bluuebunny/crossref_metadata_2025 huggingface dataset:
Chatanika/Triad observations of unstable ionization enhancements in the auroral F‐region
Authors: Vickrey James F. , Rino Charles L. , Potemra Thomas A.
Published: February 2008

Preliminary results are presented from a campaign of coordinated measurements between the Chatanika radar and the TRIAD satellite to investigate production mechanisms responsible for localized high‐latitude scintillations. The radar measured the latitudinal variations of plasma density and electric field while the satellite measured the field‐aligned current distribution with latitude. This information was used to calculate the linear growth rate of the current convective instability. We find that field‐aligned ionization enhancements, which are a common feature of the auroral F‐region, are unstable, with instability growth times of ≤ 6 minutes. The observed plasma configuration, which was already gradient drift unstable on its poleward edge, was further destabilized by a field‐aligned current of ∼ 0.8 µA/m². The presence of electron density irregularities produced in the unstable region was verified by observing VHF scintillations on the TRIAD telemetry signal.
Four similar earthquakes in central California
Authors: Geller Robert J. , Mueller Charles S.
Published: February 2008

We study four ML ‐ 2.7 earthquakes on the San Andreas Fault in Central California. The first two events occurred within five minutes of each other in November 1978; the two events in January 1979 occurred within a nine hour period. The CALNET (USGS local array) seismograms of these four events display only some general similarity. However, when low ‐ pass filtered below 5 Hz, the four events have nearly identical seismograms. The similarity is even more striking in the pass‐band below 2 Hz. This suggests that all four events are within a radius of no more than a quarter wavelength, or about 200 ‐ 400 m.

Although no definitive conclusion can be reached from a study of only four earthquakes, our results strongly suggest that the following hypothesis should be further tested: Small to moderate earthquakes may commonly be much more tightly clustered in both hypocentral location and depth than is suggested by routine locations from local arrays. The physical basis of this clustering is that the earthquakes represent repeated stress release at the same asperity, or stress concentration, along the fault surface. Identification of such asperities might be useful in understanding the sequence of events leading to the initiation of a larger earthquake.
The vagaries of variable viscosity convection
Authors: Daly Stephen F.
Published: February 2008

The wavelength dependence of convection with a temperature dependent viscosity is studied using two‐dimensional finite difference models. A steady state solution with a horizontal wavelength of eight times the depth is found to transport heat more efficiently than a solution with exactly the same parameters but with a wavelength of twice the depth. Only at the longer wavelengths (λ ≳ 8d) is it possible for the top high viscosity boundary layer to participate more fully in the flow. Since models with a constant heat flux were used this resulted in a decrease in the interior temperature of approximately 30% for the longer wavelength. It is also demonstrated that a parameterization using only a constant viscosity thermal structure and an interior viscosity is inadequate to parameterize the variable viscosity calculations described in this study. This suggests that parameterized convection schemes may not accurately resolve the thermal evolution of planetary interiors unless they can correctly include the effects of vertical viscosity structure.
Venus nighttime hydrogen bulge
Authors: Brinton H. C. , Taylor H. A. , Niemann H. B. , Mayr H. G. , Nagy A. F. , Cravens T. E. , Strobel D. F.
Published: February 2008

The concentration of atomic hydrogen in the Venus thermosphere near 165km altitude and ∼18° north latitude has been derived from Pioneer Venus in situ measurements of n(H+), n(O+), n(O), and n(CO2), under the assumption of chemical equilibrium. Altitude profiles of derived n(H) suggest that chemical equilibrium prevails to an altitude of at least 200km on the dayside and to 165 km on the nightside. Measurements below these limits were made by the ion and neutral mass spectrometers on the orbiter spacecraft between December 1978 and July 1979, while periapsis traversed a complete diurnal cycle. The hydrogen concentration is found to rise sharply at both terminators from a dayside value of ∼5 × 104 cm−3, and to exhibit an asymmetric nightside distribution with a peak density in the predawn sector approximately 400 times greater than the dayside value. Analysis suggests that wind‐induced diffusion, combined with exospheric return flow, can account for the observed hydrogen behavior. The large day‐night temperature contrast enhances advective transport, which produces the large n(H) diurnal variation; the shift of the n(H) nighttime maximum toward dawn is caused by atmospheric superrotation.
Influence of fortnightly Earth tides at Kilauea Volcano, Hawaii
Authors: Dzurisin Daniel
Published: February 2008

Analysis of 52 historic eruptions confirms the premise that fortnightly earth tides play a significant role in triggering activity at Kilauea Volcano, Hawaii. Since January 1832, nearly twice as many eruptions have occurred nearer fortnightly tidal maximum than tidal minimum (34 vs. 18). A straightforward significance test indicates that the likelihood of a fortnightly tidal influence on Kilauea eruptions is roughly 90%. This is not the case for Mauna Loa Volcano, where 37 historic eruptions have been distributed randomly with respect to the fortnightly tide. At Kilauea, stresses induced by fortnightly earth tides presumably act in concert with volcanic and tectonic stresses to trigger shallow magma movements along preexisting zones of weakness. Differences in structure or internal plumbing may limit the effectiveness of this mechanism at Mauna Loa. Tidal effects seem to be less marked at shields than at some island‐arc volcanoes, possibly because higher average volcanic stress rates in Hawaii more often override the effects of tidal stresses.
36Cl in polar ice, rainwater and seawater
Authors: Finkel R. C. , Nishiizumi K. , Elmore D. , Ferraro R. D. , Gove H. E.
Published: February 2008

