bluuebunny/crossref_metadata_2025 huggingface dataset:
Interannual coherence between North Atlantic atmospheric surface pressure and composite southern U.S.A. sea level
Authors: Maul George A. , Hanson Kirby
Published: February 2008

Annual mean sea levels along the southern United States have been examined for interannual variability. Fifteen sea level stations from Cape Hatteras to the Rio Grande that best covered the three lunar nodal cycles from 1931–1987 were selected for analysis. Linear trends, ranging from +0.2 cm/yr to +1.4 cm/yr were subtracted from their respective series, leaving remarkably similar residuals. The composite time series of the 15 residuals was compared with time series of surface air pressure over the North Atlantic Ocean during the period 1947–1987. The best correlation is a negative relationship between composite sea level and wintertime air pressure north of 45°N, and a positive relationship from 20°–45°N. The most significant correlations (−0.73 and +0.51) were found for 60°N, 20°W and for 30°N, 25°W respectively. Wintertime meridional air pressure gradient between these two latitudes represents about 50% of the variance in composite annual mean sea level. Both the sea level and air pressure time series had significant spectral peaks at 13.3 and 4.4 years, with about 52% of the covariance coming from these two periods.
The KOSI experiments
Authors: Huebner W. F.
Published: February 2008

Whipple's icy conglomerate model of the comet nucleus has enjoyed progressively increasing acceptance and success in explaining Earth‐based observations of comets since its very inception (Whipple, 1950, 1951). According to this model, the nucleus is a solid body composed of frozen gases and dust. The missions to Comet Halley in 1986, in particular the Vega and the Giotto missions, have confirmed that there is a single solid nucleus that is the root of all the observed phenomena that can be associated with an active comet. Two new comet missions (CRAF and Rosetta) are planned by NASA and ESA to extract further details about the structure and composition of the nucleus. Laboratory experiments play an important role in defining and identifying the objectives of these missions: Why are there small areas of activity on the surface while the largest parts of the nucleus appear to be dormant? What are the details of the development of the dusty gas atmosphere (coma)? What is the average tensile strength of the nucleus material? What is its detailed composition and how heterogeneous is it? What is the temperature profile below tie surface? Credible limits on the ranges of these physical and chemical properties and processes can be obtained from laboratory experiments. Although such experiments have been carried out in many laboratories in Europe, the Soviet Union, the USA, Israel, and Japan, the KOSI experiments are the first large‐scale investigations (in spatial dimensions and duration). (KOSI is an acronym for Kometensimulation, German for comet simulation.)
Extension and transtension in the plate boundary zone of the northeastern Caribbean
Authors: Speed R. C. , Larue D. K.
Published: February 2008

We propose that the Caribbean (Ca)‐North American (NA) plate boundary zone (pbz) from the Puerto Rico Trench to the Venezuelan Basin from Mona Canyon east has been in left‐transtension over the last 15–20 ma. A boundary‐normal component of extension occurs throughout the pbz and is a principal cause of the Puerto Rico Trench. Such extension is due to WNW velocity of NA‐Ca and the northward pullaway of NA from its S‐dipping slab, which is below Puerto Rico. Strike slip motion may be taken up among terranes in the pbz by rigid CCW rotation and by oblique slip at their boundaries. Rotation of the largest terrane, Puerto Rico‐Virgin Islands (PRVI), has caused such major structures as the Muertos thrust and Anegada Passage. The model implies NA‐Ca velocity estimated from Cayman transforms is more accurate than that from slip vectors from seisms in the NA slab.
Acoustic televiewer log images of natural fractures and bedding planes in the Toa Baja Borehole, Puerto Rico
Authors: Paillet Frederick L. , Goldberg David
Published: February 2008

Although borehole conditions made acoustic televiewer logging difficult in the Toa Baja borehole, more than 180 meters of continuous, acceptable quality televiewer logs were obtained in the intervals from 730 to 880 meters and from 2,515 to 2,675 meters in depth, indicating the presence of fractures that appear to be open in situ. Most of the largest, possibly open fractures in these intervals are either nearly parallel to directions given by the dipmeter log and may represent solution openings or minor washouts along bedding planes, or dip steeply to the south or southwest across bedding. The televiewer log confirms the presence of an apparently open set of fractures near 867 meters in depth, where circulation was lost during drilling, and in the interval from 2,600 to 2,650 meters in depth, where the temperature log indicates anomalous heat flow in the surrounding formation.
Fault zone deformational constraints on Paleogene tectonic evolution in southern Puerto Rico
Authors: Erikson Johan P. , Pindell James L. , Larue David K.
Published: February 2008

Paleogene deformation in south central Puerto Rico of Cretaceous‐Eocene volcaniclastic sediments and volcanic rocks is characterized by west‐northwest trending sinistral strike‐slip faults, northeast directed thrusts, and fault‐related mesoscopic folds. A west‐northwest trending belt of predominantly Eocene age sediments is flanked by Upper Cretaceous rocks; a 8–15 km wide fault zone is spatially coincident with this lithologic belt. Structural data and deformational style indicate that the area is a sinistrally transpressive, slightly north vergent, asymmetric flower structure, of which the upper portion is presently exposed in the belt of predominantly Eocene sediments. Deformational characteristics, in combination with sedimentary and tectonic evidence, constrain evolutionary scenarios of the fault zone (specifically, age and amount of displacement) and the northeastern Caribbean, as discussed herein.
The role of chlorine in the loss of 238U decay chain nuclides and 232Th from a basaltic rock
Authors: Reinitz Ilene M. , Turekian Karl K.
Published: February 2008

