Effect of the October 2003 energetic particle event on Martian surface radiation
D.A. Brain, J.G. Luhmann
F. Leblanc
R.A. Mewaldt, C.M.S. Cohen
G.T. Delory
October 2003 Event
Earth and Mars “on same field line” during record-setting Halloween event
Protons 1MeV to 1 GeV
October 2003 EventMars Global Surveyor - Electron Reflectometer Data
Energetic particles “contaminate” instrument background channels
SEP Events at Mars
• Which SEPs reach the surface?
• Do crustal fields play a role?
• What are the surface fluxes from the October 2003 event?
Which SEPs reach the surface?
http://physics.nist.gov/PhysRefData/Star/Text/contents.html
these primaries reach surface
g = 3.71 m/s2
P(0) = 6.36 mbarH = 11.1 km
Role of Crustal Fields
Test particle trajectories
• Cain(n=60) crustal field
• Isothermal CO2 atmosphere
• Release protons radially down from 1000 km
Role of Crustal Fields
Lower energies deflected more
Lower energies
absorbed higher
Deflection at Surface
Deflection is small for primaries reaching surface
Deflection near Exobase(~150 km)
Deflection at exobase can be significant for lower energy particles
Energetic Particles at 400 km
Geographic variation correlated with crustal source location is observed in MGS dayside electron “background” for the July 2002 event. This effect is observed after shock arrival.
Energetic Particles at 400 km
Geographic variation correlated with crustal source location is observed in MGS dayside electron “background” for the July 2002 event. This effect is only observed after shock arrival.
Energetic Particles at 400 km
MGS passage over crustal sources often correlated with dropouts in penetrating particles.
Energetic Particles at 400 km
Geographic variation is difficult to detect for the October 2003 event without first removing trends in the overall background flux. Still, there may be some geographic variation.
Energetic Particles at 400 km
October Eventat Surface
The time integrated GOES event spectrum resembles the SIREST SEP/SPE input spectrum
http://sirest.larc.nasa.gov/
Integrated Event Spectrum SIREST Input SPE Spectrum
October Eventat Surface GCRSEP
InputSpectra
OutputSurface Flux
neutrons (up and down)
protons
Surface radiation flux from SEPevent exceeds that from GCRs
Summary
• Crustal fields significantly deflect incident SEPs (E0 ~ 200 keV) by 100-200 km over the strongest crustal sources at altitudes of 150 km. MGS ER must be affected by protons ~200 keV at 400 km, or some other species
• The surface radiation for the October 2003 SPE was orders of magnitude greater than surface radiation from GCRs. ( Our event resembled the SIREST SPE example spectrally and in terms of interplanetary flux )