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The representation of the South American Monsoon System (SAMS) by general circulation models (GCMs) is of key relevance for a better understanding of the physical rationale behind the recent climate changes over South Tropical South America (STSA) and their expected changes in a global warming scenario. During the last four decades, STSA experienced a lengthening of the dry season associated with diverse forcings. In this work, a set of 16 GCMs historical Coupled Model Intercomparison Project Phase 6 coupled simulations were evaluated during 1979–2014 in terms of how well they reproduced the atmospheric circulation over STSA through a circulation‐patterns (CPs) approach. Nine CPs were first identified based on low‐level winds from the ERA5 reanalysis. Focus was put on the representation of CPs during the dry‐to‐wet transition season (July‐October). Model performance depended on the seasonal cycle and spatial structure of the CPs. GCMs adequately reproduced the different CPs, with lower skills in the transition seasons. GCMs tended to go from dry to wet conditions too quickly, evidencing deficiencies in the representation of the SAMS onset, related to a poor representation of the southerly wind intrusions to STSA and the variability of the South American low‐level jet. Some GCMs were able to associate the occurrence of anomalous dry and wet years with specific CPs, suggesting well‐represented physical mechanisms controlling precipitation variability. This study could identify a few GCMs that adequately simulated the CPs in STSA (among them, CESM2, CMCC‐CM2‐HR4 and MPI‐ESM1‐2‐HR), which is relevant for driving high‐resolution models and the analysis of future projections. Key Points: Some general circulation models (GCMs) adequately represented both the seasonal cycle and spatial structure of circulation patternsGCMs often struggled in representing the monsoon initiation and the variability of the South American low‐level jetGCMs tended to go from dry to wet conditions too quickly [ABSTRACT FROM AUTHOR]

Future projections in austral winter characteristics of explosive extratropical cyclones (EECs) in three CORDEX Southern Hemisphere domains (Africa-AFR, Australia-AUS and South America-SAM) are investigated. The projections are obtained with a fine resolution (25 km) Regional Climate Model (RegCM4) within the CORDEX-CORE framework driven by three Global Climate Models (GCMs: HadGEM2-ES, MPI-ESM-MR and NorESM-1 M) under the RCP8.5 scenario. The cyclone database was obtained using a tracking scheme applied to 6-hourly mean sea level pressure fields and EECs are selected using the Sanders and Gyakum criterion. EECs represent ~ 13–17% of the total number of extratropical cyclones during austral winter in the ERA-Interim reanalysis (1995–2014), while both GCMs and RegCM4 ensembles underestimate this percentage. The frequency of EECs is projected to increase in AFR and in SAM domains at the end of the twenty-first century. However, the magnitude of the projected changes needs to be considered with caution because it is smaller than the underestimations in the frequency of EECs of both ensembles in the present climate. EECs in the future will be deeper and faster but with a shorter lifetime. Eady Growth Rate composites, when EECs reach the explosive phase, indicate a less baroclinic large-scale environment in the future. On the other hand, the intensification of precipitation associated with EECs in the future indicates an increase in the contribution of the diabatic processes acting to strengthen the local baroclinicity of the EECs. [ABSTRACT FROM AUTHOR]

Climate change will result in more dry days and longer dry spells; however, the resulting impacts on crop growth depend on the timing of these longer dry spells in the annual cycle. Using an ensemble of Coupled Model Intercomparison Project phase 5 and phase 6 (CMIP5 and CMIP6) simulations, and a range of emission scenarios, here we examine changes in wet and dry spell characteristics under future climate change across the extended tropics in wet and dry seasons separately. Delays in the wet seasons by up to 2 weeks are projected by 2070–99 across South America, southern Africa, West Africa, and the Sahel. An increase in both mean and maximum dry spell length during the dry season is found across Central and South America, southern Africa, and Australia, with a reduction in dry season rainfall also found in these regions. Mean dry season dry spell lengths increase by 5–10 days over northeast South America and southwest Africa. However, changes in dry spell length during the wet season are much smaller across the tropics with limited model consensus. Mean dry season maximum temperature increases are found to be up to 3°C higher than mean wet season maximum temperature increases over South America, southern Africa, and parts of Asia. Longer dry spells, fewer wet days, and higher temperatures during the dry season may lead to increasing dry season aridity and have detrimental consequences for perennial crops. [ABSTRACT FROM AUTHOR]