Warren White, Mike Dettinger, and Dan Cayan

Scripps Institution of Oceanography, University of California San Diego, 8600 Gilman Drive, La Jolla, CA 92093-0230, USA

"Excitation of Earth's natural mode of climate variability by decadal changes in the Sun's irradiance"
Global-average upper ocean temperature fluctuated in fixed phase with changing solar irradiance on decadal period scales over the past 100 years, but its amplitude was 2 to 3 times larger than expected from the Stefan-Boltzmann radiation balance (White et al., 1997, 1998). Examining global patterns of upper ocean temperature and lower troposphere winds indicates that the Earth's ocean-atmosphere system does not respond passively to changes in the Sun's irradiance; rather, natural modes of Earth's climate variability on decadal period scales appear to be excited by the solar signal, intensifying Earth's temperature response to changing solar irradiance.

To understand how this happens, we begin by conducting a global-average upper ocean heat budget utilizing upper ocean temperatures from the SIO reanalysis and air-sea heat and momentum fluxes from the NCEP reanalysis, finding the source of global warming on decadal period scales to be the reduction in trade wind intensity during the onset phase, reducing global average latent heat flux out of the ocean. Next, we find this reduction in trade wind intensity also generating subtropical Rossby waves in the Pacific Ocean, leading to a delayed action oscillator mechanism in the ocean-atmosphere system differing little from that used to explain the El Niño-Southern Oscillation (Graham and White, 1998). We operate an intermediate coupled model of this delayed action oscillator, normally driven by white noise in sea level pressure, by superimposing upon it the Stefan-Boltzmann upper ocean temperature response to decadal changes in the Sun's irradiance.

We find the latter, with non-random phase, yielding peak spectral temperature variability on decadal period scales 2 to 3 times larger than expected from solar forcing alone.

Graham, N. and W.B. White, 1988. The El Niño a natural oscillator of the Pacific ocean/atmosphere system. Science, 240, 1293-1302.

White, W.B., J. Lean, D.R. Cayan and M.D. Dettinger, 1997. A response of global upper ocean temperature to changing solar irradiance. J. Geophys. Res. 102, 3255-3266.

White, W.B., D.R. Cayan and J. Lean, 1998. Global upper ocean heat storage response to radiative forcing from changing solar irradiance and increasing greenhouse gas/aerosol concentrations. J. Geophys. Res. 103, 21355-21366.