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Comments

A. C. Cummings, Caltech

Joint ACE/SOHO/STEREO/Wind Workshop

Kennebunkport, ME

8-11 June 2010

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Drifts carry positive particles from high latitudes to low latitudes duringA>0 portion of solar cycle. Expect positive latitudinal gradient in A>0.

Arrows reversed in A<0. Expect negative latitudinal gradient in A<0,which is the current situation.

Expect radial gradient to depend on tilt angle during current A<0 period.Not so sensitive during A>0.

Adapted from Jokipii & Thomas, 1981

Drift Patterns for qA>0

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Radial (and latitudinal) gradients showed strong dependences on current sheet tilt angle in last A<0 period(1986-1989) and more moderate dependence in A<0 – in outer heliosphere.

Gradient vs tilt in the past and the tilt model

Tilts from WilcoxSolar Observatory

Rad gradA<0

Rad gradA>0

Cummings & Stone, 1999

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Tilt at 1 AU (Wilcox Solar Observatory) is convected out by solar wind. Can work your way back from source intensity in outer heliosphere by integrating along gradient (tilt) steps. Gradients scaled by 1/r from 1987 measurements and gradient not sensitive to tilt inside 11.4 AU. Also, different fixed gradients inside 11.4 AU for A<0 vs A>0.

Tilt of HCS vs time

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Snapshot of HCS configuration in mid 1987 with locations of V1 and V2 shown.

Intensity at any radial position can be calculated from an assumed source intensity at an assumed source location.

Leske & Cummings,private communication 2009

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More detail on the “fixed” radial gradients inside 11.4 AU

• 1-4.5 AU:– A<0: 47.6 %/AU

– A>0: 25 %/AU

• 4.5-11.4 AU:– A<0 & A>0: ~12 %/AU

• Recent Ulysses-STEREO-ACE study for 2007-1008 A<0 found 48%/AU, consistent with tilt model

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Gradients of ~7-16 MeV/nuc O

C = 0.03 -> norm factor = 0.97

Rad grad = 48 ± 14 %/AU

Lat grad = 0.03 ± 0.3 %/º

Chisq = 16.2 for 16degrees of freedom

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Jokipii and co-workers

For ACRs, we also have to incorporate A<0 vs A>0 source intensity changes near helioequator.-- This is why I think it’s Ok to have GCRs be at their all-time high intensity at 1 AU but not ACRs – ACRs more sensitive to tilt than GCRs because of different source distributions.

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Result for 1968-2000.

Cummings & Stone, 1999.

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The End

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Summary

• Model needs refinement– Need to factor in motion of termination shock for one thing

• Not clear why V2 ACR and GCR intensities are lower recently– Tilt feature appears at about right time to possibly explain it but…

• Tilts are still fairly high in HS where gradient only weakly depended on tilt at 33 AU in last A<0 period in 1987

• Tilt model may work differently in HS where structures are compressed

– Good test is coming up with lower tilts on the way

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Radial Gradient of 7-25 MeV/nuc ACR O during A<0

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~40%/AU

Indirect inferencefrom 5-S/C studysuggests Gr~40%/AUfrom 1-4 AU, similar tothis result.

From Cummings et al., 1995

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Leske & CummingsProduction, 2010

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Leske & Cummingsproduction, 2010