Discrimination between cosmic ray and solar irradiance effects on clouds, and evidence for geophysical modulation of cloud thickness

Abstract

Solar activity and galactic cosmic rays (CRs) are closely inversely correlated. In studies of cloud changes associated with solar changes, the close solar activity-CR relationship can cause ambiguity in attributing the cloud changes to one factor or the other. A method for discriminating between cloud effects from these causes is described, using the 1.68 yr periodicity present in surface-based measurements of CRs but absent in radio flux measurements of solar activity. The periodicity is present in CRs and other heliospheric parameters during, at least, solar cycle 21. Daily surface radiation measurements sensitive to cloud during a similar period (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990) at Jersey and Lerwick exhibit 1.68 yr periodicities, indicating a CR, rather than solar irradiance, cloud effect. In the Jersey data, it is not possible to discriminate between 'near-cloud' (droplet charging) and 'clearair' (ion nucleation) effects, but further study of the Lerwick cloud data shows that the periodicity is present only during thick overcast cloud conditions. Bandpass filtering the cloud and CR data (passband 1.55-1.81 years) shows that the cloud thickness responds in phase with the CR flux. This modulation suggests the near-cloud effect through geophysical modulation of the air-Earth current density. Cloud thickness modulation by the air-Earth current density can occur by the charge-enhanced activation (electroactivation) of cloud droplets on the upper and lower boundaries of stratiform cloud.

Solar Influence on Global and Regional Climates

“…Voiculescu et al (2006) argue that both UV and GCRs have an effect. Harrison (2008) detected a weak 1.68-year oscillation in the long diffuse fraction data series from the Lerwick (maritime) station-an oscillation found in the open solar flux and GCR fluxes but not in the SSI or TSI variations (Rouillard and Lockwood 2004). Hence, this supports a direct effect of GCRs rather than irradiance changes.…”

Solar change and climate: an update in the light of the current exceptional solar minimum

“…The correlation of this residual was higher for GCRs than for sunspots although the sunspots were in phase; the GCRs lagged 2 years behind which would be evidence that irradiance phenomena like TSI would have to be the cause rather than the GCRs (were the correlation indeed significant). In contrast, Harrison (2008) detected the 1.68-year oscillation, known to be in GCR fluxes but largely absent in TSI data (Rouillard & Lockwood 2004), in long sequences of ground-based cloud measurements. This suggests a GCR-induced effect on cloud rather than an irradiance effect.…”

On the intrinsic timescales of temporal variability in measurements of the surface solar radiation

“…The intrinsic timescales found in these IMFs seem to match once more those pertaining to the so-called quasi-biennial oscillations (QBOs) that have been observed in solar activities and proxies with periodicities between 0.6 and 4 years (Bazilevskaya et al, 2015;Kolotkov et al, 2015;Vecchio et al, 2012), as well as in meteorological data like Harrison (2008) who identifies a 1.68-year peak in cloud cover or high-latitude stratospheric temperatures and geopotential heights (Labitzke and Loon, 1988). Nevertheless, within the scope of the current analysis, the interpretation of these lowfrequency variability components as a real, possibly QBOlike, signal is uncertain.…”