Relationship Between Frontal Systems and Lightning Over Southern South America

ABSTRACT The relationship between synoptic fronts and atmospheric electrical activity is explored in southern South America, analysing the seasonal climatology for the 2010–2021 period. Daily gridded data from the ERA5 reanalysis as well as lightning density from the WGLC database are used. Fronts are identified by an objective index that indicates their intensity, with a size threshold retaining only synoptic‐scale features. Lightning is most frequent in austral summer (December, January, February) and least in austral winter (June, July, August); frontal systems, on the other hand, are more frequent and more intense in winter and spring in Uruguay and central and northern Argentina, occurring in about 15% of the days. Lightning density mean is more uniform across the seasons, presenting two maximums, one in Paraguay and northeastern Argentina and the other off the coast of Uruguay and southern Brazil. For all seasons, more than 50% of fronts have electrical activity in central and northern Argentina; most summertime fronts over the continent present lightning. In Patagonia, about 25% of fronts have lightning; however, this represents less than 10 days per year, as atmospheric electrical activity is very infrequent in the region. In southeastern South America, more than 60% of lightning days are associated with synoptic frontal systems in winter and spring, while in summer it is less than 30%. Cold fronts with lightning occur in the region in about 16% of days in spring and winter, while warm fronts occur in about 23% and have a stronger mean lightning density than cold fronts. This is tied to the strong moisture convergence associated with warm fronts in the region as well as more intense fronts; in the same area, cold fronts with lightning present moisture divergence and overall weaker fronts.