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Michael P Hickey - One of the best experts on this subject based on the ideXlab platform.

  • Secular Variations of oh nightglow emission and of the oh intensity weighted temperature induced by gravity wave forcing in the mlt region
    Advances in Space Research, 2008
    Co-Authors: Tai Yin Huang, Michael P Hickey
    Abstract:

    Abstract Secular Variations of OH airglow (8,3) band and of the intensity-weighted temperature induced by a gravity wave packet at three latitudes in the northern hemisphere in the Mesosphere/Lower Thermosphere region are investigated using a 2-D, time-dependent, fully nonlinear OH chemistry–dynamics model. A net-cycled average survives due to wave transience and dissipation. The integrated OH (8,3) volume emission rates show a 20 percent increase induced by the wave packet. The corresponding intensity-weighted temperature shows an initial increase up to 2 percent then a gradual decrease for the remainder of the simulation time by the same wave packet. These Secular Variations could be mistaken as long-period or short-period waves in the airglow observations. Therefore, care must be taken when analyzing the data from observations.

  • on the latitudinal Variations of the non periodic response of minor species induced by a dissipative gravity wave packet in the mlt region
    Journal of Atmospheric and Solar-Terrestrial Physics, 2007
    Co-Authors: Tai Yin Huang, Michael P Hickey
    Abstract:

    A spectral full-wave model and a two dimensional (2-D), time dependent, fully nonlinear chemistry model were used to investigate the latitudinal Variations of the wave effects on the minor species in the OH chemistry in the mesosphere/lower thermosphere region. A dissipative gravity-wave packet is launched at three different latitudes propagating upward through the OH nightglow emission layer in the northern hemisphere. In addition to causing the minor species densities to fluctuate, the wave packet also causes non-periodic Secular Variations of the minor species densities as a consequence of violation of the non-acceleration conditions due to wave transience and dissipation. The associated fluxes of minor species are downward, and consequently minor species densities typically decrease at higher altitudes and increase at lower altitudes. The downward flux and subsequent chemical recombination of atomic oxygen is particularly important and can itself cause large Secular Variations of other less abundant minor species. Our studies indicate that the wave-induced non-periodic, Secular Variations are largest at high latitudes, second largest at low latitudes, and smallest at mid-latitudes.

  • Secular Variations of oi 5577 a airglow in the mesopause region induced by transient gravity wave packets
    Geophysical Research Letters, 2001
    Co-Authors: Michael P Hickey, R L Walterscheid
    Abstract:

    We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of minor species and the OI 5577 A airglow to a gravity wave packet in the mesopause region. Gravity waves affect the time-averaged distribution of minor species in the mesosphere and lower thermosphere (MLT) region through constituent fluxes induced by violation of the non-acceleration conditions due to wave transience and dissipation. In addition, wave perturbed chemistry can induce a flux of chemically active species. Simulations are performed with nominal values of eddy diffusion coefficients in the MLT region, and also using very small values in order to assess the comparative effects of diffusion and wave fluxes. The wave-driven Secular variation leads to a strong increase in airglow brightness over a time period of ∼2 hrs. In contrast to this, diffusion of minor species leads to a decrease in airglow brightness. The combined effects of the two can lead to Secular Variations of airglow brightness that resemble those for a long period (>6 hr) wave. These results have important implications for the interpretation of airglow Variations observed in the MLT region.

  • Secular Variations of atomic oxygen in the mesopause region induced by transient gravity wave packets
    Geophysical Research Letters, 2000
    Co-Authors: Michael P Hickey, R L Walterscheid, Philip G Richards
    Abstract:

    We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of atomic oxygen (O) to a gravity wave packet in the mesopause region. We demonstrate that gravity waves affect the time-averaged distribution of O in the mesosphere and lower thermosphere (MLT) region through the constituent fluxes the waves induce. Our conclusions are based on simulations of two wave packets that violate the non-acceleration conditions through transience and dissipation. The net cycle-averaged effect of the waves is to significantly increase (by as much as 50%) the O density through downward transport of O at low altitudes (≤ 90 km), and to deplete (by as much as 20%) the O density above ∼ 100 km altitude. Comparison with results obtained including only chemistry and diffusion suggests that the effects of gravity wave transport on the distribution of O in this region can be greater than the effects of eddy transport.

