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The aim of this study is to examine the ability of two modelling systems, a global and a regional, to reproduce the influence of Etesian winds on the ozone zonal distribution over Eastern Mediterranean. Specifically, the results of the global MACC (Monitoring Atmospheric Composition and Climate) reanalysis model (Integrated Forecast System - MOZART (IFS-MOZART)) and an ensemble of MACC regional air quality models (ENS) are compared versus observed data from three background monitoring stations in Central and Eastern Mediterranean (i.e. Gharb (ARB) - Malta, Finokalia (FIN) (Crete) - Greece and Agia Marina (CAO) - Cyprus). Two distinct group of days characterized by different wind flows are used for the evaluation assessment for a 5-month period (May to September) for two years (2011 − 2012). During the selected period, the Etesians are the predominant winds that blow from northern directions over the Aegean Sea, affecting ozone levels. The observed mean ozone concentrations at Eastern Mediterranean stations are about 5 ppbv higher during Etesian days than during non-selected days whereas at the Central Mediterranean station (ARB), the difference between the two groups of days is small. Furthermore, the Eastern Mediterranean stations present generally higher observed ozone levels than the Central Mediterranean station with these differences intensifying during Etesian days. The evaluation results suggest that although the two modelling systems underestimate surface ozone concentrations systematically, they can capture to a certain extend the effect of the Etesian winds on the ozone zonal distribution. Specifically, FIN station which is directly under the influence of the Etesian winds presents higher simulated ozone values compared to the other two stations in agreement with the observations. For both modelling systems, the statistical evaluation metrics are better for the Central Mediterranean station, but there is a considerable improvement for the regional modelling system indicating that the ENS reproduces better the observed ozone values and zonal distribution in comparison to the IFS-MOZART.

The Mediterranean region is a unique area characterized by a large spectrum of atmospheric phenomena, some of which have a high impact on many aspects of human activities, safety and wellbeing. The area is long considered as a hot spot of such atmospheric phenomena deserving multidisciplinary scientific attention. The scientific research that has been carried out on these high impact atmospheric processes that occur in the Mediterranean area is indeed widespread and the available international literature is very extensive. The paper touches initially the temperature and precipitation regimes, followed by a discussion of floods and droughts. The exciting cyclogenetic patterns of explosive cyclones and medicanes are presented in separate sections. The lightning activity and the presence of dust and other pollutants are also presented herein. The atmospheric chemistry of the region which is increasingly becoming of utmost importance for the area under study is distinctly discussed. Attempts to modify the weather (the precipitation, in particular) are outlined too. The effects of climatic change on various atmospheric processes are considered throughout this paper, in addition to a dedicated section on temperature and precipitation.

In this work, the spatiotemporal variability of surface solar radiation (SSR) is examined over the Eastern Mediterranean region for a 31-year period (1983–2013). The CM SAF SARAH (Satellite Application Facility on Climate Monitoring Solar surfAce RAdiation Heliosat) satellite-based product was found to be homogeneous (based on relative Standard Normal Homogeneity Tests — SNHTs, 95% confidence level) as compared to ground-based observations, and hence appropriate for climatological studies. Specifically, the dataset shows good agreement with monthly observations from five quality assured stations in the region with a mean bias of 7.1 W/m 2 or 3.8% and a strong correlation. This high resolution (0.05° × 0.05°) product is capable of revealing various local features. Over land, the SSR levels are highly dependent on the topography, while over the sea, they exhibit a smooth latitudinal variability. SSR varies significantly over the region on a seasonal basis being three times higher in summer (309.6 ± 26.5 W/m 2 ) than in winter (100.2 ± 31.4 W/m 2 ). The CM SAF SARAH product was compared against three satellite-based and one reanalysis products. The satellite-based data from CERES (Cloud and the Earth's Radiant Energy System), GEWEX (Global Energy and Water Cycle Experiment) and ISCCP (International Satellite Cloud Climatology Project) underestimate SSR while the reanalysis data from the ERA-Interim overestimate SSR compared to CM SAF SARAH. Using a radiative transfer model and a set of ancillary data, these biases are attributed to the atmospheric parameters that drive the transmission of solar radiation in the atmosphere, namely, clouds, aerosols and water vapor. It is shown that the bias between CERES and CM SAF SARAH SSR can be explained through the cloud fractional cover and aerosol optical depth biases between these datasets. The CM SAF SARAH SSR trend was found to be positive (brightening) and statistically significant at the 95% confidence level (0.2 ± 0.05 W/m 2 /year or 0.1 ± 0.02%/year) being almost the same over land and sea. The CM SAF SARAH SSR trends are closer to the ground-based ones than the CERES, GEWEX, ISCCP and ERA-Interim trends. The use of an aerosol climatology for the production of CM SAF SARAH, that neglects the trends of aerosol loads, leads to an underestimation of the SSR trends. It is suggested here, that the inclusion of changes of the aerosol load and composition within CM SAF SARAH would allow for a more accurate reproduction of the SSR trends.

