The development mechanisms of an explosive cyclone over Central Mediterranean are examined, by relating the cloud patterns in the infrared, water vapour and visible channels of the Meteosat Second Generation (MSG) satellite images, to the surface-upper air operational analyses and thermodynamic parameters, including potential and geostrophic vorticity analyses, potential and equivalent potential temperature, static stability and thermal heat fluxes. The specific case study derived from an updated climatology of Mediterranean explosive cyclones for the 2002-2010 period, being performed with the aid of the University of Melbourne Cyclone Tracking scheme (MS algorithm) and ERA-INTERIM datasets. It was found that during the ordinary cyclogenesis the increased mid-upper level relative humidity over Northern Algeria along with the enhanced moisture gradient in the area between Portugal and Spain; indicate the existence of a jet -streak, with the dry zone to be located on the cold side of the jet axis. The descent of the dry air is more pronounced within the left exit region of the jet streak in the poleward portion of an upper confluence zone. Six hours later, the eastward movement of the cloud pattern in the Northern African coasts significantly resembles the structure of a baroclinic leaf, being related to the early stages of surface frontogenesis, due to the deformation process within a strong wind field. During the time of rapid deepening, when the surface cyclone propagated from the Northern African coasts towards the area of Sicily - Gulf of Taranto, the development is characterised by the transition from the baroclinic leaf structure to the comma cloud one and finally the formation of a bent-back occlusion. © 2013 SPIE.

The dynamic and kinematic characteristics of surface explosive cyclones in the Mediterranean are examined and compared to those of ordinary cyclones. The cyclone detection is performed with the tracking algorithm developed in the University of Melbourne, using the 1° × 1° ERA-40 mean sea level pressure dataset for a 40 year period. It is verified that the explosive cyclogenesis in the Mediterranean is mainly a maritime phenomenon, occurring along the northern Mediterranean coast during the cold season. On the contrary, the ordinary cyclogenesis exhibits significant maxima in both continental and maritime environments throughout the year. The explosive cyclones are characterized by longer lifetime and greater propagation speed. They are larger and deeper in the eastern Mediterranean, whereas the ordinary cyclones are deeper in the western and larger in the eastern Mediterranean. The trend analysis revealed that both explosive and ordinary cyclones become less frequent in the Mediterranean basin, while there is a tendency for deeper ordinary cyclones over North Africa and shallower over the Aegean Sea and Cyprus. © 2013 Springer-Verlag Berlin Heidelberg.

The development mechanisms of an explosive cyclone over Central Mediterranean are examined, by relating the cloud patterns in the infrared, water vapour and visible channels of the Meteosat Second Generation (MSG) satellite images, to the surface-upper air operational analyses and thermodynamic parameters, including potential and geostrophic vorticity analyses, potential and equivalent potential temperature, static stability and thermal heat fluxes. The specific case study derived from an updated climatology of Mediterranean explosive cyclones for the 2002-2010 period, being performed with the aid of the University of Melbourne Cyclone Tracking scheme (MS algorithm) and ERA-INTERIM datasets. It was found that during the ordinary cyclogenesis the increased mid-upper level relative humidity over Northern Algeria along with the enhanced moisture gradient in the area between Portugal and Spain; indicate the existence of a jet -streak, with the dry zone to be located on the cold side of the jet axis. The descent of the dry air is more pronounced within the left exit region of the jet streak in the poleward portion of an upper confluence zone. Six hours later, the eastward movement of the cloud pattern in the Northern African coasts significantly resembles the structure of a baroclinic leaf, being related to the early stages of surface frontogenesis, due to the deformation process within a strong wind field. During the time of rapid deepening, when the surface cyclone propagated from the Northern African coasts towards the area of Sicily - Gulf of Taranto, the development is characterised by the transition from the baroclinic leaf structure to the comma cloud one and finally the formation of a bent-back occlusion. © 2013 SPIE.

The influence of microscale and mesoscale meteorology on the local scale variation of air temperature cannot be correctly simulated by the coarse resolution Global Climate Models. The scope of this work is to develop a hybrid dynamic-statistical downscaling procedure and quantify its predictive ability to estimate air temperature variability at finer spatial scales. The study focuses on the warm period of the year (June - August) and the method is applied to eight sites located in Greece with different topographical characteristics. The two-step methodology initially involves the dynamic downscaling of coarse resolution climate data via the RegCM4 regional climate model and subsequently the statistical downscaling of the modeled outputs by training site-specific artificial neural networks (ANN). The RegCM4 model is employed to enhance the representativity of the dataset, while the ANNs are used as function approximators to model the relationship between a number of atmospheric predictor variables and the observed air temperature time series. An insight of the ANN transfer function is obtained by examining the relative contribution of each input variable. The performance of the methodology is evaluated and the results indicate significant improvement from the inclusion of the ANN models in downscaling air temperature. © 2013 Global NEST Printed in Greece. All rights reserved.

The vertical structure of surface cyclonic tracks affecting the eastern Mediterranean region is studied on a climatological basis for the cold period of the year. The dataset used is the 1° × 1° ERA-40 Reanalysis for a 40-year period (1962-2001). The vertical tracking of surface cyclonic tracks was performed with the aid of the Melbourne University Vertical Tracking Algorithm. It was found that about 83 % of the cyclones were extended up to the 500-hPa level and almost 65 % up to 200-hPa level, implying that the cyclones are in general well organized. The surface tracks that originate within the examined area exhibit the smallest vertical extension, intensity, radius, and depth compared to the cyclones originating in the other sectors. Moreover, the 500-hPa counterparts for the said cyclones are mainly located to the north-west or south-west of the surface cyclone position, consistent with the baroclinic character of the Mediterranean cyclones. The zonal (eastward) component of motion predominates both at the surface and at 500 hPa. © 2012 Springer-Verlag.

The paper presents a semi-supervised weather classification method based on 850-hPa isobaric level maps. A preprocessing step is employed, where isolines of geopotential height are extracted from weather map images via an image processing procedure. Α feature extraction stage follows where two techniques are applied. The first technique implements phase space reconstruction, and yields multidimensional delay distributions. The second technique is based on chain code representation of signals, from which histogram features are derived. Similarity measures are used to compare multidimensional data and the k-means algorithm is applied in the final stage. The method is applied over the area of Greece, and the resulting catalogues are compared to a subjective classification for this area. Numerical experiments with datasets derived from the European Meteorological Bulletin archives exhibit an up to 91 % accurate agreement with the subjective weather patterns. © 2013 Springer-Verlag Wien.