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. 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.
Detection of XBP X-ray Bright Point Yohkoh soft X-ray data Hara & Nakakubo-Morimoto 2003, ApJ 589, 1062
Occurrence rate of XBP Source of magnetic fields and Depth of Formation Region Small amplitude change in XBP number over the 11-yr cycle Much larger change in AR Possibly due to difference in the origin of magnetic fields Hara & Nakakubo-Morimoto 2003, ApJ 589, 1062 XBP: Skylab+rocket Normalized Sunspot number XBP: constancy in number & small size Source region may be localized near the surface
Rotation Rate of XBP Position of XBP ( X, Y ) ( Longitude , Latitude ) , : as a function of XBP height H Yohkoh Soft X-ray data Longitude of XBP j in image 2 Longitude of XBP i in image 1 Correction factor to convert to sidereal rate Time difference Angular velocity Determined by XBP i (t 1 ) and j (t 2 ) t1t1 t2t2 tt XBP detection ( t 2 > t 1 )
Selection of Height H d / d H Hara 2009, ApJ 697, 980
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 deg Lat deg Lat deg Lat deg Lat deg Bin width ： 0.05 deg/day Angular velocity (deg/day) Hara 2009, ApJ 697, 980
Global corona EUV coronal BP (1972) Photoshperic Doppler Dashed line: Photospheric B EUV coronal BP (2004; EIT) Estimated From tracking of each BP and statistical average Hara 2009, ApJ 697, 980
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 ~0.97R s in latitudes between -60 and +60 deg. Small-scale magnetic activity localized at the top of CZ? Equivalent depth (~0.94 Rs ) of AR surface rotation rate. Hara 2009, ApJ 697, 980
Compared with another H.S. inversion results Internal rot. data from Sekii san From XBP From photospheric magnetic fields (Komm et al.)
Slower rotation rate for short-lived XBP Equator only: For samples containing many short-lived XBPs 0 < Δt < 4 hours, Rotation rate becomes (r~0.99R s ), approaching surface rotation rate. -10 < Latitude < +10 deg Hara 2009, ApJ 697, 980
Expectation from SDO data High accuracy measurement of rotation rate from EUV data of a short period of time. Examine the relation between t and . 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?
XRT
SDO 211
SDO data 4096x4096 format data: 32 MB 211 Å band selected OBS date: 2010 Oct 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
AIA 211 / 5min cadence
Test run for 5 min interval data 0 < t < 4 hr S: Lat deg S: Lat deg S: Lat deg S: Lat deg Height estimate not finished Preliminary
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).