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Modern Solar Facilities – Advanced Solar Science, 241–244 F. Kneer, K. G. Puschmann, A. D. Wittmann (eds.) c  Universitätsverlag Göttingen 2007 Modified p-modes in penumbral filaments D. S. Bloomfield1,* , A. Lagg1 , S. K. Solanki1 , and J. M. Borrero2 1 Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany 2 High Altitude Observatory, Boulder, Colorado, U.S.A. * Email: bloomfield@mps.mpg.de Abstract. A time series analysis was performed on velocity signals in a sunspot penumbra to search for possible wave modes. The spectropolarimetric photospheric data obtained by the Tenerife Infrared Polarimeter were inverted using the SPINOR code. An atmospheric model comprising two magnetic components and one stray-light component gave an optimal fit to the data. Fourier phase difference analysis between line-of-sight velocities of both magnetic components provided time delays between the two atmospheres. These delays were combined with the speeds of atmospheric wave modes and compared to height separations derived from velocity response functions to determine the wave mode. 1 Introduction Disentangling the signatures of various magnetoatmospheric (MA) waves that are supported by magnetic atmospheres is a difficult, even daunting, task. However, information may be extracted from spatially unresolved structures by spectropolarimetry. This approach uses the full Stokes polarization spectra (I, Q, U, V), allowing physical properties of the emitting plasma to be inferred through the application of appropriate model atmospheres. Here we present a method that may identify the form of wave which exists in a magnetic environment. 2 Observations Active region NOAA 10436 (Fig. 1) was observed on 21 August 2003 with the Tenerife Infrared Polarimeter (Martı́nez Pillet et al. 1999) attached to the German VTT. Full Stokes profiles were recorded for the spectral lines Fe i 15662.018 Å (effective Landé factor ḡ = 1.50) and Fe i 15665.245 Å (ḡ = 0.75) over the period 14:39-15:41 UT, yielding a time series of 250 stationary image positions on the slit at a cadence of one exposure every 14.75 s. Given the small amount of circular polarization asymmetry in the inner limbside penumbra , it is likely that these lines are not affected by gradients in the magnetic field vector or line-of-sight (LOS) velocity. Therefore, the data were inverted using the SPINOR inversion code (Frutiger 2000) and the height-independent two magnetic component model of Borrero et al. (2004). The inversion yields a magnetic field geometry consisting of a near-horizontal component (flux tube, FT) and a closer-to-vertical component (magnetic background, MB). Since the velocity variations were most strongly observed in Stokes Q the response functions (RFs) of Stokes Q to LOS velocity (Fig. 2) were calculated. The RFs of the magnetic components overlap over most part of the atmosphere, but their center-of-gravity (COG), 242 D. S. Bloomfield et al.: Modified p-modes in penumbral filaments Figure 1. Continuum intensity image of NOAA 10436. White (black) contours mark the umbral /penumbral (penumbral/quiet Sun) boundaries. The straight black line marks the slit position during the time series, the white portion the region studied, while the arrow points to disk centre. Figure 2. Height variation of combined 15662 Å and 15665 Å Stokes Q velocity response for the MB (solid) and FT (dotted) atmospheres. Vertical lines mark the COG in each component. displayed as vertical lines, reveal a distinct separation between the components. Height differences between the LOS velocity signals were taken as the separation of the COGs, while wave propagation speeds were calculated over these height ranges from the output inversion atmospheres. 3 Time Series Analysis A Fourier phase difference analysis was performed between the MB and FT velocity signals following Krijger et al. (2001). Spectra from the eleven analyzed pixels of the inner limbside penumbra are overplotted in the left panel of Figure 3. Approximately constant phase difference values were recorded in the range 2.5 − 4.5 mHz, with the probability distribution function (PDF) centred on −5.5◦ . Negative phase differences mean that the FT velocity leads the MB, agreeing with the COG heights in Figure 2 for upward wave propagation. The centroid value was converted into time delay between the signals, resulting in values ranging D. S. Bloomfield et al.: Modified p-modes in penumbral filaments 243 Figure 3. Left: Fourier phase difference spectra between the MB and FT velocities from the eleven analyzed pixels. Darker shading denotes greater Fourier coherence and larger symbol size greater cross-spectral power. Right: PDF of phase...

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