Search

A statistical technique for image processing, the maximum cross correlation (MCC) method, was utilized on sequences of NOAA-AVHRR thermal data in order to explore the surface advective current dynamics at the discharge region of the Hellespont in the North Aegean Sea. A 2D numerical flow model was also used in order to simulate the barotropic flow pattern of the surface water layer. The model was forced with diurnal wind fields obtained for the same period as the satellite infrared images. The currents (magnitude and direction) derived from the two methods compare satisfactorily despite the fact that some model simplifications were made.

In this paper, the climatological and air quality observations obtained for the periods 1974–1990 and 1983–1990, respectively, in the Greater Athens Area, are analyzed. During this period, 80 air pollution episodes, which lasted 210 d in total, were detected. The analysis of the observations allows the interpretation of air quality characteristics in terms of the climatological and meteorological factors. The importance of some characteristic indices for air pollutant dispersion conditions, such as mixing height, ventilation coefficient, temperature at 850 hPa, and temperature inversions, is discussed. The results show that the air quality in the Athens Basin is strongly affected by the meteorological conditions, especially those which are in favor of local circulations. The worst air pollution episodes are associated with anticyclonic conditions and/or advection of warm air masses.

Unsworth and Monteith`s attenuation coefficient T{sub UM} was calculated from midday cloudless sky data in Athens, Greece, for the period 1954 to 1991. An interdependence between T{sub UM} and the Linke factor T{sub L} was found and is expressed as a mathematical function. It was also shown that the minimum turbidity levels occur during the winter and maximum levels occur during summer. An analysis of the long-term variation of the attenuation coefficients depicts the deterioration of air quality during the same period. The dependence of the ratio of diffuse to global radiation on the attenuation coefficient T{sub UM}, is also presented. 26 refs., 4 figs., 1 tab.

Bulk aerosol samples were collected from three different coastal rural sites located around the Eastern Mediterranean, (i) Erdemli (ER), Turkey, (ii) Heraklion (HR), Crete, Greece, and (iii) Tel Shikmona (TS), Israel, during two distinct mineral dust periods (October, 2007 and April, 2008) in order to explore the temporal and geographical variability in the aerosol chemical composition. Samples were analyzed for trace elements (Al, Fe, Mn, Ca, Cr, Zn, Cu, V, Ni, Cd, Pb) and water-soluble ions (Cl-, NO3-, SO42-, C2O42-, Na+, NH4+, K+, Mg2+ and Ca2+). The dust events were categorized on the basis of Al concentrations > 1000 ng m(-3), SKIRON dust forecast model and 3-day back trajectories into three groups namely, Middle East, Mixed and Saharan desert. ER and TS were substantially affected by dust events originating from the Middle East, particularly in October, whilst HR was not influenced by dust transport from the Middle East. Higher AOT values were particularly associated with higher Al concentrations. Contrary to the highest Al concentration: 6300 ng m(-3), TS showed relatively lower Al and AOT. Al concentrations at ER were similar for October and April, whilst OMI-Al and AOT values were similar to 2 times higher in April. This might be attributed to the weak sensitivity of the TOMS instrument to absorbing aerosols near the ground and optical difference between Middle East and Saharan desert dusts. The lowest enhancement of anthropogenic aerosol species was observed at HR during dust events (nssSO(4)(2-)/nssCa(2+) similar to 0.13). These species were particularly enhanced when mineral dust arrived at sites after passing through populated and industrialized urban areas. (c) 2012 Published by Elsevier Ltd.

The knowledge of meteorological conditions is critical for the description of fire weather. In this paper, the mesoscale numerical meteorological model RAMS has been used to simulate the surface wind and temperature in two fire events in the region of Attica in Greece. The FARSITE (Fire Area Simulator) fire model, for the description of forest fire behavior, taking into consideration the influence of fuels, topography and weather conditions. The accuracy of the results was evaluated and confirmed that the use of suitable fuel models is very important for achieving reliable simulations for the devastating fires.

Mineral dust has a profound effect on the radiative budget and energy distribution of the atmosphere. By absorbing and scattering the solar radiation aerosols reduce the amount of energy reaching the surface. In addition aerosols enhance the greenhouse effect by absorbing and emitting longwave radiation. Desert dust forcing exhibits large regional and temporal variability due to its short lifetime and diverse optical properties further complicate the quantification of the Direct Radiative Effect (DRE). The complexity of the above processes, indicate the need of an integrated approach in order to examine these impacts. To this end the radiative transfer module RRTMG has been incorporated into the framework of the SKIRON model. The updated system was used to perform a 6-year long simulation over the Mediterranean region. As it was found, the most profound effect dust clouds have in areas away from the sources is the surface cooling through the “shading” effect. The long wave radiation forcing below and above the dust cloud is considerable and drives changes in the tropospheric temperature. In general dust particles cause warming near the ground and at mid-tropospheric layers and at the same time cooling of the lower troposphere.

