Atmospheric Chemistry and Physics Discussions, 2013
Mineral dust aerosols exert a significant effect on both solar and terrestrial radiation. By abso... more Mineral dust aerosols exert a significant effect on both solar and terrestrial radiation. 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 outgoing longwave radiation. Desert dust forcing exhibits large regional 5 and temporal variability due to its short lifetime and diverse optical properties, further complicating the quantification of the Direct Radiative Effect (DRE). The complexity of the links and feedbacks of dust on radiative transfer indicate the need of an integrated approach in order to examine these impacts.
Mesometeorological information obtained in several research projects in southern Europe has been ... more Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoontype regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Mediterranean cyclogenesis and torrential rains in autumn-winter. Because these intense rains and floods can occur anywhere in the basin, perturbations to the hydrological cycle in any part of the basin can propagate to the whole basin and adjacent regions. Furthermore, present levels of air pollutants can produce greenhouse heating, amplifying the perturbations and pushing the system over critical threshold levels. The questions raised are relevant for the new European Union (EU) water policies in southern Europe and for other regions dominated by monsoon-type weather systems.
As a part of developments in the project SKIRON, a system for operational regional weather predic... more As a part of developments in the project SKIRON, a system for operational regional weather prediction is designed and developed, for use in the Greek Meteorological Service. The implementation of the system requires a Unix computational environment and corresponding meteorological data input. The system is created as a fully automatic. Its central component is the Parallel Eta limited-area weather forecasting model. The preprocessing part of the system prepares the input data for the model. After the model execution, the postprocessing component prepares the model data for visualization and other specific applications. The Eta model is a limited-area regional-scale atmospheric model which has been mainly developed to be used for routine forecasting purposes. From January 1978, the model is used for routine forecasting in Yugoslav Weather Service; from June 1993, the model has been implemented for operational forecasts over die USA region at the National Weather Service in Washington...
NATO Science for Peace and Security Series C: Environmental Security, 2013
ABSTRACT The clouds that develop in maritime or polluted environments have significant difference... more ABSTRACT The clouds that develop in maritime or polluted environments have significant differences in their properties. A number of modeling sensitivity tests have been performed to describe the physical processes related to aerosol – cloud interactions at various stages of cloud development. Precipitation amounts and cloud structure were found to be very sensitive to changes in the size distribution and number concentrations of the aerosols. Certain combinations of CCN/IN properties and atmospheric properties may lead to significant enhancement of convection and precipitation. These interactions are not linear and it is the synergetic effects between meteorology and atmospheric chemistry that are responsible for the variation of precipitation.
ABSTRACT Flash flood induce storms are mainly of convective nature and develop at small space and... more ABSTRACT Flash flood induce storms are mainly of convective nature and develop at small space and short time scales making their predictability a particularly challenging task. The tremendous societal and economical impact of this hazard necessitates the development of accurate forecasting systems in order to advance warnings and mitigate the risk. To be able to develop a forecasting system that can accurately represent flash flood storms, we need to understand the key elements that control the generation and evolution of this type of events. This study examines the effect of topographic representation, model grid resolution and cloud microphysical properties in simulating three major flash flood storms that occurred in Northern Italy. To simulate those heavy precipitation events, the high-resolution integrated atmospheric model RAMS / ICLAMS was used with grid resolutions of 250 m, in order to properly resolve the complex physical processes and convective activity. In addition, a high resolution topography dataset of 3 arcsec from the NASA SRTM mission was implemented in the model. The sensitivity of microphysical properties and aerosol cloud interactions towards convection and precipitation over the area were examined through various model setups and simulations. The specific properties proved to play a significant role in the correct estimation of spatial distribution and quantity of precipitation, as indicated from the comparison of the model outputs with bias adjusted radar data.
This chapter describes the physicochemical mechanisms that formulate the air quality over the Med... more This chapter describes the physicochemical mechanisms that formulate the air quality over the Mediterranean region and the resulted impacts on the regional climate. At fi rst, a detailed description of the teleconnections and regional fl ow patterns that dominate in the region is provided. The dominant fl ow 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 speci fi c pollutant transport paths may in fl uence 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 120 G. Kallos et al. trends. There is particular discussion on the suspension of naturally-produced aerosols and especially desert dust particles in the region and their spatial in fl uence 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.
