Seasonal and global NO_x production by lightning estimated from the Optical Transient Detector (OTD)     

STEPHEN W. NESBITT  RENYI ZHANG  RICHARD E. ORVILLE 《Tellus. Series B, Chemical and physical meteorology》2000,52(5):1206-1215

The Optical Transient Detector (OTD) lightning data for the 12‐month period of 1996 are used to estimate the seasonal and global distributions of lightning‐produced NO _x . The relatively small viewing footprint and the low detection efficiency of the OTD sensor and other difficulties require extrapolations of the OTD data to the actual global flash distributions. Furthermore, available measurements for the ratios of intracloud (IC) to cloud‐to‐ground (CG) flashes have been used to partition lightning counts for IC versus CG flashes from the OTD observations. The resulting lightning distributions are then used to calculate the global and seasonal production of NO _x , assuming a NO production rate of 6.2×10²⁵ molecules for each CG flash and 8.7×10²⁴ molecules for each IC flash. Consequently, we find that CG flashes produce more NO _x than IC flashes despite fewer CG flashes by a factor of 3 or more. NO _x production by lightning varies seasonally in accordance with the global lightning distribution, with the maximum production occurring in the Northern Hemisphere in the local summer. The latitudinal distribution of NO _x production exhibits a strong seasonal variation outside the tropics with the production occurring mainly in the summer hemisphere, whereas in the tropics the production is high throughout the year. The annual contribution to NO _x production by lightning is higher in the Northern Hemisphere than that in the Southern Hemisphere.  相似文献   

Forecast sensitivity with dropwindsonde data and targeted observations     

ZHAO-XIA PU  STEPHEN J. LORD  EUGENIA KALNAY 《地球，A辑:动力气象学与海洋学》1998,50(4):391-410

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Sedimentary evidence for a major glacial oscillation and proglacial lake formation in the Solway Lowlands (Cumbria,UK) during Late Devensian deglaciation     

STEPHEN J. LIVINGSTONE  COLM Ó COFAIGH  DAVID J.A. EVANS  ADRIAN PALMER 《Boreas: An International Journal of Quaternary Research》2010,39(3):505-527

Livingstone, S. J., Ó Cofaigh, C., Evans, D. J. A. & Palmer, A. 2010: Sedimentary evidence for a major glacial oscillation and proglacial lake formation in the Solway Lowlands (Cumbria, UK) during Late Devensian deglaciation. Boreas, Vol. 39, pp. 505–527. 10.1111/j.1502‐3885.2010.00149.x. ISSN 0300‐9483. This paper is a sedimentological investigation of Late Devensian glacial deposits from the Solway Lowlands, northwest England, in the central sector of the last British–Irish Ice Sheet. In this region, laminated glaciolacustrine sediments occur, sandwiched between diamictons interpreted as subglacial tills. At one location the laminated sediments are interpreted as varves, and indicate the former presence of a proglacial lake. Correlation of these varves with other laminated sediments indicates that the glacial lake was at least 140 km² in area and probably much larger. Extensive beds of sand, silt and gravel throughout the Solway Basin associated with the lake demonstrate ice‐free conditions over a large area. Based on the number of varves, the lake was in existence for at least 261 years. The stratigraphic sequence of varves bracketed by tills implies a major glacial oscillation prior to the Scottish Re‐advance (16.8 cal. ka BP). This oscillation is tentatively correlated with the Gosforth oscillation at c.19.5 cal. ka BP. Subsequent overriding of these glaciolacustrine sediments during a westward‐moving re‐advance demonstrates rapid ice loss and then gain within the Solway Lowlands from ice‐dispersal centres in the Lake District, Pennines and Southern Uplands. It is speculated that the existence of this and other lakes along the northeastern edge of the Irish Sea Basin would have influenced ice‐sheet dynamics.  相似文献   

Magnesite diagenesis in redbeds: a case study from the Permian of the Northern Calcareous Alps (Tyrol, Austria)   总被引：1，自引：0，他引：1  

