73. Unusual sunquakes caused by the X9.3 flare on September 6, 2017
An X9.3 flare excited strong yet unusual sunquakes.
72. The Magnetic Mid-life Crisis of the Sun
Recent discoveries suggest that Sun-like stars experience a fundamental shift in their rotation and magnetism around middle-age. We have now identified this transition in the best available data on stellar cycles.
71. Critical Height of the Torus Instability in Two-Ribbon Solar Flares
A statistical investigation of the background magnetic field decay index reveals interesting features of the critical height for the flux rope torus instability.
70. Magnetic Flux Emergence & Decay Rates for Sunspots Observed with HMI
We quantify the emergence and decay rates of ten bipolar active regions using vector magnetic field data from HMI. Our results, placed in context with other observational and modeling results in the literature, confirm a trend that higher flux regions emerge faster and the rate is dependent on the total flux of that region.
69. Measuring Differential Rotation and Meridional Circulation by Direct Tracking of Photospheric Magnetic Features
A new method tracking individual features in a long time series of magnetograms yields new measurements of solar differential rotation and meridional circulation rate.
68. Magnetic Field Changes in the Photosphere and the Chromosphere During the X1 Flare on 2014-03-29
Rapid and irreversible changes in chromospheric magnetic field during a flare have been observed for the first time. They look surprisingly different from their photospheric counterpart.
67. The New HMI High-Cadence Vector Magnetograms
New HMI high-cadence vector magnetograms are now available. Observations every 135 or 90 seconds reveal the rapid magnetic evolution occurring during major solar eruptions.
66. A Poynting-Robertson-Like Drag at the Sun’s Surface
A new analysis using about 4 years of HMI 5-min solar p-mode limb oscillations as a rotation “tracer” finds a large velocity gradient at the top of the photosphere. It is suggested that the net effect of the photospheric angular momentum loss is similar to Poynting-Robertson “photon braking” on, for example, Sun-orbiting dust.
65. SDO Reveals the Properties of Flare-productive Sunspot Regions
A statistical study of sunspot region properties yields insights on why some are flare-productive.
64. Slow Appearance of Sunspots Challenges Theory
A comparison of the surface flow patterns in observation and numerical simulation suggests that the flux tube emerging speed has been overestimated in theories.