Matthew James Penn

H-alpha spectra of dynamic chromospheric processes in five well-observed X-ray flares

Simultaneous H-alpha and hard X-ray (HXR) spectra were obtained for five solar flares to determine the relationship of H-alpha profiles and the nonthermal part of the flare represented by the hard X-ray burst. All five flares exhibited impulsive-phase redshifted H-alpha in emission, which was temporarily and spatially associated with intense HXR emission and broad impulsive-phase H-alpha wings. A few small regions within two flares showed a blueshifted H-alpha emission which appeared only early in the impulsive phase and was temporally correlated with the HXR emission but not with broad H-alpha wings. Finally, there were both redshifted and blueshifted absorption spectra with properties fully consistent with those known for erupting and untwisting filaments. 31 refs.

A MULTI-INSTRUMENT ANALYSIS OF SUNSPOT UMBRAE

The recent solar minimum and rise phase of solar cycle 24 have been unlike any period since the early 1900s. This article examines some of the properties of sunspot umbrae over the last 17 years with three different instruments on the ground and in space: MDI, HMI and BABO. The distribution of magnetic fields and their evolution over time is shown and reveals that the field distribution in cycle 24 is fundamentally different from that in cycle 23. The annual average umbral magnetic field is then examined for the 17 year observation period and shows a small decrease of 375 Gauss in sunspot magnetic fields over the period 1996 to 2013, but the mean intensity of sunspot umbrae does not vary significantly over this time. A possible issue with sample sizes in a previous study is then explored to explain disagreements in data from two of the source instruments. All three instruments show that the relationship between umbral magnetic fields and umbral intensity agrees with past studies in that the umbral intensity decreases as the field strength increases. This apparent contradiction can be explained by the range of magnetic field values measured for a given umbral intensity being larger than the measured 375 G change in umbral field strength over time.

The Mees CCD imaging spectrograph

The Mees CCD (MCCD) instrument is an imaging spectroscopy device which uses the 25 cm coronagraph telescope and the 3.0 m Coudé spectrograph at Mees Solar Observatory (MSO) on Haleakala, Maui. The instrument works with resolving power up to R ≈ 200 000 with significant throughput from λ3934 Å (Caii K) to λ ≈ 10 000 Å. A fast guiding active mirror stabilizes the image during observations. A rapidly writing magnetic tape storage system allows observations to be recorded at 256 kbytes s−1. Currently, the MCCD is used for imaging spectroscopy of solar flares at λ6563 Å (Hα), and velocity measurements of umbral oscillations; future plans include emission line studies of active region coronae, and photospheric studies of solar oscillations.

He i Vector Magnetic Field Maps of a Sunspot and Its Superpenumbral Fine-Structure

Advanced inversions of high-resolution spectropolarimetric observations of the He i triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29xa0January 2012. Multiple atmospheric models are employed in the inversions because superpenumbral Stokes profiles are dominated by atomic-level polarization, while sunspot profiles are Zeeman-dominated, but also exhibit signatures that might be induced by symmetry-breaking effects of the radiation field incident on the chromospheric material. Wexa0derive the equilibrium magnetic structure of a sunspot in the chromosphere and furthermore show that the superpenumbral magnetic field does not appear to be finely structured, unlike the observed intensity structure. This suggests that fibrils are not concentrations of magnetic flux, but are instead distinguished by individualized thermalization. We also directly compare our inverted values with a current-free extrapolation of the chromospheric field. With improved measurements in the future, the average shear angle between the inferred magnetic field and the potential field may offer a means to quantify the non-potentiality of the chromospheric magnetic field to study the onset of explosive solar phenomena.

Imaging Spectropolarimetry of Ti I 2231 nm in a Sunspot

Spectro-polarimetric observations at 2231xa0nm were made of NOAAxa010008 near the west solar limb on 29 June 2002 using the National Solar Observatory McMath–Pierce Telescope at Kitt Peak and the California State University Northridge – National Solar Observatory infrared camera. Scans of spectra in both Stokesxa0I and Stokesxa0V were collected; the intensity spectra were processed to remove strong telluric absorption lines, and the Stokesxa0V umbral spectra were corrected for instrumental polarization. The sunspot temperature is computed using the continuum contrast and umbral temperatures down to about 3700xa0K are observed. A strong Tiu2009i line at 2231.0xa0nm is used to probe the magnetic and velocity fields in the spot umbra and penumbra. Measurements of the Tiu2009i equivalent width versus plasma temperature in the sunspot agree with model predictions. Zeeman splitting measurements of the Stokesxa0I and Stokesxa0V profiles show magnetic fields up to 3300xa0G in the umbra, and a dependence of the magnetic field on the plasma temperature similar to that which was seen using Feu2009i 1565xa0nm observations of the same spot two days earlier. The umbral Doppler velocity measurements are averaged in 16 azimuthal bins, and no radial flows are revealed to a limit of ±u2009200xa0mxa0s−1. A Stokesxa0V magnetogram shows a reversal of the line-of-sight magnetic component between the limb and disk center sides of the penumbra. Because the Tiu2009i line is weak in the penumbra, individual spectra are averaged in azimuthal bins over the entire penumbral radial extent. The averaged Stokesxa0V spectra show a magnetic reversal as a function of sunspot azimuthal angle. The mean penumbral magnetic field as measured with the Stokesxa0V Zeeman component splitting is 1400xa0G. Several weak spectral lines are observed in the sunspot and the variation of the equivalent width versus temperature for four lines is examined. If these lines are from molecules, it is possible that lines at 2230.67, 2230.77, and 2231.70xa0nm originate from OH, while the line at 2232.21xa0nm may originate from CN.

VECTOR MAGNETIC FIELD MEASUREMENTS ALONG A COOLED STEREO-IMAGED CORONAL LOOP

The variation of the vector magnetic field along structures in the solar corona remains unmeasured. Using a unique combination of spectropolarimetry and stereoscopy, we infer and compare the vector magnetic field structure and three-dimensional morphology of an individuated coronal loop structure undergoing a thermal instability. We analyze spectropolarimetric data of the He I 10830 {AA} triplet (

Cross-Calibrating Sunspot Magnetic Field Strength Measurements from the McMath-Pierce Solar Telescope and the Dunn Solar Telescope

1s2s{ }^{3}S_{1} - 1s2p{ }^{3}P_{2,1,0}

Spectropolarimetry of Atomic and Molecular Lines near 4135 nm

) obtained at the Dunn Solar Telescope with the Facility Infrared Spectropolarimeter on 19 September 2011. Cool coronal loops are identified by their prominent drainage signatures in the He I data (redshifts up to 185 km sec

Background-Induced Measurement Errors of the Coronal Intensity, Density, Velocity, and Magnetic Field

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A Decade of Diminishing Sunspot Vigor

). Extinction of EUV background radiation along these loops is observed by both the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and the Extreme Ultraviolet Imager onboard spacecraft A of the Solar Terrestrial Relations Observatory, and is used to stereoscopically triangulate the loop geometry up to heights of 70 Mm (