Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

Download Presentation

Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

Loading in 2 Seconds...

- 94 Views
- Uploaded on
- Presentation posted in: General

Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

● V-1

SHINE Nova Scotia, August 2009

● V-2

Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations

J.Kόta

University of Arizona

Tucson, AZ 85721-0092, USA

Thanks: J.R. Jokipii, J. Giacalone

kota@lpl.arizona.edu

Difference between 1 & 2 D Shocks

● Are Anomalous Cosmic Rays (ACRs) indeed accelerated at the solar wind termination shock (TS) ?

Likelyyes but

● Bluntness of TS counts

● Topology between shock & field Lines counts (cannot be modeled in 1 D)

● Model still qualitative

Do not consider other important effects, like dynamical variations

Multiple intersection explains precursor anisotropies

and ….

V-2

V-1

Displacement of the ‘nose’ helps

ACR fluxes continued

to increase into the

Heliosheath

● Temporal variaton

(Florinski Zank,2006)

● Magnetic topology

(McComas & Schwadron,

Kόta & Jokipii)

● Combination of the two?

Can be a direct result of 2D topology

Could have been foreseen (Kόta & Jokipii, 2004)

McComas and Schwadron (2006)

Blunt Shock

Injection & Acceleration at Flanks

Short time for

acceleration

Kóta and Jokipii, 2004

This Simulation: Shock & Injection stronger at nose, weaker toward tail

More TSP at nose (injection profile)

Less ACRs at nose (global feature)

Simulated spectrum

unfolds gradually

Nose-tail asymmetry

Controlled by κ┴

ACR flux continues

to increase beyond TS

- Solve Parker’s equation “backward”, with the solar wind blowing inward. What we obtain is the “chance” function which is to be convolved with injection.
- Inward wind advects trajectories back to the TS, where pseudo-particles cool-down to injection energy.
- Ideally suited for GCRs (all trajectories leave sooner ot later the heliosphere. More cumbersome for ACRs

5 MeV

Cooled down to 100 keV

Starting energy 5 MeV

Real

numbers

acceleration cooling

Nose (V-1)

Flank 60 West

ACRs are `older’ deeper in the HS

Nose

&

60E

Reverse method w larger κ Forward method w smaller κ

- ACRs are best accelerated if injected at front (more time for acceleration)
- Birthplace at Nose: Likely most of all ACRs (even those in tail) were injected at front.
- Nursery toward Flanks: TSP seen by Voyagers is the seed population of MeV ACRs. TSPs moving toward flanks during further acceleration.

- Scenario (M* ) is more efficient to accelerate energetic particles
- Voyager precursor events may have been associated with configuration M*

M*

Less efficient- More efficient

> <

●V-1

●V-2

● Magnetic field lines cross the blunt TS multiple times. This explains upstream anisotropies and :

● Two-population spectrum: ACRs start as TSPs at the nose and move toward the flanks during acceleration. Appear still modulated at the TS, and continue to increase into the heliosheath.

● 2-D Shock differs from 1-D shock (topology)

● Dependence on parameters (κ) still need to be explored .

- The distribution & spectrum of MeV ACRs turn out largely insensitive to the injection-profile along the shock.
- Lower ACR intensity is obtained at the nose even if
- injection rate and/or shock ratio is higher at nose

Reason: unfavourable topology (natural cold spot)

- To trace the history of ACRs we perform a “backward“ simulation. The solar wind is reversed and a pseudo ‘testparticle’ is released from the point of observation. What we obtain is the Green-function or chance of injected particle to become ACR

cold

hot

Along shock front

“nose”

“tail”

Distance from shock

Global structure along shock front

organized by magnetic field

ACR fluxes continued to increase beyond TS

Source outside

Shock

V. Hess 1912

Voyager-1 December 2004

Similar result from V-2 (2007)

VLISM: partially ionized

H,He

0.1/cc μG B ?

ACR

SEP

GCR