Quiettime proton fluxes in the streamer belt: information from Ulysses

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Quiet-time proton fluxes in the streamer belt
information from Ulysses

• K. Kecskeméty
• KFKI Research Inst. for Particle and Nuclear
  Physics, Budapest, Hungary
• Yu.I. Logachev, M.A. Zeldovich
•   Skobeltsyn Institute of Nuclear Physics, Moscow
  State University, Russia

21st ECRS, Koice, 11 September 2008
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Quiet-time low-flux background protons
Steady-state sources and losses
equilibrium Sources solar at lt20-30 MeV
Losses remnants of large/gradual SEP
adiabatic deceleration events
long-term history? escape at outer
boundary? micro/nano/picoflares
spectrum, release? CIR/GMIR - backstreaming
from outer heliosphere
(interplanetary shocks/ESP planetary/magnetosphe
ric pick-up galactic, anomalous)
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Energy spectrum
Suprathermal and energetic ions 100 keV - 30
MeV always present in interplanetary space,
power-law tail of Maxwellian, pick-up
from Mewaldt et al. (2001)
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Experimental difficulties very low fluxes/small
detectors instrumental background energy
misidentification 2-10 MeV 2 detectors/PHA
gt10-20 MeV galactic/anomalous contribution
Data sets used twofold coincidences, dE/dx vs.
E technique, PHA analysis instrumental
background determined with the same method as
for other detectors (SOHO EPHIN) Ulysses
COSPIN/LET (1.8-8.1 MeV) R 1 - 5.4 AU solar
activity minima 1994-1997 and 2006-2007 fast
latitude scan transient events removed, only the
quietest periods analyzed
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Radial variation 0.3 - 85 AU
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Ulysses variation with radial distance
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Latitudinal variation
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1994-97 2006-07 quiet periods
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Variation along the orbit
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Conclusions

• Radial variation
• Ulysses 2-8 MeV quiet fluxes are lower by 5 to
  10 than at Helios and Voyager, but only by 2
  lower than at Earth
• ? probably only partially due to a latitude
  effect
• Latitudinal distribution
• Lowest fluxes are 20-30 times lower beyond the
  streamer
• Pedestal between 45S and 30N
• Favours interplanetary/CIR origin vs
  solar/microflare
• Asymmetry gradual increase in northern
  hemisphere
• abrupt change in southern hemisphere
• Relation to the southward drift of heliospheric
  current sheet?
• (Mursula and Hiltula, 2003)