In a rapidly evolving operational and research framework concerning the global energy resources, new frontiers have been set for the scientific community working on environmental and renewable energy issues. In particular, new numerical techniques supporting the accurate estimation of renewable energy sources are highly emphasized. In this framework, wave energy – the energy that can be captured from sea waves – provides an alternative option with critical advantages. In the present paper, recent advances and some preliminary results obtained in two European projects will be discussed: Marina Platform and E-wave projects are focusing on the estimation of the wave energy potential in North Atlantic coastline of Europe and in Eastern Mediterranean Sea, respectively. Special emphasis is given to the utilization of numerical atmospheric and wave modeling systems able to accurately monitor the atmospheric and sea conditions in the area of interest. On the other hand, advanced statistical techniques are utilized for the local adaptation of the results and the estimation of the spatial and temporal distribution of the wave energy potential.

International audience

Numerical models that combine weather forecasting and atmospheric chemistry are here referred to as chemical weather forecasting models. Eighteen operational chemical weather forecasting models on regional and continental scales in Europe are described and compared in this article. Topics discussed in this article include how weather forecasting and atmospheric chemistry models are integrated into chemical weather forecasting systems, how physical processes are incorporated into the models through parameterization schemes, how the model architecture affects the pre dicted variables, and how air chemistry and aerosol processes are formulated. In addition, we discuss sensitivity analysis and evaluation of the models, user operational requirements, such as model availability and documentation, and output availability and dissemination. In this manner, this article allows for the evaluation of the relative strengths and weaknesses of the various modelling systems and modelling approaches. Finally, this article highlights the most prominent gaps of knowledge for chemical weather forecasting models and suggests potential priorities for future research directions, for the following selected focus areas: emission inventories, the integration of numerical weather prediction and atmospheric chemical transport models, boundary conditions and nesting of models, data assimilation of the various chemical species, improved understanding and parameterization of physical processes, better evaluation of models against data and the construction of model ensembles. We acknowledge the funding of COST ES0602, ES1004, 728, and EU TRANSPHORM. The research leading to these results has received funding from the European Union’s Seventh Framework Programme FP/2007-2011 within the project MEGAPOLI, grant agreement no. 212520. David Schultz is partially funded by Vaisala Oyj. We thank the following people for their contributions to this manuscript: Paul Agnew, Gregory Carmichael, Lucy Davis, Oriol Jorba, Mark Lawrence, Dimitros Melas, Arjo Segers, William Skamarock, and Christos Zerefos. Kenneth Schere and an anonymous reviewer provided detailed comments that improved this article. Kenneth Schere (US Environmental Protection Agency) is thanked for a thorough review of this article, and for his many valuable comments. published

We discuss the adoption of a bottom-up, resource-based vulnerability approach in evaluating the effect of climate and other environmental and societal threats to societally critical resources. This vulnerability concept requires the determination of the major threats to local and regional water, food, energy, human health, and ecosystem function resources from extreme events including those from climate but also from other social and environmental issues. After these threats are identified for each resource, then the relative risks can be compared with other risks in order to adopt optimal preferred mitigation/adaptation strategies. This is a more inclusive way of assessing risks, including from climate variability and climate change, than using the outcome vulnerability approach adopted by the Intergovernmental Panel on Climate Change (IPCC). A contextual vulnerability assessment using the bottom-up, resource-based framework is a more inclusive approach for policy makers to adopt effective mitigation and adaptation methodologies to deal with the complexity of the spectrum of social and environmental extreme events that will occurinthecomingdecadesastherangeofthreatsareassessed,beyondjustthefocus on CO2 and a few other greenhouse gases as emphasized in the IPCC assessments.

Hesham M. El-Askary1,2,3, Anup K. Prasad1,2, George Kallos4, Mohamed El-Raey5 and Menas Kafatos1,2 1School of Earth and Environmental Sciences, Schmid College of Science, Chapman University, Orange, 2Center of Excellence in Earth Observing, Chapman University, Orange, 3Department of Environmental Sciences, Faculty of Science, Alexandria University, Moharem Bek, Alexandria, 4Atmospheric Modeling and Weather Forecasting Group, School of Physics, University of Athens, Athens, 5Institute of Graduate Studies and Research, Alexandria University, Alexandria, 1,2USA 3,5Egypt 4Greece

Methods that include a combination of weather forecasting and atmospheric chemistry simulations are here referred to as chemical weather forecasting (CWF). We have selected 18 operational CWF models on regional and continental scales in Europe for a more detailed analysis. We have collected the information in a structured form, and inter-compared and evaluated the mathematical structure of these models. This information makes it possible to evaluate the relative advantages and limitations of the various modeling systems, modeling approaches and sub-models. We have also surveyed the most prominent gaps of knowledge in this field, and suggested potential priorities for future research directions. There are substantial gaps of knowledge, especially in the following fields: emission inventories, the availability and exchange of observations, the evaluation of the boundary conditions for the CWF models, the integration of numerical weather prediction and atmospheric chemical transport models, the data assimilation of the various chemical species, the understanding of several chemical and physical processes, the construction of model ensembles, and the scientific evaluation of the CWF models, including their evaluation against data.

