Abstract
AbstractThis paper assesses how well the CPTEC/INPE Brazilian Global Atmospheric Model (BAM‐1.2) and the atmospheric component of the UK Met Office Hadley Centre Global Environment Model (HadGEM3‐GC3.1) represent the main South American monsoon features. Climatological (1981–2010) ensemble means of Atmospheric Model Intercomparison Project (AMIP)‐type climate simulations are evaluated. The assessment evaluated the models’ ability to represent the South America austral summer and winter precipitation contrast and associated circulation, key South American monsoon system elements, the association between south‐east Brazil and South America precipitation, and climatological (1997/1998 to 2013/2014) distributions of rainy season onset and demise dates over south‐east Brazil (15°S–25°S, 40°W–50°W) and the core monsoon region (10°S–20°S, 45°W–55°W). Despite some identified deficiencies, both models depict the monsoon region and represent the main features, including (1) the north‐west–south‐east precipitation band and associated ascending motion over central South America; (2) the upper‐level Bolivian High and the north‐east South America trough during the summer; (3) the lower‐level South Atlantic and Pacific subtropical anti‐cyclones and (4) the low‐level jet east of the Andes. Both models represent upper‐level divergence and lower‐level convergence over the core monsoon region, and upper‐level convergence and lower‐level divergence over the Pacific and Atlantic anti‐cyclones associated with the regional Walker circulation during the pre‐monsoon (spring) and peak monsoon (summer) seasons. Convection over South America is weaker in BAM‐1.2 than observed, consistent with continental precipitation deficit. The models reproduce the dipole‐like precipitation pattern between south‐east Brazil and south‐eastern South America during the austral summer but overestimate these patterns spatial extent over the South Atlantic. Both models simulate the main observed climatological features of rainy season onset and demise dates for the two above defined investigated regions. HadGEM3 overestimates onset dates interannual variability. These results can contribute towards understanding climate and land‐use change implications for environmental sustainability and for recommending climate adaptation strategies.
Highlights
A large proportion of the South American continent has a monsoon-like precipitation regime with a wet season during the austral summer months (December, January and February, DJF) and a dry season during the austral winter months (June, July and August, JJA) (Jones and Carvalho, 2002)
The monsoon precipitation intensity (MPI; Wang et al, 2011) index defined as the ratio between the annual range [AR; computed here as the difference between austral summer (DJF) and austral winter (JJA) mean precipitation] and the annual mean (AM) precipitation was used for mapping the spatial extent of the South American monsoon system, where the DJF, JJA and annual mean values were computed over the 1981–2010 period
This study aimed at assessing the ability of a Brazilian (BAM-1.2; Coelho et al, 2021) and a UK (HadGEM3; Ridley et al, 2018; Williams et al, 2018) climate model to represent the main features of the South American
Summary
A large proportion of the South American continent has a monsoon-like precipitation regime with a wet season during the austral summer months (December, January and February, DJF) and a dry season during the austral winter months (June, July and August, JJA) (Jones and Carvalho, 2002). Cavalcanti and Raia (2017) reported that climate simulations produced with the Center for Weather Forecast and Climate Studies (CPTEC/INPE) Atmospheric Global Circulation Model (AGCM) were able to represent the atmospheric patterns associated with SAMS initiation and end phases, with different intensities with respect to the observations. Cavalcanti et al (2020) showed that the Brazilian Atmosphere Global Model (BAM-v0) depicted the SAMS domain with climate simulations reproducing a similar spatial extent as identified in observations, and adequately represented precipitation and humidity flux differences between summer and winter. García-Franco et al (2020) reported that two CMIP6 models (HadGEM3-GC3 and UKESM1) simulated the main summer monsoon precipitation and lower-level wind features; precipitation was underestimated over north-west South America and overestimated over other SAMS regions. Identified model deficiencies can be used to drive model developments and further improve predictive capabilities
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