dave brain uc berkeley space sciences lab (hi folks! sorry i couldn’t make it!)
DESCRIPTION
Space Weather Events at Mars: Spacecraft Observations and Consequences for the Atmosphere and Surface. Dave Brain UC Berkeley Space Sciences Lab (Hi folks! Sorry I couldn’t make it!). 10’s MeV ions. 10-20 keV electrons. . Count Rate. Count Rate. . ER. Energy. Energy. - PowerPoint PPT PresentationTRANSCRIPT
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