Volatilization experiments on U decay chain nuclides and Th involving the addition of CaCl2 to a basanite and heating sequentially at 1300°C were performed. The results indicate loss of 210Pb with Na and K at low Cl concentrations and 226Ra with Fe at considerably higher Cl concentrations. 238U, 230Th and 232Th were not lost by volatilization even at the highest Cl concentrations.
Fault stability inferred from granite sliding experiments at hydrothermal conditions
Authors: Blanpied M. L. , Lockner D. A. , Byerlee J. D.
Published: February 2008

Seismicity on crustal faults is concentrated in the depth interval 1–3 to 12–15km. Tse and Rice (1986) suggested that the lower bound on seismicity is due to a switch with increasing temperature from velocity weakening (destabilizing) to velocity strengthening (stabilizing) friction. They inferred this transition from friction data for dry granite; however, pore fluids exist at elevated temperatures throughout the crust, and may strongly influence strength and sliding behavior. We present new data from sliding experiments on granite at elevated T (23° to 600°) plus elevated PH2O (100 MPa),

Our results show velocity strengthening at room temperature, but velocity weakening from 100° to 350°C (except at 250°). From 350° to 600° there are systematic trends from velocity weakening to strong velocity strengthening, and from high to low friction; neither trend was seen in tests on dry granite. The velocity dependence data imply the potential for unstable slip in the interval 100° to 350°. Using a geotherm to map temperature to depth, this interval closely matches the observed earthquake distribution.
The 1990 Antarctic Ozone Hole as observed by TOMS
Authors: Newman Paul , Stolarski Richard , Schoeberl Mark , McPeters Richard , Krueger Arlin
Published: February 2008

The 1990 Antarctic ozone hole matched the record 1987 ozone hole in depth, duration, and area. During the formation phase of the hole (August), total ozone values were the lowest yet recorded. The decline rate approximately matched the record 1987 decline, and reached a minimum of 125 Dobson Units on October 4, 1990. October total ozone averages were marginally higher than 1987. As during 1987, the 1990 total ozone values within the hole slowly and steadily increased during the mid‐October through November period. The ozone hole breakup was the latest yet recorded (early December), with low ozone values persisting over the pole through December, setting a record low for December average polar ozone. Temperatures were near average during the early spring, but were below normal for the late‐spring. Temperatures in the early spring of 1990 were substantially warmer than those observed in the early spring of 1987.
Comparisons of observed northern hemisphere surface air temperature records
Authors: Elsner J. B. , Tsonis A. A.
Published: February 2008

Comparisons are made between three climatic data sets consisting of Northern Hemispheric annual surface air temperature departures over the past 100 years. It is shown that despite the large values of linear cross‐correlation between the data records, the long‐term trends are significantly different according to the bootstrapping procedure. The confidence of relying on any particular data set for assessing global climate change statistics is thus questioned.
Possible tectonomagnetic effect observed from mid‐1989 to mid‐1990, in Long Valley Caldera, California
Authors: Mueller R. J. , Johnston M. J. S. , Langbein J. O.
Published: February 2008

Precise measurements of local magnetic fields have been obtained with a differentially connected array of three proton magnetometers in the Long Valley caldera region since 1984. Two magnetometers are located inside the caldera with a third reference magnetometer located 26km southeast of the caldera. After correction for secular variation, it is apparent that an anomalous 2 nT decrease in the magnetic field occurred from mid‐1989 to mid‐1990 at the magnetometer located closest to the center of the resurgent dome inside the caldera. During this period a significant increase in geodetic strain rate of 8.5 ppm/a was observed on the two‐color geodimeter network within the caldera from October, 1989, to mid‐1990 and a dramatic increase in seismic activity occurred from December, 1989 to July, 1990. A simple dilatational point‐source model with pressure increasing by 52 Mpa from October 1989 to August 1990 at a depth of about 7km beneath the center of the resurgent dome can be fit to the strain data. If this same model is used to calculate piezomagnetic fields in the caldera, the results obtained agree with the observed local magnetic field data provided the Curie point isotherm is at a depth of ≤5km. Taken together, these magnetic, seismic and geodetic data suggest that an episode of active magmatic intrusion occurred from late 1989 to mid‐1990 at a depth of about 7–8km beneath the resurgent dome within the Long Valley caldera. Other indications of this intrusion should be evident in measurements of leveling, local gravity, and seismic imaging data.
Auroral electrodynamics at the cusp/cleft poleward boundary during northward interplanetary magnetic field
Authors: Sandholt Per Even
Published: February 2008

