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Internal Variability (internal + variability)
Selected AbstractsSmall-scale variability in surface moisture on a fine-grained beach: implications for modeling aeolian transportEARTH SURFACE PROCESSES AND LANDFORMS, Issue 10 2009Brandon L. Edwards Abstract Small-scale variations in surface moisture content were measured on a fine-grained beach using a Delta-T Theta probe. The resulting data set was used to examine the implications of small-scale variability for estimating aeolian transport potential. Surface moisture measurements were collected on a 40 cm × 40 cm grid at 10 cm intervals, providing a total of 25 measurements for each grid data set. A total of 44 grid data sets were obtained from a representative set of beach sub-environments. Measured moisture contents ranged from about 0% (dry) to 25% (saturated), by weight. The moisture content range within a grid data set was found to vary from less than 1% to almost 15%. The magnitude of within-grid variability varied consistently with the mean moisture content of the grid sets, following an approximately normal distribution. Both very wet and very dry grid data sets exhibited little internal variability in moisture content, while intermediate moisture contents were associated with higher levels of variability. Thus, at intermediate moisture contents it was apparent that some portions of the beach surface could be dry enough to allow aeolian transport (i.e. moisture content is below the critical threshold), while adjacent portions are too wet for transport to occur. To examine the implications of this finding, cumulative distribution functions were calculated to model the relative proportions of beach surface area expected to be above or below specified threshold moisture levels (4%, 7%, and 14%). It was found that the implicit inclusion of small-scale variability in surface moisture levels typically resulted in changes of less than 1% in the beach area available for transport, suggesting that this parameter can be ignored at larger spatial scales. Copyright © 2009 John Wiley & Sons, Ltd. [source] The behavior of extreme cold air outbreaks under greenhouse warmingINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2006S. Vavrus Abstract Climate model output is used to analyze the behavior of extreme cold-air outbreaks (CAOs) under recent and future climatic conditions. The study uses daily output from seven GCMs run under late-twentieth century and projected twenty-first century radiative conditions (SRES A1B greenhouse gas emission scenario). We define a CAO as an occurrence of two or more consecutive days during which the local mean daily surface air temperature is at least two standard deviations below the local wintertime mean temperature. In agreement with observations, the models generally simulate modern CAOs most frequently over western North America and Europe and least commonly over the Arctic. These favored regions for CAOs are located downstream from preferred locations of atmospheric blocking. Future projections indicate that CAOs,defined with respect to late-twentieth century climatic conditions,will decline in frequency by 50 to 100% in most of the Northern Hemisphere during the twenty-first century. Certain regions, however, show relatively small changes and others actually experience more CAOs in the future, due to atmospheric circulation changes and internal variability that counter the thermodynamic tendency from greenhouse forcing. These areas generally experience greater near-surface wind flow from the north or the continent during the twenty-first century and/or are especially prone to atmospheric blocking events. Simulated reductions in CAOs are smallest in western North America, the North Atlantic, and in southern regions of Europe and Asia. The Eurasian pattern is driven by a strong tendency for the models to produce sea-level pressure (SLP) increases in the vicinity of the Mediterranean Sea (intermodel mean of 3 hPa), causing greater advection of continental air from northern and central Asia, while the muted change over western North America is due to enhanced ridging along the west coast and the increased frequency of blocking events. The North Atlantic response is consistent with a slowdown of the thermohaline circulation, which either damps the warming regionally or results in a cooler mean climate in the vicinity of Greenland. Copyright © 2006 Royal Meteorological Society. [source] Wavelet analysis of the Lisbon and Gibraltar North Atlantic Oscillation winter indicesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2006S. Barbosa Abstract The North Atlantic Oscillation (NAO) is one of the most important climatic patterns in the Northern Hemisphere. Indices based on the normalised pressure difference between Iceland and a southern station, such as Lisbon or Gibraltar, have been defined in order to describe NAO temporal evolution. Although exhibiting interannual and decadal variability, the signals are