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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Temporal Consistency Between Gross Primary Production and Solar-Induced Chlorophyll Fluorescence in the Ten Most Populous Megacity Areas over Years

The gross primary production (GPP) of vegetation in urban areas plays an important role in the study of urban ecology. It is difficult however, to accurately estimate GPP in urban areas, mostly due to the complexity of impervious land surfaces, buildings, vegetation, and management. Recently, we used the Vegetation Photosynthesis Model (VPM), climate data, and satellite images to estimate the GPP of terrestrial ecosystems including urban areas. Here, we report VPM-based GPP (GPPvpm) estimates for the world's ten most populous megacities during 2000-2014. The seasonal dynamics of GPPvpm during 2007-2014 in the ten megacities track well that of the solar-induced chlorophyll fluorescence (SIF) data from GOME-2 at 0.5deg x 0.5deg resolution. Annual GPPvpm during 2000-2014 also shows substantial variation among the ten megacities, and year-to-year trends show increases, no change, and decreases. Urban expansion and vegetation collectively impact GPP variations in these megacities. The results of this study demonstrate the potential of a satellite-based vegetation photosynthesis model for diagnostic studies of GPP and the terrestrial carbon cycle in urban areas.

urban↗
NASA NTRS1988

Atmospheric erosion by impacts: An analytic investigation

Until recently, models for the origin and evolution of the atmospheres of terrestrial planets ignored the effects of accretionary impacts. In the 1970's, however, it was suggested that heating and/or vaporization of accreting carbonaceous-chondrite-type planetesimals could result in the release of their volatile components. Modeling of this process strongly suggests that substantial atmospheres/hydrospheres could develop this way. During most of the accretionary process, impact velocities generally differed little from the escape velocity of the growing proto-planet because most of the collisions were between bodies in nearly matching orbits. Toward the end of accretion, however, collisions were rarer but much more energetic, involving large planetesimals and higher impact velocities. It has been postulated that such impacts result in a net loss of atmosphere from a planet, and that the cumulative effect impacts during the period of heavy bombardment might have dramatically depleted the original atmospheres.

Vickery, A. M.↗
NASA NTRS2001

The FU Orionis Phenomenon and Solar Nebula Material

We summarize astronomical, meteoritic, and theoretical evidence relating to the FU Orionis phenomenon. This evidence suggests that at early times (the first few 10(exp 5) yr), the solar nebula experienced a hot phase characterized by high accretion rates (the "FU Ori epoch"), punctuated by episodic outbursts of enhanced mass flow through the inner part of the disk (less than or equal to 0.3 AU). Throughout this epoch, disk midplane temperatures exceeded 1000 K at 1 AU. Diminishing infall from the cloud core led to decreasing mass flux throughout the disk. When mass flow de creased below the value critical for outburst (5 x 10(exp -7) solar mass/yr, as suggested by thermal ionization instability models), outbursts ceased and the T Tauri epoch began. Outburst timescales are too long to explain calcium- and aluminum-rich inclusion (CAI) and chondrule formation. Volatility-dependent fractionation patterns seen in meteoritic materials suggest that solids formed beginning during a hot epoch when temperatures exceeded 1400 K, and the presence of volatiles in chondrites argues that this process continued until the nebula had cooled to below 400 K. The thermal ionization instability model for FU Ori outbursts is in quantitative agreement with astronomical observations. Its results imply that the terrestrial region of the nebula reached the hot end of this range only during a time when mass flow through the disk was high enough to trigger outbursts (i.e., the FU Ori epoch) and reached the cool end of this range only during the later T Tauri epoch. According to the models, heating of material in the terrestrial planet region during individual FU Ori outbursts would be limited to surface layers of the nebula, leaving midplane materials (which are at greater than or equal to 1000 K) largely unaffected. Alternative FU Ori models should be developed, particularly if compositional differences among chondrite clans are attributable to episodic heating.

