Magnetic nulls and super-radial expansion in the solar corona

Sarah E. Gibson, Kevin Dalmasse, Laurel A. Rachmeler, Marc L. De Rosa, Steven Tomczyk, Giuliana de Toma, Joan Burkepile, Michael Galloy

Magnetic fields in the sun's outer atmosphere -- the corona -- control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where magnetic reconnection is likely to act as a catalyst for solar activity. CoMP linear-polarization observations also provide an independent, coronal proxy for magnetic expansion into the solar wind, a quantity often used to parameterize and predict the solar wind speed at Earth. We introduce a new method for explicitly calculating expansion factors from CoMP coronal linear-polarization observations, which does not require photospheric extrapolations. We conclude that linearly-polarized light is a powerful new diagnostic of critical coronal magnetic topologies and the expanding magnetic flux tubes that channel the solar wind.

Polarimeter to Unify the Corona and Heliosphere (PUNCH)

Craig E. DeForest, Sarah E. Gibson, Ronnie Killough, Nick R. Waltham, Matt N. Beasley, Robin C. Colaninno, Glenn T. Laurent, Daniel B. Seaton, J. Marcus Hughes, Madhulika Guhathakurta, Nicholeen M. Viall, Raphael Attie, Dipankar Banerjee, Luke Barnard, Doug A. Biesecker, Mario M. Bisi, Volker Bothmer, Antonina Brody, Joan Burkepile, Iver H. Cairns, Jennifer L. Campbell, Traci Case, Amir Caspi, David Cheney, Rohit Chhiber, Matthew J. Clapp, Steven R. Cranmer, Jackie A. Davies, Curt A. de Koning, Mihir I. Desai, Heather A. Elliott, Samaiyah Farid, Bea Gallardo-Lacourt, Chris Gilly, Caden Gobat, Mary H. Hanson, Richard A. Harrison, Donald M. Hassler, Chase Henley, Alan M. Henry, Russell A. Howard, Bernard V. Jackson, Samuel Jones, Don Kolinski, Derek A. Lamb, Florine Lehtinen, Chris Lowder, Anna Malanushenko, William H. Matthaeus, David J. McComas, Jacob McGee, Huw Morgan, Divya Oberoi, Dusan Odstrcil, Chris Parmenter, Ritesh Patel, Francesco Pecora, Steve Persyn, Victor J. Pizzo, Simon P. Plunkett, Elena Provornikova, Nour Eddine Raouafi, Jillian A. Redfern, Alexis P. Rouillard, Kelly D. Smith, Keith B. Smith, Zachary S. Talpas, S. James Tappin, Arnaud Thernisien, Barbara J. Thompson, Samuel Van Kooten, Kevin J. Walsh, David F. Webb, William L. Wells, Matthew J. West, Zachary Wiens, Yan Yang

The Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission is a NASA Small Explorer to determine the cross-scale processes that unify the solar corona and heliosphere. PUNCH has two science objectives: (1) understand how coronal structures become the ambient solar wind, and (2) understand the dynamic evolution of transient structures, such as coronal mass ejections, in the young solar wind. To address these objectives, PUNCH uses a constellation of four small spacecraft in Sun-synchronous low Earth orbit, to collect linearly polarized images of the K corona and young solar wind. The four spacecraft each carry one visible-light imager in a 1+3 configuration: a single Narrow Field Imager solar coronagraph captures images of the outer corona at all position angles, and at solar elongations from 1.5 degrees (6 R$_\odot$) to 8 degrees (32 R$_\odot$); and three separate Wide Field Imager heliospheric imagers together capture views of the entire inner solar system, at solar elongations from 3 degrees (12 R$_\odot$) to 45 degrees (180 R$_\odot$) from the Sun. PUNCH images include linear-polarization data, to enable inferring the three-dimensional structure of visible features without stereoscopy. The instruments are matched in wavelength passband, support overlapping instantaneous fields of view, and are operated synchronously, to act as a single ``virtual instrument'' with a 90 degree wide field of view, centered on the Sun. PUNCH launched in March of 2025 and began science operations in June of 2025. PUNCH has an open data policy with no proprietary period, and PUNCH Science Team Meetings are open to all.