Combined latitude profiles of optical aurora, magnetic disturbances, particle precipitation and field‐aligned currents are used to investigate the electrodynamics of the cusp/cleft ionosphere during northward interplanetary magnetic field (Bz = 12 nT; By = −17 nT). An active zone of strong azimuthal plasma convection, manifested by the Svalgaard‐Mansurov effect in ground magnetic deflections (due to Hall current between pairs of Birkeland currents) and auroral structure at the poleward boundary of the cusp/cleft is observed within ∼ 1030–1230 MLT. Contrary to the typical cusp/cleft auroral activity during negative IMF Bz the discrete auroral forms in the present case move into the cusp/cleft arc, from the poleward edge. Both the optical observations and the inferred field‐aligned current/plasma flow pattern indicate a generator mechanism poleward of the cusp/cleft (i.e. associated with the plasma mantle), giving rise to strong momentum transfer and discrete electron precipitation within a ∼ 200 km wide latitudinal zone at the cusp/cleft poleward boundary, at the time of a poleward moving cusp/cleft arc. From this and other similar studies of the cusp/cleft ionosphere, we conclude that a qualitatively similar mode of solar wind‐magnetosphere interaction is operating both during northward and southward IMF.
Evidence for a seismogenic upper mantle and lower crust in the Baikal Rift
Authors: Déverchère Jacques , Houdry Frédérique , Diament Michel , Solonenko Natalia V. , Solonenko Alexandre V.
Published: February 2008

The high level seismicity of the Baikal rift zone and its spatial distribution in dense swarms and belts provide an opportunity to study the seismogenic behaviour of a continental lithosphere submitted to extension in an early stage. Using data from a regional seismological network, we analyze a significantly large set of events from an earthquake swarm located east of the nearly aseismic northern Baikal lake. We find that at least 10% of the well‐constrained events are located in the lower crust or the uppermost mantle. The fault plane solutions of earthquakes within the crust define a NW‐SE extensional stress regime perpendicular to the rift axis. Our results confirm the idea that zones of continental extension may exhibit significant rigidity. We propose to infer a migration of deformation from the northern Baikal lake to an initially stronger part of the lithosphere, i.e. the Barguzin rift and its extension to the east.
Evidence for vertical movement of fluids, Gulf Coast sedimentary basin
Authors: Land Lynton S.
Published: February 2008

Sediments between 10 and 15 km thick have prograded approximately 400 km into the small oceanic basin which formed along the southern margin of North America subsequent to early Mesozoic rifting. Redistribution of mass during burial diagenesis, and the chemistry of present‐day formation waters in Jurassic through Pleistocene formations document local kilometer‐scale, and in cases basin‐scale vertical fluid transport within the sedimentary wedge.

Fluid flow is in part driven by porosity reduction which takes place by both physical and chemical processes during burial. Vertical and horizontal transport also occurs as the result of thermally‐and salinity‐generated buoyancy effects. Input of fluids into the sedimentary wedge from the underlying crust is predicted, but not documented.
Geology and structure of Beta Regio, Venus: Results from Arecibo Radar Imaging
Authors: Senske D. A. , Head J. W. , Stofan E. R. , Campbell D. B.
Published: February 2008

Arecibo radar images of a portion of the equatorial region of Venus provide the first high resolution (1.5‐ to 2.0‐ km) synoptic coverage of Beta Regio. Within this area, tessera, a complex deformed terrain, is identified as a major geologic unit with the largest region corresponding to a plateau on the east flank of the highland. Three models are proposed to explain the origin and evolution of Beta Regio and are identified as Mantle Plume/Passive Crust, Mantle Plume/Active Crust, and Mantle Plume/Crustal Spreading. The Mantle Plume/Passive Crust model appears to be the most consistent with the geology in this region and suggests that a plume disrupts a preexisting region of tessera.
Pitch‐angle scattering of cometary ions: Computer simulations
Authors: Gary S. Peter , Miller Ronald H. , Winske Dan
Published: February 2008

Pitch‐angle evolution of newborn cometary ions is studied by means of one‐dimensional electromagnetic hybrid computer simulations of homogeneous plasmas. Newborn ions are injected into the simulations at a constant rate, with a velocity relative to the solar wind which makes an angle α with respect to the ambient magnetic field. The simulations are done with relatively weak ion injection rates commensurate with those in the distant environment of comet Halley. In response to the linear temporal growth of the fluctuating magnetic field energy, the injected ions pitch‐angle scatter toward isotropy in both the quasiparallel (0° ≤ α ≤ 60°) and quasiperpendicular (60° < α ≤ 90°) regimes. For the injection of cometary oxygen ions the simulations show pitch angle scattering rates that are essentially independent of the solar wind ion/cometary ion relative speed, and increase as the square root of the injection rate. Furthermore, the oxygen ion pitch angle scattering rate at perpendicular injection is approximately twice that in the quasiparallel regime, in qualitative agreement with observations at comet Halley.
The effect of light intensity and spectra on the reduction of thermoluminescence of near‐shore sediments from Spitsbergen, Svalbard: Implications for dating Quaternary Water‐Lain Sequences
Authors: Forman S. L. , Ennis G.
Published: February 2008

