J. Randolph Jokipii
September 10, 1939 - January 7, 2022

Professor Randy Jokipii was a pioneer in the physics of cosmic ray transport in the solar system. He discovered the 22-year cosmic ray cycle and established paradigms for the modulation of cosmic rays in the heliosphere. He also made important contributions to our understanding of the physics of particle acceleration at astrophysical shock waves.

Jokipii CV (PDF)

Our long-time friend and colleague Jack Randolph “Randy” Jokipii died on January 7, 2022. He was 82. He leaves us with many fond memories of his passion for science and education, food, and world travels. He was a major presence at the Lunar and Planetary Laboratory (LPL), playing a large role in the success of the department, educating and mentoring many students, postdocs, faculty and staff. He was often roaming the halls of the Kuiper building and enjoyed chatting about a wide variety of topics – always the great storyteller. He loved to travel and to tell of his adventures. He had over two million frequent flyer miles, and once circumnavigated the globe. He met Indira Gandhi on a trip to India, and proudly displayed a picture of the encounter in his office. Those that had the opportunity to work with him closely also remember fondly the numerous, deep, sometimes frustrating, but always productive conversations on science topics on the whiteboard in his office. Randy will be remembered for his devotion to intellectual honesty and always standing by his principles. He was a role model for younger scientists with a strong commitment to teaching physics.

Randy was born in Ironwood MI, on Sep 10, 1939. As a youth, he had a passion for astronomy, and built his own telescope, including grinding the mirror used for it. He was also proud to mention that he delivered the local newspaper in the community. He was also on the high-school ski team. He enjoyed returning to Ironwood to attend high-school reunions, including the most-recent one, his 63rd. Randy attended the University of Michigan where he earned a BSc in Physics in 1961. He attended graduate school at the California Institute of Technology, earning his PhD in Physics in 1965, working with Leverett Davis, Jr., who was a pioneer of the study of the interplanetary magnetic fields and their interaction with plasmas, such as the solar wind. During the summer of 1964, Randy worked for the Rand Corporation, and published a paper on the distribution of gases in the protoplanetary nebula. It was then that he met his wife, Bonnie. Randy then went to the University of Chicago to work with Gene Parker as a postdoctoral research associate. In 1967, he was hired as an Assistant Professor at the University of Chicago. In 1969 he moved back to California to take a position as Assistant Professor of Theoretical Physics at Caltech. In 1974, he moved to the University of Arizona, where he was hired as Professor in LPL and in the very new Department of Planetary Sciences (PtyS), with a joint appointment in Astronomy, by the new LPL director, Charles P. “Chuck” Sonett.

Randy joined LPL/PtyS at a critical point in the history of LPL. Just before Randy was hired in 1974, founder Gerard Kuiper had relinquished the LPL directorship to Sonett, an experimental space physicist working at the time on lunar magnetism with the Apollo program. Although Kuiper had conceived of the new academic department added to LPL, he was not necessarily supportive of adding faculty to do space physics theory. Kuiper died at the end of 1973, but opposition to space theory research continued to be widespread in LPL. Randy played a critical role within a small group of unofficial advisors to Sonett on the execution of a novel concept for the time: turn the observational astronomy unit LPL into LPL/PtyS, a multidisciplinary research and teaching unit operating under the rubric of solar system exploration, but staffed with observers, experimentalists, and theorists from all relevant fields, meeting the highest professional standards. With the small group of inaugural PtyS faculty, Randy designed and taught one of the first PtyS core courses for graduate students, a semester of planetary physics focused on transport theory and plasma physics. His first PtyS PhD student was Guy Consolmagno, now Director of the Vatican Observatory.

In 1975, Randy began serving as associate department head. He continued in that capacity under LPL’s next director, Bill Hubbard, who took over in 1977. Randy was a steadfast defender of the pioneering concept of LPL/PtyS as a multidisciplinary research and teaching organization, during a time of great transition and considerable turmoil. Randy also led an effort to submit a "decision package" to the Arizona legislature to fund an interdisciplinary theory program to be shared by LPL, Astronomy, and Physics. The proposal succeeded and the Theoretical Astrophysics Program was established in 1985. In 1997, Randy was named a Regents Professor in the University of Arizona. In 2001, he was elected to the National Academy of Sciences. He retired from the university in 2015, becoming Professor Emeritus. He is a fellow of both the American Geophysical Union and American Physical Society.

