On the Vitality, or Lack Thereof, in Heliospheric and Coronal Physics

Heliospheric physics is the study of all phenomena in the solar wind, which carves out the heliosphere from the local interstellar medium. Coronal physics is the study of all phenomena in the solar corona, which creates the supersonic wind and all disturbances and variations contained therein. The vitality of heliospheric and coronal physics is measured in two different ways: First, is there conventional vitality, are important observations being made, comprehensive and insightful data analyses occurring, and are the data being successfully explained using numerical models that are based upon known physical processes? Second, is there what I refer to as enhanced vitality, is there new important knowledge being discovered, are paradigm shifts occurring, is the discipline still in search of more complete understandings and not satisfied that all important governing physical processes have been identified and simply need to be applied? By any reasonable standard both heliospheric and coronal physics have achieved conventional vitality. The subject of this article is whether heliospheric and coronal physics have also achieved enhanced vitality. I have been a participant in heliospheric and coronal physics since 1967, which is only 5 years after what can be considered the founding of heliospheric and coronal physics, the confirmation that the solar wind is a supersonic outflow. The assessment of whether heliospheric and coronal physics have achieved enhanced vitality will be based upon the experiences I have had during my 55‐year career.


Perspectives of Earth and Space Scientists
FISK 10.1029/2022CN000192 2 of 8 is a measure of a field that is exciting, relevant, and worth supporting, and the absence of such discoveries is an indication of a field that is atrophying.
It is important to note for the discussion that follows that the researchers who are seeking paradigm shifts are different from and following a different path from the researchers who are pursuing conventional vitality.The researchers who are pursuing conventional vitality are attempting to explain the observed data using known physical processes.The researchers who are seeking paradigm shifts are searching for an observation that is a surprise and is not explained by the researchers pursuing conventional vitality.The researchers pursuing paradigm shifts then develop an explanation for the observation and realize that the explanation has implications for processes in other regions of space, implications that are pursued as far as they can be.The implications may be testable, in which case the new processes are validated.Even if they are not testable, they may have profound implications for processes in other regions of space that cannot be observed directly.So long as the researchers pursing conventional vitality accept the new processes as valid or at least require that they always be taken into account, a paradigm shift will occur.Clearly, in the community of researchers pursuing conventional vitality, the observer is the most important.He or she has generated and analyzed the data and explained or commissioned an explanation using known physical processes.For the pursuit of paradigm shifts it is the theoretician, who has the imagination and broad perspective to recognize that processes that occur in one region of space can reveal processes occurring in other regions and result in paradigm shifts.
Heliospheric and coronal physics, as scientific disciplines, began in 1962, when Mariner 2, en route to Venus, confirmed Gene Parker's prediction (Parker, 1958) that the solar atmosphere expands supersonically in a continuous outflow.We thus have available a 60-year history to examine for whether enhanced vitality, the search for new discoveries and paradigm shifts, was and continues to be achieved.Inherent in this examination of enhanced vitality is an examination of the willingness of the community of researchers in heliospheric and coronal physics to embrace change.The pursuit of conventional vitality relies on there being no change in the basic physical processes.The pursuit of enhanced vitality relies on the willingness of the researchers who are pursing conventional vitality to accept change.
In this examination of the willingness of the community of researchers particularly in heliospheric physics to accept change, we should take note that this community was first established when NASA was receiving extraordinary financial support for the Apollo program; at the peak of its funding for Apollo in 1965, NASA commanded 4% of the entire Federal budget.While most of this funding went to support Apollo, there was ample funding to establish the space science program of NASA.The Goddard Space Flight Center, NASA's primary space science center, was established in 1959.The Jet Propulsion Laboratory, an Army laboratory, which had built Explorer 1, was assigned to NASA in late 1958.Universities were encouraged to establish research groups, even being lured by offers to build buildings on their campuses.Grant money was plentiful, and a national community of space scientists, and for our purposes, a community of heliospheric physicists, was built.The community consisted of scientists who were trained in other fields and were attracted by the opportunities in space science, and most important by their students whose career timing was such that they completed their education while the community was being built and they found permanent positions at NASA Centers, other government laboratories and universities.NASA's efforts at community building ended in 1972, when Apollo ended.NASA's own workforce was reduced from ∼30,000 to ∼20,000.All centers underwent a Reduction in Force.
