Energetics of a double flare on November 8, 1980

Here we complete an energy balance analysis of a double impulsive hard X-ray flare. From spatial observations, we deduce both flares probably occur in the same loop within the resolution of the data. For the first flare, the energy in the fast electrons (assuming a thick-target model) is comparable to the convective up-flow energy, suggesting that these are related successive modes of energy storage and transfer. The total energy lost through radiation and conduction, 2.0 × 10²⁸ erg, is comparable to the energy in fast electrons 2.5 × 10²⁸ erg. For the second flare, the energy in the fast electrons is more than one order of magnitude greater than the energy of the convective up-flow. Total energy losses are within a factor of two lower than the calculated fast electron energy. We interpret the observations as showing that the first flare occurred in a small loop with fast electrons heating the chromosphere and resulting in chromospheric evaporation increasing the density in the loop. For the second flare most of the heating occurred at the electron acceleration site. The two symmetrical components of the Ca xix resonance line and a high velocity down-flow of 115 km s ^–1 observed at the end of the second hard X-ray burst are consistent with the flare eruption (reconnection) region being high in the flare loop. The estimated altitude of the acceleration site is 5500 km above the photosphere.     

Great Microwave Bursts and hard X-rays from solar flares

The microwave and hard X-ray characteristics of 13 solar flares that produced microwave fluxes greater than 500 solar flux units have been analyzed. These Great Microwave Bursts were observed in the frequency range from 3 to 35 GHz at Bern, and simultaneous hard X-ray observations were made in the energy range from 30 to 500 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission spacecraft. The principal aim of this analysis is to determine whether or not the same distribution of energetic electrons can explain both emissions. The temporal and spectral behaviors of the microwaves as a function of frequency and the X-rays as a function of energy were tested for correlations, with results suggesting that optically thick microwave emission, at a frequency near the peak frequency, originates in the same electron population that produces the hard X-rays. The microwave emission at lower frequencies, however, is poorly correlated with emission at the frequency which appears to characterize this common source. A single-temperature and a multitemperature model were tested for consistency with the coincident X-ray and microwave spectra at microwave burst maximum. Four events are inconsistent with both of the models tested, and neither of the models attempts to explain the high-frequency part of the microwave spectrum. A source area derived on the basis of the single-temperature model agrees to within the uncertainties with the observed area of the one burst for which spatially resolved X-ray images are available.Swiss National Science Foundation Fellow from the University of Bern.Also Energy/Environmental Research Group, Incorporated, Tucson, Arizona, and Department of Physics and Astronomy, University of North Carolina, Chapel Hill. Present address: Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland.     

Book reviews

AUSTRALIA AND ITS URBAN “CENTRES (Urbanization of the Earth No. 6) by B. Hofmeister. 19 × 28 cm, xii and 254 pages. Gebruder Borntraeger: Berlin 1988 (ISBN 3 443 37008 X) DM130 (hard).

CONTEMPORARY AUSTRALIA: Explorations in Economy, Society and Geography by D. J. Walmsley and A. D. Sorenson. 19 × 25 cm, xxiv and 328 pages. Longman Cheshire: Melbourne 1988 (ISBN 0 58271150 9) $A29.95 (soft).

WATERING THE GARDEN STATE: Water, Land and Community in Victoria 1834–1988 by J. M. Powell. 16 × 24 cm, xv and 319 pages. Allen & Unwin: Sydney 1989 (ISBN 0 04 3600 74 3) SA39.95 (hard); (ISBN 0 04 364024 9) SA24.95 (soft).

THE BUREAUCRATS DOMAIN. Space and the Public Interest in Victoria 1836–1884 by R. Wright. 15 × 23 cm, xv and 350 pages. Oxford University Press: Melbourne 1989 (ISBN 0 19 554866 3) $A39.95 (hard).

SOUTHERN APPROACHES: Geography in New Zealand edited by P. G. Holland and W. B. Johnston. 17 × 25 cm, 361 pages. New Zealand Geographical Society: Christchurch 1987 (ISBN 0 9597 863 0 9) $A56.50 (soft).     

Garnet growth at high- and ultra-high pressure conditions and the effect of element fractionation on mineral modes and composition

In this paper we show that thermodynamic forward modelling, using Gibbs energy minimisation with consideration of element fractionation into refractory phases and/or liberated fluids, is able to extract information about the complex physical and chemical evolution of a deeply subducted rock volume. By comparing complex compositional growth zonations in garnets from high-and ultra-high pressure samples with those derived from thermodynamic forward modelling, we yield an insight into the effects of element fractionation on composition and modes of the co-genetic metamorphic phase assemblage. Our results demonstrate that fractionation effects cause discontinuous growth and re-crystallisation of metamorphic minerals in high pressure rocks. Reduced or hindered mineral growth at UHP conditions can control the inclusion and preservation of minerals indicative for UHP metamorphism, such as coesite, thus masking peak pressure conditions reached in subducted rocks.Further, our results demonstrate that fractional garnet crystallisation leads to strong compositional gradients and step-like zonation patterns in garnet, a feature often observed in high-and ultra-high pressure rocks. Thermodynamic forward modelling allows the interpretation of commonly observed garnet growth zonation patterns in terms of garnet forming reactions and the relative timing of garnet growth with respect to the rock's pressure–temperature path. Such a correlation is essential for the determination of tectonic and metamorphic rates in subduction zones as well as for the understanding of trace element signatures in subduction related rocks. It therefore should be commonplace in the investigation of metamorphic processes in subduction zones.     

