Simulation of the South American climate by a coupled model with super‐parameterized convection

The climate over South America displays certain characteristics of monsoon systems which respond to seasonal development of land–ocean thermal contrast. The South American climate exhibits seasonal changes in precipitation, reversal of anomalous low-level winds and upper level anticyclone (Zhou and Lau 1998; Nogués-Paegle et al. 2002; Vera et al. 2006; Marengo et al. 2012). The austral seasonal convective heating over the Amazon and central Brazil induces Bolivian High and Nordeste Low in the circulation while the low-level easterlies from the Atlantic Ocean are steered by the Andes to the Chaco Low (Lenters and Cook 1997; Zhou and Lau 1998; Grimm et al. 2005). The precipitation and cloudiness from the Amazon to southeast Brazil extend into the Atlantic Ocean to form the South Atlantic Convergence Zone (SACZ). The South American climate reveals strong variability on intraseasonal, interannual and interdecadal time scales (Nogués-Paegle et al. 2002; Vera et al. 2006; Marengo et al. 2012). The intraseasonal variability over South America involves a dipole pattern of wet and dry conditions alternating over the SACZ and the subtropical plains (NoguésPaegle and Mo 1997; Liebmann et al. 1999; Carvalho et al. 2002a, b; Jones and Carvalho 2002). This pattern was shown to be an intraseasonal oscillation propagating northeastward (Krishnamurthy and Misra 2011), and a relation with the Madden–Julian oscillation (MJO; e.g., Madden and Julian 1994) was also indicated (Carvalho et al. 2004; Liebmann et al. 2004; Krishnamurthy and Misra 2011). In the same region, another propagating oscillation with a dipole pattern and a period of about 5.5 months exists and shows teleconnection with the North Atlantic oscillation (NAO) (Krishnamurthy and Misra 2011). Abstract The simulation of the climate over South America by a coupled ocean–atmosphere model with embedded cloud resolving model is studied on different time scales. The mean climate and the variability over South America as simulated by the superparameterized Community Climate System Model version 3 (SP-CCSM) are compared with those in the observation and in the control simulation of the CCSM3 (CT-CCSM) which employs conventional scheme of convection parameterization. The CT-CCSM is able to simulate only the longer period seasonal oscillation (SO) while the SP-CCSM is successful in simulating both the SO and the intraseasonal oscillation (ISO). The spatial structure and the propagation of the oscillations are better in the SP-CCSM. Both models are able to simulate the observed low-frequency modes of variability related to El Niño-Southern oscillation (ENSO) and Pacific decadal oscillation (PDO). While the ENSO mode in the CT-CCSM has more regular variability with a biennial time scale, the SP-CCSM simulates the ENSO mode with more irregular variability and time scale closer to the observation. The spatial structure, the relation with the Pacific and the regional variations of the observed PDO mode are better simulated by the SP-CCSM than the CT-CCSM.