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DOE OSTI2025

Air temperature and precipitation constraining the modelled wetland methane emissions in a boreal region in northern Europe

Wetland methane responses to temperature and precipitation are studied in a boreal wetland-rich region in northern Europe using ecosystem process models. Six ecosystem models (JSBACH-HIMMELI, LPX-Bern, LPJ-GUESS, JULES, CLM4.5, and CLM5) are compared to multi-model means of ecosystem models and atmospheric inversions from the Global Carbon Project and upscaled eddy covariance flux results for their temperature and precipitation responses and seasonal cycles of the regional fluxes. Two models with contrasting response patterns, LPX-Bern and JSBACH-HIMMELI, are used as priors in atmospheric inversions with Carbon Tracker Europe–CH4 (CTE-CH4) in order to find out how the assimilation of atmospheric concentration data changes the flux estimates and how this alters the interpretation of the flux responses to temperature and precipitation. Inversion moves wetland emissions of both models towards co-limitation by temperature and precipitation. Between 2000 and 2018, periods of high temperature and/or high precipitation often resulted in increased emissions. However, the dry summer of 2018 did not result in increased emissions despite the high temperatures. The process models show strong temperature and strong precipitation responses for the region (51 %–91 % of the variance explained by both). The month with the highest emissions varies from May to September among the models. However, multi-model means, inversions, and upscaled eddy covariance flux observations agree on the month of maximum emissions and are co-limited by temperature and precipitation. The setup of different emission components (peatland emissions, mineral land fluxes) has an important role in building up the response patterns. Considering the significant differences among the models, it is essential to pay more attention to the regional representation of wet and dry mineral soils and periodic flooding which contribute to the seasonality and magnitude of methane fluxes. The realistic representation of temperature dependence of the peat soil fluxes is also important. Furthermore, it is important to use process-based descriptions for both mineral and peat soil fluxes to simulate the flux responses to climate drivers.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

An inconsistency in aviation emissions between CMIP5 and CMIP6 and the implications for short-lived species and their radiative forcing

We report on an inconsistency in the latitudinal distribution of aviation emissions between the data products of phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP). Emissions in the CMIP6 data occur at higher latitudes than in the CMIP5 data for all scenarios, years, and emitted species. A comparative simulation with the chemistry–climate model ECHAM/MESSy Atmospheric Chemistry (EMAC) reveals that the difference in nitrogen oxide emission distribution leads to reduced overall ozone changes due to aviation in the CMIP6 scenarios because in those scenarios the distribution of emissions is partly shifted towards the chemically less active higher latitudes. The radiative forcing associated with aviation ozone is 7.6 % higher, and the decrease in methane lifetime is 5.7 % larger for the year 2015 when using the CMIP5 latitudinal distribution of emissions compared to when using the CMIP6 distribution. We do not find a statistically significant difference in the radiative forcing associated with aviation aerosol emissions. In total, future studies investigating the effects of aviation emissions on ozone and climate should consider the inconsistency reported here.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1976

Optical emissions from the mid-day aurora

Intensities of various optical emissions from mid-day auroras and spectral profile of N2(+) ING bands measured aboard a jet aircraft are presented. The data are compared with simple calculations based on present knowledge of the types and energy distributions of particles precipitating in the mid-day auroral region and the available cross-sections for the excitation of various optical emissions in air. The analysis concerns the interaction of magnetosheath protons with the atmosphere, electron interaction with the atmosphere, resonant scattering of sunlight by N2(+) ions, and auroral emissions around 3886 A. It is shown that most of the OI red and green line emissions in the mid-day aurora are excited by the low-energy electrons precipitating in the cusp region, but only part of the N2 and N2(+) emissions can be so accounted, while precipitating protons excite the rest of N2 and N2(+) emission. The emission feature around 3886 A observed in mid-day aurora is most likely He 3888 A blended with N2(+) ING(1, 1) band.

Sivjee, G. G.↗

NASA NTRS1976

V.L.F. emission from ring-current electrons

Characteristics of VLF emissions detected by satellite in association with enhancements of ring-current electrons during magnetic storms and substorms are described along with the associated enhancements in electron intensities and the anisotropies of the ring-current electron distribution. It is shown that the emissions are observed only when the satellite is outside the plasmasphere, that the beginning of the emissions coincides with the satellite's encounter with the large electron fluxes in that region, and that the increase in electron intensities associated with the observed emissions is limited only to low-energy electrons. The frequency distributions of emissions with peak frequencies above and below half the electron gyrofrequency at the equator is analyzed. The bimodal frequency distribution of the equatorial whistler-mode emissions is explained in terms of different production regions for emissions at frequencies above and below half the equatorial electron gyrofrequency.

