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  • 1
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    A Bayesian Monte-Carlo Inversion of Spatial Auto-Correlation (SPAC) for Near-Surface Vs Structure Applied to both Broadband and Geophone Data (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Summary〈/div〉We propose a new Bayesian method to reveal the 〈span〉Vs〈/span〉 structure of the near surface of the earth using spatial autocorrelation (SPAC) functions and apply this new method to synthetic, broadband, and geophone datasets. The principle of SPAC is introduced, and an implementation of the Bayesian Monte Carlo inversion (BMCI) for modeling SPAC coherency functions is described. To demonstrate its effectiveness, BMCI is applied to synthetic tests, data from 14 SPAC array sites in the Salt Lake Valley (SLV), Utah, and two arrays (one broadband and one geophone) located in south central Utah. The 〈span〉Vs〈/span〉 models derived from previous SPAC analysis of the 14 SLV sites differ by 10 per cent at most from those determined by BMCI and lie within uncertainties determined for the BMCI models. These agreements demonstrate the effectiveness of the BMCI method. The synthetic tests and applications to the SLV SPAC data show BMCI has great potential to resolve 〈span〉Vs〈/span〉 structure down to at least 400 m. To achieve resolution for deeper 〈span〉Vs〈/span〉 structure, longer duration deployments, wider array apertures, and additional seismometers or geophones can be employed. Additionally, when the target frequencies are greater than 0.1 Hz, there is no apparent disadvantage in using geophone data for BMCI compared to broadband data. Most significantly, BMCI places a quantifiable constraint on the uncertainties of the 〈span〉Vs〈/span〉 models as well as 〈span〉Vs30〈/span〉.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Long-term trends in precipitation and temperature across the Caribbean (2015)
    Wiley
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    Publication Date: 2015-12-23
    Description: ABSTRACT This study considers long-term precipitation and temperature variability across the Caribbean using two gridded data sets (CRU TS 3.21 and GPCCv5). We look at trends across four different regions (Northern, Eastern, Southern and Western), for three different seasons (May to July, August to October and November to April) and for three different periods (1901–2012, 1951–2012 and 1979–2012). There are no century-long trends in precipitation in either data set, although all regions (with the exception of the Northern Caribbean) show decade-long periods of wetter or drier conditions. The most significant of these is for the Southern Caribbean region which was wetter than the 1961–1990 average from 1940 to 1956 and then drier from 1957 to 1965. Temperature in contrast shows statistically significant warming everywhere for the periods 1901–2012, 1951–2012 and for over half the area during 1979–2012. Data availability is a limiting issue over much of the region and we also discuss the reliability of the series we use in the context of what is known to be available in the CRU TS 3.21 data set. More station data have been collected but have either not been fully digitized yet or not made freely available both within and beyond the region.
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 3
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    How potentially predictable is northern European winter climate a season ahead? (2011)
    Wiley
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    Publication Date: 2011-04-02
    Description: We estimate the potential predictability of European winter temperature using factors based on physical studies of their influences on European winter climate. These influences include sea surface temperature patterns in different oceans, major tropical volcanoes, the quasi-biennial oscillation in the tropical stratosphere, and anthropogenic climate change. We first assess the predictive skill for winter mean temperature in northern Europe by evaluating statistical hindcasts made using multiple regression models of temperature for Europe for winter and the January–February season. We follow this up by extending the methodology to all of Europe on a 5° × 5° grid and include rainfall for completeness. These results can form the basis of practical prediction methods. However, our main aim is to develop ideas to act as a benchmark for improving the performance of dynamical climate models. Because we consider only potential predictability, many of the predictors have estimated values coincident with the winter season being forecast. However, in each case, these values are predictable on average with considerable skill in advance of the winter season. A key conclusion is that to reproduce the results of this paper, dynamical forecasting models will require a fully resolved stratosphere. Copyright © 2011 Royal Meteorological Society and British Crown copyright, the Met Office
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 4
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    On the temporal clustering of US floods and its relationship to climate teleconnection patterns (2012)
    Wiley
    Details
    Publication Date: 2012-03-16
