Gargantuan hail in Argentina

On 8 February 2018, a supercell storm produced gargantuan (>15 cm or >6 in. in maximum dimension) hail as it moved over the heavily populated city of Villa Carlos Paz in Córdoba Province, Argentina. Observations of gargantuan hail are quite rare, but the large population density here yielded numerous witnesses and social media pictures and videos from this event that document multiple large hailstones. The storm was also sampled by the newly installed operational polarimetric C-band radar in Córdoba. During the RELAMPAGO campaign, the authors interviewed local residents about their accounts of the storm and uncovered additional social media video and photographs revealing extremely large hail at multiple locations in town. This article documents the case, including the meteorological conditions supporting the storm (with the aid of a high-resolution WRF simulation), the storm's observed radar signatures, and three noteworthy hailstones observed by residents. These hailstones include a freezer-preserved 4.48-in. (11.38 cm) maximum dimension stone that was scanned with a 3D infrared laser scanner, a 7.1-in. (18 cm) maximum dimension stone, and a hailstone photogrammetrically estimated to be between 7.4 and 9.3 in. (18.8-23.7 cm) in maximum dimension, which is close to or exceeds the world record for maximum dimension. Such a well-observed case is an important step forward in understanding environments and storms that produce gargantuan hail, and ultimately how to anticipate and detect such extreme events.Fil: Kumjian, Matthew R.. State University of Pennsylvania; Estados UnidosFil: Gutierrez, Rachel. State University of Pennsylvania; Estados UnidosFil: Soderholm, Joshua S.. Universitat Bonn; AlemaniaFil: Nesbitt, Stephen William. University of Illinois at Urbana; Estados UnidosFil: Maldonado, Paula Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Luna, Lorena Medina. National Center for Atmospheric Research; Estados UnidosFil: Marquis, James. Pacific Northwest National Laboratory; Estados UnidosFil: Bowley, Kevin A.. State University of Pennsylvania; Estados UnidosFil: Alvarez Imaz, María de Los Milagros. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Salio, Paola Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Gargantuan Hail Documenting an Extreme Forecasting Challenge

I n the scientific literature, some studies have identified “giant” hail as those stones with maximum dimensions exceeding 10 cm or 4 in. We propose a new size class for hailstones with maximum dimensions exceeding 15 cm or 6 in. (referred to here as “gargantuan hail”) to represent the upper extreme of hail sizes. As these are rare cases, only a few studies have specifically documented giant and gargantuan hail events, and most are individual case studies. One study of giant and gargantuan hailstones from the Aurora, Nebraska, storm of 2003 showed that every stone evaluated exhibited an outer (i.e., final) growth layer indicating wet growth, and in some cases this layer was of quite substantial thickness. Another study used social media reports to identify giant hail that ultimately became certified state records. It suggested that the occurrence of giant or gargantuan hail is significantly underreported. None of the aforementioned studies focused on observedtorm properties or environments. In con- trast, a 2013 study documented the synoptic and mesoscale environment of the super- cell that produced the Vivian, South Dakota, hailstone (which registers as the world re- cord for maximum dimension of 20 cm or 8 in.). Analysis indicated that the environment was indeed supportive of severe convective storms, but not indicative of such large hail as was observedFil: Kumjian, Matthew R.. State University of Pennsylvania; Estados UnidosFil: Gutierrez, Rachel. State University of Pennsylvania; Estados UnidosFil: Soderholm, Joshua S.. State University of Pennsylvania; Estados UnidosFil: Nesbitt, Stephen William. University of Illinois at Urbana; Estados UnidosFil: Maldonado, Paula Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Medina Luna, Lorena. National Center for Atmospheric Research; Estados UnidosFil: Marquis, James. Pacific Northwest National Laboratory; Estados UnidosFil: Bowley, Kevin A.. State University of Pennsylvania; Estados UnidosFil: Alvarez Imaz, María de Los Milagros. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Salio, Paola Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Spatiotemporal Characteristics of the Largest HIV-1 CRF02_AG Outbreak in Spain: Evidence for Onward Transmissions

