Influence of Anomalous Heat Sources on the South Atlantic Convergence Zone Low-Frequency Variability

Abstract:

This study identifies the locations of anomalous heat sources (AHS) that promote low-frequency variations in three components of South America Monsoon System (SAMS) associated with South Atlantic Convergence Zone (SACZ) behavior, which are: 1) the Northeastern Brazilian trough in 200hPa (NBT); 2) the Bolivian High in 200hPa (BH); and 3) the trough in 500hPa on the southeastern of South America (TS). The AHS are identified through combined analysis between anomalous outgoing longwave radiation (OLR) observed fields, only for January months from 1982 to 2011, and influence functions (IF) fields produced for January climatology basic state from numerical simulations of a global atmospheric circulation model that include in each solution of temperature tendency equation a thermal forcing in a specific grid point of model domain to mimic a diabatic heating vertical profile observed in deep convective clouds. Statistically significant linear correlations are observed among each of those components from SAMS and OLR. For NBT and BH the largest correlations are concentrated in equatorial regions, SACZ and subtropical oceans. On the other side, TS circulation correlates with convective dipole between eastern of tropical Indian Ocean and western of tropical Pacific Ocean, besides anomalous convection on the Africa, the subtropical South Pacific Ocean and the SACZ. IF for different atmospheric levels show that NBT and BH (TS) variations are related to AHS in tropical Pacific/Atlantic Oceans and SACZ (subtropical South Pacific Ocean), possibly connected with the El Niño-Southern Oscillation (Madden-Julian Oscillation - MJO). Generally, an intensification of NBT (BH) could be produced by El Niño, intensified SACZ and/or equatorial Atlantic reduced convection (by La Niña and/or SACZ/equatorial Atlantic intensified convection), whilst an intensified TS could be produced by reduced convection in central-western of subtropical South Pacific Ocean resulting from MJO variability.