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The occurrence of heat waves and cold spells has been receiving special attention in recent years due to their impact on human health, ecosystems and other aspects, such as the economy. The present work uses a Lagrangian approach to analyse the physical processes leading to temperature extremes in the Iberian Peninsula (IP) for the 20‐year period 1994–2013. Principal component analysis has also been carried out to identify the associated synoptic scale configurations. Spatial pattern analysis shows that the highest temperatures during hot events are reached in the SW region and the lowest ones in the NE, while a latitudinal gradient of 26 K was obtained for the cold events, with the lowest values in the NE regions and the Pyrenees. Most of the extremes persisted between 1 and 3 days for both hot and cold events. Rather than meridional advection, the primary cause behind the occurrence of hot extremes seems to be progressive diabatic warming, which becomes accentuated in its final stage and is caused, on the one hand, by air masses with long residence times over the IP and, on the other hand, by recirculation processes during summer days of weak baric gradient. The air masses producing the extreme cold events have faster trajectories and mainly originate in north and northeast Europe, due to a relative low in the central Mediterranean and a blocking high in the North Atlantic and/or in northeast Europe. The primary cause of occurrence of hot extremes in Iberian Peninsula (IP) is a progressive diabatic warming caused by air masses with long residence times over the IP and by recirculation processes during summer days of weak baric gradient. The extreme cold events are associated with air‐mass advection from north and northeast Europe, induced by the presence of a relative low in the central Mediterranean and a blocking high in the North Atlantic and/or in north‐eastern Europe. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper analyses the daily precipitation data recorded for the last 75-80 years in SE Spain. Prior to statistical analysis, homogeneity tests were performed to determine the usefulness of the data (recorded in six pluviometric stations). If the data were homogeneous, the Mann-Kendall test was performed to detect monotonic trends for variables such as total precipitation, number of days with precipitation greater than 1, 20 or 40 mm, number of consecutive dry days and number of consecutive wet days. Moreover, the linear tendency was calculated and accepted (or rejected) by performing a Student's t-test of the calculated residual values. The results showed, on average, a clear change in precipitation patterns for the last 20 years. Annual rainfall had decreased, with values ranging from 0 to 15%, dry periods had increased in length, and the number of rainy days had decreased (especially when high daily precipitation was considered). This latter notion did not exactly concur with the conclusions of the Intergovernmental Panel on Climate Change ( IPCC) 2014 Synthesis Report related to the study area. [ABSTRACT FROM AUTHOR]

ABSTRACT From a local point of view, in May/June, there is an important and positive 2 m temperature trend at Palma (Mallorca), which is simultaneous and highly correlated with a strong increase in the 500 hPa geopotential height. This study analyses this fact as well as the observed tendencies in a wider seasonal and geographical context. We confirm the particularly high correlation between 2 m temperature and 500 hPa geopotential during the warm months as opposed to the much weaker correlation in winter. This suggests that mechanisms for thermal changes act differently throughout the year in this region. Besides the direct radiative effect, warm season near-surface temperatures are linked to the presence of deep anticyclones, which effectively determine the northern edge of the Hadley cell. Accordingly, the strong warming trend in the area of Palma during the warm months of the year is purportedly related to the poleward extension of the Hadley cell. The fact that May/June shows the highest low-level temperature trend among all bi-monthly series is a common regional feature over a relatively wide area over the Western Mediterranean. Different geographical patterns emerge in other periods of the year. In July/August, the strongest low-level warming area drifts to the east-northeast, towards Ukraine and Russia. Coincidentally, the 500 hPa geopotential tendencies show a coherent pattern, with an intense positive trend ridge over the Western Mediterranean area in May/June, and a displacement of this ridge to the north-east in July/August. We show the connection between 500 hPa geopotential height and near-surface temperature by means of a multiple lineal regression that attributes half of the local temperature tendency in Palma to the intensification of a 500 hPa ridge centred over the Western Mediterranean and surroundings. [ABSTRACT FROM AUTHOR]

