Empirical Model of the LowEnergy Plasma in the Inner Magnetosphere

1
Empirical Model of the Low-Energy Plasma in the
Inner Magnetosphere

• J. L. Roeder, M. W. Chen, J. F. Fennell
• Space Sciences Applications Laboratory
• The Aerospace Corporation
• Los Angeles, CA USA
• R. Friedel
• Los Alamos National Laboratory
• Los Alamos, NM USA

2
Effects of Low-Energy Particles on Materials

• Low-energy (0.1-100 keV) particle environment
  induces severe effects on satellite surface
  materials
  
• Ions cause cumulative changes
• Sputtering (collisional ejection of atoms)
• Ion implantation with resulting chemical
  reactions
  
• Higher mass ions tend to be more effective for
  damage
  
• Synergetic effects of ions with electrons and
  solar ultraviolet radiation
  
• Extrapolation of NASA radiation belt models to
  low energies is too uncertain
  
• Example is Tedlar material with UV coating
  subjected to a simulated GEO environment

3
Statistical Model of Particle Flux Environment

• Model average omni directional particle flux
  spectrum as function of spatial position within
  Earths magnetosphere
  
• Fly through spatial model to accumulate an
  average ion flux spectrum over any orbit (similar
  to NASA AE8 and AP8)
  
• Data from CAMMICE/MICS and Hydra particle
  instruments on NASA Polar satellite
  
• Polar launched in 1996 into 9 x 2 RE orbit at 98
  inclination
  
• Available data
• CAMMICE/MICS data from March 1996 April 2002
• Hydra data from March 1996 present
• Model constructed in 3-d magnetic coordinates (L,
  magnetic latitude, magnetic local time) from IGRF
  model magnetic field
  
• Compare average spectrum of low energy particles
  with high energy spectra predicted by NASA models

4

• Polar has limited coverage of trapped particle
  fluxes trapped near equator
  
• Equatorial crrossings start near L 3 and move
  outward over the mission duration
  

5
CAMMICE/MICS Model

• MICS measures H-Fe ion fluxes of 1-200 keV/q with
  mass and charge state separation
  
• Major ion species in inner magnetosphere H and
  O
  
• MICS has a single field-of-view direction
  providing limited angular coverage so map in
  pitch angle to magnetic equator
  
• Averaged 5-minute intervals over 3.5 years
  February 1996 October 1999 (174 M data
  points)
  
• 12 energies
• 4 particle species H, O, He, and He
• Spatial bins
• 18 equatorial pitch angles
• 16 values of L over range 210
• Two-hour bins in magnetic local time
• Map pitch angle data from equator to latitude of
  target orbit
  
• Average all angles for omni directional flux
  spectrum

6
CAMMICE/MICS Equatorial Pitch Angle Distributions

• Total ion flux predominately H except at lowest
  energy
  
• Ion flux at ? 90 trapped at magnetic equator
  flux at lower and higher pitch angles are ions
  that mirror at higher and lower latitudes
  
• Gaps at ? 90 for L5 from poor Polar
  equatorial coverage
  
• Fitting procedure fills equatorial data gaps
  (dotted lines)
  
• Distributions harden for lower L shells due to
  energization of ions as they drift inward

7
Statistical Variation of Ion Flux

• Huge variation of ion flux with geomagnetic
  activity over 4 orders of magnitude
  
• Average (mean) flux marked by solid white line
• Dotted lines mark average plus and minus standard
  deviation
  
• Relative standard deviation 100200

8
Radial and Local Time Variations of H Flux

• Equatorially trapped H flux (90 pitch angles)
  versus L and magnetic local time
  
• Symmetric local time distributions at highest
  energy
  
• Dusk premidnight bulge for lower energies
• Dusk sector peak consistent with the known ion
  transport processes which turn ions drift inward
  from the nightside and turn eastward
  
• Peak fluxes at L4 with sharp inside boundary at
  L3
  
• Small amounts of contamination from very high
  energy protons at inner boundary near L22.5

9
Radial Variation of H Flux Spectra

• Equatorially trapped H flux spectra versus L at
  magnetic local time
  
• Model validated against published model from
  AMPTE/CCE data Milillo et al., 1999
  
