Meteorological Service of Catalonia

of Catalonia, Spain

Meteorological Service of Catalonia

of Catalonia, Spain
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Farnell C.,Meteorological Service of Catalonia | Rigo T.,Meteorological Service of Catalonia | Pineda N.,Meteorological Service of Catalonia
Atmospheric Research | Year: 2017

Several studies reported sudden increases in the total lightning flash rate (intra-cloud+cloud-to-ground) preceding the occurrence of severe weather (large hail, wind gusts associated to thunderstorms and/or tornadoes). Named “Lightning Jump”, this pattern has demonstrated to be of operational applicability in the forecasting of severe weather phenomena. The present study introduces the application of a lightning jump algorithm, with an identification of cells based solely on total lightning data, revealing that there is no need of radar data to trigger severe weather warnings. The algorithm was validated by means of a dataset severe weather events occurred in Catalonia in the period 2009–2014. Results obtained revealed very promising. © 2016 Elsevier B.V.

Pineda N.,Meteorological Service of Catalonia | Pineda N.,Polytechnic University of Catalonia | Rigo T.,Meteorological Service of Catalonia
Agricultural and Forest Meteorology | Year: 2017

Wildland fires originated by lightning in Catalonia (NE Spain) are systematically examined through the use of lightning and precipitation data. The region of study, with a Mediterranean climate, is prone to summer wildfires. Despite being mainly anthropogenic, lightning-ignited fires (10%) are relevant as they can trigger large fires. Given that the lightning efficiency in Catalonia is of 1/1400 fires per lightning, the ability to identify potential ignition candidates among the whole lightning population would be of great value to forest protection agencies. Literature reveals that lightning characteristics such as polarity or multiplicity has proven to be of limited value as predictors. Therefore, another approach is necessary to set a probability of wildfire ignition to each lightning. In this regard, the aim of this study was to explore the relationship between lightning-ignited wildfires and precipitation, as lightning-ignited wildfires in the region are often attributed to ‘dry’ lightning (lightning accompanied with little or no precipitation). Results revealed that 25% of the lightning strokes related to wildfire ignitions had no associated precipitation at all, 40% had less than 2 mm of precipitation and 90% had less than 10 mm. Results also revealed that holdover fires (ignitions with delayed arrivals) are rare in the region. Finally, results suggest that there is no apparent link between the amount of precipitation and the holdover duration, indicating that the survival phase of lightning-ignitions is mainly driven by the daily cycle of solar heating. All in all, adding information on the precipitation associated to each lightning may help focusing attention on a reduced sample of strokes and provide fire managers with valuable information about potential lightning-caused wildfires. © 2017 Elsevier B.V.

Van Der Velde O.A.,University of Barcelona | Montanya J.,University of Barcelona | Soula S.,CNRS Laboratory for Aerology | Pineda N.,Meteorological Service of Catalonia | Bech J.,Meteorological Service of Catalonia
Journal of Geophysical Research: Space Physics | Year: 2010

During the evening of 6 August 2008, a small mesoscale convective system (MCS) entered the area of radar and 2-D interferometric lightning detection system coverage in northeastern Spain and produced 17 sprites recorded by a camera at only 95-180 km distance. This study presents an analysis of the in-cloud component of the sprite-associated lightning flashes and those of other flashes. The analysis focuses on the horizontal development of sprite-producing lightning by discussing three examples, divided into the periods before the positive cloud-to-ground flash (+CG), between +CG and the end of the sprite, and the period after the sprite. Location and horizontal size of sprites appear to be well explained by the temporal and spatial development of the lightning path. The majority of sprite-producing discharges started directly at the rear side of developing and mature convective cores within the decaying MCS, either with the +CG or with preceding negative leaders. The +CG started a burst of VHF sources during which the sprite developed. Delayed carrot sprites developed after a secondary, smaller burst and were well collocated with the burst toward the rear of the MCS. The order of development of elements in a grouped sprite followed the direction of lightning propagation during the burst stage. The second part of the analysis concentrates on the metrics of sequences of VHF sources and shows that sprites are indeed produced by the largest, longest lasting discharges with particularly large line-perpendicular dimensions (37 km median compared with 11 km for +CG >25 kA). Copyright 2010 by the American Geophysical Union.