ABSTRACT Monthly rain amounts ( MRA) recorded at Fabra Observatory (Barcelona, NE Spain) since 1917-2010, are analysed from two complementary points of view. First, mono- and multifractal characteristics of MRA are compared with those corresponding to the monthly Western Mediterranean Oscillation index ( WeMOi), which affects the rainfall regime at the western Mediterranean region. Monofractality is analysed through Hurst and Hausdorff exponents, and a power law describing the dependence of MRA power spectra on frequency. The reconstruction theorem permits to quantify the complexity of the physical process by means of the correlation dimension and the Kolmogorov entropy. In agreement with this theorem, the predictive instability is also evaluated through the Lyapunov exponents. The multifractality is characterized by the critical Hölder exponent, as well as by the asymmetry and spectral width of the multifractal spectrum. Second, three predictive processes for MRA are tested. One of them is based on the assumption that MRA could be simulated by fractional Gaussian noise. The other two are, by one hand, an ARIMA( p,1,0) process for MRA; on the other hand, an adaptation of the ARIMA process for MRA taking as arguments preceding WeMOi. Finally, relationships between MRA and WeMOi confirm that outstanding MRA use to be coincident with negative WeMOi. An explanation is also proposed for the non-negligible number of MRA corresponding to positive WeMOi. [ABSTRACT FROM AUTHOR]

ABSTRACT The complexity, predictability and predictive instability of the Western Mediterranean Oscillation index ( WeMOi) at monthly scale, years 1856-2000, are analysed from the viewpoint of monofractal and multifractal theories. The complex physical mechanism is quantified by: (1) the Hurst exponent, H, of the rescaled range analysis; (2) correlation and embedding dimensions, μ* and dE, together with Kolmogorov entropy, κ, derived from the reconstruction theorem; and (3) the critical Hölder exponent, α o, the spectral width, W, and the asymmetry of the multifractal spectrum, f( α). The predictive instability is described by the Lyapunov exponents, λ, and the Kaplan-Yorke dimension, DKY, while the self-affine character is characterized by the Hausdorff exponent, H a. Relationships between the exponent β, which describes the dependence of the power spectrum S( f) on frequency f, and the Hurst and Hausdorff exponents suggest fractional Gaussian noise ( fGn) as a right simulation of empiric WeMOi. Comparisons are made with monthly North-Atlantic Oscillation and Atlantic Multidecadal Oscillation indices. The analysis is complemented with an ARIMA(p,1,0) autoregressive process, which yields a more accurate prediction of WeMOi than that derived from fGn simulations. [ABSTRACT FROM AUTHOR]

ABSTRACT Hailstorms have become a serious meteorological risk in mid-latitude countries because of their small-scale development and short time span, and their forecasting remains problematic. Moreover, the lack of reliable hailstorm databases is an important handicap for Numerical Weather Prediction (NWP) model validation, time trend studies and establishment of hailstorm relationships with global warming and climate change. However, this can be overcome by ascertaining physical relationships between favourable synoptic patterns and mesoscale trigger factors for hailstorm development in a local study area. North-eastern Spain is one of the European regions with largest number of hailstorm days ( HD) observed in the summer. Since 2001, from May through September, reliable databases of hailstorm occurrence in the middle Ebro Valley have been constructed, which include intensity, temporal frequency and spatial coordinate data. June and July 2006 had the largest number of HD in 2001-2010. With the objective of analysing meteorological factors responsible for this anomaly, atmospheric patterns at low and mid-tropospheric levels were studied. We determined a set of special synoptic configurations, with an evident deviation from climatic values generating anomalies of 850 hPa temperature relative to the characteristic values of 2001-2010 and 1950-2010. An analysis of these anomalies detected a positive trend of 850 hPa temperature and geopotential height in the western Mediterranean area. As a consequence, the characteristic synoptic circulation has changed since 1950, towards low-level patterns favouring adequate thermodynamic environments for hailstorm development in north-eastern Spain. Finally, after a cluster analysis, we studied periodicities in the monthly 850 hPa temperature field to improve knowledge for seasonal forecasting of hailstorms. [ABSTRACT FROM AUTHOR]

