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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● 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]


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


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 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)


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 -

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

Simulated spectrum

unfolds gradually

Nose-tail asymmetry

Controlled by κ┴

ACR flux continues

to increase beyond TS


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 w5 MeV ACR 10 AU off the TS

5 MeV

Cooled down to 100 keV

Starting energy 5 MeV


Chance to become 5 MeV ACR10AU off the shock

Real

numbers

acceleration cooling

Nose (V-1)

Flank 60 West


Age distibution

ACRs are `older’ deeper in the HS

Nose

&

60E

Reverse method w larger κ Forward method w smaller κ


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

  • 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:

●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

  • 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 -

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

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

VLISM: partially ionized

H,He

0.1/cc μG B ?

ACR

SEP

GCR


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