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Abstract We have developed a comprehensive catalog of the variable differential rotation measured near the solar photosphere. This catalog includes measurements of these flows obtained using several techniques: direct Doppler, granule tracking, magnetic pattern tracking, global helioseismology, as well as both time-distance and ring-diagram methods of local helioseismology. We highlight historical differential rotation measurements to provide context, and thereafter provide a detailed comparison of the MDI-HMI-GONG-Mt. Wilson overlap period (April 2010 – Jan 2011) and investigate the differences between velocities obtained from different techniques and attempt to explain discrepancies. A comparison of the rotation rate obtained by magnetic pattern tracking with the rotation rates obtained using local and global helioseismic techniques shows that magnetic pattern tracking measurements correspond to helioseismic flows located at a depth of 25 to 28 Mm. In addition, we show the torsional oscillation from Sunspot Cycles 23 and 24 and discuss properties that are consistent across measurement techniques. We find that acceleration derived from torsional oscillation is a better indicator of long-term trends in torsional oscillation compared to the residual velocity magnitude. Finally, this analysis will pave the way toward understanding systematic effects associated with various flow measurement techniques and enable more accurate determination of the global patterns of flows and their regular and irregular variations. 

Abstract We explore the performance of the Alfvén Wave Solar atmosphere Model with near-real-time (NRT) synoptic maps of the photospheric vector magnetic field. These maps, produced by assimilating data from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory, use a different method developed at the National Solar Observatory (NSO) to provide a near contemporaneous source of data to drive numerical models. Here, we apply these NSO-HMI-NRT maps to simulate three full Carrington rotations: 2107.69 (centered on the 2011 March 7 20:12 CME event), 2123.5 (centered on 2012 May 11), and 2219.12 (centered on the 2019 July 2 solar eclipse), which together cover various activity levels for solar cycle 24. We show the simulation results, which reproduce both extreme ultraviolet emission from the low corona while simultaneously matching in situ observations at 1 au as well as quantify the total unsigned open magnetic flux from these maps. 

Abstract From 1915 to 1985 the monitoring program of the Mount Wilson Observatory, one of the Observatories of the Carnegie Institution of Washington, has taken over 35,000 daily images (spectroheliograms) of the Sun in the chromospheric resonance line of CaiiK. This important database constitutes a unique resource for a variety of retrospective analyses of the state of solar magnetism on multidecadal timescales. These observations may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability for current dynamo models. We describe here a procedure to calibrate and rescale these images so that homogeneous Carrington synoptic maps can be derived for the whole period covered by these observations. Temporal variations in full-disk chromospheric activity clearly show the signature of the 11 yr solar cycle, but no evidence is found for a statistically significant north/south hemispheric asymmetry. Using a feature-tracking technique we were also able to obtain the average solar rotation profile. We find no indication of any detectable periodicity in the temporal behavior of the orthogonalized rotation rate coefficients, suggesting the global chromospheric dynamics has not changed during the 70 years investigated in this work. We found also no significant evidence in our analysis for a hemispheric asymmetry in rotation rates. 

Context. Systematic observations of magnetic field strength and polarity in sunspots began at Mount Wilson Observatory (MWO), USA in early 1917. Except for a few brief interruptions, this historical dataset has continued until the present. Aims. Sunspot field strength and polarity observations are critical in our project of reconstructing the solar magnetic field over the last hundred years. We provide a detailed description of the newly digitized dataset of drawings of sunspot magnetic field observations. Methods. The digitization of MWO drawings is based on a software package that we developed. It includes a semiautomatic selection of solar limbs and other features of the drawing, and a manual entry of the time of observations, measured field strength, and other notes handwritten on each drawing. The data are preserved in an MySQL database. Results. We provide a brief history of the project and describe the results from digitizing this historical dataset. We also provide a summary of the final dataset and describe its known limitations. Finally, we compare the sunspot magnetic field measurements with those from other instruments, and demonstrate that, if needed, the dataset could be continued using modern observations such as, for example, the Vector Stokes Magnetograph on the Synoptic Optical Long-term Investigations of the Sun platform.