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Thomas A. Schad

Bio: Thomas A. Schad is an academic researcher from University of Arizona. The author has contributed to research in topics: Sunspot & Solar telescope. The author has an hindex of 15, co-authored 48 publications receiving 1770 citations. Previous affiliations of Thomas A. Schad include Association of Universities for Research in Astronomy & University of Hawaii.


Papers
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Journal ArticleDOI
31 Aug 2007-Science
TL;DR: In this paper, the authors reported the detection of Alfven waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico.
Abstract: Alfven waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfven waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfven waves may carry sufficient energy.

763 citations

01 Dec 2007
TL;DR: An estimate of the energy carried by the waves that are spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy.
Abstract: Alfven waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun's corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfven waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfven waves may carry sufficient energy.

562 citations

Journal ArticleDOI
TL;DR: The National Science Foundation's Daniel K. Inouye solar telescope (DKIST) as discussed by the authors provides the highest-resolution observations of the Sun ever achieved with a 4-m aperture.
Abstract: We present an overview of the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10−4. Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.

161 citations

Journal ArticleDOI
TL;DR: In this paper, high-resolution spectropolarimetric observations of superpenumbral fibrils in the He I triplet with sufficient polarimetric sensitivity to infer their full magnetic field geometry are presented.
Abstract: Atomic-level polarization and Zeeman effect diagnostics in the neutral helium triplet at 10830 A in principle allow full vector magnetometry of fine-scaled chromospheric fibrils. We present high-resolution spectropolarimetric observations of superpenumbral fibrils in the He I triplet with sufficient polarimetric sensitivity to infer their full magnetic field geometry. He I observations from the Facility Infrared Spectropolarimeter are paired with high-resolution observations of the Hα 6563 A and Ca II 8542 A spectral lines from the Interferometric Bidimensional Spectrometer from the Dunn Solar Telescope in New Mexico. Linear and circular polarization signatures in the He I triplet are measured and described, as well as analyzed with the advanced inversion capability of the "Hanle and Zeeman Light" modeling code. Our analysis provides direct evidence for the often assumed field alignment of fibril structures. The projected angle of the fibrils and the inferred magnetic field geometry align within an error of ±10°. We describe changes in the inclination angle of these features that reflect their connectivity with the photospheric magnetic field. Evidence for an accelerated flow (~40 m s–2) along an individual fibril anchored at its endpoints in the strong sunspot and weaker plage in part supports the magnetic siphon flow mechanism's role in the inverse Evershed effect. However, the connectivity of the outer endpoint of many of the fibrils cannot be established.

91 citations

Journal ArticleDOI
Mark Rast1, N. B. González2, Luis R. Bellot Rubio3, Wenda Cao4, Gianna Cauzzi, Edward E. DeLuca5, Bart De Pontieu6, Lyndsay Fletcher7, Lyndsay Fletcher6, Sarah Gibson8, Philip G. Judge8, Yukio Katsukawa9, Yukio Katsukawa10, Maria D. Kazachenko1, Elena Khomenko3, Enrico Landi11, Valentin Martinez Pillet, Gordon Petrie, Jiong Qiu12, Laurel A. Rachmeler13, Matthias Rempel8, Wolfgang Schmidt2, Eamon Scullion14, Xudong Sun15, B. T. Welsch16, Vincenzo Andretta17, Patrick Antolin14, Thomas R. Ayres1, Krishnan Balasubramaniam18, Istvan Ballai19, Thomas E. Berger1, Stephen J. Bradshaw20, R. J. Campbell21, Mats Carlsson6, Roberto Casini8, Rebecca Centeno8, Steven R. Cranmer1, Serena Criscuoli, Craig DeForest22, Yuanyong Deng23, Robertus Erdélyi19, Viktor Fedun19, Catherine E. Fischer2, Sergio Javier González Manrique24, Michael Hahn25, Louise K. Harra, Vasco Manuel de Jorge Henriques6, Neal E. Hurlburt, Sarah A. Jaeggli, Shahin Jafarzadeh6, Rekha Jain19, Stuart M. Jefferies26, P. H. Keys21, Adam F. Kowalski1, Christoph Kuckein27, Jeff Kuhn15, David Kuridze28, Jiajia Liu21, Wei Liu29, Dana Longcope12, Mihalis Mathioudakis21, R. T. James McAteer30, Scott W. McIntosh8, David E. McKenzie31, Mari Paz Miralles5, Richard Morton14, Karin Muglach32, Karin Muglach33, Chris J. Nelson21, Navdeep K. Panesar29, S. Parenti34, Clare E. Parnell35, Bala Poduval36, Kevin Reardon, Jeffrey W. Reep37, Thomas A. Schad, Donald Schmit1, Rahul Sharma14, Rahul Sharma38, Hector Socas-Navarro3, Abhishek K. Srivastava39, Alphonse C. Sterling31, Yoshinori Suematsu9, Lucas A. Tarr, Sanjiv K. Tiwari29, Alexandra Tritschler, Gary Verth19, Angelos Vourlidas40, Haimin Wang4, Yi-Ming Wang37 
TL;DR: The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere as discussed by the authors.
Abstract: The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute.

