Craig DeForest’s articles


If you want to see all of my papers in chronological order, an ADS listing is easy to follow.  I’m also on Google Scholar.

Here I’ve selected the more interesting (to me), grouped in sort-of topical order.  I’m prime author on most of the ones listed, but I’ve included several where I am farther down the list.  The common theme here is that I’ve continued the particular line of research in the paper for more than just a one-off study.

Solar Polar Plumes

EUV imaging and plasma diagnostics

MSSTA V: Temperature Diagnostic Response to the Optically Thin Solar Plasma (1991)

    DeForest et al. 1991, Opt. Eng., 30, 1125.

    This was my first refereed journal article, on how to determine plasma properties of solar features using an array of

    EUV telescopes with slightly different passbands.  As it turns out, you can’t.  That has led to the notion of

    differential emission measure analysis, which is a major focus of data analysis with SDO.  This one began as an

    SPIE proceedings paper that was really a joint effort between Max Allen, Charles Kankelborg, Joakim Lindblom,

    and me.  I came in fairly late in the process, but ended up knitting all the sections together for the SPIE paper and

    hammering it into shape as a refereed article.  The 3-D spectral plots seemed so new and exciting back then.

On Resampling of Solar Images (2004)

    DeForest 2004, Sol. Phys. 219, 3.

    I started thinking about resampling back in the 1990s, and this paper sort of bubbled out of that research -- I

    did some work on polar plumes that used conformal resampling, and I hacked up some code to avoid introducing

    artifacts -- but kept thinking there must be a more general way to resample images without scrozzling them.  This

    paper (and the PDL::Transform package, a part of the Perl Data Language)  were a result of that.

On the Size of Structures in the Solar Corona (2007)

    DeForest 2007, Astrophys. J. 661, 532.

    This came out of listening to a public lecture that Alan Title gave, describing how puzzled everyone was about the

    uniform widths of coronal loops.  We saw them way back with the MSSTA in the early 1990s. (Ray O’Neal’s thesis

    has a nice description, and Jim Klimchuk, who was then a postdoc, was thinking about them even then).  I

    suddenly realized that the constant width might be an artifact -- which is more plausible: (A) the Sun violates the

    laws of physics, or (B) all PIs slightly overstate their instruments’ resolution?  The paper is really about the

    relationship between instrument performance and interpreted solar physics.

Solar Coronal Structure and Stray Light in TRACE (2009)

    DeForest, Martens, & Wills-Davey 2009, Astrophys. J. 690, 1264.

    While Meredith was working at SwRI I got interested in the Hinode/SOT PSF, to try to sharpen magnetic images as

    much as possible.  Meredith wanted to do that with TRACE data as well, and I got interested in trying to measure

    the TRACE PSF. The Venus occultation data (from 2004) turned out to be just the ticket, and we were able to

    demonstrate that TRACE scatters a large amount of incoming EUV -- invalidating some prior studies.  Data and

    sausage -- you don’t want to know, but you need to know what’s in ‘em.

Thermal and Density Structure of Polar Plumes (1993)

    Walker, DeForest, Hoover, & Barbee 1993, Sol. Phys. 25, 1203.

    I was a graduate student when working on this paper.  My advisor, Art Walker, encouraged me to develop a

    photometric film calibration curve and try to extract information about polar plumes from their 1989 rocket

    data.  I went a little farther: I’d just read Gene Parker’s seminal works on the solar wind and convinced myself

    that fitting a wind acceleration model to the intensity curves was just the ticket.  Of course, Parker-like models

    are basically hydrostatic at those altitudes, so I could’ve saved some work - but it was still fun.  I gritted my teeth

    when Art marked up my manuscript so that he was first author.  He was a good guy, but given that I still remember

     it, I think pushing for first was a mistake on his part -- one I try to avoid with my own students.