Randy was a pioneer in the physics of cosmic ray transport. He was a theorist, at a time when spacecraft measurements of the solar wind and high-energy charged particles were first being made. Randy’s work on charged particle transport still reverberates through the literature today. He was quite young in 1966, when he wrote the now classic paper Cosmic-ray Propagation. I. Charged Particle in Random Magnetic Fields, where he introduced the quasi-linear theory of charged-particle transport in turbulent magnetic fields like those seen in space. He was the first to relate the power spectrum of magnetic fluctuations to the cosmic-ray diffusion coefficients, which is a key parameter to understand a wide variety of physical phenomena in space, such as cosmic-ray modulation in the heliosphere, particle acceleration by shock waves, and solar-energetic particle emissions. There is an entire industry of researchers in both space physics and astrophysics using this theory. Randy started it all.

Perhaps one of Randy’s most notable scientific accomplishments was the prediction of the 22-year cosmic ray cycle. With LPL colleagues Gene Levy and Bill Hubbard, Randy wrote a famous paper describing the importance of cosmic ray drift motions. Later, in 1981, he wrote a paper that provided the physical foundation for the cosmic-ray drift motions in the heliosphere, which rather resemble a convection pattern. He noted that the drift patterns change with the solar magnetic cycle, which flips its sign every 11 years – taking 22 years to return to the same polarity.

Randy was also a pioneer in the large-scale computer modeling of cosmic ray transport. His codes reproduced spacecraft observations and led to many insights. Randy did not merely accept the numerical results without having a deep physical understanding of them. His well-regarded transport codes initially used idealized simple geometries and later extended to more-realistic geometries in numerous studies with his long-time colleague József Kóta. Randy also pioneered research into the physics of charged particle acceleration at shocks, authoring many papers on this subject. He was the first to note that shocks that move across the magnetic field accelerate particles at a much higher rate compared to those that move obliquely to the magnetic field. This is still the current paradigm, with important implications for the production of high-energy particles at astrophysical shocks such as those from supernovae, and from the Sun. He wrote many papers on the origin of so-called “anomalous” cosmic rays showing how acceleration of ionized interstellar atoms at the solar-wind termination shock naturally explains the observations. Randy also contributed to our understanding of how low-energy particles are accelerated at shocks – something referred to as the injection problem – through his collaboration with Joe Giacalone, who he hired as a postdoc in 1993 and who later joined the LPL/PtyS faculty.

Randy always remained committed to working collaboratively with other faculty in the department on research topics outside of heliophysics. For instance, working with Bill Hubbard, Randy contributed to the wave-optical theory of intensity fluctuations observed during occultations of stars by planetary atmospheres. A version of the theory was successfully applied to a Pluto occultation observed from the MMT telescope in 2007.

Randy was preceded in death by his wife of more than 55 years, Bonnie, and his son Galen. He is survived by sons Eron and Kevin.

Joe Giacalone and Bill Hubbard, with help from József Kóta, K. C. Hsieh, Marcia Neugebauer, and Neil Sheeley

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I remember Randy fondly, as one who was so enthusiastic about everything regarding physics. One day he had gotten these new "Bernoulli disk" storage drives and wanted to explain to everyone how they used the physics we had just learned, to keep the drive head just above the rotating platter. And his delight of demonstrating the Froude number in the lab kitchen sink. He was one of my first LPL teachers, along with Hunten and Hubbard that year, and the advisor of my office mate Lance Williams. I remember when he was starting to explain diffusion to our class, that he sat back with a far-off look and told the story of how he used to gaze into the distance at the midwestern smokestacks and figure out why they spread out like parabolas. Then he would wake from his reverie and go to the board and show us why, equations. I got to see him again just a couple of times after returning to LPL a few years ago, and he looked exactly the same as ever. But nobody stops time. By Randy, you were one of a kind.

It is difficult to describe adequately Randy’s impact on me during my years at LPL—sometime role model, sometime advocate, sometime adversary, always a real colleague. I always respected his depth of expertise in Physics and his devotion to the field of Space Physics and to LPL.  I will truly miss him.

Randy will be greatly missed. I was Joe Giacalone’s graduate student in the mid-2000s, and Randy always made sure I got to meet and learn from people I never would have known otherwise. He also invited me to his $150 a plate dinners at the AGU meeting, which I was never ambitious enough to attend. He will be remembered fondly. 

I was Randy's postdoc in 2004-2005. I have a lot of fond memories of him. It is hard to select only some of them. I remember the invitation to Christmas dinner in his house and a tour around San Francisco with him.  Lunches once per week in town, with Randy and colleagues from the lab, trying different cuisines, and discussing almost every imaginable topic. I remember his teaching, I visited a couple of his lectures, just for fun, and it was an impressive experience.

