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141.
Joëlle Gergis Ailie Jane Eyre Gallant Karl Braganza David John Karoly Kathryn Allen Louise Cullen Rosanne D’Arrigo Ian Goodwin Pauline Grierson Shayne McGregor 《Climatic change》2012,111(3-4):923-944
This study presents the first multi-proxy reconstruction of rainfall variability from the mid-latitude region of south-eastern Australia (SEA). A skilful rainfall reconstruction for the 1783–1988 period was possible using twelve annually-resolved palaeoclimate records from the Australasian region. An innovative Monte Carlo calibration and verification technique is introduced to provide the robust uncertainty estimates needed for reliable climate reconstructions. Our ensemble median reconstruction captures 33% of inter-annual and 72% of decadal variations in instrumental SEA rainfall observations. We investigate the stability of regional SEA rainfall with large-scale circulation associated with El Niño–Southern Oscillation (ENSO) and the Inter-decadal Pacific Oscillation (IPO) over the past 206 years. We find evidence for a robust relationship with high SEA rainfall, ENSO and the IPO over the 1840–1988 period. These relationships break down in the late 18th–early 19th century, coinciding with a known period of equatorial Pacific Sea Surface Temperature (SST) cooling during one of the most severe periods of the Little Ice Age. In comparison to a markedly wetter late 18th/early 19th century containing 75% of sustained wet years, 70% of all reconstructed sustained dry years in SEA occur during the 20th century. In the context of the rainfall estimates introduced here, there is a 97.1% probability that the decadal rainfall anomaly recorded during the 1998–2008 ‘Big Dry’ is the worst experienced since the first European settlement of Australia. 相似文献
142.
Chung-Lin SHIE Long S. CHIU Robert ADLER Eric NELKIN I-I LIN Pingping XIE Feng-Chin WANG R. CHOKNGAMWONG William OLSON D. Allen CHU 《大气科学进展》2009,26(6):1071-1080
Accurate sea surface flux measurements are crucial for
understanding the global water and energy cycles. The oceanic
evaporation, which is a major component of the global oceanic fresh
water flux, is useful for predicting oceanic circulation and
transport. The global Goddard Satellite-based Surface Turbulent
Fluxes Version-2 (GSSTF2; July 1987--December 2000) dateset that was
officially released in 2001 has been widely used by scientific
community for global energy and water cycle research, and regional
and short period data analyses. We have recently been funded by NASA
to resume processing the GSSTF dataset with an objective of
continually producing a uniform dataset of sea surface turbulent
fluxes, derived from remote sensing data. The dataset is to be
reprocessed and brought up-to-date (GSSTF2b) using improved input
datasets such as a recently upgraded NCEP/DOE sea surface
temperature reanalysis, and an upgraded surface wind and microwave
brightness temperature V6 dataset (Version 6) from the Special
Sensor Microwave Imager (SSM/I) produced by Remote Sensing Systems
(RSS). A second new product (GSSTF3) is further proposed with a
finer temporal (12-h) and spatial (0.25ox0.25o)
resolution. GSSTF2b (July 1987--December 2008) and GSSTF3 (July
1999--December 2009) will be released for the research community to
use by late 2009 and early 2011, respectively. 相似文献
143.
Ryan D. Mills Allen F. Glazner Drew S. Coleman 《Contributions to Mineralogy and Petrology》2009,158(2):263-281
Interaction of magma with wall rock is an important process in igneous petrology, but the mechanisms by which interactions
occur are poorly known. The western outer granodiorite of the Cretaceous Tuolumne Intrusive Suite of Yosemite National Park,
California, intruded a variety of metasedimentary and igneous wall rocks at 93.1 Ma. The May Lake metamorphic screen is a
metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation, disaggregation,
and partial melting. The chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure
of pluton/wall rock interactions. Wall rock xenoliths (mostly pelitic quartzite) are predominantly located in an elongate
horizon surrounded by a hybridized fine-grained granodiorite. Initial Sr and Nd isotopic ratios of the hybridized granodiorite
indicate significant local incorporation of crustal material. Major- and trace-element geochemical data indicate that contamination
of the granodiorite occurred via selective assimilation of both high-K and low-K, high-silica partial melts derived from pelitic
quartzite. Although the hybridized granodiorite shows significant amounts of contamination, adjacent to xenoliths the proportion
of contamination is undetectable more than a meter away. These results indicate that the chemical and isotopic variability
of the Tuolumne Intrusive Suite is not caused by magma contamination via in situ wall rock assimilation. 相似文献
144.
