Solar Dynamics Observatory
The Solar Dynamics Observatory is the first mission to be launched for NASA’s Living With a Star (LWS) Program, a program designed to understand the causes of solar variability and its impacts on Earth. SDO is designed to help us understand the Sun’s influence on Earth and Near-Earth space by studying the solar atmosphere on small scales of space and time and in many wavelengths simultaneously.
The scientific goals of the SDO Project are to improve our understanding of seven science questions:
- What mechanisms drive the quasi-periodic 11-year cycle of solar activity?
- How is active region magnetic flux synthesized, concentrated, and dispersed across the solar surface?
- How does magnetic reconnection on small scales reorganize the large-scale field topology and current systems and how significant is it in heating the corona and accelerating the solar wind?
- Where do the observed variations in the Sun’s EUV spectral irradiance arise, and how do they relate to the magnetic activity cycles?
- What magnetic field configurations lead to the CMEs, filament eruptions, and flares that produce energetic particles and radiation?
- Can the structure and dynamics of the solar wind near Earth be determined from the magnetic field configuration and atmospheric structure near the solar surface?
- When will activity occur, and is it possible to make accurate and reliable forecasts of space weather and climate?
SDO will fly three scientific experiments:
- Atmospheric Imaging Assembly (AIA)
- EUV Variability Experiment (EVE)
- Helioseismic and Magnetic Imager (HMI)
Each of these experiments perform several measurements that characterize how and why the Sun varies. These three instruments will observe the Sun simultaneously, performing the entire range of measurements necessary to understand the variations on the Sun.
SDO contains a suite of instruments that provide observations that will lead to a more complete understanding of the solar dynamics that drive variability in the Earth’s environment. This set of instruments does the following:
- Measure the extreme ultraviolet spectral irradiance of the Sun at a rapid cadence
- Make those measurements over a significant portion of a solar cycle to capture the solar variations that may exist in different time periods of a solar cycle
- Measure the Doppler shifts due to oscillation velocities over the entire visible disk
- Make high-resolution measurements of the longitudinal and vector magnetic field over the entire visible disk
- Make images of the chromosphere and inner corona at several temperatures at a rapid cadence
The Science Teams receive the data from SDO. They then process, analyze, archive, and serve the data.
HMI is an instrument designed to study oscillations and the magnetic field at the solar surface, or photosphere. HMI is one of three instruments on the Solar Dynamics Observatory; together, the suite of instruments observes the Sun nearly continuously and takes a terabyte of data a day. HMI observes the full solar disk at 6173 Å with a resolution of 1 arcsecond. HMI is a successor to the Michelson Doppler Imager on the Solar and Heliospheric Observatory.
HMI provides four main types of data: dopplergrams (maps of solar surface velocity), continuum filtergrams (broad-wavelength photographs of the solar photosphere), and both line-of-sight and vector magnetograms (maps of the photospheric magnetic field).
The Atmospheric Imaging Assembly (AIA) for the Solar Dynamics Observatory (SDO) is designed to provide an unprecedented view of the solar corona, taking images that span at least 1.3 solar diameters in multiple wavelengths nearly simultaneously, at a resolution of about 1 arcsec and at a cadence of 10 seconds or better. The primary goal of the AIA Science Investigation is to use these data, together with data from other SDO instruments and from other observatories, to significantly improve our understanding of the physics behind the activity displayed by the Sun’s atmosphere, which drives space weather in the heliosphere and in planetary environments. The AIA will produce data required for quantitative studies of the evolving coronal magnetic field, and the plasma that it holds, both in quiescent phases and during flares and eruptions. The AIA science investigation aims to utilize these data in a comprehensive research program to provide new understanding of the observed processes and, ultimately, to guide development of advanced forecasting tools needed by the user community of the Living With a Star (LWS) program.
The Extreme ultraviolet Variabilty Experiment (EVE) is designed to measure the solar extreme ultraviolet (EUV) irradiance. The EUV radiation includes the 0.1-105 nm range, which provides the majority of the energy for heating Earth’s thermosphere and creating Earth’s ionosphere (ionized plasma). This wide spectral range requies the use of multiple channels. Some key requirements for EVE are to measure the solar EUV irradiance spectrum with 0.1 nm spectral resolution and with 20 sec cadence. These drive the EVE design to include grating spectrographs with array detectors so that all EUV wavelengths can be measured simultaneously. Another key requirement for EVE is to measure the EUV radiation with an accuracy of 25% or better, thus on-board calibration channels are included to go with underflight calibration experiments to be conducted during the SDO mission.