Solar Science

A blog of solar physics

Terry Sloan replies on the Svensmark process

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Terry Sloan has written his thoughts on my calculations as to whether Svensmark’s process should cause sufficient deflection towards the Earth’s magnetic poles to be measureable:

The word ‘funnelling’ is very misleading. I do not know where it  came from – it was not from me. Forget it – here is the real story.

Cosmic rays from outside the solar system come with a very wide spectrum of energies from zero up 10^20 eV. The intensity falls off  very rapidly as the energy increases (roughly proportional to E^-2.7, i.e. one over E to 2.7 th power, where E is energy). At low energies they are mainly protons with about 20% Helium and then smaller amounts of heavier nuclei.

The sun pours pours out streams of charged particles as well and this is called the solar wind. These are usually at low energies (much below 10^9 eV). These streams of particles form electric currents which generate a magnetic field. This field is still finite out to very  large distances (up to 100 times the distance from sun to Earth – this is 100 AU, 1 AU=astronomical unit = sun Earth distance)

Imagine a cosmic ray coming from outside the solar system in the direction of the Earth. If the ray has very high energy it is hardly deflected and so can hit the Earth.

However, at lower energies it feels  a finite deflection and it does not need much of a deflection at a large distance from the Earth to miss the Earth.

Now the solar wind is stronger at the peak of the sun spot number in its 11 year cycle than at the minimum activity. Hence less of the lower  energy cosmic rays hit the Earth during solar maximum.

Have a look at a cosmic ray monitor (see and follow the links on there). You can clearly see the 11 year solar cycle on the cosmic ray rate. The rate varies by 15-20% from solar max to solar min.

The cosmic ray has not yet finished. If it manages to evade the magnetic field generated by the solar wind it then has to get through the Earth’s magnetic field. Near the Earth’s equator this field tends to be about perpendicular to a particle hitting the Earth. So again low energy particles are deflected away and do not hit the Earth.

Near the poles a cosmic ray aiming at the Earth travels parallel to these field lines which then have very little effect (remember that the force on a charged particle moving in a magnetic field is perpendicular to the velocity and the field).

Hence you see less 11 year modulation on the cosmic ray rate near the equator but a larger effect near the poles. Have a look at the Climax (somewhere near the pole) and Huancayo (close to the Equator) monitors (do a Google on them) and you will see what I mean.

I hope this helps.


Terry Sloan.

Here are plots of Climax and Huancayo that Terry was referring to:


Written by John A

August 17, 2009 at 1:55 pm

Posted in Svensmark

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