Concentrations of the cosmogenic radioisotope36Cl (t1/2=3.0×105yr) in Antarctic ice and in rain and an upper limit to the seawater value have been determined using van de Graaff accelerator high energy mass spectrometry. Chlorine‐36 concentrations in Antarctic ice lie in the range (2.5‐8.7)×106atoms36Cl/kg. Recent firn from Siple Station and ice samples collected from the Allan Hills ice field at locations where meteorites have been brought to the surface by glacial flow and ablation have36Cl contents which vary by more than a factor of three. This variation can be attributed either to the effects of atmospheric mixing and scavenging or to radioactive decay in very old ice. The36Cl concentration found in a sample of recent rainwater is much lower than has been reported in samples collected in the early 1960’s, suggesting that there has been a large decrease in the concentration of atmospheric36Cl derived from nuclear weapons tests over this time period. If measurement sensitivities can be increased somewhat, calculations indicate that the bomb spike of36Cl may potentially be a useful oceanographic mixing tracer.
Ion energetics in the Venus nightside ionosphere
Authors: Knudsen William C. , Spenner Karl , Whitten Robert C. , Miller Kent L.
Published: February 2008

The transport time required for the ionospheric ion gas to flow through an arc of one radian across the Venus terminator at the observed horizontal speed is short in comparison with the time required for the electron gas to transfer to the ion gas an amount of heat comparable to its internal energy. The transport time is approximately equal to the time required for the internal energy of the ion gas to be lost through heat conduction down into the neutral atmosphere. We define this flow condition in which the ion gas gains insignificant heat from the electron gas and loses only a moderate amount through conduction in flowing through an arc of one radian as quasiadiabatic. One important implication of this flow condition is that steady state, vertical, one dimensional energy balance models for the nightside ionosphere must be used with caution. A second implication is that bulk kinetic energy is being converted into heat energy through some dissipation mechanism. Inasmuch as we expect the plasma to expand across the terminator and thereby suffer some adiabatic cooling, we suggest that conversion of bulk kinetic energy into heat is responsible for maintaining the observed nightside ion temperature. The bulk kinetic energy at the terminator is large compared with the internal energy.
Density response of the mesospheric sodium layer to gravity wave perturbations
Authors: Shelton J. D. , Gardner C. S. , Sechrist C. F.
Published: February 2008

Lidar observations of the mesospheric sodium layer often reveal wavelike features moving through the layer. It is often assumed that these features are a layer density response to gravity waves. Chiu and Ching [1978] described the approximate form of the linear response of atmospheric layers to gravity waves. In this paper, their results are used to predict the response of the sodium layer to gravity waves. These simulations are compared with experimental observations and a good correlation is found between the two. Because of the thickness of the sodium layer and the density gradients found in it, a linear model of the layer response is not always adequate to describe gravity wave ‐ sodium layer interactions. Inclusion of nonlinearities in the layer response is briefly discussed. Experimental data is seen to contain features consistent with the predicted nonlinearities.
Hafnium isotope variations in oceanic basalts
Authors: Patchett P. J. , Tatsumoto M.
Published: February 2008

Routine low‐blank chemistry and 0.01‐0.04% precision on the ratio 176Hf/177Hf allows study of Hf isotopic variations, generated by β−‐decay of 176Lu, in volcanic rocks derived from the suboceanic mantle. Normalized to 176Hf/177Hf = 0.7325, 176Hf/177Hf ranges from 0.2828 to 0.2835, based on 24 basalt samples. 176Hf/177Hf is positively correlated with 143Nd/144Nd, and negatively correlated with 87Sr/86Sr and 206Pb/204Pb. Along the Iceland‐Reykjanes ridge traverse, 176Hf/177Hf increases southwards. The coherence of Hf, Nd and Sr isotopes in the oceanic mantle allows an approximate bulk Earth 176Hf/177Hf of 0.28295 to be inferred from the bulk Earth 143Nd/144. This requires the bulk Earth Lu/Hf to be 0.25, similar to that of the Juvinas eucrite. 60% of the Hf isotopic variation in oceanic basalts occurs among mid‐ocean ridge samples. Lu‐Hf fractionation probably decouples from Sm‐Nd and Rb‐Sr fractionation in very depleted source regions, with high Lu/Hf, and consequent high 176Hf/177Hf ratios developing in mantle residual from partial melting.
Thermally induced acoustic emission in westerly granite
Authors: Yong Chen , Wang Chi‐yuen
Published: February 2008