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT [1] This paper addresses the aerosol effects on radiation and the feedbacks on meteorolo... more ABSTRACT [1] This paper addresses the aerosol effects on radiation and the feedbacks on meteorology and photochemical activity, applying the online model RAMS/ICLAMS. The model treats meteorology and chemical pollutants on an interactive way. Cloud condensation nuclei (CCN), giant (GCCN) and ice nuclei (IN) are treated as predictive quantities. The calculation of the aerosol optical properties accounts for size-resolved mineral dust and size- and humidity-dependent optical properties of sea salt. The simulations with and without aerosol impacts reveal the complex direct and indirect mechanisms through which the alteration of radiation fluxes influences meteorology and photochemical processes. For the specific dust event, the reduction in the surface shortwave radiation over cloudless regions affected by dust, averages at ~ -75 W m-2 at 12:00 UTC per unit dust loading (1 g m-2). The increase of downwelling longwave radiation over the same areas and time, averages at ~ 40 W m-2 per unit dust loading (1 g m-2). Surface upwelling longwave radiation over Mediterranean (GMR) exhibits a complex daytime behavior. During midnight the inclusion of dust leads to larger upwelling longwave radiation fluxes over the African continent. The net downward longwave radiation over cloudless areas exhibits an increase both during noon and midnight with the inclusion of dust. The results show that the vertical structure of the dust layer governs the magnitude of the feedback on radiation. The activation of natural particles as CCN causes small changes in radiation fluxes and temperature. Precipitation is influenced more by the indirect rather than the direct and semi-direct effects.
Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 1999
The aim of this paper is to investigate the occurrence of a cloudband associated with a cold fron... more The aim of this paper is to investigate the occurrence of a cloudband associated with a cold front over the maritime area south from the Greek Peninsula. This cloudband was clearly evident on the infrared satellite picture, oriented nearly parallel to the frontal surface. The relevance of Conditional Symmetric Instability as a possible mechanism for the formation of this band is investigated through model simulations. The model analysis was performed with the three dimensional non-hydrostatic Colorado State University -Regional Atmospheric Modelhng System (CSU-RAMS). Inspection of the moist potential vorticity pattern within a cross-section perpendicular to the cloudband supported the hypothesis that Conditional Symmetric Instability was the mechanism which favoured the band formation at the leading edge of the cold Frontal surface.
1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranea... more 1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranean dust intrusion of 15-16 March, 1998. The intrusion has been associated with development of an intense cyclone over Africa. The weather and dust development processes were simulated with the Eta weather and dust prediction model. Also presented is a comparison of the model results with the Total Ozone Mass Spectrometer Aerosol Index (TOMS AI) pictures as well as with those of the surface and weather observations. The roles of the main processes responsible for the dust plume development and associated dust intrusion to the eastern Mediterranean (EM) are studied. The observation data as well as the model-simulated parameters are jointly analyzed. The analysis also includes the data from the back-trajectory computations. With the aid of the modelproduced dust profiles we studied the significant variation in the altitudes of the dust layers within the cyclone sectors. In the warm sector of the cyclone located over the Mediterranean Sea the dust layer extended up to 8-10 km. Relatively low dust concentration values were found here. In the area of the cold front over Africa the dust was restricted to the lower troposphere and the planetary boundary layer. Here the model simulated high values of the dust concentrations. The sharp TOMS AI increase over Israel and the eastern Mediterranean up to 5.0 units, further away from the dust sources, is explained by the strong winds, by the increased cyclone convergence, and the formation of a two-layer dust plume.
ABSTRACT An analytical evaluation of the perturbations to mesoscale atmospheric flows induced by ... more ABSTRACT An analytical evaluation of the perturbations to mesoscale atmospheric flows induced by thermal inhomogeneities in the convective boundary layer is presented. The time evolution of these perturbations as a function of the intensity and of the horizontal and vertical scales of the diabatic forcing is studied. The problem is approached using Laplace transform theory for the time behavior and Green function theory for the spatial structure. Results show that the growth of the atmospheric perturbations closely follows the growth of the convective boundary layer; the transient being characterized by a number of inertia-gravity oscillations of decreasing intensity. The vertical scale is determined by the depth of the convective boundary layer; and the horizontal scale is determined by the local Rossby deformation radius. Sinusoidally periodic thermal forcing induce periodic atmospheric cells of the same horizontal scale. The intensity of mesoscale cells increases for increasing values of the wave number, reaches its maximum value when the wavelength of the forcing is of the order of the local Rossby radius, and then decreases as the wavelength of the forcing decreases.
