bluuebunny/crossref_metadata_2025 huggingface dataset:
Methane production and emission in a Texas rice field
Authors: Sass R. L. , Fisher F. M. , Harcombe P. A. , Turner F. T.
Published: February 2008

To refine estimates of source strengths from agricultural wetlands and to study the process of methane production and emission, this study was carried out in rice fields at the Texas A&M University Agricultural Research and Extension Center, Beaumont, Texas, during the summer of 1989. It focussed on two fields on different soil types (Lake Charles clay and Beaumont clay) and spanned a period from shortly after permanent field flooding (June 6, 1989) until field draining prior to harvest (August 28, 1989). Integrated methane emission over 75 days ranged from 4.5 to 15.9 g m−2 . Aboveground biomass, net primary production, and root biomass were determined. Methane emission was strongly related to aboveground biomass in one of two fields studied. Laboratory incubations of soil cores show that methane production by soil bacteria is highest near the soil surface in the rice row and decreases with depth and distance from the plant. Much of the seasonal increase in total methane production is due to increasing activity at intermediate depths and distances from the plants. The temporal and spatial distribution of methane production was found to be related to root biomass. Seasonally integrated emission was 42% of methane production in both fields. Soil pore water methane and plant stem gas composition are related to the distribution in the soil of methane production and root biomass. Methane production ceased with field draining prior to harvest, even following prolonged anaerobic incubation. Methanogenesis rapidly resumed with added acetate substrate.
Inorganic nitrogen over the western North Atlantic Ocean
Authors: Hastie D. R. , Malle S. , Toom D. L. , Whelpdale D. M. , Keene W. C. , Galloway J. N. , Maben J. , Pszenny A. A. P.
Published: February 2008

The concentrations of the reactive nitrogen species NO2, NOx(= NO + NO2), NOy (the sum of all compounds of nitrogen and oxygen with the exception of N2O), particulate NO3−, and volatile NO3− were measured from ship and aircraft platforms over the western North Atlantic Ocean as part of the GCE/CASE/WATOX experiment. Air masses sampled were divided into continentally influenced and typical marine on the basis of trajectories, and radon and black carbon measurements. From the NO3− measurements on size separated aerosol and the altitude variations of volatile NO3− and particulate NO3−, a significant interaction between volatile NO3− and sea salt aerosol was indicated. The average marine concentrations measured were: 18 nmol m−3 for NO2, 29 nmol m−3 for NOx, 46 nmol m−3 for NOy, and 10 nmol m−3 for total inorganic NO3−. The reactive nitrogen species were present at concentrations some 40 times those encountered in the remote Pacific Ocean, whereas the inorganic NO3− was only 3 times higher.
Sulfur in the western North Atlantic Ocean atmosphere: Results from a summer 1988 ship/aircraft experiment
Authors: Galloway James N. , Keene William C. , Pszenny Alexander A. P. , Whelpdale Douglas M. , Sievering Herman , Merrill John T. , Boatman Joe F.
Published: February 2008

To investigate the relative importance of anthropogenic versus marine sources of sulfur in the North Atlantic Ocean troposphere, sulfur species were measured from aircraft, ship, and island based platforms as part of the Global Change Expedition/Coordinated Air‐Sea Experiment/Western Atlantic Ocean Experiment conducted during the summer of 1988. Four synoptic meteorological cases were examined: flow from highly populated North America, lightly populated North America, tropical oceanic regions, and polar oceanic regions. Literature values suggest that 2–10 μmol m−2 day−1 of (CH3)2S are emitted from the ocean to the atmosphere in marine regions associated with the first three synoptic cases. Data from this experiment indicate that 36, 16, and 14 μmol m−2 day−1, for the highly populated North America, lightly populated North America, and tropical oceanic regions synoptic cases, respectively, were deposited to the ocean's surface. Differences between previously estimated natural emissions and calculated deposition suggest that anthropogenic sources of sulfur contribute significantly to sulfur deposition for these cases. The sulfur deposition rate for the polar oceanic regions synoptic case was 20 μmol m−2 day−1 . Given the larger range of literature values for the corresponding (CH3)2S emission rate (1–14 μmol m−2 day−1 ) , however, the relative importance of the nonmarine S source is less certain in this case.
Trace elements in the North Atlantic troposphere: Shipboard results of precipitation and aerosols
Authors: Church T. M. , Véron A. , Patterson C. C. , Settle D. , Erel Y. , Maring H. R. , Flegal A. R.
Published: February 2008

