Processes and rates of sediment and wood accumulation in headwater streams of the Oregon Coast Range,USA

Channels that have been scoured to bedrock by debris flows provide unique opportunities to calculate the rate of sediment and wood accumulation in low‐order streams, to understand the temporal succession of channel morphology following disturbance, and to make inferences about processes associated with input and transport of sediment. Dendrochronology was used to estimate the time since the previous debris flow and the time since the last stand‐replacement fire in unlogged basins in the central Coast Range of Oregon. Debris flow activity increased 42 per cent above the background rate in the decades immediately following the last wildfire. Changes in wood and sediment storage were quantified for 13 streams that ranged from 4 to 144 years since the previous debris flow. The volume of wood and sediment in the channel, and the length of channel with exposed bedrock, were strongly correlated with the time since the previous debris flow. Wood increased the storage capacity of the channel and trapped the majority of the sediment in these steep headwater streams. In the absence of wood, channels that have been scoured to bedrock by a debris flow may lack the capacity to store sediment and could persist in a bedrock state for an extended period of time. With an adequate supply of wood, low‐order channels have the potential of storing large volumes of sediment in the interval between debris flows and can function as one of the dominant storage reservoirs for sediment in mountainous terrain. Copyright © 2003 John Wiley & Sons, Ltd.     

Towards semantic‐aware multiple‐aspect trajectory similarity measuring

The large amount of semantically rich mobility data becoming available in the era of big data has led to a need for new trajectory similarity measures. In the context of multiple‐aspect trajectories, where mobility data are enriched with several semantic dimensions, current state‐of‐the‐art approaches present some limitations concerning the relationships between attributes and their semantics. Existing works are either too strict, requiring a match on all attributes, or too flexible, considering all attributes as independent. In this article we propose MUITAS, a novel similarity measure for a new type of trajectory data with heterogeneous semantic dimensions, which takes into account the semantic relationship between attributes, thus filling the gap of the current trajectory similarity methods. We evaluate MUITAS over two real datasets of multiple‐aspect social media and GPS trajectories. With precision at recall and clustering techniques, we show that MUITAS is the most robust measure for multiple‐aspect trajectories.     

Century-scale nitrogen and phosphorus controls of the carbon cycle

In recent decades, humans have become a very important force in the Earth system, demonstrating that emissions (gaseous, liquid, and solid) are the cause of many of our environmental issues. These emissions are responsible for major global reorganizations of the biogeochemical cycles. The oceans are now a net sink of atmospheric CO₂, whereas in their preindustrial state they were a source; the trophic state of the coastal oceans is progressively moving toward increased heterotrophy; and the terrestrial realm is now vacillating between trophic states, whereas in preindustrial times it was autotrophic. In this paper, we present model calculations that underscore the role of human-induced perturbations in changing Earth's climate, specifically the role of anthropogenic nitrogen and phosphorus in controlling processes in the global carbon cycle since the year 1850 with projections to the year 2035. Our studies show that since the late 1940's emissions of nitrogen and phosphorus have been sequestered in the terrestrial living phytomass and groundwater. This nutrient-enhanced fertilization of terrestrial biota, coupled with rising atmospheric CO₂ and global temperature, has induced a sink of anthropogenic CO₂ that roughly balances the emission of CO₂ owing to land use change. In the year 2000, for example, the model-calculated terrestrial biotic sink was 1730 Mtons C/year, while the emission of CO₂ from changes in land use was 1820 Mtons C/year, a net flux of 90 Mtons C/year emitted to the atmosphere. In the global aquatic environment, enhanced terrestrial inputs of biotically reactive phosphorus (about 8.5 Mtons P/year) and inorganic nitrogen (about 54 Mtons N/year), have induced increased new production and burial of organic carbon in marine sediments, which is a small sink of anthropogenic CO₂. It is predicted that the response of the global land reservoirs of C, N, and P to sustained anthropogenic perturbations will be maintained in the same direction of change over the range of projected scenarios of global population increase and temperature change for the next 35 years. The magnitude of change is significantly larger when the global temperature increase is maximum, especially with respect to the processes of remobilization of the biotically important nutrients nitrogen and phosphorus.     

The signature of ENSO in the Northern Hemisphere midlatitude seasonal mean flow and high-frequency intraseasonal variability

Summary The impact of pronounced positive and negative sea surface temperature (STT) anomalies in the tropical Pacific associated with the El Niño/Southern Oscillation (ENSO) phenomenon on the atmospheric circulation in the Northern Hemisphere extratropics during the boreal winter season is investigated. This includes both the impact on the seasonal mean flow and on the intraseasonal variability on synoptic time scales. Moreover, the interaction between the transient fluctuations on these times scales and the mean circulation is examined. Both data from an ensemble of five simulations with the ECHAM3 atmospheric general circulation model at a horizontal resolution of T42 each covering the period from 1979 through 1992 and operational analyses from ECMWF for the corresponding period are examined. In each of the simulations observed SSTs for the period of investigation are given as lower boundary forcing, but different atmospheric initial conditions are prescribed.The simulations with ECHAM3 reveal a distinct impact of the pronounced SST-anomalies in the tropical Pacific on the atmospheric circulation in the Northern Hemisphere extratropics during El Niño as well as during La Niña events. These changes in the atmospheric circulation, which are found to be highly significant in the Pacific/North American as well as in the Atlantic/European region, are consistent with the essential results obtained from the analyses. The pronounced SST-anomalies in the tropical Pacific lead to changes in the mean circulation, which are characterized by typical circulation patterns. These changes in the mean circulation are accompanied by marked variations of the activity of the transient fluctuations on synoptic time scales, that are changes in both the kinetic energy on these time scales and the atmospheric transports of momentum and heat accomplished by the short baroclinic waves. The synoptic disturbances, on the other hand, play also an important role in controlling the changes in the mean circulation associated with the ENSO phenomenon. They maintain these typical circulation patterns via barotropic, but counteract them via baroclinic processes.The hypothesis of an impact of the ENSO phenomenon in the Atlantic/European region can be supported. As the determining factor the intensification (reduction) of the Aleutian low and the simultaneous reduction (intensification) of the Icelandic low during El Niño and during La Niña events respectively, is identified. The changes in the intensity of the Aleutian low during the ENSO-events are accompanied by an alteration of the transport of momentum caused by the short baroclinic waves over the North American continent in such a way that the changes in the intensity of the Icelandic low during El Niño as well as during La Niña events are maintained.With 16 Figures     

