Michael J. Thompson died on Monday, October 15, 2018, at age 59.

Prof. Michael Thompson died on October 15, 2018. He was part way through a five-week sabbatical to Tokyo when he fell ill unexpectedly after making a brief return trip home. He was 59. Michael took his undergraduate degree at Cambridge from 1978 to 1981 and is remembered as an outstanding student who later won the Tyson Medal and Prize for his scholastic achievements. He excelled in exams, including one in particular that would have a significant influence in shaping the future direction of his career: astrophysical fluid dynamics, taught by Douglas Gough. Michael was convinced he had performed badly in the exam, to the extent that he aired his frustrations and resolved never to speak to Douglas again, although he had in fact come top by some margin. Michael was so taken by the course that he decided to pursue research in this field. Wanting also to stay in Cambridge, he approached Douglas to supervise him; their lifelong friendship and working relationship developed from there.

For his Ph.D. thesis, Michael studied the impact of magnetic fields on the oscillation frequencies of stars. This was a time when helioseismology, the study of the Sun’s interior through observation of its oscillations, was becoming established as a field in its own right. His research developed around using seismology as a tool to further understanding of the internal structure and physics of stars, the Sun in particular. In 1987, Michael began a postdoctoral fellowship at Aarhus University, working with another former student of Douglas, Jørgen Christensen-Dalsgaard. He then joined the High Altitude Observatory (HAO) in Boulder in 1988, where one day he would become director.

The Internal Rotation of the Sun

During this period Michael began building a body of work investigating the internal rotation of the Sun, the research topic he is probably best known for. He was a theoretician, but displayed a strong interest in developing the methodology needed to analyze data. Indeed, he was in the forefront of developing so-called “inverse” analysis techniques — which had been used in geophysics — for application to helioseismic data, allowing the Sun’s internal rotation and structure to be inferred in great detail.

His results showed that the pattern of differential rotation observed at the Sun’s surface — with equatorial regions rotating more rapidly than the poles — penetrated the Sun’s convective envelope, but the patterns failed to match those predicted by models. Deeper down, the rotation was observed to transition across a thin layer called the tachocline to that expected of a solid body, again a surprise, and one that continues to challenge models today. Michael continued to publish key results in this area, including further work on the tachocline and variations of rotation in the outer envelope over time. These variations were revealed to carry signatures of the Sun’s activity cycle and have provided important observational constraints for those working to model the internal evolution of the Sun’s global magnetic field, which has far-reaching implications for understanding the influence the Sun has on the Earth.

As well as studying rotation, Michael also performed important calculations on the internal structure and physics of the Sun, and on evaluating different ways of performing “local” helioseismology (which holds many similarities with terrestrial seismic studies). Later in his career, Michael also worked on transferring helioseismic techniques to other Sun-like stars, where the reduced quantity and quality of data present additional challenges.

After his first spell at HAO, Michael returned to the U.K. in 1989 to take up a prestigious PPARC fellowship at Queen Mary University of London. His position was made permanent a year later. In 2001, he moved to Imperial College London to take up a professorial chair. His professional interests went much wider than physics and astronomy and, in 2004, he moved to the University of Sheffield to take on his first major administrative role, creating a new School of Mathematics and Statistics.

Michael maintained strong links with HAO, including regular research trips, and in 2003 he became a National Center for Atmospheric Research (NCAR) affiliate scientist at HAO. In 2010, those links became more permanent when Michael moved with his wife Kate to Boulder to become director of HAO and associate director of NCAR. In 2013, he was named deputy director and chief operating officer of NCAR and interim director for 13 months in 2015–16.

Michael tackled a wide variety of subjects, reflecting broad interests and an inquiring disposition. He liked to work with other people and had a range of collaborators who without fail enjoyed working with him. He was always encouraging, particularly with younger colleagues, and treated everyone the same, irrespective of their position and standing.

Michael was an unfailing supporter of theoretical investigations of the solar interior. He was a strong advocate of research excellence, convinced that understanding could only arise through a sound theoretical underpinning. Recently, he was becoming research-active once more, leading an international project to provide timely updates on the Sun’s internal rotation. That work will be completed, under the supervision of friend and colleague Jørgen Christensen-Dalsgaard. The results will serve as a fine testament to Michael’s research legacy.

Michael relaxed outside of work through music, playing piano duets with his son Robin, carol singing, and enjoying the countryside in Boulder, Yorkshire and Derbyshire. Michael will be much missed by all who knew him. He is survived by his wife Kate and son Robin (a mathematician).

Text and photo used with permission, adapted from the original article by Bill Chaplin in Astronomy & Geology [1].