Samples for trace metals in precipitation (rain, snow, and fog) and total aerosols were collected at sea as part of the GCE/CASE/WATOX expedition during August and September 1988 in the greater North Atlantic between Bermuda, Iceland, the Azores, and Barbados. The samples were collected using ultra‐clean equipment and methods for the analysis of the trace elements Al, Fe, Mn, Zn, Cu, Ni, Cd, and Pb (including stable isotopes). The samples were analyzed by graphite furnace atomic absorption spectrometry and thermal ionization mass spectrometry. Based on stable lead isotopes and retrospective isentropic air mass analyses, four air mass sources were evidenced including (1) temperate U.S. and (2) boreal Canadian westerlies, and (3) boreal and northern Europe easterlies associated with (4) Mediterranean and Saharan easterlies. Lead isotopic signatures clearly distinguished emission source regions over the North Atlantic with 206Pb/207Pb ratios of 1.19–1.22 for North American westerlies, 1.10–1.12 for European boreal easterlies, and 1.15–1.16 for Saharan trade easterlies. Also, the contrasting ratios between precipitation and aerosol demonstrate a vertical mixing of chemical sources in precipitation from contrasting air masses of different origin. The air mass trajectories were independently calculated and are in general agreement with the lead isotopic tracers. The isotopic tracers allowed more confident conclusions on air mass sources, particularly after a few days of oceanic transport. Also, the trajectories appeared to be very useful in explaining the strong variability of the trace metal concentrations during restricted periods of sampling time aboard a moving ship. To a lesser extent, the atmospheric emission sources were characterized by trace element concentrations. The occurrence of large dust loadings in the Saharan trade easterlies contributed abundant crustal elements and were also associated with enriched anthropogenic elements from southern Europe. Scavenging ratios were calculated for lead and cadmium during select periods when aerosol and precipitation were collected under the same meteorological regimes. The cadmium ratio is much greater than that of lead, indicating that cadmium and lead are each transported or scavenged on distinct populations of aerosols. For lead, the ratio is less in the North Atlantic than in the Pacific, suggesting an aerosol concentration dependence. Like the Pacific, the ratios increase for the lead, dust, and sea salt. One may thus conclude that marine scavenging ratios cannot yet be used effectively until factors such as concentration dependency and local conditions of tropospheric processing are better defined.
K corona and magnetic sector boundaries
Authors: Hansen Shirley F. , Sawyer C. , Hansen Richard T.
Published: February 2008

Solar white‐light intensity maxima form a characteristic spatial pattern at the solar root of an interplanetary sector boundary, different for +/− and for −/+ boundaries. At a sector boundary, interplanetary magnetic polarities correspond to solar follower fields in the ascending part of the solar activity cycle and to leader fields in the decline.
Electron heat flux instabilities in the solar wind
Authors: Gary S. Peter , Feldman W. C. , Forslund D. W. , Montgomery M. D.
Published: February 2008

There are at least three plasma instabilities associated with the electron heat flux in the solar wind. This letter reports the study of the unstable fast magnetosonic, Alfvén and whistler modes via a computer code which solves the full electromagnetic, linear, Vlasov dispersion relation. Linear theory demonstrates that both the magnetosonic and Alfvén instabilities are candidates for turbulent limitation of the heat flux in the solar wind at 1 A.U.
A new plasma regime in the distant geomagnetic tail
Authors: Hardy D. A. , Hills H. K. , Freeman J. W.
Published: February 2008

The three Rice Suprathermal Ion Detector Experiments have detected an extensive region of low energy plasma flow antisunward along the ordered field lines in the lobes of the geomagnetic tail at lunar distances. This particle regime resembles the “boundary layer” and “plasma mantle” observed at smaller geocentric distances and an interior flow region parallel to the magnetopause in the dayside magnetosphere. It possesses plasma characteristics uniquely different from the plasma sheet and magnetosheath. Spatially the particle regime is found exterior to the plasma sheet across essentially the entire tail and adjacent to the magnetopause on both the dawn and dusk sides of the magnetosphere. The integral flux varies from 105 to 108 ions/cm² sec ster with the differential flux peak between 50 and 250 eV/q. Temperatures range from 4 × 104 to 5 × 105 °K and number densities from .1 to 5/cm³.
Whistler‐mode signals: Group delay by crosscorrelation
Authors: Thomson N. R.
Published: February 2008

Group travel times of 18.6 kHz whistler‐mode signal from NLK, Seattle, to Wellington, New Zealand, are now being measured using the normal FSK transmissions. This is done using a mini‐computer programmed to perform real‐time cross correlations between two receivers: one receiver gets its signal from a whip aerial on which the ground wave (subionospheric mode) dominates, while the other gets its signal from a loop oriented for minimum ground wave. Group travel time can thus be measured continuously while there are whistler‐mode signals present. Delays of 0.2–0.8 seconds have been found.
Recirculation of energetic particles in Jupiter's magnetosphere
Authors: Sentman D. D. , Van Allen J. A. , Goertz C. K.
Published: February 2008

A significant new finding from analysis of Pioneer 11 observations in the magnetosphere of Jupiter is that there is net streaming of both electrons Ee > 40 keV and Ee > 560 keV and protons 0.6l < Ep < 3.41 MeV away from the planet along high latitude field lines. This result is compatible with the recent suggestion of Nishida that energetic particles undergo trans‐L shell diffusion at low altitudes without significant change of energy. Our new finding coupled with his hypothesis and other considerations provides a plausible explanation for the remarkable pitch angle distributions near the equator in the range 12 < L < 25; the presence of particles of ≈ MeV energy at the outer edge of the magnetosphere; and hence, via conventional inward diffusion processes, the presence of those having magnetic moments of several hundred MeV per gauss in the inner magnetosphere. The recirculation of energetic particles emerges as an important dynamical feature of the Jovian magnetosphere. It is also suggested that emission of energetic particles into interplanetary space occurs at the polar caps rather than at the equator.
Electron impact ionization of Io's sodium emission cloud
Authors: Carlson R. W. , Matson D. L. , Johnson T. V.
Published: February 2008