The thermoluminescence (TL) properties of silicate mineral grains have been used as geochronometers for water‐lain sediments. This study provides new insight into the limitations of TL the technique by quantifying the effects of incident wavelength and light intensity on the resetting of the TL signal. The TL residual level increases as wavelengths between 440 and 540 nm are blocked and remains unchanged after ca. 4 hours. These residual levels were maintained even after 24 hours of continuous exposure. The light intensity threshold for reduction in the TL signal is quite low, <10% of full light exposure or <1×104joules/m2. However, during the late glacial on Svalbard, and possibly in other aqueous glacial‐environments, the concentration of suspended sediment was sufficiently high to reduce the ambient light intensities to below these levels, resulting in elevated residual levels that are difficult to duplicate in the laboratory. The available thermoluminescence techniques are unsuitable for unequivocally dating water‐lain sediments because of the natural spatial and temporal variations in the solar reduction in the TL signal in turbid aqueous environments.
Ashfall dispersal for the 16 September 1986, eruption of Lascar, Chile, calculated by a turbulent diffusion model
Authors: Glaze Lori S. , Self Stephen
Published: February 2008

A two dimensional model for the dispersal of volcanic ash, modified from that of Suzuki [1983], is applied to the 16 September 1986, eruption of Lascar, in northern Chile. The result is an isopach map predicting ground concentrations of ash. The map shows two local maxima along distinct dispersal axes and predicts that the deposit was detached from the source. Predicted concentrations are in agreement with a single reported thickness measurement.
Instantaneous frequency, spectral centroid, and even wavelets
Authors: Ha S. T. T. , Sheriff R. E. , Gardner G. H. F.
Published: February 2008

The Fourier spectral centroid formula for instantaneous frequency is extended to all times and to all analytic signals and is in a convenient computable form. Examples using two different synthetic even seismic wavelets show that the peaks and troughs of their instantaneous frequency may occur at the envelope maxima or minima, with possible singularities at the envelope minima. For a purely even or odd wavelet, either a turning point or a point of inflection occurs at the wavelet center of the instantaneous frequency and envelope.
The structure of helical interplanetary magnetic fields
Authors: Goldstein M. L. , Roberts D. A. , Fitch C. A.
Published: February 2008

The interplanetary magnetic field is known to be highly helical. Although the detailed spatial structure of the fields has yet to be elucidated, the helicity spectrum has been conjectured to result from a random walk in direction of a constant magnitude magnetic field vector. We demonstrate that a model using three‐dimensional fluctuations with variations in |B| gives a good fit to the helicity spectrum as well as to other properties of the interplanetary magnetic field.
Lower Paleozoic oceanic crust in Mongolian Caledonides: SM‐ND isotope and trace element data
Authors: Kepezhinskas P. K. , Kepezhinskas K. B. , Pukhtel I. S.
Published: February 2008

Mongolian ophiolites range in age from Early Proterozoic to Middle Paleozoic with maximum of ophiolite production in Late Riphean to Early Cambrian time. One of the best examples is the Bayan‐Khongor complex which comprise serpentinized peridotite, cumulate sequence, sheeted dike unit and metavolcanics. Sm‐Nd mineral isochron obtained from upper gabbro yields the age of 569 Ma and initial Nd ratio +11.9. Chemical data for gabbros, dikes and metavolcanics reveal their oceanic nature. Both isotopic and geochemical signatures of the Bayan‐Khongor ophiolite are consistent with its origin in the plume‐related spreading ridge segment of the Paleoasiatic oceanic basin.
Time‐domain electromagnetic soundings in the vicinity of Novarupta, Katmai National Park, Alaska
Authors: Kasameyer Paul , Wilt Michael , Daily William , Felske Donald
Published: February 2008

A time‐domain electromagnetic survey was conducted near the rhyolite dome Novarupta. We found a continuous (60 to 100 m thick) high‐resistivity surface layer, which represents the unsaturated or unaltered tephra and whose base is probably the water table. This layer is thinnest near fumaroles; the largest thin areas lie under the tephra ring surrounding Novarupta, where the altered zones extend to a depth of more than 100 m. A deeper conductive layer is associated with the top of the underlying sedimentary rocks and is inferred to indicate the depth to the pre‐eruptive surface.
Prolonged enhancement in surface ultraviolet radiation during the Antarctic spring of 1990
Authors: Frederick John E. , Alberts Amy D.
Published: February 2008

Measurements of the ultraviolet solar spectral irradiance from the earth's surface at Palmer Station, Antarctica, latitude 64.8 degrees South, show behavior in the spring of 1990 which differs from that observed during the seasonal ozone depletions of the previous two years. As the Austral spring progresses, the sun rises in the sky, and the duration of daylight increases up to the summer solstice on December 21. This is naturally accompanied by increasing ultraviolet irradiances irrespective of the behavior of column ozone. If, as in 1988, the ozone depletion is confined to October and early November, the irradiances at local noon may remain at or below values characteristic of an unperturbed summer solstice. However, in 1990 enhanced irradiances persisted well into December. The largest values observed at a wavelength of 306.5 nm were approximately double those expected at summer solstice with an unperturbed ozone amount.
Physical processes in the plasma mantle of Venus
Authors: Szegö K. , Shapiro V. S. , Shevchenko V. I. , Sagdeev R. Z. , Kasprzak W. T. , Nagy A. F.
Published: February 2008