Thus, when we consider the attitudes of the community of heliospheric physicists we need to remember that the dominant scientists, experimentalists and theoreticians, for decades have been the scientists who were part of that original community build by NASA prior to 1972.The scientists in the original community were young, and in some cases just past their PhDs, and they have had long careers of leadership in heliospheric physics.So, when we ask about the fate of enhanced vitality in heliospheric physics, we need to ask whether this aging community has been willing to accept change.

My Assessment of Enhanced Vitality in Heliospheric and Coronal Physics
I was part of the original community of heliospheric physicists, barely.I began serious research on energetic particle propagation in the solar wind in 1967, 5 years after the solar wind was confirmed, and I published my first paper in 1968 (Fisk & Axford, 1968) on a model of solar flare propagation including adiabatic deceleration in the solar wind.I received my Ph.D. in 1969 and obtained my first permanent position at the Goddard Space Flight Center in 1971, just before NASA's efforts at community building ended.I published my most recent paper in March of 2022 on particle acceleration in the heliosheath and the interaction with the local interstellar medium (Fisk & Gloeckler, 2022).I have thus been a witness to and a participant in heliospheric and coronal physics, essentially from its inception to the present.Moreover, it has always been the hallmark of all the research I consider important that I have sought new discoveries and pursued paradigm shifts.I also have an interesting perspective from having paused my research career from 1983 to 1993 to undertake some challenging administrative positions, including from 1987 to 1993 when I served as NASA Associate Administrator for Space Science and Applications, a position that provided me with a broad perspective on the vitality and approach in other science disciplines.When I returned to research in 1993, I could apply this perspective to heliospheric and coronal physics.
In this section, I offer, based upon my 55-year participation in and witness of the evolution of heliospheric and coronal physics, always seeking discoveries, new processes, and paradigm shifts, my assessment of whether heliospheric and coronal physics have achieved and maintained enhanced vitality.I conclude that in recent decades, heliospheric and coronal physicists are neither accepting nor pursuing the changes that result from the pursuit of enhanced vitality.I consider this a serious threat to the future of heliospheric and coronal physics and suggest in Concluding Remarks some remedies we should pursue.
There are three separate intervals in my career: The beginning up to 1983.The interval when I had major administrative duties, from 1983 to 1993.The interval when I returned to my research career, from 1993 to the present.I will consider each interval and assess the enhanced vitality that did or did not occur.

The Beginning Through 1983
Those of us who had the good fortune of obtaining permanent positions prior to 1972 joined a field in which relatively little was understood or agreed upon, but new observations were being made that had the potential to reveal the processes and conditions in the heliosphere.The pursuit of enhanced vitality was occurring naturally in this period, simply because we knew so little.However, there was one observation in particular, to which we could apply our full procedure, explaining the observation and using this explanation to reveal processes and conditions in other regions of the heliosphere, and achieve a paradigm shift.
In the early 1970s, a new and unusual component of the energetic particle population was discovered.Hovestadt et al. (1973) andMcDonald et al. (1974) discovered that cosmic rays at energies of a few MeV per nucleon were greatly enhanced in oxygen, but not in carbon, and also had some extra helium (Garcia-Munoz et al., 1973); this new component was subsequently labeled anomalous cosmic rays, or ACRs.Initially McDonald et al. very much wanted the ACRs to be an unusual component of galactic cosmic rays (GCRs), for which there would be interesting implications for astrophysics.Fisk et al. (1974) pointed out that the composition is the same as interstellar neutral gas, which flows into the heliosphere, where it is ionized by charge exchange and photoionization, picked up by the solar wind, and convected into the outer heliosphere.Here the implications are for the heliosphere, since for this explanation to be valid, there must be an acceleration process in the outer heliosphere that raises the particle energies from 1 keV per nucleon, the energy at which they are first picked up, to ∼10 MeV per nucleon, the energy at which they are observed, following their propagation back into the inner heliosphere.The unique feature of the explanation of Fisk et al. (1974) is the ACRs must be singly charged; there is only time to ionize them once.With a single charge the ACRs are high-rigidity particles and can propagate back into the inner solar system to be observed.Moreover, it provided a test of the Fisk et al. (1974) ACR explanation, which by various means the single charge was confirmed.This was a true paradigm shift.Our understanding of the solar wind changed from a relatively benign medium, which impeded the inward diffusion of GCRs, to a medium that was capable of accelerating particles by four-orders of magnitude to cosmic ray energies.
