O. Pinto

Positive leader characteristics from high-speed video observations

values range from 0.3 to 6.0 10 5 ms 1 with a mean of 2.7 10 5 ms 1 . Contrary to what is usually assumed, downward +CG leader speeds are similar to downward CG leader speeds. Our observations also show that the speeds tend to increase by a factor of 1.1 to 6.5 as they approach the ground. The presence of short duration, recoil leaders (RLs) during the development of positive leaders reveal a highly branched structure that is not usually recorded when using conventional photographic and video cameras. The existence of the RLs may help to explain observations of UHF-VHF radiation during the development of +CG flashes. Citation: Saba, M. M. F., K. L. Cummins, T. A. Warner, E. P. Krider, L. Z. S. Campos, M. G. Ballarotti, O. Pinto Jr., and S. A. Fleenor (2008), Positive leader characteristics from high-speed video observations, Geophys. Res. Lett., 35, L07802, doi:10.1029/2007GL033000.

Statistical analysis of space-time relationships between sprites and lightning

Abstract We present a detailed statistical analysis of the association of 40 sprite events with lightning from the parent thunderstorm. Both temporal and spatial criteria were used to identify the parent cloud-to-ground (CG) lightning. Sprite images were GPS time stamped and their locations triangulated. In contrast to previous reports of nearly one-to-one association of sprites with positive cloud-to-ground (+CG) lightning, 11 events (27%) did not have a +CG recorded by the National Lightning Detection Network (NLDN), and 7 events (17%) had neither NLDN nor very low frequency (VLF) signatures associated with them. A negative cloud-to-ground (−CG) preceded one of these events by 9 ms . As expected for ∼16.7 ms integrated images, none of the sprites without a +CG had any discernible visual characteristic that would distinguish them from “regular positive sprites”. We have calculated the distribution of time intervals (Δt=tsprite−tlightning) for the sprites that had a parent +CG flash registered by the NLDN or VLF systems, and the distribution of distances between the sprite nadir positions and the flash locations registered by the NLDN. The time interval (Δt) distribution had a peak around 10– 20 ms and a mean of 30 ms (total). This distribution is broadly consistent with the characteristic single electron avalanche time scale associated with streamer growth between ∼70 and 85 km . The distribution of the distances (Δs) between the nadir point of sprites and the parent +CGs showed that approximately two-thirds of the sprites occurred within 50 km lateral displacement from the parent +CG. The parent +CG peak current distribution had a maximum at 40– 50 kA and mean of 60 kA , suggesting that high peak currents (I⩾75 kA ) are not a necessary prerequisite for sprites. The peak current distribution for all +CGs of the storm, with a maximum around 10– 20 kA and mean of 27 kA , exhibits a qualitatively different form from the peak current distribution of the parent +CGs producing sprites.

Cloud‐to‐ground lightning in southeastern Brazil in 1993: 1. Geographical distribution

About I. I million cloud-to-ground lightning flashes were recorded by a lightning positioning and tracking system in southeastern Brazil in 1993. The 1-year continuous lightning data set is the first obtained in Brazil. It has been analyzed for geographical distribution of total flash density, percentage of positive flashes, negative and positive flash densities, and negative and positive flash peak currents. The dependence of the flash density and peak current on latitude, altitude, and soil resistivity was investigated. Negative flash peak current was found to be inversely correlated with latitude, but no other significant correlation was found for flash density and peak current with these parameters. Positive flashes were found to be contaminated by intracloud flashes. The maximum total, negative, and positive flash densities were 15.5, 9.1, and 7.7 flashes/km 2 per year, respectively. The average percentage of positive flashes was 36.5%. The gcomctric means of negative and positive peak current were 30.9 kA and 17.8 kA. The high density, high percentage and low average peak current of positive flashes found in this study are probably a result of such a contamination. Neglecting positive flashes below 15 kA, assuming that they correspond to intracloud flashes erroneously identified by the system, the maximum positive and total flash densities would be 3.9 flashes/km per year and 11. 7 flashes/km 2 per year. The percentage and geometric mean peak current of positive flash would be 23% and 38. 7 kA, respectively. The results are discussed in the context of other similar measurements made at different parts of the world.

Thunderstorm and lightning characteristics associated with sprites in Brazil

[1] Astudy ofthe thunderstorm andcloud-ground lightning characteristics associated with sprite events observed in Brazil is presented. The study is based on ground and aircraft sprite observations with high sensitivity intensified CCD cameras of six different thunderstorms, GOES satellite infrared images, radar and lightning network data. A total of eighteen transient optical events were recorded at three different days in 2002 and 2003, sixteen of which exhibited vertical structures typically associated with sprites. Four thunderstorms were associated with two different cold fronts, one with a Mesoscale Convective System, and one was a local isolated thunderstorm. The sprites occurred during time periods when the percentage of positive flashes was higher than the average percentage for the storm lifetime. The lightning associated with the sprite events was all positive flashes with a mean peak current higher than the mean value for all flashes in the storms. INDEX TERMS: 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 3324 Meteorology and Atmospheric Dynamics: Lightning; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342). Citation: Pinto, O., Jr., M. M. F. Saba, I. R. C. A. Pinto, F. S. S. Tavares, K. P. Naccarato, N. N. Solorzano, M. J. Taylor, P. D. Pautet, and R. H. Holzworth (2004), Thunderstorm and lightning characteristics associated with sprites in Brazil, Geophys. Res. Lett., 31, L13103, doi:10.1029/2004GL020264.

