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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.

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).

Viana S.,AEMET | Terradellas E.,AEMET | Yague C.,Complutense University of Madrid
Journal of the Atmospheric Sciences | Year: 2010

Drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near-surface air masses in sloping terrain. The initial irruption of these flows, with sudden shifts in wind speed and direction, may result in vertical displacements of air parcels from their equilibrium position, which prove to be a common source of internal gravity waves. This paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the Stable Atmospheric Boundary Layer Experiment in Spain 2006 (SABLES2006)field campaign. Pressure differences, measured by microbarometers set at different levels of atower, help to interpret the evolution of other atmospheric variables, provide a detailed picture of the irruption of a drainage current, and reveal the formation of gravity waves at its top. The main parameters of the waves are derived from wavelet cross correlation of pressure time series, recorded by a surface array of microbarometers. The analysis yields, among other parameters, the horizontal component of the phase and group velocities of the gravity waves, which compare well with the velocity of irruption of the drainage current. Wavelet and other multiresolution techniques are also applied to sonic anemometer records to study the interaction between turbulence and larger-scale motions. The analysis shows evidence of heat flux divergence induced by the gravity waves, which may constitute a key factor for the vertical thermal profile in the nocturnal boundary layer (NBL) in situations of weak turbulence and important waveactivity. © 2010 American Meteorological Society.

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.

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.

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.

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

The goal of this paper is to show the impact of the tracer size and the temporal gap between images in atmospheric motion vector (AMV) extraction schemes. A test has been performed using NWC SAF/High Resolutions Winds AMV software for different configurations with a tracer size varying between 8 × 8 and 40 × 40 pixels and a temporal gap between images varying between 5 and 90 min. AMVs have been extracted for four different MSG/SEVIRI channels (HRVIS, VIS0.8, WV6.2, and IR10.8) over the European and Mediterranean area for a 6-month period (January-June 2010). The AMV performances have been tested against radiosonde winds and ECMWF model analysis winds. The results show a small impact of the tracer size on the number of valid AMVs, which is, however, more significant for clear air AMVs, and a significant impact of the temporal gap between images. The largest number of valid AMVs has been found in general for a temporal gap of 5 min for the 1-km pixel scale and for a temporal gap of 10 min for the 3-km pixel scale. Results also show a decrease of the mean AMV speed and the normalized BIAS (NBIAS) with larger tracer sizes, and a relatively small impact of the temporal gap on these parameters. Finally, the results show minimum values of the normalized root-mean-square vector difference (NRMSVD) for intermediate temporal gaps between 15 and 30 min with a relatively small impact of the tracer size on this parameter. © 2014 American Meteorological Society.

Bech J.,Meteorological Service of Catalonia | Pineda N.,Meteorological Service of Catalonia | Rigo T.,Meteorological Service of Catalonia | Aran M.,Meteorological Service of Catalonia | And 5 more authors.
Atmospheric Research | Year: 2011

This study presents an analysis of a severe weather case that took place during the early morning of the 2nd of November 2008, when intense convective activity associated with a rapidly evolving low pressure system affected the southern coast of Catalonia (NE Spain). The synoptic framework was dominated by an upper level trough and an associated cold front extending from Gibraltar along the Mediterranean coast of the Iberian Peninsula to SE France, which moved north-eastward. South easterly winds in the north of the Balearic Islands and the coast of Catalonia favoured high values of 0-3. km storm relative helicity which combined with moderate MLCAPE values and high shear favoured the conditions for organized convection. A number of multicell storms and others exhibiting supercell features, as indicated by Doppler radar observations, clustered later in a mesoscale convective system, and moved north-eastwards across Catalonia. They produced ground-level strong damaging wind gusts, an F2 tornado, hail and heavy rainfall. Total lightning activity (intra-cloud and cloud to ground flashes) was also relevant, exhibiting several classical features such as a sudden increased rate before ground level severe damage, as discussed in a companion study. Remarkable surface observations of this event include 24. h precipitation accumulations exceeding 100. mm in four different observatories and 30. minute rainfall amounts up to 40. mm which caused local flash floods. As the convective system evolved northward later that day it also affected SE France causing large hail, ground level damaging wind gusts and heavy rainfall. © 2010 Elsevier B.V.

Garcia-Moya J.-A.,AEMET | Callado A.,AEMET | Escriba P.,AEMET | Santos C.,AEMET | And 2 more authors.
Tellus, Series A: Dynamic Meteorology and Oceanography | Year: 2011

Numerical weather prediction (NWP) models (including mesoscale) have limitations when it comes to dealing with severe weather events because extreme weather is highly unpredictable, even in the short range. A probabilistic forecast based on an ensemble of slightly different model runs may help to address this issue. Among other ensemble techniques, Multimodel ensemble prediction systems (EPSs) are proving to be useful for adding probabilistic value to mesoscale deterministic models. A Multimodel Short Range Ensemble Prediction System (SREPS) focused on forecasting the weather up to 72 h has been developed at the Spanish Meteorological Service (AEMET). The system uses five different limited area models (LAMs), namely HIRLAM (HIRLAM Consortium), HRM (DWD), the UM (UKMO), MM5 (PSU/NCAR) and COSMO (COSMO Consortium). These models run with initial and boundary conditions provided by five different global deterministic models, namely IFS (ECMWF), UM (UKMO), GME (DWD), GFS (NCEP) and CMC (MSC). AEMET-SREPS (AE) validation on the large-scale flow, using ECMWF analysis, shows a consistent and slightly underdispersive system. For surface parameters, the system shows high skill forecasting binary events. 24-h precipitation probabilistic forecasts are verified using an up-scaling grid of observations from European high-resolution precipitation networks, and compared with ECMWF-EPS (EC). © 2011 AEMET Tellus A © 2011 John Wiley & Sons A/S.

Shutts G.,UK Met Office | Pallares A.C.,AEMET
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

The need to represent uncertainty resulting from model error in ensemble weather prediction systems has spawned a variety of ad hoc stochastic algorithms based on plausible assumptions about sub-grid-scale variability. Currently, few studies have been carried out to prove the veracity of such schemes and it seems likely that some implementations of stochastic parametrization are misrepresentations of the true source of model uncertainty. This paper describes an attempt to quantify the uncertainty in physical parametrization tendencies in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System with respect to horizontal resolution deficiency. High-resolution truth forecasts are compared with matching target forecasts at much lower resolution after coarse-graining to a common spatial and temporal resolution. In this way, model error is defined and its probability distribution function is examined as a function of tendency magnitude. It is found that the temperature tendency error associated with convection parametrization and explicit water phase changes behaves like a Poisson process for which the variance grows in proportion to the mean, which suggests that the assumptions underpinning the Craig and Cohen statistical model of convection might also apply to parametrized convection. By contrast, radiation temperature tendency errors have a very different relationship to their mean value. These findings suggest that the ECMWF stochastic perturbed parametrization tendency scheme could be improved since it assumes that the standard deviation of the tendency error is proportional to the mean. Using our finding that the variance error is proportional to the mean, a prototype stochastic parametrization scheme is devised for convective and largescale condensation temperature tendencies and tested within the ECMWF Ensemble Prediction System. Significant impact on forecast skill is shown, implying its potential for further development. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

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