Hemispheric Asymmetries of Solar Photospheric Magnetism: Radiative, Particulate, and Heliospheric Impacts

Scott W. McIntosh, Robert J. Leamon, Joseph B. Gurman, Jean-Philippe Olive, Jonathan W. Cirtain, David H. Hathaway, Joan Burkepile, Mark Miesch, Robert S. Markel, Leonard Sitongia

Among many other measurable quantities the summer of 2009 saw a considerable low in the radiative output of the Sun that was temporally coincident with the largest cosmic ray flux ever measured at 1AU. A hemispheric asymmetry in magnetic activity is clearly observed and its evolution monitored and the resulting (prolonged) magnetic imbalance must have had a considerable impact on the structure and energetics of the heliosphere. While we cannot uniquely tie the variance and scale of the surface magnetism to the dwindling radiative and particulate output of the star, or the increased cosmic ray flux through the 2009 minimum, the timing of the decline and rapid recovery in early 2010 would appear to inextricably link them. These observations support a picture where the Sun's hemispheres are significantly out of phase with each other. Studying historical sunspot records with this picture in mind shows that the northern hemisphere has been leading since the middle of the last century and that the hemispheric "dominance" has changed twice in the past 130 years. The observations presented give clear cause for concern, especially with respect to our present understanding of the processes that produce the surface magnetism in the (hidden) solar interior - hemispheric asymmetry is the normal state - the strong symmetry shown in 1996 was abnormal. Further, these observations show that the mechanism(s) which create and transport the magnetic flux magnetic flux are slowly changing with time and, it appears, with only loose coupling across the equator such that those asymmetries can persist for a considerable time. As the current asymmetry persists and the basal energetics of the system continue to dwindle we anticipate new radiative and particulate lows coupled with increased cosmic ray fluxes heading into the next solar minimum.

SunCET: A compact EUV instrument to fill a critical observational gap

James Paul Mason, Phillip C. Chamberlin, Daniel Seaton, Joan Burkepile, Robin Colaninno, Karin Dissauer, Francis G. Eparvier, Yuhong Fan, Sarah Gibson, Andrew R. Jones, Christina Kay, Michael Kirk, Richard Kohnert, W. Dean Pesnell, Barbara J. Thompson, Astrid M. Veronig, Matthew J. West, David Windt, Thomas N. Woods

The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet imager and spectrograph instrument concept for tracking coronal mass ejections through the region where they experience the majority of their acceleration: the difficult-to-observe middle corona. It contains a wide field of view (0-4~\Rs) imager and a 1~Å spectral-resolution-irradiance spectrograph spanning 170-340~Å. It leverages new detector technology to read out different areas of the detector with different integration times, resulting in what we call "simultaneous high dynamic range", as opposed to the traditional high dynamic range camera technique of subsequent full-frame images that are then combined in post-processing. This allows us to image the bright solar disk with short integration time, the middle corona with a long integration time, and the spectra with their own, independent integration time. Thus, SunCET does not require the use of an opaque or filtered occulter. SunCET is also compact -- $\sim$15 $\times$ 15 $\times$ 10~cm in volume -- making it an ideal instrument for a CubeSat or a small, complementary addition to a larger mission. Indeed, SunCET is presently in a NASA-funded, competitive Phase A as a CubeSat and has also been proposed to NASA as an instrument onboard a 184 kg Mission of Opportunity.

More of the Inconvenient Truth About Coronal Dimmings

Scott W. McIntosh, Joan Burkepile, Robert J. Leamon

We continue the investigation of a CME-driven coronal dimming from December 14 2006 using unique high resolution imaging of the chromosphere and corona from the Hinode spacecraft. Over the course of the dimming event we observe the dynamic increase of non-thermal line broadening of multiple emission lines as the CME is released and the corona opens; reaching levels seen in coronal holes. As the corona begins to close, refill and brighten, we see a reduction of the non-thermal broadening towards the pre-eruption level. The dynamic evolution of non-thermal broadening is consistent with the expected change of Alfven wave amplitudes in the magnetically open rarefied dimming region, compared to the dense closed corona prior to the CME. The presented data reinforce the belief that coronal dimmings must be temporary sources of the fast solar wind. It is unclear if such a rapid transition in the thermodynamics of the corona to a solar wind state has an effect on the CME itself.

