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Supersonic downflows in the photosphere discovered in sunspot moat regions

Supersonic downflows in the photosphere discovered in sunspot moat regions. T. Shimizu ( ISAS/JAXA, Japan), V. Martinez-Pillet, M. Collados, B. Ruiz-Cobo, R. Centeno (IAC, Spain), C. Beck (KIS, Germany), Y. Katsukawa (NAOJ, Japan).

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Supersonic downflows in the photosphere discovered in sunspot moat regions

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  1. Supersonic downflows in the photosphere discovered in sunspot moat regions T. Shimizu(ISAS/JAXA, Japan), V. Martinez-Pillet, M. Collados, B. Ruiz-Cobo, R. Centeno (IAC, Spain), C. Beck (KIS, Germany), Y. Katsukawa (NAOJ, Japan) Report a discovery from international time program observation at Canaries islands on July 2005 6th Solar-B Science Meeting@Kyoto

  2. Remarkable Stokes V profiles we have found! Photospheric Si I 10827A by TIP • Extremely red-shifted signal • Frequently observed in sunspot moat regions. 400mA => 11km/s!! wavelength Slit direction 6th Solar-B Science Meeting@Kyoto

  3. Observations • Tenerife Infrared Polarimter (TIP; Martinez Pillet et al. 1999) • Attached to German VTT, Tenerife • Four Stokes profiles of photospheric Si I line at 10827A (g=1.5) • Polarimetric Littrow Spectrograph (POLIS; Beck et al. 2005) • Simultaneous mapping of four Stokes of Fe I 6301.5A(g=1.67)/6302.5A (g=2.5) • Note: same spectral lines measured with Solar-B Spectro-Polarimter • Leading spot of AR 10781 on 3 July 2005 TIP Stokes I Si I 10827 He I 10830 POLIS Stokes I Fe I 6301.5 Fe I 6302.5 VTT 6th Solar-B Science Meeting@Kyoto

  4. Morphological properties of downflows (1) I Q U V 3.4” • Location of extremely red-shifted events 40“x45“ FOV • Red-shifted signal has opposite-polaritynear the edge of sunspot (positive)-polarity flux patches • 11 of 25 near the edge of positive-flux patch • 19 of 25 opposite-polarity red-shifted signal ([enhanced] magnetogram generated from Stokes V data) • “25 events” were found in three scan maps of a sunspot moat region. 6th Solar-B Science Meeting@Kyoto

  5. Morphological properties of downflows (2) TIP: Si 10827A POLIS: Fe I 6301.5/6302.5A I 500mA 300mA Q U 3.4” V • Size extremely small-scale phenomena • Scan direction: 0.9 – 1.2 arcsec (3 – 4 scan positions, 0.3” step) • Slit direction: 0.7 – 1.0 arcsec (4-6 pixels, 0.17”/pix) • Duration <1hr, but exactly unknown because of slit scanning observation • Observed not only in Si line but also in Fe 630nm lines • Si I 10827A + Fe I 6301.5 + FeI 6302.5 16 event (64%) • Si I 10827A + Fe I 6301.5 only 2 event ( 8%) • Si I 10827A only 7 event (28%) 6th Solar-B Science Meeting@Kyoto

  6. Estimate physical conditions • SIR inversion was applied to 7 events (Dr. Ruiz-Cobo) • 3 lines are simultaneously fitted • Assumed to have two magnetic components with constant parameters (magnetic field, velocity), and 2 different temperatures, one for each magnetic component. Event 1-0 pos 6 • Preliminary comfortable results have been derived for only limited number of events. 6th Solar-B Science Meeting@Kyoto

  7. Estimate physical conditions • The downflowing component has a higher field strength than the rest component, and it has relative downflows as large as 10 km/s. Also, the downflowing component seems to be hot by some 100 K or so. Rest magnetic component Downflowing magnetic component Event 1-0 pos 6 1533 B (gauss) 1072 2.6 12.2 v (km/s) Inclination (deg) 156 180 Temperature (K) solid dotted 6th Solar-B Science Meeting@Kyoto

  8. Discussions • downflows as large as 10 km/s • Compared with sound speed ~5 km/s (T~5500K) Alfven speed ~16 km/s (B~1500g, n~ 7x10^-8 g/cm3) • The observed downflows are supersonic but slightly below Alfven speed. • We currently think that the observed supersonic downflows may be a signature of downwarding outflow from magnetic reconnections occurring at the chromosphere or upper photosphere. • No “transient” brightenings were observed in TRACE 171A coronal images. Dutch Open Telescope Ca II H movie for map 1 (9:05-9:35UT, same FOV) 6th Solar-B Science Meeting@Kyoto

  9. Summary • We found events with extremely red-shifted Stokes V signal in sunspot moat regions. They have following properties: • Measured with photospheric Si I 10827A line but also with Fe I 630nm lines. • In order of one arcsec or smaller size. • As large as 10 km/s, which is supersonic but still below Alfven speed. • The downflowing component has a higher field strength than the rest component, and seems to be hot by some 100 K or so. • The observed supersonic downflows may be a signature of downwarding outflow from magnetic reconnections occurring at the chromosphere or upper photosphere. 6th Solar-B Science Meeting@Kyoto

  10. Further investigations with Solar-B • Full Stokes of Fe I 630nm lines will be measured in higher spatial resolution (0.16arcsec) with SOT/FPP Spectro-Polarimter. • Further understanding of this new phenomenon can be provided with Solar-B coordinated observations among SOT spectro-polarimter, filter imagers, and EIS. • Complicated Stokes profiles will be expected much more frequently. Some may be caused by flux tube dynamics, predicted by simulation (Steiner et al.). • Inversions of Stokes profiles will play key roles in interpreting such Stokes profiles. 6th Solar-B Science Meeting@Kyoto

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