Atmospheric Chemistry and Physics Discussions, 2013
Mineral dust aerosols exert a significant effect on both solar and terrestrial radiation. By abso... more Mineral dust aerosols exert a significant effect on both solar and terrestrial radiation. 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 outgoing longwave radiation. Desert dust forcing exhibits large regional 5 and temporal variability due to its short lifetime and diverse optical properties, further complicating the quantification of the Direct Radiative Effect (DRE). The complexity of the links and feedbacks of dust on radiative transfer indicate the need of an integrated approach in order to examine these impacts.
Mesometeorological information obtained in several research projects in southern Europe has been ... more Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoontype regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Mediterranean cyclogenesis and torrential rains in autumn-winter. Because these intense rains and floods can occur anywhere in the basin, perturbations to the hydrological cycle in any part of the basin can propagate to the whole basin and adjacent regions. Furthermore, present levels of air pollutants can produce greenhouse heating, amplifying the perturbations and pushing the system over critical threshold levels. The questions raised are relevant for the new European Union (EU) water policies in southern Europe and for other regions dominated by monsoon-type weather systems.
As a part of developments in the project SKIRON, a system for operational regional weather predic... more As a part of developments in the project SKIRON, a system for operational regional weather prediction is designed and developed, for use in the Greek Meteorological Service. The implementation of the system requires a Unix computational environment and corresponding meteorological data input. The system is created as a fully automatic. Its central component is the Parallel Eta limited-area weather forecasting model. The preprocessing part of the system prepares the input data for the model. After the model execution, the postprocessing component prepares the model data for visualization and other specific applications. The Eta model is a limited-area regional-scale atmospheric model which has been mainly developed to be used for routine forecasting purposes. From January 1978, the model is used for routine forecasting in Yugoslav Weather Service; from June 1993, the model has been implemented for operational forecasts over die USA region at the National Weather Service in Washington...
NATO Science for Peace and Security Series C: Environmental Security, 2013
ABSTRACT The clouds that develop in maritime or polluted environments have significant difference... more ABSTRACT The clouds that develop in maritime or polluted environments have significant differences in their properties. A number of modeling sensitivity tests have been performed to describe the physical processes related to aerosol – cloud interactions at various stages of cloud development. Precipitation amounts and cloud structure were found to be very sensitive to changes in the size distribution and number concentrations of the aerosols. Certain combinations of CCN/IN properties and atmospheric properties may lead to significant enhancement of convection and precipitation. These interactions are not linear and it is the synergetic effects between meteorology and atmospheric chemistry that are responsible for the variation of precipitation.
ABSTRACT Flash flood induce storms are mainly of convective nature and develop at small space and... more ABSTRACT Flash flood induce storms are mainly of convective nature and develop at small space and short time scales making their predictability a particularly challenging task. The tremendous societal and economical impact of this hazard necessitates the development of accurate forecasting systems in order to advance warnings and mitigate the risk. To be able to develop a forecasting system that can accurately represent flash flood storms, we need to understand the key elements that control the generation and evolution of this type of events. This study examines the effect of topographic representation, model grid resolution and cloud microphysical properties in simulating three major flash flood storms that occurred in Northern Italy. To simulate those heavy precipitation events, the high-resolution integrated atmospheric model RAMS / ICLAMS was used with grid resolutions of 250 m, in order to properly resolve the complex physical processes and convective activity. In addition, a high resolution topography dataset of 3 arcsec from the NASA SRTM mission was implemented in the model. The sensitivity of microphysical properties and aerosol cloud interactions towards convection and precipitation over the area were examined through various model setups and simulations. The specific properties proved to play a significant role in the correct estimation of spatial distribution and quantity of precipitation, as indicated from the comparison of the model outputs with bias adjusted radar data.
This chapter describes the physicochemical mechanisms that formulate the air quality over the Med... more This chapter describes the physicochemical mechanisms that formulate the air quality over the Mediterranean region and the resulted impacts on the regional climate. At fi rst, a detailed description of the teleconnections and regional fl ow patterns that dominate in the region is provided. The dominant fl ow 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 speci fi c pollutant transport paths may in fl uence 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 120 G. Kallos et al. trends. There is particular discussion on the suspension of naturally-produced aerosols and especially desert dust particles in the region and their spatial in fl uence 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.