Measuring the magnetic origins of solar flares, CMEs and Space Weather

Philip Judge, Matthias Rempel, Rana Ezzeddine, Lucia Kleint, Ricky Egeland, Svetlana Berdyugina, Thomas Berger, Joan Burkepile, Rebecca Centeno, Giuliana de Toma, Mausumi Dikpati, Yuhong Fan, Holly Gilbert, Daniela Lacatus

We take a broad look at the problem of identifying the magnetic solar causes of space weather. With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near UV part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, Hubble Space Telescope, and SKYLAB, along with 1D computations of the near-UV (NUV) spectrum and numerical experiments based on the MURaM radiation-MHD and HanleRT radiative transfer codes, we address multiple challenges. These challenges are best met through a combination of near UV lines of bright \ion{Mg}{2}, and lines of \ion{Fe}{2} and \ion{Fe}{1} (mostly within the $4s-4p$ transition array) which form in the chromosphere up to $2\times10^4$ K. Both Hanle and Zeeman effects can in principle be used to derive vector magnetic fields. However, for any given spectral line the $τ=1$ surfaces are generally geometrically corrugated owing to fine structure such as fibrils and spicules. By using multiple spectral lines spanning different optical depths, magnetic fields across nearly-horizontal surfaces can be inferred in regions of low plasma $β$, from which free energies, magnetic topology and other quantities can be derived. Based upon the recently-reported successful suborbital space measurements of magnetic fields with the CLASP2 instrument, we argue that a modest space-borne telescope will be able to make significant advances in the attempts to predict solar eruptions. Difficulties associated with blended lines are shown to be minor in an Appendix.

Historical astronomical data: urgent need for preservation, digitization enabling scientific exploration

Alexei Pevtsov, Elizabeth Griffin, Jonathan Grindlay, Stella Kafka, Jennifer Lynn Bartlett, Ilya Usoskin, Kalevi Mursula, Sarah Gibson, Valentin M. Pillet, Joan Burkepile, David Webb, Frederic Clette, James Hesser, Peter Stetson, Andres Munoz-Jaramillo, Frank Hill, Rick Bogart, Wayne Osborn, Dana Longcope

Over the past decades and even centuries, the astronomical community has accumulated a signif-icant heritage of recorded observations of a great many astronomical objects. Those records con-tain irreplaceable information about long-term evolutionary and non-evolutionary changes in our Universe, and their preservation and digitization is vital. Unfortunately, most of those data risk becoming degraded and thence totally lost. We hereby call upon the astronomical community and US funding agencies to recognize the gravity of the situation, and to commit to an interna-tional preservation and digitization efforts through comprehensive long-term planning supported by adequate resources, prioritizing where the expected scientific gains, vulnerability of the origi-nals and availability of relevant infrastructure so dictates. The importance and urgency of this issue has been recognized recently by General Assembly XXX of the International Astronomical Union (IAU) in its Resolution B3: "on preservation, digitization and scientific exploration of his-torical astronomical data". We outline the rationale of this promotion, provide examples of new science through successful recovery efforts, and review the potential losses to science if nothing it done.

Astro2020 Science White Paper: Synoptic Studies of the Sun as a Key to Understanding Stellar Astrospheres

Valentin Martinez Pillet, Frank Hill, Heidi Hammel, Alfred G. de Wijn, Sanjay Gosain, Joan Burkepile, Carl J. Henney, James R. T. McAteer, Hazel M. Bain, Ward B. Manchester, Haosheng Lin, Markus Roth, Kiyoshi Ichimoto, Yoshinori Suematsu

Ground-based solar observations provide key contextual data (i.e., the 'big picture') to produce a complete description of the only astrosphere we can study in situ: our Sun's heliosphere. The next decade will see the beginning of operations of the Daniel K. Inouye Solar Telescope (DKIST). DKIST will join NASA's Parker Solar Probe and the NASA/ESA Solar Orbital mission, which together will study our Sun's atmosphere with unprecedented detail. This white paper outlines the current paradigm for ground-based solar synoptic observations, and indicates those areas that will benefit from focused attention.

