El viento solar y su interacción con la magnetósfera...

La Heliosfera Sergio Dasso1,2

1 Instituto de Astronomía y Física del Espacio (IAFE), CONICET-UBA, Argentina 2 Departamento de Física, Facultad de Ciencias Exactas y Naturales, UBA, Argentina

Departamento de Física Juan José Giambiagi

Astropartículas y Física Solar – LAGO. Univ. San Francisco de Quito, 20-24 enero, 2014

Clase 3:

•Turbulencia en el medio interplanetario •El viento solar transitorio •Regiones de co-rotación •Estructuras transitorias

•Eyecciones de masa coronal •Nubes magnéticas interplanetarias


Turbulence in the SW

However, MHD is more complex:

•Turb MHD is anisotropic, ∃ B0 !!!

•Direction of k (respect to B0) crucial to wave modes and wave-particle interaction

•Diff theories make diff prediction about the evolution of Eb+Ek (e.g., IK’65 alternative to K41)

•For λ<λc, w-p, new physcis can dominate fluctuations (e.g., dispersion range): e-!

•Polarization turns to be crucial (branches)

•Many other differences

•In HD turbulence, the kinetic energy developes a cascade from large scale fluctuations to small scales through the “intertial range” •At a proper small scale (“dissipation range”) the fluctuations start to be damped and the energy is deposited as heating of the fluid


Turbulencia

Armstrong et al., Nature, 1981

En el medio interestelar local, desde observaciones remotas

Hay evidencia muy sólida que indica que la turbulencia está presente tanto en el medio interestelar local como en la heliosfera

?


Turbulencia


En el medio interestelar local, desde observaciones remotas En el viento solar, desde observaciones in situ

Cascada de energía magnética (Voyager at 1 AU): E~k-5/3

Transporte en escalas

(rango inercial)

From a lot of authors from 70’s to today


?


Courtesy from Bill Matthaeus

Power spectra at intertial range: -5/3 [K41]

Turbulencia


En el medio interestelar local, desde observaciones remotas En el viento solar, desde observaciones in situ

Cascada de energía magnética (Voyager at 1 AU): E~k-5/3

Transporte en escalas

(rango inercial)

From a lot of authors from 70’s to today


?

Turbulencia Alfvénica en el viento solar

Fuerte correlación entre v y b [Belcher and Davis 1971]

Estructuras de Elsässer: πρ4

Bv ±=±zAcoplamiento no lineal únicamente

si se activan ambos modos

(ondas de Alfvén)

[From Borovsky 2010] How ‘ Parkerian’ is the SW at 1AU?

Longitude deviated from the expected value, according with the Parker spiral

Distorted (advected) dipolar configuration The Sun rotates and there is a tilt between

magnetic dipole and


Corotating Interaction Regions


Estructuras de gran escala en la heliosfera observadas con técnicas de centelleo

• Se puede observar la estructura de espiral: regiones de compresión y rarificación

• Estos datos fueron observados desde Tierra con técnicas de centelleo: Fluctuaciones de intensidad de ondas de radio que responden a n y turb en SW (Bernie Jackson, para mas información: http://cassfos02.ucsd.edu/solar/tomography/)

June 23, 1994 to July 20, 1994 (Carrington Rotation 1884)


LASCO-SOHO

Ejective transient structures: Coronal Mass Ejections

Drawing 1860


Ejective transient structures: Coronal Mass Ejections

Drawing 1860

LASCO-SOHO

(2000)


From [Zurbuchen & Richardson, Space Science Rev, 2006]

•Shock waves driven by fast MCs (and a turbulent sheath of large n)

•Cold structures (low Tp)

•e-s flows along B (>100eVs): proxy of magnetic connectivity

•Smooth and large coherent rotation of B (helical structures), B increased respect to the SW

•Low plasma beta (βp) ⇒ Fmag

Parker spiral B

Snow thrower effect

Transients are ejected from the Sun toward the SW

•Subset of ICMEs observed as ‘Magnetic Clouds’ (MCs) in the SW •Observed properties: - Low Tp - Smooth and large rotation of B - Large intensity of B - Low proton plasma βp


Connectivity to the Sun Larson et al. [GRL, 1997]

•Correlation between absence of e- flux and high β value

•When suprathermal e- fluxes are not observed ... disconnection or scattering due to wave-particle interaction?

