The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

A climatology of nocturnal low-level jets (LLJs) is presented for the topographically flat measurement site at Cabauw, the Netherlands. LLJ characteristics are derived from a 7-yr half-hourly database of wind speed profiles, obtained from the 200-m mast and a wind profiler. Many LLJs at Cabauw originate from an inertial oscillation, which develops after sunset in a layer decoupled from the surface by stable stratification. The data are classified to different types of stable boundary layers by using the geostrophic wind speed and the isothermal net radiative cooling as classification parameters. For each of these classes, LLJ characteristics like frequency of occurrence, height above ground level, and the turning of the wind vector across the boundary layer are determined. It is found that LLJs occur in about 20% of the nights, are typically situated at 140-260 m above ground level, and have a speed of 6-10 m s 21 . Development of a substantial LLJ is most likely to occur for moderate geostrophic forcing and a high radiative cooling. A comparison with the 40-yr ECMWF Re-Analysis (ERA-40) is added to illustrate how the results can be used to evaluate the performance of atmospheric models.

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Legacy phosphorus (P) that has accumulated in soils from past inputs of fertilizers and manures is a large secondary global source of P that could substitute manufactured fertilizers, help preserve critical reserves of finite phosphate rock to ensure future food and bioenergy supply, and gradually improve water quality. We explore the issues and management options to better utilize legacy soil P and conclude that it represents a valuable and largely accessible P resource. The future value and period over which legacy soil P can be accessed depends on the amount present and its distribution, its availability to crops and rates of drawdown determined by the cropping system. Full exploitation of legacy P requires a transition to a more holistic system approach to nutrient management based on technological advances in precision farming, plant breeding and microbial engineering together with a greater reliance on recovered and recycled P. We propose the term 'agro-engineering' to encompass this integrated approach. Smaller targeted applications of fertilizer P may still be needed to optimize crop yields where legacy soil P cannot fully meet crop demands. Farm profitability margins, the need to recycle animal manures and the extent of local eutrophication problems will dictate when, where and how quickly legacy P is best exploited. Based on our analysis, we outline the stages and drivers in a transition to the full utilization of legacy soil P as part of more sustainable regional and global nutrient management.

Data on vessel arrangement, grouping, diameter, perforations, element length, wall thickness and helical thickenings are presented for the woody flora of Israel and adjacent regions. Within this flora the arid, Mediterranean, hygrophylic and synanthropic components are compared with each other and with information on woods from the tropical rain and monsoon forest flora of Java and the mesic cool temperate flora of North West Europe.In these floristic comparisons, vessel element length decreases from mesic to xeric vegetations and within mesic floras from tropical to cool temperate or arctic latitudes. Other characters show complex trends and individual ecological categories show very wide, overlapping ranges of wood structural possibilities. The arid flora shows the highest proportion of species with a combination of numerous narrow, and wide vessels in their wood; a high degree of vessel grouping is also most common in this ecological category. Tropical species surviving in wadis of the Negev and Sinai desert do not show this syndrome but resemble their relatives from less xeric conditions. The wood of arid species in general appears to be at least as well adapted to efficient water transport (high values for maximum vessel diameter) as to safety (provided for by numerous, narrow vessels). Vessel walls tend to be thickest in the arid flora. Spiral thickenings are most common in the Mediterranean and temperate floras and are quite infrequent in both the arid subtropical flora of the Middle East and the mesic to seasonally dry tropical flora.Factors underlying the trends observed can only partly be retraced to ecological tendencies within genera; partly they appear to depend on the predominance of species belonging to specialised families in extreme habitats like the desert.