Stray light and polarimetry considerations for the COSMO K-Coronagraph

Alfred G. de Wijn, Joan T. Burkepile, Steven Tomczyk, Peter G. Nelson, Pei Huang, Dennis Gallagher

The COSMO K-Coronagraph is scheduled to replace the aging Mk4 K-Coronameter at the Mauna Loa Solar Observatory of the National Center for Atmospheric Research in 2013. We present briefly the science objectives and derived requirements, and the optical design. We single out two topics for more in-depth discussion: stray light, and performance of the camera and polarimeter.

A new facility for airborne solar astronomy: NASA's WB-57 at the 2017 total solar eclipse

Amir Caspi, Daniel B. Seaton, Constantine C. C. Tsang, Craig E. DeForest, Paul Bryans, Edward E. DeLuca, Steven Tomczyk, Joan T. Burkepile, Thomas "Tony" Casey, John Collier, Donald "DD" Darrow, Dominic Del Rosso, Daniel D. Durda, Peter T. Gallagher, Leon Golub, Matthew Jacyna, David "DJ" Johnson, Philip G. Judge, Cary "Diddle" Klemm, Glenn T. Laurent, Johanna Lewis, Charles J. Mallini, Thomas "Duster" Parent, Timothy Propp, Andrew J. Steffl, Jeff Warner, Matthew J. West, John Wiseman, Mallory Yates, Andrei N. Zhukov, the NASA WB-57 2017 Eclipse Observing Team

NASA's WB-57 High Altitude Research Program provides a deployable, mobile, stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric airmass that can interfere with astronomical observations. We used the 2017 Aug 21 eclipse as a pathfinding mission for high-altitude airborne solar astronomy, using the existing high-speed visible-light and near-/mid-wave infrared imaging suite mounted in the WB-57 nose cone. In this paper, we describe the aircraft, the instrument, and the 2017 mission; operations and data acquisition; and preliminary analysis of data quality from the existing instrument suite. We describe benefits and technical limitations of this platform for solar and other astronomical observations. We present a preliminary analysis of the visible-light data quality and discuss the limiting factors that must be overcome with future instrumentation. We conclude with a discussion of lessons learned from this pathfinding mission and prospects for future research at upcoming eclipses, as well as an evaluation of the capabilities of the WB-57 platform for future solar astronomy and general astronomical observation.

Citizen CATE 2024: Extending Totality During the 8 April 2024 Total Solar Eclipse with a Distributed Network of Community Participants