Solubility of Pt in sulphide mattes: Implications for the genesis of PGE-rich horizons in layered intrusions 总被引:1,自引:0,他引:1
Raúl O.C. Fonseca Ian H. Campbell Hugh St. C. ONeill Charlotte M. Allen 《Geochimica et cosmochimica acta》2009,73(19):5764-5777
The partitioning of Pt in sulphide melt (matte) has been studied as a function of fS2 and fO2 at 1200 and 1300 °C. The results show that the solubility of Pt in mattes increases strongly with increasing fS2 and decreases weakly with increasing fO2. The increase in Pt solubility with increasing fS2 is attributed to Pt dissolving in the melt as a sulphide species and the weak inverse dependence of Pt solubility on fO2 to the diluting effect of increasing O in the melt at high fO2. These results, coupled with measurements of Pt solubility in silicate melts taken from the literature, allow the calculation of Pt matte/silicate-melt partition coefficients () for a range of conditions pertinent to the formation of Pt-rich horizons in layered intrusions. The calculated values range between 107 and 1011, depending on fO2 and fS2, several orders of magnitude higher than previously published values. Our preferred value for for conditions appropriate to the Merensky Reef is 107 and for the Stillwater Pt-rich horizon 108. The new results are consistent with the magmatic hypothesis for Pt-rich horizons in layered intrusions. 相似文献
145.
Rate of growth of the preserved North American continental crust: Evidence from Hf and O isotopes in Mississippi detrital zircons 总被引:2,自引:0,他引:2
Christina Yan Wang Ian H. Campbell Charlotte M. Allen Ian S. Williams Stephen M. Eggins 《Geochimica et cosmochimica acta》2009,73(3):712-728
Detrital zircons from the Mississippi River have been analyzed for U-Th-Pb, Lu-Hf and O isotopes to constrain the rate of growth of the preserved North American continental crust. One hundred and forty two concordant zircon U/Pb dates on grains mounted in epoxy, obtained by Excimer laser ablation ICP-MS method, resolved six major periods of zircon crystallization: 0-0.25, 0.3-0.6, 0.95-1.25, 1.3-1.5, 1.65-1.95 and 2.5-3.0 Ga. These age ranges match the ages of the recognized lithotectonic units of the North American continent in the hinterland of the Mississippi River. Ninety-six zircons mounted on tape, which show no age zonation and were within 7.5% of concordance, were selected to represent the six U/Pb age time intervals and analyzed for Lu-Hf and O isotope by laser ablation MC-ICP-MS and SHRIMP II, respectively. The δ18O values of the zircons show a small step increase in the maximum δ18O values at the Archean-Proterozoic boundary from 7.5‰ in the Archean to 9.5‰, and rarely 13‰, in the Proterozoic and Phanerozoic. However, the average value of δ18O in zircons changes little with time, showing that the increase in the maximum δ18O values between 2.5 and 2.0 Ga, which can be attributed to an increase in the sediment content of the source regions of younger granitoids, is largely balanced by an increase in zircons with anomalously low δ18O, which can be attributed to hydrothermally altered crust in the granitoid source region.εHfi values for the zircons range from 13.1 to −26.9. Zircons derived from juvenile crust, which we define as having mantle δ18O (4.5-6.5‰) and lying within error of the Hf depleted mantle growth curve, are rare or absent in the Mississippi basin. The overwhelming majority of zircons crystallized from melted pre-existing continental crust, or mantle-derived magmas that were contaminated by continental crust. The average time difference between primitive crust formation and remelting for each of the recognized lithotectonic time intervals, which is defined as crustal incubation time in this study, is 890 ± 460 Myr. There is also a suggestion that the crustal incubation time increases with decreasing age in the Mississippi basin, which is consistent with the declining role of radioactive heat production in the lower crust with time.The average Hf model age (1.94 Ga), weighted by fraction of zircons in the river load is in reasonable agreement with the Nd model age (1.7 Ga) for the Mississippi River. However, if the zircons are weighted by the area of North America covered by the six recognized periods of zircon crystallization the average model age is 2.35 Ga, which compares favorably with an area weighted Nd model age of 2.36 Ga. Our preferred approach is to use the measured O isotope values to constrain variations in the 176Lu/177Hf ratio of the granitic source region from which the zircons crystallized, making the assumption that zircons with mantle-like O isotopic ratios have higher 176Lu/177Hf than zircons with higher O isotope values. This method gives an average Hf model age of 2.53 Ga, which is 180 Myr older than the constant 176Lu/177Hf calculation.The area weighted zircon Hf model ages show two distinct periods of crust formation for the North American continent, 1.6-2.2 and 2.9-3.4 Ga. At least 50% of the preserved North American continental crust was extracted from the mantle by 2.9 Ga and 90% by 1.6 Ga. Two similar periods of crustal growth are also recognized in Gondwana (Hawkesworth C. J. and Kemp A. I. S. (2006) Using hafnium and oxygen isotopes in zircons to unravel the record of crustal evolution. Chem. Geol.226, 144-162.), suggesting that these may be periods of global continental crustal growth. However, we stress that more data from other continents are required before the hypothesis of episodic global continental growth can be accepted with confidence. 相似文献
146.
