations of magnetic self-organization in labora-tory and space-terrestrial plasmas will also be covered.

Beginning with a discussion of the seminal ideas ofSweet and Parker, Petschek, and Dungey, this review of

magnetic reconnection research will survey findingsfrom significant studies that have continued up to thepresent time. While theory led the early researchprogress in this area, more recent research has beendominated by experiments and numerical simulations.Since the early work is fairly well known, we place moreemphasis on recent experimental, numerical, and theo-retical work and focus on modern findings of most sig-nificance. There are a number of different views as towhich physical processes are most important for recon-nection. In particular, the relative importance of two-fluid Hall processes versus fluctuation-inducedanomalous-resistive processes is debated. Our goal is toprovide a balanced presentation of these views.

We address the following major questions which havebeen studied intensively:

!1" What are the mechanisms of magnetic reconnectionin the collisionless plasma? How does the two-fluidphysics influence the speed and dynamics of localreconnection? What determines the structure of re-connection layers?

!2" Why is the reconnection rate so fast in collisionlessplasmas? What is a scaling for reconnection rate oncollisionality?

!3" How do fluctuations and turbulence affect the re-connection dynamics? Which fluctuations are mostrelevant, how are they excited, and how do they de-termine the reconnection rate and influence the con-version of magnetic energy?

!4" How is the local physics that has been studied ingreat detail connected to the global environmentaround the reconnection layer?

A number of physics topics that are vigorously de-bated at present and not yet resolved at the moment arethe following: !1" How is magnetic energy converted tothe kinetic energy of electrons and ions? In what chan-nel does the energy flow take place? !2" How is the re-connection layer generated by a global boundary? !3"Why does reconnection occur impulsively in most cases?Keeping these questions in mind we review most of thesignificant modern experimental discoveries in magneticreconnection research and discuss many of the theoreti-cal investigations to which they have led.

In this review we make an effort to cover both themajor experimental results and space observations thathave provided useful information on the physics of mag-netic reconnection over the past few decades. This re-view is different from recent reviews which have empha-sized theoretical aspects of reconnection or results fromnumerical simulations. To cover wide physics aspects ofmagnetic reconnection, see Biskamp !2000", Priest andForbes !2000", and Birn and Priest !2007".

Our perspective is that magnetic reconnection is influ-enced and determined by both local plasma dynamics inthe reconnection region and global boundary conditions.One major question is how large-scale systems generatelocal reconnection structures through formation of cur-rent sheets—either spontaneously or via imposed

FIG. 5. !Color" Photograph !time integrated" of controlleddriven reconnection discharges !in hydrogen" in the MRX, su-perimposed with flux contours calculated from measurementsby magnetic probes !see http://mrx.pppl.gov/". Oppositely di-rected field lines are seen to meet and reconnect in the recon-nection region. From Yamada, 1999b.

606 Yamada, Kulsrud, and Ji: Magnetic reconnection

Rev. Mod. Phys., Vol. 82, No. 1, January–March 2010

MRX

Plasmas existem quaisquer lugares

Coroa solar Aurora Raios

Laboratório

Fogo

Galáxia

sinais de neônio

Reconexão Magnética (RM)

Reconexão magnética é um processo que ocorre quando plasmas magnetizados com componente antiparalela do campo magnético se encontram na pequena região.

Energia magnética

Energia cinética, térmica e aceleração de partículas

2009 September–October 395www.americanscientist.org © 2009 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact perms@amsci.org.

magnetic fields from the Sun and the Earth interconnect, which should be responsible for driving plasma flow throughout the Earth’s magnetosphere and possibly producing the aurora (as had been theorized by his graduate ad-visor, Fred Hoyle, in 1948, with whom Giovanelli had discussed his model). Since then researchers on the Earth’s magnetosphere have gradually seen Dungey’s magnetic reconnection idea move from questionable to highly con-troversial (owing to the inability at the time to make actual observations to back up the predictions) to universally accepted as the main driver of space storms around the Earth.

The idea of a connection with the aurora has also turned out to be true, but for all types of auroras except one, the link is only indirect. For the most part, the widespread and violent au-roral displays associated with severe space storms are caused by processes internal to the magnetosphere, which nonetheless rely on magnetic recon-nection at much higher altitudes for their existence (see figure 3 for an illus-tration of the process). The idea here is that magnetic fields from the Sun and the Earth reconnect on the dayside of the Earth (the side facing the Sun), af-ter which the solar wind carries the reconnected magnetic flux along the magnetopause (the boundary of the magnetosphere) to the nightside, re-sulting in a build-up of magnetic ener-gy in the tail of the magnetosphere. A second reconnection event in the tail, which reconnects northern and south-ern magnetic flux and releases the so-lar field lines, is established after some time delay (a half hour or so), and it is this event that leads to widespread magnetic and auroral activity known as the magnetospheric substorm, as well as to strong beams of high-energy particles. The question of whether re-connection triggers the substorm or is a secondary effect was answered in 2008 by the five-spacecraft NASA THEMIS mission, launched specifically to study space storms, which showed conclu-sively that reconnection is in fact the trigger mechanism.

