Space Weather Events at Mars:Spacecraft Observations and

Consequences for the Atmosphere and Surface

Dave BrainUC Berkeley Space Sciences Lab

(Hi folks! Sorry I couldn’t make it!)

MGS ER “Background”

10-20 keV electrons

Energy

Cou

nt R

ate

ER

‘High’ energy channels of electron instrument record 10-20 keV electrons and energetic ions

10’s MeV ions

Energy

Cou

nt R

ate

Comparing count rates in these 3 channels allows determination of which particle populations contribute to observations

A Space Weather Event at Mars

shock arrival

‘real’ electronspresent

‘real’ electrons present

quiet time

data dropouts

MGS observations best for obtaining timing information at 1.5 AU, and qualitative info about fluxes of 10’s MeV ions and 10-20 keV electrons

SEP Events at 1.5 AU1999-2005

More than 50 events (over 5 years) of enhanced background

Count rate exceeds 50 counts/second ~4% of the time

March 2003 SEP Event

-100

900

1900

2900

3900

4900

76.51 77.01 77.51 78.01 78.51

Day of Year (2003)co

unts

/min

ute MARIE A1 counter

Odyssey Latitude

ER background count rate

The radiation detector on Mars Odyssey saw modulations in the count rate at the S/C orbital period during a SEP event

The MGS electron instrument also saw modulations at the S/C orbital period. But the event started much later at MGS!

MARIE and ER likely sensitive to different particle energy ranges

March 2003 SEP Event

last page

• The event(s) observed by MARIE lasted beyond March 19• Largest increase in solar wind pressure occurred late on March 21, after decline in particles and during subsequent event• IMF changes direction on the 19th from dawnward to duskward• 10-20 keV electrons observed through the 25th

‘real’ electrons

Dropouts

Dropouts in ‘background’ count rate observed during SEP events

10-20 keV electrons removedAre 10’s MeV ions removed?Why do the dropouts occur?

Dropouts

Some dropouts associated with shadow entry/exit

S/C shielding effect?Electric fields?Ionospheric clouds?

Dropouts

Some dropouts associated with Martian crustal sources

?

Crustal fields exclude 10-20 keV electrons?

More Dropouts

Dropouts during more intense July 2002 event are associated primarily with leaving shadow in southern hemisphere, and crustal magnetic fields

And Still More Dropouts

No dropouts before shock arrival dropouts in 10-20 keV electrons only

Solving the MysteryObserved by MGS Electron instrument:

• Oscillation in quiet time background• Many SEP events• Elevated ‘background’ count rates during SEP events (10’s MeV ions)• 10-20 keV electrons after shock arrival• Dropouts in background count rate during SEP events

• correspond to shadow entry/exit• correspond to crustal magnetic fields

• Plenty more to do…

What is going on?• Detailed physical interpretation tantalyzingly difficult (argh!)• Dedicated instruments likely required

• SEP detector (10’s MeV to 1 GeV)• Clean electron measurements• Solar wind monitor (IMF, dynamic pressure)

SEP Event Science at Mars

1. Physics of SEP events• Propagation through heliosphere• Structure/morphology at 1.5 AU

2. Consequences for Mars• Effects at surface• Effects on atmosphere

Solar Protons at Mars

http://physics.nist.gov/PhysRefData/Star/Text/contents.html

Solar Protons at Mars

http://physics.nist.gov/PhysRefData/Star/Text/contents.html

g = 3.71 m/s2

P(0) = 6.36 mbarH = 11.1 km

Solar Protons at Mars

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

Shielding by Martian Atmosphere

protonsalphaselectrons

Martian Atmosphere

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

GCRSEP

InputSpectra

OutputSurface Flux

Surface radiation flux from SEP event comparable to or exceeds that from

GCRsOctober Eventat Surface

neutrons (up and down)

protons

Do Crustal Fields Matter?

Effects of Crustal Fields

exobase

Magnetic fields deflect low energy (few MeV) particles

Deflection of Primary Protons

small deflection at surface for high energy

protons

large deflection for lower energy protons(at higher altitudes)

Effects of Crustal Fields

For low energy particles:Less energy is deposited above crustal sources than in surrounding

areas

Summary

• The surface radiation from a large SPE can be important compared to the surface radiation from GCRs.

• Crustal fields do not strongly effect SEPs reaching the Martian surface.

• Crustal fields can have a significant effect on atmospheric energy deposition during a SPE, driving chemistry and dynamics

( Proposal to continue this work submitted to Planetary Atmospheres )

Also: Relationship discovered between the presence of intense auroral-like

electron distributions and SEP events at Mars