Maeda, K.↗

NASA NTRS1977

VLF emissions associated with enhanced magnetospheric electrons

VLF emissions and enhancements of low-energy electrons have been simultaneously observed during periods of geomagnetic disturbances by the equatorial orbiting Explorer 45 satellite. These events are characterized by the following: (1) the VLF emissions occur outside the plasmasphere in the nightside of the magnetosphere, (2) the emissions consist of two frequency regimes, one below the local electron gyrofrequency, and the other above it, (3) the emissions below the gyrofrequency are relatively broadband whistler waves characteristic of chorus, (4) the emissions above the gyrofrequency are electrostatic and typically have components near 3/2 the gyrofrequency, (5) the onset of emissions coincides with abrupt increases outside the plasmasphere in 1-10 keV electrons to intensities of the order of 10 to the 8th el/sq cm/s/sr/keV, and (6) the cessation of the emissions coincides with a drop in the electron intensities to their preenhancement levels, which are of the order of 10 to the 6th el/sq cm/s/sr/keV or less.

Anderson, R. R.↗

NASA NTRS1978

An energy-dependent map of the X-ray emission of the Perseus cluster

Results are discussed for X-ray scans of the Perseus cluster with the SAS 3 slat detectors. Counting rates in two broadband channels (1.5 to 5.5 keV and 5.5 to 15.5 keV) are compared as a function of the instrument scan angle measured from the center of emission, and it is found that the emission in the higher energy range is broader in extent. Tests for a systematic energy-dependent error in the background demonstrate that the discovered energy dependence of the Perseus cluster emission is valid. Iron line emission is determined by two methods, various models are fitted to the data, and the total cluster emission in the two energy ranges is computed. The iron line emission is determined to be 0.003 photon/sq cm per sec. It is concluded that the diffuse emission increases in the range from 1.5 to 15.5 keV within the bounds of a model involving a point source with a radius not exceeding about 3 arcmin plus a diffuse source.

Ulmer, M. P.↗

NASA NTRS1976

Introductory study of the chemical behavior of jet emissions in photochemical smog

Jet aircraft emissions data from the literature were used as initial conditions for a series of computer simulations of photochemical smog formation in static air. The chemical kinetics mechanism used in these simulations was an updated version which contains certain parameters designed to account for hydrocarbon reactivity. These parameters were varied to simulate the reaction rate constants and average carbon numbers associated with the jet emissions. The roles of surface effects, variable light sources, NO/NO2 ratio, continuous emissions, and untested mechanistic parameters were also assessed. The results of these calculations indicate that the present jet emissions are capable of producing oxidant by themselves. The hydrocarbon/nitrous oxides ratio of present jet aircraft emissions is much higher than that of automobiles. These two ratios appear to bracket the hydrocarbon/nitrous oxides ratio that maximizes ozone production. Hence an enhanced effect is seen in the simulation when jet exhaust emissions are mixed with automobile emissions.

Whitten, G. Z.↗

NASA NTRS1980

Pollutant emissions from flat-flame burners at high pressures

Maximum flame temperatures and pollutant emission measurements for NOx, CO, and UHC (unburned hydrocarbons) are reported for premixed methane air flat flames at constant total mass flow rate over the pressure range from 1.9 to 30 atm and for equivalence ratios from 0.84 to 1.12. For any given pressure, maxima typically occur in both the temperature and NOx emissions curves slightly to the lean side of stoichiometric conditions. The UHC emissions show minima at roughly the same equivalence ratios. The CO emissions, however, increase continually with increasing equivalence ratio. Flame temperature and NOx emissions decrease with increasing pressure, while the opposite is true for the CO and UHC emissions. The NOx data correlate reasonably well as a function of flame temperature only. Four flameholders, differing only slightly, were used. In general, the temperature and emissions data from these four flameholders are similar, but some differences also exist. These differences appear to be related to minor variations in the condition of the flameholder surfaces.

Maahs, H. G.↗

NASA NTRS1982

The Mg II resonance line emission at 2800 A in stars with different rotational velocities and different metal abundances

In many investigations, a study of the Mg II 2800 A emission was conducted in order to derive more information about the correlation of chromospheric emission with the properties of the convection zone. It has been suggested by Ayres and Linsky (1980) that there is a positive correlation between rotation and chromospheric emission at least for binary stars. The present investigation is concerned with such a correlation between rotation and chromospheric emission. Since large differences in rotational velocities are observed for F stars for which also strong chromospheric emission is observable, this particular study deals mainly with F stars. On the basis of observations of the Mg II emission in F and G stars, it is found that the emission is abnormally strong in close binary F stars. This may be explained by the generation of a large differential rotation due to tidal effects which may give very efficient dynamo generation of a surface magnetic field.

