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In this study, gravity waves (GWs) in the high-resolution GEOS-5 Nature Run are first evaluated with respect to satellite and other model results. Southern Hemisphere winter sources of non-orographic GWs in the model are then investigated by linking measures of tropospheric non-orographic gravity wave generation tied to precipitation and frontogenesis with absolute gravity wave momentum flux in the lower stratosphere. Finally, non-orographic GW momentum flux is compared to orographic gravity wave momentum flux and compared to previous estimates. The results show that the global patterns in GW amplitude, horizontal wavelength, and propagation direction are realistic compared to observations. However, as in other global models, the amplitudes are weaker and horizontal wavelengths longer than observed. The global patterns in absolute GW momentum flux also agree well with previous model and observational estimates. The evaluation of model non-orographic GW sources in the Southern Hemisphere winter shows that strong intermittent precipitation (greater than 10 mm h−1) is associated with GW momentum flux over the South Pacific, whereas frontogenesis and less intermittent, lower precipitation rates (less than 10 mm h−1) are associated with GW momentum flux near 60°S. In the model, orographic GWs contribute almost exclusively to a peak in zonal mean momentum flux between 70 and 75°S, while non-orographic waves dominate at 60°S, and non-orographic GWs contribute a third to a peak in zonal mean momentum flux between 25 and 30°S.

Recent observational and theoretical studies of the global properties of small-scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere. The effects of gravity waves on the large-scale circulation have long been treated via parametrizations in both climate and weather-forecasting applications. In these parametrizations, key parameters describe the global distributions of gravity-wave momentum flux, wavelengths and frequencies. Until recently, global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence. Recent satellite and other global datasets with improved resolution, along with innovative analysis methods, are now providing constraints for the parametrizations that can improve the treatment of these waves in climate-prediction models. Research using very-high-resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects, and when tested against observations these models show some very realistic properties. Here we review recent studies on gravity-wave effects in stratosphere-resolving climate models, recent observations and analysis methods that reveal global patterns in gravity-wave momentum fluxes and results of very-high-resolution model studies, and we outline some future research requirements to improve the treatment of these waves in climate simulations. Copyright © 2010 Royal Meteorological Society and Crown in the right of Canada

Tin mining carried out on the Jos Plateau since the beginning of the last century has disturbed some 320 km2 of agricultural land. Formal attempts at reclamation of this land failed, but local farmers have developed a successful informal strategy for reclamation. This paper reports on a study undertaken to comprehend the farmers’‘informal’ approach to soil fertility management. Their soil fertility management practices centre on the use of a complex combination of traditional organic manures and ‘modern’ inorganic fertilizers that they have developed entirely on the basis of experimentation. A central focus of this paper is therefore the empirical knowledge base of the farmers and an assessment of any underlying scientific explanations for their strategies, including an analysis of their assertion that different brands of NPK fertilizers differ in their nutrient value. This discussion is followed by a consideration of the difficulties in accessing and understanding empirical knowledge. It is concluded that farmers’ knowledge and understanding of the values of different fertilizers and manures does have a scientific basis. It is argued that for further agricultural development to take place on the Jos Plateau, there must be synergy between farmers’ empirical knowledge (which has led to the development of successful and effective soil fertility management strategies, unlike the attempts of the local ‘scientific’ communities) and scientific knowledge (which can identify health and environmental hazards which may not be immediately visible to farmers).

Summary 1. Individual variation in the intake rate of foraging animals arises largely from variation in two characteristics: their intrinsic ability to forage in the absence of competitors (foraging efficiency) and the detrimental effect of competitors on their intake rate (susceptibility to interference). We use a model to explore the relative importance of foraging efficiency and dominance, which influences susceptibility to interference, in determining the intake rate of foraging animals at a range of competitor densities. 2. The model is parameterized and tested for a shorebird–prey system, oystercatchers Haematopus ostralegus L. feeding on mussels Mytilus edulis L., in which interference occurs because dominant individuals steal prey from subdominant ones. In both oystercatchers which open mussels by stabbing their bill between the shell valves (stabbers) and those which hammer a hole through the shell (hammerers), foraging efficiency is predicted to be the major determinant of intake rate at competitor densities below 100–150 birds ha-1 and dominance the major determinant at higher densities. In reality, a very similar relationship is found in stabbers, but in hammerers foraging efficiency remains the most important determinant of intake rate across the full range of observed competitor densities, in contrast to the model's prediction. Oystercatchers typically forage at densities in the range 100–250 birds ha-1, in the region in which foraging efficiency and dominance are of approximately equal importance to stabbers, while foraging efficiency is most important to hammerers. We suggest reasons for the difference in the model's predictive power for stabbers and hammerers. 3. We use the model to make the general predictions that the relative importance of foraging efficiency is higher when (i) it varies more between individuals, (ii) prey encounter rate is high, (iii) handling time is short, (iv) prey stealing (kleptoparasitic) attacks occur over short distances, (v) the probability of stealing prey is low, and (vi) movement speed while foraging is low. In the oystercatcher–mussel system, prey encounter rate is lower and handling time longer than in most other shorebird–prey systems. This suggests that the importance of foraging efficiency in determining intake rate is likely to be greater in many other shorebirds. 4. Most studies of between individual variation in intake rate have focused on the importance of dominance rather than variation in foraging efficiency. Both the model predictions and field data suggest that variation in foraging efficiency may be a more important source of variation in intake rate than its previous depth of study would suggest.

The combination of a rising population and increased food demand has placed tremendous pressure on the land resources of Bangladesh. These pressures are exacerbated by the annual wet-season floods which frequently devastate much of the agricultural land. Successive governments have therefore sought international aid to assist in the development of flood control measures. Of particular importance are 14 major schemes which aim to provide protection from 20–25 year return floods by the construction of earth-embanked enclosures. There is no doubt that these schemes have been very successful in protecting valuable agricultural areas from floods and hence increasing agricultural production. There is, however, growing evidence from a range of sources for long-term deterioration in soil fertility within the project areas. The study reported here is the first to systematically examine the changes taking place in soil properties following the establishment of a flood control, drainage and irrigation project. Comparison of two soil series, sampled from within and without the project area, demonstrate that within six years of project establishment, significant adverse changes have occurred in several soil properties; these include increasing acidity and a decline in available nutrients. The changes are attributable to a combination of poor management strategies and the absence of the annual flood input of silt. As Bangladesh cannot afford any decline in agricultural output, it is vital to establish whether adverse changes recorded here are occurring in other projects. This can be achieved by the establishment of a nationwide programme of soil fertility monitoring. © 1998 John Wiley & Sons, Ltd.