太阳活动驱动气候变化空间天气机制研究进展     

周立旻  郑祥民  王世杰 《地球科学进展》2007,22(11):1099-1109

大量研究表明，从数小时到十年、百年时间尺度上的天气、气候变化受太阳活动影响显著。近年来，全球云量、北大西洋冬季气旋等气候、气象要素与银河宇宙射线通量变化、太阳能量粒子事件等空间天气事件显著的统计相关被陆续发现。在此基础上，提出太阳活动驱动气候变化空间天气机制，其基本观点是：空间天气事件通过改变云物理特性影响气象、气候，其核心是：太阳活动造成的空间天气事件与云微物理过程的联系，目前空间天气理论分化为离子诱导成核机制和全球大气电路—静电云微物理机制（简称Tinsley机制）。主要回顾和总结了近年来空间天气机制研究的发展，包括观测与理论，取得的成果，并对其未来的发展提出展望。   相似文献   

Winter-spring precipitation reconstructions from tree rings for northeast Mexico     

Jose Villanueva-Diaz  David W. Stahle  Brian H. Luckman  Julian Cerano-Paredes  Mathew D. Therrell  Malcom K. Cleaveland  Eladio Cornejo-Oviedo 《Climatic change》2007,83(1-2):117-131

The understanding of historic hydroclimatic variability is basic for planning proper management of limited water resources in northeastern Mexico. The objective of this study was to develop a network of tree-ring chronologies to reconstruct hydroclimate variability in northeastern Mexico and to analyze the influence of large-scale circulation patterns, such as ENSO. Precipitation sensitive tree-ring chronologies of Douglas-fir were developed in mountain ranges of the Sierra Madre Oriental and used to produce winter-spring precipitation reconstructions for central and southern Nuevo Leon, and southeastern Coahuila. The seasonal winter-spring precipitation reconstructions are 342 years long (1659–2001) for Saltillo, Coahuila and 602 years long (1400–2002) for central and southern Nuevo Leon. Both reconstructions show droughts in the 1810s, 1870s, 1890s, 1910s, and 1970s, and wet periods in the 1770s, 1930s, 1960s, and 1980s. Prior to 1800s the reconstructions are less similar. The impact of ENSO in northeastern Mexico (as measured by the Tropical Rainfall Index) indicated long-term instability of the Pacific equatorial teleconnection. Atmospheric circulation systems coming from higher latitudes (cold fronts or `nortes’) and others developed in the Gulf of Mexico (tropical storms, hurricanes) also influence the climatic conditions characterizing this region. The recent development of new and longer tree-ring chronologies for the region will contribute to a better understanding of the interannual and multidecadal climatic variability of northeastern Mexico.  相似文献   

Speckle filtering of Synthetic Aperture Radar images using filters with object-size-adapted windows     

Sahel Mahdavi  Bahram Salehi  Cecilia Moloney  Weimin Huang  Brian Brisco 《International Journal of Digital Earth》2018,11(7):703-729

Speckle degrades the radiometric quality of a Synthetic Aperture Radar (SAR) image. Previous methods for speckle reduction have used a fixed-size window for filtering the entire image. This, however, may not be effective for the entire image, as land covers of different sizes require different filtering windows. In this paper, a novel method is proposed by which each pixel in the image is filtered with a window appropriate for the size of object within it. The real in-phase and the imaginary quadrature components of the SAR images determine the best window size and the pixels in the intensity image are filtered using their own optimal windows. The proposed method is presented for both single- and multi-polarized SAR images, and the results of several common filters that were modified are presented. This approach is applied to two RADARSAT-2 images: one over San Francisco, California, USA and the other over St. John’s, Newfoundland and Labrador, Canada, producing results that were similar to, or outperformed, comparable filters while retaining details and suppressing speckle effectively. While the method was successful for single-look intensity data, it offers great potential for multi-look and amplitude data as well.  相似文献   

Abundance and Distribution of Reef-Associated Fishes Around Small Oil and Gas Platforms in the Northern Gulf of Mexico’s Hypoxic Zone     

David B. Reeves  Edward J. Chesney  Ryan T. Munnelly  Donald M. Baltz  Brian D. Marx 《Estuaries and Coasts》2018,41(7):1835-1847

