Folding of a single viscous layer: Exact infinitisimal-amplitude solution—reply     

R.C. Fletcher 《Tectonophysics》1979,56(3-4)

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Distribution of sulphur, and sulphide-iron and copper in bedrock associated with porphyry copper deposits, highland valley, British Columbia     

M. Olade  K. Fletcher 《Journal of Geochemical Exploration》1976,5(1-2)

A selective leach based on extraction with potassium chlorate-hydrochloric acid was used to investigate distribution of sulphide-iron and copper associated with the JA and Valley Copper deposits. Results emphasize patterns related to sulphide, versus total metal, and are shown to be consistent with mineralogical zoning in the deposits.  相似文献   

Vertical profiles of HCN, HC₃N, and C₂H₂ in Titan's atmosphere derived from Cassini/CIRS data     

N.A. Teanby  P.G.J. Irwin  S. Vinatier  C.A. Nixon  S.B. Calcutt  L. Fletcher  F.W. Taylor 《Icarus》2007,186(2):364-384

Mid-infrared limb spectra in the range 600-1400 cm⁻¹ taken with the Composite InfraRed Spectrometer (CIRS) on-board the Cassini spacecraft were used to determine vertical profiles of HCN, HC₃N, C₂H₂, and temperature in Titan's atmosphere. Both high (0.5 cm⁻¹) and low (13.5 cm⁻¹) spectral resolution data were used. The 0.5 cm⁻¹ data gave profiles at four latitudes and the 13.5 cm⁻¹ data gave almost complete latitudinal coverage of the atmosphere. Both datasets were found to be consistent with each other. High temperatures in the upper stratosphere and mesosphere were observed at Titan's northern winter pole and were attributed to adiabatic heating in the subsiding branch of a meridional circulation cell. On the other hand, the lower stratosphere was much colder in the north than at the equator, which can be explained by the lack of solar radiation and increased IR emission from volatile enriched air. HC₃N had a vertical profile consistent with previous ground based observations at southern and equatorial latitudes, but was massively enriched near the north pole. This can also be explained in terms of subsidence at the winter pole. A boundary observed at 60° N between enriched and un-enriched air is consistent with a confining polar vortex at 60° N and HC₃N's short lifetime. In the far north, layers were observed in the HC₃N profile that were reminiscent of haze layers observed by Cassini's imaging cameras. HCN was also enriched over the north pole, which gives further evidence for subsidence. However, the atmospheric cross section obtained from 13.5 cm⁻¹ data indicated a HCN enriched layer at 200-250 km, extending into the southern hemisphere. This could be interpreted as advection of polar enriched air towards the south by a meridional circulation cell. This is observed for HCN but not for HC₃N due to HCN's longer photochemical lifetime. C₂H₂ appears to have a uniform abundance with altitude and is not significantly enriched in the north. This is consistent with observations from previous CIRS analysis that show increased abundances of nitriles and hydrocarbons but not C₂H₂ towards the north pole.  相似文献   

Evidence from U–Pb zircon and ⁴⁰Ar/³⁹Ar muscovite detrital mineral ages in metasandstones for movement of the Torlesse suspect terrane around the eastern margin of Gondwanaland     