The amount, size distribution and chemical properties of cloud condensation nuclei (CCN), depend on the type of the prevailing air mass and also on local production and transportation of natural and anthropogenic particles. The aerosol properties vary in both space and time and impose significant amount of uncertainty on atmospheric research and also on future climatic projections. Cloud microphysics are very complex in nature and most of the times it is difficult to separate and identify the links and feedbacks between air quality and atmospheric processes under real atmospheric conditions. This presentation focuses on the interactions between air quality, clouds and precipitation for the area of greater Mediterranean. Mixtures of Saharan desert dust with sea-salt or with particles of anthropogenic origin, mainly sulphates and nitrates, may lead to the formation of new aerosols with different physiochemical properties. The effectiveness of airborne particles to act as CCN is examined towards their chemical composition and size distribution. Several modeling experiments, in-situ and airborne observations are analyzed and first results on the role of natural and anthropogenic particles on cloud formation and precipitation are discussed.

In this presentation, the contribution of the European aviation on the air pollution of the Mediterranean region is discussed using the new modeling tool, the Integrated Community Limited Area Modeling System (ICLAMS). The modeling system uses the approach of “online coupling” of meteorological and chemical mechanisms which studies the processes that take place in the atmosphere in an integrated way and in the same spatial and temporal resolution. The model was tested for July 2005 for Europe and the Mediterranean Region. Two simulations have been performed, one with emissions from all anthropogenic activities and the second excluding the emissions from aviation. The area that is influenced by the emissions from aviation is very large, and the most affected region is the Eastern Mediterranean and several areas in North Africa. The typical summer circulation with the prevailing west – northwest wind field over West and Central Europe favors the transport of pollutants towards East, South East Europe and North Africa leading to perturbations in the atmospheric composition especially up to 8 km above surface. The alterations in the atmospheric concentrations of O3, are discussed.

The causes of the poor air quality in Athens, Greece during the severe episode of 25–26 May 1990 has been studied, using a prognostic model (RAMS) and a three-dimensional Eulerian air quality model (CALGRID). The modeling effort indicates that the main urban area of Athens exhibited high concentrations of nitrogen oxides, the main sources of which are automobiles, while the NNE suburban area exhibited high ozone concentrations, the product of photochemical activity of the primary pollutants that were transported by the sea-breeze. The application of the models also demonstrated the need for an accurate emission inventory for improved predictions of the pollutant concentrations. It was also found that a 50% reduction of the nitrogen oxide emissions will increase the ozone levels in the downtown area substantially.

A 14-year (1977-1990) record of global solar radiation measurements performed in Athens, Greece, has been utilized to determine the distribution of radiant energy in the various wavelength bands. The monthly mean values of the irradiation ratios in the spectral intervals, blue (0.380-0525 pm), green-orange (0.525-0.630 pm), red (0630-0.710 pm), and photosynthetically active radiation (PAR) (0.380-0.710 pm) and the global irradiation (0.3-24 pm) compare favourably with values reported in the literature for different locations over a wide geographical area. The irradiation ratios exhibit seasonal variations attributable to changes in local air-mass climatology. It is observed that the proportion of the radiant energy in the various spectral bands relative to the global solar irradiation increases as sky conditions change from ‘clear’ to ‘partly cloudy’. Finally, the observed seasonal dependence of the broad-band spectral energy distribution is essentially caused by changes in the composition of the air masses (turbidity, airborne pollutants, clouds) in residence at the measurement site in the course of the year.

Based on regular climatological and air quality data from the Greater Athens Area (GAA), the air pollution episodes observed in Athens during the period 1983–1990 were analysed and classified. The main characteristics of atmospheric conditions during days with high air pollution concentrations are summarized too. Model simulations show that the worst air pollution episodes in Athens occur during days with a critical balance between synoptic and mesoscale circulations and/or during days with warm advection in the lower troposphere.

The diurnal evolution of the sea breeze hodograph over the Attic Peninsula has been studied using a three-dimensional numerical mesoscale model with fully nonlinear friction parameterization. The model results compare well with observed hodographs at three points in the modelling domain, and show that the balance of pressure gradient and terrain gradient forcing is dominant, and that this balance may result in either clockwise or anticlockwise rotation.

The temporal variation of specific humidity during morning hours was evaluated by analytic and numerical model scaling as well as by observational means. The scaling quantified (i) the gradual increase in the shelter increase humidity as the surface temperatures inversion is eroded during the morning hours; (ii) the sharp decrease in the shelter specific humidity when the newly developed boundary layer merges with the previous day's elevated neutral layer. The relation of these patterns to the early-morning thermal stratification and the Bowen ratio was estimated. Observational data supported the general features suggested by the scaling evaluations. The applied significance of the presented specific-humidity patterns is outlined.