The Phobos‐2 observations established the presence of a turbulent region on the dayside, called the mantle, just outside the magnetic barrier at Mars. This mantle is the interaction region of cold Martian ions and the shocked solar wind. This work presents the results of a study, which analyzed data from ten Pioneer Venus orbits, in order to see whether similar wave particle interaction processes also exist in the corresponding region around Venus. The first conclusion is that the apparent physical processes in the mantle are indeed similar around Venus and Mars. The planetary thermal O+ ions outside the ionopause interact with the shocked solar wind and excite electrostatic waves close to the lower hybrid frequency. These wave propagate inwards, heating first the electron and deeper down in the ionosphere the thermal ion population. The observed superthermal ions are believed to be the product of this wave particle interaction process. Our second conclusion is that the wave energy transferred to the thermal electrons is of the right magnitude (∼4×109 eV cm−2 s−1) to provide the supplemental heat source necessary to reconcile observed and calculated electron temperatures in the ionosphere.
Lunar surface: Sputtering and secondary ion mass spectrometry
Authors: Johnson R. E. , Baragiola R.
Published: February 2008

We combine laboratory and Apollo observations to describe the sputtering of the lunar surface and the composition of the ejecta with special reference to O. The atmospheric inventory appears to be dominated by micrometeorite vaporization of lunar grains. Sputtering effects are observable in the local plasma due to ion ejection, in the extended atmosphere through energetic neutral ejection, and on grain surfaces through the chemical fractionation of the redeposited sputter‐ejecta. Ionization of the micrometeorite‐vapor also contributes to the local plasma.
Two‐dimensional simulations of the ion/ion acoustic instability and electrostatic shocks
Authors: Karimabadi H. , Omidi N. , Quest K. B.
Published: February 2008

We use a newly developed 2‐D electrostatic code with particle ions and Boltzmann electrons to investigate the details of the ion/ion acoustic instability and the structure of electrostatic shocks. The ion/ion acoustic instability is thought to be operative in various regions of space plasmas, such as the plasma sheet boundary layer or the bow shock. Electrostatic shocks have also been hypothesized to exist in a variety of physical settings, such as the inner cometary coma or the auroral region. The simulation results show that for the parameters relevant to the plasma sheet boundary layer the saturation mechanism of the ion/ion acoustic instability is ion trapping. We also show that the 2‐D structure of electrostatic shocks is considerably different from that suggested by previous 1‐D simulations. The main reason for this difference is the presence of shock reflected ions, which through the ion/ion acoustic instability lead to the generation of large amplitude waves in the upstream region propagating obliquely to the shock normal. These waves play an important role in the shock dissipation process.
Odd nitrogen removal on background sulfate aerosols: Implications for the ozone hole
Authors: Pitari Giovanni , Visconti Guido
Published: February 2008

A sensitivity study is carried out for the dependence of the polar ozone loss rate on the value of the sticking coefficient γ for the reaction converting odd nitrogen into nitric acid on sulfate aerosols. In this study we use a 2D model including nitrogen and chlorine families along with an explicit condensation mechanism for polar stratospheric clouds (PSC) and a fixed distribution of background sulfate aerosols in the lower stratosphere. If only background aerosols are included negligible changes in total ozone are observed (up to ∼1%) when γ is increased from 0.02 to 0.14. If PSCs are added the same test produces a significant reduction of the ozone hole depth in Antarctica.
The frictional behavior of serpentinite: Implications for aseismic creep on shallow crustal faults
Authors: Reinen Linda A. , Weeks John D. , Tullis Terry E.
Published: February 2008

Serpentine is common in many active faults and may be responsible for aseismic creep along segments of these faults. To test this, we have conducted a series of velocity stepping experiments to determine the frictional velocity dependence of serpentinite. We slid initially bare, rough surfaces of antigorite serpentinite at room temperature, with velocities from 0.0032 to 10.0 μm/s (1.0×102 to 3.2×105 mm/yr) and normal stresses from 25 to 125 MPa. We find that the velocity dependence of serpentinite undergoes a transition from velocity weakening at fast loading velocities to velocity strengthening at slow velocities and that this change is accompanied by other changes in the constitutive behavior. These results suggest that serpentinite should not be the site of instability initiation during sliding at plate velocities, but may permit propagation of unstable slip initiated elsewhere.
Effects of depth‐variations in Creep Laws on the formation of plates in mantle dynamics
Authors: van den Berg Arie P. , Yuen David A. , van Keken Peter E.
Published: February 2008

We have studied the influences of depth‐varying rheologies on the structure of mantle convection and the near surface flow fields. Upwelling flows crossing the upper‐lower mantle boundary become considerably thinner and faster. Streamlines are concentrated near the surface and other plate‐like characteristics are enhanced by this type of rheological stratification in which the averaged effective viscosity of the upper mantle is about two orders of magnitude lower than that of the lower mantle. The presence of a lithosphere with a higher non‐linear dependence in the flow law further promotes plate‐like behavior. Plate‐like character of the top boundary‐layer is encouraged by a decreasing depth‐dependent viscosity in the non‐Newtonian upper‐mantle and by greater convective vigor.
Imaging observations of the extended sodium atmosphere of the Moon
Authors: Mendillo Michael , Baumgardner Jeffrey , Flynn Brian
Published: February 2008

