Dennis Hartmann has made outstanding contributions to climate science by innovatively employing his broad-based understanding of atmospheric physics and dynamics. Equally important is his contribution to the atmospheric science and climate community through his unselfish services. Of most direct relevance to this medal, given Roger Revelle’s contribution to the climate change field, are Dennis’s monumental works on cloud feedbacks, which are of central importance to estimates of climate sensitivity. For high clouds, Dennis’s so-called fixed anvil temperature hypothesis predicted that tropical convective anvil clouds would occur at about the same atmospheric temperature, regardless of the surface temperature. This hypothesis has been corroborated by many recent high-resolution modeling and observational studies and has provided major insight into how tropical convective anvil clouds would behave in a warming climate, with consequent positive longwave feedback. And for low clouds, with his graduate student Stephen Klein, Dennis discovered how the fractional areal coverage of stratocumulus clouds is controlled by the lower tropospheric stability. As a result of this work, the increase in this static stability anticipated in the response to carbon dioxide (CO2) increase has taken center stage in the discussion of feedbacks associated with stratocumulus clouds. Dennis has also made seminal contributions to our understanding of the interactions of eddies with zonal flow and their role in climate variability. He and his students discovered that feedback between baroclinic eddies and the zonal flow is responsible for the large degree of low-frequency variability in jet structures and the zonal mean wind, the so-called annular modes of variability, which comprise north-south shifts in the jet streams and storm tracks. Dennis’s work has proven central to our understanding of the response of these preferred annular patterns to stratospheric ozone depletion and CO2 increase. Dennis’s impact and leadership are not only through his many major original scientific contributions but also through his generous services to the climate science community. Dennis has chaired numerous important panels and committees. His unselfish service at local, national and international levels is exceptional. Dennis has also played an exemplary role in mentoring and inspiring the next generation of scientists. His highly successful book Global Physical Climatology, now in its second edition, has been an invaluable resource for students and researchers around the world with different disciplinary backgrounds, inspiring them to appreciate the truly interesting science involved in understanding the Earth’s climate and its possible future change, and has attracted them to become involved in that science. Congratulations to Dennis for this well-deserved award! — Qiang Fu University of Washington Seattle, Washington

I would like to thank my excellent colleague Qiang Fu for nominating me for the Roger Revelle Medal and my colleagues Isaac Held, Brian Hoskins and Kevin Trenberth for their letters of support. This is a very great honor, and I am humbled to receive an award with such a distinguished list of prior Revelle Medal recipients. I would also like to thank my mentors during graduate school. Abraham Oort was a very generous adviser and a great example of using data cleverly to advance scientific understanding. Suki Manabe took an interest in my progress and suggested that I investigate the new data on the Southern Hemisphere stratosphere that was coming from the Selective Chopper Radiometer on Nimbus 5. This project allowed me to combine remote sensing, radiative transfer and atmospheric dynamics. Jerry Mahlman took an interest in me and modeled the excitement for science that sustains a happy career as a researcher. My postdoc advisers were Jacques Derome and Phil Merilees at McGill University and John Gille at the National Center for Atmospheric Research. I met other inspiring people at those places, too. The Department of Atmospheric Sciences at the University of Washington was a great place for a developing young scientist, as it provided colleagues who were both encouraging and first-class examples of how to do science well. I remember many enjoyable mountain hikes with Mike Wallace, Jim Holton and Conway Leovy when I was a junior faculty member. I am now inspired by the wonderful new faculty who have joined the department. I was fortunate to work on very interesting and important problems in the geosciences and benefited from talented and generous collaborators in science. Since my thesis was on the Southern Hemisphere stratosphere, I was well positioned when the ozone hole was discovered in 1985. Wave mean-flow theory developed greatly early in my career and provided many interesting insights. I was able to work with NASA scientists on several developments in remote sensing of the radiation budget and clouds. Much credit for my success as a researcher goes to the excellent graduate students and postdocs with whom I had the opportunity to work during my time as a professor at the University of Washington. My partner, Lorraine, has provided the love and support needed to combine a happy but intense career with a happy family life. — Dennis L. Hartmann University of Washington Seattle, Washington