skip to main content

Search for: All records

Award ID contains: 1821294

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Multiple solar instrument observation campaigns are increasingly popular among the solar physics and space science communities. Scientists organize high-resolution ground-based telescopes and spacecraft to study the evolution of the complex solar atmosphere and the origin of space weather. Image registration and coalignment between different instruments are vital for accurate data product comparison. We developed a Python language package for registration of ground-based high-resolution imaging data acquired by the Goode Solar Telescope (GST) to space-based full-disk continuum intensity data provided by the Solar Dynamics Observatory (SDO) with the scale-invariant feature transform method. The package also includes tools to align data sets obtained in different wavelengths and at different times utilizing the optical flow method. We present the image registration and coalignment workflow. The aliment accuracy of each alignment method is tested with the aid of radiative magnetohydrodynamics simulation data. We update the pointing information in GST data fits headers and generate GST and SDO imaging data products as science-ready four-dimensional (x,y,λ,t) data cubes.


    Measurements of the optical turbulence profile are critical for selecting a potential new solar observational site or for characterizing an existing solar observatory. To measure the turbulence distribution to a moderate altitude above an existing observatory, current techniques use a large facility telescope with an aperture size larger than 1.0 m. This limits their application, especially in surveys to find a new potential site where no large facility telescope is available and where a portable measurement device is needed for such measurements. To address the above issues, we propose a new technique, termed the Advanced Multiple Aperture Seeing Profiler (A-MASP), which uses solar granulation to measure the daytime optical turbulence profile. The A-MASP is a portable system and thus can fully address the fundamental limitation of current optical turbulence profile measurement techniques. The A-MASP consists of two small telescopes, each with an aperture of the order of 100 mm, which can measure the turbulence profile to an altitude up to 20 km. Here, we present our A-MASP development work and its initial on-site measurements at the Big Bear Solar Observatory. In a proof-of-concept experiment, it was successfully demonstrated that the A-MASP can reliably measure the turbulence profile up to 12 km with amore »vector separation of 0.7 m between the two telescopes. The A-MASP could be used for future surveys to find potentially good observational sites.

    « less
  3. Abstract

    Obtaining high-quality magnetic and velocity fields through Stokes inversion is crucial in solar physics. In this paper, we present a new deep learning method, named Stacked Deep Neural Networks (SDNN), for inferring line-of-sight (LOS) velocities and Doppler widths from Stokes profiles collected by the Near InfraRed Imaging Spectropolarimeter (NIRIS) on the 1.6 m Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). The training data for SDNN are prepared by a Milne–Eddington (ME) inversion code used by BBSO. We quantitatively assess SDNN, comparing its inversion results with those obtained by the ME inversion code and related machine-learning (ML) algorithms such as multiple support vector regression, multilayer perceptrons, and a pixel-level convolutional neural network. Major findings from our experimental study are summarized as follows. First, the SDNN-inferred LOS velocities are highly correlated to the ME-calculated ones with the Pearson product–moment correlation coefficient being close to 0.9 on average. Second, SDNN is faster, while producing smoother and cleaner LOS velocity and Doppler width maps, than the ME inversion code. Third, the maps produced by SDNN are closer to ME’s maps than those from the related ML algorithms, demonstrating that the learning capability of SDNN is better than those ofmore »the ML algorithms. Finally, a comparison between the inversion results of ME and SDNN based on GST/NIRIS and those from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory in flare-prolific active region NOAA 12673 is presented. We also discuss extensions of SDNN for inferring vector magnetic fields with empirical evaluation.