The geometry of the sodium cloud associated with Io (Jupiter I) indicates that the lifetime of the neutral sodium atoms is an order of magnitude less than the photoionization lifetime. We suggest that ionization by thermal plasma electrons in the Jovian magnetosphere is the dominant Na loss process. Using plasma densities deduced from Pioneer 10 measurements, the lifetime and density distributions are calculated for Na and other species which may be present in the cloud around Io. Electron ionization of Na is found to be an order of magnitude faster than photoionization, in agreement with the lifetime deduced from Na cloud observations.
Diurnal and seasonal variations in atomic and molecular oxygen inferred from Atmosphere Explorer‐C
Authors: Mayr H. G. , Bauer P. , Brinton H. C. , Brace L. H. , Potter W. E.
Published: February 2008

Ion mass spectrometer data collected onboard the Atmosphere Explorer‐C satellite during the period December 1974‐January 1975 have been used to infer, via the ion chemistry, the molecular oxygen concentration near 250km. To filter out temperature induced variations the O2 densities and in situ neutral composition measurements of atomic oxygen were extrapolated down to 120km. At this level the latitudinal and diurnal variations of O are found to be consistent with the ones inferred from OGO‐6 during high levels of solar activity. The results also show that at mid to high northern (winter) latitudes the O2 concentration is about a factor of two higher than at low southern (summer) latitudes, thus revealing an apparent reversal of the winter to summer increase in O2 deduced from optical and incoherent scatter measurements during higher levels of solar activity. Considering that the winter oxygen bulge in the lower thermosphere apparently prevails throughout the solar cycle the latitudinal (annual) variations in O2 can play a decisive role in explaining the reversal of the winter anomaly during minimum solar activity. The diurnal variations in O2 reveal a pronounced minimum at 18 LT thus suggesting that photo dissociation of O2 is important.
Atmospheric electricity and earthquake prediction
Authors: Pierce E. T.
Published: February 2008

There are experimental indications that the release of radon from the ground may increase substantially before an earthquake. Illustrative calculations suggest that the observed increases would have appreciable effects on the parameters of atmospheric electricity. Typically, the fair weather conductivity near the ground would increase by some 50%, while the electric field (potential gradient) would decrease by about 30%. These alterations might be readily detectable in areas where the atmospheric electrical climate is largely unaffected by naturally disturbed weather, and where temporal changes in the electrical parameters, whether due to natural or to man‐made causes, are repetitive and therefore easily distinguishable from an earthquake effect.
Winds on Mars during the Viking season: Predictions based on a general circulation model with topography
Authors: Pollack James B. , Leovy Conway B. , Mintz Yale H. , Van Camp Warren
Published: February 2008

The Arakawa‐Mintz general circulation model of the Earth has been applied to Mars at the season of the nominal Viking Lander mission. Allowance has been made for the effects of the large Martian topography. The calculated wind fields exhibit significant zonally symmetric, topographically forced, and diurnal tidal components. Average wind speeds of 20‐25 m/sec were found at three possible landing sites, with wind speeds occasionally reaching values as much as a factor of 2 larger than these average values. If buffering by CO2 adsorbed in the regolith can be neglected, a pressure decline of about 0.8 mb is expected over the first 2 months of operation of the first lander.
Energies of backstreaming protons in the foreshock
Authors: Greenstadt E. W.
Published: February 2008

A predicted pattern of energy vs detector location in the cislunar region is displayed for proton guiding‐centers traveling upstream away from the quasi‐parallel bow shock. The pattern is implied by upstream wave boundary properties deduced by Diodato et al. (1976). In the solar ecliptic, protons are estimated to have a minimum of 1.1 times the solar wind bulk energy ESW when the wave boundary is in the early morning sector and a maximum of 8.2 ESW when the boundary is near the predawn flank.
Ultraviolet stellar occultation measurement of the H 2 and O 2 densities near 100 km in the Earth's atmosphere
Authors: Atreya S. K. , Donahue T. M. , Sharp W. E. , Wasser B. , Drake J. F. , Riegler G. R.
Published: February 2008

The density of molecular hydrogen in the earth's atmosphere has been measured between 95 km and 108 km. The technique involved use of the high resolution ultraviolet spectrometer of the Orbiting Astronomical Observatory Copernicus to observe radiation from the γ² Velorum near the R(0) line of the (0,0) Lyman absorption band at 1108Å as the star was occulted by the earth's atmosphere. The result shows H 2 densities varying from 1.05 −0.14+0.15 × 108cm−3 at 95 km to 1.1 −0.08+0.05 × 107cm−3 at 108 km. These densities agree quite well with recent theoretical predictions. The measured O 2 density profile generally agrees with the models except for a wave‐like structure between 104 km and 114 km.
Emission and enrichments of radon daughters from Etna Volcano magma
Authors: Lambert G. , Bristeau P. , Polian G.
Published: February 2008

A program of measurements in and outside the plume of Etna volcano has shown that radon daughters (as well as gaseous radon) are directly emitted from the magma. Enrichment factors have been observed : 4 for bismuth vs lead and 6 for polonium vs lead. The 210Pb total output measured for the Etna plume is an insignificant source for this nuclide.
Detection of infrasonic pulses from thunderclouds
Authors: Bohannon J. L. , Few A. A. , Dessler A. J.
Published: February 2008