CHRISTOPH SPÖTL  STEPHEN J. BURNS† 《Sedimentology》1994,41(3):543-565

The Upper Permian Gröden Formation of the Northern Calcareous Alps (Austria) is composed of alluvial fan and playa lake sediments that were deposited in intramontane basins. A conspicuous feature of these redbeds is the abundance of magnesite in the form of nodules and discrete layers in mudstones as well as intergranular cement in sandstones. Sedimentological observations indicate that the bulk of these carbonates formed during early diagenesis and were probably syndepositional. Petrographically, most magnesites consist of micrite or, less commonly, microspar. An early non-ferroan magnesite is post-dated by later stage ferroan magnesites. Nodules consisting of recrystallized, sparry magnesite were observed only at one location. The general absence of relics of a non-magnesite precursor mineral and the occurrence of shrinkage features suggest that the fine grained magnesites formed by transformation of a hydrated magnesium carbonate mineral, e.g. hydromagnesite. Carbon, oxygen, sulphur and strontium isotope ratios in conjunction with sedimentological criteria support a model of (hydro)magnesite precipitation in an inland playa lake system, which was fed by run-off from the surrounding hinterland. The scarcity of evaporites and the dominance of magnesite over calcite and dolomite suggest that the playa lake brines were low in sulphate and had high Mg/Ca ratios. The source for the high magnesium concentrations is thought to be the weathering of Devonian dolostones and associated massive magnesite deposits in the catchment area.  相似文献   

Petrogenesis of Garnet Lherzolite and Megacrystalline Nodules from the Thumb, Navajo Volcanic Field   总被引：1，自引：3，他引：1  

EHRENBERG  STEPHEN N. 《Journal of Petrology》1982,23(4):507-547

Garnet Iherzolite and megacrystalline nodules from The Thumbcomprise the deepest mantle sample recovered from the diatremesand intrusions of the Four Corners area. Discrepancies betweenvarious geothermometers applied to these nodules are believedto reflect zoning of Fe in garnets as well as problems in calibrationof the geothermometers. Because the pyroxenes are not zoned,the pyroxene solvus method probably provides more reliable temperatureestimates for this nodule suite than methods based on partitioningof Fe and Mg with garnet. The preferred T-P range of the nodules,950–1230 °C and 32–40 kb, is thought to reflecta localized perturbation of the ambient geotherm by a diapiricor igneous intrusion. Garnet Iherzolites with coarse texture show a trend from fertileto refractory compositions consistent with variable depletionby partial melting. These nodules are interpreted as previouslydepleted mantle rocks, most of which were relatively littleaffected by the thermal perturbation. Garnet Iherzolites withsheared texture are enriched in Fe and Ti relative to the coarseIherzolites and are suggested to have formed by deformationand metasomatism of the coarse lherzolites during intrusionof magma related to the thermal perturbation. The texturallydiverse ‘megacrystalline’ nodules are interpretedas precipitates from this liquid. They are similar to discretenodules from kimberlite pipes, but have unique characteristicsof their own. The above relationships are thought to recordthe process of deep-seated intrusion and partial crystallizationof evolved liquids, possibly related to the host lamprophyre,shortly before the time of eruption.  相似文献   

