bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of the fine structure of auroral kilometric radiation
Authors: Grabbe Crockett L.
Published: February 2008

Recent data from ISEE which shows a banded fine structure to AKR, with each band being separated by the ion cyclotron frequency, is the first direct evidence for the three wave mechanism proposed by Grabbe et al. [1980] for the origin of AKR. Details of the predictions of this mechanism for the band structure are presented here, and estimates of the relative intensities of the bands for particular plasma parameters are made.
Ion acoustic wave forms generated by ion‐ion streams at the Earth's bow shock
Authors: Formisano V. , Torbert R.
Published: February 2008

The electric field experiment on board ISEE‐1 had a special mode of operation in which bursts of very high time resolution measurements were stored and slowly read‐out. This mode of operation allows us to study in detail the waveforms of the large amplitude electrostatic waves observed at the Earth's bow shock in a frequency range (10‐500 Hz) not well covered previously. These waves appear to be correlated with two streams in the ion angular distribution. Our observations indicate, therefore, that the ion‐ion stream instability is the dissipation mechanism of a collisionless fast quasi‐perpendicular shock wave.
Geodetic evidence for active landward tilting of the Oregon and Washington Coastal Ranges
Authors: Reilinger Robert , Adams John
Published: February 2008

Nine leveling routes that extend inland from near the coast of Oregon and Washington indicate consistent landward tilting of the 600‐km‐long coastal ranges at about 3 × 10−8 rad yr−1. Analysis of tide gauge observations indicates tilting with roughly the same magnitude and sense as the leveling measurements. These short‐term tilt rates (10‐80 yr) are comparable with longer term rates (≈100,000 yr) deduced from tilted marine terraces. Contemporary landward tilting is interpreted to result from continuing subduction of the Juan de Fuca plate beneath North America. The similarity between long‐ and short‐term deformation suggests that present‐day subduction is occurring via aseismic creep as hypothesized by Ando and Balazs [1979]. However, recent measurements of horizontal deformation in northwest Washington, which have been interpreted to indicate elastic strain accumulation, appear to be incompatible with aseismic subduction. Additional releveling observations along the Oregon routes (last observed in 1941) and further studies of late Pleistocene deformation along the coastal region of Oregon and Washington could help determine present‐day tectonics and assess the risk of large thrust earthquakes in this area.
Escape of heated ions upstream of quasi‐parallel shocks
Authors: Edmiston J. P. , Kennel C. F. , Eichler David
Published: February 2008

We investigate the free escape of ions from the post shock plasma into the region upstream of a fast collisionless shock. We find that the accessibility of downstream ions to the upstream region depends strongly on the upstream magnetic field shock normal angle as well as the upstream plasma parameters. Post shock ions escape upstream in significant numbers for shock normal angles below about 45°, in rough accord with the observed transition between quasi‐perpendicular and quasi‐parallel shock structure. We also calculate upstream ion distribution functions that resemble those of the observed “intermediate” ions and ion beams.
Reconnection in two dimensions: Localization of vorticity and current near magnetic X‐points
Authors: Matthaeus William H.
Published: February 2008

Simulations of reconnection utilizing spectral methods show that the “reconnection zone” exhibits internal structure in the form of a current filament and a “quadrupole” of kinetic vorticity. A qualitative model of the dynamical role of these local structures is presented. It is suggested that the effect of small scale structures near the X‐point is to increase the rate of reconnection.
Polar cap size and potential: A predicted relationship
Authors: Siscoe George L.
Published: February 2008

The model of the self‐consistent interaction between magnetospheric convection and the ionosphere as developed into a general formalism in separate papers by Vasyliunas, Wolf and Southwood leads to a fundamental relationship between the radius b of the ring formed in the ionosphere by the Region 2 Birkeland current system, regarded as a dependent variable, and the cross polar cap potential Φ and polar cap radius a, regarded as independent variables. When the control of Φ on a is taken into consideration in a time dependent model, one finds that a grows much more rapidly than b. This leads to a dilemma, which substorms can be used to resolve by removing magnetic flux from the polar cap. Thinning of the plasma sheet prior to substorms emerges as a simple, geometrical consequence of the model. For a steady potential, the system evolves to a steady state for which the functional dependences of the sizes of the polar cap and the Region 2 ring on Φ are found to be (a/Re) = α Φ3/16, (b/Re) = β Φ3/16, with α and β constants which satisfy β ‐ α « (1/2) (β+α). That is, the inter‐ring separation is predicted to be much less than the radii of the rings, as is observed.
Equatorial spread F instability conditions as determined from ionograms
Authors: Abdu M. A. , de Medeiros R. T. , Sobral J. H. A.
Published: February 2008

Conditions of plasma irregularity (or Spread F) generation under the Rayleigh‐Taylor mechanism in the nighttime equatorial ionosphere are examined from ionogram data registered over Fortaleza (4°S, 38°W, mag. dip lat. −1.7°) Brazil for a one year period. The results show that local ionospheric conditions such as the bottomside F‐region electron density scale length and the ion‐neutral collision frequency at the base of the layer, at sunset hours, determine the generation of the spread F irregularities over the equator in the post sunset hours.
Natural and anthropogenic trace gases in the southern hemisphere
Authors: Rasmussen R. A. , Khalil M. A. K. , Crawford A. J. , Fraser P. J.
Published: February 2008