Evidence MountsMuch of the original evidence for the importance of magnetic reconnection in the Earth’s magnetosphere was sta-tistical—strong auroral and magnetic activity was found to be correlated with southward-directed solar-wind

magnetic fields that reconnect with the northward pointing field of the Earth. The southward fields were also associated with inward movement of the dayside boundary of the magne-tosphere, as magnetic flux is stripped from the dayside and transferred to the nightside because it is connected to the flowing solar wind. Later on, predic-tions of reconnection theory, regarding plasma outflow from the reconnection

region and magnetic penetration of the boundary, were both confirmed by spacecraft data. As more recent space-craft data pour in, especially from the European Space Agency Cluster II mis-sion (which studies how the Earth’s magnetic field interacts with the solar wind), the evidence that magnetic re-connection plays a dominant role in driving the dynamics of the magneto-sphere has become overwhelming.

Figure 2. An x-ray image of a solar coronal structure from Japan’s Hinode spacecraft (left) is overlaid with an illustration of the magnetic field lines and the reconnection region (dotted box) that pro-duces it. Computer simulations of electron populations in reconnection regions (right) have been key in deciphering more about how this event unfolds. (Left image is courtesy of the Japanese Space Agency, right image is courtesy of James Drake and Michael Shay, University of Delaware.)

bowshock

magnetopause

solarwind

Figure 3. The solar wind carries the interplanetary magnetic field (yellow lines), here oriented southward, into the northward-facing geomagnetic field lines emanating from the Earth (green lines) at the dayside of the magnetopause. The reconnection of these fields (dotted box at left) allows energy and charged particles from the solar wind to enter the magnetosphere. Open magnetic field lines (purple lines) are carried downstream in the solar wind and eventually reconnect in the distant tail of the magnetosphere (dotted box at right). This figure shows only a noon-to-midnight cross-section of the three-dimensional magnetosphere.

An x-ray image of a solar coronal structure from Japan’s Hinode spacecraft

2009 September–October 395www.americanscientist.org © 2009 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact perms@amsci.org.

magnetic fields from the Sun and the Earth interconnect, which should be responsible for driving plasma flow throughout the Earth’s magnetosphere and possibly producing the aurora (as had been theorized by his graduate ad-visor, Fred Hoyle, in 1948, with whom Giovanelli had discussed his model). Since then researchers on the Earth’s magnetosphere have gradually seen Dungey’s magnetic reconnection idea move from questionable to highly con-troversial (owing to the inability at the time to make actual observations to back up the predictions) to universally accepted as the main driver of space storms around the Earth.

The idea of a connection with the aurora has also turned out to be true, but for all types of auroras except one, the link is only indirect. For the most part, the widespread and violent au-roral displays associated with severe space storms are caused by processes internal to the magnetosphere, which nonetheless rely on magnetic recon-nection at much higher altitudes for their existence (see figure 3 for an illus-tration of the process). The idea here is that magnetic fields from the Sun and the Earth reconnect on the dayside of the Earth (the side facing the Sun), af-ter which the solar wind carries the reconnected magnetic flux along the magnetopause (the boundary of the magnetosphere) to the nightside, re-sulting in a build-up of magnetic ener-gy in the tail of the magnetosphere. A second reconnection event in the tail, which reconnects northern and south-ern magnetic flux and releases the so-lar field lines, is established after some time delay (a half hour or so), and it is this event that leads to widespread magnetic and auroral activity known as the magnetospheric substorm, as well as to strong beams of high-energy particles. The question of whether re-connection triggers the substorm or is a secondary effect was answered in 2008 by the five-spacecraft NASA THEMIS mission, launched specifically to study space storms, which showed conclu-sively that reconnection is in fact the trigger mechanism.