Data on mass-levels of PM10 measured at regional background sites across the Mediterranean Basin, available from Airbase (European Environmental Agency) and from a few aerosol research sites, are compiled. PM10 levels increase from north to south and west to east of the Basin. These variations are roughly coincident with the PM10 African mineral dust load. However, when subtracting the African dust from mean PM10 levels using a consistent methodology, the PM10 background levels are still 5-10 μg m-3 higher in the Eastern Basin (EMB) when compared with those in the Western (WMB), mainly due to the higher anthropogenic and sea spray loads. As regards for the seasonal trends, these are largely driven by the occurrence of African dust events, resulting in a spring-early summer maximum over the EMB, and a clear summer maximum in the WMB, although in this later region the recirculations of aged air masses play an important role. Furthermore, a marked seasonal trend is still evident when subtracting the African dust load. This is characterised by a high summer maximum (driven by low precipitation, high insolation) and a winter minimum (intense synoptic winds). Important inter-annual variations in the dust contribution are detected, more evident in the southern sites. These differences are generally associated with the occurrence of extreme dust events. Generally, the years with higher dust contributions over the EMB correspond with lower contributions over the WMB, and vice versa. The characterization of individual particles, collected in both basins during African dust events, by scanning electron microscopy reveals only slight differences between them. This fact probably reflects the high degree of mixture of mineral dust from different sources before the transport towards the receptor sites. © 2009 Elsevier Ltd. All rights reserved., This study was supported by the Ministry of Science and Innovation (CGL2005-03428-C04-03/CLI, CGL2007-62505/CLI, GRACCIE- CSD2007-00067), the European Union (6th framework CIRCE IP, 036961, EUSAAR RII3-CT-2006-026140). The authors would also like to acknowledge NASA/Goddard Space Flight Center, SeaWIFS-NASA Project, University of Athens, Navy Research Laboratory-USA and the Barcelona Super-Computing Centre for their contribution with TOMS maps, satellite images, SKIRON dust maps, NAAPs aerosol maps, and DREAM dust maps, respectively. The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.arl.noaa.gov/ready.html) used in this publication. We would like express our gratitude to Jesús Parga for his technical support. Finally, we would like to express our gratitude to Airbase-EEA for allowing free access to ambient PM levels recorded at a large number of sites in Europe, some of which have been used in this study.

The various processes within the atmospheric boundary layer (ABL) during precipitation events tend to thermally stabilize the ABL. Selected observations are presented in order to illustrate this thermal stabilization for convective and stratified cloud systems. A tendency towards the onset of moist-adiabatic temperature profiles is suggested during stratified precipitation events. Conceptual, analytical, and numerical model evaluations were performed, suggesting that pollutant dispersion characteristics during the postprecipitation periods are likely to be modified considerably compared to these in the preprecipitation periods. When a moist-adiabatic temperature profile is generated as a result of a precipitation event, the significance of the impact on pollutant dispersion under light wind conditions is dependent on the environmental background temperature, where in a warm environment the reduction in pollutant dispersion is most pronounced. Thermal circulations related to cool air pools typical...

The desert of Sahara is one of the major sources of mineral dust on Earth, producing around 2×108 tons/yr. Under certain weather conditions, dust particles from Saharan desert get transported over the Mediterranean Sea and most of Europe. The limiting values set by the directive EC/30/1999 of European Union can easily be exceeded by the transport of desert dust particles in the south European Region and especially in urban areas, where there is also significant contribution from anthropogenic sources. In this study, the effects of dust transport on air quality in several Greek urban areas are quantified. PM10 concentration values from stationary monitoring stations are compared to dust concentrations for the 4-year period 2003–2006. The dust concentration values in the Greek areas were estimated by the SKIRON modelling system coupled with embedded algorithms describing the dust cycle. The mean annual dust contribution to daily-averaged PM10 concentration values was found to be around or even greater than 10% in the urban areas throughout the years examined. Natural dust transport may contribute by more than 20% to the annual number of exceedances – PM10 values greater than EU limits – depending on the specific monitoring location. In a second stage of the study, the inhaled lung dose received by the residents in various Greek locations is calculated. The particle deposition efficiency of mineral dust at the different parts of the human respiratory tract is determined by applying a lung dosimetry numerical model, which incorporates inhalation dynamics and aerosol physical processes. The inhalation dose from mineral dust particles was greater in the upper respiratory system (extrathoracic region) and less significant in the lungs, especially in the sensitive alveolar region. However, in cases of dust episodes, the amounts of mineral dust deposited along the human lung are comparable to those received during exposure in heavily polluted urban or smoking areas.

