Página 1 dos resultados de 430 itens digitais encontrados em 0.462 segundos

‣ Estimation of methane and carbon dioxide surface fluxes using a 3-D global atmospheric chemical transport model; Estimation of CH₄ and CO₂ surface fluxes using a 3-D global atmospheric chemical transport model

Chen, Yu-Han, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 180 p.; 13310016 bytes; 13332590 bytes; application/pdf; application/pdf
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Methane (CH₄) and carbon dioxide (CO₂) are the two most radiatively important greenhouse gases attributable to human activity. Large uncertainties in their source and sink magnitudes currently exist. We estimate global methane surface emissions between 1996 and 2001, using a top-down approach that combines observed and simulated atmospheric CH₄ concentrations. As a secondary study, we describe our participation in a CO₂ inverse-modeling intercomparison. The available methane time-series data used in this work include observations from 13 high-frequency stations (in-situ) and 74 low-frequency sites (flask). We also construct an annually-repeating reference emissions field from pre-existing datasets of individual methane processes. For our forward simulations, we use the 3-D global chemical transport model MATCH driven by NCEP meteorology. A prescribed, annually-repeating OH field scaled to fit methyl chloroform observations is used as the methane sink. A total methane source of approximately 600 Tg yr⁻¹ best reproduces the methane growth rate between 1993-2001. Using the reference emissions, MATCH can reproduce the observed methane variations at many sites. Interannual variations in transport, including those associated with ENSO and the NAO...

‣ New techniques for seismological studies of earth structure

Gee, Lind S
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 2 v. (341 leaves); 18340495 bytes; 18340254 bytes; application/pdf; application/pdf
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by Lind Shelmerdine Gee.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990.; Includes bibliographical references (leaves 334-341).

‣ Electrokinetics in the Earth

Reppert, Philip M. (Philip Miles), 1957-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 257 leaves; 13440177 bytes; 13439934 bytes; application/pdf; application/pdf
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by Philip M. Reppert.; Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000.; Includes bibliographical references.

‣ Atmospheric propagation effects on radio interferometry

Davis, James Louis
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 284 leaves; 13200744 bytes; 13238515 bytes; application/pdf; application/pdf
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by James Louis Davis.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1986.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.; Bibliography: leaves 278-284.

‣ Precise orbit determination of the Mars Odyssey spacecraft and geodetic inversion for the Martian gravity field

Mazarico, Erwan Matías Alexandre, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75 leaves; 3866623 bytes; 3874314 bytes; application/pdf; application/pdf
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Remote sensing techniques are widely used in planetary science for acquiring precise, global inforniation about an object. One of these techniques consists of the study of the radio signals emitted by a spacecraft, from which it is possible to derive the forces acted upon it. For this project, we used the radio science data from the Mars-orbiting spacecraft "IMars Odyssey". Launched in April 2001, more than two years of daily radio tracking of this satellite are now available, allowing for Precision Orbit Determination. Using the program Geodyn, the position of the spacecraft with respect to the centre of mass of Mars is typically determined down to a few meters, while the velocity precision is better than 1 mm/s. Once a large number of orbits have been calculated, it is possible to use the residuals (misfits of the data to the modeled trajectory) to solve for some of the model parameters. Here, we determine the coefficients of the spherical harmonic expansion of the gravity field, as well as the drag coefficient of the satellite (a proxy for atmospheric density). To obtain such results, many high-precision data sets and models are combined: electromagnetic wave propagation, with tropospheric and ionospheric corrections; tracking station positions...

‣ Mechanistic, sensitivity, and uncertainty studies of the atmospheric oxidation of dimethylsulfide

Lucas, Donald David, 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 249 p.; 13305935 bytes; 13305736 bytes; application/pdf; application/pdf
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The global-scale emissions and reactivity of dimethylsulfide (CH3SCH3, DMS) make it an integral component in the atmospheric sulfur cycle. DMS is rapidly oxidized in the atmosphere by a complex gas-phase mechanism involving many species and reactions. The resulting oxidized sulfur-bearing products are hygroscopic and interact with aerosols through condensation and secondary aerosol formation. Predictions of the impacts of DMS chemistry on aerosols and climate are inhibited by the poorly understood DMS oxidation mechanism. This thesis diagnoses the gas-phase connections between DMS and its oxidation products by simulating comprehensive DMS chemistry (approximately 50 reactions and 30 species) using three atmospheric models of varying size and complexity. A diurnally-varying box model of the DMS cycle in the remote marine boundary layer is used to identify important DMS-related parameters and propagate parameter uncertainties to the sulfur-containing species. This analysis shows that the concentrations of DMS and sulfur dioxide (SO2) are sensitive to relatively few parameters. Moreover, the concentrations of DMS and SO2 are found to have factor of 2 uncertainties caused primarily (more than 60% of the variance) by uncertainties in DMS emissions and heterogeneous removal...