Pilot ground‐based optical imaging observations of the extended lunar environment were conducted at McDonald Observatory in February 1991. One set of images taken on February 20 revealed emission at the combined D1 (5896 Å) and D2 (5890 Å) lines of neutral sodium extending out to about 5 lunar radii (RM) from the center of the Moon on the sunward side and much fainter emission extending out to about 15–20 RM on the antisunward side. Peak emission (D1+D2) above the Moon's limb at a distance of 1.8 RM along the lunisolar axis was measured to be 900 Rayleighs (R), decreasing with distance as r−4. The morphology of the emitting region is qualitatively that of a comet, i.e., a bright coma centered on the Moon and an extended tail trailing away in the antisunward direction. The tail exhibits a decrease in intensity coincident with the shadow cast by the moon. The sunward extent of the sodium is used to calculate a surface ejection speed of about 2 km s−1, consistent with recent estimates of a meteor impact surface vaporization source. The data agree well with previous observations made within 1 lunar radius above the surface. Modeling yields a surface density (52 atoms cm−3) that decreases with distance as r−5 in the solar direction.
Recent trends in stratospheric total ozone: Implications of dynamical and El Chichon perturbations
Authors: Chandra S. , Stolarski R. S.
Published: February 2008

The recently reprocessed Nimbus‐7 TOMS total ozone data from 1979 to 1989 are analyzed to assess the global impact of the El Chichon volcanic eruption on stratospheric total ozone. An apparent decrease in total ozone of 5 to 6% is present during the winter of 1982–83 following the eruption of El Chichon. A regression analysis of total ozone with the equatorial zonal wind at 30 mb indicates that response to the quasi‐biennial oscillation can explain much of the observed ozone anomaly, and that the total ozone decrease which can be attributed to El Chichon is at most 2 to 4 percent. This study also suggests that the interannual variability caused by the quasi‐biennial oscillation and planetary wave activity may introduce apparent seasonal trends in total ozone and temperature in the lower stratosphere, particularly if the length of the data record is not very long. Such trends may affect the assessment of total ozone changes caused by chemical perturbations.
Dehydration in the antarctic stratosphere: Radiative effects
Authors: Mancini Eva , Pitari Giovanni , Visconti Guido
Published: February 2008

A two dimensional model is used to investigate the effects of polar stratospheric clouds on the water vapor budget in the Antarctic stratosphere. It is shown that loss of stratospheric water vapor through formation and sedimentation of large ice particles decreases infrared cooling. This cooling reduction partially compensates the decreased ozone heating due to the formation of the Antarctic hole. Such a conclusion is reached by comparing a control unperturbed situation with two cases in which an ozone hole is formed with and without polar dehydration. We show that in the case of substantial loss of stratospheric water vapor since the years of the ozone hole formation, a dynamical mechanism may be necessary to explain the observed stratospheric cooling during the Antarctic spring. In this case the combined radiative perturbation (H2O + O3) is too small to force this cooling. Instead, in the case of a negligible change of water vapor content, the O3 radiative perturbation could be entirely responsible for the observed secular cooling.
Early lidar observations of the June 1991 Pinatubo eruption plume at Mauna Loa Observatory, Hawaii
Authors: DeFoor Thomas E. , Robinson Elmer , Ryan Steven
Published: February 2008

The June 1991 eruption of the Philippine volcano Pinatubo introduced a massive plume of volcanic ash and other aerosol material into a stratosphere containing only near‐background concentrations of aerosol material. At Mauna Loa Observatory, Hawaii, the Pinatubo plume was first observed by lidar on 1 July 1991. During July and August the observable effects from this plume increased in intensity in terms of aerosol optical properties, plume height, and broad band solar radiation. Preliminary data analysis shows that the plume over Hawaii arrived in three generalized pulses or waves on approximately 3 July, 24 July, and 9 August. There was a decrease of about 13% in a broad band atmospheric transmission factor over Hawaii between June 1991 and Pinatubo affected conditions on 31 August 1991. At the end of August 1991, the Pinatubo plume over Hawaii exhibited characteristics similar in magnitude to what was observed at Mauna Loa after the El Chichon eruption in 1982. However, the early Pinatubo maximum plume heights were lower than were observed in the early months of the El Chichon plume dispersion. The Pinatubo plume was continuing to increase in magnitude and height at MLO at the end of August.
Global hybrid simulation of the solar wind interaction with the dayside of Venus
Authors: Moore K. R. , Thomas V. A. , McComas D. J.
Published: February 2008

We present a 3‐dimensional global hybrid simulation of the interaction of the solar wind with the entire dayside of Venus. The model obstacle is half the size of Venus, and planetary ion mass loading is included self‐consistently. Results are compared to observations as well as to results from gasdynamic convected field modeling. Magnetic field magnitudes and bulk flow speeds along the planet‐Sun line are comparable in both models, but only the hybrid model reproduces the experimentally observed magnetic barrier proton density depletions. The finite gyroradius of the planetary pickup ions causes a number density asymmetry in the direction of the convective (−V×B) electric field, as predicted and observed. Mass addition consistent with photoionization of the planetary neutral hot oxygen corona has little effect on the geometry of the shock, including the subsolar and terminator shock altitudes. Mass addition rates well in excess of likely values are required to significantly affect the model shock geometry. The hybrid model results imply that oxygen ions originating deep within the dayside Venus magnetic barrier are nearly fluidlike while oxygen ions produced higher on the dayside, at much lower densities, behave more as test particles. Gasdynamic modeling incorporating both fluid and test particle mass addition reproduces the O+ terminator escape flux (a few times 1024 s−1) found in the hybrid model and inferred from observations, but underestimates the escape region spatial extent. The hybrid model predictions include a shock asymmetry dependent on the upstream IMF orientation, asymmetries in the magnetic barrier position and field magnitude, an asymmetry in pickup ion speed altitude profiles, and a finite gyroradius effect asymmetry in pickup ion number density caused by field draping.
Magnetization of the ionospheres of Venus and Mars: Results from radio occultation measurements
Authors: Woo Richard , Kliore Arvydas
Published: February 2008