I am grateful to him for his kindness, inspiring time in Tucson, and quotations of his words, that I still use. Randy knew how to catch the essence of things. 

Randy was an extraordinary man. You could see it at scientific conferences, where he was a rock star for everyone. People thought, that you are a lucky guy to be his postdoc, and they were exactly right. It was an honor and an amazing experience to do physics with him. 

I am really sad and deeply moved.

It was a real privilege to get to know you a little at NAS.

Rest in Peace.

I took an independent study course on space plasma with him in 2001. The course was prepared as a regular graduate course and was converted into independent study since there were not enough students. Nevertheless, he taught the course as scheduled. If I remember correctly, I was the only student in the end. I deeply appreciate his dedication to teaching and am very glad to coauthor two papers with him. RIP.

Randy was one of my early mentors. We met in Germany at a Max Planck Institute when I was doing a postdoc. On the strength of that he invited me to Caltech for 2 years. We always had a good relationship, and he was a great help to my career. My good wishes go to his family.

Randy will certainly be missed.  He was perpetually and genuinely a mentor to all of us grad students.  It was a great pleasure to learn plasma physics from him and to learn from him through many group meetings and colloquium.  He was always an active and energetic colleague, and I was thankful to have him as part of my dissertation committee.  He encouraged me to not take things at face value and also to ask the simple but important questions.  Thanks, Randy.  Rest in peace. 

I was a graduate student between 2007 and 2012, during which Randy and colleagues had been maintaining a very active research group. I have many fond memories about conversations with Randy. I always regard Randy as my godfather in my science career and he greatly influenced me as a scientist. It is very difficult to accept that and the community has forever lost a true pioneer and leader.

Despite the enormous presence that Randy cast over the space physics community, and his sometimes gruff and slightly intimidating manner, he was always open and encouraging to new ideas regardless of their source. It mattered not whether one was an entering novice or student or a seasoned veteran of the field, Randy would always approach a new idea from the same perspective of physical integrity and robustness, and many of us owe Randy a great debt for his encouragement and support.


The key principle in dealing with Randy was a willingness and confidence to express and defend a key new idea or observation – debates with Randy were always vigorous, interesting, and fun and one always emerged from such a discussion with a better understanding and increased clarity. In fairness, one sometimes needed a slightly thick skin, but Randy was always willing to let bygones be bygones.


Randy carried these traits of demanding clarity and rigor into his professional but non-scientific activities, such as serving on committees. He would typically cut to the chase to bring out the essence of the matter under consideration. This made committee service with Randy much more efficient and more pleasant than it all too frequently becomes. Randy was always very proud of having served on the so-called “Colgate Committee,” which released a National Academy of Science report on “Space Plasma Physics: The Study of Solar System Plasmas” (1975). It was quite legendary in identifying the most important open questions facing space physics in the next decade. The study was almost a forerunner of today’s Decadal Studies and played a significant role in placing space plasma physics on a firm theoretical footing in the community. Randy, rightfully, would refer back to it frequently as a model to emulate, including when I chaired the Theory, Modeling, and Data Exploration Sub-panel of the 2001-02 Heliophysics Decadal Survey – this was one of my first major committee assignments and Randy’s support and encouragement as a committee member was invaluable.


Besides serving quite frequently with Randy on a variety of committees in one context or another, my enduring memories of Randy revolve around his participation in the Annual International Astrophysics Conference (AIAC) that we organized since 2001. Randy attended the first in Lake Arrowhead and was a fixture of the meeting for nearly 20 years, attending all but the very last of the conferences. The 18th AIAC in 2019 was dedicated to Randy’s 80th birthday. Frequently, because of the location, Randy, together with Joe Giacalone and Jozef Kota, would drive to the meetings, enduring the occasional sand storm! However, it was the meetings in Hawaii that Randy loved most, especially one meeting in Honolulu at the Sheraton Moana Surfrider hotel (now a Westin) since the restaurant featured a famous Banyan tree under which a radio show featuring Hawaiian music and culture was broadcast during Randy’s youth.


In the end, Randy’s love of science took him all over the world, fueling his stories and jokes, meeting and influencing many of us in heliophysics, leaving a legacy of science as a broad and enriching cultural activity. I was very sorry that ill health and the pandemic prevented his attending our last (19th) AIAC meeting in Santa Fe in early 2020 just as the pandemic was beginning. The enforced isolation created by the pandemic prevented us saying a proper goodbye to Randy in a place he loved while expounding on his current discoveries. He will be missed by all of us in heliophysics. Randy was a great scientist and a great character whose work and life will have an enduring impact.