In the late 1970s, heliospheric and coronal physics was the recipient of a paradigm shift generated by another field.Axford et al. (1977); Bell (1978); Blandford and Ostriker (1978), and Krymsky (1977) developed what has become known as diffusive shock acceleration for the purpose of accelerating GCRs at supernovae shocks.The method is very simple.Particles gain energy at a shock by repeatedly passing back and forth across the shock front, and each time they are compressed between the upstream and downstream magnetic irregularities, which are moving at different speeds, and the particles are accelerated.The presentation of Axford et al. (1977) was particularly straightforward, with simple formulae relating the spectral index of the accelerated particles to the 10.1029/2022CN000192 4 of 8 compression ratio of the shock.Diffusive shock acceleration was obviously directly applicable to shocks in the heliosphere and the corona, and it has been for decades now the preferred mechanism for accelerating energetic particles.

The Period From 1983 to 1993
By 1983, my focus had drifted away from research into administrative positions with increasing responsibility.First, as the Vice President of the University of New Hampshire (UNH), where I could still marginally participate in research in the group I had established at UNH.Then, from 1987 to 1993, as NASA Associate Administrator for Space Science and Applications, when no personal research was possible.
My sense of research in heliospheric and coronal physics in this period, of which I was now only an observer, was that there was no particular desire or perceived need to find new processes or to seek paradigm shifts.Quite the opposite, during this period, major numerical modeling groups with professional programmers emerged, attempting to produce comprehensive models of phenomena in the heliosphere and the corona, all based upon agreed physical processes and circumstances.There is an obvious danger in this approach which was not realized then or now.If the dominant research effort is the development of comprehensive and expensive numerical models, the means by which you explain, or illustrate, or even predict heliospheric and coronal phenomena, and these models are built on known physical processes and circumstances, there is neither interest in nor tolerance for the discovery of processes or circumstances that the models did not include, and obviously this can be an impediment to the pursuit of enhanced vitality.The only way that the development of such models could contribute to the pursuit of enhanced vitality is if the model is tested against observations, and if found wanting, is used to discover what processes are missing.However, that rarely, if ever, occurs.

The Period From 1993 to the Present
In 1993 I ended my administrative career at NASA and joined the faculty at the University of Michigan with the full intent to restart and resume my research career.I had no desire, or skill for that matter, to create a new numerical modeling group.I also could not accept the premise on which numerical models are built, that all the governing physical processes are known.Rather, I fundamentally believed that there have been or will be observations that contain surprises, which are unexplained, and which if explained and the implications of the explanation are fully exploited, will result in game changes in our understanding of the heliosphere and corona.In other words, I was determined to return to my search for new processes, new knowledge and to seek paradigm shifts.
The first such opportunity to do so came in 1995, when Ulysses, over the south pole of the Sun, observed 26-day increases in the intensity of a few hundred keV electrons and 0.5 MeV protons, which gave every evidence of having originated from corotating interaction regions within 30° of the solar equatorial plane (McKibben et al., 1995;Simnett et al., 1995).This is an unexpected and unexplained result since low-energy electrons in particular follow field lines, and the Parker spiral heliospheric magnetic field, confined to cones of constant latitude, provides no means for electrons to be transported from low to high heliographic latitudes.
The explanation for me was straightforward.The year 1995 was solar minimum, and the heliospheric magnetic field throughout much of the heliosphere originates from the polar coronal holes, which are offset from the solar rotation axis.Coronal holes are observed to rigidly rotate at the equatorial rotation rate of the Sun.The Sun differentially rotates, slower at the poles than at the equator.There is a non-radial expansion of the magnetic field from the polar coronal hole.When you put all this together (Fisk, 1996), you find that the location from which the heliospheric magnetic field is convected radially outward with the solar wind moves dramatically in latitude and the field in the heliosphere that results provides a direct magnetic connection from low to high heliographic latitudes.
