Predicting Solar Energetic Particle Events

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Predicting Solar Energetic Particle Events
Solar and Space Physics and the Vision for Space
Exploration October 16-20, 2005

• John Davis, Ron Moore,
• Edward West, Allen Gary
• NASA/MSFC/NSSTC

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Radiation Hazards in Deep Space

• Astronauts traveling in interplanetary space or
  working on the surface of the moon are subject to
  radiation exposure from high energy charged
  particles of both galactic and solar origin.
• The galactic cosmic rays provide a continuous
  radiation background of very high energy
  particles that are difficult to shield.
  Fortunately their flux is relatively low.
• The flux of solar energetic particles (SEPs) is
  typically low but not infrequently can rise
  rapidly to very high levels that pose a serious
  hazard for unprotected astronauts.
• There are currently no reliable methods for
  predicting the onset and magnitude of SEP events.
  

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Predicting SEP Events

• SEP events have their origin in the explosive
  release of magnetic energy in solar flares and
  coronal mass ejections (CMEs).
• The CME explosion is released by the reconnection
  of stressed magnetic fields, with the
  reconnection occurring in the region where the
  magnetic field is the controlling factor.
• The interaction of the outward propagating shock
  front of the CME with the solar wind accelerates
  the population of energetic particles that form
  the SEP event.
• Depending on the details of the acceleration
  processes and the magnetic connectivity between
  the flare site and the observer the energetic
  particles can arrive in times ranging from less
  than an hour to days.
• Reliable prediction of SEP events requires
  reliable prediction of the initial event, the
  shock acceleration processes and the propagation
  through interplanetary space.
• Predicting the initial explosion requires
  improved knowledge of the magnetic field at the
  reconnection site

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The Reconnection Site Magnetic Field

• Vector magnetic field measurements of the
  magnetically controlled region surrounding the
  reconnection site are essential to understanding
  the structure and dynamics of the field that
  creates the conditions that allows the
  reconnection process to occur.
• Vector field measurements above the photosphere
  are required to determine the field at the
  reconnection site and to improve calculation of
  the magnetic free energy.
• Current observations of the solar vector magnetic
  field are restricted to the photosphere where the
  gas pressure controls the behavior of the
  magnetic field.
• To understand reconnection it is essential to
  directly measure the magnetic field in the
  magnetically controlled layers above the
  photosphere.

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The Magnetic Field and the Solar Atmosphere

Because the atmospheric plasma pressure falls off
more rapidly with height than the magnetic
pressure there is a regime change from
convectively dominated (ßgt1, non-force free), to
magnetically dominated (ßlt1, force free) with a ß
1region in between.
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Measuring the Magnetic Field

• Solar magnetic fields are observed by measuring
  the polarization of magnetically sensitive
  spectral lines. Although the polarization from
  the line of sight component is relatively strong
  the polarization that results from the transverse
  components is weak, making its measurement
  difficult.
• The sensitivity of the line of sight component is
  proportional to the square root of the number of
  photons, while that of the transverse component
  is proportional to the fourth root.
• The lines that we propose to sample the solar
  atmosphere from the photosphere to the base of
  the corona are FeI(6302Å), NaI(5895Å),
  CaII(8542Å), MgII(2880Å) and CIV (1550 Å).
• We are preparing to study the polarization
  properties of the MgII and CIV lines using a
  sounding rocket payload SUMI, the Solar
  Ultraviolet Magnetograph, that will fly in late
  2006. SUMI will make exploratory observations of
  the of the two lines with the objective of
  recovering magnetic field information.

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SUMI A Solar Ultraviolet Magnetograph
SUMI is a sounding rocket instrument that will
make its first flight next year that will make
the exploratory observations of the magnetic
field structure in the transition region.
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To measure the magnetic field across the
reconnection region, from the photosphere to the
base of the corona, requires a large optical
telescope. MTRAP, the Magnetic Transition Region
Probe, is a conceptual design for a very large
solar observatory that meets these requirements.
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MTRAP Design Requirements

• The telescope collecting area was set at 20m2 in
  order to obtain reasonable transverse field
  sensitivity at CIV. Vector magnetic field
  detection thresholds are
• Longitudinal Transverse
• Photosphere 1G
  15G
• High Chromosphere 3G
  100G
• Low Transition Region 15G
  300G
• The telescope FOV is baselined at (5 x 5 arc
  minutes²) to cover a large active region.
  The angular resolution is 0.05 arc sec or 35 km
  (0.025 arc sec pixels). The FOV was set by the
  requirement to keep the energy flux density on
  the heat stop to the equivalent of one sun.
• Integration times vary from 1-10s in the
  photosphere/low chromosphere to10-100s in the
  high chromosphere low transition region.
• The strawman design has four imaging
  magnetographs (IM) and two
  spectrographs. The IMs are baselined with 4(4k x
  4k) multiport readout CCDs mounted in a square
  array. The CCDs require large full well depths
  (250Ke) to minimize the number of readouts
  required to achieve a signal to noise of 104.

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An Isometric View of MTRAPfrom a study performed
by the GSFC Instrument Synthesis and Analysis
Laboratory-December 2004
Secondary Mirrors and Alignment Mechanisms
Field Stop Plate and Radiators
20m ADAM Extendable Mast
4 ½ m ABLE Telescoping Mast
Primary Mirrors x 6
The double mast structure is necessary to allow
the light from the primaries to pass from the
outside to the inside of the boom where the
secondary mirrors are located. The stand for the
4 ½m mast doubles as the radiator for the field
stop.
Spacecraft
Instrument Section
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MTRAP in Fairing

• Payload mass estimate 1936 kg, which provides a
  30 contingency
• Power estimate 800 W

Telescoping ABLE mast, 2.4 meters diameter, 0.9
meters stowed, 4.5 meters deployed
Mechanisms (0.5 meters high)
Elephant stand (1 meter high, interface between
ADAM mast and field stop platform)
Primary mirror (one of 6)
ABLE ADAM Mast (2.4 meters stowed 20 meters
deployed behind primary mirrors
Instruments 2.8 m diameter x 1.5 m high
S/C 2.8 m diameter X 1.1 m high
Diagram from Mick Correia and Joseph Generie
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SUMMARY

• The combination of new observations (Solar-B,
  SUMI, SDO, MTRAP) and improved analytical and
  theoretical techniques for describing the
  stressed magnetic field structure will improve
  our understanding of the processes that lead to
  reconnection.
• If the events leading to reconnection follow a
  general pattern, it will be possible to develop a
  predictive capability that would provide warnings
  of hours to days of the onset and magnitude of
  the predicted event.
• Once the events leading to a reconnection event
  are well understood, more modest instrumentation
  designed specifically to search for this
  signature can be developed.