Measurement of total and condensed water mixing ratios in warm-based cumulus clouds by a jet engine evaporation technique

Summary A technique has been developed for measuring total water mixing ratio and condensed water mixing ratio in warm-based convective clouds. The jet engine compressor on a Learjet 24 is employed as an evaporator to convert all cloud condensate to vapour and the vapour density in the compressed (bleed) air is measured with a Lyman-alpha humidiometer.Sources of error in the measurement are i) a contaminant in the air lines which must be evaluated regularly by baselining the measurement against a dewpoint measurement in clear air; ii) nonisokinetic sampling at the jet inlet, which has been evaluated by monitoring the volume flow rate of air at the inlet.The Lyman-alpha humidiometer has been found to be robust and serviceable, with very slow drift properties. The drift is monitored by introducing dry nitrogen into the measurement cell.

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Zusammenfassung Eine Technik wurde entwickelt, um die Gesamt- und Kondenswassermischungsverhältnisse in konvektiven Wolken mit warmer Basis zu messen. Ein Düsentriebwerkskompressor auf einer Learjet 24 dient als Verdunster, um alles kondensierte Wasser in Dampf umzuwandeln, dessen Dichte in der ausströmenden komprimierten Luft dann mittels eines Lyman-alpha-Feuchtemeßgeräts bestimmt wird.Fehlerquellen sind zum einen die Verunreinigung der Luftstraßen, die regelmäßig ausgewertet werden muß, indem der Hintergrundswert durch Taupunktmessungen in klarer Luft bestimmt wird; zum anderen die nicht-isokinetische Probenentnahme am Triebwerkseinlaß, die aus der Volumsflußrate der Luft am Einlaß bestimmt wird.Das Lyman-alpha-Feuchtemeßgerät erwies sich als robust und wartungsextensiv, u. a. aufgrund seiner geringen Drift. Die Drift wird mittels in die Meßkammer eingeführten trokkenen Stickstoffes aufgezeichnet.

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With 10 Figures     

Regional geology and petroleum systems of the Illizi–Berkine area of the Algerian Saharan Platform: An overview

The Berkine and Illizi basins are Palaeozoic–Mesozoic intraplate depressions that preserve an over 7000 m thick sedimentary rock record and contain world-class petroleum systems with over 39 BBOE EUR hydrocarbon reserves. Regional seismic transects and a wealth of well data are used to review the tectonostratigraphic evolution of the area. The Gondwana (Palaeozoic) and Tethys (Mesozoic) supercycles make up the bulk of the Phanerozoic succession. These 1st order cycles record extensional basin formation, followed by a protracted period of overall net subsidence, and conclude with basin inversion and regional uplift during the Hercynian and Alpine orogenies respectively. Structural styles were dictated by transpressional or transtensional reactivation of mostly NNE oriented basement structural grain of Late Proterozoic–Ea.Cambrian (Pan-African) age and vertical movement of long wavelength regional highs and lows. Local tectonism is considered to be the far-field effect of plate-tectonic processes that affected the North African plate-boundaries, such as the Caledonian and Hercynian Orogenies, the opening of the Tethys and Atlantic oceans, and the Alpine Orogeny. These were accompanied by localised thermal mantle processes.     

Towards sustainable agriculture in post-apartheid South Africa

This paper assesses the possibility of sustainable agriculture in South Africa in the context of recent policy initiatives. The new environmental strategy for agriculture represents a significant break with policy initiatives developed during apartheid. The likelihood of sustainable farming practices being adopted in South Africa will, however, face at least three obstacles. These are the integrated structure of industrial farming, the concern over yields, and current political and economic changes in South African agriculture. It is argued that sustainable techniques are unlikely to develop in the large scale farming sector in the near future. If the considerable research and extension resources of the state are reoriented quickly enough, sustainable farming methods can be embraced by an emerging class of black commercial farmers.     