Oil and gas platforms (platforms) provide high-relief habitat in the northern Gulf of Mexico’s hypoxic zone that are important to associated fishes. Hypoxia develops near the bottom and reef-associated fishes utilize vertical structure in the well-oxygenated waters overlaying hypoxia. A video array was used to profile the water column and to estimate abundances and depth distributions of fishes before, during, and after summer hypoxia at platforms experiencing intense (seaward) and mild hypoxia (shoal). Gray snapper abundance increased at shoal platforms (10× greater after vs. before the hypoxia season), while abundance remained stable at seaward platforms. However, there was no significant relationship between gray snapper abundance and oxygen concentrations. Sheepshead, Atlantic spadefish, blue runner, and Atlantic bumper abundances varied throughout the summer, but there was no significant effect of hypoxia. Occupation of bottom waters by fishes was consistent throughout the study period at shoal platforms, but fishes were rarely observed in the bottom 3 m and congregated in the water immediately above the hypoxic layer when hypoxia was present at seaward platforms. Nevertheless, patterns of fish abundances were not driven by the presence or absence of hypoxia. The vertical dimension of platforms is a unique and key aspect of their ecological value, especially in the hypoxic zone, and should be considered for artificial reef management.  相似文献   

Characterisation of a Natural Quartz Crystal as a Reference Material for Microanalytical Determination of Ti,Al, Li,Fe, Mn,Ga and Ge   总被引：2，自引：0，他引：2       下载免费PDF全文

Andreas Audétat  Dieter Garbe‐Schönberg  Andreas Kronz  Thomas Pettke  Brian Rusk  John J. Donovan  Heather A. Lowers 《Geostandards and Geoanalytical Research》2015,39(2):171-184

A natural smoky quartz crystal from Shandong province, China, was characterised by laser ablation ICP‐MS, electron probe microanalysis (EPMA) and solution ICP‐MS to determine the concentration of twenty‐four trace and ultra trace elements. Our main focus was on Ti quantification because of the increased use of this element for titanium‐in‐quartz (TitaniQ) thermobarometry. Pieces of a uniform growth zone of 9 mm thickness within the quartz crystal were analysed in four different LA‐ICP‐MS laboratories, three EPMA laboratories and one solution‐ICP‐MS laboratory. The results reveal reproducible concentrations of Ti (57 ± 4 μg g^?1), Al (154 ± 15 μg g^?1), Li (30 ± 2 μg g^?1), Fe (2.2 ± 0.3 μg g^?1), Mn (0.34 ± 0.04 μg g^?1), Ge (1.7 ± 0.2 μg g^?1) and Ga (0.020 ± 0.002 μg g^?1) and detectable, but less reproducible, concentrations of Be, B, Na, Cu, Zr, Sn and Pb. Concentrations of K, Ca, Sr, Mo, Ag, Sb, Ba and Au were below the limits of detection of all three techniques. The uncertainties on the average concentration determinations by multiple techniques and laboratories for Ti, Al, Li, Fe, Mn, Ga and Ge are low; hence, this quartz can serve as a reference material or a secondary reference material for microanalytical applications involving the quantification of trace elements in quartz.  相似文献   

SWIFT-DASH: Spatial Heterodyne Spectroscopy Approach to Stratospheric Wind and Ozone Measurement     

Brian Solheim  Stephen Brown  Chris Sioris  Gordon Shepherd 《大气与海洋》2015,53(1):50-57

Abstract

Passive wind measurements using Doppler shifts from atmospheric emissions were well demonstrated by the Wind Imaging Interferometer (WINDII) and the High Resolution Doppler Imager (HRDI) instruments on the National Aeronautics and Space Administration's (NASA's) Upper Atmosphere Research Satellite, operated from 1991 to 2005. For WINDII these emissions were from visible region upper atmospheric airglow in the altitude range from 80 to 300?km. Application of the same technique in the stratosphere requires using thermal emission from a minor constituent, and an ozone line near 1133?cm^?1 (about 8.8?μm) has been identified as a suitable target line. The WINDII method employed a Doppler Michelson Interferometer, in which the wind is measured from phase shifts of a single spectral line. Isolating a single ozone spectral line is a major challenge but using Spatial Heterodyne Spectroscopy (SHS) offers a way to resolve a number of interferogram spectral components (fringes) within a narrow spectral range. The instrument is a Michelson interferometer similar to WINDII but one in which the two mirrors are replaced by diffraction gratings. A developmental instrument capable of measuring the phase shifts from several ozone lines within a spectral range of 4?cm^?1 has been designed, built, and operated in the laboratory. Simulated retrievals using the measurement parameters of this instrument demonstrate the capability of wind measurement with an accuracy better than 3?m?s^?1 over an altitude range of 24 to 60?km. The retrieval employs four spectral lines for wind and three fringe frequencies for ozone concentration (of about 30 possible), each of which provides an optimal measurement for a particular altitude range. Ozone concentrations are also provided with an accuracy better than 10% from 20 to 50?km. Further detailed tests of this instrument are planned for the future. This work is supported by the Canadian Space Agency.  相似文献   

