Longitudinal variation and waves in Jupiter’s south equatorial wind jet     

Amy A. Simon-Miller  John H. Rogers  Peter J. Gierasch  David Choi  Michael D. Allison  Gianluigi Adamoli  Hans-Joerg Mettig 《Icarus》2012,218(2):817-830

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5°S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and increasing with distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of ～140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7°N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75–100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 ± 0.7-day period. This oscillating motion has a wavelength of ～20° and a speed of 101 ± 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7°N and 7.5°S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.  相似文献   

An environmental assessment of risk in achieving good environmental status to support regional prioritisation of management in Europe     

P. Breen  L.A. Robinson  S.I. Rogers  A.M. Knights  G. Piet  T. Churilova  P. Margonski  N. Papadopoulou  E. Akoglu  A. Eriksson  Z. Finenko  V. Fleming-Lehtinen  B. Galil  F. Goodsir  M. Goren  O. Kryvenko  J.M. Leppanen  V. Markantonatou  S. Moncheva  T. Oguz  L. Paltriguera  K. Stefanova  F. Timofte  F. Thomsen 《Marine Policy》2012

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Non-linear dynamics of gravity wave driven flows in the solar radiative interior     

T. M. Rogers  K. B. MacGregor  G. A. Glatzmaier 《Monthly notices of the Royal Astronomical Society》2008,387(2):616-630

We present results of non-linear numerical simulations of gravity wave driven shear flow oscillations in the equatorial plane of the solar radiative interior. These results show that many of the assumptions of quasi-linear theory are not valid. When only two waves are forced (prograde and retrograde), oscillatory mean flow is maintained; but critical layers often form and are dynamically important. When a spectrum of waves is forced, the non-linear wave–wave interactions are dynamically important, often acting to decrease the maintenance of a mean flow. The (in)coherence of such wave–wave interactions must be taken into account when describing wave-driven mean flows.  相似文献   

Detrital zircon geochronology of the Speewah Group,Kimberley region,Western Australia: evidence for intracratonic development of the Paleoproterozoic Speewah Basin     

R. R. Ramsay  A. E. Eves  M. T. D. Wingate  G. Batt  K. Rogers 《Australian Journal of Earth Sciences》2017,64(3):419-434

Field observations integrated with new petrographic and sensitive high-resolution ion microprobe (SHRIMP) U–Pb age data for detrital zircons from the Paleoproterozoic Speewah Group of northern Western Australia provide evidence of depositional conditions, source of detritus, timing and evolution of the sedimentary rocks in the Speewah Basin. The Speewah Group is a 1.5 km-thick succession of poorly outcropping, predominantly siliciclastic rocks that preserve a fluviatile to marine, transgressive and regressive event. The Speewah Group unconformably overlies crystalline rocks of the Lamboo Province that were stabilised by the 1870–1850 Ma Hooper Orogeny, then accreted as the Kimberley region onto the North Australian Craton during the 1835–1810 Ma Halls Creek Orogeny. Unconformably overlying the Speewah Group is about 4 km of predominantly siliciclastic marine sedimentary rocks of the Kimberley Group in the Kimberley Basin. This study has detected a detrital zircon component within the Speewah Basin at 1814 ± 10 Ma, with a youngest zircon at 1803 ± 12 Ma (1σ) in fluviatile sandstones located beneath a volcaniclastic rock with magmatic zircons that have been dated at ca 1835 Ma. Previous studies proposed that the Speewah Basin developed as a retro-arc foreland basin during accretion of the North Australian Craton. We interpret the ca 1835 Ma zircons in the volcaniclastic rocks to be xenocrystic in origin. This new 20 million years younger maximum depositional age indicates that the Speewah Group in the Speewah Basin, similarly to the overlying Kimberley Group in the Kimberley Basin, developed in a post-orogenic setting on the North Australian Craton rather than in a syn-orogenic setting associated with the 1835–1810 Ma Halls Creek Orogeny.  相似文献   

Historical change in fish species distribution: shifting reference conditions and global warming effects     

Didier Pont  M. Logez  G. Carrel  C. Rogers  G. Haidvogl 《Aquatic Sciences - Research Across Boundaries》2015,77(3):441-453

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Reverberation vertical coherence and sea-bottom geoacoustic inversion in shallow water     

Ji-Xun Zhou Xue-Zhen Zhang Rogers  P.H. Simmen  J.A. Dahl  P.H. Guoliang Jin Zhaohui Peng 《Oceanic Engineering, IEEE Journal of》2004,29(4):988-999

Optimal array-processing techniques in the ocean often require knowledge of the spatial coherence of the reverberation. A mathematical model is derived for the reverberation vertical coherence (RVC) in shallow water (SW). A method for analysis of RVC data is introduced. Measured reverberation cross-correlation coefficients as a function of time and frequency, obtained during the Asian Seas International Acoustic Experiment (ASIAEX) in the East China Sea, are reported. SW reverberation from a single shot provides a continuous spatial sampling of the surrounding sound field up to several tens of kilometers and holds valuable information on the geoacoustic properties of the sea floor over this distance. SW reverberation data can, therefore, be used as the basis for a quick and inexpensive method for geoacoustic inversion and has the obvious advantage that acquiring the data in situ requires only a single platform. This paper considers the use of the vertical coherence of the reverberation as the starting point for such an inversion. Sound speed and attenuation in the sea bottom at the ASIAEX site are obtained over a frequency range of 100-1500 Hz by finding values that provide the best match between the measured and predicted RVC.  相似文献   