Matthew J. Cashman Allen C. Gellis Eric Boyd Mathias J. Collins Scott W. Anderson Brett D. McFarland Ashley M. Ryan 《地球表面变化过程与地形》2021,46(6):1145-1159
In this study, we captured how a river channel responds to a sediment pulse originating from a dam removal using multiple lines of evidence derived from streamflow gages along the Patapsco River, Maryland, USA. Gages captured characteristics of the sediment pulse, including travel times of its leading edge (~7.8 km yr−1) and peak (~2.6 km yr−1) and suggest both translation and increasing dispersion. The pulse also changed local hydraulics and energy conditions, increasing flow velocities and Froude number, due to bed fining, homogenization and/or slope adjustment. Immediately downstream of the dam, recovery to pre-pulse conditions occurred within the year, but farther downstream recovery was slower, with the tail of the sediment pulse working through the lower river by the end of the study 7 years later. The patterns and timing of channel change associated with the sediment pulse were not driven by large flow or suspended sediment-transporting events, with change mostly occurring during lower flows. This suggests pulse mobility was controlled by process-factors largely independent of high flow. In contrast, persistent changes occurred to out-of-channel flooding dynamics. Stage associated with flooding increased during the arrival of the sediment pulse, 1 to 2 years after dam removal, suggesting persistent sediment deposition at the channel margins and nearby floodplain. This resulted in National Weather Service-indicated flood stages being attained by 3–43% smaller discharges compared to earlier in the study period. This study captured a two-signal response from the sediment pulse: (1) short- to medium-term (weeks to months) translation and dispersion within the channel, resulting in aggradation and recovery of bed elevations and changing local hydraulics; and (2) dispersion and persistent longer-term (years) effects of sediment deposition on overbank surfaces. This study further demonstrated the utility of US Geological Survey gage data to quantify geomorphic change, increase temporal resolution, and provide insights into trajectories of change over varying spatial and temporal scales. 相似文献
147.
148.
149.
Markus J. Aschwanden Jong Kwan Lee G. Allen Gary Michael Smith Bernd Inhester 《Solar physics》2008,248(2):359-377
The three-dimensional (3D) modeling of coronal loops and filaments requires algorithms that automatically trace curvilinear
features in solar EUV or soft X-ray images. We compare five existing algorithms that have been developed and customized to
trace curvilinear features in solar images: i) the oriented-connectivity method (OCM), which is an extension of the Strous pixel-labeling algorithm (developed by Lee,
Newman, and Gary); ii) the dynamic aperture-based loop-segmentation method (developed by Lee, Newman, and Gary); iii) unbiased detection of curvilinear structures (developed by Steger, Raghupathy, and Smith); iv) the oriented-direction method (developed by Aschwanden); and v) ridge detection by automated scaling (developed by Inhester). We test the five existing numerical codes with a TRACE image
that shows a bipolar active region and contains over 100 discernable loops. We evaluate the performance of the five codes
by comparing the cumulative distribution of loop lengths, the median and maximum loop length, the completeness or detection
efficiency, the accuracy, and flux sensitivity. These algorithms are useful for the reconstruction of the 3D geometry of coronal
loops from stereoscopic observations with the STEREO spacecraft, or for quantitative comparisons of observed EUV loop geometries
with (nonlinear force-free) magnetic field extrapolation models. 相似文献
150.
Danielle C. Sattelberger Joyce M. Kleen Aarin-Conrad Allen Richard O. Flamm 《地理信息系统科学与遥感》2017,54(1):1-19
The largest Florida manatee (Trichechus manatus latirostris) aggregation at a natural warm-water site occurs in Kings Bay, Crystal River, FL. In accordance with the Manatee Recovery Plan, manatee protection areas within Kings Bay have been created by the United States Fish and Wildlife Service (USFWS) and the State of Florida including a year-round refuge designation and seven Federal manatee sanctuaries during the winter manatee season (15 November–31 March). Over the last 30 years, an increase in manatee counts has been observed in Kings Bay which has prompted the need to review existing manatee protection measures. Aerial survey data collected between 1983 and 2012 were used to examine the seasonal change in manatee distribution within Kings Bay to assess the effectiveness of current sanctuary sizes and locations. Regression analysis suggested a significant change in manatee abundance among the winter seasons (p < 0.05). The average winter manatee counts increased by 4.81 animals per year over the 30-year period. Spatially explicit maps using geographic information system (GIS) analysis revealed a strong correlation between high manatee density and artesian springs in Kings Bay during the winter seasons. Highest abundances were identified at three locations: King Spring, Three Sisters Springs, and Magnolia Springs, which coincide with preexisting sanctuary designations. Additional coverage is advocated to support the overflow of manatees outside of sanctuary boundaries. As density patterns were not uniform across summer periods, a consideration of additional boat speed regulations is recommended. 相似文献