Journal of Geophysical Research: Atmospheres, 2014
ABSTRACT [1] This paper addresses the aerosol effects on radiation and the feedbacks on meteorolo... more ABSTRACT [1] This paper addresses the aerosol effects on radiation and the feedbacks on meteorology and photochemical activity, applying the online model RAMS/ICLAMS. The model treats meteorology and chemical pollutants on an interactive way. Cloud condensation nuclei (CCN), giant (GCCN) and ice nuclei (IN) are treated as predictive quantities. The calculation of the aerosol optical properties accounts for size-resolved mineral dust and size- and humidity-dependent optical properties of sea salt. The simulations with and without aerosol impacts reveal the complex direct and indirect mechanisms through which the alteration of radiation fluxes influences meteorology and photochemical processes. For the specific dust event, the reduction in the surface shortwave radiation over cloudless regions affected by dust, averages at ~ -75 W m-2 at 12:00 UTC per unit dust loading (1 g m-2). The increase of downwelling longwave radiation over the same areas and time, averages at ~ 40 W m-2 per unit dust loading (1 g m-2). Surface upwelling longwave radiation over Mediterranean (GMR) exhibits a complex daytime behavior. During midnight the inclusion of dust leads to larger upwelling longwave radiation fluxes over the African continent. The net downward longwave radiation over cloudless areas exhibits an increase both during noon and midnight with the inclusion of dust. The results show that the vertical structure of the dust layer governs the magnitude of the feedback on radiation. The activation of natural particles as CCN causes small changes in radiation fluxes and temperature. Precipitation is influenced more by the indirect rather than the direct and semi-direct effects.
Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere, 1999
The aim of this paper is to investigate the occurrence of a cloudband associated with a cold fron... more The aim of this paper is to investigate the occurrence of a cloudband associated with a cold front over the maritime area south from the Greek Peninsula. This cloudband was clearly evident on the infrared satellite picture, oriented nearly parallel to the frontal surface. The relevance of Conditional Symmetric Instability as a possible mechanism for the formation of this band is investigated through model simulations. The model analysis was performed with the three dimensional non-hydrostatic Colorado State University -Regional Atmospheric Modelhng System (CSU-RAMS). Inspection of the moist potential vorticity pattern within a cross-section perpendicular to the cloudband supported the hypothesis that Conditional Symmetric Instability was the mechanism which favoured the band formation at the leading edge of the cold Frontal surface.
1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranea... more 1] Presented herein is an analysis of an exceptionally intensive central and eastern Mediterranean dust intrusion of 15-16 March, 1998. The intrusion has been associated with development of an intense cyclone over Africa. The weather and dust development processes were simulated with the Eta weather and dust prediction model. Also presented is a comparison of the model results with the Total Ozone Mass Spectrometer Aerosol Index (TOMS AI) pictures as well as with those of the surface and weather observations. The roles of the main processes responsible for the dust plume development and associated dust intrusion to the eastern Mediterranean (EM) are studied. The observation data as well as the model-simulated parameters are jointly analyzed. The analysis also includes the data from the back-trajectory computations. With the aid of the modelproduced dust profiles we studied the significant variation in the altitudes of the dust layers within the cyclone sectors. In the warm sector of the cyclone located over the Mediterranean Sea the dust layer extended up to 8-10 km. Relatively low dust concentration values were found here. In the area of the cold front over Africa the dust was restricted to the lower troposphere and the planetary boundary layer. Here the model simulated high values of the dust concentrations. The sharp TOMS AI increase over Israel and the eastern Mediterranean up to 5.0 units, further away from the dust sources, is explained by the strong winds, by the increased cyclone convergence, and the formation of a two-layer dust plume.
ABSTRACT An analytical evaluation of the perturbations to mesoscale atmospheric flows induced by ... more ABSTRACT An analytical evaluation of the perturbations to mesoscale atmospheric flows induced by thermal inhomogeneities in the convective boundary layer is presented. The time evolution of these perturbations as a function of the intensity and of the horizontal and vertical scales of the diabatic forcing is studied. The problem is approached using Laplace transform theory for the time behavior and Green function theory for the spatial structure. Results show that the growth of the atmospheric perturbations closely follows the growth of the convective boundary layer; the transient being characterized by a number of inertia-gravity oscillations of decreasing intensity. The vertical scale is determined by the depth of the convective boundary layer; and the horizontal scale is determined by the local Rossby deformation radius. Sinusoidally periodic thermal forcing induce periodic atmospheric cells of the same horizontal scale. The intensity of mesoscale cells increases for increasing values of the wave number, reaches its maximum value when the wavelength of the forcing is of the order of the local Rossby radius, and then decreases as the wavelength of the forcing decreases.
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Papers by G. Kallos