Bell, K. R.↗
NASA NTRS2016

A51F-0123: Model Analysis of Tropospheric Aerosol Variability and Sources over the North Atlantic During NAAMES 2015-2016

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is a five-year Earth-Venture Suborbital-2 Mission to characterize the plankton ecosystems and their influences on remote marine aerosols, boundary layer clouds, and their implications for climate in the North Atlantic. While marine-sourced aerosols have been shown to make important contributions to surface aerosol loading, cloud condensation nuclei and ice nuclei concentrations over remote marine and coastal regions, it is still a challenge to differentiate the marine biogenic aerosol signal from the strong influence of continental pollution outflow. We examine here the spatiotemporal variability and quantify the sources of tropospheric aerosols over the North Atlantic during the first two phases (November 2015 and May-June 2016) of NAAMES using a state-of-the-art chemical transport model (GEOS-Chem). The model is driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) from the NASA Global Modeling and Assimilation Office (GMAO). It includes sulfate-nitrate-ammonium aerosol thermodynamics coupled to ozone-NOx-hydrocarbon-aerosol chemistry, mineral dust, sea salt, elemental and organic carbon aerosols, and especially a recently implemented parameterization for the marine primary organic aerosol emission. The simulated aerosols over the North Atlantic are evaluated with available satellite (e.g., MODIS) observations of aerosol optical depths (AOD), and aircraft and ship aerosol measurements. We diagnose transport pathways for continental pollution outflow over the North Atlantic using carbon monoxide, an excellent tracer for anthropogenic pollution transport. We also conduct model perturbation experiments to quantify the relative contributions of terrestrial and oceanic sources to the aerosol loading, AOD, and their variability over the North Atlantic.

aerosols↗
NASA NTRS1985

Terrestrial Analogs for Planetary Wrinkle Ridges

Wrinkle ridges are common physiographic features on the terrestrial planets. Their origin has remained enigmatic, although two different types of models, volcanic and tectonic, have been proposed. The major impediment to deciphering the origin of wrinkle ridges has been the lack of a terrestrial analog. Seven terrestrial analogs were discussed, two in detail. Their implications for the origin for planetary wrinkle ridges were considered. All of the terrestrial analogs were formed in compressional environments and are the surface breaks of thrust faults.

Plescia, J. B.↗
NASA NTRS1986

A model of impulsive acceleration and transport of energetic particles in Mercury's magnetosphere

A qualitative model of substorm processes in the Mercury magnetosphere is presented based on Mariner 10 observations obtained in 1974-1975. The model is predicated on close analogies observed with the terrestrial case. Particular emphasis is given to energetic particle phenomena as observed by Mariner on March 29, 1974. The suggestion is supported that energetic particles up to about 500 keV are produced by strong induced electric fields at 3 to about 6 Mercury radii in the Hermean tail in association with substorm neutral line formation. The bursts of energetic particles produced are, in this model, subsequently confined on closed field lines near Mercury and drift adiabatically on quasi-trapped orbits for many tens of seconds. Such gradient and curvature drift of the particles can explain prominent periodicities of 5-10 s seen in the Mariner for greater than 170-keV electron flux profiles.

Baker, D. N.↗
NASA NTRS1994

Early differentiation of the Moon: Experimental and modeling studies and experimental and modeling studies of massif anorthosites

NASA grant NAG9-329 was in effect from 3/1/89 to 8/31/94, the last 18 months being a no-cost extension. While the grant was in effect, the P.I., coworkers, and students gave 22 talks and poster sessions at professional meetings, published 12 articles in referred journals (one more is in press, and another is in review), and edited 2 workshop reports relevant to this project. Copies of all the publications are appended to this report. The major accomplishments during the grant period have derived from three quarters: 1) the application of quantitative models of fractional crystallization and partial melting to various problems in planetary science, such as the petrogenesis of picritic glasses and mare basalts and the implications of the SNC meteorites for martian evolution; 2) an experimental study of silicate liquid immiscibility relevant to early lunar differentiation and the petrogenesis of evolved highlands rocks; and 3) experimental studies of massif anorthosites and related rocks that provide terrestrial analogs for the proposed origin of lunar anorthosites by multistage processes. The low-pressure aspects of the quantitative models were developed by the P.I. in the 1980s with NASA support and culminated with a paper comparing the crystallization of terrestrial and lunar lavas. The basis for the high-pressure modifications to the quantitative models is a data set gleaned from high pressure melting experiments done at Lamont and is supplemented by published data from other labs that constrain the baric and compositional dependences of various liquidus phase boundaries such as olivine/orthopyroxene, relevant to the melting of the mantles of the terrestrial planets. With these models it is possible to predict not only the thermal and compositional evolution of magmatic liquids ranging in composition from lumar mare basalt to terrestrial calc-alkaline basalts, but also the small increments of fractional melting that are produced when mantle rises adiabatically. Copies of the crystallization/melting programs have been given to several colleagues in planetary science. Additionally, a series of computer graphics programs, based on the algorithms in the crystallization programs have been developed that display liquidus diagrams appropriate to input compositions.

