Atmospheric Research 

Abstract: A formulation is developed in which the contribution of the far wings of collisionally broadened spectral lines to the water vapor continuum absorption is established. The effects of deviations from the impact (Lorentz) line shape due to duration of collision effects are treated semi-empirically to provide agreement with experimental results for the continuum absorption and its temperature-dependence. The continua due to both water-water molecular broadening (self-broadening) and water-air molecular broadening (foreign broadening) are discussed. Several atmospheric validations of the present approach are presented.

Abstract: A new cloud microphysical parameterization is described. Features of this new scheme include: the use of generalized gamma distributions as the basis function for all hydrometeor species; the use of a heat budget equation for hydrometeor classes, allowing heat storage and mixed phase hydrometears; partitioning hydrometeors into seven classes (including separate graupel and hail categories) ; the use of stochastic collection rather than continuous accretion approximations and extension of the ice nucleation scheme to include homogeneous nucleation of ice from haze particles and cloud droplets. The versatility and credibility of the new scheme is explored, using sensitivity experiments for a simple two-dimensional convective cloud simulation.

Abstract: Proximity sounding analysis has long been a tool to determine environmental conditions associated with different kinds of weather events and to discriminate between them. It has been limited, necessarily, by the spatial and temporal distribution of soundings. The recent development of reanalysis datasets that cover the globe with spatial grid spacing on the order of 200 km and temporal spacing every 6 h allows for the possibility of increasing the number of proximity soundings by creating ‘‘pseudo-soundings.’’ We have used the National Center for Atmospheric Research (NCAR)/United States National Centers for Environmental Prediction (NCEP) reanalysis system to create soundings and find environmental conditions associated with significant severe thunderstorms (hail at least 5 cm in diameter, wind gusts at least 120 km h � 1 , or a tornado of at least F2 damage) and to discriminate between significant tornadic and non-tornadic thunderstorm environments in the eastern United States for the period 1997–1999. Applying the relationships from that region to Europe and the rest of the globe, we have made estimates of the frequency of favorable conditions for significant severe thunderstorms. Southern Europe has the greatest frequency of significant severe thunderstorm environments, particularly over the Spanish plateau and the region east of the Adriatic Sea. Favorable significant tornadic environments are found in France and east of the Adriatic. Worldwide, favorable significant thunderstorm environments are concentrated in equatorial Africa, the central United States, southern Brazil and northern Argentina, and near the Himalayas. Tornadic environments are by far the most common in the central United States, with lesser areas in southern Brazil and northern Argentina. Published by Elsevier B.V.

Abstract: This paper presents a detailed review of the different de-icing techniques, already developed and in development, which could be applied to the conductors and wires of electric power lines. After a bibliographical search in various data banks, on de-icing processes, more than 30 techniques at different stages of development, capable of removing ice and assuring anti-icing protection, have been identified in different fields such as air and rail transport, electrical networks, telecommunications, etc. Although many techniques have not yet made it beyond the concept stage, some are used in several of the sectors previously mentioned. The following is a comparative evaluation of all these techniques, thermal, mechanical and passive, based on energy efficiency and practicability. It is recommended to favor the mechanical techniques over thermal methods that have been developed, but require more energy. Specific development projects and feasibility studies on the most attractive techniques have finally been identified as steps for progress in power line de-icing.

Abstract: This paper is the second in a series of articles describing the new microphysics scheme in the Regional Atmospheric Modeling System (RAMS). In this part, a new two-moment microphysical parameterization is described. The proposed scheme predicts the mixing ratio and number concentration of rain, pristine ice crystals, snow, aggregates, graupel and hail. The general gamma distribution is the basis function used for hydrometeor size in each category. Additional features include: use of stochastic collection for number concentration tendency; breakup of rain droplets formulated into the collection efficiency; diagnosis of ice crystal habit dependent on temperature and saturation; evaporation and melting of each species assuming that the smallest particles completely disappear first; and more complex shedding formulations which take into account the amount of water mass on the coalesced hydrometeor. Preliminary sensitivity testing of the new microphysical scheme in an idealized convective simulation shows that the two-moment prediction scheme allows more flexibility of the size distribution enabling the mean diameter to evolve in contrast to the one-moment scheme. Sensitivity to the prescribed input parameters such as cloud droplet concentrations and the shape parameter v is demonstrated in the model results.