In this study, forecast errors in dust vertical distributions were analyzed. This was carried out by using quantitative comparisons between dust vertical profiles retrieved from lidar measurements over Rome, Italy, and those predicted by models. Three models were used: the four-particle-size Dust Regional Atmospheric Model (DREAM), the older one-particle-size version of the SKIRON model from the University of Athens (UOA), and the pre-2006 one-particle-size Tel Aviv University (TAU) model. SKIRON and DREAM are initialized on a daily basis using the dust concentration from the previous forecast cycle, while the TAU model initialization is based on the Total Ozone Mapping Spectrometer aerosol index (TOMS AI). The quantitative comparison shows that (1) the use of four-particle-size bins in the dust modeling instead of only one-size bin improves dust forecasts, (2) cloud presence could contribute to additional dust forecast errors in SKIRON and DREAM, (3) as far as the TAU model is concerned, its forecast errors were mainly caused by technical problems with TOMS measurements from the Earth Probe satellite. As a result, dust forecast errors in the TAU model could be significant even under cloudless conditions.

RAMS-Hg and CMAQ-Hg are two state-of-the-science integrated modelling systems developed to study the complex chemical transformation, transport and deposition of atmospheric mercury. In the present study model results using RAMS-Hg are both compared with observations from the Hg deposition network (MDN) and wet deposition of Hg results using CMAQ-Hg. A preliminary validation of the RAMS-Hg model as well as quantitative estimation of the advantages of the proposed approach on coupling mercury processes to an atmospheric modelling system is presented. Model validation indicated that the comprehensive model simulated reasonably well the wet deposition measurements of Hg at the MDN sites.

Particulate matter of anthropogenic and/or natural origin in the atmosphere is considered a parameter causing multiple effects on the environment of local and remote locations. The presence of absorbing and/or scattering aerosols in the lower troposphere can affect the atmospheric radiation through the modification of both short- and long-wave components. On a shorter term, aerosols can cause the modification of environmental conditions by influencing atmospheric temperature and dynamics. Atmospheric photochemistry is also affected by the presence of increased particle concentrations due to the alteration of UV and visible radiation fluxes and therefore the modification of the j -values (photolysis rates) of the photochemical reactions. Physiographic characteristics and climatic conditions in the Mediterranean Region are followed by excessive solar radiation leading to high photochemical activity in the Region. In addition long-range transport of fine particles is very common in the area. In this work we focus on the distribution of fine desert particles in the greater Mediterranean Region since Saharan dust is the desert responsible for many severe dust outbreaks that influence the Region. We examine the impact of increased desert dust concentration on the photochemistry of the region. For this purpose, advanced atmospheric and photochemical models are implemented with the aid of air pollutant measurements from stations in the region. The models used are the RAMS atmospheric model, the SKIRON/Eta atmospheric modeling system with the implementation of dust module, and the CAMx photochemical model. Sensitivity tests performed with and without the influence of dust load on the photolysis rates showed some interesting results in the formation and production of gases like ozone, nitrogen oxides, and nitric acid, and aerosols like sulfates and nitrates. The preliminary results of these simulations will be thoroughly discussed in this presentation.

International audience; This paper describes a new project trying to harmonise approaches to wave and wind modelling offshore, helping the short-term forecasting and wake research communities by establishing virtual laboratories, offering specialised workshops, and setting up expert groups with large outreach in the mentioned fields. Currently, a good number of research projects is underway on the European and national level in the fields of short-term forecasting of wind power, offshore wind and wave resource prediction, and offshore wakes in large wind farms. The leaders of those research projects are assuming the function of a multiplier towards the larger research and user community. In the fields of short-term forecasting and offshore energy resource, Expert Groups will be formed to act as the central focus point for external stakeholders. The liaison with other groups will also include groups outside of Europe. To facilitate the spread of knowledge, a number of workshops is planned. One of them took place just before this conference on the topic of best practice in the use of short-term forecastingsystems, where utilities with a combined experience of over 50 years and a combined wind power installation of over 30 GW could share their experiences and views on the best use of those systems. A preliminary overview of the resulting best practice guide will be given. One issue hampering the progress in our fields is the difficulty of getting access to good data. In most cases, data on offshore wind or power is strictly confidential, and also data on onshore wind power, especially in conjunction with numerical weather predictions, is not easy to come by. One example of a good testing procedure comes from the Anemos project, where in all 6 test cases were defined, to be run by all involved institutes. This idea is taken to the next level with the set-up of two Virtual Laboratories, one for offshore wake modelling, the other one for short-term forecasting. Both laboratories will be well-defined and maybe already open for business by the time of the workshop.

