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Van Der Velde O.A.,Polytechnic University of Catalonia | Montanya J.,Polytechnic University of Catalonia | Soula S.,CNRS Laboratory for Aerology | Pineda N.,Meteorological Service of Catalonia SMC | Mlynarczyk J.,AGH University of Science and Technology
Journal of Geophysical Research D: Atmospheres

Thirty-five sprite-producing lightning flashes were recorded in nine nights in different seasons at the east coast of Spain with a 3D Lightning Mapping Array (LMA) since July 2011. A low-frequency time-of-arrival network provided data on emissions from return strokes and intracloud processes and a very-high-frequency interferometer network produced complementary lightning data. This study analyzes the bidirectional development of flashes in order to understand the positioning and timing of the positive cloud-to-ground stroke (+CG) and its consequences for charge neutralization by negative leaders, affecting sprite morphology. A summary of negative leader extents, altitudes, and speeds before and after the + CG stroke is provided, as well as positive leader origins and inferred speeds. Negative leader speeds exhibited modes at 105 and 5 × 105 m s-1. Five examples with different evolutions are discussed: (1) Slow bidirectional development with negative leader termination before the + CG stroke; (2) Fast bidirectional development with the negative leader continuing after the + CG stroke. (3) Slow-fast bidirectional development with a negative leader exhibiting a sudden lowering and speed increase; (4) Fast secondary bidirectional development from an in-cloud horizontal positive leader. Negative leaders propagated rapidly into the upper positive charge layer, continuing after the + CG stroke; (5) Slow bidirectional development with a long negative leader (50 km) subject to cutoff while the original positive leader remained trapped inside negative charge. A + CG stroke subsequently occurred under the old negative leader channel. Carrot sprites tended to be associated with fast extending leaders after the stroke, columniform/mixed sprites with slower side branches. ©2014. American Geophysical Union. All Rights Reserved. Source

Alomar M.,Polytechnic University of Catalonia | Bolanos-Sanchez R.,National Oceanography Center | Sanchez-Arcilla A.,Polytechnic University of Catalonia | Sairouni A.,Meteorological Service of Catalonia SMC
Proceedings of the Coastal Engineering Conference

Parametric wave growth curves are commonly used to empirically calculate wave height under fetch limited conditions and to tune the source functions of spectral wave models. There is not a unique wave growth function and many deviations from the first similarity laws have been reported. The applicability of the commonly used functions in variable wind conditions is expected to be limited. In this study we calculated wave growth curves with data from an instrumental set-up in the north-western Mediterranean. This region is characterized by non-homogeneous wind conditions (both in time and space). The first growth functions we calculated from the observations suggested higher wave growth rates than previously described by other authors. A close look to the sources of discrepancy in the calculations under such wind conditions revealed the importance to accurately separate sea from swell and to use only locally generated sea. The source of the wind data used for the scaling law is thought to be responsible for the remaining discrepancies from the commonly used growth functions. Wind and wave data from a high resolution simulation were used to calculate the growth functions from a spectral wave model, and to explore the importance of using in-situ wind measures to scale the variables. Simulated wave growth rates are lower than observed and lower than previously reported by other authors. Wind measurements from the most offshore buoy seem to be representative enough of the winds over the entire area. The results support the applicability of the well-known functions in the region of interest when certain conditions are met; i.e. pure wind sea conditions, and choosing a representative wind speed to scale the variables. Source

Pineda N.,Meteorological Service of Catalonia SMC | Esteban P.,Institute dEstudis Andorrans CENMA IEA | Esteban P.,University of Barcelona | Trapero L.,Institute dEstudis Andorrans CENMA IEA | And 3 more authors.
Physics and Chemistry of the Earth

In the present study, we use a Principal Component Analysis (PCA) to characterize the surface 6-h circulation types related to substantial lightning activity over the Catalonia area (north-eastern Iberia) and the Principality of Andorra (eastern Pyrenees) from January 2003 to December 2007. The gridded data used for classification of the circulation types is the NCEP Final Analyses of the Global Tropospheric Analyses at 1° resolution over the region 35°N-48°N by 5°W-8°E. Lightning information was collected by the SAFIR lightning detection system operated by the Meteorological Service of Catalonia (SMC), which covers the region studied. We determined nine circulation types on the basis of the S-mode orthogonal rotated Principal Component Analysis. The " extreme scores" principle was used previous to the assignation of all cases, to obtain the number of final types and their centroids. The distinct differences identified in the resulting mean Sea Level Pressure (SLP) fields enabled us to group the types into three main patterns, taking into account their scale/dynamical origin. The first group of types shows the different distribution of the centres of action at synoptic scale associated with the occurrence of lightning. The second group is connected to mesoscale dynamics, mainly induced by the relief of the Pyrenees. The third group shows types with low gradient SLP patterns in which the lightning activity is a consequence of thermal dynamics (coastal and mountain breezes).Apart from reinforcing the consistency of the groups obtained, analysis of the resulting classification improves our understanding of the geographical distribution and genesis factors of thunderstorm activity in the study area, and provides complementary information for supporting weather forecasting. Thus, the catalogue obtained will provide advances in different climatological and meteorological applications, such as nowcasting products or detection of climate change trends. © 2010 Elsevier Ltd. Source

Barcons J.,Meteorological Service of Catalonia SMC | Barcons J.,Barcelona Supercomputing Center | Folch A.,Barcelona Supercomputing Center | Afif A.S.,Meteorological Service of Catalonia SMC | Miro J.R.,Meteorological Service of Catalonia SMC
Atmospheric Research

The progress in data assimilation techniques that incorporate weather observations into high-resolution numerical weather prediction models is challenging because of handling surface data in terrain misrepresentation, balance approximations, instrument errors and sensor representativeness. In the framework of operational numerical weather prediction, two data assimilation systems are compared using conventional observations from surface Automatic Weather Stations (AWS), a three-dimensional variational analysis (3DVAR) and the Local Analysis and Prediction System (LAPS). The goal is to study the ability of these two systems to assimilate data from AWS and to assess which performs better for near-surface wind and temperature fields to initialize a short-range 1-km resolution forecast with the Weather Research and Forecasting (WRF) model. Results show that the 3DVAR assimilation patterns are unrealistic given the inhomogeneous nature of the near-surface fields in complex terrains. In contrast, LAPS analyses show a heterogeneous assimilation pattern, more consistent with the complexity of the terrain and the observations. During the model spin-up period, simulations initialized using both data assimilation methods approach rapidly the control simulation, initialized without assimilation. However, the 1. km resolution forecasts initialized with LAPS exhibit a significant improvement, particularly for the wind field module. © 2015 Elsevier B.V. Source

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