Recurrent Cosmic Ray Variations in 2007-2008

József Kόta & J.R. JokipiiUniversity of Arizona, LPL

Tucson, AZ 85721-0092, USA

23rd ECRS, Moscow, Russia, July 5, 2012

kota@lpl.arizona.edu

● V-1

- Outline -

• 200-2008 was a Year of Recurrent Variations: the quiet Sun, moderate tilt angle, & stable CIRs* led to 27-day CR variations (Leske et al, Modzelewska et al., 2011).

• We present numerical simulations using our re-vitalized 3-D CR code assuming stable co-rotation. We discuss qualitative, general features of simulation results

• Briefly discuss numerical simulations of Jovian electrons, which also showed remarkable recurrent variations (Kecskemėty et al., 2011)

* CIR = Corotating Interaction Region

Formation of Corotating Interaction Region

• CIRs are the result of tilted magnetic dipole + solar rotation: later emitted fast wind overtakes the earlier emitted slow wind. CIRs form typically beyond 1 AU

Equatorial cutFast wind from coronal holes

Recurrent Variations in 2007-2008

Leske et al, ICRC, Beijing, 2011) Modzelewska et al, 2011

CR

SW

B

Interpretation of 27-day CR wave

• Cosmic ray intensity is higher where the solar wind is slower. Modzelewska et al., 2011 relates CR flux, J, to V*B (electric field)

• The rate of CR decrease (dJ/dt) is higher in the stronger magnetic field of compressed regions (Burlaga’s CR-B law)

dJ/dt ~ - B

implying non-local connection between CR & B

Example of Earlier Numerical Simulation

o Assume perfect co-rotation. SW & B are specified near the Sun (caveat: V kept radial)

o Global 3-D transport code solves Parker’s diffusive equation in co-rotating frame

Current Simulation & Implications

o Take symmetric dipole configuration but place Earth off-equator

o CR Intensity peaks at low speed (Modzelewska)

o Intensity falls sharply at strong B (Burlaga-law, Kota & Jokipii, 1991)

o Connection between CR flux and plasma parameters may not be local

A<0 (blue) applies

Jovian Electrons

• Leske et al (2011) presented and interesting study using near-Earth and Stereo A & B observations. Electron fluxes did not show any clear correlation with CIR structures.

• In simulations Jupiter is a moving source in the corotating frame.

• We expect combined effect of CIR + magnetic connection

Earth/Jupiter go around in 27/26 days

Simulation of Jovian Electrons - 2

Simulation of Jovian Electrons - 4

Jovian Electons: Time dependence

Note: fluxes at Earth & Stereos follow the flux near Jupiter which changes in 26-day wave according to CIRs.

These results are in qualitative agreement with Kecskemėty et al. (2011) who find rather 26 than 27 day variations (non-local origin.)

Lesson

● “Make everything as simple as possible, but not simpler “

CR fluxes are notuniquely determined by local plasma & B

Summary/Conclusion

• The Sun was very quiet while its magnetic axis remained moderately high during 2007-2008 , which lead to a remarkably stable CIR structure. Corresponding 27-day CR variations were clearly present (Leske et al., 2011; Modzelewska et al., 2011)

• We have re-vitalized our earlier 3-D CR transport/acceleration code to simulate these recurrent variations. Simulations results are qualitative agreement with observational findings: (e.g. CR max at slow wind, intensity decrease at strong B)

• While the mechanism cannot be definitely identified (there are alternative explanations) , the connection between CR flux and B need not be local

• Jovian electrons tend to point to non-local origin of the recurrent CR variations as well.

The End

2. Diffusive Particle Transport: Parker’s Equation (1965)

Diffusive transport equation of energetic charged particles:

- assumes near isotropic distribution

Diffusion(anisotropic) Drift Convection Cooling/

Acceleration

Source

Related to regular gyro- motion

Polarity/charge dependent

Mixed system

Classic CIR-Calculation (Fisk & Lee, 1980)

• Fisk & Lee (1980) assume κ~r, which allows analytical approximation is but highly simplified

• Model results are in good qualitative agreement with observations.

Harder spectrum at the reverse shock

Simulation of Jovian Electrons - 1

Simulation of Jovian Electrons - 3