An absolute prince of a man! Randy's no-nonsense approach to astrophysics, science administration and life in general was always an inspiration to me, and no doubt many others. He was frank and honest with me in our conversations and I knew he was someone worthy of my trust and respect. He was a very talented physicist and mathematician who successfully made the difficult journey from analytic theory to numerical simulation avoiding the pitfalls and traps that snared many of his colleagues. [I was a Parker graduate student from 1980-1983. Randy's academic genealogy via Leverett Davis Jr, William Vermillion Houston, Alfred Dodge Cole, and Eli Whitney Blake Jr hops across the Atlantic and connects to giants like Kirchoff and Bunsen. ]

I started at the University of Chicago in 1965 as a post-doc under Gene Parker as did Randy at precisely the same time. We managed to do a few joint papers concerning interstellar power spectra effects before Randy left for Cal Tech. He was a very able person and we used to often discuss many subjects while we worked togethernot excluding the quality of some of the faculty. I remember being severely depressed when Randy left for he was 1/3 of the theory group at that time However over the years I have followed his career with some sense of awe and it was a pleasure to see how he expanded once he hit Arizona. My interests took me away from cosmic ray astrophysics as a main theme as I worked on economic risk theory and its applications so that I lost the thread of his career. I reckon; under different conditions we might have worked together again but it was not to be. My memories of those early years at Chicago are still vivid and so I thank Randy for his abilities. Sleep well having earned the relaxation after a long successful career.

In 1971, I realized that I was too old to do balloon experiments and decided to visit Randy at Caltech to learn how to do theory. By 1988, this had worked out well enough to Justify my sabbatical at Arizona, where I worked closely with Randy. A notable result was the paper "Cosmic-Ray Viscosity", written with Randy and Greg Morfill.

In addition to Randy's willingness to address daunting Intellectual challenges and administrative headaches, he was also unafraid of arduous physical activities. For example, he occasionally rode his motorcycle from Arizona to northern Michigan, to visit his mother. These trips ended when the motorcycle threw him off just before destroying itself by hitting a roadside tree.

Randy Jokipii was my friend, mentor, and colleague. It was a privilege to know and work with this giant of Space Physics. I will miss him.

Randy was an inspiration. I was lucky to first meet him at the first Elmau workshop on CIRs and had many opportunities thereafter.  He was an excellent story-teller - both for science as well as anecdotes. He was a teacher to many of us youngsters and left a lasting impression on me in how passionately he argued about science. I will miss him.

I was very lucky to be hired as post-doctoral researcher, and later staff scientist, in the group led by J. R. Jokipii and his very long term collaborators and friends (J. Giacalone & J. Kota). Among many memories, an inquisitive mindset and insuppressible curiosity for nature shine as much as a rare intellectual honesty. These qualities, rarely held by the same person both at such a high level, were shared and transmitted to his students and collaborators. Many conversations, never interested in pleasing a colleague or friend, maybe to obtain a favor in return, but always centered on the scientific content. A vivid memory: he was convinced more than 95% of science publications are not original work but simply reproduction of previous results. He would constantly encourage to attempt new avenues, and to look the physical essence of an observation or a model. Always citing the example of the “Colgate committee” that he was part of to motivate theoreticians to do theory.

On daily basis, by passing by my office, he would stop to tell a funny anecdote, to challenge the theoretical understanding of a space craft observation, to comment about a just appeared (and wrong or incomplete in a way that he would immediately detect) theoretical paper. There was always something to learn from these conversations. By contemplating the wonderful library in his office one could sense both the breadth and the depth of his scientific interests.

His impact on space physics and astrophysics, most notably in the theory of charged particle diffusion in turbulence and particle acceleration at shocks, is alive through at least an entire generation of space physicists and astrophysicists who learnt from his papers, his lessons as well as his questions at conferences, meetings. I was also lucky to publish some papers with him and experiencing how more difficult would be to convince him than an average referee of a physical argument. Thanks Randy!

I am so sorry to hear of Randy's passing. I knew Randy through our interactions at scientific meetings and some longer conversations when I once had the pleasure of visiting UA, when Randy also invited me to his home. I always admired him as a scientist, regarding him as one of the field's most important figures. He always had insightful comments to share at meetings and was genuinely interested in what others had to say. I will miss him. Our field is diminished by his departure.

