We analyzed the correlation of the solar magnetograms and Dopplergrams from SOHO/MDI and SDO/HMI respectively. It is found that the full disk correlation coefficient of Dopplergrams is more than 0.80 between SOHO/MDI and SDO/HMI. The full disk correlation coefficient of magnetograms is about 0.73 and is more than 0.95 for active regions only. We also analyzed the distribution of the cross helicity （velocity-magnetic-field correlation） on the solar surface. It is found that the latitude distributions of the cross helicity based on SOHO/MDI data and SDO/HMI data have similar tendencies, and in the analysis of solar active regions the amplitude of the horizontal component of the mean cross helicity is about two times the line-of-sight one.
This research aims for an objective identification, tracking, and a statistical analysis of the Moving Magnetic Features (MMFs) around sunspots using SOHO/MDI high-resolution magnetograms. To this end, we develop a computerized tracking program and study the motion and magnetism of the outflows of MMFs around 26 sunspots. Our method locates 4-27 MMFs per hour, with higher counts for large sunspots. We differentiate MMFs into type α that have a polarity opposite to the parent sunspots, and type β that share the sunspot's polarity. These sunspots' MMF subsets exhibit a wide range of central tendencies which have distinctive correlations with the sunspots. In general, α-MMFs emerge farther from the sunspot, carry less flux, and move faster than β-MMFs. The typical α/β-MMFs emerge at 2.2 - 8.1/0.1 - 3.2 Mm outside the penumbra limb, with lifetimes of 1.1 - 3.1/1.3 - 2.0 h. They are 1.1 - 6.6/1.4 - 3.6 Mm2 in area and carry 1.4 - 12.5/4.8 - 11.4 ×1018 Mx of flux. They travel a distance of 2.7 - 5.9/2.8 - 3.6 Mm with the speed of 0.5 - 0.9/0.4 - 0.7 km/s. Compared to the α-MMFs produced by large sunspots, those of small spots are smaller. They emerge closer to sunspot, move farther, live longer, and carry less flux. β-MMFs show much less correlation with the sunspots. The flux outflow carried by the MMFs ranges from 0.2 to 8.3 × 1019Mx· h-1 and does not show obvious correlation with the sunspots' evolution. The frequency distributions of the MMFs' distance traveled, area, and flux are exponential. This suggests the existence of numerous small, weak, and short-timescale magnetic objects which might contribute to the sunspot flux outflow.
This paper summarizes current helicity measurements in the solar active regions (ARs). There is a basic agreement with the "hemispheric sign rule (HSR)" of the current helicity among different vector magnetographs through two solar cycles, but there is a large dispersion of the fraction of ARs following the HSR. In our sample, there are 50%-78% ARs in solar cycle 22 and 44%-79% ARs in cycle 23 following the HSR. A variation is also found in the fraction of the ARs following the HSR between different instruments even when the same ARs are selected. The difference also exists for the same instrument when the selected ARs are different. There are some differences in the variation of HSR with solar cycle for the individual helicity parameter inferred from different instruments. Factors which influence the correlation of different data sets are analyzed.
In this paper, we study the correlation between the expansion speed of two-ribbon flares and the magnetic field measured in the ribbon location, and compare such correlation for two events with different magnetic configurations. These two events are: an M1.0 flare in the quiet sun on September 12, 2000 and an X2.3 flare in Active Region NOAA 9415 on April 10, 2001. The magnetic configuration of the M1.0 flare is simple, while that of X2.3 event is complex. We have derived a power-law correlation between the ribbon expansion speed (V r) and the longitudinal magnetic field (Bz) with an empirical relationship V r = A×Bz-δ, where A is a constant and δ is the index of the power-law correlation. We have found that δ for the M1.0 flare in the simple magnetic configuration is larger than that for the X2.3 flare in the complex magnetic configuration.