In situ measurements by the Pioneer Venus orbiting spacecraft, conducted during solar maximum only, have shown that magnetization (permeation of large‐scale magnetic fields) of the ionosphere of Venus occurs under high solar wind dynamic pressure and that this takes place most frequently near the subsolar region. Magnetization is also revealed in electron density profiles by the presence of disturbed topside plasma and/or a ledge near the altitude of 200 km. In this paper we use remote sensing radio occultation measurements to study magnetization of the ionospheres of Venus and Mars based on these characteristics. For Venus we take advantage of the unique data set consisting of 148 electron density profiles deduced from Pioneer Venus radio occultation measurements. We demonstrate that radio occultation measurements yield results on frequency of occurrence of magnetization during solar maximum that are similar to those obtained from the Pioneer Venus in situ magnetic field measurements. During solar minimum, for which direct ionospheric measurements have never been made, we find that magnetization of the Venus ionosphere is more pervasive than at solar maximum. Magnetization extends to higher solar zenith angles (SZA) and appears stronger than at solar maximum. These results confirm that during solar minimum, the high solar wind dynamic pressure state is more prevalent at Venus because the ionospheric plasma pressure is weaker than at solar maximum. Comparison of a large number of electron density profiles of Mars (deduced from radio occultation measurements by the Viking 1 and 2 and Mariner 9 spacecraft for SZA > 46°) with those of Venus shows an absence of the ledge and disturbed topside plasma observed in the Venus profiles. These results, however, do not constitute evidence against magnetization of the ionosphere of Mars, as Shinagawa and Cravens (1989) have shown in their one‐dimensional MHD models that, even when the ionosphere of Mars is highly magnetized, the magnetic structure differs from that at Venus, and a ledge does not form in its electron density profiles.
The determination of time‐stationary two‐dimensional convection patterns with single‐station radars
Authors: Freeman M. P. , Ruohoniemi J. M. , Greenwald R. A.
Published: February 2008

At the present time, most ground‐based radar estimations of ionospheric convection use observations from single‐station facilities. This approach requires certain assumptions as to the spatial and/or temporal uniformity of the convection. In this paper we present a critical examination of the accuracy of these vector velocity determinations, using realistic modeled flow patterns that are time‐stationary but not spatially uniform. We find that under certain circumstances the actual and inferred flow fields show considerable discrepancy, sometimes not even agreeing in the sense of flow direction! Specifically, we show that the natural curvature present in ionospheric convection on varying spatial scales can introduce significant error in the velocity estimate, particularly when the radius of curvature of the flow structure is less than or equal to the radar range to the scattering volume. The presence of flow curvature cannot be detected by radars which determine velocities from measurements in two viewing directions, and it might not be detected by radars using azimuth scanning techniques. Thus we argue that every effort should be made to measure the ionospheric convection by bidirectional or multidirectional observations of a common ionospheric volume and that a synthesis of coherent and incoherent radar observations from different sites is preferable to multidirectional single‐station observations using either radar alone. These conclusions are applicable to any Doppler measurement technique and are equally valid for high‐latitude wind patterns using Fabry‐Perot interferometer techniques.
Subcritical multiple‐ion shocks
Authors: Motschmann U. , Sauer K. , Roatsch T. , McKenzie J. F.
Published: February 2008

Low Mach number collisionless shocks in a multiple‐ion plasma are investigated theoretically using multiple‐ion Rankine‐Hugoniot relations (MIRHR) and hybrid simulations. The derived MIRHR permit tractable solutions for perpendicular shocks. It is found that starting from a synchronous flow of a mixture of different ion species, light ions and heavy ions jump to different downstream velocities. Although the resulting differential velocities between the species are unstable, they produce coherent gyration of the ion species around each other. This gyration excites standing ion hybrid waves in the downstream region. Both of these effects (the jump of different ion species to different downstream velocities and the excitation of the ion hybrid waves) are confirmed by hybrid simulations.
Ion distributions at the dayside magnetopause
Authors: Smith M. F. , Rodgers D. J.
Published: February 2008

We present ion phase space distributions, from the AMPTE UKS ion instrument, for a crossing of the dayside magnetopause on October 2, 1984, during typical southward IMF conditions. We observe D‐shaped field‐aligned phase space distributions of magnetosheath plasma earthward of and hot magnetospheric ions sunward of the magnetopause current layer. The existence of such D‐shaped magnetosheath plasma distributions has been predicted as a signature of reconnection. In addition, the observed ion distributions are in stress balance across the magnetopause, and the de Hoffman‐Teller frame velocity obtained from the stress balance calculation is in agreement with the observed distribution function cutoff speed. These new observations thus provide further evidence that, at least for southward IMF conditions, reconnection is an important mechanism by which solar wind plasma penetrates into the magnetosphere.
Superposed epoch analysis of the substorm plasma sheet
Authors: Baumjohann W. , Paschmann G. , Nagai T. , Lühr H.
Published: February 2008

