2003 fall agu san francisco, ca 8 december 2003
DESCRIPTION
Observations of the Anisotropies of Enhanced MeV Ion Fluxes at Voyager 1 at 85 AU A. C. Cummings and E. C. Stone, Caltech L. F. Burlaga, GSFC N. F. Ness , Bartol F. B. McDonald, U. Md. W. R. Webber, NMSU. 2003 Fall AGU San Francisco, CA 8 December 2003. Summary. - PowerPoint PPT PresentationTRANSCRIPT
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Observations of the Anisotropies of Enhanced MeV Ion Fluxes at Voyager 1
at 85 AU
A. C. Cummings and E. C. Stone, CaltechL. F. Burlaga, GSFC
N. F. Ness, BartolF. B. McDonald, U. Md.W. R. Webber, NMSU
2003 Fall AGU
San Francisco, CA
8 December 2003
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Summary
• Cosmic Ray Subsystem 5-MeV proton flow anisotropies at V1 in 2002/2003 are large, variable, and generally outward along the azimuthal field
• Average radial anisotropy for 2002/195-2003/38 is small– In agreement with LECP observations
– Could be because V1 was downstream of the termination shock
– However, because the radial streaming must be continuous across the shock, the radial streaming upstream of the shock should also be small (Jokipii, Kota, and Merenyi, Ap.J,. 405, 782-786,1993)
• ACR spectra do not show spectral unfolding expected if V1 crossed the main portion of the shock (McDonald et al., 2003)
• Magnetic field data show no evidence that V1 crossed the termination shock (Burlaga et al., 2003)
• In this case, the small radial streaming suggests the particles are coming from the termination shock and not from an interplanetary shock co-moving with the solar wind, for which a convective anisotropy would be observed
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CRS instrument on Voyager 1
B
A
C
D
11.25 inches
H2
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Boresights of five CRS telescopes on Voyager 1
Note (A+B)/(C+H2)is good indicatorof azimuthal flow
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4.1-6 MeV protons during 2002-2003
Black > red => azimuthal flow generally along
nominal field line away from solar
direction
Beams of particles are
present ~70% of the time
(143 of 208 days have ratios
significantly > 1)
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5-parameter model for particle distribution
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Model results for 10 days in 2002
Dots are plotted where 2 1.
Dark blue blobs show where max flux is. Red blobs are where min flux is.
Blue plus signsshow magnetic field locations on some of the days.
Agreement is good in this stretch of data with good statistics.
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Azimuths for selected and
unselected data
Magnetic field data selected such that estimated uncertainty on polar and azimuth are <20 deg.
Particle data selection based on reduced 2 of fluxes from 5 telescopes. For large 2 the agreement with magnetic field data is pretty good.
Even the “all” particle data show that the flow is generally azimuthal and outward along field line.
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5-parameter model for particle distribution with net radial and azimuthal anisotropy shown
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Particle anisotropies in R & T
del R =(JR-J-R)/(JR+J-R)del T =(JT-J-T)/(JT+J-T)
Equivalent to definitionof 1st order anisotropy
Radial streaming is near zero in all panels. (Expected Compton-Getting anisotropy for 400 km/s wind is shown as vertical dashed line.)
Azimuthal streaming is mostly outward along the nominal field line direction.
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He spectra for three periods
ACRs are heavilymodulatedwhen lowenergy increase atV1 appears.
So, accordingto current models, V1would notappear to beat the TS.
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Summary
• Cosmic Ray Subsystem 5-MeV proton flow anisotropies at V1 in 2002/2003 are large, variable, and generally outward along the azimuthal field
• Average radial anisotropy for 2002/195-2003/38 is small– In agreement with LECP observations
– Could be because V1 was downstream of the termination shock
– However, because the radial streaming must be continuous across the shock, the radial streaming upstream of the shock should also be small (Jokipii, Kota, and Merenyi, Ap.J,. 405, 782-786,1993)
• ACR spectra do not show spectral unfolding expected if V1 crossed the main portion of the shock (McDonald et al., 2003)
• Magnetic field data show no evidence that V1 crossed the termination shock (Burlaga et al., 2003)
• In this case, the small radial streaming suggests the particles are coming from the termination shock and not from an interplanetary shock co-moving with the solar wind, for which a convective anisotropy would be observed