Concentrations of CCl3F (F‐11), CCl2F2 (F‐12), CHClF2 (F‐22), C2Cl3F3 (F‐113), CH3CCl3, CCl4, C2Cl4 (PCE), CH3I, CHCl3, CO, CH3Cl, CH4, N2O, and OCS were measured in and above the boundary layer (0–4 km) of the southern hemisphere (latitudes 30°S–40°S, longitudes 138°E–146°E) during November 1981. The measurements were made by EC/GC, GC/FID, EC/GC/TP and GC/MS (GC‐gas chromatography; EC‐electron capture; FID‐flame ionization detector; TP‐temperature programmed; MS‐mass spectroscopy). The concentrations are reported, the results are analyzed statistically to uncover differences of concentration in and above the boundary layer and unusual observations are explained.
Trends in stratospheric concentrations of trace gases in the Northern Hemisphere during the years 1974–1979
Authors: Leifer R. , Larsen R. , Toonkel L.
Published: February 2008

During the years 1974‐1979 the CCl3F concentration in the Northern Hemisphere stratosphere increased by a factor of 2. The annual rates of increase were directly related to annual rates of emissions at the surface of the earth. The production data for fluorocarbons, published by the Chemical Manufacturers Association, show a decline in the yearly rate of emission of CCl3F during the last decade. The yearly percent increase in the mean stratospheric concentration in the Northern Hemisphere has shown a similar decline. Data for CCl4, CCl2F2 and SF6 also show a slowing in the annual rate of increase in the stratospheric mean concentration. The calculated globally averaged concentration of N2O in the Northern Hemisphere remained constant at 249±7 n1/1 during the years 1976‐1979.
Erosion of frozen sulfur dioxide by ion bombardment: Applications to Io
Authors: Melcher C. L. , LePoire D. J. , Cooper B. H. , Tombrello T. A.
Published: February 2008

The erosion of frozen SO2 due to bombardment by both light and heavy ions (He and F) was measured for bombarding energies of 0.08 to 1.3 MeV/amu. The number of SO2 molecules ejected from the target per incident ion (i.e., the sputtering yield) was 50 for 1.5 MeV He ions and 7300 for 6 MeV F ions. Ion bombardment followed by heating produced an oxygen/sulfur residue which was much more stable against subsequent ion bombardment than the initial frozen SO2. The erosion rate of SO2 frost on Jupiter's moon Io depends strongly on the elemental composition and energy spectra of the magnetospheric ion flux which bombards the surface. The combined effects of ion bombardment and heating which produced residues on our target substrates may also occur on Io from magnetospheric ion bombardment and heating by volcanism. Our experimental results compare favorably with a new model of the sputtering process which considers the energy loss of the incident ion to electronic excitation in the target.
Electromagnetic wave energization of heavy ions by the electric “phase bunching” process
Authors: Mauk B. H.
Published: February 2008

Magnetic "wave trapping" and what is termed here electric "phase bunching" are shown to be the high and low energy behaviors which result when a magnetized heavy ion interacts with a nearly resonant electromagnetic cyclotron wave. The properties of electric "phase bunching" are explored by computer simulation. Because these properties match observations it is concluded that the strongly cyclotron phase bunched and energized helium ions, observed in association with waves in the earth's geostationary magnetosphere, are generated by this electric "bunching" process.
Coherent annual and interannual variations in temperature and height fields in the tropical troposphere and lower stratosphere
Authors: Gage K. S. , Reid G. C.
Published: February 2008

Radiosonde observations of temperature and height fields for 1953‐1969 have been analyzed for five tropical Pacific stations (Ponape, Guam, Yap, Eniwetok and Koror). These data have been combined to form monthly means averaged over all years and stations and annual means averaged over all stations.

The analysis reveals a coherent annual variation consistent with the well‐known annual temperature wave in the tropics, i.e., a tropospheric cycle with warmest temperatures around April and May, and a roughly out‐of‐phase lower stratospheric cycle with coldest temperatures during the period December‐May. Comparing year‐to‐year variations in the tropospheric and lower stratospheric thermal fields, we find the out‐of‐phase relationship preserved. Periods of warm anomalies in the troposphere coincide with periods of cold anomalies in the stratosphere and vice versa. These observations are consistent with annual and inter‐annual variations in the intensity of the Hadley cell circulation.
The effect of polarization on radar detection of lightning
Authors: Mazur Vladislav , Walker Gene B.
Published: February 2008

The polarization dependence of lightning echoes received with a 23‐cm wavelength radar is estimated theoretically and experimentally. The reduction in the lightning radar cross‐section due to the transmission of circular polarization instead of linear is measured to be about 4 dB and is much smaller than the 15‐30 dB reduction in reflectivity of weak precipitation regions. The 8.7 dB average reduction in reflectivity maxima has been observed. This leads to an increase in the detected lightning flash rate by as much as 40%. The radar cross‐section ratio of circular to linear polarization obtained experimentally suggests that lightning elements tend to be horizontally oriented.
A refined gravity model from Lageos (GEM‐L2)
Authors: Lerch F. J. , Klosko S. M. , Patel G. B.
Published: February 2008

