Central-West Argentina Summer Precipitation Variability and Atmospheric Teleconnections

Abstract

The interannual-to-multidecadal variability of central-west Argentina (CWA) summer (October–March) precipitation and associated tropospheric circulation are studied in the period 1900–2010. Precipitation shows significant quasi cycles with periods of about 2, 4–5, 6–8, and 16–22 yr. The quasi-bidecadal oscillation is significant from the early 1910s until the mid-1970s and is present in pressure time series over the southwestern South Atlantic. According to the lower-frequency spectral variation, a prolonged wet spell is observed from 1973 to the early 2000s. The precipitation variability shows a reversal trend since then. In that wet epoch, the regionally averaged precipitation has been increased about 24%. The lower-frequency spectral variation is attributed to the climate shift of 1976/77. From the early twentieth century until the mid-1970s, the precipitation variability is associated with barotropic quasi-stationary wave (QSW) propagation from the tropical southern Indian Ocean and the South Pacific, generating vertical motion and moisture anomalies at middle-to-subtropical latitudes east of the Andes over southern South America. The QSW propagation could be related to anomalous convection partly induced by tropical anomalous SSTs in the western Indian Ocean (WIO). It could also be linked to another midlatitude source along the storm tracks, to the east of New Zealand. After 1976/77, the precipitation variability is associated with equatorial symmetric circulation anomalies linked to El Niño–Southern Oscillation (ENSO)-like warmer conditions. Positive moisture anomalies are consistently observed at lower latitudes in association with inflation of the western flank of the South Atlantic anticyclone. Outside of this, the precipitation variability is unrelated to ENSO.

Statistical downscaling of daily precipitation and temperatures in southern La Plata Basin

“…In the eastern margin of the domain analysed, there is a strong consensus concerning the progressive increase up to the present of annual rainfall mainly due to the increases in rainfall during the summer (de Barros Soares et al, ; Saurral et al, ). Whereas to the southwest, the region underwent a sudden rise in summer precipitation by mid‐1970s owing to the influence of the 1976/1977 climate transition (Agosta and Compagnucci, ), which caused the shift towards the west of the agricultural barrier of the humid Pampas (border between the humid and semi‐arid regions). However, these precipitation trends seem to have reversed after the early 2000s (Maenza et al, ).…”

Climate change and precipitation variability over the western ‘Pampas’ in Argentina

“…The climate shift is coincident with a phase change of the PDO index, which has determined a ‘La Niña‐like’ decadal regime before and an ‘El Niño‐like’ decadal regime afterwards (Ebbesmeyer et al ., ; Mantua et al ., ; Solomon et al ., ). Furthermore, given the outstanding magnitude of the mid‐1970s shift, Jacques‐Coper and Garreaud () agreed with Agosta and Compagnucci () that the climate shift effects on southern South America climates seem to be unprecedented during the 20th century. In our analysis, we have found that the equatorial Pacific basin also plays a relevant role in regulating precipitation variability at interannual scale during the long‐term dry period observed from the 1920s to the 1960s, and during the transitional epoch related to the climatic shift in the mid‐1970s.…”

The 18.6‐year nodal tidal cycle and the bi‐decadal precipitation oscillation over the plains to the east of subtropical Andes, South America

“…Such a climate favours grape production under irrigation to such an extent that this is the main grape‐growing region in Argentina (Agosta et al ., ). The relationship between the NC summer precipitation variability and the tropospheric circulation at interannual scale has been intensively examined by Agosta and Compagnucci (, ). The bi‐decadal oscillation in the NC summer precipitation results in alternating wet and dry spells, lasting approximately 9 years each, from the early 1900s until the early 1970s (Compagnucci et al ., ).…”

“…From 1973 to the early 2000s, a wet spell is observed perturbing the bi‐decadal oscillation towards lower frequencies. As a consequence of the extended wet spell, the regionally averaged precipitation undergoes an increase of about 24% in the last decades (Agosta and Compagnucci, ). The precipitation increment is in agreement with the changes in the frequency of the principal modes associated to the synoptic tropospheric circulation in southern South America resulting from the 1976/1977 climate transition (Agosta and Compagnucci, ).…”