H/T to Michele Casati who flagged up this paper on suggestions. I don’t have time to read it all through but it looks interesting, and hopefully people with knowledge of wavelet analysis might take a look and report their views. Looks to me like Joanna Haigh might start re-educating herself with papers like this.
In this paper we analyze the geographical distribution of the climate response to external forcing (solar, volcanic and geomagnetic) on the periods of 11 and 22 years. As a climate characteristic we use the data of the air-surface temperature (regional data sets). The analysis is performed by the wavelet phase/coherence technique which is applied to the solar (sunspot numbers), volcanic (Dust Veil Index), geomagnetic (C9-index) activities and the temperature data on interannual timescales for the common time interval covering most of the 20th century. Besides, we analyze the statistics of the temperature response to the solar and geomagnetic factors on the periods of 11 and 22 years for different geographical sectors. In particular, we find the existence of a combined forcing of solar and volcanic activity on the Earth temperature on the 11-year period in the second half of the 20th century over the globe, whereas a set of stations (mostly in North Atlantic) shows a coherence between solar activity and the Earth temperature on the 11-year periodicity even in absence of the combined effect; it was found that the maximal number of stations demonstrating statistically significant amplitudes of wavelet spectra corresponds to the wavelet cross coherence between geomagnetic activity and the Earth air-surface temperature on the periods about 22 years during the time interval without intensive volcanic eruptions capable to change significantly the level of DVIGlobal.
Full paper download here