A study on possible solar and geomagnetic effects on the precipitation over northwestern Argentina

TERESITA HEREDIA; ANA G. ELIAS

ADVANCES IN SPACE RESEARCH

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2013

0273-1177

The precipitation over Tucuman (26.8° S; 65.2° W), which is representative of the Northwestern region of Argentina, is analyzed in search of an association with solar and geomagnetic activity, with the purpose of contributing to the controversial issue on the connection between climate variation and anthropogenic vs. natural forcing. Monthly time series of precipitation, sunspot number (Rz), and aa index were used for the period 1884-2010. A wavelet analysis was performed first which, due to the time series length, shows significant results only for periodicities lower than 32 years. Due to the transient character and non-constant phase of the results, any sustained wavelet coherence between precipitation and either sunspots or aa could be noticed. Moving averages and correlations were also assessed. The 11 and 22-year running mean of precipitation is positively correlated to Rz and aa when the whole period of analysis is considered. However, a shift in the long-term behavior of precipitation is noticed around 1940, which implies different correlation values with Rz and aa when the period before or after this year are considered. This result points out a solar-driven long-term modulation which would coincide with the monotonic increase expected at this tropical-subtropical latitude as consequence of the increasing greenhouse gases concentration. The solar cycle length is also considered for this statistical study and partly confirms the results obtained with Rz and aa. A physical explanation based on geomagnetic activity and total solar irradiance effects over atmospheric circulation is proposed to support the statistical result. Considering our results, we conclude that there may be a connection between precipitation and solar variability for time-scales greater than 11 years which needs deeper analysis and broader geographical coverage in order to be validated and discernible from greenhouse gases effects. We emphasize the idea of the importance of recognizing and quantifying the different forcing acting on precipitation (or any other climate parameter), which sometimes can be barely evident from a solely statistical analysis.