Polar Plume Anatomy: Results of a Coordinated Observation (1997)

    DeForest, Hoeksema, Gurman, Thompson, Plunkett, Howard, Harrison, & Hassler 1997, Sol. Phys. 175, 393.

    This is a summary paper of the first coordinated science campaign that SOHO executed.  We were in cruise phase

    on the way to L-1, and Rick Bogart (who is acknowledged) suggested that we ought to off-point SOHO to look at

    the South pole, since the MDI hi-res magnetograms would almost never be available there.  I was too naive to

    realize what a political minefield I was entering, and dove in to organize a big JOP and get some nice plume data.

    Miraculously, everything went Right and nobody’s instrument broke.  A lot of useful stuff came from that run.

Observation of Polar Plumes at High Solar Altitudes (2001)

    DeForest, Plunkett, & Andrews 2001, Astrophys. J. 546, 569.

    This came out of a followup to the 1997 paper -- just how high up do polar plumes go?  That turns out to be a very

    interesting question. Several groups were doing interesting, but conflicting and/or inconclusive, work on whether

    plumes make an imprint on the solar wind.  We put together a deep-exposure campaign with LASCO C-3 and

    showed that plumes extend at least 30Rs from the Sun.  Mike Andrews later left NRL, but was great to work with.

Solar Polar Plume Lifetime and Coronal Hole Expansion (2001)

    DeForest, Lamy, & Llebaria 2001, Astrophys. J. 560, 490.

    This came from an argument between Philippe Lamy and me over polar plume lifetime, back in 1998.  Hours, or

    weeks? Turns out both points of view were right, in a way.  In the meantime we managed to get an independent

    measure of the superradial expansion in the coronal hole, which agreed nicely with the white-light results. 

Observation of Quasi-periodic Compressive Waves in Solar Polar Plumes (1998)

    DeForest & Gurman 1998, Astrophys. J. 501, L217.

    We got a little lucky on this one - looking at the high-cadence EIT data for the JOP-39 results (Polar Plume Anatomy,

    up above), Joe Gurman and I both thought we saw some motion in the plumes.  I worked up a simple background

    subtraction, and cooked up a running-difference periodogram graphic -- and by gosh there were some interesting

    things in there!  I presented it at SPD 1997, still not sure what we were looking at.  We eventually convinced

    ourselves that the speeds wouldn’t be so uniform if they were chunks of material.  Leon Ofman may have priority on

    detecting coronal waves, using two-altitude measurements with UVCS - he knew what he was looking for, while this

    stuff took us by surprise.  It was a very exciting time to be at GSFC -- so much was going on all at once!

Slow Magnetosonic Waves in Coronal Plumes (1999)

    Ofman, Nakariakov, & DeForest 1998, Astrophys. J. 514, 441.

    Leon cooked up a very nice 1-D MHD model and simulated the polar plume wave data.  He was the one who

    showed that these really must be slow magnetosonic waves: nothing else behaves that way.  Both Leon and

    Valery are terrific guys to work with.  Lots of fun, very sharp.

High-Frequency Waves Detected in the Solar Atmosphere (2004)

    DeForest 2004, Astrophys. J. 617, 89.

    This got me pretty excited -- I got my hands on some very high speed FUV data that the TRACE team collected

    (to look at bright point dynamics) and drilled down to see if any propagating waves were to be found in them.

    I found a very faint ridge-like spectrum in the k-ω diagram.  Since few things make sloped ridges like that, I wrote

    it up -- but there really hasn’t been another instrument looking in that frequency range, and this measurement is

    pretty far down under the systematic noise floor.  Several folks (including Mats Carlsson) have said that TRACE

    shouldn’t be able to see anything in this band, casting further doubt on the result.  If/when the RAISE rocket gets

    good data, we should be able to corroborate or falsify the result, and get this off my scientific “plate”.

Are “EIT Waves” Fast-Mode MHD Waves? (2007)

    Wills-Davey, DeForest, & Stenflo 2007, Astrophys. J. 664, 556.

