SOLAR CAUSES OF GLOBAL VARIABILITY


A scientific field may be said to be in trouble when one particular paradigm dominates that field (Akasofu, 1996). The paradigm challenged by the work proposed here is that most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations (IPCC, 2007). During the last decades there is accumulating evidence that solar activity and  interplanetary conditions play an important role in the global climate variability (e. g. Marsh and., Svensmark, 2003, Haigh, 2007, Gray et al, 2010, Kossobokov et al. 2010, Le Mouel el et al. 2009, Dima et al, 2005, Dobrica et al, 2008).  These findings are opposed to those arguing that solar signal is small, some correlations are purported or statistics is applied incorrectly (e. g. Kristjansson et al, 2004, Laut, 2004, Legras et al., 2010). This subject is extremely controversial at international level, requiring active, intensive research.

 

CLOUD COVER: ESSENTIAL COMPONENT IN THE TERRESTRIAL RADIATION BUDGET.


Clouds have both a cooling effect, by reflecting short-wave solar radiation back to space, and a warming effect, by reducing the loss to space of the long-wavelength radiation. The resulting net radiative effect depends on cloud altitude, composition, particle structure. It is generally considered that high clouds (HC) tend to heat, while low clouds (LC) tend to cool the low troposphere, except for ice surfaces. Habilomatis et al. (2005) showed that the cooling effect of clouds has decreased  by about 2 W/m2 at the  top of atmosphere (decadal-scale trend 1.2 W/m2) and by 2.8 W/m2 at the surface, over a 17-year period (1984-2000), possibly contributing to recent temperature increase. Consequently, the study of solar modulation of the cloud cover is of outmost importance for solar-climate relationship, since a small variation  in the cloud cover leads to important modifications of the terrestrial radiation budget (Svensmark and Friis-Christensen, 1997).

The variability of the solar irradiance (the solar parameter that is fully accepted by the entire community as the direct driver of the climate) is too small to explain the observed solar signal in variations of climate parameters (temperature) (Gray et al., 2010). There is increasing interest in the indirect effect of solar variability on climate, based on mechanisms involving other solar proxies, i.e. cosmic rays (CR), solar ultraviolet irradiance (UVI) that could amplify the solar signal (Harrison, 2004, Usoskin et al, 2004, Voiculescu et al, 2006, 2007, Erlykin et al, 2010). CR and UVI are anti-correlated, since a high UV flux is the result of a higher solar activity and an increased heliospheric magnetic field, which reduces the galactic CR flux. Thus a CR effect might mask the UVI influence and  viceversa.

 

SOLAR EFFECTS ON CLOUD COVER


The lack of consensus whatsoever about any of the possible relationships (Haigh, 2007) and the tremendous need of quantifying, as much as possible, the solar contribution to climate variability, reflect both the motivation and the timeliness of choosing this research topic. The present proposal aims to get an image of the individual effect of the two solar proxies, CR and  UVI, on cloud cover, using  an interdisciplinary approach involving knowledge from atmospheric physics, space physics, climatology and advanced statistical tools.

 

SELECTED REFERENCES


  • Akasofu S.I., Search for the “unknown” quantity in the solar wind: A personal account, J. Geophys. Res.,  101, A5, 10531-10540 (1996)
  • Dima, M., G. Lohmann, I. Dima,  Solar-induced and internal climate variability at decadal time scales, Int. J. Climatol. 25,  713–733 (2005).
  • Dobrica, U., Demetrescu,C., Boroneant,C., Maris,G., Solar and geomagnetic activity effects on climate at regional and global scales: case study., R. J. Atmos. Sol.-Terr.Phys., doi:10.1016/j.jastp.2008.03.022 (2008)
  • Erlykin A.D,  T.Sloan, A.W.Wolfendale , Correlations of clouds, cosmic rays and solar irradiation over the Earth, Journal of Atmospheric and Solar-Terrestrial Physics, 72 151–156 (2010)
  • Gray L.J., J. Beer, M. Geller, J.D. Haigh, M. Lockwood, K. Matthes ,U. Cubasch, D Gleitmann, G. Harrison, L. Hood, J. Luterbacher, G. A. Meehl, D.Shindell1, B. van Geel1, W. White, Solar Influences on Climate, Review of Geophysics, Reviews of Geophysics, 48, RG4001 /  1 - 53, 8755, 1209/10/2009RG000282 (2010)
  • Habilomatis, G., N. Hatzianastassiou, I. Vardavas, Modelling the effect of clouds on the shortwave radiation budget at global scale for the 17-year period 1984-2000, Geophysical Research Abstracts, Vol. 7, 08842, EGU 2005
  • Haigh, J. D, Solar variability and climate, Space Weather, ed. J. Lilenstein, 65–81 (2007)
  • Harrison, R. G., The global atmospheric electrical circuit and climate, Surveys in Geophsyics, 25, 441-484 (2004).
  • Intergovernmental Panel on Climate Change,. In: Solomon, S. (Ed.), Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, New York (2007)
  • Kristjansson, J.E., Kristiansen, J., Kaas, E. Solar activity, cosmic  rays, clouds and climate an update. Adv. Space Res. 34, 407–415 (2004).
  • Kossobokov, V., J. L. LeMouel, V. Courtillot., A statistically significant signature of multi-decadal solar activity changes in atmospheric temperatures at three European stations, Journal of Atmospheric and Solar-Terrestrial Physics 72 595–606 (2010)
  • Laut, P., Solar activity and terrestrial climate: an analysis of some purported correlations, Journal Atmos. Sol-Terr Phys., 65, 801-812 (2003)
  • Legras B., O. Mestre, E. Bard, and P. Yiou, A critical look at solar-climate relationships from long temperature series, Clim. Past, 6, 745-758, doi:10.5194/cp-6-745-2010 (2010).
  • Le Mouel, J.L.,Blanter,E.,Shnirman,M.,Courtillot,V., Evidence for solar forcing invariability of temperatures and pressures in Europe, .J. Atmos. Sol.- Terr. Phys.71, 1309–1321,doi:10.1016/j.jastp.2009.05.006 (2009).
  • Marsh, N., Svensmark, H. Solar influence on Earth’s climate. Space Sci. Rev. 107, 317–325, (2003).
  • Svensmark, H., Friis-Christensen, E.,. Variation of cosmic ray flux and global cloud coverage—a missing link in solar–climate relationships. Journal of Atmospheric and Terrestrial Physics 59, 1225 (1997)
  • Usoskin, I.G. M. Voiculescu, G.A. Kovaltsov, K. Mursula, Correlation between clouds at different  altitudes and solar activity: Fact or Artifact?, Journal of Atmospheric and Solar-Terrestrial Physics, 68 2164–2172 (2006).
  • Voiculescu, M. I. G. Usoskin, and K. Mursula, Different response of clouds to solar input, Geophysical Research. Letters, 33, L21802, doi:10.1029/2006GL027820 (2006)
  • Voiculescu, M. I. G. Usoskin, and K. Mursula, Effect of ENSO and volcanic events on the Sun-cloud link, Advances in Space Research, 40, 1140–1145 (2007)