‣ The biogeochemistry and residual mean circulation of the southern ocean

Ito, Takamitsu, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 244 p.; 16113089 bytes; 16145227 bytes; application/pdf; application/pdf
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I develop conceptual models of the biogeochemistry and physical circulation of the Southern Ocean in order to study the air-sea fluxes of trace gases and biological productivity and their potential changes over glacial-interglacial timescales. Mesoscale eddy transfers play a dominant role in the dynamical and tracer balances in the Antarctic Circumpolar Current, and the transport of tracers is driven by the residual mean circulation which is the net effect of the Eulerian mean circulation and the eddy-induced circulation. Using an idealized, zonally averaged model of the ACC, I illustrate the sensitivity of the uptake of transient tracers including CFC11, bomb-[Delta]¹⁴C and anthropogenic CO₂ to surface wind stress and buoyancy fluxes over the Southern Ocean. The model qualitatively reproduces observed distribution of CFC11 and bomb-[Delta]¹⁴C , and a suite of sensitivity experiments illustrate the physical processes controlling the rates of the oceanic uptake of these tracers. The sensitivities of the uptake of CFC11 and bomb-[Delta]¹⁴C are largely different because of the differences in their air-sea equilibration timescales. The uptake of CFC11 is mainly determined by the rates of physical transport in the ocean, and that of bomb-[Delta]¹⁴C is mainly controlled by the air-sea gas transfer velocity. Anthropogenic CO₂ falls in between these two cases...

‣ A time-varying subsidence parameterization for the atmospheric boundary layer

Flagg, David D. (David Douglas)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 56 p.; 3024157 bytes; 3026415 bytes; application/pdf; application/pdf
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This study examines the effect of a time-varying parameterization for subsidence in the atmospheric boundary layer (ABL) on a one-dimensional coupled land-atmosphere model. Measurements of large-scale divergence in the ABL are scarce and often marred by error, providing the motivation to model this important physical process and estimate its values from indirect but related observations. Constant parameterizations of-large- scale divergence and/or subsidence velocity are adequate for periods within a characteristic synoptic time scale, but longer studies require a parameterization that yields to local atmospheric change. After confirming the potential significance of subsidence in the ABL, this experiment investigates two key areas: (1) the ability to model subsidence change as a response to estimated time-varying model error and (2) the net improvement and potential benefits of this enhancement. This study indicates a consistent reduction of root-mean-square error scores for the time-varying subsidence (divergence) parameter scheme versus a constant parameterization for the 2 m specific humidity measurement, with negligible change to the 2 m temperature measurement.; (cont.) Model error does not improve explicitly, in spite of the presumed improvement to model physics. However...

‣ A thermotectonic framework for the growth and stabilization of the eastern Kaapvaal craton, southern Africa

Schoene, Robert Blair
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 385 p.
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Continents are an amalgamation of crust and mantle lithosphere assembled over -4 Gyr and are therefore our best record of the early Earth. Exposures of rocks -3.0-3.7 Ga cover -20,000 km2 of eastern S. Africa and Swaziland, and provide a record of the continental assembly and subsequent stabilization of the eastern Kaapvaal craton. This thesis uses structural, geochronological, thermochronological and isotopic constraints to examine the tectonothermal processes responsible for the growth and stabilization of this portion of Mesoarchean lithosphere. Field mapping was focused on terrane-bounding shear zones and syntectonic plutons, and in combination with ID-TIMS U-Pb zircon geochronology and Sm-Nd analysis, places sub-Myr constraints on the timing, distribution, and kinematics of magmatism and deformation during growth and modification of continental lithosphere. Detailed U-Pb apatite and titanite thermochronological datasets are used in combination with finite difference numerical modeling to determine non-linear temperature-time paths for rocks between -650-300 °C from 3.45-3.08 Ga - providing a sensitive indicator of tectonic and magmatic processes in the middle to lower crust.; (cont.) From 3.2 to 3.3 Ga, multiple microcontinental fragments with distinct age and Nd isotopic characteristics were assembled along an oblique subduction zone boundary...

