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Processes that enhance predictability of surface Processes that enhance predictability of surface temperature in southeastern South America during temperature in southeastern South America during May-July May-July Unidad de Ciencias de la Atmósfera – Facultad de Ciencias - Universidad de la República - Uruguay Marcelo Barreiro [email protected]. uy Potential Predictability We run experiments using an AGCM (Speedy, T31L8) forced with prescribed sea surface temperatures in different basins. A 10-member ensemble was constructed for each basin: GOGA - Global Ocean-Global Atmosphere: historical SST everywhere POGA - historical SST between 50S-30N in Pacific Ocean, climatology elsewhere. AOGA - historical SST between 50S-30N in Atlantic Ocean, climatology elsewhere. Model results are compared with the NCEP-NCAR reanalysis. Correlation of observed surface temperature with the ensemble mean shows a maximum in May-June-July for GOGA and POGA, the same season when Niño34 has large correlation. Analysis of Variance (ANOVA) of surface temperature for MJJ The maps below show the percentage of variance due to SST-influence. Eve In observations warm MJJ seasons are associated with a surface anticyclonic circulation located off SESA that induces northerly flow. In the upper atmosphere there is also a well defined anticyclonic circulation. Tropical Pacific SST anomalies and a warming off south Brazil accompany these circulation features. Model simulations show that the observed anomalies can be decomposed into a component due to ENSO captured in the regresions for GOGA, and a component due to internal atmospheric variability shown in the regresion for an experiment where the AGCM is coupled to a slab ocean (where ENSO is absent by construction). = OBSERVATIONS GOGA AGCM+SLAB OCEAN + Both ENSO and internal variability induce northerly surface flow, but the anticyclone in upper levels is only associated with internal variability. Abstract: The main source of potential predictability of surface temperature in SESA [65°W- 47°W,19°S-37°S] during May-July is related to El Niño-Southern Oscillation (ENSO), which increases the northerly flow bringing warm air to the region. The air-sea thermodynamic coupling off-SESA plays a role, increasing the persistence of the atmospheric anomalies. U850 U850 U850 U200 U200 U200 SST SST SST GOGA POGA AOGA Role of thermodynamic coupling We perfomed two additional experiments: GOGA-SACL – as GOGA except in S. Atlantic where climatological SST is imposed. GOGA-SAML- as GOGA except in S. Atlantic where the AGCM is coupled to a slab ocean. The thermodynamic air-sea coupling in the South Atlantic increases the potential predictability of the surface temperature over SESA for all seasons (above left). This is related to an increase in the persistence of the surface temperature anomalies (above right). OBSERVATIONS GOGA-SACL GOGA-SAML Persistence of temperature anomalies over SE Correlation of simulated with observed temperature Circulation anomalies associated with variability of surface temperature over SESA during MJJ