A refined gravity field model, Goddard Earth Model GEM‐L2, has been derived using the Lageos orbital data yielding better baseline measurements for the analysis of tectonic plate motion. This field also contributes to an improved understanding of long wavelength features, such as the sea slope across broad ocean basins, through its significant improvement of the long wavelength geoid (through degree and order 4). The geoid for these terms has an accuracy estimated at ± 8 cm in GEM‐L2. GEM‐L2, as in all recent Goddard Earth Models, relies heavily on the precise near‐Earth satellite laser ranging data, in this case provided by NASA's Crustal Dynamics Program. Two and a half years of Lageos laser data acquired from over 20 well‐distributed stations were combined with the existing data from the best satellite‐derived model, GEM‐9, to develop the new Lageos model. Testing shows that the Lageos gravity field error at long wavelengths is less than half that for GEM‐9. Independent tests using well determined longitude accelerations of 24‐hour satellites have verified the improved accuracy of the new model. A comparison of global laser "base" stations from independent data sets of alternating 15 day data segments over the 2 1/2 years of Lageos show total inter‐station positioning to ± 1.8 cm when using this new field. The same comparison using the 1979 versus the 1980 Lageos data yields ± 5.2 cm; this difference in agreement reflects the change in data distribution and other systematic errors along with the tectonic motion which has occurred between these chronologically distinguishable data sets. Five day average polar motion values with a precision of 10 cm and change in length of day values accurate to better than .5 msec have been derived in the solution. The adjustment of these parameters are necessary to achieve the accurate stations and geopotential results in GEM‐L2.
Paleomagnetic data from the Coso Range, California and current status of the Cobb Mountain normal geomagnetic polarity event
Authors: Mankinen Edward A. , Grommé C. Sherman
Published: February 2008

Two basalt flows which erupted about 1.08 m.y. ago in the Coso Range, California, have normal magnetic polarity and thus provide additional evidence for the Cobb Mountain normal polarity event. A review of available data confirms that this event was of geomagnetic origin. A mean age of 1.10 ± 0.02 m.y. B.P. for the Cobb Mountain normal polarity event was found to best fit all available radiometric and geologic data.
Remote sensing of energetic particle boundaries
Authors: Daly P. W.
Published: February 2008

A discussion of the possible ways in which various surfaces such as the magnetopause, topology interfaces, and source boundaries (plasma sheet or flux transfer events) can be remotely sensed by energetic particles is presented, together with results of computer simulations of particles in a model magnetopause. The conclusions are that these boundaries can indeed be detected from a distance, but that care must be taken to identify the nature of the particle gradient, particularly if more than one gyro‐radius is being employed. The distances to the boundary calculated from the simple absorbing wall model will over‐estimate the true separation, but the direction determined from the simple model should be correct.
Energetic ion beam in the Earth’s magnetotail lobe
Authors: Lui A. T. Y. , Krimigis S. M.
Published: February 2008

Occurence of a prominent peak in the ion energy spectrum at energies of 0.1 to 0.7 MeV is observed by the IMP‐8 spacecraft during an energetic particle burst in a plasma “dropout” interval at about 37 Re in the earth’s magnetotail. This unusual characteristic in the spectrum is detected for about 2 minutes. By fitting the observed ion spectra to a drifting Kappa distribution, it is found that the ion population can be described as a hot beam with number densities 4 × 10−7 to 5 × 10−4 cm−3 and temperatures 15 to 45 keV, jetting tailward at speeds of 3500 to 7000 km/s. The energy flux density associated with the beam can be as high as 8 × 10−2 ergs cm−2 sec−1.
Optical emissions induced by spacecraft‐atmosphere interactions
Authors: Torr Marsha R.
Published: February 2008

During 1974 while analyzing photometer data obtained from the Atmosphere/Explorer‐C satellite, a significant brightness enhancement was discovered surrounding the velocity vector of the instrument. This enhancement appeared to be generated as a result of the interaction of the spacecraft with the atmosphere at a relative velocity of 8 km/sec. The enhancement was found to be inversely dependent on altitude and to have a broad spectral characteristic (the range covered was 3371 Å to 7320 Å) with the most intense effect occuring at the longer wavelengths. In this paper we review these earlier findings, and relate them to the observations of similar glows associated with the Space Shuttle. We also discuss glows that have been studied in laboratory experiments and others that have been reported on various rocket flights. We report a significant brightness enhancement associated with the vehicle wake.
Temperature measurements in the Earth's stratosphere using a limb scanning visible light spectrometer
Authors: Rusch D. W. , Mount G. H. , Zawodny J. M. , Barth C. A. , Rottman G. J. , Thomas R. J. , Thomas G. E. , Sanders R. W. , Lawrence G. M.
Published: February 2008

The temperature of the earth's atmosphere between 40 and 50 km is inferred from measurements of Rayleigh scattered sunlight by a visible‐light spectrometer on the Solar Mesosphere Explorer spacecraft. The RMS deviation of the satellite measurements from conventional rocket measurements is 5°K above 45 km and 2‐3°K below 45 km. The satellite data are compared to model temperatures for March, 1982.
Expansion of the aftershock zone following the Vanuatu (New Hebrides) Earthquake on 15 July 1981
Authors: Chatelain Jean‐Luc , Cardwell Richard K. , Isacks Bryan L.
Published: February 2008