Here we present an exploratory statistical analysis aimed at the minimization of the 'screen bias' from affected ancient air temperature time series over the Western Mediterranean. Our approach lies in the statistical analysis of about 6 years of daily paired temperature observations taken using the ancient Montsouri shelter and the modern Stevenson screen for daily maximum ( Tx) and minimum ( Tn) temperature data recorded at two experimental sites: the meteorological gardens of La Coruña and Murcia, Spain (locations under the influence of the Oceanic/Atlantic/Galician and Mediterranean arid and semi-arid climate types, respectively), where ongoing field trials have been carried out. Descriptive statistical analysis of the paired series shows pre-sheltered temperatures tended to induce a strong warm bias in Tx data (of about 1 °C at the annual scale but with a clear seasonal cycle with higher values in summer and lower in winter), while Tn readings have a small (∼0.2 °C, and sustained all year round) cold bias compared to the modern period. Statistical relationships between the screen bias and other related meteorological variables show the highest correlation coefficients between the 'screen bias' and Tx, Tn and the diurnal temperature range (DTR) recorded under the replicated ancient shelters at both locations and point to the reliability of these variables as potential predictors of the Δ Tx. We generate a parsimonious regression model based on the data from both experimental sites, which takes into account polynomial terms of lower order for the predictor variables ( Tx and DTR recorded under the ancient shelter) and harmonic terms, in order to represent the seasonal cycle of the screen bias. The goodness-of-fit of the model is satisfactory, as it explains up to 51.7% of the additional Δ Tx variability. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A new monthly precipitation database has been developed for conterminous provinces in Spain by exploiting the total amount of data available at Spanish Meteorological Agency (AEMET, formerly INM). The new MOPREDAS (monthly precipitation database of Spain) database has been constructed by using all 6821 original data series that have been recorded for at least 10 years. These provide a total of 2670 complete, homogeneous series for the period 1946-2005, and are the most complete and extensive monthly precipitation dataset available in Spain at present. MOPREDAS has been created with the aim of analysing the behaviour of precipitation in the conterminous provinces of Spain, and to help validate the downscaling of climate models on a detailed spatial level. To this end, the station data were also interpolated on a regular grid, at 1/10 of degree of resolution, over the whole Spain. Trend analysis confirms great spatial and temporal variability in the behaviour of precipitation across Spain. The monthly precipitation trends vary from month to month, from coherent spatial trend patterns in March, June (both with a general and significant negative trend) and October (general positive trends), to highly regionalized trend patterns in July (with positive trends in north-west and mainly negative in the remainder), February and April (positive and negative trends in the south-east, respectively). These results suggest that both global and local factors affect the spatial distribution of trends in the Iberian Peninsula. Mountain ranges seem to be the most significant geographical factor in determining the spatial distribution of monthly trends on a detailed, sub-regional spatial scale. These results show that it is possible to accurately delineate the areas affected by different precipitation trends if a dense spatial database is available. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article presents an analysis of monthly precipitation trends in Iberian Peninsula's eastern Mediterranean fringe. The analysis show high temporal and spatial variability. Trends for winter months are prevailed by an East-West gradient with a latitudinal temporal change. Positive trends are primarily situated in coastland areas and negative ones in overriding inland.

The article offers information on the automated sea breeze selection technique based on sea-level pressure differences of Western Mediterranean Oscillation (WeMO). WeMO has defined regional teleconnection pattern for the western Mediterranean basin allowing the objective quantification of the synoptic circulation factor on the occurrence of sea breezes. The associated WeMO index (WeMOi) was used as an initial objective filter to the sea breeze database created for Alicante, a reference synoptic station, and performing a manual selection method for 1999-2000. A wind speed and direction data from 9 coastline meteorological stations are used to assess the WeMOi applicability to the Iberian Mediterranean coast and the Balearic Isles.

Seasonal precipitation variability in the east of the Iberian Peninsula is weakly linked to the North Atlantic Oscillation (NAO) during autumn and winter. For the purpose of improving the study of its performance, low-frequency variability patterns specific to the Mediterranean basin have been searched for. In this way, the Western Mediterranean Oscillation (WeMO) has been defined by means of the dipole composed, in its positive phase, by the anticyclone over the Azores and the depression over Liguria, and its index (WeMOi), as a result of the difference of the standardised values in surface atmospheric pressure in San Fernando (Spain) and Padua (Italy). This new index allows the detection of the variability relevant to the cyclogenesis next to the western Mediterranean basin, which determines in a predominant way the types of rainfall in the Gulf of Valencia. In this area, the WeMO is significantly better than the NAO to explain the monthly pluviometric anomalies during these seasons. Also, a daily resolution of the WeMOi can provide a useful tool to forecast torrential rainfall events in the north-western zones of the Mediterranean (eastern part of the Iberian Peninsula and the south of France), and such significantly daily rainfall frequencies for different thresholds. Copyright © 2006 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