C.J. Adams  M.E. Barley  I.R. Fletcher  & A.L. Pickard 《地学学报》1998,10(4):183-189

New U–Pb detrital zircon ages from Triassic metasandstones of the Torlesse Terrane in New Zealand are compared with ⁴⁰Ar/³⁹Ar muscovite data and together, reveal four main source components: (i) major, Triassic–Permian (210–270 Myr old) and (ii) minor, Permian–Carboniferous (280–350 Myr old) granitoids (recorded in zircon and muscovite data); (iii) minor, early middle Palaeozoic, metamorphic rocks, recorded mainly by muscovite, 420–460 Myr old, and (iv) minor, Late Precambrian–Cambrian igneous and metamorphic complexes, 480–570 Myr old, recorded by zircon only. There are also Proterozoic zircon ages with no clear grouping (580–1270 Myr). The relative absence of late Palaeozoic (350–420 Myr old) components excludes granitoid terranes in the southern Lachlan Fold Belt (Australia) and its continuation into North Victoria Land (East Antarctica) and Marie Byrd Land (West Antarctica) as a potential source for the Torlesse. The age data are compatible with derivation from granitoid terranes of the northern New England Orogen (and hinterland) in NE Australia. This confirms that the Torlesse Terrane of New Zealand is a suspect terrane, that probably originated at the NE Australian, Permian–Triassic, Gondwanaland margin and then (200–120 Ma) moved 2500 km southwards to its present New Zealand position by the Late Cretaceous (90 Ma). This sense of movement is analogous to that suggested for Palaeozoic Mesozoic terranes at the North American Pacific margin.  相似文献   

Long-term evolution of the aerosol debris cloud produced by the 2009 impact on Jupiter     

A. Sánchez-Lavega  G.S. Orton  R. Hueso  L.N. Fletcher  E. García-Melendo  I. de Pater  H.B. Hammel  A. Simon-Miller  F. Marchis  O. Mousis  J. García-Rojas  M. Cecconi  K. Noll  S. Pedraz  P. Kalas  W. Golisch  P. Sears  V. Reddy  R. Binzel  W. Grundy  J. Emery  A. Rivkin  C. Thomas  D. Trilling  K. Bjorkman  A.J. Burgasser  H. Campins  T.M. Sato  Y. Kasaba  J. Ziffer  R. Mirzoyan  H. Bouy 《Icarus》2011,214(2):462-476

We present a study of the long-term evolution of the cloud of aerosols produced in the atmosphere of Jupiter by the impact of an object on 19 July 2009 (Sánchez-Lavega, A. et al. [2010]. Astrophys. J. 715, L155-L159). The work is based on images obtained during 5 months from the impact to 31 December 2009 taken in visible continuum wavelengths and from 20 July 2009 to 28 May 2010 taken in near-infrared deep hydrogen-methane absorption bands at 2.1-2.3 μm. The impact cloud expanded zonally from ∼5000 km (July 19) to 225,000 km (29 October, about 180° in longitude), remaining meridionally localized within a latitude band from 53.5°S to 61.5°S planetographic latitude. During the first two months after its formation the site showed heterogeneous structure with 500-1000 km sized embedded spots. Later the reflectivity of the debris field became more homogeneous due to clump mergers. The cloud was mainly dispersed in longitude by the dominant zonal winds and their meridional shear, during the initial stages, localized motions may have been induced by thermal perturbation caused by the impact’s energy deposition. The tracking of individual spots within the impact cloud shows that the westward jet at 56.5°S latitude increases its eastward velocity with altitude above the tropopause by 5-10 m s⁻¹. The corresponding vertical wind shear is low, about 1 m s⁻¹ per scale height in agreement with previous thermal wind estimations. We found evidence for discrete localized meridional motions with speeds of 1-2 m s⁻¹. Two numerical models are used to simulate the observed cloud dispersion. One is a pure advection of the aerosols by the winds and their shears. The other uses the EPIC code, a nonlinear calculation of the evolution of the potential vorticity field generated by a heat pulse that simulates the impact. Both models reproduce the observed global structure of the cloud and the dominant zonal dispersion of the aerosols, but not the details of the cloud morphology. The reflectivity of the impact cloud decreased exponentially with a characteristic timescale of 15 days; we can explain this behavior with a radiative transfer model of the cloud optical depth coupled to an advection model of the cloud dispersion by the wind shears. The expected sedimentation time in the stratosphere (altitude levels 5-100 mbar) for the small aerosol particles forming the cloud is 45-200 days, thus aerosols were removed vertically over the long term following their zonal dispersion. No evidence of the cloud was detected 10 months after the impact.  相似文献   