Acoustic data obtained from thunderstorm observations during 1975 near Socorro, New Mexico, and during 1976 at J. F. Kennedy Space Center, Florida, exhibited single, infrasonic pulses superimposed on the thunder signals arriving from the cloud in each of several thunder records. Only the Socorro data have been quantitatively analysed thus far. These data show infrasonic pulses with periods of about 0.5 sec and amplitudes of about 0.1 N/m². We argue that these pulses were not generated by lightning channel heating. The pulse waveform is characterized by an initial compression followed by a rarefaction. Acoustic source reconstruction place the origins of these pulses in the cloud within essentially the same volume of space as the horizontal portions of the lightning channels. This volume is presumably the storage region for the charge participating in the lightning events. If the pulses are electrostatic in origin as predicted by Dessler [1973], then the data indicate a rapid (0.5 sec) intensification of the field prior to discharge.
Conjugate photoelectron fluxes observed on Atmosphere Explorer C
Authors: Peterson W. K. , Doering J. P. , Potemra T. A. , McEntire R. W. , Bostrom C. O.
Published: February 2008

High resolution energy spectra of the flux of precipitating photoelectrons which arise from solar illumination of the area near the magnetic conjugate point have been measured with the Photoelectron Spectrometer Experiment on the Atmosphere Explorer C Spacecraft. Conjugate photoelectrons have been observed when the spacecraft was well away from the terminator at local solar zenith angles up to 160°. The shape of the observed electron energy spectrum is almost identical to that reported for high altitude photoelectron spectra from the Atmosphere Explorer E Spacecraft by Doering et al., 1976. Identification of the residual spectral features in the energy spectra of the conjugate photoelectrons shows that to within the experimental uncertainty of ± 1 eV, the photoelectrons from the magnetic conjugate point have not experienced any acceleration. The magnitude of the observed conjugate photoelectron flux varies considerably between passes, but in some cases the 250 km flux has been observed to be as much as half of the magnitude of the escaping photoelectron flux at 300 km near the sunlit conjugate point. Observations of the precipitating and backscattered flux provide a direct measurement of the low energy (10 eV ‐ 60 eV) electron albedo.
Weber function computation in the interference reflected‐head wave amplitude
Authors: Marks L. W. , Hron F.
Published: February 2008

In the critical region, the complex amplitude of the interfering system of a head wave and its associated reflected wave can be described by a single formula for all eight types of interference waves. The formula consists of transmission, reflection and head wave coefficients, geometrical parameters of the layers and an appropriate Weber function. The real and imaginary parts of the Weber function can be shown to be the solutions of a system of first order differential equations. The system may be solved numerically with the help of existing subroutines in the computer software libraries. Upon determining the Weber function, one may construct amplitude‐distance curves for the interference reflected‐head waves of any desired type. Some properties of the amplitude‐distance characteristics can be directly inferred from the Weber function. The very good matching between this method and asymptotic ray theory outside the critical region suggests that a combination of the two would provide an efficient technique for ray amplitude calculation.
Io’s surface composition: Observational constraints and theoretical considerations
Authors: Fanale Fraser P. , Johnson Torrence V. , Matson Dennis L.
Published: February 2008

Observations of line emission from neutral and ionic species in the Io‐surrounding cloud, reflectance studies and theoretical considerations suggest Io’s surface is unlike that of any other body in the solar system. The cloud has a peculiar composition which we show is probably not due to cloud/surface fractionation. Io’s surface may be largely covered with an endogenically produced mixture of S and dehydrated salts, or by accretion‐fractionated compounds modified by charged particle bombardment.
Preliminary estimation of average tropospheric HO concentrations in the northern and southern hemispheres
Authors: Singh Hanwant B.
Published: February 2008

The global budget and hemispheric distribution of methyl chloroform (CH3CCl3) have been used to determine the average residence times of CH3CCl3, and HO radical concentrations, in the two hemispheres. It is concluded that a global average residence time (τa) of about 8 years best fits the observational data. It is further shown that the residence time of CH3CCl3 in the northern hemisphere (τn) is probably significantly longer than in the southern hemisphere (τs). While the ratio of τn/τs is quite sensitive to interhemispheric exchange rates (τe) and the north/south concentration gradients of CH3CCl3, a strong case for
can nevertheless be made. Best estimates suggest that the global average HO concentration
is most compatible with the observed data. The distribution of HO in the two hemispheres is, however, found to be asymmetric with southern hemispheric HO concentrations 1.6 to 3 times higher than the northern hemispheric values. It is inferred that this HO gradient is caused by atmospheric carbon monoxide, which is a principal sink for HO. The implications of these hemispheric HO asymmetries and the uncertainties involved are discussed.
Flushing of the continental shelf south of Cape Hatteras by the Gulf Stream
Authors: Blanton Jackson O. , Pietrafesa Leonard J.
Published: February 2008

Onslow Bay, an embayment south of Cape Hatteras in the South Atlantic Bight, responds to discrete southwestward and northeastward wind stress events. Occasionally, dramatic onshore‐offshore flow cycles occur that appear triggered by a large‐scale disturbance probably originating in the Gulf Stream. Winds and offshore disturbances drive a well‐defined circulation pattern from which it is estimated that Onslow Bay is flushed every 2 months. This agrees quite well with a freshwater removal rate of about 2.7 months and a Gulf Stream entrainment removal rate of 3 months.
The ionosphere and airglow of Venus: Prospects for Pioneer Venus
Authors: Cravens T. E. , Nagy A. F. , Chen R. H. , Stewart A. I.
Published: February 2008

In December of 1978, the Pioneer Venus Orbiter/Probe (PV) Missions will conduct a comprehensive investigation of the ionosphere of Venus. The purpose of this paper is to bring into focus our very limited current knowledge of the chemistry and physics of the Cytherean ionosphere in preparation for the major changes in this understanding that are undoubtedly going to occur as the result of the Pioneer Venus observations.

