Multiscale clustering of heavy and light small particles in turbulent channel flow at high Reynolds numbers

To understand the fundamental mechanism of the clustering of heavy and light small particles in high-Reynolds-number wall turbulence, we conduct direct numerical simulations of particle dispersions in turbulent channel flow at the friction Reynolds number Reτ=2000. Heavy and light particles form clusters with different shapes, and the cluster size is larger for particles with longer relaxation time. To reveal the origin of these multiscale clusters of particles, we investigate particle distributions around multiscale vortices. Vortices tend to sweep out heavy particles and tend to attract light ones with a relaxation time comparable with their turnover time. These clustering phenomena due to coherent vortices can occur irrespective of their size, existing height and the friction Reynolds number. We can therefore explain the multiscale nature of particle clustering in terms of the time scale matching between particles and vortices

Factors responsible for co-dominance of two beech species in a cool temperate forest in central Japan: interspecific comparison of spatial distribution and growth traits

To understand the co-existence mechanisms of related species,the recruitment processes of Fagus crenata and F. japonica were censused during 3 and 4 years from emergence, respectively, in a cool-temperate forest in Japan. The distributional properties and the growth traits were compared between two Fagus species. To evaluate the distributional properties, the spatial abundance of seedlings was estimated by a generalized linear model (GLM), with explanatory variables such as topographic variables, light conditions, the presence of dwarf bamboo, and the abundance of the overstory. To evaluate the growth traits under herbivory pressure, both the elongated shoot length and the proportion of recovery frompredation (re-growth) were also compared. No spatial segregation and no species-specific differences were detected by GLM, which was consistent throughout the census period. Only F. japonica exhibited a slope-related distribution, while F. crenata exhibited no topographical dependence, indicates the distributional overlaps. For the growth traits, contrasting trends were detected, F. crenata was superior in shoot growth, whereas the proportion of regrowth was higher in F. japonica than F. crenata. We concluded that co-dominance of these species was not attributed to the spatial segregationbut to the trade-off between growth and resistance to herbivory

Potential use and implementation of ensemble forecasting

Thesis (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2007.Includes bibliographical references (p. 102-112).This thesis discusses ensemble forecasting, a promising new weather forecasting technique, from various viewpoints relating not only to its meteorological aspects but also to its user and policy aspects. Ensemble forecasting was developed to overcome the limitations of conventional deterministic weather forecasting. However, despite the achievements of ensemble forecasting techniques and efforts to put them into operation, the implementation and utilization of ensemble forecasting seems limited in society. This thesis studies meteorological aspects, potential uses and value, and policy issues to give an overall picture of ensemble forecasting and suggests directions of measures to increase its utilization. Conventional weather forecasting cannot achieve perfect forecasts due to the chaotic nature of the atmosphere and imperfect analyses of the current atmosphere. The imperfect description of numerical weather prediction models in the forecasting process is another source of the disparity between forecasts and the real atmosphere. Conventional weather forecasting offers only a single scenario, which sometimes fails to predict the actual weather; ensemble forecasting provides probabilistic weather forecasts based on multiple weather scenarios.(cont.) This thesis also illustrates potential uses and values of ensemble forecasting. Ensemble forecasting could help disaster management officers prepare for probable hazardous conditions. It is also useful for risk management in business. Using concepts of information values and real options, this thesis demonstrates that ensemble forecasting can be valuable in decision making. Potential uses of ensemble forecasting in agriculture and the wind electricity sectors are also discussed. Implementation of ensemble forecasting requires huge costs, so collaboration within weather sectors and with non-weather sectors is key. Relationships between public, private, and academic sectors in the weather world are analyzed in this thesis. The public-private relationship seems characterized by dilemmas in both sectors. As for the public-academic relationship, there are different situations in the US and in Japan due to differences in research environment and policies. International collaboration and partnerships between weather sectors and non-weather sectors are also discussed. If all these collaborations among the sectors work well, then ensemble forecasting can give rise to a new generation of weather forecasting.by Susumu Goto.S.M