statistically rather featureless and therefore it is difficult to discriminate between different types of stochastic models. In this study, Lisbon and Gibraltar NAO winter indices are analysed using the discrete wavelet transform discrete wavelet transform(DWT). A multi-resolution analysis (MRA) is carried out for a scale-based description of the indices and the wavelet spectrum is used to identify and estimate long-range dependence. The degree of association of the two NAO indices is assessed by estimating the wavelet covariance for the two signals. The scale-based approach inherent to the discrete wavelet methodology allows a scale-by-scale comparison of the signals and shows that although the short-term temporal pattern is very similar for both indices, the long-term temporal structure is distinct. Furthermore, the degree of persistence or ,memory' is also distinct: the Lisbon index is best described by a long-range dependent (LRD) process, while the Gibraltar index is adequately described by a short-range process. Therefore, while trend features in the Lisbon NAO index may be explainable by long-range dependence alone, with no need to invoke external factors, for the Gibraltar index such features cannot be interpreted as resulting only from internal variability through long-range dependence. Copyright © 2006 Royal Meteorological Society. [source] SEISMIC FACIES ANALYSIS BASED ON 3D MULTI-ATTRIBUTE VOLUME CLASSIFICATION, DARIYAN FORMATION, SE PERSIAN GULFJOURNAL OF PETROLEUM GEOLOGY, Issue 2 2006P. Farzadi Interpretation of recently acquired 3D seismic data from the adjacent Sirri C and D oilfields in the SE Persian Gulf indicates that a 3D interpretation of seismic facies is crucial to resolve the internal stratal geometries of the Aptian Dariyan Formation. This carbonate formation passes southward into the Shu'aiba Formation, a prolific reservoir rock of similar facies in the UAE. Lack of exposures and limited cored intervals have forced reliance on the seismic data for evidence of the depositional environment and the internal architecture of potential reservoir rocks. The progradational nature of the Dariyan Formation and the occurrence of carbonate build-ups within it make this stratal geometry complex. The complex internal heterogeneity of the build-ups and presence of seismic noise make mapping of the build-ups in 3D space using conventional seismic interpretation tools difficult, despite the availability of high-quality 3D seismic data covering the area. The high quality seismic and limited well data from this field is one of the few datasets of this kind presented in the literature. A procedure for the hierarchical multi-attribute analysis of seismic facies using Paradigm's Seis Facies software is used in this study to provide a 3D interpretation of the stratal patterns. Principal component analysis reduces the noise and redundant data by representing the main data variances as a few vector components in a transformed coordinate system. Cluster analysis is performed using those components which have the greatest contribution to the maximum spread of the data variability. Six seismic attribute volumes are used in this study and the result is a single 3D classified volume. Important new information obtained from within the Dariyan Formation gives new insights into its stratigraphic distribution and internal variability. This method of processing seismic data is a step towards exploring for subtle stratigraphic traps in the study area, and may help to identify exploration targets. [source] Near Eastern Neolithic genetic input in a small oasis of the Egyptian Western DesertAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Martina Kujanová Abstract The Egyptian Western Desert lies on an important geographic intersection between Africa and Asia. Genetic diversity of this region has been shaped, in part, by climatic changes in the Late Pleistocene and Holocene epochs marked by oscillating humid and arid periods. We present here a whole genome analysis of mitochondrial DNA (mtDNA) and high-resolution molecular analysis of nonrecombining Y-chromosomal (NRY) gene pools of a demographically small but autochthonous population from the Egyptian Western Desert oasis el-Hayez. Notwithstanding signs of expected genetic drift, we still found clear genetic evidence of a strong Near Eastern input that can be dated into the Neolithic. This is revealed by high frequencies and high internal variability of several mtDNA lineages from haplogroup T. The whole genome sequencing strategy and molecular dating allowed us to detect the accumulation of local mtDNA diversity to 5,138 ± 3,633 YBP. Similarly, theY-chromosome gene pool reveals high frequencies of the Near Eastern J1 and the North African E1b1b1b lineages, both generally known to have expanded within North Africa during the Neolithic. These results provide another piece of evidence of the relatively young population history of North Africa. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] | ||||||||||