Differential Rotation of coronal BP and

Source Region of their Magnetic Fields

H. Hara

NAOJ

2011 Jun 29

Leverhulme – Probe the Sun 1st Workshop at MSSL

X-ray/EUV coronal bright points• Found in the 1960’s soft X-ray imaging data of sou

nding rocket programs.• Appear almost uniformly over the solar surface.• Bipoles are observed at photosphere below CBPs.• CBP associated bipoles are mostly canceling bipole

s.• The number density does not change much in the1

1-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 XBPSource 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+rocketNormalizedSunspot 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 rateTime difference

Angular velocity Determined byXBP i (t1) and j (t2)

t1 t2tXBP detection

( t2 > t1 )

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 L

orentz function• Accuracy 0.01 deg/day

1.4m/s　（→ possible to measure

torsional oscillation 　　　　 from much more dat

a 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

Bin width： 0.05 deg/dayAngular velocity (deg/day)Hara 2009, ApJ 697, 980

Global corona

EUV coronal BP (1972)

PhotoshpericDoppler

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 ~0.97Rs 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. datafrom Sekii san

From XBP

From photosphericmagnetic fields(Komm et al.)

Slower rotation rate for short-lived XBP

Equator only:For samples containingmany short-lived XBPs0 < Δt < 4 hours,

Rotation rate becomes (r~0.99Rs ), 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• 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

AIA 211 / 5min cadence

Test run for 5 min interval data

0 < t < 4 hr

S: Lat. 00-05 deg

S: Lat. 20-25 deg

S: Lat. 30-35 deg

S: Lat. 40-50 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).