Impacts of the Pacific-South American modes in mid-latitudes are sensitive to tropical SST anomalies location

CAMPITELLI, ELIO; DÍAZ LEANDRO; VERA CAROLINA

Conferencia; 13th meeting of the International Conference on Southern Hemisphere Meteorology and Oceanography; 2022

American Meteorological Society

The Pacific-South American modes (PSA1 and PSA2) represent two out-of-phase sides of a meridionally propagating wave train that originates in the eastern equatorial Pacific and travels towards the South Atlantic. They are associated with significant precipitation and temperature anomalies in South America and are part of the ?atmospheric bridge? response to El Niño-Southern Oscillation (ENSO). Since the PSA are phase-varying, meridionally-propagating modes, they are not well represented by traditional Empirical Orthogonal Functions (EOF) or fourier decomposition. Therefore we decompose zonal asymmetries of springtime 200hPa and 50hPa geopotential height poleward of 20ºS using Complex EOF (cEOF). Using this methodology a PSA-like wave wave train is obtained as the second cEOF (cEOF2), with the Imaginary component highly correlated with the PSA1 and the Real component highly correlated with the PSA2. While the Real cEOF2 shows no clear tropical forcing, the Imaginary cEOF2 is associated with ENSO-like Sea Surface Temperature (SST) anomalies, strong wave activity flux emanating from the tropics and significant precipitation anomalies in Oceania and South America. Central Pacific ENSO SST anomalies tend to shift the cEOF2 towards the negative Real phase, while Eastern Pacific ENSO SST anomalies shift it towards the positive Real phase. This change in phase dramatically alters the impacts of the cEOF2 in precipitation and temperature for SH extratropics. On the other hand, the magnitude of the cEOF2 is only weakly affected by the magnitude of tropical SST anomalies indicating that the location of SST anomalies is crucial in determining the atmospheric response and its associated impacts.