I also realized that the motions in latitude at the Sun of the heliospheric magnetic field would be restricted by another important discovery of the Ulysses mission, perhaps its most important discovery, the component of the solar magnetic field that opens into and forms the magnetic field in the heliosphere, the so-called open magnetic flux of the Sun, is highly organized, two hemispheres with opposite magnetic polarity, separated by a single large-scale current sheet (Balogh et al., 1995) that lies near the solar equator at solar minimum and rotates through the solar poles at solar maximum, thereby accomplishing the magnetic field reversal of the Sun as observed in the heliosphere.Because of this organization, the open magnetic flux of the Sun is difficult to eliminate.There must be reconnection between oppositely directed open magnetic fields, which can only occur at the current sheet, and to eliminate the open flux, the reconnection must occur within the Alfven point, creating a U-shaped loop that is convected outward with the solar wind.There is no evidence that this elimination process occurs at all, and certainly not on a large scale, with the result that the open magnetic flux of the Sun has an underlying constant component.Thus, at solar minimum the systematic motions in latitude driven by the geometry and differential rotation of the polar corona holes cannot result in motions across or ending at the current sheet and must close with motions in longitude.The proposed process by which these longitudinal motions occur is reconnection between open field lines and coronal loops, and systematic displacement of the open field lines (Fisk & Schwadron, 2001).At solar minimum, the open magnetic flux of the Sun, the heliospheric magnetic field, is undergoing a closed global circulation.
The implications of the motions of open magnetic flux at the Sun and its consequences for the heliospheric magnetic field were readily accepted by the heliospheric research community, since after all the motions provide a simple explanation for the Ulysses observation of low-energy particles at high latitudes.The more significant implications of the motions of open flux were for coronal and solar physics.The research group that I established at Michigan, which at the time included Nathan Schwadron and Thomas Zurbuchen, developed a holistic model for the behavior of the solar magnetic field and the acceleration of the solar wind.The model was based on three basic concepts: there is emerging magnetic flux on the Sun in the form of small coronal loops; the Sun differentially rotates; and the open magnetic flux is organized into two regions separated by a single current sheet.From these basic concepts, it is possible to develop a series of interlocking processes for the distribution of open flux including into closed field regions; on where coronal holes are likely to form; on the field reversal of the solar magnetic field, including implications for the solar dynamo; on the heating and acceleration of the solar wind, etc.There are aspects of this holistic model that have found their way into the models of coronal physicists.There is no aspect of the model that received serious consideration by solar physicists.In no case, was the holistic nature and completeness of the model given serious consideration.It is a failing of our disciplines that we focus our research on small details, without regard to the context, or the larger implications of what we are observing and attempting to explain.And when someone like me and my research group shows that the accepted big picture, the context for the research, is wrong, inconsistent with significant observations, there is no mechanism for even encouraging the required rethinking.Every aspect of our research enterprise, from funding to peer-acceptance, rewards incremental progress, even down the wrong path.In this context, a consensus for and pursuit of major changes seems unlikely.
