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Differential Rotation of coronal BP and Source Region of their Magnetic Fields

Differential Rotation of coronal BP and Source Region of their Magnetic Fields. H. Hara NAOJ 2011 Jun 29. Leverhulme – Probe the Sun 1 st Workshop at MSSL. X-ray/EUV coronal bright points. Found in the 1960’s soft X-ray imaging data of sounding rocket programs.

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Differential Rotation of coronal BP and Source Region of their Magnetic Fields

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  1. Differential Rotation of coronal BP andSource Region of their Magnetic Fields H. Hara NAOJ 2011 Jun 29 Leverhulme – Probe the Sun 1st Workshop at MSSL

  2. X-ray/EUV coronal bright points • Found in the 1960’s soft X-ray imaging data of sounding rocket programs. • Appear almost uniformly over the solar surface. • Bipoles are observed at photosphere below CBPs. • CBP associated bipoles are mostly canceling bipoles. • The number density does not change much in the11-year activity cycle. • Differential rotation rate is quite similar to that of the quiet–Sun photospheric magnetic fields.

  3. Detection of XBP Yohkoh soft X-ray data X-ray Bright Point Hara & Nakakubo-Morimoto 2003, ApJ 589, 1062

  4. Occurrence rate of XBPSource of magnetic fields and Depth of Formation Region Small amplitude change in XBP number over the 11-yr cycle Possibly due to difference in the origin of magnetic fields • XBP: constancy in number & small size • Source region may be localized near the surface Much larger change in AR XBP: Skylab+rocket Normalized Sunspot number Hara & Nakakubo-Morimoto 2003, ApJ 589, 1062

  5. Rotation Rate of XBP t1 ( t2 > t1 ) t2 Yohkoh Soft X-ray data t XBP detection Position of XBP ( X, Y )  ( Longitude , Latitude  ) , : as a function of XBP height H Longitude of XBP i in image 1 Longitude of XBP j in image 2 Angular velocity Determined by XBP i (t1) and j (t2) Correction factor to convert to sidereal rate Time difference

  6. Selection of Height H d / d H Hara 2009, ApJ 697, 980

  7. Rotation rate from many XBP pairs • ~4 yr Yohkoh data used • Shape of distribution • Symmetric • Voigt function containing Lorentz function • Accuracy 0.01 deg/day  1.4m/s 　（→ possible to measure torsional oscillation from much more data in a shorter period ） • Higher accuracy expected from SDO data of much more shorter period Lat. 00-05 deg Lat. 10-15 deg Lat. 20-25 deg Lat. 30-35 deg Lat. 45-50 deg Angular velocity (deg/day) Bin width：0.05 deg/day Hara 2009, ApJ 697, 980

  8. Estimated From tracking of each BP and statistical average EUV coronal BP (1972) EUV coronal BP (2004; EIT) Global corona Dashed line: Photospheric B Photoshperic Doppler Hara 2009, ApJ 697, 980

  9. Howe et al. 2000, Sci. 287, 2456 Angular rotation rate：connectivity between inside and XBP Angular rotation rate of XBP defined by 8 <Δt < 24 hrs coincides with that at ~0.97Rs in latitudes between -60 and +60 deg. Hara 2009, ApJ 697, 980 Small-scale magnetic activity localized at the top of CZ? Equivalent depth (~0.94 Rs ) of AR surface rotation rate.

  10. Compared with another H.S. inversion results Internal rot. data from Sekii san From photospheric magnetic fields (Komm et al.) From XBP

  11. Slower rotation rate for short-lived XBP Equator only: For samples containing many short-lived XBPs 0 < Δt < 4 hours, Rotation rate becomes  (r~0.99Rs ), approaching surface rotation rate. -10 < Latitude < +10 deg Hara 2009, ApJ 697, 980

  12. Expectation from SDO data • High accuracy measurement of rotation rate from EUV data of a short period of time. • Examine the relation between tand . • Measurement of torsional oscillation • Measurement of meridional flow from long-lived BP • Detection of longitudinal rotation anomaly • Implication of width in the XBP histograms • Some information on the supergranular flows/diffusion?

  13. XRT

  14. SDO 211

  15. SDO data • 4096x4096 format data: 32 MB • 211Å band selected • OBS date: 2010 Oct 31 • 12 sec cadence: 7200 images / day • Reduced to 1024x1024 format by pixel summing • ~3500 CBP detection for 6.7min run from 2Kx2K data • ~1600 CBP detection for 40sec run from 1Kx1K data • Software development needs for reducing the analysis time. • Data selected to reduce the process time • 5 min interval data; ~280 images / day • 1 min interval data; ~1400 images / day

  16. AIA 211 / 5min cadence

  17. Test run for 5 min interval data Height estimate not finished 0 <  t < 4 hr S: Lat. 00-05 deg S: Lat. 20-25 deg S: Lat. 30-35 deg S: Lat. 40-50 deg Preliminary

  18. Summary • The rotation of small-scale magnetic fields is examined by XBP/CBP from its differential rotation profile. • There is a depth at which the XBP rotation rate coincide with the internal rotation rate over a wide latitude range. The depth is located at the top of the convection zone. • Limited examination on the rotation rate of XBP from Yohkoh SXT data can largely be improved by SDO/AIA data as expected in Hara (2009, ApJ).

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