Quasi-Wavelet Model of Von Kármán Spectrum of Turbulent Velocity Fluctuations

The von Kármán spectra of turbulent temperature andvelocity fluctuations have been widely used in the literature on turbulenceand electromagnetic, seismic, and acoustic wave propagation in random media.In this paper we provide a phenomenological motivation for the vonKármán velocity spectrum in terms of the quasi-wavelet model ofturbulence developed recently. In this model, turbulence is represented as asuperposition of self-similar localized eddies of many different scales. Wefind a functional form for these eddies that yields the von Kármán velocity spectrum exactly. We also show that other eddy functions producevelocity spectra that have the same general form as the von Kármán spectrum, and we consider possible quasi-wavelet representations of the`Kansas' spectrum and the `-1' spectrum. We also present asystematic determination, based on turbulence similarity theories, of theparameters of the von Kármán spectra of temperature and velocityfluctuations in an unstable atmospheric boundary layer.     

Source enrichment processes responsible for isotopic anomalies in oceanic island basalts

A new method has been developed to separate the compositional variations in ocean island basalts into those that result from variations in source composition and from the melting process itself. The approach depends on correlations between isotope ratios, which can only come from source inhomogeneities, and elemental concentrations. Analysis of three data sets shows that the inhomogeneities beneath Theistareykir, in NE Iceland, Kilauea and Pitcairn can be produced by subduction of oceanic islands and volcanic ridges. The thicknesses of the lithosphere on which such islands were constructed and potential temperatures of the plumes that produced them can be estimated from the geochemical observations. Model ages are harder to determine, though simple assumptions give about 400 Ma for the Theistareykir source and 1.2 Ga for Kilauea. The model may also provide a physical explanation for the commonly used isotopic classification of ocean island basalts, with the isotopic composition changing from HIMU through EMII to EMI as the melt fraction increases. These results have been obtained from a small number of data sets obtained from ocean island basalts erupted in small areas during short time intervals. More such observations are needed to discover whether geochemical observations from other islands are consistent with the same model.     

Cusp geometry in MHD simulations

The MHD simulations described here show that the latitude of the high-altitude cusp decreases as the IMF swings from North to South, that there is a pronounced dawn–dusk asymmetry at high-altitude associated with a dawn–dusk component of the IMF, and that at the same time there is also a pronounced dawn–dusk asymmetry at low-altitude. The simulations generate a feature that represents what has been called the cleft. It appears as a tail (when the IMF has a B_y component) attached to the cusp, extending either toward the dawn flank or the dusk flank depending on the dawn–dusk orientation of the IMF. This one-sided cleft connects the cusp to the magnetospheric sash. We compare cusp geometry predicted by MHD simulations against published observations based on Hawkeye and DMSP data. Regarding the high-altitude predictions, the comparisons are not definitive, mainly because the observations are incomplete or mutually inconsistent. Regarding the low-altitude prediction of a strong dawn–dusk asymmetry, the observations are unambiguous and are in good qualitative agreement with the prediction.     

Gamma-ray bursts and Swift

Now that the Swift satellite is up and running, Paul O'Brien, Julian Osborne and Keith Mason report on the ideas and observations that this fast-moving autonomous observatory is investigating.     

Residues of toxaphene decrease in estuarine fish after removal of contaminated sediments

To determine if toxaphene residues in edible fish tissue decreased after removal of contaminated sediments from an estuarine site in 1999, 51 composite samples representing six finfish species were collected in 2001 and analyzed using gas chromatography with electron capture and negative ion mass spectrometric detection. The grand mean total toxaphene residue concentration on a wet weight basis (ΣTOX_wet) was 1,400 ± 3,500 ng g⁻¹ (range: < 18 to 18,000 ng g⁻¹) and was positively correlated with extractable lipid. On a lipid basis, the mean ΣTOX_lip was 26 ± 33 μg g¹, which decreased with increasing distance from the study site. Although benthically-oriented species, such as spot (Leiostomus xanthurus) and striped mullet (Mugil cephalus), exhibited higher mean ΣTOX_wet than those of higher trophic level fish, mean ΣTOX_lip were not significantly different among species. The grand mean ΣTOX for 2001 was 3.8 (wet) and 2.6 (lipid) times less than corresponding preremedial action (1997) concentrations, suggesting that bioavailable toxaphene residues in this system have been reduced. Forage species, such as croaker (Micropogonias undulatus), mullet, and spot, preferentially accumulate toxaphene residues in this system and may serve as vectors of organochlorine contaminants in the estuarine and coastal ocean food web.     

