Photodissociation effects of solar u.v. radiation

This paper reviews the current knowledge of u.v. solar irradiances beyond 120 nm measured during solar cycle 21. Parameters required to calculate the atmospheric attenuation of the u.v. radiation and the photodissociation rate of neutral constituents are discussed. The effect of scattering is also considered.     

The lifetimes of sunspot moats

In the standard model of the solar convective zone, turbulent eddies transport entropy rather than temperature. We consider the turbulent mean field equations for the convective zone, including entropy transport, and show that the zone can be unstable to larger scale motion which we identify with the supergranulation and giant cells.     

PETROLOGY OF EETA79006 AND IMPLICATIONS FOR THE FORMATION OF POLYMICT EUCRITES

A newly found polymict eucrite, EETA79006, is described. Lithic clasts are similar to those found in howardites and fall into four groups: fine-grained (aphanitic), coarse-grained, basaltic, and cataclastic. All have eucritic compositions and differ mainly in cooling and deformation histories. Some basaltic clasts cooled faster than others and may be impact melts. Analysis of pyroxene and feldspar in the matrix and in 20 lithic clasts indicates that the matrix was not derived from the observed lithic clast population. This meteorite and similar polymict eucrites may have formed by addition of younger more fractionated lithic clasts to the regolith of the parent body.     

Movements,failure and climatic control of the Veslemannen rockslide,Western Norway

On September 5, 2019, the Veslemannen unstable rock slope (54,000 m³) in Romsdalen, Western Norway, failed catastrophically after 5 years of continuous monitoring. During this period, the rock slope weakened while the precursor movements increased progressively, in particular from 2017. Measured displacement prior to the failure was around 19 m in the upper parts of the instability and 4–5 m in the toe area. The pre-failure movements were usually associated with precipitation events, where peak velocities occurred 2–12 h after maximum precipitation. This indicates that the pore-water pressure in the sliding zones had a large influence on the slope stability. The sensitivity to rainfall increased greatly from spring to autumn suggesting a thermal control on the pore-water pressure. Transient modelling of temperatures suggests near permafrost conditions, and deep seasonal frost was certainly present. We propose that a frozen surface layer prevented water percolation to the sliding zone during spring snowmelt and early summer rainfalls. A transition from possible permafrost to a seasonal frost setting of the landslide body after 2000 was modelled, which may have affected the slope stability. Repeated rapid accelerations during late summers and autumns caused a total of 16 events of the red (high) hazard level and evacuation of the hazard zone. Threshold values for velocity were used in the risk management when increasing or decreasing hazard levels. The inverse velocity method was initially of little value. However, in the final phase before the failure, the inverse velocity method was useful for forecasting the time of failure. Risk communication was important for maintaining public trust in early-warning systems, and especially critical is the communication of the difference between issuing the red hazard level and predicting a landslide.

     

Towards household food security in Ghana: assessment of Ghana’s expanded forest plantation programme in Asante Akim South District

This study primarily presents a contribution analysis of the outcomes of the expanded forest plantation programme (EFPP) as a community-based forest governance intervention to enhance household food security. A cross sectional research design with simple random sampling technique was used to select the study sites and respondents. In all, four (4) out of ten (10) settlements implementing the EFPP in the Asante Akyim South District of Ghana were selected. Questionnaires were administered to 80 beneficiaries proportionally selected from the study sites and in-depth interviews were conducted with key stakeholders implementing the programme. The discussion of the results was informed by the theory of change analysis framework to assess the contribution of the programme to household food security. The theory of change tool helped to identify progress towards the achievement of potential and probable outcomes of the programme. The findings reveal that the availability of food crops at the household level and the district at large increased through the EFPP. Between the years 2011 and 2013, 2763.1426 Metric Tonnes (Mt) of food crops were produced from 444.4046 ha of land in the district from the programme. Also, an average of GH¢ 229 ($72) comprising both monthly allowances received for planting and nurturing trees and income derived from the sale of food crops produced increased the economic power and livelihood outcomes of beneficiaries. This has had a contributing effect on the physical availability and accessibility of food crops at the household level. Hence, scaling up the EFPP to cover many beneficiaries, and a budget allocation for the food crop production component of the programme through the provision of improved crop seeds for interplanting would promote food production and security at the household and district levels.     

Impact of textural patterns on modeled rock weathering rates and size distribution of weathered grains

Rock texture has a critical influence on the way rocks weather. The most important textural factors affecting weathering are grain size and the presence of cracks and stylolites. These discontinuities operate as planes of mechanical weakness at which chemical weathering is enhanced. However, it is unclear how different rock textures impact weathering rates and the size of weathered grains. Here, we use a numerical model to simulate weathering of rocks possessing grain boundaries, cracks, and stylolites. We ran simulations with either synthetic or natural patterns of discontinuities. We found that for all patterns, weathering rates increase with discontinuity density. When the density was <~25%, the weathering rate of synthetic patterns followed the order: grid > honeycomb > Voronoi > brick wall. For higher values, all weathering rates were similar. We also found that weathering rates decreased as the tortuosity of the pattern increased. Moreover, we show that textural patterns strongly impact the size distributions of detached grains. Rocks with an initial monomodal grain size distribution produce weathered fragments that are normally distributed. In contrast, rocks with an initial log-normal size distribution produce weathered grains that are log-normally distributed. For the natural patterns, weathering produced lower modality distributions.