Solar Physics

KIPAC members with the Stanford Solar Observatories Group take part in observational and theoretical research on the physics of the Sun. They study important solar characteristics ranging from the violent processes in the Sun's core to the source of variations in the solar wind, with a particular emphasis on understanding solar variability (for example, determining the cause of the Sun's 11-year sunspot cycle) and how it impacts the Earth. 


Stanford's Solar Group comprises about 20 scientists and staff who operate the Wilcox Solar Observatory (WSO) in the Stanford hills, the now-retired Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO), and its successor, the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). As part of the SDO program, the Solar Group operates the Joint Science Operations Center (JSOC) which provides analysis capability and houses the data archives of WSO, MDI, HDI, and the Atmospheric Imaging Assembly (AIA), another SDO instrument developed in collaboration with the Lockheed Martin Solar Astrophysics Laboratory. This archive is one of the most extensive collections of solar data in existence; for example, WSO data extends back to 1975.


Solar Group researchers use HMI Dopplergrams (see image below), which provide maps of the velocity of the solar surface, giving insight into movement in the solar interior. This area of study, called helioseismology, is analogous to Earth-bound seismology. The Dopplergram data helps scientists develop new ways to measure plasma flows, thermal structure, and possibly detect magnetic fields throughout the solar convection zone out to the photosphere. Continuously collected HMI data also provides insight into processes happening on time scales from the 11-year solar cycle to a few minutes duration. Magnetohydrodynamic simulations of the outer convection zone enable the exploration of near surface interaction between waves, magnetic fields, and convective turbulence. Researchers can measure the meridional flows that are part of the driving forces behind the solar dynamo, new methods to detect near surface motions that order and shred active regions, and methods to detect erupting active regions hours or days before they begin to disrupt the surface or corona.

Recent Dopplergram from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. (Credit: SDO.)
Recent Dopplergram. (Credit: SDO.)


HMI magnetograms (see below), which map the magnetic fields on the Sun's surface—both by themselves and in conjunction with coronal images from the AIA instrument—researchers study the interaction of changing magnetic fields with the coronal plasma with the goal of learning how to estimate probabilities of flares and the initiation of coronal mass ejections (CMEs). Flares and CMEs are the source of many of the important aspects of space weather.

Recent magnetogram from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory. (Credit: SDO.)  ​
Recent magnetogrom. (Credit: SDO.)


Solar Group researchers are also interested in the solar cycle and its variations from one decade to the next. Forty-five years of data from the WSO allows comparisons of large scale magnetic fields over almost half a century and supports examinations of historic data spanning hundreds of years as well as helping to constrain dynamo models to the real Sun.

Beyond SDO

In addition to data from the three Stanford-led solar observing instruments, HMI, MDI, and WSO, Solar Group members participate in analysis and interpretation of data from other ground-based programs and space instrumentation. For example, KIPAC professor Philip Scherrer is a co-investigator of the Polarametric and Helioseismic Imager, an instrument on the ESA/NASA Solar Orbiter which launched February 9, 2020, while KIPAC staff scientist Todd Hoeksma is a co-investigator of the Solar Orbiter's Magnetometer.

A Solar Group proposal to establish a future Science Center as part of the DRIVE program has been selected for further development. DRIVE, which stands for Diversity, Realize, Integrate, Venture, Educate, is a multi-agency initiative focused on supporting larger projects in heliophysics that call for extensive teamwork to deliver breakthrough science.

Please see the Stanford Solar Observatory Group's website for detailed information.