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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