We have performed theoretical calculations of the energetics of the Cytherean ionosphere and we conclude that the PV measurements will find elevated ion and electron temperatures, resulting primarily from energy fluxes associated in some manner with the solar wind, and acting directly on the ion gas. Ultraviolet dayglow intensities were also calculated and we anticipate that the PV will observe hundreds of kR’s of CO2 related emission features such as the CO Cameron bands. Nightside ionosphere calculations were also made assuming the precipitation of energetic electrons as an ionization source, in order to reproduce observed (Venera 9, 10; Mariner 10) nightside electron density profiles. The intensities of some of the resulting emission features are also calculated.
Lidar observations of wave‐like structure in the atmospheric sodium layer
Authors: Rowlett J. R. , Gardner C. S. , Richter E. S. , Sechrist C. F.
Published: February 2008

The University of Illinois (Urbana) lidar system has been developed to study the atmospheric sodium layer near 90 km altitude through the mechanism of resonance scattering. The photocount data are processed using digital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Lidar photocount data processed using this filtering technique show wave‐like structures in the sodium layer which move downward with time. The waves have typical wavelengths of 3‐15 km and phase velocities of less than 1 m s−1. The movement of these structures seems to be independent of the motion of the bottomside of the layer, which also has been observed to move up or down by as much as 2 km over a period of a few hours. The presence of these motions is attributed to gravity waves and tidal oscillations present in the layer.
Measurements of electron density structure in striated barium clouds
Authors: Baker K. D. , Ulwick J. C.
Published: February 2008

Results are presented of the first measurements of detailed structure of electron density within striated vapor releases in the ionospheric F‐region. Six rocket probes penetrated ion clouds in three separate barium release events (two in each case) and showed considerable enhancement in F‐region electron density over the normal background ionization. In four traversais the electron density exceeded 10 cm−3 with the maximum of 5 × 106cm−3 observed in one case. Two showed dramatic structure in the electron density profiles associated with the passage through striated portions of the cloud. These structures had spatial extent as measured by the rocket probe normal to the terrestrial magnetic field of hundreds of meters with the density changing factors in the range from 2 to 10 as the probe passed into and out of the structures. The change of density on some of the features had particularly fast drop off corresponding to less than 20 meters travel normal to the magnetic field. The spectral power distribution of the irregularity amplitudes versus wavenumber scale size could be roughly described as a power law with a spectral index of from −2 to −3 within the striated regions. These results are in good agreement with predictions of the
gradient drift instability mechanism as depicted by the simulation studies of Scannapieco, et al. [1976] in the late time nonlinear regime.
Alteration of glass as a possible source of clay minerals on Mars
Authors: Gooding James L. , Keil Klaus
Published: February 2008

Thermodynamic calculations show that, under present Martian surface conditions, favorable gas‐solid weathering products of feldspar glasses should include beidellites (clays of the montmorillonite series) + carbonates + quartz. The gas‐solid weathering of mafic Silicate glass (of volcanic or impact origin) may similarly favor the production of metastable Fe‐rich montmorillonite clays. Simple mass‐balance calculations suggest that gas‐solid weathering of a Martian proto‐regolith containing 10% glass could conceivably produce a global blanket of clays at a rate ≥ 0.4 cm/109 yr. The production rate should be expected to increase significantly with the glass content and rate of reworking of the proto‐regolith and with the availability of water. Complete extraction of altered glass from a lunar‐like proto‐regolith might yield a global Martian clay blanket ∼10‐100 cm in thickness.
Stratospheric fluorine: A comparison between theory and measurements
Authors: Sze Nien Dak
Published: February 2008

Profiles for key stratospheric fluorine species are presented along with HF:HCl ratio. Discrepancies between theory and observation are examined and their implications are discussed. Our results indicate that the HF:HCl ratio depends critically on OH concentration between 20‐30 km and it might provide an indirect check on the present stratospheric OH chemistry or H2O abundances which are of central importance to stratospheric chemical processes.
Stratigraphic correlation of the radar‐detected subsurface interface in Mare Crisium
Authors: Maxwell Ted A. , Phillips R. J.
Published: February 2008

The delineation of spectrally distinct units in Mare Crisium allows a more complete interpretation of the single subsurface interface detected by the Apollo lunar sounder experiment. This interface is approximately 1400 m below the surface in the central mare region of Crisium, and 1000 m below the surface in the eastern bench region. Based on the power of the returned signal, and the small difference in dielectric constant of returned lunar basalts, it is probable that this interface represents a buried regolith between two major basin‐filling episodes. The contact between spectral Units 1 and 2 is the most likely cause for the radar‐reflecting interface. Based on this model, the thickness of Unit 3 is 400 m in the eastern part of the mare, and that of Unit 2 is 1000 m. Estimates of the original depth/diameter relations of Pierce are consistent with excavation of an older basalt from below a depth of 1400 m.
VHF radar studies of tropospheric velocities and irregularities using spaced antenna techniques
Authors: Röttger J. , Vincent R. A.
Published: February 2008