Following a large (Ms=7.0), interplate earthquake on 15 July 1981 in the Vanuatu (New Hebrides) Islands, the area defined by the aftershocks dramatically increased over a two week period of time. The aftershocks were located using the Cornell/ORSTOM seismograph network that has been monitoring earthquakes with magnitudes larger than mb=2.9 in the region since mid‐1978. In the first few hours following the mainshock, the area defined by the aftershocks was consistent with the rupture zone of a typical interplate earthquake with the observed seismic moment of 5.8 × 1026 dyne‐cm. However, during the 16 days following the mainshock, the area of the aftershock zone increased to approximately 10 times the area of expected coseismic rupture. The final aftershock zone included earthquakes that were located within the overriding and descending plates as well as along the interplate fault zone. The migration of aftershocks away from the rupture zone of the 1981 mainshock indicates that, at least in some cases, the aftershock zone can overestimate the extent of coseismic rupture.
An exploratory study of the thermal conductivity of methane hydrate
Authors: Cook J. G. , Leaist D. G.
Published: February 2008

Recent discoveries of natural gas hydrates in permafrost and sub‐oceanic environments have led us to measure the thermal conductivity of methane hydrate. A guarded hot‐plate cell was constructed and tested with various ice specimens. We find the conductivity of methane hydrate near −60°C is 0.45 W/mK, a value close to that obtained for other clathrate hydrates by us and others. It is much lower than for ice (by a factor of about 5), so that a logging tool based on this property should prove to be of use in identification of gas hydrates in permafrost zones.
Reconnection in the Jovian magnetosphere
Authors: Nishida A.
Published: February 2008

In the nightside Jovian magnetosphere, Voyager 1 and 2 detected signatures of reconnection. The anti‐sunward streaming events, recognized and designated as magnetospheric winds by Krimigis et al., were clearly associated with the northward inclination of the magnetic field. The reconnection is likely to be due to the need to adjust the length of the extended nightside field lines to the dimension of the dayside magnetosphere, but it is not a steady‐state feature and shows considerable variability. In addition to these events, there were numerous occasions where northward and southward field polarities were mixed at the neutral sheet. These latter events were observed by Voyager 2 beyond about 80 RJ where the observed field across the neutral sheet exceeded the dipole field strength, and they probably represent the product of the tearing mode.
Ring coupling model: Implications for substorm onsets
Authors: Crooker N. U. , Siscoe G. L.
Published: February 2008

In the ring coupling model the criterion for substorm onset is the narrowing of the auroral oval to some critical limit. The auroral oval is taken to be the annulus bounded by Rings 1 and 2, corresponding to the locations of the Iijima‐Potemra Regions 1 and 2 Birkeland currents. It is shown that this criterion is met following both southward and northward turnings of the interplanetary magnetic field (IMF). The behavior of the rings in response to typical variations in the north‐south component of the IMF produces a variety of observed substorm sequence patterns. The energy source for substorms in the model is the solar wind energy stored in the magnetotail, whereas the energy for geomagnetic storms comes directly from the solar wind. The model is consistent with the half‐wave rectifier response of the magnetosphere to the IMF.
Magnetic turbulence and diffusion processes in the magnetopause boundary layer
Authors: Gendrin R.
Published: February 2008

The thickness of the magnetopause boundary layer can be explained by anomalous cross‐field diffusion of magnetosheath protons resonating with either electrostatic or electromagnetic waves (Tsurutani and Thorne, 1982). Whereas the first mechanism was favored by these authors on the basis of ISEE measurements, GEOS data, which are obtained when the magnetosphere is contracted, seem to show that the second one may be more important, at least during disturbed conditions. The special relationship which exists between the proton resonant energy and the frequency of right‐handed electromagnetic waves leads to a preferential diffusion of protons of a few keV. The ability of electromagnetic waves to evacuate the energy dissipated during the generation of turbulence is also discussed.
Localized plasma depletion in the ionosphere and the equatorial spread F
Authors: Basu B. , Coppi B.
Published: February 2008

A spatially localized gravity driven instability is proposed to be the likely candidate for the observed kilometer scale‐size density irregularities in the bottomside equatorial F region. It is noted that the classical Rayleigh‐Taylor instability, which relies on the frozen‐in condition (implying E·B=O) and is of the flute‐type (k·B=O), is not compatible with the experimental observations of density perturbations that have a finite extent along the magnetic field lines, while dissipative localized modes, which allow the plasma to move through the magnetic field as a result of finite electrical resistivity effects are consistent with such experimental findings. These modes have three‐dimensional structures with wavelengths in the east‐west direction (λϕ) of the order of a few kilometers.
Separation of high‐frequency PN phases and mantle refracted P phases at distances between 6° and 18° in the western Pacific by ocean bottom seismograph array
Authors: Ouchi Toru , Nagumo Shozaburo , Kasahara Junzo , Koresawa Sadayuki
Published: February 2008

Observations of high‐frequency (HF) Pn phases by an oceanbottom seismometer (OBS) array were made at distances between 6° and 18° in the north‐western Pacific. At this distance range, mantle‐refracted P phases arrive earlier than HF‐Pn phases. These two phases are successfully separated for near surface earthquakes by applying appropriate filtering, since the dominant frequencies of HF‐Pn phases are higher than 6 Hz and the frequencies of mantle‐refracted P phases are rather low, about 3 Hz. The apparent velocities of HF‐Pn phases in this distance range are estimated to be from 8.3 to 8.1 km/sec or even lower, while those of mantle‐refracted P waves are from 8.4 to 8.6 km/sec. The reported value of 8.33 km/sec for Hf‐Pn phases appears to be an average of both HF‐Pn and mantle‐refracted P phases. Therefore, these observations suggest that a proposed additional HF‐Pn wave guide for the higher velocity of 8.33 km/sec is questionable.
Current channelling, the consequences for electromagnetic soundings
Authors: Fischer Gaston
Published: February 2008