‣ Modeling the dynamics and depositional patterns of sandy rivers

Jerolmack, Douglas J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 215 leaves
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This thesis seeks to advance our understanding of the dynamic nature, spatial organization and depositional record of topography in sand-bedded rivers. I examine patterns and processes over a wide range of scales, on Earth and Mars. At the smallest scale, ripples and dunes (bedforms) arise spontaneously under most natural flow conditions, acting as the primary agents of sediment transport and flow resistance in sandy rivers. I use physical modeling in a laboratory flume to explore the feedbacks among bedform geometry, fluid flow and sediment transport. Field observations of dunes in the North Loup River, Nebraska, show that bed roughness displays a statistical steady state and robust scaling. Motivated by these data, I develop a nonlinear stochastic surface evolution model for the topography of sandy rivers which captures the essence of bedform evolution in space and time. I then use a simplified kinematic model for bedform evolution to simulate the production of stratigraphy from migrating dunes, allowing a more accurate reconstruction of river flow conditions from preserved bedform remnants in rocks. At the channel scale I examine the conditions that lead to avulsion, the rapid abandonment of a river channel in favor of a new course at lower elevation.; (cont.) Simple scaling arguments and data from 30 natural systems reveal that anastomosing (multi-branch) rivers and distributary deltas are morphologies that arise when avulsion is the dominant mechanism of channel adjustment. I apply these arguments to the Niobrara River...

‣ Modeling and inversion of self-potential data

Minsley, Burke J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 251 p.
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This dissertation presents data processing techniques relevant to the acquisition, modeling, and inversion of self-potential data. The primary goal is to facilitate the interpretation of self-potentials in terms of the underlying mechanisms that generate the measured signal. The central component of this work describes a methodology for inverting self-potential data to recover the three-dimensional distribution of causative sources in the earth. This approach is general in that it is not specific to a particular forcing mechanism, and is therefore applicable to a wide variety of problems. Self-potential source inversion is formulated as a linear problem by seeking the distribution of source amplitudes within a discretized model that satisfies the measured data. One complicating factor is that the potentials are a function of the earth resistivity structure and the unknown sources. The influence of imperfect resistivity information in the inverse problem is derived, and illustrated through several synthetic examples. Source inversion is an ill-posed and non-unique problem, which is addressed by incorporating model regularization into the inverse problem. A non-traditional regularization method, termed "minimum support," is utilized to recover a spatially compact source model rather than one that satisfies more commonly used smoothness constraints. Spatial compactness is often an appropriate form of prior information for the inverse source problem. Minimum support regularization makes the inverse problem non-linear...

‣ The structure and thermal tectonics of planetary lithospheres : mid-ocean ridges and lunar impact basins

Bratt, Steven Richard
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: ix, 386 p.
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by Steven Richard Bratt.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.; Vita.; Includes bibliographies.

‣ Interannual variability of air-sea fluxes of carbon dioxide and oxygen

McKinley, Galen Anile, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 169 p.
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The currently observed increase in atmospheric CO2 due anthropogenic emissions is substantially slowed by natural processes that incorporate CO2 into the terrestrial biota and the ocean. Year-to-year changes in the CO2 growth rate that exceed variations in the fossil fuel source indicate a significant variability in these global CO2 sinks. However, the enormous complexity of the terrestrial and oceanic biogeochemical systems that absorb atmospheric CO2 makes these sinks extremely difficult to understand and precisely quantify. Many techniques, including the interpretation of the relative changes in atmospheric CO2 and O2/N2, ocean modeling, and atmospheric data inversions, have been employed to estimate the mean and variability of global CO2 sinks. However, uncertainty remains large. The goal of this thesis is to improve understanding of global CO2 sinks by considering (1) the error in the atmospheric O2/N2 partitioning method due to the neglect of interannual variability in the air-sea fluxes of 02, and (2) the interannual variability of the ocean CO2 sink.; (cont.) A global, high-resolution ocean general circulation model is used to estimate the magnitude and understand the mechanisms of interannual variability in air-sea fluxes of both CO2 and 02. I find that the global variability in the fluxes of both gases are dominantly forced by large-scale physical processes governing upper ocean dynamics...