Background and Aim: The circulating recombinant form 02_AG (CRF02_AG) is the predominant clade among the human immunodeficiency virus type-1 (HIV-1) non-Bs with a prevalence of 5.97% (95% Confidence Interval-CI: 5.41–6.57%) across Spain. Our aim was to estimate the levels of regional clustering for CRF02_AG and the spatiotemporal characteristics of the largest CRF02_AG subepidemic in Spain.Methods: We studied 396 CRF02_AG sequences obtained from HIV-1 diagnosed patients during 2000–2014 from 10 autonomous communities of Spain. Phylogenetic analysis was performed on the 391 CRF02_AG sequences along with all globally sampled CRF02_AG sequences (N = 3,302) as references. Phylodynamic and phylogeographic analysis was performed to the largest CRF02_AG monophyletic cluster by a Bayesian method in BEAST v1.8.0 and by reconstructing ancestral states using the criterion of parsimony in Mesquite v3.4, respectively.Results: The HIV-1 CRF02_AG prevalence differed across Spanish autonomous communities we sampled from (p < 0.001). Phylogenetic analysis revealed that 52.7% of the CRF02_AG sequences formed 56 monophyletic clusters, with a range of 2–79 sequences. The CRF02_AG regional dispersal differed across Spain (p = 0.003), as suggested by monophyletic clustering. For the largest monophyletic cluster (subepidemic) (N = 79), 49.4% of the clustered sequences originated from Madrid, while most sequences (51.9%) had been obtained from men having sex with men (MSM). Molecular clock analysis suggested that the origin (tMRCA) of the CRF02_AG subepidemic was in 2002 (median estimate; 95% Highest Posterior Density-HPD interval: 1999–2004). Additionally, we found significant clustering within the CRF02_AG subepidemic according to the ethnic origin.Conclusion: CRF02_AG has been introduced as a result of multiple introductions in Spain, following regional dispersal in several cases. We showed that CRF02_AG transmissions were mostly due to regional dispersal in Spain. The hot-spot for the largest CRF02_AG regional subepidemic in Spain was in Madrid associated with MSM transmission risk group. The existence of subepidemics suggest that several spillovers occurred from Madrid to other areas. CRF02_AG sequences from Hispanics were clustered in a separate subclade suggesting no linkage between the local and Hispanic subepidemics

Study of the impact of the WRF model configuration on deterministic and probabilistic forecasts for a case of convection initiation in Sierras de Córdoba, Argentina

La determinación de la ubicación y el tiempo de iniciación de la convección (IC) es un aspecto crucial de la predicción y alerta meteorológica de fenómenos de alto impacto asociados con la convección profunda. Argentina central, particularmente la región de las Sierras de Córdoba (SDC), se caracteriza por la ocurrencia regular de profundas celdas convectivas. Estas celdas pueden alcanzar características supercelulares produciendo en algunos casos granizo grande y ocasionalmente tornados. El modelado numérico de la convección húmeda profunda presenta varios desafíos asociados al espaciamiento horizontal de los puntos de retícula, a las diferentes parametrizaciones físicas que se consideran y a las condiciones iniciales y de borde (en el caso de simulaciones regionales). En este trabajo de tesis se estudia el impacto asociado a la elección de diferentes parametrizaciones físicas y condiciones iniciales y de borde en la IC. Para analizar la sensibilidad de la IC en las SDC, se utilizó el modelo Weather Research and Forecasting (WRF) con un espaciamiento horizontal de los puntos de retícula de 3 km para estudiar una supercelda marginal iniciada el 17 de octubre de 2017. Se construyó un conjunto de simulaciones utilizando 3 parametrizaciones de la microfísica (WSM6, Thompson y Morrison) y 2 parametrizaciones de la capa límite planetaria (CLP) (Universidad de Yonsei y Mellor Yamada Janjic). Además, se estudió la sensibilidad de las condiciones iniciales y de borde, considerando como forzantes a 2 análisis globales diferentes: el European Centre for Medium-Range Weather Forecast model (ECMWF), y el Global Data Assimilation System (GDAS). Es decir que se generaron 12 simulaciones para analizar el caso de estudio. La elección de los modelos globales como condiciones iniciales y de borde resultaron fundamentales para la IC y posterior desarrollo de la celda convectiva. Una de las mayores diferencias entre ambos modelos fue la disponibilidad de humedad en niveles bajos, que luego fue observada en las simulaciones WRF impactando en la resolución regional de la situación. En cuanto a las parametrizaciones, aquellas asociadas a la CLP son las que más influyeron en determinar el tiempo y la ubicación de la IC. En la segunda parte del trabajo, se seleccionaron las configuraciones que mejor desempeño tuvieron en los pronósticos determinísticos para generar pronósticos probabilísticos. Para los mismos se utilizaron como condiciones iniciales y de borde, el ensamble de pronósticos ECMWF y el Global Ensemble Forecast System (GEFS). Para analizar la predictibilidad del entorno asociado a la IC, se estudiaron diversas variables poniendo foco en la distribución espacial y los rangos de valores de cada una de ellas. Si bien se pueden identificar diferencias tanto entre las parametrizaciones físicas utilizadas y las condiciones de borde e iniciales, hay una gran concordancia entre todas las configuraciones en cuanto a la presencia de un entorno propicio a la IC. En cuanto a la ubicación, horario y el número de IC, varían significativamente entre las configuraciones (al igual que en las simulaciones determinísticas) siendo escasa la cantidad de miembros en que la IC fue cercana a la ubicación de la observación.Determining the location and time of convection initiation (CI) is a crucial aspect of weather forecasting and warning of high-impact events associated with deep convection. Central Argentina, particularly the Sierras de Córdoba (SDC) region, is characterized by the regular occurrence of deep convective cells. These cells can reach supercellular characteristics, producing in some cases large hail and occasionally tornadoes. The numerical modeling of deep moist convection presents several challenges associated with the horizontal spacing of the grid points, the different physical parameterizations that are considered, and the initial and boundary conditions (in the case of regional simulations). In this thesis work, the impact associated with the choice of different physical parameterizations and initial and boundary conditions in CI is studied. To analyze the sensitivity of the CI in the SDC, the Weather Research and Forecasting (WRF) model with a 3 km horizontal spacing of the grid points was used to study a marginal supercell started on October 17th, 2017. A set of simulations using 3 microphysics parameterizations (WSM6, Thompson and Morrison) and 2 planetary boundary layer (PBL) parameterizations (Yonsei University and Mellor Yamada Janjic) were considered. In addition, the sensitivity of the initial and boundary conditions was studied, using 2 different global analyzes: the European Center for Medium-Range Weather Forecast model (ECMWF), and the Global Data Assimilation System (GDAS). In other words, 12 simulations were generated to analyze the case study. The choice of global models as initial and boundary conditions was fundamental for the CI and subsequent development of the convective cell. One of the major differences between both models was the presence of humidity at low levels, which was later observed in the WRF simulations, impacting the regional resolution of the situation. Regarding the parameterizations, those associated with the PBL are the ones that had the most influence in determining the time and location of the CI. In the second part of the work, the configurations that had the best performance in deterministic forecasts were selected to generate probabilistic forecasts. For this, the ECMWF forecast ensemble and the Global Ensemble Forecast System (GEFS) were used as initial and boundary conditions. To analyze the predictability of the environment associated with CI, several variables were studied, focusing on the spatial distribution and their ranges of values. Although differences can be identified between the physical parameterizations and the boundary and initial conditions, there is a strong agreement between all the configurations regarding the presence of an environment conducive to CI. For the location, time and the number of CI, there were also differences between the configurations (as in the deterministic simulations), being small the number of members in which the CI was close to the location of the observation.Fil: Alvarez Imaz, María de los Milagros. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