Interpretation,reliability and accuracies of parameters deduced by the spaced antenna method in middle atmosphere applications

The spaced antenna method has proved to be an important and relatively inexpensive radar technique for making measurements of atmospheric wind velocities and other parameters. This discussion examines the reliability and accuracies of various parameters which can be measured with the technique.After a brief introduction, a series of comparisons of winds measured by the spaced antenna method and simultaneously by other techniques are presented. It is concluded that when using weak partial reflections in the height range 0–100km, the spaced antenna technique provides reliable estimates of the neutral air motion. Following this the assumptions made in applying the method are considered in more detail. The possibility of systematic errors and the likelihood of erroneous measurements are examined, and the accuracy of any particular measurement of wind speed is discussed. Previous objections to the technique are discussed, and in general shown to be invalid.Other parameters apart from wind speeds can be measured with the spaced antenna technique, such as pattern scale, the rate of natural fading, and angles of arrival. The meanings of these parameters are discussed in terms of physical quantities such as turbulent energy dissipation rates, small-scale gravity wave velocity fluctuations, and aspect sensitivities of scatterers, and it is indicated when and how these derived parameters can be applied to deduce meaningful physical quantities. The need for great caution in making these interpretations is discussed; for example it is not always possible to use the rate of natural fading to estimate the intensity of turbulence, although in some cases this is possible. Finally, interferometric applications of spaced antenna systems are discussed.     

A method for evaluating horizontal well pumping tests

Predicting the future performance of horizontal wells under varying pumping conditions requires estimates of basic aquifer parameters, notably transmissivity and storativity. For vertical wells, there are well-established methods for estimating these parameters, typically based on either the recovery from induced head changes in a well or from the head response in observation wells to pumping in a test well. Comparable aquifer parameter estimation methods for horizontal wells have not been presented in the ground water literature. Formation parameter estimation methods based on measurements of pressure in horizontal wells have been presented in the petroleum industry literature, but these methods have limited applicability for ground water evaluation and are based on pressure measurements in only the horizontal well borehole, rather than in observation wells. This paper presents a simple and versatile method by which pumping test procedures developed for vertical wells can be applied to horizontal well pumping tests. The method presented here uses the principle of superposition to represent the horizontal well as a series of partially penetrating vertical wells. This concept is used to estimate a distance from an observation well at which a vertical well that has the same total pumping rate as the horizontal well will produce the same drawdown as the horizontal well. This equivalent distance may then be associated with an observation well for use in pumping test algorithms and type curves developed for vertical wells. The method is shown to produce good results for confined aquifers and unconfined aquifers in the absence of delayed yield response. For unconfined aquifers, the presence of delayed yield response increases the method error.     

An interesting nebular object in LDN 288

In this paper the results of multiwavelength investigation of an unusual nebular object SNO 85 are presented. In 2MASS images this object looks like a star with a jet. In DSS2 R image the end of the jet is connected with an interesting symmetric structure, consisting of arcs and loops. Such a structure is seen also in the opposite direction from the central star; it favors the existence of two opposite jets, which repeat the rotation and precession movements of the central star. The results of ¹²CO observations of the dark nebula LDN 288, connected with SNO 85, are also given. From these observations the following results were obtained: SNO 85 is situated in a dense condensation and the neighbor B type star GSC 0625400181 is surrounded by a hollow cavity. The velocity of the dark cloud is ∼2.5 km/s and its distance is estimated as (380–990) pc. The object SNO 85 itself is associated with an IRAS point source IRAS 17547-1832, the infrared colors of this source are typical for a non-evolved source embedded in the dense dark cloud. This region is perhaps a star formation one because there is also another star with a straight jet in the vicinity of B type star GSC 0625400181. Published in Astrofizika, Vol. 49, No. 4, pp. 621–629 (August 2006).     

Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos,Western Australia

Prehistoric storm records are relatively scarce in most parts of the world. This article presents storm records derived from coral rubble‐based geological archives of the Houtman Abrolhos Archipelago located off the west coast of Australia, where the southernmost coral reefs of the Indian Ocean are found. Winter storm swell from the circum‐Antarctic ‘Brave Westerlies’, as well as tropical cyclone waves, have left numerous ridge systems on dozens of islands of the archipelago, all composed of coral rubble from adjacent reefs. At three islands, seven ridge systems were dated by three different methods: U‐series (68 dates), radiocarbon (64 dates), electron spin resonance (7 dates); 139 radiometric dates span the last 5500 years of the Holocene. In contrast to the geomorphological interpretation, the age sequences show ‘inversions’, hiatuses and different ages for the same ridge, all pointing to complicated ridge formation processes. Time gaps, some exceeding 1000 years, are interpreted as phases of erosion and not as phases without storm activity. Copyright © 2012 John Wiley & Sons, Ltd.