Paul Cassak

West Virginia University

2015 James B. Macelwane Medal Winner

Paul Cassak, Bethany List Ehlmann, Colette L. Heald, Matt Jackson, and Kate Maher were awarded the 2015 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2015 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding early career scientist.”


Paul Cassak has made groundbreaking contributions to our understanding of magnetic reconnection, which operates in the boundary regions of planetary magnetospheres and the solar corona as well as having great significance in laboratory plasma physics and plasma astrophysics. Good examples of Paul’s groundbreaking research are his work on asymmetric reconnection and reconnection with a flow shear. Early models of reconnection, where magnetic fields effectively break and release their stored energy, treated symmetric systems for simplicity. However, most realistic systems, especially planetary magnetospheres, have different magnetic fields, densities, and/or bulk flow speeds across the boundary region. Just as simulation studies on the topic were beginning in earnest, Paul performed a first-principles calculation predicting the properties of reconnection in asymmetric systems for generic conditions and has since included the effects of plasma flow. These results have facilitated the analysis of satellite data and may be important for predicting solar wind–magnetosphere coupling, a key aspect of space weather phenomena.

In the solar context, his work on the initiation of reconnection through which built-up magnetic energy is released explosively has been influential. It was generally assumed that reconnection, when it happens, is always fast (matching solar flare and magnetospheric substorm time scales), but if it’s always fast, how can it be explosive? Paul’s research answered this question, which had lingered for decades. In a series of papers, Paul showed that when a current sheet separating opposing magnetic fields forms and has large width, resistive effects dominate, and the fields reconnect relatively slowly. When the sheet thins to kinetic scales, collisionless effects abruptly become dominant, and reconnection becomes much faster. Paul’s research showed that there exists a vast parameter regime in which both types of reconnection are stable. He developed several innovative tests of this hypothesis and successfully validated it; the results may be crucial for understanding solar flares.

These and other unique new results in Paul’s impressive body of work have helped revitalize the field of magnetic reconnection and have significantly changed its course.

As an associate professor at West Virginia University, Paul is an active mentor in the fields of space and plasma physics, publishing important papers with his students. As a teacher, he developed novel active-learning materials for graduate courses in plasma physics. His service activities for AGU include chairing the Scarf Award Committee, being an associate editor for Journal of Geophysical Research, and serving on the Space Physics and Aeronomy Policy Committee.

—James L. Burch, Southwest Research Institute, San Antonio, Texas


Thank you, Jim, for the kind citation. I guess all those years of not being popular in high school really paid off! My sincere thanks to the Macelwane Medal Committee, my nominators, and AGU for their efforts for the community.

An honor like this is truly humbling and makes me reflect on the people who contributed to my career, especially four people I’ve never even written papers with. Jim Burch is the principal investigator of the Magnetospheric Multiscale (MMS) mission, which successfully launched in March 2015. In his “spare” time, he was the lead on my nomination. As long as our community has science-driven and civic-minded people like Jim, we’ll be in good shape. Joe Borovsky shared my work with many people, Jim Klimchuk opened doors for me, and Kile Baker believed in me. All of you give the community something to aspire to.

Words cannot express my gratitude to my mentors, especially my doctoral and postdoctoral advisers Jim Drake (Maryland) and Mike Shay (Delaware). I met you accidentally in 2002 and feel extremely lucky to be able to call you mentors, colleagues, and friends.

I have learned much from my colleagues in solar and space physics; an incomplete list includes Dr. Dorelli, Dr. Eriksson, Dr. Fuselier, Dr. Glocer, Dr. Gosling, Dr. Matthaeus, Dr. Mullan, Dr. Murphy, Dr. Phan, Dr. Servidio, Dr. Swisdak, and Dr. Wilder.

I am grateful to my supportive colleagues at West Virginia University, especially Earl Scime. I am forever indebted to you for your guidance and support.

I have been fortunate to have a supportive family throughout my life. My mother, Kit, my father, Barry, and my brother, Todd, have been there for me through thick and thin.

To my love, Julie Bryan, I’ll never know how I got such a great wife. You are funny and serious, patient and encouraging, thoughtful, sweet, smart, and, most of all, supportive. Did I mention smart? And funny? It’s been a pleasure and privilege to go through time with you. Thank you for making me a better person.

Finally, James Macelwane treasured his students. I too have collaborated with outstanding students (Dr. Malakit, Dr. Parashar, Dr. Shepherd, Dr. Komar, Dr. Beidler, and the future Dr. Haggerty, Dr. Doss, and Dr. French), who have enriched my scientific pursuits immeasurably. To all the students reading this—know that you can make important contributions to science and be successful with a lot of hard work and a little luck. Remember that devoting a career to the pursuit of knowledge is an honor.

—Paul Cassak, West Virginia University, Morgantown