Multiheight Analysis of Multiheight Analysis of Asymmetric Stokes Profiles Asymmetric Stokes Profiles

in a Solar Active Regionin a Solar Active Region

Na DengNa Deng

Post-Doctoral Researcher at California State University Northridge (CSUN)

ObservationObservation

NSO/HAO Advanced Stokes Polarimeter (ASP)

FeI 630.15 & 630.25 Line PairPhotosphere

MgI b2 517.27 LineLow Chromosphere

FeI Continuum Image Mimic Magnetogram

Active Region NOAA 9661Active Region NOAA 9661

96612001 Oct 17NOAA 9661

Near Disc Center

Intensity + Magnetic Polarity

rb

rb

AA

AAAsymmetry

Stokes AsymmetriesStokes Asymmetries

Large gradient of magnetic field along LOS

Large gradient of velocity field along LOS

Inhomogeneous atmosphere that contains two or more magnetic components

Spatially unresolved flows, i.e., superposition of components with large Doppler velocity relative to

each other.

Spatially unresolved mixed polarities

Spreading of Stokes signals due to seeing and diffraction

Origin of Stokes AsymmetriesOrigin of Stokes Asymmetries

Stokes Asymmetry ImagesStokes Asymmetry Images

50 km 200 km 600 km

Photosphere Photosphere Low Chromosphere FeI 630.25 FeI 630.15 Mg b 517.27

630.25 630.15 517.27

Extremely Strong Down Flows along Neutral LineExtremely Strong Down Flows along Neutral Line

Line Center Shift of Stokes‒I

630.25 630.15 517.27

Zero-Crossing Shift of Stokes‒V

Intensity Image Magnetogram

Dopplergram (Intensity) + (Dopplergram)

MDI high-resolution data reinforce ASP observations. They show at the same locations strong downflows with mean speed of 0.98 km/s and maximum speed of 1.28 km/s. While the limb side Evershed flow of the nearby alpha spot is only about 0.36 km/s.

MDI High-Resolution Data on 2001/10/17MDI High-Resolution Data on 2001/10/17

Horizontal penumbral Evershed flow channels get bended downward when they encounter strong vertical field of another umbra with opposite polarity. Therefore, horizontal Evershed flow becomes downflow at the boundary between outer penumbra of one polarity and umbra of the other polarity.

InterpretationInterpretation

Future WorkFuture Work

Collaborate with Dr. Thomas Wiegelmann to study 3D evolution of the active region associated with the flare occurred on Oct 19th. Compare the difference in the extrapolated result between different input boundary conditions: photospheric vector magnetogram and vector magnetogram in low chromosphere.

Available Data:

Vector magnetograms in both photosphere and low chromosphere

On Oct 16, 17, and 19.