Boehm-Vitense, E.↗

NASA NTRS1984

Secondary electron emission characteristics of ion-textured copper and high-purity isotropic graphite surfaces

Experimentally determined values of true secondary electron emission and relative values of reflected primary electron yield for untreated and ion textured oxygen free high conductivity copper and untreated and ion textured high purity isotropic graphite surfaces are presented for a range of primary electron beam energies and beam impingement angles. This investigation was conducted to provide information that would improve the efficiency of multistage depressed collectors (MDC's) for microwave amplifier traveling wave tubes in space communications and aircraft applications. For high efficiency, MDC electrode surfaces must have low secondary electron emission characteristics. Although copper is a commonly used material for MDC electrodes, it exhibits relatively high levels of secondary electron emission if its surface is not treated for emission control. Recent studies demonstrated that high purity isotropic graphite is a promising material for MDC electrodes, particularly with ion textured surfaces. The materials were tested at primary electron beam energies of 200 to 2000 eV and at direct (0 deg) to near grazing (85 deg) beam impingement angles. True secondary electron emission and relative reflected primary electron yield characteristics of the ion textured surfaces were compared with each other and with those of untreated surfaces of the same materials. Both the untreated and ion textured graphite surfaces and the ion treated copper surface exhibited sharply reduced secondary electron emission characteristics relative to those of untreated copper. The ion treated graphite surface yielded the lowest emission levels.

Curren, A. N.↗

NASA NTRS1984

Wave emissions from dc and modulated electron beams on STS 3

During the third Space Shuttle Columbia flight (STS 3) in March 1982, investigations were conducted to assess the electrical, electromagnetic, and plasma environment of the orbiter and to diagnose wave emissions and related plasma effects due to the injection of an electron beam into the surrounding ionosphere. Attention is given to wave emissions and related plasma processes which were stimulated by the first electron beam emissions from the Space Shuttle. The on-orbit measurements are compared to measurements made in a space simulation chamber. Instrumentation and operations are considered along with the plasma effects of beam emissions, wave emissions from dc beams, wave emissions from VLF-modulated beams, and wave emissions from ELF-modulated beams.

Shawhan, S. D.↗

NASA NTRS1985

Far-infrared line emission from the galaxy

The diffuse 157.74 micron (CII) emission from the Galaxy was sampled at several galactic longitudes near the galactic plane including complete scan across the plane at (II) = 2.16 deg and (II) = 7.28 deg. The observed (CII) emission profiles follow closely the nearby (12)CO (J=1to0) emission profiles. The (CII) emission probably arises in neutral photodissociation regions near the edges of giant moleclar clouds (GMC's). These regions have densities of approximately 350 cm(-3) and temperatures of approximately 300 K, and amount to 4x10(8) solar mass of hydrogen in the inner Galaxy. The total 157.74 micron luminosity of the Galaxy is estimated to be 6x10(7) solar luminosity. Estimates were also made of the galactic emission in other far-infrared (FIR) cooling lines. The (CII) line was found to be the dominant FIR emission line from the galaxy and the primary coolant for the warm neutral gas near the galactic plane. Other cooling lines predicted to be prominent in the galactic spectrum are discussed. The 145.53 micron (OI) emission line from the Orion nebula was also measured.

Stacey, G. J.↗

NASA NTRS1985

Emission features in the 4-13 micron spectra of the reflection nebulae NGC 7023 and NGC 2023

Spectroscopy from 4 to 13 microns of the visual reflection nebulae NGC 7023 and NGC 2023 has been obtained. These data, together with previous work from 1 to 4 microns, show that the spectra of these sources consist of a relatively flat continuum from 1 to 13 microns and six emission features at 3.3, 3.4, 6.2, 7.7, 8.6, and 11.3 microns. The observations rule out equilibrium thermal emission for the features and continuum in reflection nebulae, and point toward a nonequilibrium emission mechanism such as thermal emission from thermally fluctuating small grains or fluorescence from large molecules. The similarity of the emission feature spectra in reflection nebulae to those in other sources suggests a universal emission mechanism, thus implying nonequilibrium emission mechanisms in other sources.

