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The primary goal of the Helioseismic and Magnetic Imager (HMI) investigation is to study the origin of solar variability and to characterize and understand the Sun's interior and the various components of magnetic activity. The HMI investigation is based on measurements obtained with the HMI instrument as part of the Solar Dynamics Observatory (SDO) mission. HMI makes measurements of the motion of the solar photosphere to study solar oscillations and measurements of the polarization in a spectral line to study all three components of the photospheric magnetic field. HMI produces data to determine the interior sources and mechanisms of solar variability and how the physical processes inside the Sun are related to surface magnetic field and activity. It also produces data to enable estimates of the coronal magnetic field for studies of variability in the extended solar atmosphere. HMI observations will enable establishing the relationships between the internal dynamics and magnetic activity in order to understand solar variability and its effects, leading to reliable predictive capability, one of the key elements of the Living With a Star (LWS) program.

The broad goals described above will be addressed in a coordinated investigation in a number of parallel studies. These segments of the HMI investigation are to observe and understand these interlinked processes:
  • Convection-zone dynamics and the solar dynamo;
  • Origin and evolution of sunspots, active regions and complexes of activity;
  • Sources and drivers of solar activity and disturbances;
  • Links between the internal processes and dynamics of the corona and heliosphere;
  • Precursors of solar disturbances for space-weather forecasts.

These goals address long-standing problems that can be studied by a number of immediate tasks. The description of these tasks reflects our current level of understanding and will obviously evolve in the course of the investigation.
To satisfy the measurement requirements of the investigation, the HMI instrument will produce filtergrams in a set of polarizations and spectral line positions at a regular cadence for the duration of the mission that meet these basic requirements:
  • Stabilized 1 arc-second resolution full-disk Doppler velocity and line-of-sight magnetic flux images at least every 50 seconds
  • Stabilized 1 arc-second resolution full-disk vector-magnetic images of the longitudinal solar magnetic field at least every 90 seconds

In addition, the HMI investigation will provide sufficient computing capability to convert these raw filtergram measurements into a set of observables and derived data products that satisfy the HMI science objectives and that will be made available to all interested investigators. The primary observables (Dopplergrams, longitudinal and vector magnetograms, and continuum intensity images) will be constructed from the raw filtergrams will be made available at full resolution and cadence. Other derived products such as subsurface flow maps, far side activity maps, and coronal and solar wind models that require longer sequences of observations shall be produced and made available.

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Page last revised Monday, July 12, 2010 23:01