I investigate the possible long term decrease in umbral magnetic field strengths from 1998-2006. Whereas a decrease of 800 Gauss in umbral magnetic fields has been reported between 1998 and 2012, the HMI and MDI data indicate a decrease of only around 300 Gauss. The continuing availability of the excellent HMI data set will allow us to continue to refine this study as solar cycle 24 evolves.
We examine the polarization of light emitted by a loop prominence system, near the Fe I line (6173 Å). It has a linearly polarized component, at times up to the level expected from pure Thomson scattering.
Reports of white-light ejecta above the limb of the Sun and imaged without the aid of a true coronagraph are exceedingly rare. Here we report the successful use of HMI to observe flare effects in the corona by the use of differencing as a substitute for an actual occulter.
Analysis of HMI vector magnetic field data before and after a flare illustrate how the energy released can result in a collapse of loop structures, and how the effects can be observed on the solar surface.
The Venus transit of 2012 allowed us to measure the solar radius around 6173Å with HMI: we obtained a value of 959.58″ at 1 AU, with a systematic uncertainty larger than 0.27″.
We present observations from SDO/HMI of a magnetic transient observed in NOAA 11429 during the M7.9 flare on 13 March 2012. The observed transient showed an impulsive rotation of the field vector in response to the white-light flare.
We analyze umbral area, magnetic field, and umbral intensity of the sunspots during the rising phase of cycle 24. We do not find a significant variation in either sunspot physical properties or distribution of sunspot umbral area from previous cycles.
Solar meridional circulation, if mechanically driven and thermally
braked, contains two cells in latitude; generating two cells in depth,
recently observed by SDO/HMI, is a new challenge to theory.
Even though Solar Cycle 24 is weak, it has still produced some large sunspots. We list the largest sunspots as observed by HMI and discuss some aspects of the data.
Hemispheric helicity preference in groups of active regions with different properties suggests different origins of magnetic twist.