    « less
  4. Abstract

    We present a detailed study of very strong magnetic fields in the NOAA Active Region (AR) 12673, which was the most flare productive AR in solar cycle 24. It produced four X-class flares including the X9.3 flare on 2017 September 6 and the X8.2 limb event on September 10. Our analysis is based on direct measurements of full Zeeman splitting of the Fei1564.85 nm line using all Stokes I, Q, U, and V profiles. This approach allowed us to obtain reliable estimates of the magnitude of magnetic fields independent of the filling factor and atmosphere models. Thus, the strongest fields up to 5.5 kG were found in a light bridge (LB) of a spot, while in the dark umbra magnetic fields did not exceed 4 kG. In the case of the LB, the magnitude of the magnetic field is not related to the underlying continuum intensity, while in the case of umbral fields we observed a well-known anticorrelation between the continuum intensity and the field magnitude. In this study, the LB was cospatial with a polarity inversion line ofδ-sunspot, and we speculate that the 5.5 kG strong horizontal fields may be associated with a compact twisted flux rope atmore »or near the photosphere. A comparison of the depth of the Zeemanπandσcomponents showed that in the LB magnetic fields are, on average, more horizontal than those in the dark umbra.

    « less
  5. Abstract

    In this study, we analyze high-spatial-resolution (0.″24) magnetograms and high-spatial-resolution (0.″10) Hαoff-band (± 0.8 Å) images taken by the 1.6 m Goode Solar Telescope to investigate the magnetic properties associated with small-scale ejections in a coronal hole boundary region from a statistical perspective. With one and a half hours of optical observations under excellent seeing, we focus on the magnetic structure and evolution by tracking the magnetic features with the Southwest Automatic Magnetic Identification Suite (SWAMIS). The magnetic field at the studied coronal hole boundary is dominated by negative polarity with flux cancellations at the edges of the negative unipolar cluster. In a total of 1250 SWAMIS-detected magnetic cancellation events, ∼39% are located inside the coronal hole with an average flux cancellation rate of 2.0 × 1018Mx Mm−2hr−1, and ∼49% are located outside the coronal hole with an average flux cancellation rate of 8.8 × 1017Mx Mm−2hr−1. We estimated that the magnetic energy released due to flux cancellation inside the coronal hole is six times more than that outside the coronal hole. Flux cancellation accounts for ∼9.5% of the total disappearance of magnetic flux. Other forms of its disappearance are mainly due to fragmentation of unipolar clusters or mergingmore »with elements of the same polarity. We also observed a number of significant small-scale ejections associated with magnetic cancellations at the coronal hole boundary that have corresponding EUV brightenings.

    « less
  6. Abstract

    Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare that occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a partial eruption of a twisted filament observed in Hαby the Goode Solar Telescope at the Big Bear Solar Observatory. The extreme ultraviolet (EUV) and X-ray signatures of the event are generally consistent with the standard scenario of eruptive flares, with the presence of double flare ribbons connected by a bright flare arcade. Intriguingly, this partial eruption event features a microwave counterpart, whose spatial and temporal evolution closely follow the filament seen in Hαand EUV. The spectral properties of the microwave source are consistent with nonthermal gyrosynchrotron radiation. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600 to 1400 Gauss from its apex to the legs. The results agree well with the nonlinear force-free magnetic model extrapolated from the preflare photosphericmore »magnetogram. We conclude that the microwave counterpart of the erupting filament is likely due to flare-accelerated electrons injected into the filament-hosting magnetic flux rope cavity following the newly reconnected magnetic field lines.