Amaro J.,Meteorological Service of Catalonia | Gayaa M.,AEMET | Aran M.,Meteorological Service of Catalonia | Llasat M.C.,University of Barcelona
Natural Hazards and Earth System Science | Year: 2010

One of the aims of the MEDEX project is to improve the knowledge of high-impact weather events in the Mediterranean. According to the guidelines of this project, a pilot study was carried out in two regions of Spain (the Balearic Islands and Catalonia) by the Social Impact Research group of MEDEX. The main goal is to suggest some general and suitable criteria about how to analyse requests received in Meteorological Services arising out of the damage caused by weather events. Thus, all the requests received between 2000 and 2002 at the Servei Meteorològic de Catalunya as well as at the Division of AEMET in the Balearic Islands were analysed. Firstly, the proposed criteria in order to build the database are defined and discussed. Secondly, the temporal distribution of the requests for damage claims is analysed. On average, almost half of them were received during the first month after the event happened. During the first six months, the percentage increases by 90%. Thirdly, various factors are taken into account to determine the impact of specific events on society. It is remarkable that the greatest number of requests is for those episodes with simultaneous heavy rain and strong wind, and finally, those that are linked to high population density. © 2010 Author(s).

Pineda N.,Meteorological Service of Catalonia | Bech J.,Meteorological Service of Catalonia | Rigo T.,Meteorological Service of Catalonia | Montanya J.,Polytechnic University of Catalonia
Atmospheric Research | Year: 2011

On the night from 1st to 2nd of November 2008, a multi-cell storm coming from the Mediterranean produced severe weather in the coastal area of Catalonia (NE Spain): ground-level strong damaging wind gusts, a tornado - which caused F2 damage - and heavy rainfall. A general overview of the synoptic framework, damage observed and a radar analysis is given in the first part of the study. This second part is mostly centered on the detailed analysis of the total lightning behavior, its relationship with radar-derived storm parameters, and total lightning correlation with hazardous weather. The purpose is to bring more evidence about the outstanding role of total lightning in severe weather surveillance tasks. The analysis of the storm cells life cycle has showed similar trends between the total lighting flash rates and radar-derived parameters like the area of reflectivity above 30. dBZ at 7-km. Regarding lightning trends, a lightning "jump" pattern - an abrupt increase of the total lightning rate in a short period of time - has been related to severe weather. On the contrary, cloud-to-ground lightning data did not show any pattern related to severe weather. In comparison to other parameters, like the IC:CG ratio, the lightning "jump" pattern seems more robust to forecast in a short-term basis the possible occurrence of severe weather. © 2010 Elsevier B.V.

Rigo T.,Meteorological Service of Catalonia | Pineda N.,Meteorological Service of Catalonia | Bech J.,Meteorological Service of Catalonia
Natural Hazards and Earth System Science | Year: 2010

Monitoring thunderstorms activity is an essential part of operational weather surveillance given their potential hazards, including lightning, hail, heavy rainfall, strong winds or even tornadoes. This study has two main objectives: firstly, the description of a methodology, based on radar and total lightning data to characterise thunderstorms in real-time; secondly, the application of this methodology to 66 thunderstorms that affected Catalonia (NE Spain) in the summer of 2006. An object-oriented tracking procedure is employed, where different observation data types generate four different types of objects (radar 1-km CAPPI reflectivity composites, radar reflectivity volumetric data, cloud-to-ground lightning data and intra-cloud lightning data). In the framework proposed, these objects are the building blocks of a higher level object, the thunderstorm.

