Natural variations of tropical width and recent trends

Abstract The temporal evolution of the tropical width since 1979 is investigated in observations and models by using metrics based on outgoing radiation, 6.7 µm brightness temperature, and atmospheric reanalysis. The maximum 20 year widening as seen in radiation by satellites occurred during 1993–2012 and was associated with a global sea surface temperature (SST) change that resembles the El Niño–Southern Oscillation/Pacific Decadal Oscillation in the Pacific region. Idealized experiments with Community Atmospheric Model version 5 reveal that Tropical Pacific SST pattern largely accounts for the widening. A number of Coupled Model Intercomparison Project Phase 5 coupled models can simulate, without any type of forcing, this satellite‐inferred tropical widening and its associated Pacific SST pattern. While model‐simulated widenings are consistent for all metrics, the two reanalysis‐based widenings are inconsistent internally and with the satellite‐based and model widenings. Our results reinforce suggestions that observed widenings can be explained by internal variability as captured by climate models, though this depends on whether reanalysis trends are regarded as reliable.