Analysis of long-term potential gradient variations measured in the Argentinian Andes

Abstract

Continuous measurements of the potential gradient are being recorded at the CASLEO astronomical observatory near to the Andes Mountain of Argentina, since 2010 (Latitude: 31°47.88′S, Longitude: 69°17.7′W, Altitude: 2552 masl). This study aims to use the potential gradient diurnal variation in fair weather conditions, which we named ‘standard curve’, to examine its correlation with the ‘universal’ Carnegie curve and to investigate its dependence with aerosol amount and lightning occurrences. In addition, a spectral analysis was performed to our data. The aerosol optical depth is recorded by an AERONET station at CASLEO, while the lightning occurrences was obtained from the STARNET network. For the analysis, the average of monthly, seasonal and annual electric field curves was determined. We found that the shape of these curves is preserved from year to year indicating their high reliability. The correlation between the standard curve for CASLEO and the Carnegie curve was found to be high (r = 0.94). However, some significant local effects were also found. We determined that these local effects in the standard curve may be associated to the convective process, which is more predominant during summertime than wintertime. The inspection of the seasonal variation of the potential gradient and the lightning occurrences showed a high similarity only after removing the effects of aerosols. Apart from this, the spectral analysis exposed a daily, annual and 165-day oscillation in the potential gradient.