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<p>This study aimed to evaluate the temporal variability and spatial patterns of the Southern Annular Mode (SAM) using Coupled Model Intercomparison Project Phase 6 (CMIP6) models on a monthly time scale. It employed the SAM index, which was computed for Atmospheric Model Intercomparison Project (AMIP) and historical experiments and compared with reanalysis datasets [NCEP-DOE Reanalysis 2 (NCEP2) and ECMWF Reanalysis 5 (ERA5)] from 1979 to 2014. The results suggest that the widely reported austral summer contrasting SAM increasing trend at around 2000 is replicated by the AMIP models at the monthly timescale. Most AMIP and historical model simulations exhibit SAM variability comparable to that of the reanalyses, consistent with their respective AMMEs. Moreover, in relation to the SAM phase changes between models and reanalyses, models from historical simulations that replicate the SAM’s variability are significantly associated with changes in its negative phases. Further analysis suggests that external and internal variations contribute to SAM’s variations. Significant periodic components at interannual scales in the SAM index are better reproduced by most AMIP models than historical simulations, and models from both experiments failed to capture the quasi-decadal component of the SAM. Spatially, the observed SAM suggests that most of the individual models and the AMME for AMIP simulations can capture the basic spatial patterns of the monthly SAM, featuring an opposite sign between the middle and high latitudes, with a zonal three-wave structure in the middle latitudes coupled with a zonal asymmetric structure. This study concluded that, while the overall skill of the historical and AMIP simulations is nearly comparable in terms of the trend and variability of the SAM, the AMIP simulations were more proficient than the historical simulations in capturing the periodic components and spatial patterns of the SAM. Moreover, the model’s performance had limitations, particularly in replicating the trend magnitude and quasi-decadal cycle. This study provided a comprehensive assessment of CMIP6 models’ performance in simulating SAM characteristics, aiding the development of more accurate predictive tools to understand climate dynamics in the Southern Hemisphere and beyond.</p>

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Assessing the spatio-temporal variability of the monthly southern annular mode in coupled model intercomparison project phase 6 models

  • 期刊论文

  • 发表日期：

    2026年3月5日

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  • Dickson Mbigi,
  • Laban Lameck Kebacho,
  • Exavery Kisesa Makula,
  • Paul Tilwebwa Shelleph Limbu,
  • Rajabu Juma Mangara,
  • Zacharia Florence Mtewele,
  • Wilfred Kessy

摘要

This study aimed to evaluate the temporal variability and spatial patterns of the Southern Annular Mode (SAM) using Coupled Model Intercomparison Project Phase 6 (CMIP6) models on a monthly time scale. It employed the SAM index, which was computed for Atmospheric Model Intercomparison Project (AMIP) and historical experiments and compared with reanalysis datasets [NCEP-DOE Reanalysis 2 (NCEP2) and ECMWF Reanalysis 5 (ERA5)] from 1979 to 2014. The results suggest that the widely reported austral summer contrasting SAM increasing trend at around 2000 is replicated by the AMIP models at the monthly timescale. Most AMIP and historical model simulations exhibit SAM variability comparable to that of the reanalyses, consistent with their respective AMMEs. Moreover, in relation to the SAM phase changes between models and reanalyses, models from historical simulations that replicate the SAM’s variability are significantly associated with changes in its negative phases. Further analysis suggests that external and internal variations contribute to SAM’s variations. Significant periodic components at interannual scales in the SAM index are better reproduced by most AMIP models than historical simulations, and models from both experiments failed to capture the quasi-decadal component of the SAM. Spatially, the observed SAM suggests that most of the individual models and the AMME for AMIP simulations can capture the basic spatial patterns of the monthly SAM, featuring an opposite sign between the middle and high latitudes, with a zonal three-wave structure in the middle latitudes coupled with a zonal asymmetric structure. This study concluded that, while the overall skill of the historical and AMIP simulations is nearly comparable in terms of the trend and variability of the SAM, the AMIP simulations were more proficient than the historical simulations in capturing the periodic components and spatial patterns of the SAM. Moreover, the model’s performance had limitations, particularly in replicating the trend magnitude and quasi-decadal cycle. This study provided a comprehensive assessment of CMIP6 models’ performance in simulating SAM characteristics, aiding the development of more accurate predictive tools to understand climate dynamics in the Southern Hemisphere and beyond.