Saturday, April 12, 2008

On Solar Links: Sloan Responds To Shaviv

Earlier in April, Terry Sloan and A.W. Wolfendale published a paper in which they offered an apparent refutation of Henrik Svensmark's theories linking solar activity to Global Warming. The paper is here, my post on it here. Yesterday, astrophysicist N.J. Shaviv published an on-line critique in which he suggests that Sloan and Wolfensdale have made three mistakes in their paper:

Two arguments are based on the expectation for effects which are much larger than should actually be present. In the third argument, they expect to see no phase lag, where one should actually be present. When carefully considering the link, Sloan and Wolfendale did not raise any argument which bares any implications to the validity or invalidity of the link.

I contacted Terry Sloan yesterday afternoon via email and asked him if he would like to respond to Mr. Shaviv's arguments, and he asked me to post the following:

Dear Shaviv,

I would like to correct the factual errors in your blog.

1. Concerning cosmic rays. Muons, neutrons and the soft component of cosmic rays are all produced from the interactions of the primaries in the upper atmosphere. So the thickness of atmosphere above them is irrelevant. This is a factual error in your paper.

You say we should have compared with ionization chamber data - no such long term data exist either for shielded ion chambers (only sensitive to muons) or unshielded (sensitive to ionization from both muons and electrons). If such data had existed we would have used them.

The Ususkin et al computations of the solar modulation of the total ionization in cycle 22 are compatible with our neutron monitor curve. So our analysis is safe.

2. Your fig 2 from the other Usoskin et al paper is for a highly selected data sample with a large correlation coefficient - not the global average with which we compare. Hence your fig 2 has little to do with our analysis using global averages. We stuck to global averages because in the original Marsh and Svensmark work they computed from the globally averaged dip in cycle 22 that the radiative forcing was 1.4 W m^-2 if all the dip was caused by CR. We set out either to confirm whether the dip was due to CR or not and if not to set a limit on the fraction of it which could come from this source. As we could find no corroborative evidence that it was due to ionization we set a limit. Our limit says that the radiative forcing cannot be more than 23% of 1.4 W m^-2.

3. Forbush decreases - the changes in the CR rate were averaged over the same time intervals as the changes in the LCC - so we have done this correctly and not incorrectly as you imply. The Forbush decreases usually take place over times between days to a month.

Regards, Terry Sloan.

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