‣ Optimal estimation of the surface fluxes of chloromethanes using a 3-D global atmospheric chemical transport

Xiao, Xue, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 210 p.
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The four chloromethanes - methyl chloride (CH3Cl), dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4), are chlorine-containing gases contributing significantly to stratospheric ozone depletion and having adverse health effects. Large uncertainties in estimates of their source and sink magnitudes and temporal and spatial variations currently exist. GEIA inventories and other bottom-up emission estimates are used to construct a priori maps of surface fluxes of these species. The Model of Atmospheric Transport and CHemistry (MATCH), driven by NCEP interannually varying meteorological fields, is then used to simulate the trace gas mole fractions using the a priori emissions and to quantify the time series of sensitivities of tracer concentrations to different aseasonal, seasonal, and regional sources and sinks.We implement the Kalman filter (with the unit pulse response method) to estimate both constant (if applicable) and time-varying surface fluxes on regional/global scales at a monthly resolution for the three short-lived species between 2000-2004, and the continental industrial emissions and global oceanic sink for CCl4 at a 3-month resolution between 1996-2004. The high frequency observations from AGAGE...

‣ Formation of ozone and growth of aerosols in young smoke plumes from biomass burning; Formation of O₃ and growth of aerosols in young smoke plumes from biomass burning

Alvarado, Matthew James
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 324 p.
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The combustion of biomass is a major source of atmospheric trace gases and aerosols. Regional and global-scale models of atmospheric chemistry and climate take estimates for these emissions and arbitrarily "mix" them into grid boxes with horizontal scales of 10-200 km. This procedure ignores the complex non-linear chemical and physical transformations that take place in the highly concentrated environment of the young smoke plumes. In addition, the observations of the smoke plume from the Timbavati savannah fire [Hobbs et al., 2003] show much higher concentrations of ozone and secondary aerosol matter (nitrate, sulfate, and organic carbon [OC]) in the smoke plume than are predicted by current atmospheric chemistry models. To address these issues, we developed a new model of the gas- and aerosol-phase chemistry of biomass burning smoke plumes called ASP (Aerosol Simulation Program). Here we use ASP to simulate the gas-phase chemistry and particle dynamics of young biomass burning smoke plumes and to estimate the errors introduced by the artificial mixing of biomass burning emissions into large-scale grid boxes. This work is the first known attempt to simultaneously simulate the dynamics, gas-phase chemistry, aerosol-phase chemistry...

‣ Surface uplift, fluvial incision, and geodynamics of plateau evolution, from the western margin of the Central Andean plateau

Schildgen, Taylor F. (Taylor Frances)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 154 leaves
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The Colca-Majes and Cotahuasi-Ocona rivers in southwest Peru that cut through the western margin of the Andean plateau en route to the Pacific Ocean incised canyons over 3 km deep in response to late Cenozoic surface uplift. This latest uplift represents a fundamental shift in the style and magnitude of surface deformation that had been ongoing since at least late Cretaceous time, but only relatively recently created what represents the only major barrier to atmospheric circulation in the Southern Hemisphere. Studying canyon incision history as a proxy for surface uplift offers a promising route to understanding how climate and tectonics have interacted throughout the evolution of the Central Andean plateau. In this thesis, a combination of bedrock low-temperature thermochronology (apatite and zircon (UTh)/He techniques), 40Ar/39Ar dating of valley-filling volcanic flows, and three-dimensional thermal modeling using a modified version of Pecube were applied to investigate the incision history of the rivers. Results suggested between 2.6 and 3.0 km of incision occurred in the deepest reaches of the canyons starting at ca. 10 to 11 Ma and ending between 2.3 and 3.5 Ma. The onset of surface uplift that is likely to have driven incision probably did not precede incision by more than one million years...

‣ Atmospheric contribution to the dissipation of the gravitational tide of Phobos on Mars

Thayalan, Vid
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 29 p.
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Here, we investigate the possibility of a significant atmospheric contribution to the tidal dissipation of the Phobos-Mars system. We apply the classical tidal theory and we find that most of gravitational forcing is projected into the first symmetric Hough mode which has an equivalent depth of about 57 km and it is significantly trapped in the vertical. Therefore, no significant dissipation occurs through the vertical propagation of energy and subsequent breaking of the tidal wave as the wave amplifies with height. Alternatively, from the energy stored in the first trapped mode we estimate that the time scale required for the dissipative mechanisms to account for the total dissipation of the tides is of order 102s. This time scale is unrealistically short, since it would contradict observations of propagating thermal tides in Mars atmosphere. Therefore we conclude that the dissipation of the tidal potential that explains the observed acceleration of Phobos most likely occurs within the solid planet.; by Vid Thayalan.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.; Includes bibliographical references (p. 29).

