1. The Helioseismic and Magnetic Imager (HMI) on NASA’s Solar Dynamics Observatory (SDO) has continuously measured the vector magnetic field, intensity, and Doppler velocity in solar flares and over the entire solar disk since May 2010. The regular cadence of 45 seconds for line-of-sight and 12 minutes for vector measurements enables reliable investigations of photospheric conditions before, during, and after events both locally and globally. Active region indices can be tracked and conditions in the overlying corona can be modeled. A few examples show the utility of the data and demonstrate that some care must be exercised when the HMI data are used to investigate time variations. HMI Observations of Solar Flares in Solar Cycle 24 Todd Hoeksema, Monica Bobra, Sebastien Couvidat, and Xudong Sun Stanford University SHARP Parameter Table. HMI Data Series: hmi.sharp_720s Active-region parameters are stored as keywords in each SHARP series. This table lists the active-region parameter keywords with a brief description and formula. The keyword for the calculated uncertainty is given in the last column. Each parameter represents either a mean, sum, or integral of the distribution in the high-confidence part of the HMI Active Region Patch. Many parameters were adapted from Leka &Barnes (2003b). See Bobra et al. (2014).2003b 24 S320 p.34 SHARPs are automatically identified HMI Active Region Patches that include vector magnetic field data and local quantities computed from the field every 12 minutes that can be used for characterization and prediction of solar activity. Shown below are 3 field components for AR 11429 on 7 March 2012 in Cylindrical Equal Area coordinates. Bobra & Couvidat (2014) used a machine learning method to predict flares from SHARP quantities using a catalog of 285 M-class and 18 X-class flares. See also Ilonidis, Bobra & Couvidat S320.13.04 on Friday. Various tools exist to survey, display, and retrieve SHARP and other HMI magnetic data. jsoc.stanford.edu & hmi.stanford.edu/magnetic One of the most studied HMI Active Regions was the first to produce an X-class flare in Cycle 24, AR 11158 in February, 2015. The upper figure at right shows the Bz field from HMI and the AIA 171 image about 5 hours before the flare in the left column. The right panels show the computed vertical current density and the field lines from a non-linear force free field calculation for the region (Sun et al. 2012). The second figure at right shows the evolution of the field, AIA and NLFFF current density at times before and after the flare occurred at 01:35 on 15 February. The third figure illustrates changes from before (left column) to after (right column) the flare. The upper panels show a cross section of the horizontal current, J h, above the flare ribbon indicated in the lower rows. The second row shows the large change in the horizontal field component. The third row shows much smaller changes in the vertical field component. The permanent loop contraction is consistent with magnetic implosion scenario. By far the largest and most flare-productive sunspot group of Cycle 24 appeared in October 2014. Surprisingly, none of AR 12192’s 6 X- class flares produced CMEs observed at Earth. Sun et al. (2015) compared this regions with two other large-flare producing regions, AR 11158 &11429. Even though AR 12192 had large total energy, total free energy, and other such extensive parameters, its intensive quantities, such as the ratio of free to potential energy, twist, and current helicity, were less, which was consistent with confined flares. The figure above shows AR 12192 near central meridian passage. The arrows in the left intensity image show regions where there was sunspot separation; the left image overplots flare ribbons observed by AIA during the X3 flare on 24 October 2014. The lower panel shows the GOES x-ray flux during the disk passage and the panel on the right shows the composite negative image of the flare in several AIA EUV lines. The plot below compares the three regions. AR 12192 is on the left, AR 11429 center, and AR 11158 on the right. The top panels show the pre- flare Bz maps with the locations of the primary neutral line shaded in yellow. Note the size scale differences. The second row shows the integrated current flowing within 11 Mm of the surface computed with a NLFFF model. The bottom panel shows the median and standard deviation of the field strength (black) and decay index n (d(ln Bh)/d ln(z) in green) above the primary neutral line in each region as a function of height. The figure below compares the pre- and post-flare conditions in the same active regions. The top panels show the differences in the horizontal component of the photospheric magnetic field. The second row shows for each region the pre- and post-flare Q- maps, the logarathm of the ‘squashing factor’ along a vertical cut above the flare site (indicated in the top panel). The bottom panel shows the hanges in connectivity before and after the flares. The height in the bottom panels is stretched for clarity. AR 12192 is more ‘potential’ and has a stronger overlying field. The estimated free energy is large and sufficient to power the large number of observed flares. The changes observed in field, Q-maps and field connectivity are smaller in the confined flares. Some Caveats: Most HMI Observables do have systematic 24-hour variations that must be taken into account when performing time series analysis of various physical quantities. Also, during strong flares emission in certain wavelengths can cause distortion in the line profiles that are not properly interpreted by inversions.