R L Walterscheid - One of the best experts on this subject based on the ideXlab platform.

  • Secular Variations of oi 5577 a airglow in the mesopause region induced by transient gravity wave packets
    Geophysical Research Letters, 2001
    Co-Authors: Michael P Hickey, R L Walterscheid
    Abstract:

    We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of minor species and the OI 5577 A airglow to a gravity wave packet in the mesopause region. Gravity waves affect the time-averaged distribution of minor species in the mesosphere and lower thermosphere (MLT) region through constituent fluxes induced by violation of the non-acceleration conditions due to wave transience and dissipation. In addition, wave perturbed chemistry can induce a flux of chemically active species. Simulations are performed with nominal values of eddy diffusion coefficients in the MLT region, and also using very small values in order to assess the comparative effects of diffusion and wave fluxes. The wave-driven Secular variation leads to a strong increase in airglow brightness over a time period of ∼2 hrs. In contrast to this, diffusion of minor species leads to a decrease in airglow brightness. The combined effects of the two can lead to Secular Variations of airglow brightness that resemble those for a long period (>6 hr) wave. These results have important implications for the interpretation of airglow Variations observed in the MLT region.

  • Secular Variations of atomic oxygen in the mesopause region induced by transient gravity wave packets
    Geophysical Research Letters, 2000
    Co-Authors: Michael P Hickey, R L Walterscheid, Philip G Richards
    Abstract:

    We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of atomic oxygen (O) to a gravity wave packet in the mesopause region. We demonstrate that gravity waves affect the time-averaged distribution of O in the mesosphere and lower thermosphere (MLT) region through the constituent fluxes the waves induce. Our conclusions are based on simulations of two wave packets that violate the non-acceleration conditions through transience and dissipation. The net cycle-averaged effect of the waves is to significantly increase (by as much as 50%) the O density through downward transport of O at low altitudes (≤ 90 km), and to deplete (by as much as 20%) the O density above ∼ 100 km altitude. Comparison with results obtained including only chemistry and diffusion suggests that the effects of gravity wave transport on the distribution of O in this region can be greater than the effects of eddy transport.

Lawrence A Hardie - One of the best experts on this subject based on the ideXlab platform.

  • Secular Variations in precambrian seawater chemistry and the timing of precambrian aragonite seas and calcite seas comment and reply reply
    Geology, 2004
    Co-Authors: Lawrence A Hardie
    Abstract:

    In her comment on my paper on Secular Variations in Precambrian seawater chemistry, Dr. Sumner has argued that aragonite pseudomorphs are abundant in the 2.5–2.6 Ga Campbellrand-Malmani carbonates of the Transvaal Basin, South Africa, occurring mainly as fibrous cements replaced by calcite

  • Secular Variations in precambrian seawater chemistry and the timing of precambrian aragonite seas and calcite seas
    Geology, 2003
    Co-Authors: Lawrence A Hardie
    Abstract:

