Plasma flows and magnetic fields in solar active

regions and coronal holes

Eckart MarschMPI für Sonnensystemforschung

Seminar der Sonnengruppe am MPS, Lindau, 6 September 2005

Coronal holes and active regionsAims:

Search for the possible relationships between plasma flow (nascent solar wind), ultraviolet emission and the structure and strength of the magnetic field.

Means:

Direct comparison of the deduced velocity field (Doppler shifts from SUMER) and VUV line radiances with the extrapolated photospheric magnetic field (from MDI and Kitt Peak magnetograms) in various coronal structures.

Magnetic coupling: Results from recent analyses of SUMER and MDI data, exploiting magnetic field extrapolations

The coronal magnetic field• Closed loops and streamers

• Coronal funnels and holes

• Magnetic transition region(magnetic network)

Modelling by extrapolation(Potential, force-free, MHD)

Coronal model field Magnetic carpet

Schrijver et al.

Title et al.

The source regions of the fast solar wind in coronal holes

Insert: SUMERNe VIII 77 nm at 630 000 K

ChromosphericnetworkDoppler shiftsRed: downBlue: up

Outflow at lanesand junctions!

Image: EIT Corona in Fe XII 19.5 nm at 1.5 MK

Note: The modified rest wavelength of NeVIII at 77 nm as determined by using SUMER data leads to an average blue shift in CHs (Peter & Judge 1999; Dammasch et al. 1999).

Hassler et al., Science 283, 811, 1999

Equatorial coronal hole

Kitt Peak magnetogram

Date: 5 November 1999 FOV: 252" х 300"Time: 17:07UT—21:07UT Spectral lines: Si II (1533 Å, ~0.02 MK ), Detector: A C IV (1548 Å, ~0.1 MK), Slit: 2 Ne VIII (770 Å, in 2nd order, ~0.63 MK)

Xia, Marsch, Wilhelm, A&A, 424, 1025, 2004

Magnetogram and Doppler shiftB positive

B negative

Blueshift

Redshift

CH 8 Nov. 1999

From left to right: MDI Magnetogram, HI Lyβ, CII, OVI Contours indicate network lanes as outlined in continuum

Xia, Marsch, Wilhelm, A&A, 424, 1025, 2004

Outflow in coronal holeAverage blue shift (relative to C I) : 7.5 km/s for dark region; 4 km/s for bright region

Left: NSO/KP magnetogram + contoursof Doppler shift (Ne VIII at 770 Å)

Right: Dopplergram + contour of radiance (indicating EUV BPs in CH)

Xia, Marsch, and Curdt, A&A, 399, L5, 2003

Magnetic network loops and funnelsStructure of transition region Magnetic field of coronal funnel

Hackenberg et al., Space Sci. Rev., 87, 207, 1999Dowdy et al., Solar Phys., 105, 35, 1986

Network model: (1) Gabriel (1976): static model(2) Dowdy et al. (1986): funnels and (small) loops(3) Axford et al. (1992): magnetic furnace by reconnection

Height profiles in funnel flows

1 10 100 1000 1 10 100 1000Height / M m Height / M m

T / K V / km s-1106

105

1000

100

10 v

vc

• Heating by wave sweeping

• Steep temperature gradients• Critical point at 1 RS

Hackenberg, Marsch, Mann, A&A, 360, 1139, 2000

Loops and funnels in CH

CH boundarySUMER raster field

Wiegelmann, Xia, and Marsch, A&A, 432, L1, 2005

Loops and funnels in CH

Field lines: brown open, and yellowclosed

Correlation: Field topology and plasma outflow (blue in open field)

Wiegelmann, Xia, and Marsch, A&A, 432, L1, 2005

Solar active region

Kitt Peak magnetogram

Date: 2 August 1996 FOV: 120" х 120"Time: 12:51 UTC Spectral lines: H I (1025 Å, ~ 0.04 MK) Detector: A N V (1238 Å, ~ 0.19 MK), Slit: 6 Ne VIII (770 Å, in 2nd order, ~ 0.63 MK)

Marsch, Wiegelmann, Xia A&A, 428, 629, 2004

Sunspot and active region

Force-free magnetic field extrapolation

Seehafer, Solar Physics 58, 215, 1978j = α B

definitions

symmetry

Magnetic field and Doppler shift

Photosphere0 Mm

C IV

red: down

Transitionregion10 Mm

Ne VIII

blue: upinclination angle (degree)

field magnitude B/G

Flows and fields in active region I

force-free magnetic field

Coronal magnetic field topology in three dimensions for AR 7953. Field lines with Bz > 50 G on the photosphere are plotted. The color coding represents the strength.

SUMER Dopplergram in NeVIII (λ 77 nm) and a 2-D-projection of some reconstructed field lines, with α = -1.1 10-8 m-1. Additional contours of the magnetic field strength on the photosphere are also shown.

E. Marsch, T. Wiegelmann, L.D. Xia, A & A, 428, 629, 2004

Flows and fields in active region II

Left: Magnetic field strength as a function of the normalized coordinate along a single flux tube. Right: Inferred current density distribution, showing spatial asymmetry and current concentration at one foot point.

updown

Left: Mass flux density, defined as v I1/2, in arbitrary units and inferred from Doppler shift and radiance of Ne VIII (λ 77 nm), in dependence on coordinate along the loop.