Observations of the troposphere with a VHF radar using a large antenna for transmission and small spaced antennas for reception show that atmospheric velocities measured by the drifts method agree well with balloon winds. Many of the echoes from the middle troposphere appear to come from horizontally stratified layers. Studies of the irregularity structure by measurement of the spatial coherence of these echoes and of their angular spectra by interferometric techniques show that many echoes are caused essentially by specular reflection.
Observations of two distinct populations of bow shock ions in the upstream solar wind
Authors: Gosling J. T. , Asbridge J. R. , Bame S. J. , Paschmann G. , Sckopke N.
Published: February 2008

Observations upstream of the earth's bow shock with the LASL/MPI fast plasma experiments on ISEE 1 and 2 reveal the presence of two distinct and mutually exclusive populations of low energy (≤ 40 keV) ions apparently accelerated at the bow shock. The first of these, the "reflected" population, is characterized by 1) sharply peaked spectra seldom extending much above ∼ 10 keV/ion and 2) relatively collimated flow coming from the direction of the shock. On the other hand, the "diffuse" ions are distinguished by relatively flat energy spectra above ∼ 10 keV and broad angular distributions. They are by far the most commonly observed upstream ion event. A close causal association is suggested between the diffuse ion population in the upstream solar wind and energetic plasma ions observed within the magnetosheath.
The mechanism of splintering during rime growth
Authors: Mossop S. C. , Wishart E. R.
Published: February 2008

We present evidence that the production of secondary ice particles during rime growth on a moving body is greater at low velocities relative to the number of drops accreted (over the range 1.4 to 3 m s−1). This favours the hypothesis that ‘splintering’ is due to the formation, round the periphery of the drop, of an ice shell which later shatters. Shell formation is more likely if drops land lightly and do not spread over the ice substrate.
The magnetic anomaly model of the Jovian magnetosphere: Predictions for Voyager
Authors: Dessler A. J. , Vasyliunas V. M.
Published: February 2008

The magnetic anomaly model, in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes, has been put forth to account for the various observed Jovian magnetospheric phenomena that show evidence of Jovian longitudinal asymmetry or planetary spin periodicity. From this model, normalized by empirical fitting to Pioneer 10 and 11 flyby data and to ground‐based radio data, a series of predictions are made that are subject to test by the forthcoming flybys of Jupiter by Voyagers 1 and 2. These predictions cover: (1) the longitude range and time intervals of enhanced interaction between Io (and possibly Europa) and Jupiter's ionosphere, (2) plasma, energetic particle, and magnetic field periodicities in the outer magnetosphere, and (3) the sub‐space‐craft System III longitude and the time, modulo 10 hours, of the first and subsequent magneto‐pause crossings.
A theoretical study of stratospheric trace species variations during a solar eclipse
Authors: Wuebbles Donald , Chang Julius S.
Published: February 2008

A one‐dimensional transport‐kinetics model is used to examine the variations in stratospheric minor species concentrations expected to occur during an eclipse of the sun. The short chemical lifetime of some of the important stratospheric species suggest that significant variations in concentration of some species are expected. Species which show large diurnal behavior, such as NO and OH, should be expected to have especially noticeable changes during the eclipse. Such variations during an eclipse, if measured, could provide a validation for the short response time chemistry in several catalytic cycles currently used in models of stratospheric chemistry.
Magnesium isotopic variations in hibonite from the Murchison Meteorite: An ion microprobe study
Authors: Macdougall J. D. , Phinney D.
Published: February 2008

Ion microprobe measurements show that some hibonite crystals from refractory‐rich inclusions in Murchison contain isotopically anomalous Mg. The observed effects include (1) the largest mass fractionation ever observed in nature for this element, ∼10% per mass unit; (2) small 26Mg excesses; (3) isotopic variability on a scale of microns or less in individual grains. These observations are corroborative evidence for the primitiveness of the Murchison inclusions. More importantly, they indicate that the types of Mg isotopic anomalies previously observed in Allende and Leoville inclusions are not confined to CV meteorites.
Observations of differences between regions of current flowing into and out of the ionosphere
Authors: Cattell Cynthia , Lysak Robert , Torbert R. B. , Mozer F. S.
Published: February 2008

A correlative study of field‐aligned currents, upflowing ions and electrostatic shocks has been made using data from the S3‐3 satellite. Upflowing ions with pitch angle distributions that are peaked at an angle to the magnetic field ("conics") are observed in all auroral current regions, but upflowing ions with distributions peaked along the field ("beams") are seen only in upward current regions. Thus, indirect evidence for parallel electric fields is seen in regions of upward current, but not in regions of downward current. Electrostatic shocks are usually observed in the current sheet associated with the polar cap convection boundary. In the evening, when this current is upward, shocks are largest. Indirect evidence for parallel electric fields is seen in regions of upward current, but not in regions of downward current. The altitude and magnetic local time dependence of upflowing ions and electrostatic shocks may be explained by the physical consequences of the differing particle populations carrying current into and out of the ionosphere. The data suggest that current‐driven turbulence plays a crucial role in energizing particles in the auroral zone.
Preliminary results from the Pioneer Venus Orbiter infrared radiometer: Temperature and dynamics in the upper atmosphere
Authors: Elson Lee S.
Published: February 2008