Staurolite Stability in a Part of the System Fe-Al-Si-O-H   总被引：1，自引：0，他引：1  

RICHARDSON  STEPHEN W. 《Journal of Petrology》1968,9(3):467-488

The following reactions, believed to be analogous to those whichdefine the maximum extent of staurolite-quartz compatibilityat moderate oxygen fugacity in metamorphic rocks, have beendetermined in terms of hydrous fluid pressure and temperature.The O: H composition ratio of the fluid was controlled withthe quartz-fayalite-magnetite (QFM) buffer assemblage. (I) Fe-staurolitequartz almandine+sillimanite+water. (II) Fe-staurolitequartz Fe-cordierite+sillimanite+water. (III) Fe-chloritoid+sillimanite Fe-staurolite+quartz+water. In addition, two reactions which delineate part of the stabilitylimits of Fe-cordierite have been investigated: (IV) Fe-cordierite almandine+sillimanite+quartz. (V) Fe-cordierite hercynite+sillimanite+quartz. The experimental information has been used to predict boundariesto the PT fields of all quartz and QFM-buffered fluid-bearingassemblages involving Fe-staurolite, Fe-cordierite, Fe-chloritoid,almandine, and sillimanite. Using information from this andother studies, three mineral assemblages are recognized whichare stable at similar temperatures but different fluid pressures.In order of decreasing pressure they are: (a) Above 5 kb: staurolite, quartz, kyanite, fluid; (b) Between 1.5 and 8.5 kb (outer limits; in natural rocks thisfield will have a much narrower pressure range) staurolite,quartz, cordierite, fluid. (c) Below 3.5 kb: Fe-cordierite, andalusite, fluid of oxygenfugacity equivalent to the quartz-fayalite-magnetite assemblage. These phase assemblages may be the equivalents of naturallyoccurring mineral facies, but this must be proven in the field.In addition the absence of cordierite from rocks of appropriatecomposition and temperature of formation betokens total pressuresgreater than 3–5 kb. ¹Present address: Grant Institute of Geology, West Mains Road, Edinburgh 9, Scotland.  相似文献   

Geochemical and Isotopic Heterogeneities along an Island Arc-Spreading Ridge Intersection: Evidence from the Lewis Hills, Bay of Islands Ophiolite, Newfoundland   总被引：1，自引：0，他引：1  

KURTH-VELZ  MICHAELA; SASSEN  ANDREAS; GALER  STEPHEN J. G. 《Journal of Petrology》2004,45(3):635-668

This study focuses on the origin of magma heterogeneity andthe genesis of refractory, boninite-type magmas along an arc–ridgeintersection, exposed in the Lewis Hills (Bay of Islands Ophiolite).The Lewis Hills contain the fossil fracture zone contact betweena split island arc and its related marginal oceanic basin. Threetypes of intrusions, which are closely related to this narrowtectonic boundary, have been investigated. Parental melts inequilibrium with the ultramafic cumulates of the PyroxeniteSuite are inferred to have high MgO contents and low Al₂O₃,Na₂O and TiO₂ contents. The trace element signatures of thesePyroxenite Suite parental melts indicate a re-enriched, highlydepleted source with 0·1 x mid-ocean ridge basalt (MORB)abundances of the heavy rare earth elements (HREE). Initial_Nd values of the Pyroxenite Suite range from -1·5 to+0·6, which overlap those observed for the island arc.Furthermore, the Pyroxenite Suite parental melts bear strongsimilarities to boninite-type equilibrium melts from islandarc-related pyroxenitic dykes and harzburgites. Basaltic dykessplit into two groups. Group I dykes have 0·6 x MORBabundances of the HREE, and initial _Nd values ranging from +5·4to +7·5. Thus, they have a strong geochemical affinitywith basalts derived from the marginal basin spreading ridge.Group II dykes have comparatively lower trace element abundances(0·3 x MORB abundances of HREE), and slightly lower initial_Nd values (+5·4 to +5·9). The geochemical characteristicsof the Group II dykes are transitional between those of GroupI dykes and the Pyroxenite Suite parental melts. Cumulates fromthe Late Intrusion Suite are similarly transitional, with _Ndvalues ranging from +2·9 to +4·6. We suggest thatthe magma heterogeneity observed in the Lewis Hills is due tothe involvement of two compositionally distinct mantle sources,which are the sub-island lithospheric mantle and the asthenosphericmarginal basin mantle. It is likely that the refractory, boninite-typeparental melts of the Pyroxenite Suite result from remeltingof the sub-arc lithospheric mantle at an arc–ridge intersection.Furthermore, it is suggested that the thermal-dynamic conditionsof the transtensional transform fault have provided the prerequisitefor generating magma heterogeneity, as a result of mixing relationshipsbetween arc-related and marginal basin-related magmas. KEY WORDS: Bay of Islands ophiolite; transform (arc)–ridge intersection; boninites; rare earth elements, Nd isotopes  相似文献   