Structural evolution within the Luning–Fencemaker fold-thrust belt, Nevada: progression from back-arc basin closure to intra-arc shortening     

Sandra J Wyld  Johannah W Rogers  James E Wright 《Journal of Structural Geology》2001,23(12):1141

The Luning–Fencemaker fold-thrust belt (LFTB) of central Nevada reflects major Mesozoic shortening in the western US Cordillera, and involved contractional deformation in Triassic and lower Jurassic back-arc basinal strata. Structural analyses in the Santa Rosa Range, in the northern LFTB, provide new insight into the evolution of this belt. Four phases of deformation are recognized in the Santa Rosa Range. D₁ involved tight to isoclinal folding, cleavage development under low-grade metamorphic conditions, and reverse faulting. This deformation phase reflects NW–SE shortening of 55–70% in the Early and/or Middle Jurassic. D₂ structures are similar in orientation to D₁ but involved much less overall strain and are well developed only to the southeast. D₂ appears to be related to thrusting along the eastern margin of the LFTB in the Middle and/or Late Jurassic. D₃ deformation reflects very minor shortening (<5%) in a subvertical direction, and is tentatively interpreted to reflect stresses generated during initial intrusion of mid-Cretaceous plutons in the area. D₄ deformation demonstrably occurred synchronously with emplacement of Cretaceous granitoids dated at 102 Ma (U–Pb zircon) based on syntectonic relations between D₄ structures and thermal metamorphism associated with intrusion, and an upgrade in D₄ strain in the thermally softened metamorphic aureoles of the intrusions. This last phase of deformation reflects minor regional NE–SW shortening, coupled with localized strain associated with pluton emplacement.Formation of the LFTB structural province was accomplished during the D₁ and D₂ phases of deformation, and most shortening occurred during the D₁ event. This Jurassic deformation led to structural closure of the back-arc basin by top-to-the-SE tectonic transport and development of a largely ductile fold-thrust belt. Subsequent deformation (D₃ and D₄) is >50 m.y. younger and unrelated to development of the LFTB. The younger deformation reflects a combination of minor regional shortening, interpreted to be related to the Cretaceous Sevier orogeny, plus localized shortening related to emplacement of Cretaceous intrusions.  相似文献   

Late cenozoic alkali-olivine basalts of the Basin-Range Province,USA     

William P. Leeman  John J. W. Rogers 《Contributions to Mineralogy and Petrology》1970,25(1):1-24

Petrographic and chemical analyses demonstrate that late Cenozoic mafic lavas from the Basin-Range Province, western United States, are predominantly alkali-olivine basalts. Associated with these lavas are lesser volumes of basaltic andesite which appear to be differentiates from the more primitive alkali basalts. Late Cenozoic basalts from adjacent regions (Columbia River Plateau, Snake River Plain, Yellowstone area, High Cascades and Sierra Nevada) are predominantly tholeiitic. This apparent petrologic provincialism is supported by complementary variations in heat flow, seismic velocities, crustal thickness, magnetic anomalies and geologic setting.Alkali-olivine basalts from Japan and eastern Australia are analogous to those from the Basin-Range province both in composition and tectonic environment. It is suggested that these lavas are the products of a unique environment characterized by high heat flow and a thin crust.Recent melting experiments on peridotites and basalts and measurements of heat flow allow limits to be placed on the depth of origin of Basin-Range alkali-olivine basalt magmas. It is proposed that these lavas are produced by partial melting (less than 20%) of peridotitic mantle material at depths between 40 and 60 km in response to an elevated geothermal gradient. The basaltic andesites may be derived from hydrous alkali basalt magma by fractionation at depths of 30 to 40 km.  相似文献   

Composition of the Precambrian Llano Uplift,central Texas,U.S.A.     

Linda A. Johnson  John J.W. Rogers  Richard M. Nagy 《Geochimica et cosmochimica acta》1976,40(11):1419-1420

The Llano uplift exposes rocks of approximately 1000 m.y. age. The weighted average composition of the exposed crust is: 70.7% SiO₂; 0.35% TiO₂; 13.6% A1₂O₃; 3.4% total Fe as Fe₂O₃; 1.1% MgO; 2.6% CaO; 3.3% Na₂O; and 4.4% K₂O. This composition is similar to, but more potassic, than equivalent estimates for the Canadian shield.  相似文献   

Pan-African ages from a Tibesti Massif batholith,southern Libya     

W.J. Pegram  J.K. Register  P.D. Fullagar  M.A. Ghuma  J.J.W. Rogers 《Earth and Planetary Science Letters》1976,30(1):123-128

The northwestern portion of the Tibesti Massif in south-central Libya consists of a complex granitic batholith (the Ben Ghnema batholith) surrounded by medium- to low-grade metamorphic wall rocks. Rb-Sr whole-rock analyses of a suite of calc-alkaline rocks from the batholith give an age of about 560 m.y. and an initial⁸⁷Sr/⁸⁶Sr ratio of about 0.706.This age is within the accepted range of the Pan-African orogeny which caused extensive plutonism throughout much of northwestern Africa. The relatively low initial ratio suggests that the magma was derived in the lower crust-upper mantle region and perhaps experienced some degree of mixing with older sialic material.  相似文献