Link nature between low cloud amounts and cosmic rays through wavelet analysis

Abstract

Although much evidence implying correlations between low cloud cover variations and solar activity, the physical phenomenon explaining this is still poorly pronounced. Seventeen years of monthly averaged low cloud cover data from the International Satellite Cloud Climatology Project (ISCCP) are examined towards amplitude antipodal aa-index and sunspot number. We have used in our previous study [24] Morlet wavelets to examine the processes and structures behind the variability of solar activity indicators and galactic cosmic rays variations. Morlet wavelets analysis continues to prove its power in this study field. Thus we invest in the present work Morlet wavelets tool to examine closely the possible links between solar activity and climate. The purpose of this work is to examine once for all the geomagnetic aa-index and sunspot number variations towards low cloud cover amounts variations. One of the procedures to analyse non-stationary series, to discern whether there is a linear relation or not between low cloud amounts variations on a side and the geomagnetic aa-index and the solar activity on the other side is by means of wavelet method. Thus we have analysed variations in time, we arose hidden periods and structures being able to highlight a physical causal link between solar, geomagnetic activity and low cloud cover. Indeed besides of well-known 11 years cycle which was found common to all parameters, low cloud amounts, geomagnetic aa-index and sunspot number, three structures of 5–7 months, 12–13 months and 60–70 months (5–5.8 years) were found common to low cloud amounts variation and geomagnetic aa-index variations. Thus the iterative method used particularly in this study for extrapolation revealed more closely common hidden structures. If relatively long periods such as 11 years cycles highlight globally the GCR-cloud connection, the community of structures and short periods highlighted through this Morlet analysis zoom prove closely the link between these parameters and low cloud amount as a measure of climate. The Morlet wavelet analysis and our new iterative procedure for extrapolation prove with a good agreement that it is a suitable tool to reveal really hidden common structures and cycles. This analysis should be an answer to GCR-climate link around which several questions were discussed.