POSSIBLE LONG-TERM TREND FORCINGS OF THE SUMMER PRECIPITATION OVER TUCUMÁN, ARGENTINA
Franco Medina, Flavia Bazzano, Teresita Heredia y Ana Elias
The long term variation of total and daily maximum precipitation over Tucuman during summer is analyzed in this work. Precipitation data cover the period 1911-2016 and was measured at the Experimental Agroindustrial Obispo Colombres (EEAOC). Total precipitation presents a significant positive linear trend during the whole period due to the 1956 climatic jump, while maximum daily precipitation presents a significant trend only during 1956-1994. Taking into account that the South American monsoon is a strong determinant of precipitation regimes in Northern of Argentina, the correlation with atmospheric circulation variables is analyzed: upper troposphere zonal wind (U) in the Bolivian High region and lower troposphere meridional wind (V) in the Chaco Low region, together with pressure (P) and temperature (T) in the South Atlantic region. There is a good statistical agreement between precipitation series and these variables when the whole period is considered due to all these series present a general linear trend. In the sub-period 1960-2012 total precipitation presents a ~20-year quasi-periodicity in phase with P, and have no correlation with U and V. Maximum daily precipitation instead correlates better with velocity variables during this same period, which in turn are linked to the regional convection. The association with the oceanic variability is analyzed finding good correlation with the Pacific Decadal Oscillation (PDO) during the second half of twentieth century. Finally, the possible role on the trends of the global CO2 increase and the polar column O3 depletion is analyzed. There is a significant positive correlation with CO2, similar to that with T, due to the general increasing trend in both series, and negative correlation with O3 due to, in addition to the opposed trends in both series, they have a coincident sign-trend change in ~1960.