The summertime Eastern Mediterranean experiences among the highest worldwide near-surface ozone values often exceeding the EU air-quality standard for human health protection. Downward transport of stratospheric ozone-rich air masses through tropopause folds has been shown to significantly contribute to these high tropospheric ozone levels. The summer circulation over the Eastern Mediterranean is dominated by large-scale subsidence and persistent northerly winds, the Etesians, as well as tropopause fold activity affecting tropospheric ozone levels and variability. This is the first study that directly investigates the connections of the Etesians with tropopause folds and tropospheric ozone over the Eastern Mediterranean region using the state-of-the-art ECHAM5/MESSy Atmospheric Chemistry (EMAC) climate model and a tropopause fold identification algorithm for the period June‐August 1979 to 2013. Model validation against reanalysis and observational measurements indicates that EMAC simulates well the sea level pressure gradient over the Aegean Sea reproducing the occurrence frequency of the Etesians. The shared variance between the simulated and the observed year-to-year frequency of the Etesian winds is higher than 80%. The year-to-year variability of summertime tropopause folds frequency is significantly correlated with the Etesian winds with a correlation coefficient close to 0.7. In addition, a significant increase of the fold activity and the ozone concentrations are observed during intense Etesians. Our findings may have implications for air quality studies and could support human health policy, as the Etesians coincide with favorable conditions for the formation of tropopause folds and stratosphere-to-troposphere transport and therefore, with enhanced ozone levels over the Eastern Mediterranean.

The main objective of the present study is the assessment of the non-radiative impact on the lower troposphere air quality of the intense biomass burning events that took place in the Eastern Mediterranean, when wild forest fires were burning in Peloponnesus (Greece) at the end of August 2007. The MM5-CAMx modeling system was applied in the Eastern Mediterranean in high spatial and temporal resolution for the period 23 to 31 August 2007, forced by biomass burning emission fluxes from the Global Fire Emissions Database (version 3.0), in day-to-day temporal and 0.1° spatial variability from the Global Fire Assimilation System. Enhancements of the CO and NOx concentrations over almost the entire modeling domain were estimated due to the biomass burning, which were more pronounced over the burnt areas and maximum over the Peloponnesus forest fires. The domain-wide near surface mean concentration was higher by + 6% for CO and + 11% for NOx because of the biomass burning. The near surface O 3 values were reduced over the fire hot spots but increased over the greater part of the modeling domain. On the 26th August 2007, the maximum O 3 concentrations reduction of about 12 ppb (i.e. − 34%) was calculated over the Peloponnesus fires while the highest O 3 increase of about 27 ppb (i.e. + 52%) was estimated over the sea at 500 km downwind the Peloponnesus large forest fires. The process analysis revealed that on that day, the inclusion of the biomass burning emissions resulted in an enhancement of the daytime gas phase O 3 production in the boundary layer in the Eastern Mediterranean and during some daytime hours in a change of the chemical regime from O 3 destruction to O 3 production. From 6 to 16 UTC, the O 3 photochemistry in the boundary layer was VOC-sensitive close to the Peloponnesus fires, gradually changing to NOx-sensitive in the downwind fire plume. In the same period, the maximum impact on the oxidizing capacity of the boundary layer was an increase by 0.25 ppt for OH and a reduction by 13 ppt for HO 2 mean concentrations over the Peloponnesus forest fires and an increase by 12 ppt for HO 2 in the downwind plume.