My second opportunity to introduce new processes and potential paradigm shifts came when Voyager 1 crossed the termination shock and did not observe that the ACRs were accelerated at the termination shock.Rather, immediately downstream from the termination shock, Voyager 1 observed that the spectrum of particles with energies less than a few MeV/nucleon is a power-law with a specific spectral index, a differential intensity spectrum in energy, with spectral index of −1.5, or if expressed as a distribution function in velocity, the spectral index is −5 (Decker et al., 2006;Gloeckler et al., 2008).Remarkably, when Voyager 2 crossed the termination shock 4 years later, the exact same spectrum was observed.These Voyager observations caused George Gloeckler to go back and look at the spectrum of suprathermal tails observed by Ulysses and ACE, and he found, with a careful transformation into the frame of the solar wind, that there were −5 spectra everywhere: particularly downstream from shocks, but also in regions where there were no shocks.Everywhere there is a region where particles are being accelerated locally, the spectra of the suprathermal tails have a spectral index of −5.This was then an ideal case for pursuing a paradigm change.There was no acceleration theory known at that time that automatically yields a single common spectral shape for the tails on the distribution function, a power-law spectrum with spectral index of −5.Diffusive shock acceleration yields power-law spectra, but with variable spectral indices depending on the compression ratio at the shock.Besides, the −5 spectra are observed with no shock nearby.Stochastic acceleration is more likely to yield exponential spectra.So, guided by the need to explain the unique spectral shape, I developed a new acceleration mechanism, a pump acceleration.Pump acceleration will occur in a constant volume, thermally isolated system (no net inflow or outflow of particles), in which both the thermal and energetic particle populations are undergoing adiabatic compressions and expansions.These are the conditions in subsonic regions downstream from shocks, where the −5 spectra are commonly observed.In a compression region, particles gain energy and in surrounding expansion regions they FISK 10.1029/2022CN000192 6 of 8 loss energy, which at higher energies creates spatial gradients between the compression and the expansion region.Particles can escape from the compression region by diffusion, before the compression region turns into an expansion region, with the result that the particles are pumped up in energy, and the spectrum of the accelerated particles has a spectral index of −5.The concept was simple, but the math to describe it was challenging, because the standard approach in stochastic acceleration, which is based on a mean and variable distribution function, is inappropriate in a situation in which a particle interacts with the collective behavior of all other particles.The best description of the observations of −5 spectra and the math required to derive the equation that describes the time evolution of the spectrum of particles accelerated by pump acceleration is in Fisk and Gloeckler (2014).
Unfortunately, as with the reluctance of solar physicists to accept that there are new processes, the pump acceleration mechanism has not been accepted or applied by heliospheric and coronal physicists.There appear to be two reasons for this.First, it was rejected by older theoreticians, who could not understand that it is possible to accelerate particles by interacting with the collective motions of all other particles.Second, the heliospheric and coronal physics communities have so embraced diffusive shock acceleration as the acceleration mechanism of choice, that serious consideration of another acceleration mechanism was resisted.This is particularly true of acceleration in regions that we do not observe directly, such as CMEs.It never occurs to a coronal physicist that the pump acceleration mechanism in the interior of the CME might be a better choice than external diffusive shock acceleration.In the case of acceleration of ACRs in the heliosheath, Fisk and Gloeckler (2022) recently demonstrated that pump acceleration is the mechanism by which the ACRs are accelerated, but many researchers have persisted with their expectation that diffusive shock acceleration, in this case at the termination shock, is the only possible acceleration mechanism.
We pride ourselves in heliospheric physics in doing research and developing concepts that are applicable to astrophysics.The pump acceleration mechanism is one such concept, as is demonstrated by Fisk and Gloeckler (2012), who showed that relativistic pump acceleration can explain the GCR spectrum, both the slope and the so-called knee, and some specific variations in the He/H ratio.Pump acceleration applied to the galaxy as a whole explains a puzzle in GCR acceleration, how can particles with gyro-radii larger than the scale sizes of supersonic shocks be accelerated.Unfortunately, perhaps because pump acceleration has not been accepted in the heliosphere, it has also not received any consideration in astrophysics.
My final example of the difficulties in pursuing enhanced vitality in heliospheric physics is Voyager in the heliosheath.The Principal Investigators (PIs) on the Voyagers were chosen in the mid 1970s.Some have died and been replaced by somewhat younger investigators, but most are the original investigators now in their 80s.When Voyager 1 crossed the termination shock in 2004, the Voyager PIs had every expectation that it would be just be another plasma like the many they had studied in their careers.Downstream of the termination shock, the heliosheath is a subsonic region, which should have constant particle pressure, and in a normal plasma, with a single equation of state, constant density.The density was not measured on Voyager 1, the plasma detector had failed at Saturn.However, based on Voyager 2 plasma density measurements, the constant density was expected to be low.So, when Voyager 1 encountered a boundary where the energetic particles accelerated in the heliosheath escaped, and Gurnett et al. (2013) were able to measure plasma waves, which are a direct measurement of plasma density, and found a much higher density, comparable to the expected density in the interstellar medium, the Voyager PIs enthusiastically claimed they had passed into interstellar space.In doing so, the Voyager PIs stated that the heliosheath is a rather uninteresting place, just another conventional plasma.
