The 2015 Julius Bartels Medal is awarded to Sami Solanki for his truly exceptional work that has provided understanding of the Sun and is of fundamental importance to studies of Earth’s past global climate, present regional climates, and to space weather effects on mankind’s operational systems.
Sami Solanki is an outstanding solar and solar-terrestrial physicist. His truly exceptional work has provided understanding of the Sun that is of fundamental importance to studies of Earth’s past global climate, present regional climates, and to space weather effects on mankind’s operational systems. He combines an encyclopaedic knowledge, precision, thoroughness, intuition and great organisation in his work.
Solanki’s work on reconstructing total and spectral solar irradiance from solar magneto-grams is both unique and groundbreaking. This work has led to the SATIRE (Spectral And Total Irradiance REconstruction) models, a set of physics-based models that have proved that the magnetic field at the Sun’s surface is the source of irradiance variations on timescales longer than a day. The models are also playing a crucial role in developing our understanding of UV spectral solar irradiance variability, the importance of which had previously been seriously underestimated.
Solanki’s work on open solar flux has had a seminal influence in two other areas to which Solanki has made huge contributions. The first is in the understanding and application of data on the abundances of cosmogenic radionuclides stored in stratified terrestrial reservoirs such as ice sheets and tree trunks. The open flux modelling gave us the ability to extend the observed open flux and the geomagnetic reconstructions back to the Maunder minimum which, in turn, has given us a crucial new understanding of secular change in comic ray modulation. Perhaps the most important realisation was that the space age was a relatively unusual period in terms of solar activity.
Another most outstanding area of research is his combination of work on open flux and irradiance. Reconstructions of total solar irradiance had previously scaled the variation between the Maunder minimum and modern cycles using surveys of stars thought to be analogous to the Sun. This proved to be invalid because the surveys were small and the stars were often not true solar analogues. Solanki’s work enabled a physics-based alternative to be developed. The magnitude of the secular change in the solar irradiance is of special importance for climate models. He was first to point out the crucial role of the solar ephemeral magnetic regions in this context. Reconstructions of the past solar surface magnetic flux and of consequent irradiances have been made from both sunspot and cosmogenic isotope data, covering 400 years and 9,300 years respectively.
He has led a very fine body of observational work related to a variety of solar phenomena, including waves and field line loops in the solar corona. He recently led the SUNRISE balloon-borne project, which obtained the highest resolution images of the Sun in the 200–400 nm wavelength range, critical for understanding ozone chemistry in the Earth’s atmosphere.
He has also made massive contributions to the field in general. He established, and acts as editor of, the Living Reviews in Solar Physics journal, he has enthusiastically supported young scientists in the development of their careers, and has personally supervised about 40 successful PhD students to date.