    When Meredith was working at SwRI she spent a long time developing the concept of nonlinear MHD waves

    (perhaps some form of solitary wave) to explain EIT waves (shock fronts analogous to, but different from, Moreton

    waves).  We worked on this together for a while - mostly with me kibitzing and Meredith doing the heavy lifting.  It’s

    a nice piece of work, and probably the best explanation I’ve yet seen for the EIT wave phenomenon.

Wave motion on the Sun

Fluxon modeling of Low-Beta Plasmas (2007)

    DeForest, & Kankelborg 2007, JASTP 69, 116.

    This is the description paper for fluxon modeling, a concept that Charles and I arrived at independently around the

    turn of the millennium.  We merged our efforts, and by 2004 we had a working code that could solve toy problems.

    We submitted this paper in Summer 2005, and it took over two years to be published!  You can find out about

    current fluxon work at the FLUX wiki.

Reconnectionless CME Eruption: Putting the Aly-Sturrock Conjecture to Rest (2009)

    Rachmeler, DeForest, & Kankelborg 2009, Astrophys. J. 693, 1431.

    This paper was a long time in coming, partly because we had to work hard to vet the fluxon model, and partly

    because student papers always take a little extra time.  It was Laurel Rachmeler’s first paper.  She did a terrific job

    of demonstrating a new type of ideal MHD instability, driving a stake through the heart of the Aly-Sturrock

    Conjecture (which was, for a long time, a strong argument against a magnetic driver for CMEs).

MHD modeling and plasma stability

Solar Magnetic Tracking I: Software Comparison and Recommended Practices (2007)

    DeForest, Hagenaar, Lamb, Parnell, & Welsch 2007, Astrophys. J. 666, 576.

    This was the inaugural paper of the Magnetic Tracking Workshop, which first met in 2004 November to reconcile

    results from several different tracking/vision codes applied to magnetograph data.  We found that results are

    strongly dependent on assumptions that were being made by individual authors but not described in papers,

    and established a cross-comparison strategy to guide future tracking work.

Solar Magnetic Tracking II: The Apparent Unipolar Origin of Quiet-Sun Flux (2008)

    Lamb, DeForest, Hagenaar, Parnell & Welsch 2008, Astrophys. J. 674, 520.

    This was the first “real” science result to come out of the tracking workshops -- pretty strong evidence that the

    solar dynamo is dominated by as-yet-unresolved scales.  The analysis technique came directly out of heated

    debate in the 2004 meeting and was the subject of our next meeting as well.  The write-up was Derek’s first

    student paper.  He did us proud.  Now if he would just submit the effing manuscript for Paper III...

Quiet-Sun: A Comparison of SOT and MDI fluxes (2008)

    Parnell, DeForest, Hagenaar, Lamb, & Welsch 2008, ASP Conf Ser. 397, 31.

    This was the first direct intercalibration of MDI and Hinode/SOT (NFI).  It came out of calibration work in MTW-3, as

    we tried to get to the bottom of the effect Derek wrote about (above).

Generation, Evolution, and Destruction of Solar Magnetic Fields (2009)

    Keil, Rimmele, & DeForest 2010, Astro2010 White Papers, #153.

    This was really an advocacy paper on why the ATST is important to solar physics, but it turned into a nifty little

    review of the state of dynamo physics and magnetic measurement techniques.

A Power-Law Distribution of Solar Magnetic Fields over more than Five Decades in Flux (2009)

    Parnell, DeForest, Hagenaar, Johnston, Lamb, & Welsch 2009, Astrophys. J. 698, 75.

    This is my favorite result to come out of the magnetic tracking workshops so far, even though it is a serendipitous

    side result that is not part of the main “SMT” series of papers.  Clare took cleaned, conditioned data from each of

    the workshops and made a simple scaled-to-the-whole-sun probability distribution function for them.  Remarkably,

    it showed a power law over the entire range of scales we observe, with no break in the exponent -- food for

    thought indeed, as it implies that a single mechanism dominates both the smallest and largest observable scales,

    belying the notion of  a two-dynamo Sun. 