    An extension of the seawater Secular-variation model that successfully predicted the observed timing of Phanerozoic MgSO 4 vs. KCl marine evaporites and aragonite seas vs. calcite seas has been applied to the prediction of the Secular Variations in the major ion chemistry of seawater and aragonite seas vs. calcite seas during the Precambrian. Testing of the predictions was based on those Precambrian seafloor carbonate precipitates that have been interpreted by others to have formed originally as aragonite. Of 16 examples of Precambrian seafloor aragonite, 14 fall within the 6 periods of aragonite seas predicted for the Late Archean–Proterozoic by the model, 1 falls on the transition between an aragonite sea and calcite sea, and 1 falls in a period of calcite seas. This strong correlation supports the following predictions of the model: (1) Precambrian seawater was a saline NaCl water with Ca > HCO 3 since at least the Late Archean. (2) The major ion compositions of Precambrian seawater chemistry and their Secular Variations are in the same ranges as those of Phanerozoic seawater. (3) The Mg/Ca mole ratio in seawater has controlled the types of CaCO 3 polymorphs that have precipitated from Earth9s oceans throughout the Phanerozoic and most, if not all, of the Precambrian.

Philip G Richards - One of the best experts on this subject based on the ideXlab platform.

  • Secular Variations of atomic oxygen in the mesopause region induced by transient gravity wave packets
    Geophysical Research Letters, 2000
    Co-Authors: Michael P Hickey, R L Walterscheid, Philip G Richards
    Abstract:

    We employ a 2-dimensional, time-dependent, fully nonlinear model of minor species in the mesopause region and our Spectral Full-Wave Model to simulate the response of atomic oxygen (O) to a gravity wave packet in the mesopause region. We demonstrate that gravity waves affect the time-averaged distribution of O in the mesosphere and lower thermosphere (MLT) region through the constituent fluxes the waves induce. Our conclusions are based on simulations of two wave packets that violate the non-acceleration conditions through transience and dissipation. The net cycle-averaged effect of the waves is to significantly increase (by as much as 50%) the O density through downward transport of O at low altitudes (≤ 90 km), and to deplete (by as much as 20%) the O density above ∼ 100 km altitude. Comparison with results obtained including only chemistry and diffusion suggests that the effects of gravity wave transport on the distribution of O in this region can be greater than the effects of eddy transport.

Castro Antonio - One of the best experts on this subject based on the ideXlab platform.

  • Secular Variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?
    'Geological Society of America', 2021
    Co-Authors: Castro Antonio, Rodríguez Carmen, Fernández Carlos, Aragón Eugenio, Pereira, Manuel Francisco, Molina, José Francisco
    Abstract:

    This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a Secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel mélange. Subsequent melting of subducted mélanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk mélanges and the peridotite. Our proposal follows model predictions on the formation of mélange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the Secular geochemical Variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.This research was funded by the Spanish Agency of Science and Technology (Projects CGL2013–48408–C3–1–P and PGC2018–096534-B-I00) and the University of Huelva. Rodriguez is grateful for a Juan de la Cierva postdoctoral research grant. This is IBERSIMS publication 49.Peer reviewe

  • Secular Variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?
    'Geological Society of America', 2021
    Co-Authors: Castro Antonio, Molina Palma, José Francisco
    Abstract:

    This research was funded by the Spanish Agency of Science and Technology (Projects CGL201348408-C3-1-P and PGC2018-096534-B-I00) and the University of Huelva. Rodriguez is grateful for a Juan de la Cierva postdoctoral research grant. This is IBERSIMS publication 49.This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a Secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (Sr-87/Sr-86 and Nd-143/Nd-144) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel melange. Subsequent melting of subducted melanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk melanges and the peridotite. Our proposal follows model predictions on the formation of melange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the Secular geochemical Variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.Spanish Agency of Science and Technology CGL201348408-C3-1-P PGC2018-096534-B-I00University of HuelvaJuan de la Cierva postdoctoral research gran

  • Secular Variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary : Was mélange melting involved?
    2021
    Co-Authors: Castro Antonio, Fernández Carlos, Aragón Eugenio, Pereira, Manuel Francisco, Rodríguez, Carmen Cristófol, Molina, José F.
    Abstract:

    This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a Secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel mélange. Subsequent melting of subducted mélanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk mélanges and the peridotite. Our proposal follows model predictions on the formation of mélange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the Secular geochemical Variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.Facultad de Ciencias Naturales y Muse