Science update: Thermal characteristics of the cold-point tropopause region in CMIP5 models

J. Kim and co-authors focus on the cold-point tropopause region as simulated by CMIP-5 models in a new JGR article. They look at the climatology, seasonality, and intraseasonal to interannual variability of the temperature field near the cold-point tropopause (CPT) in all CMIP-5 models for both historical simulations and future projections (using RCP8.5). The CPT temperature is estimated using both the 100-hPa and zero-lapse-rate (ZLR) temperatures. The historical simulations reproduce the spatio-temporal structure of the CPT temperature as well as the interannual variability associated with ENSO and the intraseasonal variability associated with equatorial waves successfully. However, the models show non-negligible biases in several aspects: 1) most models have a warm bias around the CPT; 2) large inter-model differences occur in the amplitude of the seasonal cycle in 100-hPa temperature; 3) several models overestimate lower stratospheric warming in response to volcanic aerosols; 4) temperature variability associated with the quasi-biennial oscillation and Madden-Julian oscillation is absent in most models; 5) equatorial waves near the CPT exhibit a wide range of variations among the models with unrealistically persistent Kelvin waves in several models. In terms of future projections, the models predict a robust warming at both the 100hPa and ZLR levels, but cooling at the 70hPa level. Most models also project a weakened seasonal cycle of temperature at both 100hPa and 70hPa levels. These findings may have important implications for cross-tropopause water vapour transport and related global climate change and variability. The full abstract can be found here.