Sellgren, K.↗

NASA NTRS1986

The emission of atoms and molecules accompanying fracture of single-crystal MgO

The emission of particles due to deformation and fracture of materials has been investigated. The emission of electrons (exoelectron emission), ions, neutral species, photons (triboluminescence), as well as long wavelength electromagnetic radiation was observed; collectively these emissions are referred to as fractoemission. This paper describes measurements of the neutral emission accompanying the fracture of single-crystal MgO. Masses detected are tentatively assigned to the emission of H2, CH4, H2O, CO, O2, CO2, and atomic Mg. Other hydrocarbons are also observed. The time dependencies of some of these emissions relative to fracture are presented for two different loading conditions.

Dickinson, J. T.↗

NASA NTRS1987

Diffuse infrared emission of the galaxy: Large scale properties

A quantitative analysis of Infrared Astronomy Satellite (IRAS) data in the galactic plane shows that: about 66% of the power radiated in the 100 micron band comes from the diffuse medium, the other 33% coming from well identified luminous sources. The diffuse emission has almost constant colors throughout the Galaxy, similar to the local cirrus colors. The sources have a much lower 12 micron/25 micron and a much high 60 micron/100 micron emission ratio than the diffuse component, giving a very striking anticorrelation in the color-color diagrams. The separation between one narrow and a second broader component shows that the molecular component does not provide much more than one half of the diffuse emission in the molecular ring: this implies a 4 pi nuI(nu) emissivity at 100 microns for the atomic component of about 2.4 x 10 to the minus 30th watts per H atom, 10 times higher than the emissivity of the molecular component at the same galactocentric radius. The atomic component emissivity measures the interstellar radiation field density. The temperature distribution of the 2 components is discussed comparing IRAS data with measures of the 900 micron emission of the galactic plane, which appears to be dominated by cold dust in the narrow component.

Puget, J. L.↗

NASA NTRS1987

The origin of the diffuse galactic IR/submm emission: Revisited after IRAS

Balloon observations are compared with Infrared Astronomy Satellite observations. There was good agreement for the longitudinal profiles. However, the dust emission observed by IRAS, contrary to the balloon observations which show dust emission only within the absolute value of b is equal to or less than 3 degrees, extends all the way to the galactic pole. The model fits were repeated using more recent parameters for the distribution of interstellar matter in the galactic disk and central region. The IR luminosities are derived for the revised galactic distance scale of solar radius - 8.5 Kpc. A total IR luminosity of 1.2 E10 solar luminosity is obtained, which is about one third of the estimated stellar luminosity of the Galaxy. The dust emission spectrum lambdaI(sub lambda) attains it maximum at 100 microns. A secondary maximum in the dust emission spectrum occurs at 10 microns, which contains 15% of the total IR luminosity of the Galaxy. The galactic dust emission spectrum was compared with the dust emission spectra of external IRAS galaxies. The warm dust luminosity relates to the present OB star formation rate, while flux densities observed at longer submm wavelengths are dominated by cold dust emission and thus can be used to estimate gas masses.

Cox, P.↗

NASA NTRS1987

The NII 2143 A emission in the dayglow

Observations of the N II 2143 A emission in the earth's dayglow were obtained by a rocket-borne spectrograph flown on Nov. 9, 1981, and Aug. 11, 1982. The ultraviolet spectra were analyzed using synthetic spectra to separate the contribution of the 2143 A emission from the overlapping nitric oxide gamma band. The 2143 A column emission rate profiles for both flights were quite similar with peak column emission intensities of approximately 500 Rayleighs at an altitude of 160 km. When the observed column emission rate profiles were compared with theoretical calculations, the production efficiency of this emission was found to be 0.10 + or - 0.04. The 2143 A emission varies by more than a factor of 3 over the solar cycle and therefore should be useful as an indicator of the solar EUV flux.

Cleary, D. D.↗

NASA NTRS1988

Methane emissions to the troposphere from the Amazon floodplain

The magnitudes of CH4 emissions to the troposphere from the Amazon River floodplain and the mechanism of these emissions were investigated using the data of 94 individual flux measurements made along a 1700-km stretch of the river during July/August 1985. The overall average rate of CH4 emission from wetlands was found to be 390 mg CH4/sq m per day, with the highest emissions (590 mg CH4/sq m per day) attributed to the water surfaces covered by aquatic macrophytes. Ebullition was the dominant mechanism of emission, accounting for 85 percent of the total. Surface-water CH4 concentrations were highly supersaturated, averaging 6.4 micromolar. The annual emission of CH4 from the Amazon Basin to the troposphere, estimated from the area and the known emission rate, is about 10 CH4 Tg/yr, indicating the importance of the area in the global atmospheric CH4 cycle.

Devol, Allen H.↗