Larson et al. [GRL, 1997]

Estimation of the leg’s length:

L~1.2AU L=velec(tf-t0)

t0:type III burst tf:in situ (e- beam: Lungmuir) (e-: 20KeV) ωe~ne

1/2

(14MHz →10KHz)


Open and closed fields in magnetic clouds

• Counterstreaming suprathermal electrons indicate field lines connected to the Sun at both ends (closed)

• On average, clouds are nearly half open

Shodhan et al. [2000]

Suprathermal (320 eV) electron pitch angle distributions for 8 Nov 04

magnetic cloud

closed open


Local simplification: Cylindrical slide of the MC


Modeling magnetic clouds

From in situ observed B possible to ‘orient’ the local

axis of the flux rope, to model it, and to compute the content of MHD invariants


Cross-section: ~ circular (due to magnetic tension)

reconstruction of the magnetic field from 1D data (magnetic + plasma pressure balance) ( Liu et al. 2008 )

MC

Cross-section shape of MCs from multispacecraft observations

(assuming a Grad Shafranov equilibrium)


From Nakwacki et al., 2008

Magnetic clouds are astrophysical objects with very low proton plasma beta ( ~ 10-1 – 10-2),

so that their internal dynamics is expected to be controlled mainly by magnetic fields


Linear Force Free Field [Lundquist, ArkFys 1950]

])2()2([ 01000 φzB rJrJB ττ +=

)(2 00 cte==×∇ ττ BB

•τ(r)=dϕ/dz=Bϕ(r)/rBz(r): amount of magnetic field twist •τ0=τ(r~0) •B0 is the magnetic field intensity at the cloud axis

Taylor’s state B=Bz(r)z + Bφ(r)φ

Fluxes and H from models


MCs and ICMEs typically show expansion (larger velocity in the front and smaller in the back)

From Nakwacki et al., 2008

•Possible to (in situ) observe expansion along the radial direction (from the Sun) •But, strong deformation of helical structure is expected if expansion is significantly different in the other directions •So that, approximately isotropic expansion is expected


Different MCs observed at different solar distances D (good for studies of global expansion)

Large uncertainties (only a few observed events)

Modeling evolution of MCs from assuming: (i) conservation of mass, magnetic fluxes

(ii) isotropic self-similar expansion (iii) S~D

Then, np~D-3, B~D-2

S~D0.97

B~D-1.8

[From Kumar & Rust, JGR 1996]

Better determination of scale law exponents (more events): S~D0.8±0.1 [e.g., Bothmer & Schwenn ‘98; Leitner et al. JGR’07; Gulisano et al., 2010]

Improvements

Moving boundary model [Demoulin & Dasso A&A‘09]: For SW pressure decay as Psw(D)~D-np,

global expansion expected as S ~ Dnp/4 ~ D0.7


Cumulative flux Fy/L

0)(, =∫ropeflux

cloudy xBdx

∫=x

Xcloudy

cloudy

in

xBdxL

xF)'('

)(,

.,

x y

Xin

From ∇•B=0 and invariance of B along the main axis of the cloud (valid to a general 2D-shape!):


Cumulative flux Fy/L

0)(, =∫ropeflux

cloudy xBdx

∫=x

Xcloudy

cloudy

in

xBdxL

xF)'('

)(,

.,

x y

[from Dasso et al., A&A 2006]

By,cloud

Cancelation of Fy,cloud at a magnetic discontinuity

Xin

From ∇•B=0 and invariance of B along the main axis of the cloud (valid to a general 2D-shape!):

•Agreement between diff. authors on start MC.

•However, diff. end boundaries chosen by previous authors

[Lepping et al., JGR’97; Larson et al., GRL’97; Janoo et al., JGR’98]


Back

Back !!

Possible explanation: The flux rope was partially pealed from its front.

However, B in the ‘back’ still organized, showing ~ properties of a flux rope and not of SW

-Also found in other MCs [Dasso et al., 2007, Mostl et al., 2008,

Ruffenach et al., 2012]

-Reconnection is efficient in heliosphere because Hall effect increases its rate

[e.g., Morales et al., JGR 2005]

-Reconnection in ICMEs boundaries (from observations [Gosling et al., 2005]; from numerical simulations

[Taubenschuss, 2010])

Magnetic Reconnection? Back was part of flux rope before?

Erosion affects geoeffectiveness! (less amont of flux lower time range for Bs)


Fin clase 3

El viento solar y su interacción con la magnetósfera...

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