The epoch is passing. Randy Jokipii was a brilliant theoretician with a clear view and great ideas. His contribution to our understanding of cosmic-ray transport and modulation is crucial and curved into the cornerstones, making him one of the classical cosmic-ray researchers

Sincere condolences to his family and colleagues.

Ilya Usoskin

I still remember my first meeting with Randy in the 1960s when he came to Berkeley to give an invited seminar.  Afterward, he, Bob Lin, and I had dinner at a small nearby restaurant at which it was obvious that I was partaking (mostly listening) in cutting edge discussions of solar energetic particles.   I always appreciated his direct and often confrontational participation in various conferences.  When he disagreed and argued with someone, you could always get the basic point of the disagreement.  The longer I have worked in SEP research, the more I have come to appreciate his fundamental contributions to the field.  He also had a knack for pointing out many of the ironies of teaching and research in casual conversations, which were always entertaining.   Along with many others, I will be missing him.

I send my sincere sympathies to Randy’s family upon their loss.   
Randy was such an important figure and contributor in the space physics research and academic communities.   He will be sorely missed.  
Randy and I shared an apartment with two other graduate students in the 400 block of San Vicente Boulevard in Santa Monica during the summer of 1962.   That’s when I first met him.  The four of us (Randy at CalTech and George Questor, Bruce L. R. Smith, and me at Harvard) were summer employees of the RAND Corporation.   It was quite a summer of much work and recreation and swimming in the apartment pool and the “social” environment.  Every time we met over the subsequent decades Randy would speak of that summer and recall the many adventures we all had. 
I, as an experimentalist, was privileged to serve with Randy and Charlie Kennel on the Colgate Committee in the late 1970s.   As Randy related, this committee, composed as well of leading laboratory and theory plasma physicists, really established the basis for solid theory in space plasma physics and was the genesis of what is now the Heliophysics Division at NASA.  Subsequently I was happy to serve over the years with Randy on other advisory committees including the Committee on Solar and Space Physics and the first decadal study of solar and space physics.  Most importantly, I always valued my technical discussions with him in person or on the phone when I was involved at times with research related to solar energetic particles.  
Randy contributed fundamentally to advancing space research in our nation, and world-wide.  He will very much be missed. 
Louis J. Lanzerotti, New Vernon, New Jersey

I first met Randy at the Cosmic Ray conference in Denver 50 years ago. I had just been asked by ApJ to referee a paper that Randy had submitted - and to my dismay I found that he had made a mathematical mistake - and this from the Guru of Cosmic Ray Physics… I decided to locate him at the Conference and talk to him. His answer - „Jokipii does not make mistakes!“ Ok, maybe…but next day he telephoned Helmut Abt to cancel the paper, then he sought me out to thank me for telling him rather than show him up through official channels and invited me to visit him - perhaps I might like to work with him. Wow - I did not expect that. But this was the beginning of a long friendship and collaboration with summer visits filled with good science, good food and fun - but also sharing some of the tragedies that life unfortunately has to offer. With Randy’s departure to another place Physics has lost a great character and many of us have lost a great friend.

I send my sincere sympathy to Randy’s family upon his loss.   
Randy was such an important figure for so long in space physics research. 
Randy and I shared an apartment with two other graduate students in the 400 block of San Vicente Boulevard in Santa Monica during the summer of 1962.   That’s when I first met him.   The four of us (Randy at CalTech and George Questor, Bruce L. R. Smith and me at Harvard) were employees of the RAND Corporation.  It was quite a summer, filled with hard work, touring LA, swimming in the apartment complex pool, and the ambiance of the “social” scene.  We were frequently joined by another summer employee, Michael Intriligator, later to be the husband of space physicist Devrie Intriligator.   When we met over the subsequent decades, Randy would always relate stories remembered from that summer.  

As an experimentalist, I was privileged to serve with Randy and Charlie Kennel on the Colgate Committee in the late 1970s.   As Randy related, this Committee, composed as well of leading laboratory-based plasma physicists, established the basis for solid theoretical work in space physics.  The Committee was also the basis of the establishment of what is now the Heliophysics Division of NASA.  

Over the years I happily served on advisory bodies with Randy, including the Committee on Solar and Space Physics and the first decadal study of solar and space physics.   More importantly, at those times when I was engaged in topics related to solar energetic particles, I always valued my discussions and conversations, in person and by phone, with him.   

Randy contributed so significantly to space physics research, in our nation and worldwide.   His voice will be missed. 
Louis J. Lanzerotti, New Vernon, New Jersey