HMI Investigation Overview

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HMI Investigation Overview

• Philip Scherrer
• HMI Principal Investigator
• pscherrer_at_solar.stanford.edu
• This presentation available at
• http//hmi.stanford.edu/Presentations

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HMI Investigation Overview Outline

• Investigation Overview
• Science Objectives
• How HMI works
• Helioseismology What is it?
• Data Products and Objectives
• Inside HMI
• Data Center
• Science Team
• Web Links

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Investigation Overview - 1
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 Suns interior and the various
components of magnetic activity. HMI measures
of the motion of the solar photosphere to study
solar oscillations and HMI measures the
polarization in a spectral line to obtain all
three components of the photospheric magnetic
field.
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Investigation Overview - 2
The basic HMI measurements are filtergrams
images of the Suns photosphere made through a
very narrow-band filter tunable to a set of six
specific wavelengths across one spectral line.
The raw observations must be processed into
higher level data products before analysis can
proceed. HMI produces data products suitable 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
products to enable estimates of the low and far
coronal magnetic field for studies of variability
in the extended solar atmosphere.
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Investigation Overview - 3
HMI observations will enable establishing the
relationships between the internal dynamics and
magnetic activity. This is a prerequisite to
understanding possible physics-based solar
activity forecasts. Active participation of the
HMI Team in collaboration with the other SDO
instrument teams and the LWS community is
necessary to achieve the HMI science goals. HMI
data and results will be made available to the
scientific community and the public at large
through data export, publications, and an
Education and Public Outreach program.
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HMI Science Objectives

• HMI science objectives are grouped into five
  broad categories
• Convection-zone dynamics and the solar dynamo
• How does the solar cycle work?
• Origin and evolution of sunspots, active
  regions and complexes of activity
• What drives the evolution of spots and active
  regions?
• Sources and drivers of solar activity and
  disturbances
• How and why is magnetic complexity expressed as
  activity?
• Links between the internal processes and
  dynamics of the corona and
• heliosphere
• What are the large scale links between the
  important domains?
• Precursors of solar disturbances for
  space-weather forecasts.
• What are the prospects for predictions?

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HMI How It Works
HMI consists of a telescope, tunable filter,
camera, and necessary electronics. HMI images
the Sun in four polarizations at six wavelengths
across a spectral line. The position of the
line tells us the velocity while the shape
changes of the line in different polarizations
tell us the magnetic field direction and strength
in the part of the Suns surface seen by each
pixel. Long gap-free sequences of velocity
measurements are needed to use the techniques of
helioseismology.
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Magnetic Field Sample Profile
HMI measures magnetic fields by sampling the
Zeeman split line in multiple polarizations. The
figure shows the six sample positions and
polarized spectral components for a 3000G field
as found in sunspot umbra.
The green and red curves are Left and Right
circular polarized components and allow
measurement of the line-of-sight projection of
the field. Analysis of both polarizations is
required to infer the Doppler velocity and
line-of-sight magnetic flux. For vector fields
four states of linear and circular polarization
are needed to infer the field strength and
direction.
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Helioseismology What Is It?
Helioseismology is the study of solar interior
structure and dynamics by analysis of the
propagation of waves through the Suns interior.
The Sun is filled with acoustic waves with
periods near five minutes.

• These waves are refracted upward by the
  temperature gradient and reflected inward by the
  drop in density at the surface
• The travel times of these waves depends on the
  temperature, composition, motion, and magnetic
  fields in the interior.
• The visible surface moves when the waves are
  reflected enabling their frequency, phase, and
  amplitude to be measured.
• Analysis of travel times over a multitude of
  paths enables inference of internal conditions.

