The solar dynamo and the convective rolls

The most sophisticated attempts to model the convection zone have yielded results in which the angular velocity increases outwards and the largest scales of convection take the form of banana cells aligned with the rotation axis. However, not only does the sign of the angular velocity gradient present problems for dynamo theory, but attempts to detect banana type cells have so far been unsuccessful. Although by no means conclusive, current tracer, spectropic, and radiative data all tend to support models of azimuthal rolls encircling the axis as the fundamental mode.It is shown here that convective upflows and downflows are preferentially generated along the rotation axis and thus initially the large-scale eddies may take the form of azimuthal rolls surrounding the poles. It is then shown that such a system may generate a progressive dynamo wave propagating from pole to equator. Since Parker has shown that an azimuthal magnetic toroid can generate a thermal shadow above it which suppresses its buoyancy, the corresponding temperature deficit so formed becomes the natural site for the downflow of the azimuthal rolls. Thus as the dynamo propagates towards the equator, so will the convective rolls. Finally the compatibility of the most recent helioseismology data with the azimuthal roll model is discussed.Solar Cycle Workshop Paper.     

Diurnal variations in,and influences on,concentrations of particulate and dissolved arsenic and metals in the mildly alkaline Wallkill River,New Jersey,USA

Diurnal variations in particulate and dissolved As and metal concentrations were observed in mildly alkaline water from a wetlands site on the Wallkill River in northwestern New Jersey. The site, underlain by glacial sediments over dolomite bedrock, is 10 km downstream from a mined area of the Franklin Marble, host to Zn ores, also As and Mn minerals. In mid-September 2005, maxima and minima in dissolved-oxygen-concentration and pH, typically caused by photosynthesis and respiration, occurred at 2000 and 0800 hours. Concentrations of dissolved As (1.52–1.95 μg/L) peaked at dusk (2000 hours), whereas dissolved Mn and Zn concentrations (76.5–96.9 and 8.55–12.8 μg/L, respectively) were lowest at dusk and peaked at 1000 hours. These opposing cycles probably reflect sorption and desorption of As (an anion), and Mn and Zn (cations) as pH varied throughout the 24-h period. Doubly-peaked cycles of B, Cl, SO₄, and nutrients also were observed; these may result from upstream discharges of septic-system effluent. Both recoverable amd particulate Al, Fe, Mn, and Zn concentrations peaked between 0200 and 0600 hours. The particulate metals cycle, with perturbations at 0400 hours, may be influenced by biological activity.     

Common cause or common concern? The role of common lands in the post-productivist countryside

Summary The aim of this paper is to contribute towards a better understanding of the contemporary position of commons as a land resource, and to evaluate whether commons have a distinct role to play in today's 'post-productivist' countryside. Following the government's recent recognition of the multi-functional role of commons, the paper sets out to investigate whether this can be achieved through existing agri-environmental schemes. A case study of commons in the Cambrian Mountains (Wales) enables an assessment of the compatibility of one recent agri-environmental scheme, the ESA scheme, with commons management. It is concluded that new legislation and policy are needed, and that agri-environmental policy may provide an opportunity to develop a framework within which the management of common land can be improved to meet conservation and amenity as well as farming objectives.     

Measuring surface-layer fluxes of heat and momentum using optical scintillation

An experiment is described showing that an optical scintillation instrument gives reliable values of heat and momentum fluxes in the surface layer, subject to the usual restrictions of homogeneity and steady state. This instrument measures the turbulence inner scale and refractive-index structure parameter, which are used to obtain the fluxes from Monin-Obukhov similarity relationships. The instrument gives space-averaged values over a propagation path that can range in length from tens to hundreds of meters. The history of the use of optical propagation to estimate fluxes is reviewed.     

Sediment accumulation rates in Conowingo reservoir as determined by man-made and natural radionuclides

The Susquehanna River is the major contributor to sediment loadings in the Chesapeake Bay. Because many environmental contaminants are associated with suspended particulates, the degree of particle retention within the reservoirs of the lower Susquehanna River is an important consideration in evaluating contaminant loadings to the Chesapeake Bay. Profiles of weapons-test Cs-137, nuclear power plant-related Cs-134 and Cs-137, and naturally-derived Pb-120 were used to estimate rates of sediment accretion in the conowingo Reservioir, an impoundment of the Susquehanna River along the Maryland-Pennsylvania border. Net accretion rates ranged from about 2 cm yr^?1 downstream of a nuclear power plant cooling discharge to a high of about 7 cm yr^?1 at the mount of an incoming creek. Slight, but consistent, increases in the annual rate of accretion since the creation of the reservoir in 1928 are apparent. The current net average annual sediment load reatined by the reservoir is estimated to be 0.4×10⁶ to 1.5 × 10⁶ metric tons yr^?1. The retained sediment load represents about 8–23% of the long-time average sediment input to the reservoir.     

The Taylor Creek Rhyolite of New Mexico: a rapidly emplaced field of lava domes and flows

The Tertiary Taylor Creek Rhyolite of southwest New Mexico comprises at least 20 lava domes and flows. Each of the lavas was erupted from its own vent, and the vents are distributed throughout a 20 km by 50 km area. The volume of the rhyolite and genetically associated pyroclastic deposits is at least 100 km³ (denserock equivalent). The rhyolite contains 15%–35% quartz, sanidine, plagioclase, ±biotite, ±hornblende phenocrysts. Quartz and sanidine account for about 98% of the phenocrysts and are present in roughly equal amounts. With rare exceptions, the groundmass consists of intergrowths of fine-grained silica and alkali feldspar. Whole-rock major-element composition varies little, and the rhyolite is metaluminous to weakly peraluminous; mean SiO₂ content is about 77.5±0.3%. Similarly, major-element compositions of the two feldsparphenocryst species also are nearly constant. However, whole-rock concentrations of some trace-elements vary as much as several hundred percent. Initial radiometric age determinations, all K–Ar and fission track, suggest that the rhyolite lava field grew during a period of at least 2 m.y. Subsequent ⁴⁰Ar/³⁹Ar ages indicate that the period of growth was no more than 100 000 years. The time-space-composition relations thus suggest that the Taylor Creek Rhyolite was erupted from a single magma reservoir whose average width was at least 30 km, comparable in size to several penecontemporaneous nearby calderas. However, this rhyolite apparently is not related to a caldera structure. Possibly, the Taylor Creek Phyolite magma body never became sufficiently volatile rich to produce a large-volume pyroclastic eruption and associated caldera collapse, but instead leaked repeatedly to feed many relatively small domes and flows.The new ⁴⁰Ar/³⁹Ar ages do not resolve preexisting unknown relative-age relations among the domes and flows of the lava field. Nonetheless, the indicated geologically brief period during which Taylor Creek Rhyolite magma was erupted imposes useful constraints for future evaluation of possible models for petrogenesis and the origin of trace-element characteristics of the system.     

Comments on ’a Numerical Simulation of Boundary-Layer Flows Near Shelterbelts‘ by H. Wang and E. Takle

We implemented the windbreak model of Wang and Takle to investigate whythose authors could have obtained better agreement with the Bradley andMulhearn wind reduction measurements in the far lee of a fence, than wasobtained by Wilson using a very similar model. According to our experiencethe improvement of the Wang-Takle simulations (relative to Wilson's)largely arises from their having used a too-shallow computational domain(8H, versus Wilson's 47H; H being the windbreak height).