Sarah A. Kovac, Amir Caspi, Daniel B. Seaton, Paul Bryans, Joan R. Burkepile, Sarah J. Davis, Craig E. DeForest, David Elmore, Sanjay Gosain, Rebecca Haacker, Marcus Hughes, Jason Jackiewicz, Viliam Klein, Derek Lamb, Valentin Martinez Pillet, Evy McUmber, Ritesh Patel, Kevin Reardon, Willow Reed, Anna Tosolini, Andrei E. Ursache, John K. Williams, Padma A. Yanamandra-Fisher, Daniel W. Zietlow, John Carini, Charles H. Gardner, Shawn Laatsch, Patricia H. Reiff, Nikita Saini, Rachael L. Weir, Kira F. Baasch, Jacquelyn Bellefontaine, Timothy D. Collins, Ryan J. Ferko, Leticia Ferrer, Margaret Hill, Jonathan M. Kessler, Jeremy A. Lusk, Jennifer Miller-Ray, Catarino Morales, Brian W. Murphy, Kayla L. Olson, Mark J. Percy, Gwen Perry, Andrea A. Rivera, Aarran W. Shaw, Erik Stinnett, Eden L. Thompson, Hazel S. Wilkins, Yue Zhang, Angel Allison, John J. Alves, Angelica A. Alvis, Lucinda J. Alvis, Alvin J. G. Angeles, Aalasia Batchelor, Robert Benedict, Amelia Bettati, Abbie Bevill, Katherine Bibee Wolfson, Christina Raye Bingham, Bradley A. Bolton, Iris P. Borunda, Mario F. Borunda, Adam Bowen, Daniel L. Brookshier, MerRick Brown, Fred Bruenjes, Lisa Bunselmeier, Brian E. Burke, Bo Chen, Chi-Jui Chen, Zhean Chen, Marcia Chenevey Long, Nathaniel D. Cook, Tommy Copeland, Adrian J. Corter, Lawson L. Corter, Michael J. Corter, Theresa N. Costilow, Lori E. Cypert, Derrion Crouch-Bond, Beata Csatho, Clayton C. Cundiff, Stella S. Cundiff, Darrell DeMotta, Judy Dickey, Hannah L. Dirlam, Nathan Dodson, Donovan Driver, Jennifer Dudley-Winter, Justin Dulyanunt, Jordan R. Duncan, Scarlett C. Dyer, Lizabeth D. Eason, Timothy E. Eason, Jerry L. Edwards, Jaylynn N. Eisenhour, Ogheneovo N. Erho, Elijah J. Fleming, Andrew J. Fritsch, Stephanie D. Frosch, Sahir Gagan, Joshua Gamble, Caitlyn L. Geisheimer, Ashleyahna George, Treva D. Gough, Jo Lin Gowing, Robert Greeson, Julie D. Griffin, Justin L. Grover, Simon L. Grover, Annie Hadley, Austin S. Hailey, Katrina B. Halasa, Jacob Harrison, Rachael Heltz Herman, Melissa Hentnik, Robert Hentnik, Mark Herman, Brenda G. Henderson, David T. Henderson, J. Michael Henthorn, Thomas Hogue, Billy J. House, Toni Ray Howe, Brianna N. Isola, Mark A. Iwen, Jordyn Johnson, Richard O. Johnson, Sophia P. Jones, Hanieh Karimi, Katy R. Kiser, Michael K. Koomson, Morgan M. Koss, Ryan P. Kovacs, Carol A. Kovalak Martin, Kassidy Lange, Kyle Lawrence Leathers, Michael H. Lee, Kevin W. Lehman, Garret R. Leopold, Hsiao-Chun Lin, Heather Liptak, Logan Liptak, Michael A. Liptak, Alonso Lopez, Evan L. Lopez, Don Loving, April Luehmann, Kristen M. Lusk, Tia L. MacDonald, Ian A. Mannings, Priscilla Marin, Christopher J. Martin, Jamie Martin, Alejandra Olivia Martinez, Terah L. Martinez, Elizabeth S. Mays, Seth McGowan, Edward M. McHenry, Kaz Meszaros, Tyler J. Metivier, Quinn W. Miller, Adam V. Miranda, Carlos Miranda, Pranvera Miranda, David M. W. Mitchell, Lydia N. Montgomery, Christopher P. Morse, Lillie B. Moore, Ira S. Morse, Raman Mukundan, Patrick T. Murphy, Nicarao J. Narvaez, Ahmed Nasreldin, Thomas Neel, Travis A. Nelson, Ellianna Nestlerode, Adam Z. Neuville, Brian A. Neuville, Allison Newberg, Jeremy L. Nicholson, Makenna F. Nickens, Sining Niu, Jedidiah O'Brien, Luis A. Otero, Jacob A. Ott, Joel A. Ott, Justin M. Ott, Michael E. Ott, Shekhar Pant, Ivan Parmuzin, Eric J. Parr, Sagar P. Paudel, Courtney M. Payne, Hayden B. Phillips, Elizabeth R. Prinkey, Kwesi A. Quagraine, Wesley J. Reddish, Azariah Rhodes, Stephen Kyle Rimler, Carlyn S. Rocazella, Tiska E. Rodgers, Devalyn Rogers, Oren R. Ross, Benjamin D. Roth, Melissa Rummel, John F. Rusho, Michael W. Sampson, Sophia Saucerman, James Scoville, Martin Wayne Seifert, Michael H. Seile, Thomas G. Skirko, Asad Shahab, David C. Smith, Emily R. Snode-Brenneman, Cassandra Spaulding, Neha Srivastava, Amy L. Strecker, Aidan Sweets, Morghan Taylor, Deborah S. Teuscher, Owen Totten, Stephen Totten, Stephanie Totten, Andrew Totten, Corina R. Ursache, Susan V. Benedict, Yolanda Vasquez, R. Anthony Vincent, Alan Webb, Walter Webb, Roderick M. Weinschenk, Sedrick Weinschenk, Cash A. Wendel, Elisabeth Wheeler, Bethany A. Whitehouse, Gabriel J. Whitehouse, David A. Wiesner, Philip J. Williams, John A. Zakelj