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The Remote sensing of Electrification, Lightning, And Meso-scale/micro-scale Processes with Adaptive Ground Observations (RELAMPAGO) and the Cloud, Aerosol, and Complex Terrain Interactions Experiment Proposal (CACTI) field campaigns provided an unprecedented thirteen-disdrometer dataset in Central Argentina during the Intensive (IOP, 15 November to 15 December 2018) and Extended (EOP, 15 October 2018 to 30 April 2019) Observational Periods. The drop size distribution (DSD) parameters and their variability were analyzed across the region of interest, which was divided into three subregions characterized by the differing proximity to the Sierras de Córdoba (SDC), in order to assess the impact of complex terrain on the DSD parameters. A rigorous quality control of the data was first performed. The frequency distributions of DSD-derived parameters were analyzed, including the normalized intercept parameter (log N w ), the mean volume diameter ( D 0 ), the mean mass diameter ( D m ), the shape parameter (μ), the liquid water content (LWC), and the rain rate (R). The region closest to the SDC presented higher values of log N w , lower D 0 , and higher μ , while the opposite occurred in the farthest region, i.e., the concentration of small drops decreased while the concentration of bigger drops increased with the distance to the east of the SDC. Furthermore, the region closest to the SDC showed a bimodal distribution of D 0 : the lower values of D 0 were associated with higher values of log N w and were found more frequently during the afternoon, while the higher D 0 were associated with lower log N w and occurred more frequently during the night. The data were analyzed in comparison to the statistical analysis of Dolan et al. 2018 and sorted according to the classification proposed in the cited study. The log N w - D 0 and LWC- D 0 two-dimensional distributions allowed further discussion around the applicability of other mid-latitude and global precipitation classification schemes (startiform/convection) in the region of interest. Finally, three precipitation case studies were analyzed with supporting polarimetric radar data in order to relate the DSD characteristics to the precipitation type and the microphysical processes involved in each case. [ABSTRACT FROM AUTHOR]

Thunderstorms in southeastern South America (SESA) stand out in satellite observations as being among the strongest on Earth in terms of satellite-based convective proxies, such as lightning flash rate per storm, the prevalence for extremely tall, wide convective cores and broad stratiform regions. Accurately quantifying when and where strong convection is initiated presents great interest in operational forecasting and convective system process studies due to the relationship between convective storms and severe weather phenomena. This paper generates a novel methodology to determine convective initiation (CI) signatures associated with extreme convective systems, including extreme events. Based on the well-established area-overlapping technique, an adaptive brightness temperature threshold for identification and backward tracking with infrared data is introduced in order to better identify areas of deep convection associated with and embedded within larger cloud clusters. This is particularly important over SESA because ground-based weather radar observations are currently limited to particular areas. Extreme rain precipitation features (ERPFs) from Tropical Rainfall Measurement Mission are examined to quantify the full satellite-observed life cycle of extreme convective events, although this technique allows examination of other intense convection proxies such as the identification of overshooting tops. CI annual and diurnal cycles are analyzed and distinctive behaviors are observed for different regions over SESA. It is found that near principal mountain barriers, a bimodal diurnal CI distribution is observed denoting the existence of multiple CI triggers, while convective initiation over flat terrain has a maximum frequency in the afternoon. [ABSTRACT FROM AUTHOR]

The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain. [ABSTRACT FROM AUTHOR]

The Global atmospheric Electric Circuit (GEC) sustains the fair weather (FW) electric field, or potential gradient (PG). In this article, we analyze PG measurements recorded between 2017 and 2021 at the Instituto de Investigaciones Científicas y Técnicas para la Defensa (CITEDEF) in Buenos Aires, Argentina, to calculate the daily PG (FW) curve and examine whether local PG measurements capture the GEC signal. With the aim of supporting future common methodologies that do not rely on meteorological data for FW identification - and hence aid inter-comparisons, we rely on previously developed statistical methodologies to propose a FW selection based on the absolute deviation from the median of the data series. Using this methodology we filtered FW days and showed that the local PG (FW) curve had a significant correlation of 0.83 with the Carnegie curve. In order to test the extent to which the local daily PG (FW) curve captures the global thunderstorm signal, the area of thunderstorms was calculated at both global and regional scales using data from the Thunder Hour Database (http://thunderhours.earthnetworks.com). The PG (FW) curve was shown to have a good correlation with the daily median variation of the global thunderstorm area on both annual and quarterly scales. Additionally, the analysis of coincident aerosol optical thickness (AOD) measurements by the AERONET network and temperature observations helped to conclude that local effects such as pollution from a near highway are not dominating the PG (FW) curve behaviour. Both analyses allowed us to conclude that the GEC signal can be detected in Buenos Aires. [Display omitted] • The daily PG curve (FW) in Buenos Aires has a correlation of 0.83 with the Carnegie curve with 95% confidence. • The daily PG (FW) curve in Buenos Aires has a seasonal variation that accompanies the global changes of thunderstorm areas. • Local effects such as pollution from a near highway are not dominating the PG (FW) curve behaviour. [ABSTRACT FROM AUTHOR]

