Rodrigo E. Bürgesser

Lightning in Western Patagonia

On the basis of 8 years (2005–2012) of stroke data from the World Wide Lightning Location Network we describe the spatial distribution and temporal variability of lightning activity over Western Patagonia. This region extends from ~40°S to 55°S along the west coast of South America, is limited to the east by the austral Andes, and features a hyper-humid, maritime climate. Stroke density exhibits a sharp maximum along the coast of southern Chile. Although precipitation there is largely produced by cold nimbostratus, days with more than one stroke occur up to a third of the time somewhere along the coastal strip. Disperse strokes are also observed off southern Chile. In contrast, strokes are virtually nonexistent over the austral Andes—where precipitation is maximum—and farther east over the dry lowlands of Argentina. Atmospheric reanalysis and satellite imagery are used to characterize the synoptic environment of lightning-producing storms, exemplified by a case study and generalized by a compositing analysis. Lightning activity tends to occur when Western Patagonia is immersed in a pool of cold air behind a front that has reached the coast at ~40°S. Under these circumstances, midlevel cooling occurs before and is more prominent than near-surface cooling, leading to a weakly unstable postfrontal condition. Forced uplift of the strong westerlies impinging on the coastal mountains can trigger convection and produces significant lightning activity in this zone. Farther offshore, large-scale ascent near the cyclones center may lift near-surface air parcels, fostering shallow convection and dispersing lightning activity.

Charge separation in updraft of convective regions of thunderstorm

analyzed for three different velocities: 6, 8 and 11 m s 1 . The ambient temperature was varied in the range 5t o 30� C and the effective water content between 0 to 2gm 3 . Charge diagrams of the sign of the electric current on the graupel as a function of the ambient temperature and the effective liquid water content for each velocity are presented. The results indicate that increasing the velocity leads to negative particle charging during riming at higher velocity and the implications of these findings to non-severe

Mechanism for electric charge separation by ejection of charged particles from an ice particle growing by riming

Experimental evidence is presented that shows that substantial electric charge separation can occur by the ejection of charged particles during the riming process. Measurements were performed at temperatures between � 15 and � 30 jC, velocities between 10 and 30 m s � 1 and cloud water contents between 0.2 and 1 g m � 3 . Results show that positively or negatively charged particles were detached from an artificial hailstone, with individual charges ranging between � 0.3 and 0.5 pC. This mechanism could separate approximately 5 pC min � 1 cm � 2 of hail surface area. The charge of the ejected particle depends on the environmental temperature. Charge separation was detected at air velocities above 17 m s � 1 , which indicates that the mechanism could operate in the presence of hailstones larger than 1 cm in diameter. This mechanism is distinct from the usual noninductive mechanism and does not require ice particle collisions to separate electric charge. The physical mechanism has not been elucidated yet, but the results suggest that the ejected particles could be produced by splashing of droplets impinging on the artificial hailstone or by detachment of rime fragments accreted on it. D 2003 Elsevier B.V. All rights reserved.

Electric atmospheric activity in Argentina, a study for estimating the annual death rate by lightning

The information about lightning activity is fundamental to atmospheric surveillance. Few countries in the world have their own lightning detection networks which allow monitoring the lightning activity inside their national borders. The World Wide Lightning Location Network (WWLLN) provides global lightning data, which was already used to characterize the lightning activity in several regions of the world. The aim of the present work is the use of the lightning data obtained by the WWLLN to make an analysis on the lightning activity over Argentina between the years 2005-2012. These data are used to estimate the annual death rate by lightning in the region. The estimation is based on a model proposed by Chandima Gomes, and Ab Kadir [1]. The obtained results could help to promote protective behaviors in the population.

Diurnal patterns in lightning activity over South America

Satellite observations of lightning flash distribution data are used to examine the diurnal cycle of lightning activity over the tropical and subtropical regions of South America. A harmonic analysis is used to study the spatial variations in the peak and strength of diurnal lightning activity across this area. Results show that in the northern and central regions of South America, the times of maxima in lightning activity was concentrated from late afternoon to evening hours (between 14:00 and 18:00 local time), which may be associated with the peaking of the local convective activity connected with heating of the surface caused by daytime insolation. In subtropical South America, particularly in the area limited by 25°S, 35°S of latitude and 70°W, 50°W of longitude, the time of maximum lightning activity was shifted to nocturnal hours, extending from close to midnight to early morning hours. This behavior can be associated to the peak in mesoscale convective systems in the region which occurs in the morning hours. The annual flash densities in the tropical and subtropical parts of the continent were found to have comparable magnitudes. However, the contribution of the continental tropics to the global electric circuit dominates over the continental subtropics contribution throughout all seasons, since the surface covered by the tropical region is more than twice the area covered by the subtropical region.

GeoRayos a new aplication for severe weather warning

This work presents a lightning jump algorithm (LJA): “GeoRayos” to detect severe weather; it is based on the algorithm presented by Schultz et al. (2011) [1]. The lightning data used in this study came from the World Wide Lightning Location Network which is a real-time, world-wide and ground network. In this study, the lightning activity occurred during spring and summer of 2013 on the region [20-50]S of latitude and [50“70]W of longitude was examined. The LJA was validated by using information of severe weather occurrence in the report “Estudio de los Tornados en la Rep. Argentina” this unpublished report (M. L. Altinger de Schwarzkopf, personal communication) provides severe phenomena occurred since 1930 to the present, also we used information from the National Weather Service in Argentina, local argentinean media, and radar data. The spatial and time distributions of lightning jumps were analyzed by using different spatial and temporal scales.