Assessment of the CMIP5 global climate model simulations of the western tropical Pacific climate system and comparison to CMIP3

Abstract

A set of 27 global climate models from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) ensemble are assessed for their performance for the purpose of making future climate projection studies in the western tropical Pacific and differences to Coupled Model Inter-comparison Project Phase 3 (CMIP3) are assessed. The CMIP5 models show some improvements upon CMIP3 in the simulation of the climate in the western tropical Pacific in the late 20th century. There are fewer CMIP5 models with very poor skill scores than in CMIP3 for some measures and a small group of the well-performing models in CMIP5 have lower biases than in an equivalent group from CMIP3. These best-performing models could be particularly informative for studying certain climate sensitivities and feedbacks in the region. There is evidence to reject one model as unsuitable for making regional climate projections in the region, and another two models unsuitable for analysis of the South Pacific Convergence Zone (SPCZ). However, while there have been improvements, many of the systematic model biases in the mean climate in CMIP3 are also present in the CMIP5 models. They are primarily related to the shape of the transition between the Indo-Pacific warm pool and equatorial cold tongue, and the associated biases in the position and orientation of the SPCZ and Inter-Tropical Convergence Zone, as well as in the spatial pattern, variability and teleconnections of the West Pacific monsoon, and the simulation of El Niño Southern Oscillation. Overall, the results show that careful interpretation and consideration of biases is required when using CMIP5 outputs for generating regional climate projections for the western tropical Pacific, particularly at the country scale, just as there was with CMIP3.

The Sea Level Response to External Forcings in Historical Simulations of CMIP5 Climate Models*

“…Currently, coupled climate models do not yet have a perfect representation of various modes of climate variability, such as the El Niño-Southern Oscillation (ENSO) or the Pacific decadal oscillation (PDO). However, the simulation of the western tropical Pacific climate variability and processes has improved for the new generation of climate models (CMIP5) with respect to the CMIP3 generation (e.g., Bellenger et al 2014;Grose et al 2014). In addition, Monselesan et al (2015) showed that, for sea level and sea surface temperature, the spatiotemporal characteristics of the variances over various frequencies or bands in the CMIP5 control runs and the observations are in reasonable agreement for those periods and regions where there are reliable observations.…”

Sea-Breeze Dynamics and Convection Initiation: The Influence of Convective Parameterization in Weather and Climate Model Biases

“…The representation of rainfall and the atmospheric circulation over the Maritime Continent is particularly poor in GCMs, and errors are apparent in both coupled and atmosphere-only climate model simulations (Flato et al 2013;Grose et al 2014). In coupled models, including the Met Office Unified Model (MetUM), precipitation rates tend to be overestimated over the Maritime Continent, primarily as a result of a cold tongue SST bias in the Pacific (Irving et al 2011).…”

Interannual and Decadal Variability in Tropical Pacific Sea Level

“…In this critical region of anomalously fast sea level-rise, the rise rate can be modulated by decadal to multi-decadal variability related to the low frequency Southern Oscillation Index (SOI) and Pacific Decadal Oscillation (PDO) [11]. In general, CMIP5 models show improved performance over CMIP3 in the western tropical Pacific, but continue to show significant biases in both mean state and variability [12]. This currently presents a challenge in predicting future SLR especially for vulnerable island nations of this region.…”