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 )