Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing

Abstract

More Than the Sum of the Parts The radiative output of the Sun varies distinctly with the 11-year cycle of sunspots, although the change in energy output is small—less than a tenth of a percent in magnitude. Nevertheless, that small variation produces changes in sea surface temperatures two or three times as large as it should, and the mechanism by which this occurs has remained unclear. Meehl et al. (p. 1114 ; see the news story by Kerr ) employ three global, coupled climate models to simulate this phenomenon. Two mechanisms appear to act in conjunction to cause this ocean response: a change in the abundance of stratospheric ozone owing to fluctuations of shortwave solar forcing; and a coupled surface ocean-atmosphere response. This combination of effects enhances precipitation maxima, reduces low-latitude cloud cover, and lowers the temperature of surface waters in the tropical Pacific Ocean, resulting in the larger warm-to-cold variation.