Landslide and tsunami hazard at Yate volcano,Chile as an example of edifice destruction on strike-slip fault zones

The edifice of Yate volcano, a dissected stratocone in the Andean Southern Volcanic Zone, has experienced multiple summit collapses throughout postglacial time restricted to sectors NE and SW of the summit. The largest such historic event occurred on 19th February 1965 when ～6.1–10?×?10⁶ m³ of rock and ice detached from 2,000-m elevation to the SW of the summit and transformed into a debris flow. In the upper part of the flow path, velocities are estimated to have reached 40 m s^?1. After travelling 7,500 m and descending 1,490 m, the flow entered an intermontane lake, Lago Cabrera. A wavemaker of estimated volume 9?±?3?×?10⁶ m³ generated a tsunami with an estimated amplitude of 25 m and a run-up of ～60 m at the west end of the lake where a settlement disappeared with the loss of 27 lives. The landslide followed 15 days of unusually heavy summer rain, which may have caused failure by increasing pore water pressure in rock mechanically weathered through glacial action. The preferential collapse directions at Yate result from the volcano’s construction on the dextral strike-slip Liquiñe-Ofqui fault zone. Movement on the fault during the lifetime of the volcano is thought to have generated internal instabilities in the observed failure orientations, at ～10° to the fault zone in the Riedel shear direction. This mechanically weakened rock may have led to preferentially orientated glacial valleys, generating a feedback mechanism with collapse followed by rapid glacial erosion, accelerating the rate of incision into the edifice through repeated landslides. Debris flows with magnitudes similar to the 1965 event are likely to recur at Yate, with repeat times of the order of 10² years. With a warming climate, increased glacial meltwater due to snowline retreat and increasing rain, at the expense of snow, may accelerate rates of edifice collapse, with implications for landslide hazard and risk at glaciated volcanoes, in particular those in strike-slip tectonic settings where orientated structural instabilities may exist.     

Major and trace element distributions around active volcanic vents determined by analyses of grasses: implications for element cycling and bio-monitoring

Samples of grass were collected at Masaya Volcano (Nicaragua; Rhynchelytrum repens and Andropogon angustatus) and the Piton de La Fournaise (around the April 2007 eruptive vent, La Réunion; Vetiveria zizanioides) to investigate the controls on major and trace element concentrations in plants around active volcanic vents. Samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements, and atomic absorption spectroscopy for Hg. At Masaya, As, Cu, Mo, Tl and K concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume. Similar variability was found in A. angustatus for Al, Co, Cs, Hg and Mg. At the Piton de La Fournaise, the patterns of variability in V. zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow. These results suggest that exposure to volcanic emissions is, for many elements, the main control on compositional variability in vegetation growing on active volcanoes. Thus, vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles.     

CLIMATOLOGY: THE CHALLENGE FOR THE EIGHTIES

Geographical climatology must systematically investigate the exchanges of heat, water, and momentum that occur at or near the earth's surface. Our discipline should focus upon surface features described under the general term “topoclimatology”as well as upon transfer processes occurring in the planetary boundary layer. Climatologists must increase their understanding of the synergistic relationships among climatic processes, surface features, and human actions. Methods of data collection, summary, analysis, and display also need to be improved. These challenges must be met in order that we may develop a better understanding of climate and improve our quantitative climatic analogues.     

Assessment of some spatial and temporal issues in landslide initiation within the Río Aguas Catchment, South–East Spain

A research programme underway in south–east Spain has the overall aim of developing a long-term landscape evolution model for the Tertiary depositional basins that lie within the eastern part of the Betic cordillera. As part of the work it has become apparent that there are multiple natural hazards to development in the region, and the nature and distribution of these is presently under investigation. For one hazard, namely landsliding, a database of over 300 cases has been compiled within one defined 425 km² river catchment, namely the Río Aguas. Evaluation of the database has demonstrated that the contemporary distribution of landslides correlates with areas of steepest slopes across a range of the different lithologies. However, the “slope” component of the landscape is controlled by a wave of incision associated with a river capture event c. 100000 years ago which locally increased erosion by between 5 and 10 times. This event was a function of differential uplift between the depositional basins and resulted in over-steepened slopes within parts of the catchment which have yet to reach equilibrium in this evolving landscape.