The presumed occurrence in the crust of the Earth of concentrated currents which are not caused by local induction is at present a controversial subject. Trying to assess the effects such so‐called "injected channel currents" may have on magnetotelluric (MT) and geomagnetic deep soundings (GDS), we have looked at the way currents of purely internal origin would manifest themselves in records of electromagnetic soundings. If all the electromagnetic fields are the result of true local induction these fields will combine above the structure into a nearly perfect standing wave. If, however, anomalous currents are injected from outside, the fields will comprise an additional travelling wave which gives away the injected currents. Therefore, the conclusion from quasi‐static theory that it is impossible, over a one‐dimensional structure, to separate internal and external fields cannot be upheld and MT and GDS soundings will be affected by these anomalous injected currents.
Periodic intensity variation in [SIII] 9531A emission from the Jupiter plasma torus
Authors: Roesler F. L. , Scherb F. , Oliversen R. J.
Published: February 2008

The intensity variation of [SIII] 9531 A line emission from the hot plasma torus of Jupiter was measured from Kitt Peak National Observatory during April 1982 using a scanning Fabry‐Perot spectrometer with a field of view 2 RJ in diameter centered at 6 RJ on the centrifugal equator. During the observational period, which covered 43 rotations of Jupiter, the intensities showed a periodic variation consistent with a zone of enhanced emission approximately 90° in longitude rotating with a period of 10.2 hours, or 2.8% longer than Jupiter' rotational period.
Source of stable remanence in chromite ores
Authors: Kumar Anil , Bhalla M. S.
Published: February 2008

Rock magnetic investigations of both the natural chromite ores and their purified chromite concentrate (Mg.6Fe.4Cr1.4Al.6O4) were carried out. These include, measurement of natural and saturation remanent magnetism and their stability with respect to alternating field and thermal demagnetisation, IRM acquisition studies, saturation magnetisation versus temperature studies and high field (1000 mT) hysteresis characteristics. From these studies it was observed that the medium/high coercivity component of remanence is associated with the chromite minerals and is carried largely or entirely by them. Therefore, it is concluded that chromites carry permanent magnetisation of palaeomagnetic significance. However, this result is in sharp contrast to the assumption in the literature that the spinels of the above composition are non‐magnetic. The study has also demonstrated that the magnetic properties of artificial Fe‐Cr spinels do not conform to their natural analogues. Reasons for the discrepancy have been postulated.
Experiments on TRM intensity dependence on cooling rate
Authors: Brown Elizabeth McClelland
Published: February 2008

Palaeointensity studies have an important role to play in understanding the origin and time variation of the geomagnetic field. However, theoretical considerations indicate that the intensity of magnetization recorded by a rock or archaeological sample will be dependent on the rate at which it cooled as well as field magnitude. Experiments on synthetic magnetite and titanomagnetites of varying grain sizes indicate that for acicular magnetite at low concentration, slower cooled TRM is stronger than faster cooled TRM, but for all other samples slower cooled TRM is weaker. This is the predicted behaviour. However the magnitude of the effect is much greater than the predicted kinetic effects and indicates that the magnetization of sub‐microscopic magnetite‐rich inclusions in the titanomagnetites strongly controls the TRM intensity of the matrix.
Evaluation of effective eddy diffusive coefficients using radar observations of turbulence in the stratosphere
Authors: Woodman R. F. , Rastogi P. K.
Published: February 2008

Radar observations show that thin persistent layers of turbulence occur sporadically in the troposphere and stratosphere. Two probabilistic approaches are used to show that the vertical eddy diffusivity due to such layers is of the order of 0.2‐0.3 m²/sec in the lower stratosphere. An actual realization of turbulent layers, derived from the radar observations at Arecibo, is used in a numerical approach to obtain a profile of eddy diffusivity. It is suggested that turbulence plays a significant role in the vertical transport of trace constituents in the stratosphere.
Air pollution studies in the Norwegian Arctic
Authors: Joranger E. , Ottar B.
Published: February 2008

Measurements of sulfur pollutants at stations in the Norwegian Arctic, 1977‐1983, show persistent annual variations with maximum values in the winter season. These are mostly due to low‐level transport of polluted air from industrial areas in northern USSR. The pulsating character of the air pollution episodes is related to the synoptic scale pressure variations. Aircraft measurements in March 1983 show the presence of thin stratified layers of polluted air at elevated tropospheric levels. In summer the Arctic air is generally very clean, and elevated concentrations are mainly due to a direct transfer from source areas in northwestern Europe across the Norwegian Sea. The aircraft measurements show that the Arctic aerosol has a narrow and very homogeneous size distribution, indicating a stable aerosol that is not subject to chemical reactions and further growth.
Correlated sediment thickness, temperature gradient and excess pore pressure in a marine fault block basin
Authors: Abbott Dallas , Menke William , Hobart Michael , Anderson Roger N. , Embley Robert W.
Published: February 2008

