New paper: Clouds blown by the solar wind

This paper suggests a terrestrial impact on cloud cover from the interplanetary electric field (IEF) via the global electric circuit. A primer video on the GEC is below.

Clouds blown by the solar wind M Voiculescu et al 2013 Environ. Res. Lett. 8 045032 doi:10.1088/1748-9326/8/4/045032

Abstract

In this letter we investigate possible relationships between the cloud cover (CC) and the interplanetary electric field (IEF), which is modulated by the solar wind speed and the interplanetary magnetic field. We show that CC at mid–high latitudes systematically correlates with positive IEF, which has a clear energetic input into the atmosphere, but not with negative IEF, in general agreement with predictions of the global electric circuit (GEC)-related mechanism. Thus, our results suggest that mid–high latitude clouds might be affected by the solar wind via the GEC. Since IEF responds differently to solar activity than, for instance, cosmic ray flux or solar irradiance, we also show that such a study allows distinguishing one solar-driven mechanism of cloud evolution, via the GEC, from others.

Introduction

There is high interest today in quantifying the solar contribution to climate change. Despite the progress in understanding the processes driving the Earth’s climate, quantifying the natural sources of climate variability, especially regarding solar effects, remains elusive (Solomon et al 2007, Gray et al 2010).

Although climate models are highly sophisticated and include many effects, they are not perfect and observational evidences are modest and ambiguous. Empirical evidences suggest a causal relationship between solar variability and climate, particularly in the pre-industrial epoch (Bond et al 2011), but possible mechanisms are unclear and qualitative. The balance between reflected radiation from space and Earth at different wavelengths contributes to temperature variation in a significant manner (Hartmann et al 1992), thus cloud cover play a major role in the terrestrial radiation budget. Modeling cloud contribution to climate at different spatial and temporal scales is probably the most challenging area of climate studies (Vieira and da Silva 2006). Despite increasing number of solar-cloud studies, there is no clear understanding of solar effect on cloud cover. Indirect mechanisms are proposed that would amplify the relatively small solar input and could explain solar-related variability observed at different time scales (from days to decades) in various cloud parameters, as for instance cloud cover (Udelhofen and Cess 2001, Marsh and Svensmark 2000, Voiculescu and Usoskin 2012) or cloud base height (Harrison et al 2011, Harrison and Ambaum 2013).

One indirect mechanism relates to the fact that the solar spectral irradiance varies significantly in the UV band, whose effect is limited to the stratosphere, thus a stratosphere–troposphere–ocean coupling, ‘top-down’ effect, is required (Gray et al 2010, Meehl et al 2009, Haigh et al 2010). Another mechanism relies on possible variations of atmospheric aerosol/cloud properties, affecting the transparency/absorption/reflectance of the atmosphere and, consequently, the amount of absorbed solar radiation. Two possible physical links have been proposed: one via the ion-induced/mediated nucleation by cosmic ray induced ionization (CRII) (Dickinson 1975, Svensmark and Friis-Christensen 1997, Carslaw et al 2002, Kazil and Lovejoy 2004, Yu and Turco 2001) and the other via the global electric circuit (GEC) effects on cloud/aerosol properties (Tinsley 2000, Harrison and Usoskin 2010). The former mechanism might be hardly distinguishable from noise, especially at short-term scale, as demonstrated using in situ/laboratory experiments (e.g., Carslaw 2009, Kulmala et al 2010, Enghoff et al 2011, Kirkby et al 2011) and statistical studies (e.g., Calogovic et al 2010, Dunne et al 2012). Opposing, studies of Svensmark et al (2009), Enghoff et al (2011), Svensmark et al (2013), Yu et al (2008) have shown that an impact of ionization on new particle formation and cloud condensation nuclei (CCN) exists. Thus it is possible that the CRII-nucleation mechanism operates at longer time scales, but it might be spatially limited to the polar stratosphere (Mironova et al 2012). On the other hand, the GEC-related mechanism may be important (e.g., Tinsley 2000, Harrison and Usoskin 2010, Rycroft et al 2012), particularly for low-clouds and some links have been shown to exist between atmospheric electricity properties and cloud evolution/formation (Harrison et al 2013).

Since all solar drivers correlate to some extent, it may be difficult to evaluate which driver or combination of drivers is the best candidate for cloud cover modulation. An attempt to differentiate between solar irradiation (total or UV) and CRII effects on cloud cover has been made by Kristjánsson et al (2004), Voiculescu et al (2006, 2007), Erlykin et al (2010), who showed that various mechanisms might act differently at different altitudes and geographical locations. However, the GEC is affected by the solar activity in a different way, via the interplanetary electric field (IEF), so that only positive IEF plays a role, while negative IEF does not. Positive IEF corresponds to a interplanetary magnetic field (IMF) with a southward component, or negative z-component, which favors a direct energy transfer from solar wind to the magnetosphere and to ionosphere. For negative IEF (positive z-component of the IMF) the transfer is much less efficient and only a very small percentage of the solar wind energy is transferred to the magnetosphere (e.g. Dungey 1961, Papitashvili and Rich 2002, Siingh et al 2005). Thus, in contrast to other potential solar drivers which are expected to exert a monotonic influence, IEF is expected to affect clouds only when IEF is positive. This feature has a potential of separating the IEF effect from other drivers. Here we present results of correlation studies between the interplanetary electric field (IEF) and cloud cover, which might indicate the most probable mechanism that might affect cloud cover. We discuss here mainly results obtained for low cloud cover (LCC), but we also refer to middle- (MCC) and high-clouds (HCC).

Conclusion

Here we present a result of an empirical study showing that there is a weak but statistically significant relation between low cloud cover at middle–high latitudes in both Earth’s hemispheres and the interplanetary electric field, that favors a particular mechanism of indirect solar activity influence on climate: global electric circuit affecting cloud formation. We show that all characteristics of the relationship are in line with what is expected if the interplanetary electric field affects cloud cover via the global electric circuit:

(1) the low cloud cover shows a systematic correlation, at interannual time scale, with positive interplanetary electric field, at mid- and high-latitude regions in both hemispheres;

(2) there is no correlation between low cloud cover and interplanetary electric field in tropical regions;

(3) there is no correlation between low cloud cover and negative interplanetary electric field over the entire globe.

As an additional factor, cosmic ray flux may also affect cloud cover in the presence of positive interplanetary electric field. No clear effect of cosmic ray flux during periods of negative IEF was found.

Similar, but less statistically significant results were found also for middle and high cloud cover, suggesting that the primary effect is on low-clouds. The fact that the found statistical relation exists only for the periods of positive IEF and not for negative IEF disfavors other potential mechanisms of sun–cloud relations at mid–high latitudes, such as via ion-induced/mediated nucleation or UVI influence. However, the latter might work at low–mid latitudes. Although this empirical study does not give a clue for an exact physical mechanism affecting the clouds, as discussed above, it favors a particular solar driver, solar wind with the frozen-in interplanetary magnetic field, that affects the global electric current system at Earth. The result suggest that further research of solar-terrestrial influence ought to focus more also on this direction.

=============================================================

The paper is open source, see it here:

http://iopscience.iop.org/1748-9326/8/4/045032/article

Related: No increase of the interplanetary electric field since 1926  (Sager and Svalgaard 2004)

Related articles

• Claim: Solar activity not a key cause of climate change, study shows (wattsupwiththat.com)