CIRs: Acceleration and transport to high latitudes

József Kóta & Joe Giacalone w/ thanks to J.R. Jokipii

The University of Arizona,

Tucson, AZ 85721-0092

2006 Shine Workshop, Zermatt Utah, August 2006

kota@lpl.arizona.edu

- Outline -

• CIR accelerated particles appear as recurrent low-energy events

• 1st polar pass of Ulysses: CIR events at high latitudes, where no similar variation in Vsw and/or B present.

• Simulations for GCR and low energies• Energy loss and modulation for low-energy

particles• Illustrative examples• Compressive acceleration• Summary/Conclusions

Ulysses observations

• Recurrent variations in V & B

• Corresponding dips in GCR

• Enhancements at low energies – continue to be present to highest latitudes

Transport to high latitudes

Interpretation

o Fisk field

o Cross-field transport (Kóta & Jokipii, 1995,1999).

- Parker’s equation

- accelerated population wherever divV<0

- cross-field transport κ┴/κ║≈ 0.02-0.05

+ Also explains why electrons lag behind ion

events

Recurrent particle events at high latitudes: Simulation

Simulated Vsw, B, & GCR fluxes Low-energy ion/electronsNote delay for electrons

electrons

ions

Cooling along spiral field

Curvature drift against VxB electric field

VxB field• Charged particles lose energy even if they move along the spiral field.

• Reason curvature drift. More effective at tight spiral (no loss for radial B)

dp/dt ~ p

Δlnp ~ t

Cooling: Numerical Examples

• Parker spiral field at latitude 30o

• Input: power law spectrum at 15 AU

• Fokker-Planck equation for focused transport

- Scatterfree: Dμ = 0

- Hemispherical (λ=inf.)

- Diffusive: Dμ = w*(1-μ2)/2λ

Field-aligned TransportSkilling (1970), Ruffolo 1995), Isenberg (1997) Kóta & Jokipii (1997):

Fokker-Planck equation:

Coefficients:

inertial parallel perpendicular

d/dt (ln n/B) d/dt(ln B)

Net compressiondivided into paralleland perpendicularcomponents

Frozen in !!!

Math

• Transport coefficients for corotating field:

Conservation

`Modulation’ for scatterfree propagation

Scatterfree (Dμ=0, λ=inf.) Hemispherical (λ=inf.)

Dashed: input at 15AU

15 AU10 AU 5 AU 1 AU

Note discontinuity at 15 AU

Scattering included

Fluxes at different radial distances 1AU fluxes for different λ-s

1, 5

, 1

0,

15

AU

λ(A

U)

= 1

.5,

3.5

, 7

.5,

in

f.

Compressive acceleration

o Mason et al (2002) observed energetic particles that must had been accelerated at < 1 AU where shock had not yet been formed

o Giacalone et al (2002) interpreted this in terms of compressive diffusion acceleration. Acceleration occurs wherever plasma is compressed (dn/dt > 0). It can be effective if

VΔx/κxx < 1

Summary -- CIRs

o CIR accelerated particles can reach high latitudes via cross field diffusion

o Particles lose energy while moving along (curved) field lines even in scatterfree case

o Compression acceleration may occur before shock is formed

Zermatt/Matterhorn