ABSTRACT

1
ABSTRACT Investigators using the Helioseismic
and Magnetic Imager (HMI) will study the origin
of solar variability and will characterize and
understand the interior of the Sun and the
various components of magnetic activity. HMI is
part of the Solar Dynamics Observatory (SDO) a
satellite scheduled for launch into
geosynchronous orbit in 2009. SDO is NASAs
first Living With a Star (LWS) mission. HMI will
measurement motions of the solar photosphere to
study solar oscillations and will measure
polarization to study the vector magnetic field.
HMI will help establish the relationships between
the internal dynamics and magnetic activity in
order to understand solar variability and its
effects. The prime goal of the mission is to
develop the knowledge needed for a reliable
predictive capability, one of the key elements of
the International Living With a Star (ILWS)
program. The Michelson Doppler Imager (MDI)
instrument on SOHO has been making helioseismic
and magnetic field observations of the Sun since
the beginning of Solar Cycle 23. HMI will
continue these important measurements from space
into the next solar cycle. The HMI instrument is
an evolution of the successful MDI design with
key improvements in resolution, image cadence,
continuity, and vector magnetic field measurement
capabilities. Filtergrams of the Fe I spectral
line at 617.3 nm made with the HMI tunable narrow
band filter system determine motions of the solar
photosphere to study solar oscillations.
Polarization measurements in this same spectral
line enable determination of all three components
of the photospheric magnetic field. The web site
hmi.stanford.edu provides more information.