The physical and chemical processes involved in the mercury cycle in the atmosphere are very complicated and need special treatment. At the framework of the EU/DG-XII project MAMCS a significant effort has been devoted for the development of appropriate models for studying the mercury cycle in the atmosphere. In addition, an improved emission inventory is created while monitoring data in various locations in Europe are selected and used for model calibration and inter-comparison. Our model development includes the incorporation of almost any type of source (point or area), gas and aqueous phase chemistry, gas-to-particle conversion, wet and dry deposition, air-water exchange processes etc. The development was performed within two well-known atmospheric modeling systems: the Regional Atmospheric Modeling System (RAMS) and the SKIRON/Eta. There are several reasons for performing the development of the mercury cycle modeling within these two models: The main reason for using RAMS is its unique capability of two-way interactive nesting of any number of grids which is considered as absolutely necessary for studying near-source dispersion of mercury species. Additional capabilities are the full microphysical parameterization for wet processes, the detailed parameterization of surface processes and the non-hydrostatic formulation. The main reason for using the SKIRON/Eta model for development is its unique capability of describing the dust cycle (uptake, transport, deposition) and the existence of a viscous sub-layer formulation which is necessary for description of mercury fluxes from the sea surface. In both models the mercury cycle formulation is called simultaneously at each time-step in order

In the present study, multi-scale analysis of the atmospheric circulation and photochemical processes was performed in order to investigate the behavior of photochemical plumes emitted from urban coastal areas. The simulations were combined with regional scale marine boundary layer airborne measurements of the atmospheric oxidants. The results showed a strong interaction between local and regional scale fluctuations. The previously identified main routes of transport were confirmed as routes of photochemical fluctuations. The key factor is the marine boundary layer. The plume maintains its characteristics inside this stable layer and the diurnal fluctuation of NOy in association with precursor VOCs define oxidant concentration at remote areas.

In recent years there is a growing need in hydrology for high-resolution precipitation predictions. Accurate quantitative precipitation forecasts at various spatiotemporal scales can be made by the atmospheric numerical models that utilize sophisticated parameterization schemes to represent the various physical processes. Two soil parameterization schemes are presented here: a) the bucket model which is a simple single-layer scheme and was the first one to be used in numerical models, and b) the multilayer Oregon State University scheme which is currently utilized in operational and research mode. A number of successful short-term predictions of severe precipitation events are also presented. These predictions were produced by various full-physics numerical models, such as the SKIRON/Eta modeling system, RAMS and the UKMO Unified model, under different forcing mechanisms. The performance of the models in representing the spatiotemporal variability of precipitation is mainly discussed. In general, the atmospheric numerical models exhibited a skill in providing accurate short-term predictions of the spatiotemporal variability and severity of precipitation. Keywords: numerical modeling; SKIRON/Eta; RAMS; HYPACT; Unified Model; severe precipitation events; land-surface parameterizations; short-term forecasts

[1] An extended domain limited area model was implemented for seasonal-range simulations to assess the effect of tropical Pacific SST perturbations on weather patterns over Europe and Mediterranean. The experimental method consisted of Skiron/Eta model integrations with coarse and fine grid increment using artificially-modified as well as analysis SST forcing. The selected period was August–October 1997. Model simulations with coarse grid increment produced a weak signal in the precipitation pattern and the synoptic scale circulation over Europe, implying a damping of the North Atlantic atmospheric response to the tropical Pacific SST perturbation. Fine resolution experiments suggested an amplified dynamic response providing a direct link between tropical Pacific SST and North Atlantic synoptic circulation. The output signal is mainly attributed to the effective representation of the regional/mesoscale atmospheric features due to the model implementation with a fine mesh grid.

International audience; This paper presents the objectives and the research work carried out in the frame of the ANEMOS project on short-term wind power forecasting. The aim of the project is to develop accurate models that substantially outperform current state-of-the-art methods, for onshore and offshore wind power forecasting, exploiting both statistical and physical modeling approaches. The project focus on prediction horizons up to 48 hours ahead and investigates predictability of wind for higher horizons up to 7 days ahead useful i.e. for maintenance scheduling. Emphasis is given on the integration of high-resolution meteorological forecasts. For the offshore case, marine meteorology is considered as well as information by satellite-radar images. Specific modules are also developed for on-line uncertainty and prediction risk estimation. An integrated software platform, 'ANEMOS', is developed to host the various models. This system will be installed by several end-users for on-line operation at onshore and offshore wind farms for prediction at a local, regional and national scale. The applications include different terrain types and wind climates, on- and offshore cases, and interconnected or island grids. The on-line operation by the utilities will allow validation of the models and an analysis of the value of wind prediction for a competitive integration of wind energy in the developing liberalized electricity markets.

Mineral dust, produced by wind erosion over arid and semi-arid areas of North Africa, may transport away to the Middle East, Mediterranean, Europe, even into and across the Atlantic Ocean (Kallos et al., 2002). This material transported away from its origin is considered as an important climate and environment modifier. Dust particles by absorbing and backscattering both the incoming solar radiation and the infrared outgoing radiation modify the Earth’s radiation budget (Andreae, 1996). In addition, they alter the cloud microphysics processes acting as cloud condensation nuclei and having pH < 7.0 play a role in neutralization of the acid rains (Hedin and Likens, 1996). Also with the long-range dust transport, important nutrients are transported from their sources to other regions and may significantly modify the biogeochemistry of these marine and terrestrial ecosystems (Swap et al., 1996). For example, the deposition of the North African dust material on the Mediterranean Sea provides important nutrients, such as nitrogen species, phosphorus and iron, which may enhance the marine productivity. Some summer algal blooms in the Mediterranean Sea may be explained by such Saharan dust deposition (Dulac et al., 1996). Guerzoni et al. (1999) have estimated the amount of the atmospheric dust mass deposited on Mediterranean region to be ∼40×106 tons. Even though, they turned out to this magnitude by measured atmospheric mass flux at 9 coastal sites (which is considered as a small number of sites for such a work), this is considered as a valuable estimation since it is the only one found so far.