GPS,Galileo, QZSS and IRNSS differential ISBs: estimation and application

Knowledge of inter-system biases (ISBs) is essential to combine observations of multiple global and regional navigation satellite systems (GNSS/RNSS) in an optimal way. Earlier studies based on GPS, Galileo, BDS and QZSS have demonstrated that the performance of multi-GNSS real-time kinematic positioning is improved when the differential ISBs (DISBs) corresponding to signals of different constellations but transmitted at identical frequencies can be calibrated, such that only one common pivot satellite is sufficient for inter-system ambiguity resolution at that particular frequency. Recently, many new GNSS satellites have been launched. At the beginning of 2016, there were 12 Galileo IOV/FOC satellites and 12 GPS Block IIF satellites in orbit, while the Indian Regional Navigation Satellite System (IRNSS) had five satellites launched of which four are operational. More launches are scheduled for the coming years. As a continuation of the earlier studies, we analyze the magnitude and stability of the DISBs corresponding to these new satellites. For IRNSS this article presents for the first time DISBs with respect to the L5/E5a signals of GPS, Galileo and QZSS for a mixed-receiver baseline. It is furthermore demonstrated that single-frequency (L5/E5a) ambiguity resolution is tremendously improved when the multi-GNSS observations are all differenced with respect to a common pivot satellite, compared to classical differencing for which a pivot satellite is selected for each constellation.     

Snow depth estimation accuracy using a dual-interface GPS-IR model with experimental results

GPS Solutions - Measuring snow depth using the GPS interferometric reflectometry is an active microwave remote sensing technique and an emerging approach because of its relatively large spatial...     

Evaluation and comparison of spatial interpolators

This study evaluates 15 different estimators to determine their relative merits in estimating block concentrations at contaminant waste sites. The evaluation was based on 54 subsets of data drawn from an exhaustive set of 19,800 data. For each subset, 198 block estimates were made with each estimator. The measurements of estimation quality were a linear loss function and a more standard statistic, the mean square error. The linear loss function showed that seven of the estimators produced scores close enough to be within the same statistical population. Results based on the mean square error were similar. The surprising results of this study were that inverse distance and inverse distance squared both produced better scores than kriging.     

Genesis and continuity of quaternary sand and gravel in glacigenic sediment at a proposed low-level radioactive waste disposal site in east-central Illinois

The Illinois Department of Nuclear Safety has characterized the Martinsville Alternative Site (MAS) for a proposed low-level radioactive waste disposal facility. The MAS is located in east-central Illinois approximately 1.6 km (1 mi) north of the city of Martinsville. Geologic investigation of the 5.5-km² (1380-acre) site revealed a sequence of chiefly Illinoian glacigenic sediments from 6 to 60 m (20–200 ft) thick overlying two major bedrock valleys carved in Pennsylvanian strata. Relatively permeable buried units include basal, preglacial alluvium; a complex of intraglacial and subglacial sediment; englacial deposits; and supraglacial fluvial deposits. Postglacial alluvium underlies stream valleys on and adjacent to the site. In most areas, the buried sand units are confined by low-permeability till, lacustrine sediment, colluvium, and loess. The distribution and thickness of the most extensive and continuous buried sand units have been modified considerably by subglacial erosion, and their distributions have been influenced by the buried bedrock valleys. The most continuous of the various sand units were deposited as preglacial and postglacial alluvium and are the uppermost and lowermost stratigraphic units at the alternative site. Sand units that were deposited in englacial or ice-marginal environments are less continuous. Aquifer pumping tests, potentiometric head data, and groundwater geochemistry analyses indicate minimal interaction of groundwater across localized interconnections of the permeable units.     

Survey of Rural Wells in Missouri for Pesticides and Nitrate

Two hundred and one rural wells were sampled in eight agricultural areas of Missouri. Samples were analyzed for 25 pesticides and nitrate. Forty-three percent of the wells sampled had at least one pesticide detection. Thirteen percent of the wells had at least one detection ≧ 1 ppb and these concentrations were confirmed. Only one well exceeded U.S. EPA Health Advisory levels. Twenty-two percent of the wells exceeded the U.S. EPA Drinking Water Standard for nitrate. Pesticide detections were most strongly correlated to well depth. Nitrate levels were primarily related to well depth, well construction methods, and well siting.     

Complementary Investigative Techniques for Site Assessment with Low-Level Contaminants

A remedial investigation (RI) was performed in an area downgradient from an abandoned missile silo at Vandenberg Air Force Base, California, as part of the United States Air Force Installation Restoration Program (IRP). A number of complementary investigative techniques were used to assure a reliable assessment of site contamination. These included the review of aerial photographs, the use of an organic vapor analyzer (OVA) and carbon adsorption/mass spectrometer (MS) method to conduct a soil-gas survey; magnetic and electromagnetic geophysical surveys; bedrock permeability testing; and the chemical analysis of soil, sediment, surface water, and ground water samples. The results from this investigation revealed the presence of an undocumented landfill and a small trichloroethylene plume in ground water at concentrations ranging from 6.7 ppb to 31 ppb. The investigation also identified local ground water flow direction, provided strong evidence of the location of potential sources of contamination, and defined the downgradient extent of ground water contamination. Because the identified contaminants have not as yet reached the environmentally sensitive wetland at the base of the slope below this facility, there is still time to propose remedial alternatives that would serve to protect this environmentally sensitive area.