HR: 0830h
AN: GC31B-0181    [PDF]
TI: The Roles of El Nino and Solar Forcing on Cloud Cover
AU: * Rohde, R A
EM: bobbyr@socrates.berkeley.edu
AF: UC Berkeley, Department of Physics, LeConte Hall 7300, Berkeley, CA 94720 United States
AU: Levine, J
EM: jlevine@socrates.berkeley.edu
AF: UC Berkeley, Department of Physics, LeConte Hall 7300, Berkeley, CA 94720 United States
AU: Muller, R A
EM: ramuller@lbl.gov
AF: UC Berkeley, Department of Physics, LeConte Hall 7300, Berkeley, CA 94720 United States
AB: Although cloud cover has a very strong effect on climate, its behavior is so poorly understood that its role is frequently neglected. A potential breakthrough occurred with initial reports that cloud cover could be driven by variations in cosmic rays (H. Svensmark \& E. Friis-Christensen, J. Atmos. Solar-Terr. Phys. v. 59, n. 11, pp 1225-32, 1997, and N.D. Marsh \& H. Svensmark, Space Sci. Rev., pp 1-16, 2000). In this paper we report a detailed analysis of recently extended data now available from the International Satellite Cloud Climatology Project. In a surprise, we find that the major driving force for cloud cover is ENSO (El Nino / Southern Oscillation). In addition, we do find a weak but significant response to solar forcing; however, in contradiction to the previous reports, we find no stronger relationship to cosmic rays than to other solar parameters. For the majority of the 23 cloud types available to us, interannual variability is dominated by changes that follow the NINO3 index of Pacific sea surface temperatures. In particular, increases in high-altitude and vertically extensive cloud cover are observed to follow the motions of warm water throughout the El Nino cycle. Even far from the Pacific, many cloud cover changes are observed to correlate with El Nino, and these data provide a new and previously unexplored tool for understanding the global nature and influence of the El Nino / Southern Oscillation. In contrast, solar forcing of cloud cover is observed in, at most, a few cloud types. Only in the cloud type emphasized by Svensmark, low-altitude clouds detected in the infrared, does the dominant mode of interannual variability make a good match with solar forcing. The extended cloud record provides continued support for solar forcing of this cloud type; however, unlike Svensmark, we find no empirical reason to prefer cosmic ray flux as the forcing mechanism over any other type of solar cycle variation (e.g. irradiance or UV flux changes). Our observations indicate that while the internal redistributions of heat and precipitation associated with El Nino are the dominant influence on most cloud types, there is a weak but significant response to solar forcing present in at least part of the cloud volume.
DE: 0320 Cloud physics and chemistry
DE: 1620 Climate dynamics (3309)
DE: 1650 Solar variability
DE: 2104 Cosmic rays
DE: 4522 El Ni¤o
SC: Global Climate Change [GC]
MN: 2003 Fall Meeting