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Roman-Cascon C.,Complutense University of Madrid | Yague C.,Complutense University of Madrid | Viana S.,AEMET | Sastre M.,Complutense University of Madrid | And 3 more authors.
Quarterly Journal of the Royal Meteorological Society | Year: 2015

Near-monochromatic gravity waves (GWs) associated with a mesoscale convective system (MCS) were detected during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign in Lannemezan (France) on 21 June 2011. These GWs are analyzed using available instrumental data (e.g. an array of microbarometers, a microwave system Humidity And Temperature PROfiler (HATPRO) and an ultra-high-frequency (UHF) wind profiler). Pressure oscillations of up to 0.5 hPa were recorded after a pronounced pressure drop of 1.4 hPa, identified as the MCS weak low. Wavelet analysis and evaluated wave parameters confirm the occurrence of such GWs (period ~9 min, horizontal wavelength ~7 km), which propagated from southwest to northeast, i.e. in the same direction of propagation as the MCS. Observational evidence suggests the downdraughts associated with the rear-inflow jet at the weak low zone of the MCS as the most likely generator mechanism of the GWs. However, the complex orography and proximity of the Pyrenees to the field campaign could also play an important role. Wave propagation was possible through the ducting mechanism, favoured by the existence of a critical level in a wind-sheared environment around 2000 m above ground level. Wave-like motions related to the passage of the GWs were also observed in other atmospheric parameters close to the surface and within the lower troposphere. The effects of GWs on the surface fluxes have also been analyzed through Multi-Resolution Flux Decomposition (MRFD) methods. © 2014 Royal Meteorological Society.

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).

Tampieri F.,CNR Institute of atmospheric Sciences and Climate | Yague C.,Complutense University of Madrid | Viana S.,AEMET
Boundary-Layer Meteorology | Year: 2015

Observations of the stable boundary layer (SBL) obtained during the SABLES98 experiment are analyzed in order to investigate the vertical variations of the momentum flux $$\tau >0$$τ>0, the heat flux $$Q$$Q ($$<$$<0 in stable conditions) and the turbulent kinetic energy $$E$$E. The traditional SBL is identified on the basis of the momentum and heat fluxes respectively decreasing and increasing with height; the vertical scales obtained from the profiles of $$\tau $$τ, $$Q$$Q and $$E$$E give indications about the depth of the boundary layer, and are shown to be different for the different statistical moments. The upside-down SBL cases are defined by the momentum flux and the turbulent kinetic energy increasing with height, while the heat flux can increase or decrease with height. Also in this case the vertical scales differ for the different statistical moments. The observations show that the stability (evaluated from the gradient Richardson number or the Obukhov length) is not a univocal index that discriminates between traditional and upside-down cases. The scales allow a compact description of the vertical structure of the traditional and upside-down SBL in terms of the considered statistical moments and of the gradient Richardson number, and are used to interpret the variation of the Obukhov length with height. © 2015, Springer Science+Business Media Dordrecht.

Udina M.,University of Barcelona | Soler M.R.,University of Barcelona | Viana S.,AEMET | Yague C.,Complutense University of Madrid
Quarterly Journal of the Royal Meteorological Society | Year: 2013

In this study, starting from an observational case of internal gravity waves (IGWs) generated at the top of a drainage flow during the SABLES2006 field campaign, we aim to reproduce the IGWs and their origin through mesoscale meteorological modelling. We used the Weather Research and Forecast (WRF) model with fine horizontal resolution (1 km), testing the model capabilities to simulate the IGWs through a WRF fixed physics package option but two different planetary boundary layer schemes, the Mellor-Yamada-Janjić (MYJ) and the Yonsei University (YSU). The comparison between model simulations and measurements from a 100 m meteorological tower reveals that the MYJ scheme simulation gives much better results, as it better represents the main features of the density current measured by the tower instruments, although the event is predicted to occur sooner than it is observed to occur. The study has also shown the capacity of this scheme to detect the oscillations in temperature and specific humidity generated by the arrival of the density current. In contrast, the YSU scheme captures the arrival of the current on time but it fails to correctly track its properties and therefore it does not reproduce the gravity waves with the current arrival. In addition, wave parameters calculated from model outputs (MYJ) using the wavelet method reveal waves with longer periods and longer wavelengths (T=20-22 min and λ=8-10 km) than those calculated from measurements (T=9.2 min and λ=3.5 km) using the same technique. © 2012 Royal Meteorological Society.

Borde R.,EUMETSAT | Garcia-Pereda J.,AEMET
Journal of Atmospheric and Oceanic Technology | Year: 2014

The goal of this paper is to show the impact of the use of the wind guess (WG) in atmospheric motion vector (AMV) extraction schemes. The study has been performed using the Satellite Application Facility on Support to Nowcasting and Very Short Range Forecasting (NWCSAF) High Resolution Winds AMV software. Target box sizes varying from 8 × 8 to 40 × 40 pixels and temporal gaps varying from 5 to 60 min have been considered for two configurations that useWGand do not use the wind guess (NWG) to locate the search area in the tracking process. AMVs have been extracted for four different Meteosat Second Generation (MSG) Spinning Enhanced Visible and Infrared Imager (SEVIRI) channels [high-resolution visible (HRVIS), visible 0.8μm (VIS0.8), water vapor 6.2μm (WV6.2), and infrared 10.8μm (IR10.8)] over the European and Mediterranean area for a 6-month period (January-June 2010). The AMVs' performances have been tested against radiosonde wind observations and ECMWF NWP model wind analysis. The results show an impact on the amount of valid AMVs extracted by each configuration. Not using the wind guess produces more valid AMVs when large target boxes and short temporal gaps are used. It is the opposite when small target boxes and long temporal gaps are used. The results also show a general increase in the mean AMV speed, and a general reduction of the normalized bias and the normalized root-mean-square vector difference for all the tested channels and configurations, when the wind guess is not used to locate the search area. © 2014 American Meteorological Society.

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