Treating risk as relational on shore platforms and implications for public safety on microtidal rocky coasts     

Kamstra  Peter  Cook  Brian  Kennedy  David M.  Brighton  Barbara 《Natural Hazards》2018,91(3):1299-1316

Natural Hazards - Drowning on rocky coasts is a problem with global significance, but it is a particularly acute issue in Australia where rocky coasts account for 19% of coastal drownings. The risk...  相似文献   

Siliceous microfossil changes in impact and reference lakes in the uranium mining region of the Athabasca basin in northern Saskatchewan     

Kathleen R. Laird  Biplob Das  Brian F. Cumming 《Journal of Paleolimnology》2015,53(4):367-383

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Patterns of basin fill in Triassic turbidites of the Nanpanjiang basin: implications for regional tectonics and impacts on carbonate‐platform evolution          下载免费PDF全文

Daniel J. Lehrmann  Daniel H. Chaikin  Paul Enos  Marcello Minzoni  Jonathan L. Payne  Meiyi Yu  Alexa Goers  Tanner Wood  Paula Richter  Brian M. Kelley  Xiaowei Li  Yanjiao Qin  Lingyun Liu  Gang Lu 《Basin Research》2015,27(5):587-612

The Nanpanjiang Basin occurs in a key position for resolving controversies of basin tectonics and patterns of plate assembly at the junction between south China and Southeast Asian plates. Paleocurrent measurements indicate that siliciclastic turbidites in the basin were sourced by the Precambrian Jiangnan uplift to the northeast, the Precambrian Yunkai uplift to the southeast and the Triassic Songma suture to the south. Detrital zircon geochronology reveals Archean (2500 Ma), Paleoproterozoic (1800–1900 Ma), Neoproterozoic (900–1000 Ma) and Paleozoic (420–460 Ma) ages consistent with derivation from the Jiangnan and Yunkai uplifts. A large Permian‐Triassic peak of 250 Ma is present in the southern basin and attenuates northward suggesting derivation from an arc developed along the Songma suture. Sandstone QFL compositions average 65/12/23% and plot in the recycled orogen field except for a few samples in the southern basin that fall in the dissected arc field. The compositions are consistent with derivation from Precambrian basement that includes orogenic complexes. In the southern basin, Middle Triassic turbidites contain greater lithics and feldspars and Lower Triassic turbidites have volcaniclastic composition consistent with derivation from a southerly arc. Our preferred interpretation is evolution from remnant basin to a large peripheral foreland with southward subduction and convergence with Indochina along the Songma suture. The previously proposed Dian‐Qiong zone is not a suture as its map location places it within carbonate platforms bounded by identical stratigraphy. The Nan‐Uttaradit zone is too distant to have provided voluminous siliciclastic flux to the basin. The Nanpanjiang Basin provides an example of the evolution of an exceptionally large foreland with far‐field rejuvenation of Precambrian uplifts and carbonate platforms that were significantly influenced by siliciclastic flux. The timing and pattern of turbidite basin fill impacted platform evolution by enabling margin progradation in areas proximal to siliciclastic sources, whereas platforms distant from sources were driven to aggradation and extreme relief with large‐scale gravitational sector collapse.  相似文献   

Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network   总被引：1，自引：0，他引：1       下载免费PDF全文

Kathryn A. Dyl  Gretchen K. Benedix  Phil A. Bland  Jon M. Friedrich  Pavel Spurný  Martin C. Towner  Mary Claire O'Keefe  Kieren Howard  Richard Greenwood  Robert J. Macke  Daniel T. Britt  Angela Halfpenny  James O. Thostenson  Rebecca A. Rudolph  Mark L. Rivers  Alex W. R. Bevan 《Meteoritics & planetary science》2016,51(3):596-613

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS‐XRD, element mapping via energy dispersive spectroscopy [EDS], and X‐ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67?0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α‐quartz and a rim of both low‐ and high‐Ca pyroxene. The mineralogy allows the calculation of the temperatures and ?(O₂) characterizing thermal metamorphism on the parent body using both the two‐pyroxene and the olivine‐chromite geo‐oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ?(O₂) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.  相似文献