Magnetic Tracking and the Solar Dynamo

Solar Wind Imaging (“Heliospheric Imaging” and outer coronal imaging)

Observations of Detailed Structure in the Solar Wind at 1 AU with STEREO/HI-2 (2011)

    DeForest, Howard & Tappin, Astrophys. J. 783, 103.

    This is our first report on the successful extraction of quantitative solar wind feature brightnesses from the HI-2 data.

    It arose from a discussion in Fall 2010 between Tim Howard and myself -- we had been funded to study how CME

    onset models affected modeled CMEs in interplanetary space, and I was shocked to discover that existing data

    weren’t then capable of constraining our models.  We spent a couple of months cracking that nut, and the new data

    opened new worlds of understanding of the solar wind.

Inner Heliospheric Flux Rope Evolution via Imaging of Coronal Mass Ejections (2012)

    Howard & DeForest 2012, Astrophys. J. 746, 64.

    Our initial paper reported on observation of interesting features at high elongation angles; this is the first paper to

    unify the full SECCHI field of view for morphological tracking of a CME from the Sun to the Earth.  We demonstrated

    that the pre-CME cavity in the corona can be preserved intact (though distorted) as a magnetic cloud at 1 A.U.

Disconnecting Solar Magnetic Flux (2012)

    DeForest, Howard & McComas, Astrophys. J. 745, 36.

    One of the first things we saw in the reduced heliospheric data was a peculiar “V” shaped feature zooming outward

    around 1 A.U. in the HI-2 data.  We traced it back to the Sun, working backward in time through the data archive,

    and found that it was newly disconnected magnetic flux.  We used kinematic effects to measure the amount of

    magnetic flux in the feature, estimated the disconnection rate of IMF from the Sun from this mechanism, and

    (as a side note but perhaps equally importantly) demonstrated that driving heliospheric features outward from the

    Sun doesn’t affect their speed very much -- only their mass accumulation rate.

The Thomson Surface series I: Reality & Myth (2012); II: Polarization (2013); III: Tracking Features in 3D (2013)

    Howard & DeForest, Astrophys. J. 752, 130;

    DeForest, Howard & Tappin, Astrophys. J. 765, 44;

    Howard, Tappin, Odstrcil & DeForest, Astrophys. J. 765, 45

    When we started diving into the mass calculation for “Disconnecting Solar Magnetic Flux” (above), I was surprised

    to learn just how disorganized the literature was on Thomson imaging in general -- also to learn just how many

    misconceptions seemed to have crept into the literature and popular consciousness.  We reworked the basic

    theory of detection and demonstrated something that should have been obvious all along -- heliospheric imagers

    are really quite good at detecting features over a huge range of solar angles.  During the development of the initial

    paper, it became clear that we needed a trilogy, to cover polarization and its application to CMEs.

Tracking Coronal Features from the Low Corona to Earth: A Quantitative Analysis of the 2008 Dec 12 CME (2013)

    DeForest, Howard & McComas, Astrophys. J. 769, 43

    This is the paper for which we started the whole heliospheric analysis project, connecting the first geoeffective

    CME of the STEREO era with its origins on the Sun.  We nearly broke this paper into two, because the EUV

    analysis of the pre-event structure was so complex and surprising.  We expand a bit on the fundamental result

    of Howard & DeForest 2012 (up above) and discuss interpretation of the different “zones” that are detectable in situ.