Data from the infrared radiometer aboard the Pioneer Venus Orbiter are examined and interpreted within the context of zonally averaged temperatures and circulation in the upper atmosphere of Venus. Surprisinglythe northern hemisphere pole is warmer than the equator throughout most of the region sampled. This implies both a rapid decrease with height of the 100 m/s cloud top winds previously observedand the probable existence of large (50 to 100 m/s) meridional winds.
Low frequency radio emissions from Jupiter: Jovian kilometric radiation
Authors: Kurth W. S. , Barbosa D. D. , Scarf F. L. , Gurnett D. A. , Poynter R. L.
Published: February 2008

A new component of the Jovian radio spectrum has been observed by the plasma wave instruments on Voyagers 1 and 2 at frequencies ranging from about 10 to 56 kHz or higher. This Jovian kilometric radiation is characterized by storms of emissions lasting typically 45 minutes at 56.2 kHzhowever some events persist for as long as four hours. The storms usually exhibit impulsive bursts with time scales of a few seconds to several minutesalthough some events show smoothly varying intensities as a function of time. High resolution frequency‐time spectrograms reveal a continuum‐like background with more intensenarrowband features superimposed. The narrowbandor discretefeatures tend to decrease in frequency with increasing timefalling ∼ 1 kHz in 5 to 60 seconds. The maximum power emitted assuming an isotropic radiator near Jupiter and a bandwidth for the most intense bursts of ∼ 10 kHz is about 109 watts. The Jovian kilometric radiation is most likely observed within ±45° of 200° System III longitudeλIII although there is a secondary maximum near λIII = 25°
Rapid growth of atmospheric cluster ions at the cold mesopause
Authors: Arnold F. , Joos W.
Published: February 2008

Composition measurements of proton hydrate ions at the cold summer polar mesopause conducted by use of an improved experimental method reducing cluster ion dissociation revealed the presence of ions more massive than observed previously. Time constants for ion hydration derived from the data decrease steeply with decreasing temperature becoming as low as about 2 seconds at the mesopause for temperatures around 130 K. This is interpreted as being due to the occurence of indirect ion hydration involving N2‐association followed by CO2‐ and H2O‐switching. Aeronomic implications are discussed.
Threshold windspeeds for sand on Mars: Wind tunnel simulations
Authors: Greeley R. , Leach R. , White B. , Iversen J. , Pollack J.
Published: February 2008

Wind friction threshold speeds (u*t) for particle movement (saltation) were determined in a wind tunnel operating at martian surface pressure with a 95 percent CO2 and 5 percent air atmosphere. The relationship between friction speed (u*) and free‐stream velocity (u∞) is extended to the critical case for Mars of momentum thickness Reynolds numbers (Reθ) between 425 and 2000. It is determined that the dynamic pressure required to initiate saltation is nearly constant for pressures between 1 bar (Earth) and 4 mb (Mars) for atmospheres of both air and CO2; however, the threshold friction speed (u*t) is about 10 times higher at low pressures than on Earth. For example, the u*t (Earth) for particles 210 µm in diameter is 0.22 m s−1 and the u*t (Mars, 5 mb, 200 K) is 2.2 m s−1.
Product distribution for the reaction of HO2 with CℓO
Authors: Leu Ming‐Taun
Published: February 2008

The product distribution for the reaction of HO2 with CℓO has been studied by a discharge flow/mass spectrometry/resonance fluorescence apparatus. The upper limits of the reaction channel producing HCℓ + O3 are 1.5% at 298K and 3.0% at 248K. The reaction product, HOCℓ, in the other channel, HOCℓ + O2, has been detected. The reaction proceeds mainly through this channel.
Photodissociation of isotopically heavy O2 as a source of atmospheric O3
Authors: Cicerone R. J. , McCrumb J. L.
Published: February 2008

18O16O is the sixth most abundant gas in the atmosphere after 14N14N, 16O16O, Ar, 15N14N and H2O. From available data on line positions in the Schumann‐Runge (S‐R) bands (175 < λ < 205 nm) of 18O16O we estimate its atmospheric photodissociation rates. In the high stratosphere and mesosphere this proposed source of O and O3 could be significant compared to photodissociation of 16O16O although our estimates are subject to several uncertainties that are discussed. We calculate the transmission of solar radiation through the S‐R bands of 18O16O and 16O16O with transmission functions averaged over individual S‐R bands. Line‐by‐line calculations will be needed to refine our estimates but certain spectroscopic data are not yet available.
Reconsideration of the relations between S and P Station anomalies in North America
Authors: Romanowicz Barbara A. , Cara Michel
Published: February 2008

The relation between S and P station anomalies is classically assumed to be linear. We reconsider this relation in the light of recent surface and body wave studies concerning the U.S., which suggest lateral variations of more than one independent physical parameter, such as thickness of a layer, in the first 200 to 300 km of the mantle. This implies breaking up the travel time data into provinces within which only one parameter can be assumed to vary. We apply this to U.S. data from ISC bulletins for the period 1964‐73, and find that the new correlations are more easily interpreted in terms of known physical processes in the upper mantle.
On the infrared radiative properties of CO2 ice clouds: Application to Mars
Authors: Hunt Garry E.
Published: February 2008

We have investigated the effect on the observed 20 µm brightness temperatures measured by the IRTM instrument, of the presence of cloud layers of CO2 ice particles. The results show that such clouds have a profound effect, and a layer corresponding to visible thickness of ∼0.5, can create brightness temperatures of 120‐130K, even when the surface is at 150K. This suggests that these clouds may also contribute to the effect of brightness temperatures below the CO2 frost point, which have been observed over the southern winter polar region.