The role of atmospheric forcings and WRF physical set-up on convective initiation over Córdoba, Argentina

The accurate determination of the location and timing of convective initiation (CI) is a crucial aspect of forecasting and high impact weather warning systems associated with deep convection. Central Argentina, particularly the Sierras de Córdoba (SDC), is characterized by the regular occurrence of deep convective cells that reach supercell characteristics producing large hail and occasionally tornadoes. In order to analyze the sensitivity of the CI over SDC, an ensemble of 12 simulations with the WRF model at convection-permitting resolution (3 km.) was carried out to study a marginal supercell initiated on October 17, 2017 at the SDC foothills. The ensemble was built using 3 different microphysics (MP) parameterizations (WSM6, Thompson and Morrison) and 2 planetary boundary layer (PBL) parameterizations (Yonsei University and Mellor Yamada Janjic). Also, the sensitivity of initial and boundary conditions is considered by forcing the model with 2 different global analyses: the European Centre for Medium-Range Weather Forecast (ECMWF) model, and the Global Data Assimilation System (GDAS). The two different forcing data show low-level moisture differences, which later modulate the life-cycle of the simulated cells. A tracking algorithm was used to capture their life-cycle, and CI was detected at both the hills and the plains. Simulations forced with ECMWF analyses tend to show better results with characteristics closer to the ones observed including: initiation over the eastward slope of SDC, stronger cells and slow propagation. Among all simulations analyzed, the best performance was obtained with the combination of Thompson MP and Yonsei University PBL schemes.Fil: Alvarez Imaz, María de Los Milagros. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Salio, Paola Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Dillon, María Eugenia. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Fita Borrell, Lluís. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; Argentin

Mesoscale influences on the development of a dryline in Argentina: A modelling case study

Drylines are a frequent feature of the atmospheric circulation in Argentina. Recent work described their climatological characteristics and synoptic-scale processes associated with their formation. However, little is known about the mesoscale processes that are relevant for their life cycle. In this paper, we investigate the influence of these mechanisms on the formation and movement using a case-study approach. Also, the relationship between these mechanisms and convective initiation near the dryline is investigated. A typical northern Patagonia dryline is simulated using the Weather Research and Forecasting (WRF) with an horizontal resolution of 3 km. The FLEXible PARTicle dispersion-WRF is also used to study some of the processes from a Lagrangian perspective. During the quiescent period corresponding to dryline formation and intensification, the dryline strengthens along the axis of a thermally-induced surface trough that promotes differential moisture advection. Also, convergence along the dryline is enhanced during night-time by the inertial oscillation ahead of the dryline and by the development of a thermally-driven circulation between the elevated terrain in northern Patagonia and the adjacent plains. These two mechanisms contribute to enhancing the intensity of the moisture gradient and to trigger deep moist convection. Under a period of stronger synoptic forcing, the dryline intensifies in response to the confluence induced by the deepening surface trough and moves away from the terrain elevations. Its movement during this period is driven by horizontal dry advection and the vertical mixing enhanced by the entrainment into the boundary layer of extremely dry air, whose origin can be traced back to the mid-levels over the Pacific Ocean. When the magnitude of the low-level westerly winds increase, moister air from lower levels cross the barrier, contributing to weakening the moisture gradient at the dryline.Fil: Bechis, Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Ruiz, Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Salio, Paola Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Cancelada, Maite. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Alvarez Imaz, María de Los Milagros. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; Argentin