Turbulence in the Solar Wind Measured with Comet Tail Test Particles (2015)

    DeForest, Matthaeus, Howard & Rice, Astrophys. J. 812, 108

    This is a follow-up to one of the earliest observations made with STEREO/HI-1: a beautiful movie of the highly

    unusual comet Encke, taken at the beginning of the mission (2007).  Encke’s ion tail is very unusual -- it is not

    nearly as “feathery” as many other comets’ tails, which means that you can treat it as a stream of test particles

    following the solar wind.  The movie itself is very evocative of turbulence.  We tracked over 200 features in the tail

    across the field of view, and treated them as test particles in the solar wind flow, to analyze the turbulent profile

    there.  As of 2017, the result is still not fully understood.  (About the same time, Nour-Eddine Raouafi did some

    analysis on a similar comet and demonstrated that the weird tail is probably a reflection of extensive heating over

    time: all the really light ions have probably already evaporated.)

The Feasibility of Heliospheric Imaging from Near Earth (2015)

    DeForest & Howard, Astrophys. J. 804, 126

    We’d been taking a lot of flak for advocating that heliospheric imaging is possible from LEO -- after all, SMEI

    suffered from some background brightness effects.  To demonstrate one can overcome them, Tim Howard

    degraded a bunch of STEREO/HI-2 images with simulations of worst-case scenarios, and I reconstructed the

    original images.  Worked like a champ.

The Utility of Polarized Heliospheric Imaging for Space Weather Prediction (2016)

    DeForest, Howard, Webb, & Davies, Sp. Wx. 14, 32

    This was a discussion of how to apply the techniques of solar wind imaging to track space weather effects across

    the inner solar system. It was a ton of fun to develop: weather prediction operations have a completely different set

    of requirements than scientific investigation.  This work is also a testament to solid peer review.  We took a lot of

    heat from three separate anonymous referees with conflicting viewpoints, but ultimately satisfied them all.  If they

    weren’t anonymous they would now be co-authors: they had some good insights that helped the paper.

Fading Coronal Structure and the Onset of Turbulence in the Young Solar Wind (2016)

    DeForest, Matthaeus, Viall, & Cranmer, Astrophys. J. 828, 66

    This paper was a long time in coming: as early as 2011 we’d noticed that the solar wind appears different than

    the corona, in the HI-1 images: it is not nearly as striated.  Back then, for some presentations, I did some work

    processing coronagraph images the same way we treat the solar wind data from HI-1 and HI-2, but never really

    followed through.  This spring, Dr. Viall expressed some interest, and the four of us dug into the result.  We were

    able to demonstrate that the difference is real, and is most likely due to the onset of hydrodynamic turbulence

    at the top of the corona.  Exciting times!

Scientific Programming (Perl Data Language)

Practical Magick with C, PDL, and PDL::PP (2015)

    DeForest & Glazebrook 2015..

    This is a document I wrote with input from Karl Glazebrook (original author of Perl Data Language) on how to write

    add-on routines for PDL.  PDL is my data-processing development environment of choice -- it has enabled much of

    the work I’ve published in the scientific literature.  PDL uses a metalanguage (PP) to compile quasi-C-language

    routines into vectorized operators -- and then incorporate them into PDL on the fly.  This is a comprehensive guide

    on how to do that.  It’s not “science”, but it has proved helpful to more than one aspiring scientific programmer.

Stereoscopic Spectroscopy for Efficient Spectral Imaging and Magnetography (2004)

    DeForest, Elmore, Bradford, Elrod, & Gilliam 2004, Astrophys. J. 616, 600.

    Although this is not well cited, it is a paper of which I am quite proud:  an introduction to the idea of stereoscopic

    spectroscopy to measure Doppler shifts.  This came out of a discussion a couple of years earlier, in which Charles

    Kankelborg (who was visiting SwRI at the time) discussed his concept for MOSES - an EUV sounding rocket that

    would try to separate the He II and Si XI lines near 30.4nm in the EUV.  I had a flash intuition that you could do

    better than line separation using spatial derivatives, and it turned out to work.  This paper outlines the basic theory

    and describes the first magnetic measurements made this way, at the Dunn Solar Telescope (ab)using the existing

    ASP instrumentation that David Elmore had built.  SHAZAM (used in 2009) was built on this concept.