The objective of this study was to explore the ability of 3 regional climate models (RCMs), CNRM-Aladin, C4I-RCA3 and KNMI-RACMO along with their parental global climate models (GCMs), ARPEGE and ECHAM5, to represent the relationship between large-scale atmospheric circulation and climate extremes in the Mediterranean region. Subsequently, an evaluation and inter-comparison of these 3 RCM/GCM couples for the present climate was performed. For this purpose, the Regularised Canonical Correlation Analysis (RCCA) was employed and 4 extreme climate indices of temperature and precipitation were used to define extreme events over the study region. The evaluation of these relationships was carried out against gridded observational and reanalysis datasets. It was found that the observed upper air large scale patterns related to climate extremes in the Mediterranean are not very well reproduced by the RCM/GCM couples in all seasons. In addition, in many cases, the coupled models display patterns of extreme climate indices which are not consistent with the accompanied upper level circulation. Furthermore, all coupled models display substantial deficiencies in simulating precipitation extremes. In the case of summer data, the ability of all 3 models is limited, possibly because the strength of the large-scale atmospheric flow decreases, the control exerted by the lateral boundary conditions is weaker, and the nested models are mainly governed by local processes. © Inter-Research 2011.

A comparison of two objective climatologies of explosive cyclones in the Mediterranean region is performed. The results are derived from two different mean sea-level pressure reanalysis data resolutions, but from the same assimilation model, in order to quantify the pure impact of higher resolution on the identification and characteristics of explosive cyclones, when the assimilation model is the same. The explosive cyclones were identified with the aid of the Melbourne University automatic cyclone finding and tracking scheme over a 40-year period, using the 6-hourly analyses of ERA-40 mean sea-level pressure (MSLP) on: (a) 2.5 × 2.5 and (b) 1 × 1 latitude-longitude grid. The comparison of the two datasets revealed the significant role of the increase in spatial resolution of MSLP data on the identification and tracking process, and the number of the explosive cyclones in the high-resolution dataset is almost four times greater than the respective one in the lower resolution dataset. However, the comparison of explosive cyclone characteristics, including spatial and temporal variations of explosive deepening, revealed differences in the geographical distribution of the location of the maximum explosive deepening and average explosive cyclone Laplacian of the central pressure. These differences are due to the identification in the higher resolution set of smaller scale and secondary explosives along the strongly baroclinic northern Mediterranean boundaries, south of the Alps and the Pyrenees. Explosive deepening appears a bias to the daytime period from 12 to 18 Coordinated Universal Time (UTC) for both datasets, which is more prominent in the LR dataset. Statistically significant difference of pressure tendency between the two datasets appear for the daytime period from 06 to 12 UTC, accounting for better representation of orographic forcing in the HR dataset. © 2011 Springer-Verlag.

An objective climatology of explosive cyclones is performed over a 40-year period (1962-2001), for the Mediterranean region with the aid of the Melbourne University automatic cyclone finding and tracking scheme. The major temporal and spatial characteristics of Mediterranean explosive cyclones are investigated, including frequency, movement, generation and dissipation, scale, depth, and intensity. It was verified that the explosive cyclogenesis in the Mediterranean is a rather rare phenomenon that occurs mainly from November to March. Explosive cyclones preferentially form along the northern Mediterranean coast, with maximum density in the Ligurian and Aegean Seas. The cyclogenesis mechanism that predominates in their development is characterized by an interaction of a short and an open long wave in a pre-existing development (referred to as the KF mechanism). There are distinct differences between Western Mediterranean and Eastern Mediterranean explosive cyclones. Although explosive cyclones tend to form in the Western Mediterranean, their scale and depth is greater in the Eastern Mediterranean. Explosive cyclones more likely move from the main cyclogenetic areas in the Western Mediterranean along specific eastward paths over southern Italy and the Ionian Sea where they dissipate or they generate in Eastern Mediterranean and move north-eastwards to the Black Sea or eastwards to Cyprus and Middle East. © 2010 Royal Meteorological Society.

An experimental campaign has been conducted in the frame of the European Commission funded network of excellence ECATS, at Athens International Airport (AIA), Greece, from 13 to 25 September 2007. In order to quantify the background air quality and study the influence of meteorological conditions and airport emissions to the broader region, the analysis was extended to the greater Messogia Plain of Attica, Greece. Mixing height was estimated taking into account measurements from remote sensing and surface based single point instrumentation. According to the analysis, the air quality over Messogia Plain is mainly controlled by the intensity and the direction of the background flow. Under low background wind conditions, the development of local flows (sea and land breeze cells) over the greater area preserves high concentrations of air pollutants which are mainly attributed to the airport emissions, the local activities and traffic. When the background flow is strong, the diurnal cycle of all concentrations was significantly reduced by more than 50%, due to the advection and the subsequent mixing of the lower atmosphere. In order to identify and quantify the various processes linked with meteorology and air quality, the Hilbert-Huang transform was selected to be applied on the air-quality time-series data. The calculated Hilbert spectra of the main pollutants showed that meteorology plays a prescriptive role on the evolution of air pollutants, determining the influence of the local scale characteristics at each station. © 2011 Elsevier Ltd.