Jovian temperature and cloud variability during the 2009-2010 fade of the South Equatorial Belt     

Leigh N. Fletcher  G.S. Orton  A.A. Simon-Miller  M.H. Wong  P.G.J. Irwin  P.A. Yanamandra-Fisher 《Icarus》2011,213(2):564-580

Mid-infrared 7-20 μm imaging of Jupiter from ESO’s Very Large Telescope (VLT/VISIR) demonstrate that the increased albedo of Jupiter’s South Equatorial Belt (SEB) during the ‘fade’ (whitening) event of 2009-2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800 mbar increased by 80% between May 2008 and July 2010, making the SEB (7-17°S) as opaque in the thermal infrared as the adjacent equatorial zone. After the cessation of discrete convective activity within the SEB in May 2009, a cool band of high aerosol opacity (the SEB zone at 11-15°S) was observed separating the cloud-free northern and southern SEB components. The cooling of the SEBZ (with peak-to-peak contrasts of 1.0 ± 0.5 K), as well as the increased aerosol opacity at 4.8 and 8.6 μm, preceded the visible whitening of the belt by several months. A chain of five warm, cloud-free ‘brown barges’ (subsiding airmasses) were observed regularly in the SEB between June 2009 and June 2010, by which time they too had been obscured by the enhanced aerosol opacity of the SEB, although the underlying warm circulation was still present in July 2010. Upper tropospheric temperatures (150-300 mbar) remained largely unchanged during the fade, but the cool SEBZ formation was detected at deeper levels (p > 300 mbar) within the convectively-unstable region of the troposphere. The SEBZ formation caused the meridional temperature gradient of the SEB to decrease between 2008 and 2010, reducing the vertical thermal windshear on the zonal jets bounding the SEB. The southern SEB had fully faded by July 2010 and was characterised by short-wave undulations at 19-20°S. The northern SEB persisted as a narrow grey lane of cloud-free conditions throughout the fade process.The cool temperatures and enhanced aerosol opacity of the SEBZ after July 2009 are consistent with an upward flux of volatiles (e.g., ammonia-laden air) and enhanced condensation, obscuring the blue-absorbing chromophore and whitening the SEB by April 2010. These changes occurred within cloud decks in the convective troposphere, and not in the radiatively-controlled upper troposphere. NH₃ ice coatings on aerosols at p < 800 mbar are plausible sources of the suppressed 4.8 and 8.6-μm emission, although differences in the spatial distribution of opacity at these two wavelengths suggest that enhanced attenuation by a deeper cloud (p > 800 mbar) also occurred during the fade. Revival of the dark SEB coloration in the coming months will ultimately require sublimation of these ices by subsidence and warming of volatile-depleted air.  相似文献   

Possible liquid water origin for Atacama Desert mudflow and recent gully deposits on Mars     

J.L. Heldmann  C.A. Conley  A.J. Brown  L. Fletcher  C.P. McKay 《Icarus》2010,206(2):685-690

Evidence of recent gully activity on Mars has been reported based on the formation of new light toned deposits within the past decade, the origin of which remains controversial. Analogous recent light toned gully features have formed by liquid water activity in the Atacama Desert on Earth. These terrestrial deposits leave no mineralogical trace of water activity but rather show an albedo difference due to particle size sorting within a fine-grained mudflow. Therefore, spectral differences indicating varying mineralogy between a recent gully deposit and the surrounding terrain may not be the most relevant criteria for detecting water flow in arid environments. Instead, variation in particle size between the deposit and surrounding terrain is a possible discriminator to identify a water-based flow. We show that the Atacama deposit is similar to the observed Mars gully deposits, and both are consistent with liquid water activity. The light-toned Mars gully deposits could have formed from dry debris flows, but a liquid water origin cannot be ruled out because not all liquid water flows leave hydrated minerals behind on the surface. Therefore, the Mars deposits could be remnant mudflows that formed on Mars within the last decade.  相似文献   