41 citations


Cited by
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Journal ArticleDOI
TL;DR: The Interface Region Imaging Spectrograph (IRIS) as mentioned in this paper provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 arcsec and up.
Abstract: The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 – 0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s−1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 – 1358 A, 1389 – 1407 A, and 2783 – 2834 A, including bright spectral lines formed in the chromosphere (Mg ii h 2803 A and Mg ii k 2796 A) and transition region (C ii 1334/1335 A and Si iv 1394/1403 A). Slit-jaw images in four different passbands (C ii 1330, Si iv 1400, Mg ii k 2796, and Mg ii wing 2830 A) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative–MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

1,238 citations

Journal ArticleDOI
TL;DR: The Interface Region Imaging Spectrograph (IRIS) as mentioned in this paper is a small explorer spacecraft that provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec.
Abstract: The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV 1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

1,034 citations

Journal ArticleDOI
07 Dec 2007-Science
TL;DR: Estimates of the energy flux carried by these waves and comparisons with advanced radiative magnetohydrodynamic simulations indicate that such Alfvén waves are energetic enough to accelerate the solar wind and possibly to heat the quiet corona.
Abstract: Alfven waves have been invoked as a possible mechanism for the heating of the Sun's outer atmosphere, or corona, to millions of degrees and for the acceleration of the solar wind to hundreds of kilometers per second. However, Alfven waves of sufficient strength have not been unambiguously observed in the solar atmosphere. We used images of high temporal and spatial resolution obtained with the Solar Optical Telescope onboard the Japanese Hinode satellite to reveal that the chromosphere, the region sandwiched between the solar surface and the corona, is permeated by Alfven waves with strong amplitudes on the order of 10 to 25 kilometers per second and periods of 100 to 500 seconds. Estimates of the energy flux carried by these waves and comparisons with advanced radiative magnetohydrodynamic simulations indicate that such Alfven waves are energetic enough to accelerate the solar wind and possibly to heat the quiet corona.

907 citations

Journal ArticleDOI
TL;DR: An examination of prediction techniques for the solar cycle is examined and a closer look at cycles 23 and 24 is taken.
Abstract: The Solar Cycle is reviewed. The 11-year cycle of solar activity is characterized by the rise and fall in the numbers and surface area of sunspots. We examine a number of other solar activity indicators including the 10.7 cm radio flux, the total solar irradiance, the magnetic field, flares and coronal mass ejections, geomagnetic activity, galactic cosmic ray fluxes, and radioisotopes in tree rings and ice cores that vary in association with the sunspots. We examine the characteristics of individual solar cycles including their maxima and minima, cycle periods and amplitudes, cycle shape, and the nature of active latitudes, hemispheres, and longitudes. We examine long-term variability including the Maunder Minimum, the Gleissberg Cycle, and the Gnevyshev-Ohl Rule. Short-term variability includes the 154-day periodicity, quasi-biennial variations, and double peaked maxima. We conclude with an examination of prediction techniques for the solar cycle.

890 citations

Journal ArticleDOI
28 Jul 2011-Nature
TL;DR: Observations of the transition region of the chromosphere and the corona are reported that reveal how Alfvénic motions permeate the dynamic and finely structured outer solar atmosphere.
Abstract: Alfven waves — travelling oscillations of ions and magnetic field — were first detected in the Sun's corona in 2007, but at amplitudes too small to explain the mystery of where the energy comes from to heat corona gases to millions of degrees and accelerate the solar wind to speeds of hundreds of kilometres per second. New observations of the transition region and corona reveal ubiquitous outward-propagating Alfvenic motions that have amplitudes of the order of 20 kilometres per second and periods of the order of 100–500 seconds throughout the quiescent atmosphere. The observations show that coronal waves fill the whole atmosphere and are sufficiently strong to play a major part in the energetics of the outer solar atmosphere. Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2–6). Alfven waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun’s magnetic field lines into the corona. Previous observations7 of Alfvenic waves in the corona revealed amplitudes far too small (0.5 km s−1) to supply the energy flux (100–200 W m−2) required to drive the fast solar wind8 or balance the radiative losses of the quiet corona9. Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvenic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvenic motions observed have amplitudes of the order of 20 km s−1 and periods of the order of 100–500 s throughout the quiescent atmosphere (compatible with recent investigations7,10), and are energetic enough to accelerate the fast solar wind and heat the quiet corona.

619 citations