The methodology is demonstrated with a dataset of thunderstorms whose main characteristics, along the complete life cycle of the convective structures (development, maturity and dissipation), are described statistically. The development and dissipation stages present similar durations in most cases examined. On the contrary, the duration of the maturity phase is much more variable and related to the thunderstorm intensity, defined here in terms of lightning flash rate. Most of the activity of IC and CG flashes is registered in the maturity stage. In the development stage little CG flashes are observed (2% to 5%), while for the dissipation phase is possible to observe a few more CG flashes (10% to 15%). Additionally, a selection of thunderstorms is used to examine general life cycle patterns, obtained from the analysis of normalized (with respect to thunderstorm total duration and maximum value of variables considered) thunderstorm parameters. Among other findings, the study indicates that the normalized duration of the three stages of thunderstorm life cycle is similar in most thunderstorms, with the longest duration corresponding to the maturity stage (approximately 80% of the total time). © Author(s) 2010.

Barrera-Escoda A.,Meteorological Service of Catalonia | Cunillera J.,Meteorological Service of Catalonia
Advances in Geosciences | Year: 2010

In this work the MM5 mesoscale model is used in order to analyse the temporal evolution of the precipitation for the period 1971-2000 in Catalonia (NE Iberian Peninsula). Three one-way nested domains with 135, 45 and 15 km horizontal grid resolution and 23 vertical levels have been used. The simulation is performed nesting MM5 into the ERA40 reanalyses. Dynamical nudging is applied to the first domain. However, nudging is not applied in the second and third domains. In order to assess the performance of the developed methodology (main spatio-temporal precipitation characteristics), the results obtained in each simulation are compared with those obtained from ERA40 and observational data. The results show a climatologically reliable distribution of the simulated precipitation spatial patterns for annual, semi-annual, spring and summer precipitation compared to those obtained from 1100 rain gauges covering the whole study area. For winter and autumn the goodness of the results is much lower. Furthermore, the results for 15-km outputs are better than the 45-km ones. The simulations also reproduce well the evolution of annual anomalies for Catalonia and the probability density function (PDF) of monthly mean precipitation. They also improve the precipitation outputs from ERA40, which present an important negative trend and a drier PDF for the period 1971-2000. On the other hand, extreme values are not well reproduced by the simulation. Despite this fact, hydric extremes derived from extreme values (i.e. extreme rainy days and flood records) are well captured by the model. © 2010 Author(s).

Pages M.,Meteorological Service of Catalonia | Miro J.R.,Meteorological Service of Catalonia
Meteorological Applications | Year: 2010

This study took place in the Pyrenees Range, in the northeastern Iberian Peninsula. The Pyrenees extend longitudinally, separating the Iberian Peninsula from the rest of Europe, and high peaks around 3000 m arise from deep valleys. As a mountain range it creates a barrier to advection, in this case from the north and south, and typical meteorological phenomena of mountainous areas occur within it (inversions, Foehn effect, extreme wind-chill, snow storms). Thus, two specific valleys in Catalonia were considered, Val d'Aran and Cerdanya. In both valleys automatic weather stations (AWSs) are available at similar heights. Although these valleys are only 100 km apart, they have different climates. However, the main reason for developing the study was that Numerical Weather Prediction (NWP) has problems when forecasting temperatures in complex terrain areas, mainly in the valley floor in winter season. Firstly, different equations based on a multilinear regression were obtained for each weather station. Multilinear regression was considered in this case as the most suitable downscaling method and data used were provided by the AWSs and MM5 (PSU/NCAR mesoscale model) numerical weather prediction model outputs. These equations were obtained to set up a Geographically Weighted Regression (GWR) method, although this one was modified and changed to a Vertically Weighted Regression (VWR) in order to create vertical temperature profiles. © 2009 Royal Meteorological Society.