In this paper an attempt was made to identify the in/out of state contributions of mercury sources to the total deposited mercury over the State of New York. The transport, transformation and deposition of mercury in New York State are also discussed.

Many studies indicate that the atmosphere is a significant and in some cases the dominant pathway by which specific elements are transported from the land to the open sea. The Mediterranean Sea is a semi-enclosed basin, that continuously receives anthropogenic substances from the industrialized European country, and sporadically, from the arid region of the Sahara desert, nearly the 90% of the total amount of aerosols that reach the sea surface. The Mediterranean is a predominantly oligotrophic basin with areas of high productivity limited to areas influenced by runoff, rivers or upwelling. In situ biogeochemical measurements indicate that atmospheric deposition can induce significant productivity changes. The present work aims to use SeaWiFS satellite data and the SKIRON atmospheric model to provide an estimate of the temporal and spatial variability in the atmospheric forcing (dust events) and in the marine biological response (blooms), and to evaluate the overall contribution of these Saharan dust events to the fertility of the Mediterranean Sea. Although biological dynamic is meanly driven by the circulation features of the basin, results show that the atmospheric nutrient deposition gives some evident response in the biological activity.

The dust amounts deposited on the surface depends critically upon the seasonal varia- bility of the dust cycle in the atmosphere. Analyses of ground and satellite-based obser- vations can lead to useful results in relation to the seasonal variability of dust deposition. However, to gain a feeling of the magnitude and the geographical distribution of the dust deposition on ground surfaces and on coastal and open seas, the use of a credible numerical model is considered essential. In this study, using the SKIRON/Eta weather forecasting system, a database of seasonal amounts of dust deposited on Mediterranean Sea and Europe has been created.

[1] In the framework of the European Union-funded project “Investigation of Cloud by Ground-based and Airborne Radar and Lidar” (CARL) the Regional Atmospheric Modeling System (RAMS) was used in order to study ice crystal formation and evolution in a cold cloud formation during a field program over Palaiseau, France. Sensitivity tests were performed so as to bind the uncertainty from various factors controlling model results. Emphasis is given to the sensitivity of the model with respect to the shape parameter of gamma distribution in the cloud microphysics module. Sensitivity analysis of the model was also performed in relation to the initialization of the simulation. The results are compared to in situ and remote sensing observations of the cloud formation. The analysis revealed that the model was able to reproduce the cloud characteristics (e.g., the spatial and temporal variability of the phenomena and the cloud geometry) in a satisfactory way. A detailed comparison of the model results with aircraft data showed that the model-calculated water content and number concentration deviate significantly for the small-size particle bin (2–47 microns) but are in good agreement for the medium- (25–800 microns) and large-size (200–6400 microns) bins. The differences for the smaller particles can partially be attributed to both poor performance of the microphysical algorithms and instrument inaccuracies. Some differences for the larger particles can be attributed either to the definition of the cloud boundaries by the model or to disturbances caused by the ascent path of the aircraft or both. The time of model initialization is also an important factor affecting cloud formation during the first few hours of the simulation. The performed simulations and model/data intercomparisons showed that RAMS is able to reproduce most of the microphysical parameters of cold cloud formations satisfactorily while utilizing conventional meteorological fields and observations for initial and boundary conditions.

The mesoscale model UAM-AERO coupled with the prognostic meteorological model RAMS has been applied to study the dynamics of photochemical gaseous species and particulate matter processes in the eastern Mediterranean area between the Greek mainland and the island of Crete. In addition, the regional NILU-CTM model is used for the determination of the background air quality data. The modeling platform is applied to simulate atmospheric conditions for the period between 11-30 July 2000. In the current paper the spatial and temporal distribution of gaseous and particulate matter pollutants has been extensively studied together with identification of major emission sources in the area.

[1] Societally and environmentally important resources can be separated into five major categories: water, food, energy, human health, and ecosystem function. These resources, however, are intimately interlinked. Water, for example, is required for each of the other four resources. Estimating availability of water resources, as well as other resources, requires an assessment of the threats they face.