Fisk and Gloeckler viewed this very differently.They argued that the Voyager PIs' interpretation of the heliosheath and the heliopause was not based on physical reality, nor consistent with many observations.Thus, this was an unexplained observation, and as with other unexplained observations, it has the potential to yield new processes, reveal new conditions, and a paradigm shift.Fisk and Gloeckler (2014) built a model based on the principle that the pickup ions and ACRs are a separate gas from the thermal solar wind, and have the dominate pressure in the heliosheath.With this principle, they demonstrated that Gurnett et al. were simply observing compressed solar wind, and the heliopause declared by the Voyager PIs is nothing more than an internal surface separating magnetic field lines that close in the heliosheath from magnetic field lines that connect to and cross the actual heliopause, located well beyond the heliopause of the Voyager PIs.
However, the Voyager PIs had spoken, they had crossed the heliopause and were now in interstellar space, and it has become part of the public lore that Voyager 1 is the first human-made object to leave the solar system.The 10.1029/2022CN000192 7 of 8 aspirations of Fisk and Gloeckler to show that the heliosheath is not the dull place of the Voyager PIs, but rather a plasma unlike any we have been able to study, were dashed.
There is a recent paper by Dialynas et al. (2021) reanalyzing Voyager 1 data, which Fisk and Gloeckler (2022) show provides confirmation of every aspect of the Fisk and Gloeckler (2014) model.Will minds be changed, unlikely.But they should be.

Concluding Remarks
The three examples cited in the previous section of my attempts to introduce enhanced vitality into heliospheric and coronal physics, find new processes, achieve paradigm shifts, all failed because the changes I proposed were not accepted by the community of heliospheric and coronal physicists who were pursuing conventional vitality.No new process that I proposed was found to be physically incorrect or inconsistent with observations.They were simply judged not to be needed.In the first example, the model for the solar magnetic field and the acceleration of the solar wind was the most comprehensive and the most radical.And required reconsideration of some well accepted processes.The solar physicists, in particular, relying on their numerical models and remote observations, seemed unwilling to even entertain that they could learn something from in situ observations of the open magnetic flux of the Sun in the heliosphere.Even coronal physicists were unwilling to consider radical new concepts.In the second example, the community of heliospheric and coronal physicists could not imagine that they needed a new mechanism to accelerate energetic particles beyond diffusive shock acceleration that has served them well since the late 1970s, and aging theoreticians could not imagine that a new acceleration mechanism, pump acceleration, was even possible.In the third example, my efforts to show that the heliosheath was a most interesting and unusual plasma were defeated by the aging Voyager PIs, who could not imagine that the heliosheath was anything more than the conventional plasmas they had studied countless times during their long careers.
I consider that this complacency that all processes are known and simply need to be applied, no new discoveries, no new information is necessary, will seriously limit the respect that is given to heliospheric and coronal physics.We will find ourselves relegated to the backwater of NASA's science divisions.Astrophysics, Planetary Science, even Earth Science pride themselves on the discoveries they are making.
The question is what can be done to change the mindset of the community of heliospheric and coronal physicists to seek and accept change.One simple action is to recognize that the original heliospheric community established by NASA before 1972, whose members have dominated the field for decades, are leaving the field, sometimes by death, and there is an opportunity to reexamine and challenge the research that has or has not been done in this period of stagnation in heliospheric physics.Even more important, the agencies that fund our research, NASA and the NSF, should actively encourage proposals for research that seeks change, and find a way to overcome the resistance of review panels whose members are likely to be of the mindset that change is not necessary.We also need to have a healthy skepticism about the validity of the numerical models that are developed to explain heliospheric and coronal processes, all of which are based upon what the developer considers to be known physical processes.We need to ask whether the models really explain and are consistent in detail with observations.Frankly, it is more interesting to those who seek change to learn of the models' failures rather than their successes, since failures can reveal processes that the model did not include.
I have enjoyed my 55-year career in heliospheric and coronal physics.I will admit to being disappointed by my inability to bring change, and I am particularly disappointed that the changes I consider essential for developing accurate models for important phenomena such as space weather have not been adopted.Nonetheless, I remain optimistic that truth will be discovered, that new generations will seek the truth; they will not be satisfied with the conventional wisdom, nor the established model.They will insist that we develop more complete understandings.We will again be a field in which discoveries are made, paradigm shifts are occurring.