On 10 November 2018, during the RELAMPAGO field campaign in Argentina, South America, a thunderstorm with supercell characteristics was observed by an array of mobile observing instruments, including three Doppler on Wheels radars. In contrast to the archetypal supercell described in the Glossary of Meteorology, the updraft rotation in this storm was rather short lived (;25 min), causing some initial doubt as to whether this indeed was a supercell. However, retrieved 3D winds from dual-Doppler radar scans were used to document a high spatial correspondence between midlevel vertical velocity and vertical vorticity in this storm, thus providing evidence to support the supercell categorization. Additional data collected within the RELAMPAGO domain revealed other storms with this behavior, which appears to be attributable in part to effects of the local terrain. Specifically, the IOP4 supercell and other short-duration supercell cases presented had storm motions that were nearly perpendicular to the long axis of the Sierras de Córdoba Mountains; a long-duration supercell case, on the other hand, had a storm motion nearly parallel to these mountains. Sounding observations as well as model simulations indicate that a mountain-perpendicular storm motion results in a relatively short storm residence time within the narrow zone of terrain-enhanced vertical wind shear. Such a motion and short residence time would limit the upward tilting, by the left-moving supercell updraft, of the storm-relative, antistreamwise horizontal vorticity associated with anabatic flow near complex terrain. [ABSTRACT FROM AUTHOR]

• This work presents the longest radar-based climatology of supercells storms using weather radar data in central Argentina. • Predominance of cyclonic supercells (a ratio of 90 • The characteristics of the pre-convective environments associated with supercells in Paraná have yielded similarities to Córdoba region (Argentina). • The Storm Relative Helicity deficit in the 0–1 and 0–3 km layers generates the greatest differences between the pre-convective environments associated with supercells between central and Eastern Argentina and U.S. Great Plains. • The previous point suggests the need to adapt the thresholds of those environmental parameters that particularly depend on the helicity relative to the storm in central-eastern Argentina if they are to be used for forecasting purposes in this region. Some of the strongest storms on Earth occur over central-eastern Argentina. These storms are associated with severe weather phenomena such as big hail, heavy rain, intense wind gusts, and, occasionally, tornadoes. The relatively recent expansion of the radar network in this area brings the chance to better characterize severe weather storms. This study presents a nine-year climatology of supercells (SCs) and their associated mesocyclones (MCs) based on radar data over central Argentina, together with a preliminary analysis of the thermodynamic environment in which they develop. We propose an MC detection algorithm based on the Non-Maximum Suppression (NMS) technique and a subjective classification. The MCs have shown a mean lifetime of 73 min, with their maximum intensity located at 4.7 km above ground level (AGL) on average. The monthly frequency of SCs in central-eastern Argentina is similar to that reported in previous studies near the Sierras de Córdoba, with two relative maxima, one in November and the other one in February, and with an absolute minimum in June. The diurnal cycle shows an absolute maximum at around 0100 UTC (2200 local time) and a minimum between 0900 and 1500 UTC (0600 and 1200 local time). Based on the results obtained here, the pre-convective environments associated with SCs in the Paraná region are very similar to its analogs in the Sierras de Córdoba. They are characterized by high values of convective instability and vertical wind shear. Storm relative helicity (in the low and middle layers) and wind shear in the first kilometer above the surface are lower than those found in the U.S. Great Plains. Although the analysis shows that there are environmental parameters that can discriminate well between SC and non-SC events, their values are shown to be far from the thresholds considered in the U.S. Results hence suggest the need to adapt the thresholds of some of the parameters studied here, particularly those based on storm-relative helicity, to central-eastern Argentina. [ABSTRACT FROM AUTHOR]