Glacio-lacustrine stratigraphy,aquifer characterization and contaminant transport: a case study in South Lake Tahoe,California, USA     

Craig W. Morgan  Graham M. Kent  Gordon G. Seitz  Michaela Novak 《Hydrogeology Journal》2008,16(5):981-994

A hydrogeologic model that has been used by many researchers and consultants to describe an area of South Lake Tahoe, California, USA impacted by MTBE contamination describes a relatively homogeneous unconfined aquifer comprised of poorly sorted glacial outwash deposits, within which water-supply wells are able to exert significant alteration in natural groundwater flow. A re-examination of the area’s hydrogeology is presented, which supports a layered heterogeneous aquifer system constructed of alternating fine and coarser-grained glacio-lacustrine depositional units. This re-evaluation was accomplished through a review of lithologic logs across an area of approximately 1 km², combined with observations of significant hydraulic head differences and knowledge of the depositional environments controlled by Pleistocene Lake Tahoe high stands. Many of the fine-grained units observed at depths from 6 to 15 m, although relatively thin, are generally continuous and serve as significant barriers to groundwater flow. The vertical migration of contamination across these fine-grained units to deeper groundwaters was facilitated by cross-screened monitoring wells installed as part of site investigation activities. This conclusion highlights the importance of geologic characterization and proper monitoring well construction at contaminated site investigations.

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Electronic supplementary material   The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Michaela NovakEmail:

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The wavelength variation of the granule/intergranule contrast     

R. J. Bray 《Solar physics》1982,77(1-2):299-302

Modern measurements of the granule contrast are reviewed and compared with a curve showing the wavelength variation to be expected on the assumption of black-body emission as well as with the predictions of recent inhomogeneous models. The difference in effective temperature between granules and intergranular lanes is 270–280 K.  相似文献   

A refined measurement of the sunspot radiative flux deficit     

R. J. Bray 《Solar physics》1981,69(1):3-8

New measurements of the radiative flux deficits of two large sunspots are presented, based on detailed isophotometric maps. Results are given separately for umbrae and penumbrae. The umbral and penumbral deficits are 4–5 × 10¹⁰ and 1–1.5 × 10¹⁰ erg cm^–2 s^–1 respectively, the larger figures ref to the larger spot. Over limited areas centered on the umbral cores the deficits for the two spots amount to 76 and 86% of the photospheric flux.  相似文献   

Hydrothermal fluids associated with seafloor mineralization at two southern Kermadec arc volcanoes,offshore New Zealand   总被引：2，自引：0，他引：2  

Cornel E. de Ronde  Kevin Faure  Colin J. Bray  Debra A. Chappell  Ian C. Wright 《Mineralium Deposita》2003,38(2):217-233

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Appropriate model use for predicting elevations and inundation extent for extreme flood events     

Davor Kvočka  Roger A. Falconer  Michaela Bray 《Natural Hazards》2015,79(3):1791-1808

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Flood hazard assessment for extreme flood events     

Davor Kvočka  Roger A. Falconer  Michaela Bray 《Natural Hazards》2016,81(3):1569-1588

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Seasonal evaluation of rainfall estimation by four cumulus parameterization schemes and their sensitivity analysis     

Asnor Muizan Ishak  Michaela Bray  Renji Remesan  Dawei Han 《水文研究》2012,26(7):1062-1078

Sustainable water resources management require scientifically sound information on precipitation, as it plays a key role in hydrological responses in a catchment. In recent years, mesoscale weather models in conjunction with hydrological models have gained great attention as they can provide high‐resolution downscaled weather variables. Many cumulus parameterization schemes (CPSs) have been developed and incorporated into three‐dimensional Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model 5 (MM5). This study has performed a comprehensive evaluation of four CPSs (the Anthes–Kuo, Grell, Betts–Miller and Kain–Fritsch93 schemes) to identify how their inclusion influences the mesoscale model's precipitation estimation capabilities. The study has also compared these four CPSs in terms of variability in rainfall estimation at various horizontal and vertical levels. For this purpose, the MM5 was nested down to resolution of 81 km for Domain 1 (domain span 21 × 81 km) and 3 km for Domain 4 (domain span 16 × 3 km), respectively, with vertical resolutions at 23, 40 and 53 vertical levels. The study was carried out at the Brue catchment in Southwest England using both the ERA‐40 reanalysis data and the land‐based observation data. The performances of four CPs were evaluated in terms of their ability to simulate the amount of cumulative rainfall in 4 months in 1995 representing the four seasonal months, namely, January (winter), March (spring), July (summer) and October (autumn). It is observed that the Anthes–Kuo scheme has produced inferior precipitation values during spring and autumn seasons while simulations during winter and summer were consistently good. The Betts–Miller scheme has produced some reasonable results, particularly at the small‐scale domain (3 km grid size) during winter and summer. The KF2 scheme was the best scheme for the larger‐scale (81 km grid size) domain during winter season at both 23 and 53 vertical levels. This scheme tended to underestimate rainfall for other seasons including the small‐scale domain (3 km grid size) in the mesoscale. The Grell scheme was the best scheme in simulating rainfall rates, and was found to be superior to other three schemes with consistently better results in all four seasons and in different domain scales. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Some comments on the photographic subtraction method of determining chromospheric velocities     

R. J. Bray 《Solar physics》1973,30(2):335-344

The photographic subtraction formula expressing the Doppler signal in terms of line-of-sight velocity is rederived and the conditions governing its validity are carefully stated. By appealing to the observed profiles of individual bright and dark mottles it is shown that, in the case of H observations of the quiet chromosphere, two essential conditions are violated.An analysis based on Beckers' (1964) theoretical mottle profiles shows that, assuming the correctness of his model, the photographic subtraction method correctly maps regions of zero velocity and, provided the original photographs are taken sufficiently far from the centre of H, gives the correct signs of any line-of-sight velocities present. However, at H ± 0.25 Å the method gives inconsistent signs. Moreover, at all wavelengths in the line the magnitude of the Doppler signal depends not only on velocity but also on the source function S, optical thickness t ₀, and line broadening parameter ₀. Accordingly, there is no one-to-one correspondence between velocity and the Doppler signal since S, in particular, shows considerable variation from place to place over the quiet chromosphere.An alternative procedure which obviates these difficulties is suggested. It is also based on Beckers' model and yields a calibrated measure of the velocity in terms of ₀ (assumed constant) which is independent of spatial variations in S and t ₀.  相似文献   

High-resolution photography of the solar chromosphere     

R. E. Loughhead  R. J. Bray  E. J. Tappere  J. G. Winter 《Solar physics》1968,4(2):185-195

A new telescope designed for high-resolution photography of the chromosphere is described. It is mounted in the open air on a 15-m tower and is provided with air suction shields to cool all surfaces exposed to the sun's rays. The best moments for photography are selected by a seeing monitor. The highest resolution so far attained is 0. 75 of arc, compared with a theoretical resolution limit at H of 0. 55.  相似文献   

Bandpass calibration of a wideband spectrometer using coherent pulse injection     

Nipanjana Patra  Justin D. Bray  Paul Roberts  Ron D. Ekers 《Experimental Astronomy》2017,43(2):119-129

We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment.  相似文献