drift models and polar field for cosmic rays propagation stefano della torre 11th icatpp, como 5-9...
TRANSCRIPT
Drift models and polar field
for cosmic rays propagation
Stefano Della Torre
11th ICATPP, Como 5-9 october 2009
Outline•Cosmic Rays propagation
in different period/polarity
•Drift Models
•Solar Wind
•Heliosphere
•Conclusions
Modulation
A>0 A<0
Tilt Angle from Wilcox Obs.
Shikaze et al. 2007
Boella et. Al. 2001
Modulation
There is a strong dependence of the modulation from the polarity of the field
Variation between two consecutive minimum(it change the Field polarity)
Rate of flux in two consecutive period with similar solar activity
Boella et. Al. 2001
The Cosmic Rays propagation inside the heliosphere is described by the Parker equation
U Cosmic Rays number density per unit interval of kinetic energy
Cosmic Rays propagation
Diffusion
Small Scale Magnetic
Field irregoularity
ConvectionPresence of
the solar wind moving out
from the Sun
Energetic Loss
Due to adiabatic expansion of the
solar wind
Drift
Large Scale structure of
magnetic field(e.g. gradients)
Along the equatorial region, where the magnetic field invert his polarity, we have Neutral Sheet Drift
Neutral Sheet
Sheet with |B|=0
-> charge dependent
-> Magnetic polarity dependent
Magnetic Drift
Drift
This Effect is greater during solar minimum periods, when the Heliosferic Magnetic Field (HMF) have a regular
topology, and vanishing during Solar Maxima due to chaotic behavior of the field line
Potgieter et al. 1985
Neutral Sheet
Coronal Magnetic Field lines at Solar minimum Activity
The combination with the Solar Rotation cause a tilt of the Neutral Sheet; causing the so called “ballerina skirt”
effect around the Eclittica Plane
The amplitute of this oscillation is called Tilt Angle ()
And it depends of Solar activity: e.g. minimum activity -> 10°, maximum activity ->
>75°
Neutral Sheet DriftPotgieter & Moraal (1985)
Burger & Potgieter (1989)
Wavy Neutral Sheet - Hattingh & Burger (1995)
Ordinary Drift
NS drift
Transition Function that emulate the effect of a wavy neutral sheet
2D Approximation
er
r
R22
N
S
during solar Minimum
AMS-01 (1998)
CAPRICE (1994)
Tilt Angle () < 30°
Solar WindHigh Solar ActivityLow Solar Activity
)cos(10 VVSWUlysses measurement
Agreement with dataAgreement with data
Modified Heliospheric Magnetic Field
A
We use a Simple
Parker’s Field
With a Polar modification as in Jokipii & Kòta 1989
Polar Cosmic Rays access reduced
Agreement with Agreement with datadata
A solar Magnetic perturbation generated TODAY on the Sun, will get the Heliopause in
Dynamic view of HMF
month
We divide the heliosphere in 14 region, with previous solar condition each
AMS-01 view of heliosphere
A Cosmic Particle in average will remain 1 month into heliosphere
Agreement with dataAgreement with data
In all simulation presented we use PM model
30°
A>0 A<0
BESSHigh Solar Activity
AMS-01Low Solar Activity
IMAXMiddle solar
activity
CAPRICELow Solar Activity
Experimental Data
NymmikEmpirical Model.One parameter model:
smoothed sunspot number in the months previous the oservations data.
For All NucleiActually the ISO
standard for space qualification.
Increase of precision compared with Nymmik model
Our Average variance = 5%Nymmik Average variance = 16%
Conclusions
• We develop a 2D - MonteCarlo Stochastic
program that reproduces Cosmic rays data in
different solar periods using a dynamic view of
HMF.
• We use a modified Magnetic field that reduces
the drift contribute in polar regions.
• We find that during solar minimum both
PM and WNS model reproduce data with
confidence; increasing solar activity only
PM model does that.
• The Solar wind latitudinal dependency is
relevant in order to reproduce data