The atmospheric part of the mercury cycle is considered as very complicated because of the various physicochemical processes involved. The temporal and spatial scales of various processes are varying according to mercury species. While Hg0 is considered as long-range transport pollutant, HgII is fast reacting and deposits quickly (wet and dry). HgP has behaviour similar to the other particulate in the atmosphere. There is enough evidence now about the various disturbances in what are considered as background quantities. The most important reasons are (i) the increase of emissions from sources like coal burning, waste incinerators, cement production, mining etc, (ii) the lack of understanding of important physicochemical processes like fluxes, transport, transformation and deposition. Because of these verified disturbances, during the last years, a considerable effort has been devoted to reduce the mercury emissions. At the framework of the EU/DG-XII project MAMCS a significant effort has been devoted at the development of appropriate models for studying the mercury cycle in the atmosphere. The model development is performed within the atmospheric models RAMS and SKIRON/Eta. In this development we tried to transfer and utilize the modeling techniques applied in conventional air pollution modelling studies. In addition, we had to develop new methodologies for processes like re-emissions from soil and water bodies and gas to particle formation. The developed modeling systems have been applied in the Mediterranean Region where the multi-scale atmospheric processes (thermal and mechanical circulations at regional and mesoscale) are considered as important, according to a number of past air pollution studies. Seasonal-type of simulation has been performed and annual deposition patterns have been estimated. As it was found, the regional-scale pattern and the trade wind systems (from North to South) and the photochemistry are the key factors for controlling the mercury deposition, especially the HgP.

Despite vigorous attempts to control the ozone problem during the past three decades, ozone levels in many areas over the Eastern United States continue to exceed the National Ambient Air Quality Standards. Until recently, photochemical models were applied to simulate historical ozone episodic events to examine the future ozone non-attainment problem. When the model’s ability to reproduce the observed ozone air quality was deemed acceptable, control measures needed to meet and maintain the ozone standards were evaluated using projected emissions inventories and historical episodic meteorological conditions. Since the episodic meteorological events under which the model has performed best may never occur in the future, there is an inherent uncertainty in the controls identified as required to comply with the ozone standards.

(1990). Some Evaluations of the Effect of Ambient Temperature on Plume Rise. Journal of the Air & Waste Management Association: Vol. 40, No. 7, pp. 1020-1022.

In several studies during the past, the urban plumes have been extensively considered. In these studies, the spatial and temporal scales of episodic conditions have been described and emphasis was given to the formation and evolution of air pollution episodes within city limits (or in an area covering a few tens of kilometers around the city) and for a time period of one to two days. Moreover, the weather phenomena exhibiting strong diurnal variations (e. g. sea/land-breezes, upslope/downslope and drainage flows, orographic effects, heat islands etc.) were emphasized. The influence of the regional scale phenomena in such cases was not considered on a systematic manner. Actually, the role of phenomena with wavelengths larger than a few tens of kilometers was considered as not important for the formation of a specific air quality over the city of consideration. During the last few years, the influence of regional scale forcing on the formation of specific air quality conditions was found to be important. Kallos et al. (1993) reported that the regional scale phenomena should contribute significantly in the formation of specific air quality conditions in the Greater Athens Area (GAA). Luria et al. (1996) showed that significant degradation of the air quality in some areas should be attributed to regional scale transport phenomena. While the physicochemical properties of various urban plumes have been described at the urban scale with the aid of organized experimental campaigns and/or mesoscale and photochemical modeling (e. g. Ziomas, 1996), not enough attention was paid to the properties of the urban plume as it is passing to areas relatively far from its origin. Consequently, the urban plume impact on remote locations has not been extensively studied. Such phenomena should be considered as very important in some cases, especially in areas with specific characteristics like the Mediterranean Region.

Saharan dust storms are the main source of the atmospheric dust in the Mediterranean region. Once injected to the atmosphere, dust may pass long distances under favourable meteorological conditions before it deposits to the ground or sea surfaces. Typically, several hundreds millions of tonnes of dust is transported away from sources annually (D’Almeida, 1986). Continuous presence of dust in the atmosphere causes diverse climatic and environmental effects. For example, dust modifies radiation properties of the air through absorption and scattering of the solar energy on dust particles (e. g. Chen et al., 1995). Recent estimate of Tegen and Fung (1994) shows that mineral dust may decrease the net radiation for about 1 Wm−2, revealing thus the fact that it could be a significant climate forcing factor. Another environmental effect of the dust process is dust deposition on the sea surface, which may significantly change the marine biochemical properties (e. g. Martin and Fitzwater, 1988; Kubilay and Saydam, 1995). Also, the atmospheric dust may significantly influence human activities: for example, it reduces the visibility, causing thus problems in the air and ground traffic; during dust storms, increased number of eye and respiratory organs infections is recorded, too.

It is well known that many air quality problems are associated with various so-called mesoscale features. When mesoscale circulations are developed in a given region, they influence the ventilation and thereby the air quality in the area. The most important mesoscale features are circulations exhibiting a diurnal cycle. To such circulation types belong land-sea breezes, internal boundary layers, up-slopes, down-slopes and drainage flows, as well as flow systems created by urban heat islands. They result in the development of sharp flow gradients and vertical stratification which affect the air quality in the considered region. These mesoscale circulations are mainly due to differential heating of the surface in the region which may i.e. be due to variations in surface type. Another category of mesoscale circulations is related to mechanical effects such as blocking and channelling forced by the topography of the region.