Distinguishing Propagation vs. Launch Physics of Astrophysical Jets and the Role of Experiments

The absence of other viable momentum sources for collimated flows leads to the likelihood that magnetic fields play a fundamental role in jet launch and/or collimation in astrophysical jets. To best understand the physics of jets, it is useful to distinguish between the launch region where the jet is accelerated and the larger scales where the jet propagates as a collimated structure. Observations presently resolve jet propagation, but not the launch region. Simulations typically probe the launch and propagation regions separately, but not both together. Here, I IDentify some of the physics of jet launch vs. propagation and what laboratory jet experiments to date have probed. Reproducing an astrophysical jet in the lab is unrealistic, so maximizing the benefit of the experiments requires clarifying the astrophysical connection.     

Hydraulic redistribution by deeply rooted grasses and its ecohydrologic implications in the southern Great Plains of North America

Perennial bioenergy crops with deep (>1 m) rooting systems, such as switchgrass (Panicum virgatum L.), are hypothesized to increase carbon storage in deep soil. Deeply rooted plants may also affect soil hydrology by accessing deep soil water for transpiration, which can affect soil water content and infiltration in deep soil layers, thereby affecting groundwater recharge. Using stable H and O isotope (δ²H and δ¹⁸O) and ³H values, we studied the soil water conditions at 20–30 cm intervals to depths of 2.4–3.6 m in paired fields of switchgrass and shallow rooted crops at three sites in the southern Great Plains of North America. We found that soil under switchgrass had consistently higher soil water content than nearby soil under shallow-rooted annual crops by a margin of 15%–100%. Soil water content and isotopic depth profiles indicated that hydraulic redistribution of deep soil water by switchgrass roots explained these observed soil water differences. To our knowledge, these are the first observations of hydraulic redistribution in deeply rooted grasses, and complement earlier observations of dynamic soil water fluxes under shallow-rooted grasses. Hydraulic redistribution by switchgrass may be a strategy for drought avoidance, wherein the plant may actively prevent water limitation. This raises the possibility that deeply rooted grasses may be used to passively subsidize soil water to more shallow-rooted species in inter-cropping arrangements.     

Closure of a hyperextended system in an orogenic lithospheric pop‐up,Western Pyrenees: The role of mantle buttressing and rift structural inheritance

The Early Cretaceous hyperextended Mauléon rift is localized in the north‐western Pyrenean orogen. We infer the Tertiary evolution of the Mauléon basin through the restoration of a 153‐km‐long crustal‐scale balanced cross‐section of the Pyrenean belt, which documents at least 67 km (31%) of orogenic shortening in the Western Pyrenees. Initial shortening, accommodated through inversion of inherited crustal structures, led to formation of a pop‐up structure, in which the opposite edges underwent similar shortening with different tectonic reactivation styles, localized versus. distributed. Underthrusting of the Iberian margin accommodated further convergence, forming the Axial Zone antiformal stack of crustal nappes within a lithospheric pop‐up. Thin‐skinned and thick‐skinned structures propagated outward from the heart of this pop‐up, a block of strong mantle acting as a buttress inhibiting complete inversion of the Mauléon rift basin.     

Stately home geology: the building stones of Tyntesfield Manor

Visiting a stately home open to the public can be a geological excursion in addition to a journey into social history. This is an experience akin to Darwin speculating whether his next landfall would present him with ‘igneous or metamorphic’ rocks to test his early geological knowledge, even before he had received Lyell's Principles when the Beagle reached Buenos Aires. In Britain the prospects are good when the house is Victorian or Edwardian, and we are facing the rich industrialists investing his wealth in opulent interiors within a High Gothic external architecture. In the West of England, this can be tested by a visit to Tyntesfield, a mansion acquired by the National Trust to the south of Bristol in South West England in 2002. Reputed to be little changed from being a family home, it has become a place where booking a timed visit is advised, such is public interest. It also has an added interest in that the Trust is in receipt of a grant from the Heritage Lottery Fund in order to carry out repairs and refurbishment of the many ancillary buildings of the landscaped estate. The work is proceeding alongside public visits, so offering insight into building conservation.     

Environmental controls of wood entrapment in upper Midwestern streams

Wood deposited in streams provides a wide variety of ecosystem functions, including enhancing habitat for key species in stream food webs, increasing geomorphic and hydraulic heterogeneity and retaining organic matter. Given the strong role that wood plays in streams, factors that influence wood inputs, retention and transport are critical to stream ecology. Wood entrapment, the process of wood coming to rest after being swept downstream at least 10 m, is poorly understood, yet important for predicting stream function and success of restoration efforts. Data on entrapment were collected for a wide range of natural wood pieces (n = 344), stream geomorphology and hydraulic conditions in nine streams along the north shore of Lake Superior in Minnesota. Locations of pieces were determined in summer 2007 and again following an overbank stormflow event in fall 2007. The ratio of piece length to effective stream width (length ratio) and the weight of the piece were important in a multiple logistic regression model that explained 25% of the variance in wood entrapment. Entrapment remains difficult to predict in natural streams, and often may simply occur wherever wood pieces are located when high water recedes. However, this study can inform stream modifications to discourage entrapment at road crossings or other infrastructure by applying the model formula to estimate the effective width required to pass particular wood pieces. Conversely, these results could also be used to determine conditions (e.g. pre‐existing large, stable pieces) that encourage entrapment where wood is valued for ecological functions. Copyright © 2010 John Wiley & Sons, Ltd.     

Anthropogenic activities amplify wildfire occurrence in the Zagros eco-region of western Iran

Natural Hazards - The aim of this study was to improve our understanding of factors that affect the spatial distribution of wildfire occurrences at the regional scale. We employed the random...     

An early warning system for wave-driven coastal flooding at Imperial Beach,CA

Natural Hazards - Waves overtop berms and seawalls along the shoreline of Imperial Beach (IB), CA when energetic winter swell and high tide coincide. These intermittent, few-hour long events flood...     

Lagrangian modelling of multi-dimensional advection-diffusion with space-varying diffusivities: theory and idealized test cases

To efficiently simulate the advection-diffusion processes along and across density surfaces, we need to deal with a diffusivity tensor containing off-diagonal elements (Redi, J Phys Oceanogr, 12:1154–1158, 1982). In the present paper, the Lagrangian model, in case of a space-varying diffusivity tensor, is developed. This random walk model is applied for two idealized test cases for which the analytical solutions are known. Results of the testing show that the Lagrangian approach provides accurate and effective solutions of advection-diffusion problems for general diffusivity tensor.