    « less
  7. Context. Solar observations of carbon monoxide (CO) indicate the existence of lower-temperature gas in the lower solar chromosphere. We present an observation of pores, and quiet-Sun, and network magnetic field regions with CO 4.66 μm lines by the Cryogenic Infrared Spectrograph (CYRA) at Big Bear Solar Observatory. Aims. We used the strong CO lines at around 4.66 μm to understand the properties of the thermal structures of lower solar atmosphere in different solar features with various magnetic field strengths. Methods. Different observations with different instruments were included: CO 4.66 μm imaging spectroscopy by CYRA, Atmospheric Imaging Assembly (AIA) 1700 Å images, Helioseismic and Magnetic Imager (HMI) continuum images, line-of-sight (LOS) magnetograms, and vector magnetograms. The data from 3D radiation magnetohydrodynamic (MHD) simulation with the Bifrost code are also employed for the first time to be compared with the observation. We used the Rybicki-Hummer (RH) code to synthesize the CO line profiles in the network regions. Results. The CO 3-2 R14 line center intensity changes to be either enhanced or diminished with increasing magnetic field strength, which should be caused by different heating effects in magnetic flux tubes with different sizes. We find several “cold bubbles” in the CO 3-2 R14more »line center intensity images, which can be classified into two types. One type is located in the quiet-Sun regions without magnetic fields. The other type, which has rarely been reported in the past, is near or surrounded by magnetic fields. Notably, some are located at the edge of the magnetic network. The two kinds of cold bubbles and the relationship between cold bubble intensities and network magnetic field strength are both reproduced by the 3D MHD simulation with the Bifrost and RH codes. The simulation also shows that there is a cold plasma blob near the network magnetic fields, causing the observed cold bubbles seen in the CO 3-2 R14 line center image. Conclusions. Our observation and simulation illustrate that the magnetic field plays a vital role in the generation of some CO cold bubbles.« less
    Free, publicly-accessible full text available January 1, 2024
  8. Abstract Diagnosing the spatiotemporal pattern of magnetic flux on the Sun is vital for understanding the origin of solar magnetism and activity. Here, we report a new form of flux appearance, magnetic outbreak, using observations with an extremely high spatial resolution of 0.″16 from the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. Magnetic outbreak refers to an early growth of unipolar magnetic flux and its later explosion into fragments, in association with plasma upflow and exploding granulations; each individual fragment has flux of 10 16 –10 17 Mx, moving apart with a velocity of 0.5–2.2 km s −1 . The magnetic outbreak takes place in the hecto-Gauss region of pore moats. In this study, we identify six events of magnetic outbreak during 6 hr observations over an approximately 40″ × 40″ field of view. The newly discovered magnetic outbreak might be the first evidence of the long-anticipated convective blowup.
    Free, publicly-accessible full text available December 27, 2023
  9. Aims. On the Sun, jets in light bridges (LBs) are frequently observed with high-resolution instruments. The respective roles played by convection and the magnetic field in triggering such jets are not yet clear. Methods. We report a small fan-shaped jet along a LB observed by the 1.6m Goode Solar Telescope (GST) with the TiO Broadband Filter Imager (BFI), the Visible Imaging Spectrometer (VIS) in H α , and the Near-InfraRed Imaging Spectropolarimeter (NIRIS), along with the Stokes parameters. The high spatial and temporal resolution of those instruments allowed us to analyze the features identified during the jet event. By constructing the H α Dopplergrams, we found that the plasma is first moving upward, whereas during the second phase of the jet, the plasma is flowing back. Working with time slice diagrams, we investigated the propagation-projected speed of the fan and its bright base. Results. The fan-shaped jet developed within a few minutes, with diverging beams. At its base, a bright point was slipping along the LB and ultimately invaded the umbra of the sunspot. The H α profiles of the bright points enhanced the intensity in the wings, similarly to the case of Ellerman bombs. Co-temporally, the extreme ultraviolet (EUV)more »brightenings developed at the front of the dark material jet and moved at the same speed as the fan, leading us to propose that the fan-shaped jet material compressed and heated the ambient plasma at its extremities in the corona. Conclusions. Our multi-wavelength analysis indicates that the fan-shaped jet could result from magnetic reconnection across the highly diverging field low in the chromosphere, leading to an apparent slipping motion of the jet material along the LB. However, we did not find any opposite magnetic polarity at the jet base, as would typically be expected in such a configuration. We therefore discuss other plausible physical mechanisms, based on waves and convection, that may have triggered the event.« less
    Free, publicly-accessible full text available November 1, 2023
  10. Evans, Christopher J. ; Bryant, Julia J. ; Motohara, Kentaro (Ed.)
    Free, publicly-accessible full text available August 29, 2023