Longhi, John↗
NASA NTRS1986

Computer modeling of photodegradation

A computer program to simulate the photodegradation of materials exposed to terrestrial weathering environments is being developed. Input parameters would include the solar spectrum, the daily levels and variations of temperature and relative humidity, and materials such as EVA. A brief description of the program, its operating principles, and how it works was initially described. After that, the presentation focuses on the recent work of simulating aging in a normal, terrestrial day-night cycle. This is significant, as almost all accelerated aging schemes maintain a constant light illumination without a dark cycle, and this may be a critical factor not included in acceleration aging schemes. For outdoor aging, the computer model is indicating that the night dark cycle has a dramatic influence on the chemistry of photothermal degradation, and hints that a dark cycle may be needed in an accelerated aging scheme.

Guillet, J.↗
NASA NTRSDate not supplied

Stellar Energetic Particle-driven Production of Biologically Relevant Molecules in Atmospheres of Young Earth-like Exoplanets Around Active G-K Stars

The chemistry of N2, CO2, CH4-rich atmospheres of terrestrial-type exoplanets around active G-K stars is a complex problem: the star's ionizing radiation in the form of X-ray and Extreme UV radiation and the precipitating energetic particles accelerated in coronal mass ejection driven shocks can drive complex chemistry in the exoplanetary atmosphere, and ignite the production of complex molecules (Airapetian et al., 2016). We developed a set of atmospheric models to simulate the formation of organic molecules that can be considered as atmospheric pre-biosignatures from exoplanets around active stars. The model has recently been extended to account for the production of ions, their role in the enhanced chemistry in the lower atmosphere, as well as the interaction of these ions with the aerosols. We applied the photochemical-collisional model to simulate the chemistry of a young terrestrial-type exoplanets resembling the Hadean Earth to highlight the creation of atmospheric pre-biosignatures, relevant greenhouse gases, and the presence of aerosols driven by stellar activity sources. We also discuss the impact of that modified atmospheric chemistry on the exoplanetary climate.

Guillaume Philippe Gronoff↗
NASA NTRS2001

Model of Wave Driven Flow Oscillation for Solar Cycle

At low latitudes in the Earth's atmosphere, the observed zonal flow velocities are dominated by the semi-annual and quasi-biennial oscillations with periods of 6 months and 20 to 32 months respectively. These terrestrial oscillations, the SAO and QBO respectively, are driven by wave-mean flow interactions due to upward propagating planetary-scale waves (periods of days) and small-scale gravity waves (periods of hours). We are proposing (see also Mayr et al., GRL, 2001) that such a mechanism may drive long period oscillations (reversing flows) in stellar and planetary interiors, and we apply it to the Sun. The reversing flows would occur below the convective envelope where waves can propagate. We apply a simplified, one dimensional, analytical flow model that incorporates a gravity wave parameterization due to Hines (1997). Based on this analysis, our estimates show that relatively small wave amplitudes less than 10 m/s can produce zonal flow amplitudes of 20 m/s, which should be sufficient to generate the observed variations in the magnetic field. To produce the 22-year period of oscillation, a low buoyancy frequency must be chosen, and this places the proposed flow in a region that is close to (and below) the base of the convective envelope. Enhanced turbulence associated with this low stability should help to generate the dynamo currents. With larger stability at deeper levels in the solar interior, the model can readily produce also oscillations with much longer periods. To provide an understanding of the fluid dynamics involved, we present numerical results from a 2D model for the terrestrial atmosphere that exemplify the non-linear nature of the wave interaction for which a mechanical analog is the escapement mechanism of the clock.