Characteristics of Autumn Precipitation Trends in the Northeastern United States

Previous research has shown that the northeastern United States experienced a significant increase in precipitation during the twentieth century, especially during the autumn. This shift toward wetter conditions can be explained by examining trends in daily precipitation characteristics. Early season precipitation changes in the western portion of the study area were associated with increases in the frequency of precipitation‐days. Later in the season a coincident increase in precipitation‐day intensity enhanced these trends. Tropical storms had little influence on autumn precipitation increases. The study suggests that, instead, changes in regional atmospheric circulation may be responsible for changing precipitation characteristics.     

Real-time measurement of volcanic SO2 emissions: validation of a new UV correlation spectrometer (FLYSPEC)

A miniaturized, lightweight and low-cost UV correlation spectrometer, the FLYSPEC, has been developed as an alternative for the COSPEC, which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes. Field experiments have been conducted with the FLYSPEC at diverse volcanic systems, including Masaya (Nicaragua), Poás (Costa Rica), Stromboli, Etna and Vulcano (Italy), Villarica (Chile) and Kilauea (USA). We present here those validation measurements that were made simultaneously with COSPEC at Kilauea between March 2002 and February 2003. These experiments, with source emission rates that ranged from 95 to 1,560 t d⁻¹, showed statistically identical results from both instruments. SO₂ path-concentrations ranged from 0 to >1,000 ppm-m with average correlation coefficients greater than r ²=0.946. The small size and low cost create the opportunity for FLYSPEC to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed.     

CO2 Mitigation by Agriculture: An Overview

Agriculture currently contributes significantly to the increase of CO2 in the atmosphere, primarily through the conversion of native ecosystems to agricultural uses in the tropics. Yet there are major opportunities for mitigation of CO2 and other greenhouse gas emissions through changes in the use and management of agricultural lands. Agricultural mitigation options can be broadly divided into two categories: (I) strategies to maintain and increase stocks of organic C in soils (and biomass), and (ii) reductions in fossil C consumption, including reduced emissions by the agricultural sector itself and through agricultural production of biofuels to substitute for fossil fuels.Reducing the conversion of new land to agriculture in the tropics could substantially reduce CO2 emissions, but this option faces several difficult issues including population increase, land tenure and other socio-political factors in developing countries. The most significant opportunities for reducing tropical land conversions are in the humid tropics and in tropical wetlands. An important linkage is to improve the productivity and sustainability of existing agricultural lands in these regions.Globally, we estimate potential agricultural CO2 mitigation through soil C sequestration to be 0.4-0.9 Pg C y-1, through better management of existing agricultural soils, restoration of degraded lands, permanent "set-asides" of surplus agricultural lands in temperate developed countries and restoration of 10-20% of former wetlands now being used for agriculture. However, soils have a finite capacity to store additional C and therefore any increases in C stocks following changes in management would be largely realized within 50-100 years.Mitigation potential through reducing direct agricultural emissions is modest, 0.01-0.05 Pg C y-1. However, the potential to offset fossil C consumption through the use of biofuels produced by agriculture is substantial, 0.5-1.6 Pg C y-1, mainly through the production of dedicated biofuel crops with a smaller contribution (0.2-0.3 Pg C y-1) from crop residues.Many agricultural mitigation options represent "win-win" situations, in that there are important side benefits, in addition to CO2 mitigation, that could be achieved, e.g. improved soil fertility with higher soil organic matter, protection of lands poorly suited for permanent agriculture, cost saving for fossil fuel inputs and diversification of agricultural production (e.g. biofuels). However, the needs for global food production and farmer/societal acceptability suggest that mitigation technologies should conform to: (I) the enhancement of agricultural production levels in parts of the world where food production and population demand are in delicate balance and (ii) the accrual of additional benefits to the farmer (e.g., reduced labor, reduced or more efficient use of inputs) and society at large.