Schulte L.,University of Barcelona | Pena J.C.,Meteorological Service of Catalonia | Carvalho F.,University of Barcelona | Schmidt T.,Schmidt Information and Webdesign | And 3 more authors.
Hydrology and Earth System Sciences | Year: 2015

A 2600-year long composite palaeoflood record is reconstructed from high-resolution delta plain sediments of the Hasli-Aare floodplain on the northern slope of the Swiss Alps. Natural proxies compiled from sedimentary, geochemical and geomorphological data were calibrated by textual and factual sources and instrumental data. No fewer than 12 of the 14 historically recorded extreme events between 1480 and the termination of the Hasli-Aare river channel correction in 1875 were also identified by coarse-grained flood layers, log(Zr / Ti) peaks and factor 1 anomalies. Geomorphological, historical and instrumental data provide evidence for flood damage intensities and discharge estimations of severe and catastrophic historical floods. Spectral analysis of the geochemical and documentary flood series and several climate proxies (TSI, δ18O, tree-rings, NAO, SNAO) identify similar periodicities of around 60, 80, 100, 120 and 200 years during the last millennia, indicating the influence of the North Atlantic circulation and solar forcing on alpine flood dynamics. The composite floodplain record illustrates that periods of organic soil formation and deposition of phyllosilicates (from the medium high catchment area) match those of total solar irradiance maxima, suggesting reduced flood activity during warmer climate pulses. Aggradation with multiple sets of flood layers with increased contribution of siliciclasts from the highest catchment area (plutonic bedrock) (e.g. 1300-1350, 1420-1480, 1550-1620, 1650-1720 and 1811-1851 cal yr AD) occurred predominantly during periods with reduced solar irradiance, lower δ18O anomalies, cooler summer temperatures and phases of drier spring climate in the Alps. Increased water storage by glaciers, snow cover and snow patches susceptible to melting processes associated with rainfall episodes and abrupt rises in temperature substantially increased surface runoff on slopes and discharges of alpine rivers. This interpretation is in agreement with the findings that the severe and catastrophic historical floods in the Aare since 1670 occurred mostly during positive SNAO (Summer North Atlantic Oscillation) pulses after years or even decades dominated by negative SNAO and cooler annual temperatures. © Author(s) 2015.

Bech J.,University of Barcelona | Pineda N.,Meteorological Service of Catalonia | Rigo T.,Meteorological Service of Catalonia | Aran M.,Meteorological Service of Catalonia
Atmospheric Research | Year: 2013

On the 8 of March 2010 a heavy snowfall accompanied by lightning occurred over Catalonia (NE Spain), in the Western Mediterranean. Total lightning observations included 101 cloud-to-ground flashes and 169 intra-cloud flashes. Precipitation amounts in 24. h exceeded 100. mm and snow depths over low altitude terrain, where snow is rare, surpassed 30. cm. Snow accumulations collapsed the regional communication transport network and the border with France was closed several hours. Occurrence of wet snow combined with increasingly strong winds caused widespread damage over large forest areas estimated in more than 20. MEur and affected dramatically the high voltage power line distribution grid due to ice accretion, particularly in NE Catalonia where 33 high power electrical towers were knocked down. The meteorological framework at synoptic scale was dominated at low levels by a northern flow over Iberia due to a blocking high pressure system on the British Isles, and an upper level cold trough, which favoured a rapid cyclogenesis over the Mediterranean (9.2. hPa drop in 12. h). Weather radar observations indicated predominance of stratiform precipitation and some low-topped convection, with maximum reflectivities and tops mostly below 40. dBZ and 4. km respectively. The presence of mesoscale gravity waves, caused by wind-shear instability, is suggested as a triggering element for convection and subsequent lightning. Comparison of accumulated precipitation and lightning maps indicated clusters of lightning data unrelated to precipitation maxima. Further investigation of total lightning characteristics and co-located radar observations suggested a triggering effect by tall telecommunication towers inducing cloud-to-ground flashes and subsequent intra-cloud lightning. © 2012 Elsevier B.V.

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