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Monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2) are used to examine the year-by-year variability of precipitation over the Mediterranean Basin and its changes over the period 1979-2010. The results show that the mean annual precipitation averaged over the study area has slightly increased from 1979 to 2010 by 1.28mm or by 0.2% (trend not statistically significant at the 95% confidence level). Nevertheless, examining the trends at a local scale, spatial and temporal patterns are revealed, with opposite trends in adjacent areas and increasing precipitation in summer and autumn against almost unchanged or decreasing precipitation in winter and spring, respectively. Inter-decadal changes of precipitation are detected, with precipitation decreasing in the 1980s, then increasing through the late 1990s and finally declining in the 2000s before levelling off since 2007. These changes are significantly anti-correlated (R=-0.57, up to -0.66 in winter) with the North Atlantic Oscillation (NAO) index, thus confirming the critical role of this large-scale teleconnection for the regional precipitation over the basin.

The precipitation regime over the Mediterranean basin is investigated for the period 1979-2010 using monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2). The results show that a clear contrast exists between the more rainy northern part of the study region (Southern Europe) and the drier southern area (North Africa, Iberian Peninsula) and between the western sides (rainsides) of the Iberian, Italian and Balkan peninsulas and their eastern sides (rainshadows). The mean annual precipitation averaged over the study area is P = 593 ± 203 mm year-1, but it has a strong spatial variability ranging from 20 mm year-1 (North Africa) to 1500 mm year-1 (Alps). A significant seasonal variability exists, with the early winter and late autumn months (November and December) being the wettest with precipitation amounts larger than 60 mm month-1. The GPCPv2 satellite precipitation data are satisfactorily correlated with rain gauge measurements from 433 stations within the study area (correlation coefficient R = 0.78 for all stations on a yearly basis, with values ranging between 0.72 and 0.82, depending on the season) with a slight overestimation. They also compare well with the higher spatial and temporal resolution Tropical Rainfall Measuring Mission (TRMM) data, which supports the validity of the present study.

Summarization: A deterministic model for atmospheric longwave radiation transfer was used with climatological data to predict the mean monthly zonal (10° latitudinal zones) longwave radiation budget at the Earth's surface and at the top of the atmosphere for the Northern Hemisphere. The climatological data were obtained from the International Satellite Cloud Climatology Project (1983-1990), and from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project. The model's outgoing fluxes agree within 4 Wm-2, on average, with the corresponding values determined from the Earth Radiation Budget Experiment (1985-1989) satellite data. The validation of the model for the top-of-atmosphere radiation budget allows one to obtain a better understanding of the important processes that govern the transfer of the longwave radiation for each season and zone. At the surface, validation of the predicted downwelling radiation is difficult owing to the lack of extensive ground-based measurements. However, we have made intercomparisons with other model predictions and with ground-based measurements that were available. The predictions of the model for the surface longwave radiation budget provide a measure against which simpler algorithms, derived from ground-based measurements, can be compared and used to convert satellite climatologies to a globally distributed surface longwave radiation budget for climatic studies. Presented on: Journal of Geophysical Research: Atmospheres

This chapter describes the physicochemical mechanisms that formulate the air quality over the Mediterranean region and the resulted impacts on the regional climate. At first, a detailed description of the teleconnections and regional flow patterns that dominate in the region is provided. The dominant flow patterns during the different seasons of the year determine the transport paths of air pollutants and aerosols towards and across the study area. The analysis on the characteristics of the air pollution transport is separated for the different parts of the Mediterranean region (eastern, western and entire), since the sources of pollutants that reach at different points in the region vary, while specific pollutant transport paths may influence the wider Mediterranean area. Similarities and differences in patterns are discussed. The air quality over the region, as recorded from black/organic carbon, ozone, aerosol observations, is extensively discussed, along with seasonal variabilities and annual trends. There is particular discussion on the suspension of naturally-produced aerosols and especially desert dust particles in the region and their spatial influence on the aerosol levels. At the last part of the chapter, the major impacts of the transport and transformation processes (natural and anthropogenic pollutants) on the regional climate are discussed. The impacts of aerosols are distinguished in direct (the impacts on radiation budget), health (the amounts of inhaled particles and impacts on health) and indirect effects (impacts on clouds and precipitation), are discussed on qualitative and quantitative way. © 2013, Springer Science+Business Media Dordrecht.

