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Montanya J.,University of Barcelona | van der Velde O.A.,University of Barcelona | March V.,University of Barcelona | Romero D.,University of Barcelona | And 2 more authors.
Atmospheric Research

This paper summarizes results obtained by the 2009-2010 field campaigns conducted in northeastern Spain using a high speed camera, VHF interferometer, VLF lightning location system and scintillation detectors for energetic radiation. The main purpose was to obtain new insight into the lightning processes which emit x/γ radiation. For just one (very close) lightning strike, 99 x-ray pulses were emitted within 0.86. ms and had an energy higher that 10. keV. This burst was associated with the final stages of a downward negative leader. The high-speed camera data also allowed to identify various previously unreported features in different types of cloud-to-ground lightning flashes. At video frame rates of 10,000. fps, some branches of negative leaders of cloud-to-ground flashes were illuminated for the duration of only one frame. During positive cloud-to-ground flashes, the high speed videos showed an intense activity of recoil leaders. In the case of intra-cloud lightning, the VHF interferometer network did not present a clear relation between detections and visible leader. Instead, bursts of VHF detections corresponded visually to a long-lasting bright channel under the cloud base. © 2011 Elsevier B.V. Source

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

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). Source

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

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. Source

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

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. Source

Coll J.R.,Rovira i Virgili University | Aguilar E.,Rovira i Virgili University | Prohom M.,Meteorological Service of Catalonia | Sigro J.,Rovira i Virgili University
Cuadernos de Investigacion Geografica

Long-term drought variability and trends were assessed in Barcelona at annual and seasonal scale for the period 1787-2014 and sub-periods 1851-2014, 1901-2014 and 1951-2014 to identify changes in drought patterns across time. High quality and adjusted monthly temperature and precipitation series were required for this purpose. The Standardized Precipitation Index (SPI), based on precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI), based on the difference between precipitation and reference evapotranspiration (ET0), were calculated to describe temporal drought fluctuations. Therefore, major droughts and wet events were identified and an accurate analysis of drought severity, magnitude and duration were also carried out. Both drought indices provided similar results related to drought variability and trends in Barcelona across time, although the SPEI showed larger drought severity than SPI especially during the second half of the 20th century. Trends analysis revealed a significant drying trend at annual scale according to the SPEI since mid-19th century while the SPI did not show changes in drought patterns. At seasonal scale, both the SPI and SPEI found a clear drying trend only for summer (JJA) during the current period (1951-2014), although the SPEI was indicating the trend towards drier conditions for the whole period (1787-2014). Drought severity in SPEI series increased 13% during the second half of the 20th century compared with the whole period under study while drought magnitude and duration did not present significant changes in both the SPI and SPEI series. The increasing atmospheric evaporative demand associated to the large temperature rising experienced in Barcelona during the last decades could have played a substantial role in explaining the increase of drought severity and trends found in the SPEI series. © Universidad de La Rioja. Source

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