Distributions for storm surge extremes     

Todd L. WaltonJr 《Ocean Engineering》2000,27(12)

The present paper is an attempt to assess a variety of potential probabilistic models for the meteorologically driven storm surge component of a long term water level observation record at Sandy Hook, New Jersey. Simple assumptions are made with regard to the record, and the fitting of the extreme values of the data are assessed graphically in observation space for determining quality of fit in the upper tail of the data. Results are presented which show a comparison of typical distributions utilized along with some distributions not before utilized for coastal storm surge.  相似文献   

Optical off-nuclear spectra of quasar hosts and radio galaxies     

David H. Hughes  Marek J. Kukula  †  James S. Dunlop  Todd Boroson 《Monthly notices of the Royal Astronomical Society》2000,316(1):204-224

We present optical (∼3200 to ∼9000 Å) off-nuclear spectra of 26 powerful active galaxies in the redshift range 0.1≤ z ≤0.3, obtained with the Mayall and William Herschel 4-m class telescopes. The sample consists of radio-quiet quasars, radio-loud quasars (all with −23≥ M _V ≥−26) and radio galaxies of Fanaroff–Riley Type II (with extended radio luminosities and spectral indices comparable to those of the radio-loud quasars). The spectra were all taken approximately 5 arcsec off-nucleus, with offsets carefully selected so as to maximize the amount of galaxy light falling into the slit, whilst simultaneously minimizing the amount of scattered nuclear light. The majority of the resulting spectra appear to be dominated by the integrated stellar continuum of the underlying galaxies rather than by light from the non-stellar processes occurring in the active nuclei, and in many cases a 4000-Å break feature can be identified. The individual spectra are described in detail, and the importance of the various spectral components is discussed. Stellar population synthesis modelling of the spectra will follow in a subsequent paper.  相似文献   

Circulation anomalies associated with tropical-temperate troughs in southern Africa and the south west Indian Ocean     

M. Todd  R. Washington 《Climate Dynamics》1999,15(12):937-951

Daily rainfall variability over southern Africa (SA) and the southwest Indian Ocean (SWIO) during the austral summer months has recently been described objectively for the first time, using newly derived satellite products. The principle mode of variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region. These represent the location of cloud bands associated with tropical temperate troughs (TTT). This study objectively identifies major TTT events during November to February, and on the basis of composites off NCEP reanalysis data describes the associated atmospheric structure. The two phases of the rainfall dipole are associated with markedly contrasting circulation patterns. There are also pronounced intra-seasonal variations. In early summer the position of the temperate trough and TTT cloud band alternates between the SWIO and southwest Atlantic. In late summer the major TTT axis lies preferentially over the SWIO, associated with an eastward displacement in the Indian Ocean high. In all months, positive events, in which the TTT cloud band lies primarily over the SWIO, are associated with large-scale moisture flux anomalies, in which convergent fluxes form a pronounced poleward flux along the cloud band. This suggests that TTT events are a major mechanism of poleward transfer of energy and momentum. Moisture transport occurs along three principle paths: (1) the northern or central Indian Ocean (where anomalous fluxes extend eastward to the Maritime Continent), (2) south equatorial Africa and the equatorial Atlantic, (3) from the south within a cyclonic flow around the tropical-temperate trough. The relative importance of (2) is greatest in late summer. Thus, synoptic scale TTT events over SA/SWIO often result from large-scale planetary circulation patterns. Hovmoeller plots show that TTT development coincides with enhanced tropical convection between 10°–30°E (itself exhibiting periodicity of around 5 days), and often with convergence of eastward and westward propagating convection around 40°E. Harmonic analysis of 200 hPa geopotential anomalies show that TTT features are forced by a specific zonally asymmetric wave pattern, with wave 5 dominant or significant in all months except February when quasi-stationary waves 1, 2 and 3 dominate. These findings illustrate the importance of tropical and extratropical dynamics in understanding TTT events. Finally, it is suggested that in November–Januar TTT rainfall over SA/SWIO may be in phase with similar rainfall dipole structures observed in the South Pacific and South Atlantic convergence zones. Received: 11 August 1998 / Accepted: 28 May 1999  相似文献   

Small Purge Method to Sample Vapor from Groundwater Monitoring Wells Screened Across the Water Table          下载免费PDF全文

Robert E. Sweeney  George Todd Ririe 《Ground Water Monitoring & Remediation》2017,37(4):51-59