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Helioseismology - 2
The wave reflections result in oscillations of
the surface. These motions are a few hundred
m/s and are superimposed on the 1500 m/s
granulation, 400 m/s supergranulation, 2000 m/s
solar rotation and 3500 m/s SDO orbit. The
dynamic range of HMI must accommodate all these
motions in addition to the line splitting
equivalent to 3000 m/s from sunspot magnetic
fields.
Measurements must be often enough to resolve the
oscillations (c. 45 seconds). Sequences must be
long enough to resolve phase and frequency yet
short enough to sample the evolving structures.
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Time-Distance Helioseismology Example
Waves going in all directions are reflected at
each point on the surface. Cross-correlations of
the time series observed at pairs of points (A,B)
reveal the integrated travel-time along the
interior path that connects A with
B. Differences between the A?B and B?A
directions arise from bulk motion along the
path. Analyses of travel-time maps provide maps
of flows and temperatures beneath the surface.
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Vector Magnetic Field
Traditional solar magnetic measurements provide
only the line-of-sight magnetic flux.
Experience has shown that the full vector field
is necessary to understand the connectivity in
and between active regions. Inversions of
polarization measurements provide all three
components of the field as well as the
filling-factor of the unresolved magnetic
elements. Long sequences of vector field data
have yet to be measured. We expect to learn a
lot.
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Solar Domain of HMI Helioseismology
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HMI Data Product Examples

1. Sound speed variations relative to a standard
   solar model.
2. Solar cycle variations in the sub-photospheric
   rotation rate.
3. Solar meridional circulation and differential
   rotation.
4. Sunspots and plage contribute to solar irradiance
   variation.
5. MHD model of the magnetic structure of the
   corona.
6. Synoptic map of the subsurface flows at a depth
   of 7 Mm.
7. EIT image and magnetic field lines computed from
   the photospheric field.
8. Active regions on the far side of the sun
   detected with helioseismology.
9. Vector field image showing the magnetic
   connectivity in sunspots.
10. Sound speed variations and flows in an emerging
    active region.

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Primary Science Objectives

• Convection-zone dynamics and solar dynamo
• Structure and dynamics of the tachocline
• Variations in differential rotation.
• Evolution of meridional circulation.
• Dynamics in the near-surface shear layer.
• Origin and evolution of sunspots, active regions
  and complexes of activity
• Formation and deep structure of magnetic
  complexes.
• Active region source and evolution.
• Magnetic flux concentration in sunspots.
• Sources and mechanisms of solar irradiance
  variations.
• Sources and drivers of solar activity and
  disturbances
• Origin and dynamics of magnetic sheared
  structures and delta-type sunspots.
• Magnetic configuration and mechanisms of solar
  flares and CME.
• Emergence of magnetic flux and solar transient
  events.
• Evolution of small-scale structures and magnetic
  carpet.
• Links between the internal processes and
  dynamics of the corona and heliosphere
• Complexity and energetics of solar corona.
• Large-scale coronal field estimates.

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HMI Data Products and Objectives
Magnetic Shear
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Instrument Overview Optical Path
Optical Characteristics Focal Length 495
cm Focal Ration f/35.2 Final Image Scale
24?m/arc-sec
Filter Characteristics Central Wave Length
613.7 nm Bandwidth 0.0076 nm Tunable Range 0.05
nm Free Spectral Range 0.0688 nm
Camera Characteristics Format 4096x4096
pixels Pixels 12m Exposure 150ms Read time
2-sec
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HMI Optics Package
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HMI Inside the Box
HMI will obtain 32 16-megapixel images each minute
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SDO Spacecraft - HMI Components
HMI Optics Package
HMI Electronics Box
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HMI and AIA JSOC Architecture
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HMI/AIA JSOC - (Joint Science Operations
Center)

• Data Capture from SDO ground system
• Archive of telemetry and processed data
• Distribution to team and exports to all users
• HMI and AIA processing to level-1
• HMI higher level science data products

• Expect to archive 1000TB/yr
• Metadata stored in PostgreSQL database
• Image data is stored online and on tape (LTO-4)
• Pipeline processing system to generate standard
  products
• Special products computed automatically on
  demand

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HMI Institutional Roles
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HMI Co-Investigator Science Team
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HMI web page http//hmi.stanford.edu This
presentation available at http//hmi.stanford.edu
/Presentations Data access http//jsoc.stanford.e
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