Measurements of temperature gradient and excess pore pressure in the surficial sediment of a fault block basin in the Guatemala Basin correlate with sediment thickness. The temperature gradient is smaller and the excess pore pressure gradient is more negative in areas of thinner sediment. This correlation is explained by postulating downward pore water advection within the sediments, with flow velocities on the order of 10−9 to 10−8 m/s in the thinnest sediments and much less flow in the thickest sediments. Sediment physical properties and pore water chemistry also support this interpretation. Since the conductive heat flow of the basin as a whole is less than one third that predicted by sea floor spreading models, the oceanic basement may be the site of a vigorous hydrothermal circulation system. The pore water advection in the sediments may be driven by this larger scale circulation.
A multisatellite study of the plasma sheet dynamics at substorm onset
Authors: Sauvaud J. A. , Saint‐Marc A. , Dandouras J. , Rème H. , Korth A. , Kremser G. , Parks G. K.
Published: February 2008

A multi‐satellite study has been conducted on the temporal relationship between energetic particle injections observed at the geostationary orbit onboard GEOS‐2 and decreases of thermal plasma sheet particle fluxes ("plasma sheet thinnings") observed in the more distant geomagnetic tail onboard the ISEE‐1 and ‐2 spacecraft. A case by case analysis as well as a statistical study of 100 events recorded from February to May 1979 and 1980 show that particle injection and particle flux decrease are detected to within less than 5 minutes of each other, for an average intersatellite distance of 15.7 RE. The observed spread in Δt corresponds best to Alfvén wave transit times. These particle phenomena are observed at the onset of the auroral zone magnetic bays. The results reported here suggest that the dynamics of the inner and outer boundaries of the plasma sheet are closely related to each other and controlled by large scale processes that develop at substorm onset inside the magnetospheric tail and result in a cross‐tail current disruption.
Spectral characteristics of two types of low latitude aurorae
Authors: Tinsley B. A. , Rohrbaugh R. P. , Rassoul H. , Barker E. S. , Cochran A. L. , Cochran W. D. , Wills B. J. , Wills D. W. , Slater D.
Published: February 2008

Auroral emissions at low latitudes appear to be due to energy loss from trapped ring current ions or electrons of energy of order of 1eV rather than keV electrons accelerated along field lines as in the ordinary polar aurora. Two types of low latitude aurorae have been observed in Texas in our measurements during the last few years. The features observed to predominate in the first type are N2+1N bands showing high vibrational/rotational development, OI 7774 Å emissions, and sometimes Hydrogen Balmer β emissions. These spectral characteristics indicate precipitation of the ring current particles themselves, directly as ions, and/or indirectly as energetic neutrals following charge transfer with exospheric H or O neutrals. The second type consists predominantly of [OI]6300Å and [NI] 5200 Å emission and other features of excitation potential only a few eV, with spectral characteristics indicating excitation by electrons from a population with kT ∼ 1eV. The second type can give the brighter displays more easily visible to the naked eye, although the first appears to be more frequent. The time variations of the emissions have been found to be closely related to fluctuations of periods less than an hour in the magnetograms from nearby observatories.
Atomic recombination into excited molecular ‐ A possible mechanism for shuttle glow
Authors: Green Byron David
Published: February 2008

A class of mechanisms is presented which could give rise to the observed glow above Shuttle surfaces exposed to energetic collisions with ambient atmospheric constituents as the Shuttle sweeps through its orbit. The collisional energies involved are sufficient to dissociate atmospheric N2 upon impact with the Shuttle surfaces. The N‐atoms formed can recombine on or over the surfaces to produce high vibrational levels of the N2 A(³∑u+) electronic state. At Shuttle altitudes, collisional quenching is negligible and the metastable N2 (A, high v) molecules slowly radiatively decay to form N2 B(³∏g) molecules on a millisecond time scale. The B state molecules then rapidly radiate to the A state producing the red N2 First Positive Bands. This mechanism can explain both the spatial and spectral distributions of the observed glow.
In situ porosity distribution using geophysical tomography
Authors: Daily W. D. , Ramirez A. L.
Published: February 2008

A geotomograph of an in‐situ fractured granite rockmass has been quantitatively interpreted to yield estimates of porosity distribution. This was accomplished by comparing the tomograph‐measured electromagnetic properties of the rock with laboratory measurements of the rock's electromagnetic properties at various known water contents. These estimates of water content are interpreted as values of rockmass porosity because the formation is fully saturated.
Substorm associated traveling compression regions in the distant tail: Isee‐3 Geotail observations
Authors: Slavin J. A. , Smith E. J. , Tsurutani B. T. , Sibeck D. G. , Singer H. J. , Baker D. N. , Gosling J. T. , Hones E. W. , Scarf F. L.
Published: February 2008

While in the lobes of the distant magnetotail, ISEE‐3 encountered regions of compressed magnetic field, δB/Bo=0.3‐0.1, at a rate of several per day. The duration of these events was 5 to 20 minutes and they were observed 10 to 30 minutes following the onset of substorm activity near the earth. During each event, the lobe magnetic field tilted first northward and then southward with the inflection point near the time of peak field strength. Following the compression events, the lobe field weakened and retained a southward component for 20 to 40 minutes. It is suggested that these traveling compression regions (TCR’s) are the lobe signatures of plasmoids moving rapidly down the tail in the plasma sheet. Comparison of ISEE‐3 compression event times with substorm onset times yielded propagation speeds of 350 to 750 km/s.
Simultaneous observation of HF‐enhanced plasma waves and HF‐wave self‐focusing
Authors: Frey A. , Duncan L. M.
Published: February 2008