The averaged data almost form a straight line.

Magnetic flux tube in the active region AR 7953.

E. Marsch, T. Wiegelmann, L.D. Xia, A & A, 428, 629, 2004

Polar coronal hole

Overview(A) Sun in EIT wavelength window around 19.5 nm. The white rectangle indicates the size of the SUMER raster scan. A comparison of the structures was made only for the smaller rectangle.(B) Magnetic field vertical component from –70 to 70 G (C) Si II radiance in arbitrary units (chromosphere)(D) C IV radiance in arbitrary units (transition region)(E) Ne VIII Doppler shifts along the LOS, ranging from –15 km/s to 15 km/s. (F) Comparison between the Ne VIII Doppler shift (hatched regions with outflow speeds higher than 7 km/s) and the magnetic field angle, with0° indicating vertical and 90° horizontal orientation at a height of 20.6 Mm.

Magnetic field in source region

funnel

polar hole

Tu, Zhou, Marsch, et al., SW11, in press, 2005

Correlating field with radiation

Results from the linear correlation analyses. The asterisks indicate the average values in each vertical bin, with one standard deviation. (A) Plot of the Ne VIII Doppler shift versus |Bz/B| at 20.6 Mm. (B) Plot of the square root of the Si II radiance versus |Bz| at 4.0 Mm.

Height variation of correlation

(A) The solid line gives the coefficient (normalized by 0.50) between line radiance and Bz for Si II, the dotted line the coefficient (normalized by 0.18) for C IV. The dashed line gives the coefficient (normalized by 0.39) between the Ne VIII blueshift and |Bz /B|.

(B) Radial variations of the line radiances of Si II, C IV and Ne VIII, and of the continuum at 154.31 nm, which is indicated by the dash-dot line. The solid line indicates Si II, the dotted C IV, and the dashed Ne VIII. All radiances are normalized to their maximum values. The data were taken across the limb.

To indicate the precision by which one can determine the maximum height, we have drawn horizontal bars extending between the two locations where the coefficients (radiances) drop below 95% of their maxima.

Flows and funnels in coronal hole

Tu, Zhou, Marsch, et al., Science, 308, 519, 2005

Correlations

fieldinclinaton

fieldstrength

fieldinclinaton

fieldstrength

Funnel geometry

Funnelconstrictionby adjacentloops!

Area expandsby a factor of 10

Not of canopytype! Field only declinesby a factor of 6

Mass and energy supply

Sketch to illustrate the scenario of the solar wind origin and mass supply. The plot is drawn to show that supergranular convection is the driver of solar wind outflow in coronal funnels. The sizes and shapes of funnels and loops shown are drawn according to the real scale sizes of the magnetic structures.

Wave energy supply byreconnection in magnetic furnace

Axford and McKenzie, 1992, and Space Science Reviews, 87, 25, 1999

Alfvén waves out

Loopsdown

New flux fed in at sides byconvection (t ~ 20 minutes)

FE = 107 erg cm-2 s-1

Staticfield

Gabriel (1976)

„Picoflares“

Low correlation height in quiet sun

22 September 1996

476'‘east

66'‘west

Two-dimensional maps of Bz extrapolated to 1.4 Mm (top) and and 2.1 Mm (bottom). The scale for the color coding of is given on the top of each panel. The solid lines show contours of the radiance, which ranks in the top 20% of all values in the plot, for the C IV line (top) and the Si II line (bottom). Slit center always at 411'' north.

Tu, Zhou, Marsch, et al., ApJ, 624, L133, 2005

Radiance versus magnetic field

Quiet Sun

2.1 Mm1.4 Mm

Dependence of the square root of the radiance (ne) of the C IV (left) and Si II (right) VUV emission lines are shown (asterisks) in dependence on the vertical magnetic field strength |Bz|. The uncertainties are represented by the standard deviations of the averages. The solid lines give linear fits. The correlation coefficient in both cases is 0.98.

Correlation height in quiet sun

Tu, Zhou, Marsch, et al., ApJ, 624, L136, 2005

Conclusions

MagneticMagnetic fieldfield extrapolationextrapolation togethertogether withwithradianceradiance and Doppler and Doppler mapsmaps in in variousvarious lineslinesenablesenables oneone to to determinedetermine emissionemission heightsheightsand and flowflow geometrygeometry (in (in loopsloops and and funnelsfunnels).).UsingUsing ((forceforce--freefree) ) fieldfield extrapolationextrapolation allowsallowsusus to to interpretinterpret VUV VUV emissionsemissions in in termsterms of of fieldfield structuresstructures and to and to establishestablish thethe dynamicdynamicmagneticmagnetic couplingcoupling of of thethe atmosphericatmospheric layerslayers..

Plasma flows and magnetic fields in solar active regions and coronal holesThe coronal magnetic fieldThe source regions of the fast solar wind in coronal holesMagnetic network loops and funnelsHeight profiles in funnel flowsLoops and funnels in CHLoops and funnels in CHSunspot and active regionForce-free magnetic field extrapolationMagnetic field and Doppler shiftOverviewMagnetic field in source regionCorrelating field with radiationHeight variation of correlationFlows and funnels in coronal holeCorrelationsFunnel geometryMass and energy supplyWave energy supply by reconnection in magnetic furnaceLow correlation height in quiet sunRadiance versus magnetic fieldCorrelation height in quiet sunConclusions