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 Niño- or La Niña-like pattern. This study reveals that so long as an El Niño- or La Niña-like change in the tropical climate state occurs, changes in two important negative feedback components of the El Niño-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 Niño-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.
All Science Journal Classification (ASJC) codes
- Atmospheric Science