Intense HF‐radiowaves of the ordinary mode transmitted from the ground enhance plasma waves near the reflection height. These have been extensively studied in the past by the use of Incoherent‐Scatter‐Radars. Intense HF‐radiowaves propagating in the ionosphere also produce electron density irregularities with scale sizes much larger than the HF wavelength of ∼ 60 m. These have been observed by radio star intensity scintillations. For the past 2 years a new method was used at Arecibo, P.R. which allows radar‐ and scintillation‐measurements at 430 MHz to be performed simultaneously along the same line of sight. The scale sizes deduced from the scintillation measurements are shorter than the scale sizes observed with the radar and are inconsistent with the HF‐power density thresholds predicted by existing theories.
winds at St. Peter and St. Paul Rocks during the first sequal year
Authors: Garzoli Silvia L. , Katz Eli Joel
Published: February 2008

Wind observations were obtained during the first nine months of the SEQUAL field program from a station maintained at St. Peter and St. Paul (SPP) rocks. Winds are very steady from May to November and very unsteady during April when the Intertropical Convergence Zone (ITCZ) crosses the site. Wind stress components are computed and comparison with 1979 data shows that the onset of the winds occurred one month earlier in 1983 but is of similar amplitude. The spectral analysis of the wind shows a significant increase in the variance for periods between 3‐5 days and 10‐15 days.
Simulation of the seasonal cycle in the Tropical Atlantic Ocean
Authors: Philander S. G. H. , Pacanowski R. C.
Published: February 2008

Simulation of the seasonal cycle in the tropical Atlantic Ocean with a multi‐level primitive equation numerical model yields remarkably realistic results including the separation of the Brazilian Current from the coast and the reversal of the Countercurrent.
Frame modulus reduction in sedimentary rocks: The effect of adsorption on grain contacts
Authors: Murphy William F. , Winkler Kenneth W. , Kleinberg Robert L.
Published: February 2008

The adsorption of vapor on the internal surface of a sandstone reduces its frame moduli. A theoretical model has been developed which predicts the weakening as a function of fluid chemistry and effective pressure. The model is based on well established contact theory and surface chemistry. Frame moduli are directly proportional to the stiffness of the grain contacts. The contact stiffness is dependent on surface energy. We show how the adsorption of various chemicals onto quartz surfaces lowers the surface energy, thereby weakening the contact stiffness. The predicted variation of frame moduli with the partial pressure and chemical species is qualitatively consistent with recent experimental results. The calculations suggest that the chemical effect is only significant at low effective pressures. At high pressures, the elastic loading dominates the contribution due to surface energy.
Errors in the anisotropy of magnetic susceptibility and magnetic remanence of unconsolidated sediments produced by sampling methods
Authors: Gravenor C. P. , Symons D. T. A. , Coyle D. A.
Published: February 2008

Samples from glacial varves were obtained by cutting cubes and by pushing plastic cubical containers into the sediment. The anisotropy of magnetic susceptibility results show that the mean angular difference in the kmax direction can be altered by 32° by pushing in the sample containers in a north to south versus an east to west direction. The values of lineation and Q are raised or lowered dependent upon the direction of push and the original fabric direction.

Mean remanence directions can deviate by as much as 43° in a single clay layer dependent upon the direction in which the sample containers are inserted into the sediment. Corresponding changes in mean intensity of the remanence also demonstrate that the remanence has been affected by pushing in sample containers. The overall results underline the need to adopt trustworthy procedures for the sampling of soft sediments deposited by settling and traction.
Year‐to‐year CO2 variations at Amsterdam Island in 1980‐83
Authors: Ascencio‐Parvy J. M. , Gaudry A. , Lambert G.
Published: February 2008

The atmospheric CO2 concentrations at Amsterdam Island (37°41′S; 77°47′E) from October 1980 to November 1983 showed an increase rate of 0.11 ppm/month for a 3‐year average with considerable variability within each year: 0.06‐0.14 ppm/month in 1981, 0.04‐0.12 in 1982 and 0.13‐0.25 in 1983. The natural evasion of oceanic CO2 following the 1982/1983 El Nino event could account for a part of the anomalous change.
Geodynamic mixing in the mesosphere boundary layer and the origin of oceanic islands
Authors: Allègre Claude J. , Turcotte Donald L.
Published: February 2008

Since the isotopic heterogeneity of ocean island basalts (OIB) is of variable character and requires billions of years to evolve, we propose to explain the observed heterogeneity by mixing between delaminated continental lithosphere, a continental crustal component, depleted mantle and pristine mantle. Such mixing occurs in a boundary layer located at the bottom of the upper mantle from which ascending blobs rise.
Aircraft measurements of ammonia and nitric acid in the lower troposphere
Authors: LeBel Peter J. , Hoell James M. , Levine Joel S. , Vay Stephanie A.
Published: February 2008

