Joseph V. Hollweg
Joint Appointment Department of Physics
Ph.D., Massachusetts Institute of Technology
Research Interests: Dynamics of the solar atmosphere and solar wind, waves in plasmas.
The Sun's atmosphere exhibits a wide range of complex dynamic phenomena. At any instant of time there are about one million high-speed jets of gas, called spicules, on the Sun. There is a continual outflow, called the solar wind, of solar plasma into interplanetary space. The region just below the Sun's visible surface is filled with sound waves. The solar corona and the underlying chromosphere are constantly in motion. And there are frequent impulsive releases of energy, such as solar flares and coronal mass ejections. The solar atmosphere contains complex configurations of magnetic field which are also in a constant state of agitation. The magnetic and kinetic energy in the Sun's atmosphere is continually being converted into heat. The corona is heated to several million Kelvins, and some of this thermal energy enables the solar wind to be accelerated to high speeds and escape the Sun's gravity. The chromosphere and spicules are also heated to more modest temperatures. But the details of these processes are not understood.
Our research is concerned with developing theoretical models for the sources of momentum and energy that are required to explain the observed motions and heating. We have emphasized the roles of waves, which transport both momentum and energy and can therefore accelerate and heat the solar plasma. Understanding the physics of waves in the solar atmosphere is challenging. The waves propagate in a very structured medium, and they undergo complicated nonlinear interactions leading to shock formation, instabilities, and turbulence.
Our program has been supported by grants from NASA and the NSF . Hollweg has also been involved with experimental programs on the SOHO mission.
Hollweg was awarded the 1992 James Arthur Prize for Solar Physics by the Harvard-Smithsonian Center for Astrophysics, and in 2002 he was elected Fellow of the American Geophysical Union "for outstanding research on topics throughout the corona and solar wind and for consistently clear elucidation of the fundamental physical processes involved". He officially retired in 2006, but still maintains an office at UNH and continues his research projects and collaborations.