• Peak magnitudes agree with factor of 2
• Many but not all spectral and spatial features
  agree
  
• Faint spectral peaks at 35 keV due imperfect
  calibration match between low and high energy
  MICS channels. Negligible effects on orbital
  averaged flux

10
Comparison of AMPTE/CCE with CAMMICE/MICS Protons
11
Radial and Local Time Variations of O Flux

• Equatorially trapped O flux (90 pitch angles)
  versus L and magnetic local time
  
• L and local time distributions of O ions very
  similar to H
  
• Symmetric local time distributions at highest
  energy
  
• Dusk premidnight bulge for lower energies
• O spectrum much softer than H very few ions
  above 50 keV
  
• At lowest energy O ion flux comparable or larger
  than H flux

12
Radial Variation of O Flux Spectra

• Equatorially trapped O flux spectra versus L at
  magnetic local time
  
• No published model available for validation
  Milillo et al. 1999 analyzed only H
  
• Calibration match between low and high energy O
  channels is better than H, so no obvious
  spectral artifacts
  
• Lack of high energy O compared with H is
  consistent with the increase in the charge
  exchange loss process with energy for O

13
CAMMICE/MICS Ion Flux Time Series for GPS Orbit

• One-year average omni directional total ion flux
  for GPS orbit
  
• Ephemeris at 1-minute resolution
• Satellite magnetic coordinates and total ion flux
  shown for typical 2-day interval from the year
  
• H flux at most energies decreases rapidly with
  radius. So, as upper limit, flux for L10 set
  equal to value at L10. Possible problem with low
  energy O

14
Hydra Model

• Six years of data averaged (March 1996 early
  2002)
  
• Fluxes accumulated in spatial bins
• L (0.1 width)
• magnetic local time (1 hour)
• magnetic latitude (10 deg)
• Spectra interpolated to fixed set of energies to
  match data from various instrument operational
  modes
  
• Spectra re-interpolated over 50 bins (0.0214
  keV)
  
• Hydra model only for high inclination orbits such
  as GPS. Gaps in Polar orbit coverage at low
  latitudes not yet filled by interpolation or
  modeling.

15
Hydra Ion Flux Distribution in GPS Orbit

• Distribution of ion flux versus energy measured
  by Hydra averaged over GPS orbit
  
• High time resolution of Hydra instrument results
  in large number of measurement points for each
  bin
  
• Ion flux spectrum monotonically decreasing with
  energy
  
• Statistical variation is over 3 orders of
  magnitude, similar to MICS variation. Relative
  standard deviation 100 200

16
Average Particle Flux Spectrum in GPS Orbit

• H dominant above a few keV but O comparable to
  H at 12 keV
  
• CAMMICE/MICS H matches AP-8 spectrum 50200
  keV
  
• Hydra ions smoothly join to CAMMICE/MICS H and
  O at 1 keV
  
• Standard deviation of flux is 100150 of
  average value
  
• Negligible variation of flux between GPS orbital
  planes
  
• Ion mass composition for E

17
Average Flux Spectrum in GEO

• CAMMICE/MICS and NASA models averaged over
  arbitrary GEO trajectory
  
• Compared with LANL model Korth et al., 1999
• GEO measurements from all of 1996
• Magnetospheric Plasma Analyzer (MPA) data at 1
  eV40 keV assumed protons
  
• Excellent agreement between models
• Much softer high energy H spectra, as expected

18
Average Ion Flux Spectrum in GEO and GPS Orbit

• Negligible difference in O spectrum for two
  orbits
  
• Hardening of H spectrum consistent with
  acceleration of ions as they drift inward into
  high magnetic regions
  
• Lack of energetic O ions at GPS due to the known
  increase in O charge exchange losses at high
  energy

19
Summary

• Hydra, CAMMICE and AP8 can specify average
  spectrum over energy range from 10 eV to 5 MeV
  
• Excellent agreement between all ion models
• O ion flux equal to proton flux at 12 keV and
  H dominates at higher energies
  
• Almost identical O spectrum in GEO and GPS
  orbits
  
• Use Polar TIMAS data to extend ion composition
  below 1 keV and CEPPAD IPS to extend protons up
  to 1.5 MeV
  
• Compare models of Polar data with other missions
  including CRRES and SCATHA