Evaluation and Projection of the Climatic Characteristics of Aleutian Low Based on CMIP5 Models

The observed sea surface temperature, sea level pressure and multi-model simulations of the Coupled Model Inter-comparison Project 5 (CMIP5) are explored to analyze the temporal and spatial variation of the Aleutian Low (AL) index in the North Pacific. Furthermore, the decadal cycle variability is evaluated and the long-term trend is estimated based on simulations of the CMIP5. Results show that the CMIP5 multi-model simulations can well reproduce the climatology and variability of the AL circulation. Specifically, the simulated AL is sensitive to simulated sea surface temperature in the East Pacific. However, the comparison of the CMIP5 multi-model ensemble results and observations indicates that the intensity of the standard deviation of the ensemble mean is stronger than that of the observation, while the model ability for standard deviation simulation is worse than that for mean climate state simulation. Also, 16 out of the 22 CMIP5 models can reproduce the decadal oscillation cycle of the AL. In the Historical experiment, there is a large disagreement over the long-term trend of AL among the model results. It is suggested that the AL strengthens and extends northward under two typical Representation Concentration Pathway scenarios (i.e. RCP4.5 and RCP8.5), particularly under the RCP8.5 scenario. More significant annual and inter-decadal variations are found under the RCP8.5 scenario. It is also noted that the ensemble mean and most of the models can forecast the AL intensity and its northward extension. However, the reason for the eastward extension of AL is still controversial.