The first simultaneous measurements of ammonia and nitric acid in the troposphere have been made from an aircraft using a tungsten oxide denuder system. Vertical profiles of NH3 and HNO3 taken over coastal Virginia and Maryland in March and September, 1983, at altitudes from 150 m to 3000 m, show mixing ratios that decrease with altitude. Ammonia profiles show substantial seasonal variation, while nitric acid profiles do not. Using the measured profiles, we calculate, with a one‐dimensional photochemical model, life‐times due to heterogeneous loss of 1 day for HNO3 and 10 days for NH3. In contrast, NH3 profiles up to 5300 m over the North Atlantic ocean during August, 1982 show mixing ratios that increase slightly with altitude. These data represent the first ammonia profiles measured over the ocean. We suggest that the increase in NH3 with altitude is a result of an ammonia‐rich continental air mass advected over the ocean followed by the dissolution of NH3 in the marine boundary layer on water‐covered sea salt particles.
Global transport of atmospheric smoke following a major nuclear exchange
Authors: Haberle Robert M. , Ackerman Thomas P. , Toon Owen B. , Hollingsworth Jeffery L.
Published: February 2008

A fully interactive zonally symmetric general circulation model is used to simulate the transport and evolution of a massive smoke cloud that is likely to form in the atmosphere following a major nuclear war. The presence of such a cloud significantly alters the simulated circulation and the subsequent transport of the smoke particles themselves. While the model indicates a tendency for interhemispheric exchange, the most immediate effect is that the radiatively active particles are carried into the stratosphere by the generation of strong vertical motions and intense convection regardless of their initial injection altitudes.
In‐situ measurements of nitric oxide in the high latitude upper stratosphere
Authors: Horvath Jack J. , Frederick John E.
Published: February 2008

A rocket‐launched parachute‐deployed chemiluminescence sensor measured the vertical profile of nitric oxide from Poker Flat, Alaska, latitude 65.13 degress North, in August 1984 and in January and February 1985. All data refer to daylight periods shortly after local noon and cover altitudes from a lower limit of 27‐30 km up to 48‐53 km. Between 35 and 45 km the results indicate a large seasonal variation, with wintertime mixing ratios being roughly a factor of two above summer values. The winter profiles contained sharp positive vertical gradients that persisted through the highest altitudes observed, and near 50 km the mixing ratio from the Feburary flight exceeded that seen in summer by a factor of four. Above the stratopause the mixing ratio observed in February increased dramatically and between 52 and 53 km reached 148.9 ppbv, an order of magnitude greater than typical mid‐latitude values measured with this instrument. Such behavior is consistent with the absence of photodissociation in winter and a downward flux of odd nitrogen arising from a source located significantly higher than the stratopause, almost surely in the lower thermosphere. These results clearly support the existence of a vertical coupling between diverse regions of the atmosphere in the high latitude winter.
Origin of mantle peridotite and komatiite by partial melting
Authors: Herzberg C. T. , O'Hara M. J.
Published: February 2008

Theoretical calculations and some preliminary experimental observations show that the liquidus and solidus temperatures for each of a wide range of upper mantle peridotite and komatiite compositions become coherent at high pressures. This suggests that these materials may have been liquids in eutectic‐like equilibrium (rather than peritectic‐like) with mantle assemblages. It is shown that the major element geochemistry of 83 mantle peridotites and 61 komatiites define a trend which is not primarily due to an olivine control process; rather it is interpreted to represent the pressure‐induced compositional trace of eutectic liquids in equilibrium with mantle assemblages from 4 to 15 GPa. If the bulk Earth is chondritic in composition these phase equilibrium constraints would imply that the upper mantle had formed from the whole mantle as an ultrabasic partial melt, the transition zone and lower mantle being the complementary eclogite and pyroxenite residua. This is consistent with mineralogical interpretations of seismic data for the present‐day Earth which call for a peridotite upper mantle and pyroxene‐like transition zone and lower mantle.
Heat flow from the West African Shield
Authors: Brigaud Frédéric , Lucazeau Francis , Ly Saidou , Sauvage Jean François
Published: February 2008

The heat flow over Precambrian shields is generally lower than over other continental provinces. Previous observations at 9 sites of the West African shield have shown that heat flow ranges from 20 mW m −2 in Niger to 38‐42 mW m −2 in Liberia, Ghana and Nigeria. Since some of these values are lower than expected for Precambrian shields, it is important to find out whether or not they are representative of the entire shield before trying to derive its thermal structure. In this paper, we present new heat flow determinations from seven sites of the West African shield. These indicate that the surface heat flow is comparable with that of other Precambrian shields in the world.
Early Mesozoic tectonic history of the boundary area, east‐central Alaska
Authors: Foster Helen L. , Cushing Grant W. , Keith Terry E. C. , Laird Jo
Published: February 2008

Thrust faulting in the Yukon‐Tanana Upland of east‐central Alaska has long been hypothesized, but few thrust faults have been definitely identified. In the Boundary area near the international border between Alaska and Canada metamorphic rocks of the amphibolite facies have been thrust over rocks of the greenschist facies. Subordinate thrust faults and imbrication occur within both groups of rocks. Brecciation, slickensides, slickenfibers, rootless, isoclinally folded quartz bands, and abrupt lithologic changes from gneiss and amphibolite to quartz‐white mica‐chlorite schist characterize the thrust zone. Ultramafic rocks occur locally on or near the thrust plane. Thrusting is postulated to have occurred when a terrane composed of the amphibolite facies rocks converged with rocks along the continental margin of North America in Late Triassic and Early Jurassic time.