Semestral Journal of Centro Argentino de Meteorólogos, which is published  since 1970 and serves on the Core of Argentine Scientific Journals since 2005. Meteorologica publishes original papers in the field of atmospheric sciences and oceanography.

Registration number of intellectual property: RL-2018-42420861-APN-DNDA#MJ

ISSN 1850-468X

Volume 40 – N°1 MORE NOTES FROM THIS ISSUE

LOW FREQUENCY VARIATIONS OF SEASONAL PRECIPITATION IN THE ‘PAMPA AMARILLA’ REGION AND POSIBLE FORCINGS

Germán Russián, Eduardo Agosta y Rosa Compagnucci

Servicio Meteorológico Nacional, Buenos Aires, Argentina
Facultad de Ciencias Físico-Matemáticas e Ingeniería, Pontificia Universidad Católica Argentina,Buenos Aires, Argentina
Departamento de Ciencias de la Atmósfera y los Océanos, Facultad de Ciencias Exactas y Naturales,Universidad de Buenos Aires, Buenos Aires, Argentina
Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina

Manuscript received on 20 january 2014, in final form 10 june 2014

ABSTRACT

The annual cycle of precipitation in the ‘Pampa Amarilla’ region (RPA), in Central Argentina, is studied. Most of the RPA has maximum in March, followed in November and December and minimum in winter. The accumulated from October to March (summer) is significantly different from the accumulated from April to September (winter). Variations, trends and changes of the time series in these two seasons were analyzed. On the central and northern La Pampa Province, selected long time series show significant positive linear-trend change of about 44% of the regional average in summer. After a prolonged drought (1930-1950) the summer shift burst in the seventies (north- central La Pampa), and in the sixties (east-central La Pampa Province) . This sudden change has produced a long extended wet phase until the early two thousands. The Seventies shift may be associated with the change in the average conditions of the sea surface temperature (SST) of equatorial central Pacific. For the prolonged wet phase (1969-2009) in central and northern RPA there is an increase (decrease) in summer (winter) precipitation while towards central southwestern RPA, the changes are negative and significant. Exploring the tropospheric circulation and SST reveals that the interannual variability of precipitation is modulated by remote tropic-extratropic teleconnections. Any connection with the Southern Annular Mode is discarded. In summer, the interaction mechanism is the modulation of the subtropical jet stream in the South Pacific toward South America, caused by circulation anomalies of the Hadley cell over the central equatorial Pacific. The mechanism could be associated with the lower and higher frequency of El Niño phenomena. In winter, the teleconnection is given by propagation of quasi-stationary Rossby waves from the equatorial region of the western Pacific. The centers of action in the surroundings of South America generate a blocking-like perturbation of the westerlies along the meridian 80oW. Other possible forcings are raised and discussed.

Keywords: Precipitation, atmospheric-oceanic teleconnection, Pampa Amarilla, Central Argentina, The El Niño-Southern Oscillation