Sedimentation in an actively tilting half-graben: sedimentology and stratigraphy of Late Tournaisian–Viséan (Mississippian, Lower Carboniferous) carbonate rocks in south County Wexford, Ireland     

ZSOLT R. NAGY  IAN D. SOMERVILLE†  JAY M. GREGG  STEPHEN P. BECKER  KEVIN L. SHELTON‡  ANDREW G. SLEEMAN§ 《Sedimentology》2005,52(3):489-512

The Wexford Basin (south-eastern Ireland) is a NE–SW-trending sedimentary basin containing carbonates and evaporites deposited during the Late Tournaisian and Viséan. Two separate depositional areas are defined on the basis of facies and facies associations. Sediments were deposited in inner ramp, lagoonal and peritidal environments near Rosslare, and in a more open-marine, shallow- to moderately deep-water, mid to outer ramp environment in the western area around Duncormick. Thick breccia deposits that occur in the Wexford Basin formed as a result of (i) fault movement that produced syn-sedimentary debris flows in the Late? Chadian (Breccia type I); (ii) dissolution of anhydrite/gypsum and subsequent collapse of sedimentary strata (Breccia type II); and (iii) fracturing and brecciation of porous rock caused by the movement of high temperature, late diagenetic fluids along fault planes (Breccia type III). The NE–SW facies polarity displayed by both sedimentary successions was the result of NW–SE extension and the reactivation of the NE–SW-trending Wexford Boundary Fault during the Chadian. Extension at the SE margin of the basin with downthrow to the NNW gave the basin a half-graben character. Thickening of the debris flow deposits to the SW suggests that while the half-graben was being tilted it also underwent a NE–SW block rotation due to an axial component of that normal fault.  相似文献   

A National Park Revisited Assessing Change in Recreational Use of Arthur's Pass National Park     

STEPHEN R. ESPINER  DAVID G. SIMMONS 《New Zealand geographer》1998,54(1):37-45

At a time of increasing visitation and activity diversification, the relationship between use and conservation of New Zealand's national parks is under scrutiny. During this period it is especially important that resource use is understood and monitored over time. Using a replicative format this paper documents the findings of two visitation studies undertaken in Arthur's Pass National Park fifteen years apart. The findings suggest that, despite some strong elements of stability, there are indications of considerable change in use patterns at this site. Data presented are acquiescent in supporting the thesis that Arthur's Pass National Park is undergoing a transition initially shaped by wider social and economic pressures and manifest at the Park by increasing use for commercial purposes, an intensification of use, and increasing numbers of visitors from overseas. While continued research into visitation trends is encouraged, the authors also advise that the challenge of replicative studies in natural resource settings should not be underestimated.  相似文献   

Upper-regime parallel lamination as the result of turbulent sediment transport and low-amplitude bed forms   总被引：3，自引：0，他引：3  

CHRIS PAOLA  STEPHEN M. WIELE  MARY A. REINHART 《Sedimentology》1989,36(1):47-59

A series of laboratory experiments has been carried out in which parallel-laminated deposits were produced from an upper-regime plane bed. The laminae had thicknesses of a few mm and could be traced continuously over distances up to the length and width of the depositional area (0–3 m by 1–5m). Fluctuations in bed elevation were measured both during deposition and at equilibrium; much of the bed fluctuation occurs at time scales that are too long to be due directly to turbulence, as most theories for lamina formation would require. We suggest instead that extremely low-amplitude bed forms are present even on apparently flat beds and that the migration of these bed forms produces laterally continuous lamination. All the lamination produced in the laboratory experiments was normally graded. Using high-speed photography it was observed that the normal grading results from rapid deposition of a layer of loosely packed coarse sand several grain-diameters thick followed by the slow sieving-out of a well packed surface layer of finer sand. The initial deposition is the result of small-scale turbulent fluctuations in boundary shear stress. The sieving-out that follows results in a smooth surface whose low friction coefficient temporarily inhibits further deposition; we term this process ‘glazing’. The alignment of small-scale turbulent scour-and-fill structures along the paths traced by migrating bedform troughs produces laterally continuous parallel lamination.  相似文献