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Predicted shift in the 13C/12C ratio of atmospheric carbon dioxide
Authors: Keeling Charles D. , Bacastow Robert B. , Tans Pieter P.
Published: February 2008

Knowledge of recent global changes in the rare isotopic species 13CO2 in atmospheric carbon dioxide does not now distinguish whether the land biosphere is a source or sink for fossil fuel carbon dioxide. The question is critically dependent on isotopic fractionation between the atmosphere and ocean water: if the isotopic fractionation factor for CO2 uptake at the air‐ocean boundary, αam, is approximately 0.986, as is the case for strongly alkaline solutions, the 13CO2 content of atmospheric CO2 is insensitive to changes in the biosphere; if αam is approximately unity, as now seems likely for ocean water, very accurate measurements, over the next decade or longer, will permit an estimate to be made of the net global loss or gain of biospheric carbon.
Electron energy distributions measured during electron beam/plasma interactions
Authors: Jost R. J. , Anderson H. R. , McGarity J. O.
Published: February 2008

In the large vacuum facility at the NASA‐Johnson Space Center an electron beam was projected ˜ 20 m parallel to B from a gun with variable accelerating potential (1.0 to 2.5kV) to an aluminum target. The ionospheric neutral pressure and field were approximated. Beam electron energy distributions were measured directly using an electrostatic deflection analyzer and indirectly with a detector that responded to the X‐rays produced by electron impact on the target. At low currents the distribution is sharply peaked at the acceleration potential. At high currents a beam plasma discharge occurs and electrons are redistributed in energy so that the former energy peak broadens to 10‐15 percent FWHM with a strongly enhanced low energy tail. At the 10% of maximum point the energy spectrum ranges from < ½ to ∼ 1.2 times the gun energy. The effect is qualitatively the same at all pitch angles and locations sampled.
The case against UV photostimulated oxidation of magnetite
Authors: Morris Richard V. , Lauer H. V.
Published: February 2008

We have studied the kinetics of magnetite oxidation in O2‐bearing atmospheres in the presence of electromagnetic radiation. No perceptible oxidation of magnetite by ultraviolet (UV) photostimulation occurred. These results do not corroborate previous conclusions by Huguenin (1973a,b; 1974) as to the occurrence of this process. Therefore, although we cannot totally rule out the possibility that the process actually occurs, we conclude that there is not yet a basis in laboratory experiments for inferring that UV photostimulated oxidation of magnetite occurs naturally on the surface of Mars.
SO2 Frost: UV‐visible feflectivity and Io surface coverage
Authors: Nash D. B. , Fanale F. P. , Nelson R. M.
Published: February 2008

The discovery of SO2 gas in Io's atmosphere and possible frost on Io's surface prompted us to measure the spectral reflectance of laboratory SO2 frost in the range 0.24 ‐ 0.85 µm. The frost samples were grown in suitable vacuum at 130°K and bi‐directional reflectance spectra were obtained by illuminating at 20° and observing at 60° from the sample normal. The spectrum of typical SO2 frost has very low reflectivity (2 ‐ 5%) at 0.30 µm, a steep absorption edge rising at 0.32 µm, maximum reflectivity (75 ‐ 80%) at 0.4 µm, and uniformly high reflectance throughout the visible and near infrared. These results, when compared with Io's full‐disk, Earth‐based reflectance spectrum, suggest that SO2 frost is not the dominant component of Io's optical surface layer. Various calculated UV‐visible spectra for mixtures of SO2 frost with other plausible surface components (sulfur allotropes and sodium sulfide) provide a good match to Io's spectrum and limit optically thick SO2 frost coverage to less than about 20% of Io's average projected surface area; this limit varies from a high of ∼ 25% on the leading hemisphere to a low of ∼ 10% on the sub‐Jupiter hemisphere.
Laboratory measurements of stratospheric sodium ion reactions
Authors: Perry R. A. , Rowe B. R. , Viggiano A. A. , Albritton D. L. , Ferguson E. E. , Fehsenfeld F. C.
Published: February 2008

Several association and switching reactions involving clusters of Na+ ions with stratospheric neutral molecules have been examined at temperatures ≤ 420 K with a flow‐tube apparatus. These measurements indicate that sodium compounds, NaX, that react with the H3O+·nH2O ions in the stratosphere will convert these ions into the clusters NaOH2+·nH2O, thereby supporting the recent assignment of these clusters as some of the ions observed during stratospheric rocket and balloon flights. Moreover, the rate constants for the association of Na+ with N2 and CO2, together with the bond dissociation of Na+·N2 and Na+·CO2 clusters, support the contention that the formation of the sodium cluster ions in the mesoshere can greatly increase the effective rate of electron recombination with sodium ions.