As many studies reveal, the western Mediterranean exhibits a high frequency of cyclone centres. Most of them are small and weak, but in some cases they are related to heavy rain and/or strong wind events. The climatological study of Mediterranean cyclones is the first crucial step to the better understanding and forecasting of such events. In the present paper, a method to objectively detect and track mean sea-level (MSL) cyclones for the western Mediterranean is described. Furthermore, the three-dimensional characterization of each MSL cyclone is performed by means of several parameters. This includes the vorticity, thermal and humidity fields at different pressure levels where the cyclone is detected, as well as the wind speed profile and the moist stability over the MSL cyclone. Both methodologies are illustrated and validated by a real case: an intense event of the well-known Genoa cyclone. Detection, tracking and three-dimensional characterization are applied to an 8-year (from June 1995 to May 2003) database of numerical analyses. The result is a MSL cyclone database for the western Mediterranean with a description of their three-dimensional structure. For a better analysis, cyclones are grouped in three different ways: by thickness, season and region of detection. Results show that western Mediterranean cyclones are located in specific geographical regions and that their location depends on the season. Several cyclones are weak and shallow, mainly because of thermal and/or orographic causes. On the contrary, other cyclones are large and intense and extend throughout the whole troposphere. Differences in cyclone structure depending on the location and season are also discussed. Copyright © 2006 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

The relationship between springtime (March–May) precipitation in the western Mediterranean area and several North Atlantic teleconnection patterns of low-frequency variability is analysed for the period 1948–89. Singular value decomposition analysis (SVDA) of the springtime monthly mean fields for the three paired combinations of 300 hPa geopotential height–precipitation, 300 hPa zonal wind–precipitation and 300 hPa meridional wind–precipitation has shown that their covariability is dominated by two main large-scale atmospheric circulation patterns. In every SVD combination, the first mode relates precipitation anomalies to the east Atlantic jet pattern. Above-normal rainfall anomalies are linked with a blocking pattern affecting Iberian weather. The second covariability mode for the three SVD As takes into account the response of the precipitation to the North Atlantic oscillation (NAO) pattern. An enhanced spring NAO pattern is related to positive (negative) precipitation anomalies over the southern (northern) western Mediterranean. Through these two modes, the North Atlantic large-scale atmospheric dynamics explains about 50% of the total spring precipitation variability in the western Mediterranean area. A Monte Carlo approach has allowed setting the statistical significance of the modes obtained and to assess the effectiveness of the western Mediterranean precipitation response to the teleconnection patterns. Copyright © 2004 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

An automated procedure has been developed to detect and select mesoscale cyclones and describe their tracks by means of the numerical analysis model, the HIRLAM(INM)-0.5°, operational at the Spanish Institute of Meteorology (INM). This procedure gives us a description of features of these cyclones, such as their frequency of appearance, geographical distribution and horizontal dimensions, and it also enables us to study the movement and the evolution of the cyclone centres. This procedure was developed in order to obtain an automated database of Mediterranean cyclones. To check the performance of this method, the distribution of cyclones was compared with the distribution obtained from a manual catalogue of mesoscale cyclones, and selected cases were studied using both methods. Some results obtained for the western Mediterranean are presented. A large number of cyclones are detected and most of them are located in specific zones, such as the Gulf of Genoa, south of the Pyrenees, south of the Iberian Peninsula and the Alboran Sea. The cyclones follow preferred tracks, which are different depending on the season. Copyright © 2001 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The Mediterranean Sea is a region that possesses a high frequency of cyclones. Many of them are lee depressions and so, mesoscale and weak, but others are strong and cover a wide area. In this study some characteristics of surface cyclones in the Western Mediterranean are presented. First a database was built from hand analyses of sea-level pressure from 1992 to 1995. Next, a similar database was obtained from the LAM-INM (Limited Area Model of the Instituto Nacional de Meteorología of Spain) objective analyses of the 1000 hPa geopotential field. Results show an important increase in the number of cyclones when a mesoscale analysis is carried out. Most of the Western Mediterranean cyclones are mesoscale and weak, and they are not uniformly distributed in space and in time. On the one hand, there are some areas with a high concentration of cyclones. The location of some of them, close to the main mountain ranges, suggests their possible orographic origin. On the other hand, in some areas the cyclones are present during the whole year, but in other areas are seasonally distributed. Finally, a study of typologies of the cyclones was conducted by using the cluster analysis technique. The classification was performed from the intensity of the cyclones and the shape of the sea-level pressure around the centre. Results are similar from both databases and so the existence of seven typologies have been identified. Copyright © 2000 Royal Meteorological Society [ABSTRACT FROM AUTHOR]