ALBERT

Description: In Synthetic Aperture Radar (SAR) imagery, signatures of coherent atmospheric structures, due to sea surface roughness modulation by surface winds, are usually well detected. In the present study, the wind field derived from the Envisat Advanced SAR (ASAR) sensor has been analyzed and compared with those simulated with a regional atmospheric model in a case study over an area located in the eastern Mediterranean Sea, extending southward and eastward of Crete island. This is a region subject to complex wind patterns, due to the interaction of the almost steady northerly Etesian wind with the orography of the islands in the region. The ASAR Wide Swath Mode images provide datasets at resolutions exceptionally high compared to model data, appropriate for investigating the mesoscale phenomena on the marine atmospheric boundary layer and to retrieve the surface wind field. The latter has been obtained with a methodology based on the 2-D Continuous Wavelet Transform, suitable to isolate the backscatter patterns on the base of energy and scale considerations. Numerical simulations with the Weather Research and Forecasting (WRF) model have been performed using three 2-way nested domains, the inner one covering the area of interest with a resolution of 1 km. Several simulations, using different diffusion and boundary layer parameterization schemes, have been performed in a case study corresponding to mountain lee waves detected in the ASAR image. The 10 m winds resulting from the numerical experiments have been compared to those retrieved from the ASAR, both quantitatively and qualitatively, in order to analyze the correspondence of observed and simulated wind structures.

Description: The dispersion analysis of airborne contaminants including radioactive substances from industrial or nuclear facilities is an important issue for air quality maintenance and safety assessment. In Japan, many nuclear power plants are located at complex coastal terrains. In these cases, terrain effects on the turbulent flow and plume dispersion should be investigated. In this study, we perform Large-Eddy Simulation (LES) of turbulent flow and plume dispersion over a 2-dimensional hill flow and investigate the characteristics of mean and fluctuating concentrations.

Description: The EU FP7 Project MEGAPOLI: "Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation" (http://megapoli.info) brings together leading European research groups, state-of-the-art scientific tools and key players from non-European countries to investigate the interactions among megacities, air quality and climate. MEGAPOLI bridges the spatial and temporal scales that connect local emissions, air quality and weather with global atmospheric chemistry and climate. The suggested concept of multi-scale integrated modelling of megacity impact on air quality and climate and vice versa is discussed in the paper. It requires considering different spatial and temporal dimensions: time scales from seconds and hours (to understand the interaction mechanisms) up to years and decades (to consider the climate effects); spatial resolutions: with model down- and up-scaling from street- to global-scale; and two-way interactions between meteorological and chemical processes.

Description: During the last decade a new field of atmospheric modelling – the chemical weather forecasting (CWF) – is quickly developing and growing. However, in the most of the current studies and publications, this field is considered in a simplified concept of the off-line running chemical transport models with operational numerical weather prediction (NWP) data as a driver. A new concept and methodology considering the chemical weather as two-way interacting meteorological weather and chemical composition of the atmosphere is suggested and discussed. The on-line integration of mesometeorological models and atmospheric aerosol and chemical transport models gives a possibility to utilize all meteorological 3-D fields in the chemical transport model at each time step and to consider feedbacks of air pollution (e.g. urban aerosols) on meteorological processes/climate forcing and then on the atmospheric chemical composition. This very promising way for future atmospheric simulation systems (as a part of and a step to Earth System Modelling) will lead to a new generation of models for meteorological, environmental and chemical weather forecasting. The methodology how to realise the suggested integrated CWF concept is demonstrated on the example of the European Enviro-HIRLAM integrated system. The importance of different feedback mechanisms for CWF is also discussed in the paper.

Description: The meteorological impacts on pollen emission and spread in a typical Central European forest of mixed deciduous and coniferous trees are investigated. Pollen samples as well as meteorological measurements have been conducted during the flowering period of spring flowering tree species in 2009. An episodic event of pollen transport to the study area is analyzed in detail with the aid of hourly backwards trajectories. The results indicate that the experimental set-up was well designed for a thorough meteorological analysis of the pollen counts.

Description: The SAL (Structure, Amplitude, Location) method is used for verification of precipitation forecasts at horizontal grid spacings ranging from 2.5 km to 25 km, using a high-resolution 1 km precipitation analysis as a reference. The verification focuses on a summertime period with predominantly convective precipitation. The verification domain contains lowland as well as alpine areas. Evaluation of the individual SAL components shows that with regard to area mean values (A) the benefit of high resolutions models becomes apparent only in high impact weather situations. For the summertime period studied, the subjective impression of better structured precipitation fields (S) in higher resolution models can generally be confirmed. The most significant improvement appears to be associated with explicit simulation of deep convection.

Description: The problem of a hard contradiction between limited possibilities of meteorological observations and uncontrolled complication of the present-day weather forecasting models, and its consequences for the planetary wave predictability are considered with examples from the ECMWF short- and medium-range H500 forecasts for the Northern Hemisphere. A supposition is voiced that this problem adds difficulties to the weekly predictability limit overcoming.

Description: The planetary boundary layer (PBL) is a part of the Earth's atmosphere where turbulent fluxes dominate vertical mixing and constitute an important part of the energy balance. The PBL depth, h, is recognized as an important parameter, which controls some features of the Earth's climate and the atmospheric chemical composition. It is also known that h varies by two orders of magnitude on diurnal and seasonal time scales. This brief note highlights effects of this variability on the atmospheric near-surface climate and chemical composition. We interpret heat capacity parameter of a Budyko-type energy balance model in terms of quasi-equilibrium h. The analysis shows that it is the shallowest, stably-stratified PBL with the smallest h that should be of particular concern for climate modelling. The reciprocal dependence between the PBL depth and temperature (concentrations) is discussed. In particular, the analysis suggests that the climate characteristics during stably stratified PBL episodes should be significantly more sensitive to perturbations of the Earth's energy balance as well as emission rates. On this platform, h from ERA-40 reanalysis data, the CHAMP satellite product and the DATABASE64 data were compared. DATABASE64 was used to assess the Troen-Mahrt method to determine h through available meteorological profile observations. As it has been found before, the shallow PBL requires better parameterization and better retrieval algorithms. The study demonstrated that ERA-40 and CHAMP data are biased toward deeper h in the shallow polar PBL. This, coupled with the scarcity of in-situ observations might mislead the attribution of the origins of the Arctic climate change mechanisms.

Description: This study analyzes the tornado event on 27 July 2002 at Athens International Airport (Eleutherios Venizelos), a suburban area located at the east of Athens. The tornado was formed approximately at 10:20 UTC and characterized as T4 (Torro Scale). A synoptic discussion of the ECMWF analysis charts from the surface up to the 500 hPa geopotential height level is presented along with the daily composite anomaly (reference period: 1968–1996) of the relative meteorological parameters from NCEP/NCAR reanalysis dataset. The vertical profile of the atmosphere is also presented, and derived from the operational sounding of the nearest upper air meteorological station to the tornado incidence site. The dynamic indices of the atmosphere revealed unstable atmospheric conditions capable for thunderstorm formation. The tornado caused injuries to a woman due to the shift of a parked airplane during the disembarkation procedure and also several damage at the airport facilities.

Description: The process of formation of a large scale spot-like structure of the cumulative deposition pattern due to a powerful elevated finite lifetime source is studied using numerical solutions of a model diffusion problem. A possible cause of spottiness at regional scale, namely the diurnal cycle of the vertical turbulent mixing intensity in the atmospheric boundary layer, is investigated. It is shown that the atmospheric boundary layer diurnal cycle can cause the appearance of the spot-like structure when the source lifetime, t*, is much shorter than the diurnal period, T.