Acceleration of acrs at a blunt termination shock 2 d simulations
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● V-1. SHINE Nova Scotia, August 2009. ● V-2. Acceleration of ACRs at a Blunt Termination Shock: 2-D Simulations. J. K ό ta University of Arizona Tucson, AZ 85721-0092, USA Thanks: J.R. Jokipii, J. Giacalone. [email protected] Difference between 1 & 2 D Shocks.

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

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Acceleration of acrs at a blunt termination shock 2 d simulations

● 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

[email protected]


Acceleration of acrs at a blunt termination shock 2 d simulations

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


Acceleration of acrs at a blunt termination shock 2 d simulations

Voyager-1 fooled us with (1) “anti-sunward” precursor anisotropiesSolution: field line intersects the TS multiple times.

Multiple intersection explains precursor anisotropies

and ….

V-2

V-1

Displacement of the ‘nose’ helps


Voyagers fooled us with 2 spectra did not unfold at crossing the ts solution field lines

Voyagers fooled us with(2) spectra did not unfold at crossing the TSSolution: field lines .….?

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)


Acceleration of acrs at a blunt termination shock 2 d simulations

McComas and Schwadron (2006)

Blunt Shock

Injection & Acceleration at Flanks

Short time for

acceleration

Kóta and Jokipii, 2004


2d simulation of blunt ts offset circle no latitudinal motion

2D simulation of Blunt TS (offset circle)- no latitudinal motion -

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

More TSP at nose (injection profile)

Less ACRs at nose (global feature)


2 d simulation offset circle cont d

2 D simulation (offset circle) cont’d

Simulated spectrum

unfolds gradually

Nose-tail asymmetry

Controlled by κ┴

ACR flux continues

to increase beyond TS


Tracing back acrs

Tracing back ACRs

  • 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


Backward tracing starting w 5 mev acr 10 au off the ts

”Backward tracing” starting w5 MeV ACR 10 AU off the TS

5 MeV

Cooled down to 100 keV

Starting energy 5 MeV


Chance to become 5 mev acr 10au off the shock

Chance to become 5 MeV ACR10AU off the shock

Real

numbers

acceleration cooling

Nose (V-1)

Flank 60 West


Age distibution

Age distibution

ACRs are `older’ deeper in the HS

Nose

&

60E

Reverse method w larger κ Forward method w smaller κ


Implications

Implications:

  • 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.


One word on precursor events possible scenarios for voyager

One word on Precursor Events:Possible scenarios for Voyager

  • Scenario (M* ) is more efficient to accelerate energetic particles

  • Voyager precursor events may have been associated with configuration M*

M*

Less efficient- More efficient

> <


Summary

Summary:

●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 .


Global features are insensitive injection profile

Global features are insensitive injection profile

  • 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


Illustrative example of 2 d shock field shock angle alternates

Illustrative example of 2-D shock- field/shock angle alternates -

cold

hot

Along shock front

“nose”

“tail”

Distance from shock

Global structure along shock front

organized by magnetic field


Motivation where is the source is history repeating itself do we need a new paradigm likely not

Motivation: where is the source?is history repeating itself ?Do we need a new paradigm ? Likely not

ACR fluxes continued to increase beyond TS

Source outside

Shock

V. Hess 1912

Voyager-1 December 2004

Similar result from V-2 (2007)


Global structure of heliosphere

Global structure of Heliosphere

VLISM: partially ionized

H,He

0.1/cc μG B ?

ACR

SEP

GCR


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