More than 43,000 plasma and magnetic field measurements with the AMPTE/IRM satellite in the magnetotail are used for a superposed epoch analysis of the conditions in the near‐Earth plasma sheet around 39 major substorm onsets. In the central plasma sheet, the magnetic field elevation, the ion bulk speed, and the ion temperature all show marked rises during the substorm expansion phase. Somewhat less pronounced increases of all three parameters are found in the plasma sheet boundary layer. But here the substorm effects are typically seen during the recovery phase. In the near‐Earth neutral line substorm model, the latter finding would indicate that the recovery phase begins when reconnection has proceeded to plasma sheet boundary layer field lines. Since the temporal evolution of ion temperature and ion density are anticorrelated especially in the central plasma sheet, we argue that the strong plasma heating during substorms occurs in a nonadiabatic fashion.
Estimating radiated power from a conducting tethered satellite system
Authors: Donohue D. J. , Neubert T. , Banks P. M.
Published: February 2008

In anticipation of the upcoming TSS‐1 experiment, theoretical calculations are made of radiated power from a conducting tethered satellite system. The radiation results from the steady motion of the system through the ionospheric plasma and it is stimulated by collection and emission of charge by the noninsulated surfaces of the tethered end connectors. A model of the current system is developed which incorporates the tether wire, satellite surfaces, and sheath currents. The radiation impedance of the current model is calculated using the previously developed theory of Barnett and Olbert (1986). The results confirm the low‐frequency Alfvén wave description with a predicted radiation impedance of a few tenths of an ohm in the Alfvén wave limit. Calculations are also made in the lower hybrid and whistler wave band. A larger impedance of ∼13 Ω is found for the frequency range ∼5–50 kHz. By estimating the passive ion current drawn by the system a prediction of the total radiated power is also made. The result of 0.38 mW raises the question of whether or not wave emissions from a passive current collecting system may be detectable by either ground‐ or space‐based platforms.
Drift wave instability in the Io plasma torus
Authors: Huang T. S. , Hill T. W.
Published: February 2008

We present a linear normal‐mode analysis of low‐frequency electrostatic drift waves in the Io plasma torus, providing a kinetic description of the centrifugal interchange instability of the torus regulated by coupling to Jupiter's ionosphere. We assume a periodic potential perturbation with azimuthal wavenumber m≫1 and solve a boundary value problem to obtain the wave dispersion relation and radial eigenfunction. For given m the growing mode is a standing wave in the corotating reference frame. If the outer torus boundary is taken as a discontinuity, the growth rate is proportional to m times the torus flux tube content times the ion drift frequency, divided by the Pedersen conductivity of Jupiter's ionosphere. The inner torus boundary has a modest stabilizing effect for azimuthal wavelengths greater than the radial thickness of the torus. The finite slope of the outer torus density profile has a more pronounced stabilizing effect, reducing the growth rate by the factor 2β/m, where β∼2 is the exponent of the assumed power law decline of flux tube content with distance. Even so, the e‐folding time is of the order of 1 hour, much less than the inferred residence time of torus ions. The growth rate can be further reduced dramatically by the stabilizing effect of an as‐yet unobserved ring current distribution, the “impoundment” effect proposed by Siscoe et al. (1981). Various theoretical models of global radial transport in Jupiter's magnetosphere, including corotating convection, interchange diffusion, and transient flux tube convection, can be understood as plausible nonlinear evolutions of electrostatic drift waves. Further observations and/or numerical simulations are needed to ascertain the relative importance of these transport mechanisms.
Ionospheric effects of the March 13, 1989, magnetic storm at low and equatorial latitudes
Authors: Batista Inez S. , de Paula E. R. , Abdu M. A. , Trivedi N. B. , Greenspan M. E.
Published: February 2008

The great geomagnetic storm of March 13, 1989 (Σ Kp = 60, Ap = 246) caused severely anomalous behavior in the equatorial and low latitude ionosphere in the Brazilian longitude sector. The ionograms over Fortaleza (4°S, 38°W) indicated F region upward plasma drifts exceeding 200 m s−1 at 1830 LT as compared to normal values of 40 m s−1 for this epoch. Large negative phases were observed in foF2 over Fortaleza and Cachoeira Paulista (22.5°S, 45°W) and in total electron content measured over São José dos Campos (23°S, 46°W). The equatorial ionization anomaly was totally absent either because of its anomalous expansion to higher latitudes or because of inhibition of its development on the two nights following the storm. Many anomalous variations in F region peak density and height, occurring simultaneously with sharp variations on H component of magnetic field over Fortaleza and with auroral substorms, give strong evidence of penetration of magnetospheric electric fields to equatorial and low latitudes. Auroral type sporadic E and night E layers are observed after 1830 LT over Cachoeira Paulista, the latter showing peak electron density of about 6×104 el cm−3, therefore comparable to the E layer peak density in the morning hours at that station. The Fortaleza ionograms show the presence of the F1 layer at night, a phenomenon that has never been observed over our two stations before. The role played by electric fields penetrating from high to low latitudes, particle precipitation, and composition changes in explaining the observations is discussed.