Recent variations in surface solar radiation (SSR) at the beginning of the 21st century (2000-2007) were determined at scales ranging from local/regional to hemispherical/global, on the basis of radiative transfer computations and information from satellites, reanalyses and surface measurements. Under all-sky conditions, in the Northern Hemisphere (NH) there is no clear dimming/brightening signal after 2000, whereas in the SH there is a more clear dimming arising from both increasing clouds and aerosols. Dimming is observed over land and ocean in the Southern Hemisphere (SH), and over oceans in the NH, whereas a slight brightening occurred over NH land. However, opposite tendencies are found even within the same continent, indicating the need to assess SSR changes at regional/local scales apart from hemispherical/global ones. Copyright (c) 2011 Royal Meteorological Society Atmospheric Science Letters

The evolution of the atmospheric circulation over Europe and the Mediterranean during fog events in Ioannina, north-western Greece, is examined for the period 19572002. A 24-h period starting at 12:00 UTC is defined as a fog day, when at least one of the present and/or past weather codes of the corresponding SYNOPs refers to fog. A sequence of such fog days is defined as a fog event. In total, 1019 fog events are found during the period under study. A methodology scheme using S-mode factor analysis and K-means cluster analysis is applied to the patterns of 850 hPa air temperature and 1000 and 500 hPa geopotential heights for the day before the initiation, the first day of occurrence and the day after the dissipation of fog, resulting in the classification of the 1019 fog events into ten clusters. For each one of the ten clusters, the mean 00:00 UTC patterns of the above parameters are constructed for 3 days. These patterns correspond to the evolution of the atmospheric circulation associated with fog formation and dissipation in the Ioannina region. Most of the patterns are characterized by anticyclonic activity or a weak southerly flow over Greece. The differences among the ten clusters refer mainly to the position and the intensity of the surface and upper air synoptic systems involved. Copyright (c) 2011 Royal Meteorological Society International Journal of Climatology

The spatial and temporal distribution of the downward solar radiation (DSR) at the Earth's surface, which is a key parameter for the Earth-atmosphere climate system, is studied on a global scale by applying the multivariate statistical method of factor analysis (FA) on mean monthly DSR values for the period 1984-2000 for winter and summer. DSR fluxes have been computed with a physical deterministic radiation transfer model, which uses satellite and reanalysis climatological input data. FA objectively groups grid points with common temporal variability of solar radiation, identifying areas with characteristic solar radiation variability and revealing teleconnection patterns. The globally distributed DSR exhibits strong variability and can be represented by about 30 factors (sub-areas) explaining approximately 85% of the total variance. The main factors are located in the tropical Pacific (El Nino Southern Oscillation), the northern Pacific (Aleutian low), desert areas (Africa, Middle East, and Australia), and oceanic areas (storm track zone around 60 S). Furthermore, some of these areas are teleconnected indicating common DSR variability in remote places of the Earth. The primary physical parameter for the co-variability of surface solar radiation is found to be cloud cover. The time series of the factor scores (solar radiation) exhibit features associated with natural climatic phenomena (e. g. NAO, ENSO), thus revealing that DSR might be considered as an indirect indicator for these phenomena. On the other hand, DSR determines these phenomena through its effects on major climate parameters such as surface temperature or evaporation, thus playing a key role in their formation and explanation. Finally, our analysis revealed some statistically significant trends of solar radiation, for example, a reduction in the northern Pacific and an increase in tropical and subtropical regions, which are important for global dimming/brightening and associated surface warming of the Earth. Copyright (C) 2009 Royal Meteorological Society International Journal of Climatology