Evidence MountsMuch of the original evidence for the importance of magnetic reconnection in the Earth’s magnetosphere was sta-tistical—strong auroral and magnetic activity was found to be correlated with southward-directed solar-wind

magnetic fields that reconnect with the northward pointing field of the Earth. The southward fields were also associated with inward movement of the dayside boundary of the magne-tosphere, as magnetic flux is stripped from the dayside and transferred to the nightside because it is connected to the flowing solar wind. Later on, predic-tions of reconnection theory, regarding plasma outflow from the reconnection

region and magnetic penetration of the boundary, were both confirmed by spacecraft data. As more recent space-craft data pour in, especially from the European Space Agency Cluster II mis-sion (which studies how the Earth’s magnetic field interacts with the solar wind), the evidence that magnetic re-connection plays a dominant role in driving the dynamics of the magneto-sphere has become overwhelming.

Figure 2. An x-ray image of a solar coronal structure from Japan’s Hinode spacecraft (left) is overlaid with an illustration of the magnetic field lines and the reconnection region (dotted box) that pro-duces it. Computer simulations of electron populations in reconnection regions (right) have been key in deciphering more about how this event unfolds. (Left image is courtesy of the Japanese Space Agency, right image is courtesy of James Drake and Michael Shay, University of Delaware.)

bowshock

magnetopause

solarwind

Figure 3. The solar wind carries the interplanetary magnetic field (yellow lines), here oriented southward, into the northward-facing geomagnetic field lines emanating from the Earth (green lines) at the dayside of the magnetopause. The reconnection of these fields (dotted box at left) allows energy and charged particles from the solar wind to enter the magnetosphere. Open magnetic field lines (purple lines) are carried downstream in the solar wind and eventually reconnect in the distant tail of the magnetosphere (dotted box at right). This figure shows only a noon-to-midnight cross-section of the three-dimensional magnetosphere.

Burch e Drake, 2009, American Scientist

Emissão de massa coronal (CME)

CME atinge à magnetosfera terrestree acontece RM!

Reconexão magnética da coroa solar

Tempestade/sub-tempestade magnética

reconexão

reconexão

Se a tempestade magnética for muito intensa?

On March 13, 1989 the entire province of Quebec, Canada suffered an electrical power blackout. Hundreds of blackouts occur in some part of North America every year. The Quebec Blackout was different, because this one was caused by a solar storm!

http://www.nasa.gov/topics/earth/features/sun_darkness.html

“Blackout no Canadá em 1989”

Clima Espacial

Reconexão magnética na magnetopausa terrestreutilizando dados do satélite POLAR

(No ponto de vista da escala macroscópica)

1. As distâncias de linha de reconexão estimada até o local da reconexão observada

2. Condição do modelo do Gonzalez e Mozer 1974

3. Associação de eventos de reconexão com parâmetros do vento solar

4. Dependência de hora local magnética e latitude com a amplificação magnética

Satélite POLAR

De fevereiro até maio de 2001, 2002, e 2003, com 9,5 Re de apogeu,74 eventos de reconexão magnética foram obitidos

na baixa latitude da parte diurna da magnetopausa.

2001 2002 2003

1996

y

x

z

y

Ao Sol

Terra

x: sol-terray: leste-oestez: norte-sul

Órbitas do satélite POLAR

Polar Fast Plasma Analyzer - HYDRA (13.8 second resolution)Polar MFE (6 second resolution)

magnetosheath

Magnetosphere Magnetosphere

Dados de campo magnético e plasma:Um Exemplo

From UCLA/IGPP Polar Magnetometer Interactive Data Server and NASA/GSFC CDAWeb

MagnetosphereBsp Magnetosphere

magnetosheath

Modelo do Gonzalez-Mozer 1974

sinβ =B2 −B1cosα

(B21 + B2

2 − 2B1B2cosα)1/2

sin(α− β) =B1 −B2cosα

(B21 + B2

2 − 2B1B2cosα)1/2

(também Sonnerup, 1974; Hill, 1975)

α: O ângulo entre a bainha magnética (B1) e magnetosfera (B2)β: O ângulo entre magnetosfera e linha-X

Linha-X

Quando !<", não acontecerá reconexão!

ZGSM

YGSM

X-line

satellite

8 6 4 2 0 2 4 6 88

6

4

2

0

2

4

6

8

YGSM (Re)

Z GSM

(Re)

IMF By > 0

D <= 0.5Re0.5Re < D <= 1Re1Re < D <= 2Re2Re < D <= 3ReD > 3Re

B2

B1

As distâncias de linha de reconexão estimada até o local da reconexão observada

Existem os eventos mais próximos à linha-Xna região equatorial.

(leste-oeste)

(norte-sul)

120

90

60

30

0

B sh (n

T)

-120 -90 -60 -30 0 30 60 90 120

Bspcos !(nT)

Reconnection condition

Non-reconnection condition

Bsh > Bsp cosα

Condição do modelo de Gonzalez e Mozer 1974

Bsh = Bsp cosα

cam

po m

agné

tico

na b

ainh

a m

agné

tica

campo magnético na magnetosfera

y’

z’z

y

!