Energetic electron precipitation at the South Atlantic Magnetic Anomaly: a review

Abstract This paper reviews the status of knowledge concerning energetic electron precipitation at the South Atlantic Magnetic Anomaly (SAMA). The main purpose is to place recent results in the context of the long-standing problems about energetic electron precipitation at the SAMA region. A synopsis of results achieved in the last two decades, in relation to the various physical mechanisms responsible for precipitating energetic electrons, are also presented. The major uncertainties in the understanding of the energetic electron precipitation at the SAMA include: (1) temporal and spatial precipitation changes from magnetically quiet to disturbed periods; (2) the role of wave-induced precipitation processes.

Cloud‐to‐ground lightning in southeastern Brazil in 1993: 2. Time variations and flash characteristics

About 1.1 million cloud-to-ground lightning flashes were recorded by a lightning positioning and tracking system in southcastern Brazil in 1993. The data have been analyzed in terms of their monthly, scasonal (summer/winter), and diurnal (local time) variations. The monthly variation shows a double peak characteristic of tropical lightning activity. The seasonal variation indicates that most flashes occur in the spring and summer seasons, with less than 25% occurring in the autumn and winter. The lightning flash polarity and multiplicity were found to be very similar in the summer and winter seasons. Radiation field and direct current lightning data were obtained in towers located in the same region of the network to verify the multiplicity data obtained by the network. The results indicate that the multiplicity obtained by the system is much lower than that obtained by radiation field measurements of close lightning in the same region of Brazil. The lightning flash peak current were found to be larger in the summer than in the winter, in contrast with results obtained in other parts of the world. The diurnal variation of the negative flashes shows in the summer and winter seasons the same behavior, with a peak around 1500-1800 LT, associated with the maximum convective activity in the afternoon. The diurnal variation of positive flashes, in turn, shows this behavior only in the winter. In the summer, it shows a maximum around 1400-1500 LT, with a secondary peak at 1900 LT. However, considering only positive flashes with peak currents higher than 15 kA, the diurnal distribution in the summer is similar to that for negative flashes. This fact indicates that the positive flashes with a peak current less than 15 kA are probably intracloud flashes erroneously identified by the network. The results are discussed in association with the findings presented in paper 1 [Pinto et al., this issue] and compared with results obtained in other parts of the world.

Cloud‐to‐ground lightning flash characteristics in southeastern Brazil for the 1992–1993 summer season

A lightning positioning and tracking system (LPATS) has been used for the first time to obtain the cloud-to-ground flash characteristics in southeastern Brazil during the 1992-1993 summer season. About 300,000 flashes to ground were recorded. The lightning data are presented in terms of polarity, multiplicity, first-stroke peak current, stroke of maximum peak current, and local time occurrence. The preliminary results are compared with lightning data obtained by several authors in other parts of the world.

The South Atlantic Magnetic Anomaly : three decades of research

Abstract This brief review of advances in our understanding of some physical processes related to the South Atlantic Magnetic Anomaly (SAMA) is intended to highlight specific issues on which further research is needed. The discussion focuses on the origin of the SAMA, the geomagnetic storm-related effects and the impact of the SAMA on orbiting spacecraft.

A seven-year study about the negative cloud-to-ground lightning flash characteristics in Southeastern Brazil

Abstract A seven-year study of negative cloud-to-ground (CG) lightning flash characteristics in southeastern Brazil is presented. The study is based on approximately 10 million flashes recorded by a Lightning Position and tracking system lightning detection network from November 1988 to December 1995. The data set is the longest ever obtained in the tropics using an almost constant network configuration. It provides a unique opportunity to study the long-term annual, monthly, and local time distributions of the number, intensity (peak current) and multiplicity of negative CG flashes in the tropics. The annual distribution of the number of flashes has variations as large as 80%. The variations does not show any clear relationship with any meteorological parameter, possibly indicating the complex interactions of different processes responsible for the lightning activity. The monthly and local time distributions seem to follow closely the related distributions of air temperature. The annual distribution of peak current shows an average value of 40.4 kA and has a significant decrease from 1991 to 1994, apparently related to an El Nino seasonal effect. The monthly distribution of peak current shows lower values in the winter, in contrast with the results recently reported for the United States, and seems to be related to the monthly distribution of the number of flashes. The local time distribution of the peak current seems also to be related to the local time distribution of the number of flashes; however, the dependency is less evident. The annual distribution of multiplicity has a systematic decrease during the period, with no apparent relationship with any of the variables studied. The monthly distribution of multiplicity is consistent with the hypothesis that the multiplicity is related to the average height of thunderstorms. The local time distribution of multiplicity, in turn, shows a sunrise/sunset effect. The results are compared to similar ones obtained in other regions of the world.

Monthly distribution of cloud‐to‐ground lightning flashes as observed by lightning location systems

Figure 1. RINDAT sensor configuration at the end of2004. Also indicated is the region considered in thisanalysis.Figure 2. Normalized mean monthly distribution of thenumber of CG flashes observed at different countries forlong time periods.Figure 3. Normalized mean monthly distribution of thepercentage of positive CG flashes observed at differentcountries for long time periods.Figure 4. Normalized mean monthly distribution of thepositive peak current of CG flashes observed at differentcountries for long time periods.