Mayr, Hans G.↗
NASA NTRS2019

Multimodel Analysis of Future Land Use and Climate Change Impacts on Ecosystem Functioning

Land use and climate changes both affect terrestrial ecosystems. Here, we used three combinations of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP1xRCP26, SSP3xRCP60, and SSP5xRCP85) as input to three dynamic global vegetation models to assess the impacts and associated uncertainty on several ecosystem functions: terrestrial carbon storage and fluxes, evapotranspiration, surface albedo, and runoff. We also performed sensitivity simulations in which we kept either land use or climate (including atmospheric CO2) constant from year 2015 on to calculate the isolated land use versus climate effects. By the 2080–2099 period, carbon storage increases by up to 87 ± 47 Gt (SSP1xRCP26) compared to present day, with large spatial variance across scenarios and models. Most of the carbon uptake is attributed to drivers beyond future land use and climate change, particularly the lagged effects of historic environmental changes. Future climate change typically increases carbon stocks in vegetation but not soils, while future land use change causes carbon losses, even for net agricultural abandonment (SSP1xRCP26). Evapotranspiration changes are highly variable across scenarios, and models do not agree on the magnitude or even sign of change of the individual effects. A calculated decrease in January and July surface albedo (up to −0.021 ± 0.007 and −0.004 ± 0.004 for SSP5xRCP85) and increase in runoff (+67 ± 6 mm/year) is largely driven by climate change. Overall, our results show that future land use and climate change will both have substantial impacts on ecosystem functioning. However, future changes can often not be fully explained by these two drivers and legacy effects have to be considered.

Krause, A.↗
NASA NTRS1978

Ice clathrate as a possible source of the atmospheres of the terrestrial planets

The presence and compositions of atmospheres on the terrestrial planets do not follow directly from condensation models which would have earth accreting near 500 K. No single mechanism yet proposed adequately accounts for the abundances of noble gases and carbon and nitrogen in the atmospheres. We show that the composition of clathrates forming at low temperatures in cold regions of the nebula can be predicted. Addition of about 1 ppm clathrate material to the earth can explain observed abundances of Ar, Kr, and Xe. Condensation and adsorption processes occurring at 400-500 K are necessary to explain the observed abundances of Ne, H2O, C, and N. Possible sources of clathrates could be cometary bodies formed in the outer solar system.

Sill, G. T.↗
NASA NTRS1983

Ice-rich moons and the physical properties of ice

Many of the moons of the outer planets in the solar system consist to a substantial degree of water and other ices. Such ices are thought to make up at least half, by mass, of all condensed material in the outer solar system. The surfaces and interiors of these icy satellites have undergone considerable geologic evolution, and in some cases may still be active today. So that these processes can be understood, certain critical data on the behavior of water and other ices at low (ca. 100 K) temperatures and high (ca. 10 kbar) pressures are needed. Given such data, various techniques for modeling planetary interiors can be tested to see which models best describe the conditions observed on these bodies; such models may then be used to study larger, terrestrial planets.

Consolmagno, G. J.↗
NASA NTRS1984

The earth as a planet - Paradigms and paradoxes

The independent growth of the various branches of the earth sciences in the past two decades has led to a divergence of geophysical, geochemical, geological, and planetological models for the composition and evolution of a terrestrial planet. Evidence for differentiation and volcanism on small planets and a magma ocean on the moon contrasts with hypotheses for a mostly primitive, still undifferentiated, and homogeneous terrestrial mantle. In comparison with the moon, the earth has an extraordinarily thin crust. The geoid, which should reflect convection in the mantle, is apparently unrelated to the current distribution of continents and oceanic ridges. If the earth is deformable, the whole mantle should wander relative to the axis of rotation, but the implications of this are seldom discussed. The proposal of a mantle rich in olivine violates expectations based on evidence from extraterrestrial sources. These and other paradoxes force a reexamination of some long-held assumptions.

Anderson, D. L.↗
NASA NTRS1993

Space plasma physics research

During the course of this grant, work was performed on a variety of topics and there were a number of significant accomplishments. A summary of these accomplishments is included. The topics studied include empirical model data base, data reduction for archiving, semikinetic modeling of low energy plasma in the inner terrestrial magnetosphere and ionosphere, O(+) outflows, equatorial plasma trough, and plasma wave ray-tracing studies. A list of publications and presentations which have resulted from this research is also included.

Comfort, Richard H.↗