资源环境科技发展态势分析平台

The tropical Pacific climate state response to both the 21st-century greenhouse gas forcing and orbital forcing on a glacial-interglacial timescale tends to resemble either an El Nino- or La Nina-like pattern. This study reveals that so long as an El Nino- or La Nina-like change in the tropical climate state occurs, changes in two important negative feedback components of the El Nino-Southern Oscillation (ENSO) system, dynamical damping by mean thermal advection (MA) and thermo-dynamical damping (TD), largely offset each other. For example, under the El Nino-like condition, weaker trade winds due to a relaxed zonal sea surface temperature (SST) gradient reduce the mean zonal and meridional currents in the equatorial Pacific oceanic mixed layer, causing a reduction in MA, while wider expansion and enhanced activity of climatological convective clouds due to a warmer ocean surface intensifies negative SST-cloud-shortwave feedback. As a result, a change in ENSO activity in changing climate is mainly ruled out not by the change in negative feedback effect, but by the change in positive feedback effect.