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Moisture Variability (moisture + variability)
Selected AbstractsThe role of moisture cycling in the weathering of a quartz chlorite schist in a tropical environment: findings of a laboratory simulationEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2005Tony Wells Abstract Long-term weathering of a quartz chlorite schist via wetting and drying was studied under a simulated tropical climate. Cubic rock samples (15 mm × 15 mm × 15 mm) were cut from larger rocks and subjected to time-compressed climatic conditions simulating the tropical wet season climate at the Ranger Uranium Mine in the Northern Territory, Australia. Fragmentation, moisture content and moisture uptake rate were monitored over 5000 cycles of wetting and drying. To determine the impact of climatic variables, five climatic regimes were simulated, varying water application, temperature and drying. One of the climatic regimes reproduced observed temperature and moisture variability at the Ranger Uranium Mine, but over a compressed time scale. It is shown that wetting and drying is capable of weathering quartz chlorite schist with changes expected over a real time period of decades. While wetting and drying alone does produce changes to rock morphology, the incorporation of temperature variation further enhances weathering rates. Although little fragmentation occurred in experiments, significant changes to internal pore structure were observed, which could potentially enhance other weathering mechanisms. Moisture variability is shown to lead to higher weathering rates than are observed when samples are subjected only to leaching. Finally, experiments were conducted on two rock samples from the same source having only subtle differences in mineralogy. The samples exhibited quite different weathering rates leading to the conclusion that our knowledge of the role of rock type and composition in weathering is insufficient for the accurate determination of weathering rates. Copyright © 2005 John Wiley & Sons, Ltd. [source] European Alpine moisture variability for 1800,2003INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2007G. van der Schrier Abstract Moisture availability for the European Greater Alpine region (GAR) (43°N,49°N and 4°E,19°E) for the period 1800,2003 is analyzed on the basis of maps of monthly self-calibrating Palmer Drought Severity Index (scPDSI) with a 10, × 10, spatial resolution. To represent the impact of seasonal snow cover on the water budget, a simple snow-accumulation and snowmelt model is added to the water balance calculations on which the (self-calibrating) Palmer Drought Severity Index is based. Over the region as a whole, the late 1850s into the 1870s and the 1940s to the early 1950s stand out as persistent and exceptionally dry periods, whereas the first two decades of the nineteenth century and the 1910s were exceptionally wet periods. Dividing the Greater Alpine Region into four subregions, with the subregions based on coherence of precipitation variability, we find a large degree of heterogeneity in the behavior of the drought index over the subregions. The driest summers on record, in terms of the amplitude of the index averaged over the Alpine region, are 1865 and 2003. In these years, 75.6% and 85.1% of the region was suffering from a moderate drought (or worse). The areas northwest of the high mountains were affected most severely in the 1865 drought, whereas the 2003 drought impacted all subregions more equally. By substituting climatological monthly mean temperatures, from the period 1961,1990, for the actual monthly means in the parameterization for potential evaporation, an estimate is made of the direct effect of temperature on drought. It is observed that a major cause for the vast areal extent of the area affected by the summer drought in the last decade is the high temperatures. Temperatures in the 12 months preceding and including the summer of 2003 explain an increase in the area percentage with moderate (or worse) drought of 31.2%. Copyright © 2006 Royal Meteorological Society [source] Impact of soil moisture on the development of a Sahelian mesoscale convective system: a case-study from the AMMA Special Observing PeriodTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S1 2010Christopher M. Taylor Abstract Interactions between the land and atmosphere play an important role in the precipitation of the Sahel. The African Monsoon Multidisciplinary Analysis Special Observing Period provided observations with which to illuminate potential feedback mechanisms. This case-study highlights a major storm which developed over northern Mali in an area where a research aircraft was surveying the atmospheric response to soil moisture features. Soil moisture variability is characterized using satellite land-surface temperature data whilst cloud images illustrate the evolution of the storm and its relationship to the surface. Measurements in the planetary boundary layer (PBL) indicate mesoscale variations in pre-storm humidity and temperature consistent with high evaporation from wet soils. The storm developed above a dry surface within a wetter region with cells first appearing along a wet,dry soil boundary. This suggests that the storm was triggered in association with low-level convergence driven by the soil moisture pattern. A gravity wave propagating away from a remote mature storm also appears to have played an important role in the initiation, though only in the region of the soil moisture contrast did deep convection become established. Once organised into a Mesoscale Convective System, convection developed over wet areas as well as dry, and indeed at this stage, convection became more intense over wetter soils. This behaviour is consistent with the large gradients in PBL humidity. The study illustrates the complexity of soil moisture,convection feedback loops and highlights the mechanisms which may operate at different stages of a storm's life cycle. Copyright © 2009 Royal Meteorological Society [source] | ||||||||||