Sea-level and reef accretion history of Marine Oxygen Isotope Stage 7 and late Stage 5 based on age and facies of submerged late Pleistocene reefs,Oahu, Hawaii     

Clark E. Sherman  Charles H. Fletcher  Ken H. Rubin  Kathleen R. Simmons  Walter H. Adey 《Quaternary Research》2014

In situ Pleistocene reefs form a gently sloping nearshore terrace around the island of Oahu. TIMS Th–U ages of in situ corals indicate that most of the terrace is composed of reefal limestones correlating to Marine Oxygen Isotope Stage 7 (MIS 7, ~ 190–245 ka). The position of the in situ MIS 7 reef complex indicates that it formed during periods when local sea level was ~ 9 to 20 m below present sea level. Its extensiveness and geomorphic prominence as well as a paucity of emergent in situ MIS 7 reef-framework deposits on Oahu suggest that much of MIS 7 was characterized by regional sea levels below present. Later accretion along the seaward front of the terrace occurred during the latter part of MIS 5 (i.e., MIS 5a–5d, ~ 76–113 ka). The position of the late MIS 5 reefal limestones is consistent with formation during a period when local sea level was below present. The extensiveness of the submerged Pleistocene reefs around Oahu compared to the relative dearth of Holocene accretion is due to the fact that Pleistocene reefs had both more time and more accommodation space available for accretion than their Holocene counterparts.  相似文献   

A two‐dimensional model of hydraulic performance of stormwater infiltration systems     

D. Browne  A. Deletic  G. M. Mudd  T. D. Fletcher 《水文研究》2013,27(19):2785-2799

Stormwater infiltration systems are a popular method for urban stormwater control. They are often designed using an assumption of one‐dimensional saturated outflow, although this is not very accurate for many typical designs where two‐dimensional (2D) flows into unsaturated soils occur. Available 2D variably saturated flow models are not commonly used for design because of their complexity and difficulties with the required boundary conditions. A purpose‐built stormwater infiltration system model was thus developed for the simulation of 2D flow from a porous storage. The model combines a soil moisture–based model for unsaturated soils with a ponded storage model and uses a wetting front‐tracking approach for saturated flows. The model represents the main physical processes while minimizing input data requirements. The model was calibrated and validated using data from laboratory 2D stormwater infiltration trench experiments. Calibrations were undertaken using five different combinations of calibration data to examine calibration data requirements. It was found that storage water levels could be satisfactorily predicted using parameters calibrated with either data from laboratory soils tests or observed water level data, whereas the prediction of soil moistures was improved through the addition of observed soil moisture data to the calibration data set. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Exoplanet atmospheres with EChO: spectral retrievals using EChOSim     

Joanna K. Barstow  Neil E. Bowles  Suzanne Aigrain  Leigh N. Fletcher  Patrick G. J. Irwin  Ryan Varley  Enzo Pascale 《Experimental Astronomy》2015,40(2-3):545-561

We demonstrate the effectiveness of the Exoplanet Characterisation Observatory mission concept for constraining the atmospheric properties of hot and warm gas giants and super Earths. Synthetic primary and secondary transit spectra for a range of planets are passed through EChOSim [13] to obtain the expected level of noise for different observational scenarios; these are then used as inputs for the NEMESIS atmospheric retrieval code and the retrieved atmospheric properties (temperature structure, composition and cloud properties) compared with the known input values, following the method of [1]. To correctly retrieve the temperature structure and composition of the atmosphere to within 2 σ, we find that we require: a single transit or eclipse of a hot Jupiter orbiting a sun-like (G2) star at 35 pc to constrain the terminator and dayside atmospheres; 20 transits or eclipses of a warm Jupiter orbiting a similar star; 10 transits/eclipses of a hot Neptune orbiting an M dwarf at 6 pc; and 30 transits or eclipses of a GJ1214b-like planet.  相似文献