"

∇×B = µoJ

−∂Bz

∂x= µoJy

∆B

L= −µoJy

∆B = Bsh sin(β − α)−Bsp sinβ

Bsp

Bsh

Bsh = Bsp cosα

∆B = −Bsp sinα cos(β − α)

35 30 25 20 15 10 5 035

30

25

20

15

10

5

0

!"#"$% &'(") *

! "#"$%

Jy = Bsp sinα cos(β − α)/µoL

Linha-X

Jy = Bsp sinαµoL

Maximização de corrente elétricaao longo da linha-X!

A lei de Ampère

Associação de eventos de reconexão com parâmetros do vento solar

A pressão dinâmicaICMEs+MCs

CIRpós-CIRs

90

75

60

45

30

15

0

X-li

ne A

ngle

!(d

eg)

18161412108642

IMF Magnitude (nT) 90

75

60

45

30

15

0

X-li

ne A

ngle

!(d

eg)

0.12 3 4 5 6 7

12 3 4 5 6 7

102 3

Plasma Beta

90

75

60

45

30

15

0

X-li

ne A

ngle

!(d

eg)

181614121086420

Flow Pressure (nPa)grande dispersão

-180

-135

-90

-45

0

45

90

135

180

Eclip

tic a

zim

utha

l Ang

le (d

egre

e)

1615141312111098

Magnetic Local Time (hour)

Dependência de hora local magnética e latitude com a amplificação magnética

90 ~ 180°

30

25

20

15

10

5

0

Am

plifi

catio

n Fa

ctor

-40 -30 -20 -10 0 10 20 30 40

GSE latitude (degree)

20

15

10

5

0

Frequency of occurrence

30

25

20

15

10

5

0

Am

plifi

catio

n Fa

ctor

1615141312111098

Magnetic Local Time (hour)

20

15

10

5

0

Frequency of occurrence

θ

Magnetopausa

IMF

YGSM

XGSM

Terra

Alta frequência de ocorrência

(leste-oeste)

(sol-terra)

Vento solarEarth

O efeito de inclinação do dipolo magnético

30

25

20

15

10

5

0

Am

plifi

catio

n Fa

ctor

-40 -30 -20 -10 0 10 20 30 40

GSE latitude (degree)

20

15

10

5

0

Frequency of occurrence

30

25

20

15

10

5

0A

mpl

ifica

tion

Fact

or1615141312111098

Magnetic Local Time (hour)

20

15

10

5

0

Frequency of occurrence

Dependência de hora local magnética e latitude com a amplificação magnética

Taxa de reconexão(No ponto de vista da escala microscópica)

MagnetosferaBainha magnética

Inflow:Vi

Outflow:VA

R =Vi

VA=

BN

BL

L

N

Etan = ViBL = VABN

Na fronteira das duas regiões, a componete tangential do campo elétrico é contínua.

Então, a taxa de reconexão é dada por

Região de difusão

Taxa de reconexão β =nkBT

B2/2µo

Taxa de reconexão

β =nkBT

B2/2µo

Mozer et al. 2002 PRL

E+V ×B = ηJ+1

neJ×B− 1

ne∇ ·Pe +

me

ne2∂J

∂t

Efeito do termo Hall(estudo em andamento)

A lei de Ohm generalizada

60

40

20

0

20

40

60

!"

#$%&'()*+,-./01)!(2/-34(567(5889

16:25:06 :10 :15 :20 :25 :3020

0

20

:"

;<=;()-(3;

>

Ex’NBz’By’

magnetosfera bainha magnéticaBz +

Bz -

Ex +

Ex -By +

By -

N

Mozer et al. 2002 PRL

Órbita do POLAR

Depêndencia de parâmetros de plasma Comparação com teoria de reconexão

Colaboração nacional/internacional

GSFC/NASA: Dr. David G. SibeckUniv. West Virginia: Dr. Paul CassakUC Berkeley: Prof. Forrest S. Mozer

USP: Dra. Flavia R. Cardoso

RECONEX/INPE: Dr. Odim Mendes JuniorDra. Maria Virgínia AlvisDra. Cristiane LoeschDr. Arian Ojeda GonzalezMarcos V. D. SilveiraVitor Souza (GSFC/NASA)Paulo Ricardo JauerGerman Farinas Perez

Prof. Eugene N. Parker

18 - 21 Março, 2014

O pioneiro de teoria de reconexão magnética

e “o pai” do vento solar