    Description: This article examines whether the temporal clustering of flood events can be explained in terms of climate variability or time-varying land-surface state variables. The point process modelling framework for flood occurrence is based on Cox processes, which can be represented as Poisson processes with randomly varying rate of occurrence. In the special case that the rate of occurrence is deterministic, the Cox process simplifies to a Poisson process. Poisson processes represent flood occurrences which are not clustered. The Cox regression model is used to examine the dependence of the rate of occurrence on covariate processes. We focus on 41 stream gauge stations in Iowa, with discharge records covering the period 1950–2009. The climate covariates used in this study are the North Atlantic Oscillation (NAO) and the Pacific/North American Teleconnection (PNA). To examine the influence of land-surface forcing on flood occurrence, the antecedent 30 d rainfall accumulation is considered. In 27 out of 41 stations, either PNA or NAO, or both are selected as significant predictors, suggesting that flood occurrence in Iowa is influenced by large-scale climate indices. Antecedent rainfall, used as a proxy for soil moisture, plays an important role in driving the occurrence of flooding in Iowa. These results point to clustering as an important element of the flood occurrence process. Copyright © 2012 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 5
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    Estimation of trends in extreme melt-season duration at Svalbard (2012)
    Wiley
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    Publication Date: 2012-04-15
    Description: A time series of monthly mean surface temperatures taken at Svalbard airport, Spitzbergen, for the period 1912–2010 was examined for changes in melt-season length. The annual melt-season length was constructed from daily temperature estimates based on the monthly data using smoothing splines. We argue that the changes in annual melt-season length are linked to variability in regional sea surface temperatures, the mean Northern Hemisphere surface temperature and the North Atlantic Oscillation (NAO) index. A regression model for the melt-season length with these three parameters as predictors, explained about 40% of the observed variance. The annual mean melt season for the period from 1912 to 2010 was estimated to be 108 days, and the linear trend was 0.17 days/year. The risk of having positive extremes in the melt season increased with increasing Northern Hemisphere surface temperature and the regional sea surface temperatures. On the basis of our study of past observations, the 100-year return length of the melt season at Svalbard was predicted to change from the current 95% confidence interval of 131 (108, 138) days to 175 (109, 242) days with 1 °C warming of both regional sea surface temperature and the mean Northern Hemisphere surface temperature. Copyright © 2011 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 6
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    Why dry? Investigating the future evolution of the Caribbean Low Level Jet to explain projected Caribbean drying (2012)
    Wiley
    Details
    Publication Date: 2012-04-15
    Description: Under global warming the Caribbean is projected to be significantly drier by century's end during its primary rainy season from May to November. The PRECIS regional model is used to simulate the end-of-century (2071–2100) manifestation of the Caribbean Low Level Jet (CLLJ) under two Intergovernmental Panel on Climate Change (IPCC) global warming scenarios. The CLLJ is a feature of the Intra-American seas which during its July peak is dynamically linked to a brief mid-summer drying and interruption of the Caribbean rainy season. The regional model captures the CLLJ's present-day spatial and temporal characteristics reasonably well, simulating both the boreal winter (February) and summer (July) peaks. Under global warming there is an intensification of the CLLJ's core strength from May through November. The intensification is such that by October the CLLJ is of comparable core strength to its present-day peak in July. The persistence of the strong CLLJ beyond July and through November is linked to the perpetuation of a dry pattern in the Caribbean in the future. In contrast, the boreal winter manifestation of the CLLJ is largely unaltered in the future. Copyright © 2012 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 7
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    On the temporal clustering of US floods and its relationship to climate teleconnection patterns (2012)
    Wiley
    Details
    Publication Date: 2012-04-15
    Description: This article examines whether the temporal clustering of flood events can be explained in terms of climate variability or time-varying land-surface state variables. The point process modelling framework for flood occurrence is based on Cox processes, which can be represented as Poisson processes with randomly varying rate of occurrence. In the special case that the rate of occurrence is deterministic, the Cox process simplifies to a Poisson process. Poisson processes represent flood occurrences which are not clustered. The Cox regression model is used to examine the dependence of the rate of occurrence on covariate processes. We focus on 41 stream gauge stations in Iowa, with discharge records covering the period 1950–2009. The climate covariates used in this study are the North Atlantic Oscillation (NAO) and the Pacific/North American Teleconnection (PNA). To examine the influence of land-surface forcing on flood occurrence, the antecedent 30 d rainfall accumulation is considered. In 27 out of 41 stations, either PNA or NAO, or both are selected as significant predictors, suggesting that flood occurrence in Iowa is influenced by large-scale climate indices. Antecedent rainfall, used as a proxy for soil moisture, plays an important role in driving the occurrence of flooding in Iowa. These results point to clustering as an important element of the flood occurrence process. Copyright © 2012 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
    Published by Wiley
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  • 8