Groundwater monitoring wells are present at most hydrocarbon release sites that are being assessed for cleanup. If screened across the vadose zone, these wells provide an opportunity to collect vapor samples that can be used in the evaluation of vapor movement and biodegradation processes occurring at such sites. This paper presents a low purge volume method (modified after that developed by the U.S. EPA) for sampling vapor from monitoring wells that is easy to implement and can provide an assessment of the soil gas total petroleum hydrocarbon (TPH) and O₂ concentrations at the base of the vadose zone. As a result, the small purge method allows for sampling of vapor from monitoring wells to support petroleum vapor intrusion (PVI) risk assessment. The small purge volume method was field tested at the Hal's service station site in Green River, Utah. This site is well‐known for numerous soil gas measurements containing high O₂ and high TPH vapor concentrations in the same samples which is inconsistent with well‐accepted biodegradation models for the vapor pathway. Using the low purge volume method, monitoring wells were sampled over, upgradient, and downgradient of the light nonaqueous phase liquid (LNAPL) footprint. Results from our testing at Hal's show that vapor from monitoring wells over LNAPL contained very low O₂ and high TPH concentrations. In contrast, vapor from monitoring wells not over LNAPL contained high O₂ and low TPH concentrations. The results of this study show that a low purge volume method is consistent with biodegradation models especially for sampling at sites where low permeability soils exist in and around a LNAPL source zone.  相似文献   

Impacts of a Rural Subdivision on Groundwater Quality: Results of Long-Term Monitoring     

Todd W. Rayne  Kenneth R. Bradbury  Jacob J. Krause 《Ground water》2019,57(2):279-291

A rural subdivision in south central Wisconsin was instrumented with monitoring wells and lysimeters before, during, and after its construction to examine the impacts of the unsewered subdivision on groundwater quality and quantity. Prior to construction, the 78-acre (32 ha) site was farmland. Sixteen homes were constructed beginning in 2003. Initial monitoring from 2002 to 2005 showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/L and some detections of the herbicide atrazine. Our 12-year study shows that the transition from agricultural to residential land use has changed groundwater quality in both negative and positive ways. Although groundwater elevations showed typical seasonal fluctuations each year, there were no measurable changes in groundwater levels or general flow directions during the 12-year study period. Chloride values increased in many wells, possibly as a result of road salting or water softener discharge. Nitrate concentrations varied spatially and temporally over the study period, with some initial concentrations substantially above the drinking water standard. In some wells, nitrate and atrazine levels have declined substantially since agriculture ceased. However, atrazine was still present at trace concentrations throughout the site in 2014. Wastewater tracers show there are small but detectable impacts from septic effluent on groundwater quality. Particle traces based on a groundwater flow model are consistent with the hypothesis that septic leachate has impacted groundwater quality.  相似文献   

A composite spessartite–appinite intrusion from Port-na-Blagh,County Donegal,Ireland     

R. Elsdon  S. P. Todd 《Geological Journal》1989,24(2):97-112

A sheet-like appinite from Breaghy Head, North Donegal, is closely associated with a spessartite intrusion. Field, mineralogical, and geochemical similarities indicate that the parent magmas were very similar, and the appinite magma may have been derived from the spessartite by small degrees of crystal fractionation. The appinite is divided into an amphibole-rich lower part and a felsic upper part; the mineralogical contrast between the two is best explained by two-pulse intrusion of a batch of spessartitic magma within which amphibole and pyroxene had already segregated due to crystal settling or flow sorting. Unlike other Caledonian appinites, the Breaghy Head intrusion is not one of a cluster, and appears to be an isolated development. Possible reasons for its location are discussed.  相似文献   

MATLAB Algorithm Availability Simulation Tool     

Shau-Shiun Jan  Wyant Chan  Todd Walter 《GPS Solutions》2009,13(4):327-332

This paper describes a set of MATLAB functions currently being developed for Space Based Augmentation System (SBAS) availability analysis. This toolset includes simulation algorithms that are constantly being developed and updated by various working groups. This set of functions is intended for use as a fast, accurate, and highly customizable experimental test bed for algorithm development. A user-friendly interface has also been developed for the tool. It is open source and can be downloaded from the Stanford GPS Research Laboratory web site (). Therefore, it provides a common ground for different working groups to compare their results. This paper demonstrates the utility of this toolset by analyzing the SBAS service volume models for the Conterminous United States. The paper describes the functionality provided within the software, and shows an example set of contour plots which are the means for investigating how different algorithms and parameters impact availability.  相似文献