‣ The surface of Mars : morphology and process

Aharonson, Oded, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 136 p.; 12072454 bytes; 12072213 bytes; application/pdf; application/pdf
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The goal of this work is a quantitative description of the morphology of the surface of Mars, in order to constrain the nature of processes acting during the ancient past through today. Emphasis is placed on linking geometric properties to physical mechanisms. Surface smoothness on Mars is distinctive in the vast northern hemisphere plains. Amazonis Planitia is remarkable in its smoothness, exhibiting an rms variation in topography of < 2 m over a 100-km baseline, that is most comparable to planetary surfaces that are depositional in origin. The region of concentrated hematite mineralization in Sinus Meridiani is also relatively smooth, but neither region forms a closed basin. Mars' slope distribution is longer tailed than those of Earth and Venus, indicating a lower efficiency of planation processes relative to relief-building tectonics and volcanics. The shallower long-wavelength portion of the lowlands' topographic power spectrum relative to the highlands' can be accounted for by a simple model of sedimentation such as might be expected at an ocean's floor, but the addition of another process such as cratering is necessary to explain the spectral slope in short wavelengths. Large drainage systems on Mars have geomorphic characteristics that are inconsistent with prolonged erosion by surface runoff. We find the topography has not evolved to an expected equilibrium terrain form...

‣ Atmospheric delay modeling for satellite laser altimetry

Quinn, Katherine J. (Katherine Jane), 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 126 p.; 11892049 bytes; 11891811 bytes; application/pdf; application/pdf
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NASA's Ice, Cloud, and Land Elevation Satellite (ICESat) is a laser altimetry mission with the primary purpose of measuring the mass balance of the ice sheets of Greenland and Antarctica. It will provide 5 years of topography measurements of the ice, as well as land and ocean topography. In order to accurate topography measurements the laser altimeter ranges must be corrected for certain biases. Atmospheric delay is one such bias. As the laser pulse travels through the atmosphere it will be refracted, introducing a delay into the travel time. This delay must be estimated to correct the ranges and the delay estimations need to be validated. Of particular concern are errors in the delay estimates that have the same characteristics as the expected mass balance variations. The main focus of this dissertation is to formulate algorithms for calculating the ICE-Sat atmospheric delay and estimate the expected delay values and errors. Our atmospheric delay algorithm uses numerical weather model data to estimate delay values. We have validated these algorithms using Automatic Weather Stations (AWS) in the polar regions and GPS data over the globe. The GPS data validation was also augmented by in-situ meteorology measurements at some the stations. The GPS validation process additionally allowed us to investigate the estimation of precipitable water vapor using GPS data. The validation studies have shown that our atmospheric delay algorithm errors are well within the ICESat error budget of 20 mm. The overall global delay errors are estimated to be approximately 5.4 mm and the polar delay errors are 12.2 mm. There are no discernible biases in the error and the seasonal variations in error magnitudes are well characterized.; by Katherine J. Quinn.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

‣ Modeling the impact of atmospheric moisture transport on global ice volume

Nisancioglu, Kerim Hestnes, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 154 leaves; 3334069 bytes; 3376332 bytes; application/pdf; application/pdf
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Following Milankovitch's original hypothesis most model studies of changes in global ice volume on orbital time scales have focused on the impact of ablation on ice sheet mass balance. In most cases, poleward moisture flux is fixed and accumulation of snow only depends on local temperature. In this study, a simple coupled atmosphere-ice process model is introduced. An improved representation of the atmospheric hydrological cycle is included, and accumulation is related to the meridional flux of moisture by large scale baroclinic eddies. The ice sheets in the Northern Hemisphere respond to both precession and obliquity frequencies when the model is forced with seasonal insolation. Obliquity variations are introduced by the impact of earth's tilt on the meridional temperature gradient and the poleward flux of moisture, whereas precession governs surface melting by regulating summer temperatures. The response of the ice sheet to obliquity and precession is comparable, and significantly smaller than what is observed in the oxygen isotope record of the late Pliocene and early Pleistocene (2.7 - 0.8 Ma BP). This suggests that in order to successfully reproduce the strong 41 Ka periodicity observed in the record, other mechanisms must be involved such as nonlinear self-sustained...