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    The crustal structure of Ellesmere Island, Arctic Canada--teleseismic mapping across a remote intraplate orogenic belt (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-30
    Description: Ellesmere Island in Arctic Canada displays a complex geological evolution. The region was affected by two distinct orogenies, the Palaeozoic Ellesmerian orogeny (the Caledonian equivalent in Arctic Canada and Northern Greenland) and the Palaeogene Eurekan orogeny, related to the opening of Baffin Bay and the consequent convergence of the Greenland plate. The details of this complex evolution and the present-day deep structure are poorly constrained in this remote area and deep geophysical data are sparse. Receiver function analysis of seven temporary broad-band seismometers of the Ellesmere Island Lithosphere Experiment complemented by two permanent stations provides important data on the crustal velocity structure of Ellesmere Island. The crustal expression of the northernmost tectonic block of Ellesmere Island (~82°–83°N), Pearya, which was accreted during the Ellesmerian orogeny, is similar to that at the southernmost part, which is part of the Precambrian Laurentian (North America-Greenland) craton. Both segments have thick crystalline crust (~35–36 km) and comparable velocity–depth profiles. In contrast, crustal thickness in central Ellesmere Island decreases from ~24–30 km in the Eurekan fold and thrust belt (~79.7°–80.6°N) to ~16–20 km in the Hazen Stable Block (HSB; ~80.6°–81.4°N) and is covered by a thick succession of metasediments. A deep crustal root (~48 km) at ~79.6°N is interpreted as cratonic crust flexed beneath the Eurekan fold and thrust belt. The Carboniferous to Palaeogene sedimentary succession of the Sverdrup Basin is inferred to be up to 1–4 km thick, comparable to geologically-based estimates, near the western margin of the HSB.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 9
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    Estimation of trends in extreme melt-season duration at Svalbard (2011)
    Wiley
    Details
    Publication Date: 2011-11-22
    Description: A time series of monthly mean surface temperatures taken at Svalbard airport, Spitzbergen, for the period 1912–2010 was examined for changes in melt-season length. The annual melt-season length was constructed from daily temperature estimates based on the monthly data using smoothing splines. We argue that the changes in annual melt-season length are linked to variability in regional sea surface temperatures, the mean Northern Hemisphere surface temperature and the North Atlantic Oscillation (NAO) index. A regression model for the melt-season length with these three parameters as predictors, explained about 40% of the observed variance. The annual mean melt season for the period from 1912 to 2010 was estimated to be 108 days, and the linear trend was 0.17 days/year. The risk of having positive extremes in the melt season increased with increasing Northern Hemisphere surface temperature and the regional sea surface temperatures. On the basis of our study of past observations, the 100-year return length of the melt season at Svalbard was predicted to change from the current 95% confidence interval of 131 (108, 138) days to 175 (109, 242) days with 1 °C warming of both regional sea surface temperature and the mean Northern Hemisphere surface temperature. Copyright © 2011 Royal Meteorological Society
    Print ISSN: 0899-8418
    Electronic ISSN: 1097-0088
    Topics: Geosciences , Physics
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  • 10
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    Characterization of crustal structure by comparing reflectivity patterns of wide-angle and near vertical seismic data from the Parnaíba Basin, Brazil (2019)
    Oxford University Press
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Recently an ambitious experiment combining deep seismic surveys from near-vertical and wide-angle acquisition methods was carried out in Brazil. The seismic lines are essentially coincident and crossed the Parnaíba Basin from west to east near latitude 5°S. Here, the wide-angle reflection and refraction (WARR) and deep seismic reflection (DSR) results, which were previously interpreted independently, are compared by directly correlating WARR interfaces converted to TWTT with the major reflective horizons identified in the zero-offset image and by considering coincident reflectivity patterns displayed in both data sets. This integrated WARR and DSR analysis allowed a spatial association of the apparently acoustically featureless crust imaged in the DSR profile to the high reflectivity observed in the WARR data. Numerical tests and elastic modelling show that variations of the elastic properties of the crust, particularly as they are characterized by low 〈span〉Vp〈/span〉 and 〈span〉Vs〈/span〉 contrasts with a possible increase of the 〈span〉Vp〈/span〉/〈span〉Vs〈/span〉 ratio, can only weakly explain the observed reflectivity patterns but that fine-scale lithological heterogeneity within the crust is capable of replicating the observed contrasting seismic responses. The segment of the Parnaíba Basin crust that is characterized by fine-scale lithological heterogeneity lies directly above a mafic crustal underplate defined by the WARR model and was named as the Grajaú domain on the basis of WARR-derived velocity model. The applied methodologies allow added value to be taken from the independent seismic data sets and provide new information about crustal structure that may have important implications for overlying intracontinental basin evolution.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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