The acoustic emission of Westerly granite subjected to temperature changes up to 120° at various heating rates from 0.4 to 12.5°C/min was studied. A threshold temperature of 60 to 70°C appeared to exist for this range of heating rate, above which A.E. began to occur profusely with increasing temperature. Above the threshold temperature, the rate of A.E. depended strongly on the rate of heating. However, a thermal ‘Kaiser’ effect appeared to exist such that in cyclic heating and at temperatures below the maximum temperature reached in the previous cycle, very few A.E. occurred irrespect of the heating rate in the subsequent cycles. We suggest that there is an equilibrium state of the thermally induced cracks, which is a function of temperature but is independent of the heating rate; in the slower experiment, the equilibrium state of crack extension is achieved by slower growth, which is associated with smaller amounts of acoustic emission.
Anomalous magnetizations in 3.4 B.Y. old Barberton Mountain land samples
Authors: Cisowski Stanley M.
Published: February 2008

The ratio of natural remanence (NRM) to saturation remanence (IRMs) is found to be exceedingly high for a number of basaltic to ultramafic samples from the 3.4 billion year old Barberton Mountain Land greenstone belt, South Africa. Although conventional paleointensity methods indicate paleofields of several oersteds, demagnetization curves plotted on logarithmic scale clearly show the NRM in these samples to be unlike thermal remanence (TRM). It seems most probable that the observed NRM is a chemical remanence (CRM) related to the greenschist metamorphic event, and that the intense magnetizations are perhaps the result of internally generated, rather than external fields. The probability that the intense magnetization observed in these ancient terrestrial samples is unrelated to the strength of the external field suggests caution in the interpretation of paleointensity results from extraterrestrial materials.
Viscous demagnetization and the longevity of paleomagnetic polarity messages
Authors: Denham Charles R.
Published: February 2008

Viscous decay of magnetic polarity messages in rocks is slowed 3‐to‐6 fold by the reversing nature of the geomagnetic field, compared with the effect expected in a field that is constantly polarized oppositely to the original remanence. The process is studied analytically and numerically for the known geomagnetic polarity sequence, as well as for simulated sequences having constant‐length and Poisson‐distributed lengths of polarity intervals. For equal average‐interval lengths, the random Poisson reversing process causes more rapid decay than does the periodic reversing process.
Observations of water flow with high resolution Doppler sonar
Authors: Lhermitte Roger
Published: February 2008

A coherent pulse Doppler sonar with a few centimeters range resolution provides effective monitoring of slow water velocity with excellent resolution. The experiments presented in the paper were conducted with a sonar transducer resting on the floor of a waterway influenced by tidal effects with the transducer producing a beam tilted from the horizontal. All the results are shown in the form of Doppler Spectra composed of radial velocity estimates separated by a few mm/s, which are presented at adjacent range gates spaced by 4.5 or 9 cm, so that a vertical profile of horizontal velocity extending from the waterway bottom to the water surface is derived from the data. Continuous monitoring of these profiles shows considerable detail in the evolution of the ebb/flood characteristics of the flow during tidal cycles.
Seasat Sar cross‐section modulation by surface winds: Goasex observations
Authors: Thompson T. W. , Weissman D. E. , Gonzalez F. I.
Published: February 2008

Seasat radar observations of the Gulf of Alaska by the Synthetic Aperture Radar (SAR) and the Wind Speed Scatterometer (SASS) indicates that L‐band backscatter is modulated by wind speed and possibly by wind direction. In particular, L‐band radar cross‐section of the ocean at 23°±3° angle of incidence and wind speeds between 5m/s and 20m/s is related to wind speed and direction by the following:

urn:x-wiley:00948276:media:grl1526:grl1526-math-0001
where σo = L‐band radar cross‐sectionU = wind speedϕ = wind‐radar anglea = 0.5 ± 0.1b = 0.05 ± 0.05This relationship suggests that a combination of Seasat SAR and Scatterometer data may yield high resolution maps of surface winds.
The arrival of the Mount St. Helens eruption cloud over Europe
Authors: Meixner F. X. , Georgii H.‐W. , Ockelmann G. , Jäger H. , Reiter R.
Published: February 2008

The stratospheric aerosol layer between 15 and 25 km altitude is an important factor in the balance of the global radiation budget. The eruption of the Mount St. Helens in Washington, USA, on 18 May 1980 violated the quasi stationary situation in the stratosphere which was established after the decay of the post‐Fuego aerosol during the years 1974 to 1976. At tropopause level the cloud was observed over the east coast of the US and Canada on 21 May 1980. The further transport over the Atlantic was estimated by first guess trajectory constructions. The arrival of the eruption cloud over Europe was observed by the authors employing in‐situ techniques and remote sensing. The in‐situ measurements of atmospheric SO2 were performed during an aircraft ascent up to 13.7 km on 26 May 1980 over southern Scandinavia. In contrast to an aircraft ascent over southern Germany on 24 May 1980 a tenfold increase in SO2 mixing ratio at tropopause level was observed.

Remote sensing by ground based ruby lidar at Garmisch‐Partenkirchen (47.5°N, 11°E) from 25 May to 29 May 80 indicates an aerosol peak at a height of 11 to 12 km, which was initially coupled to the tropopause, but later clearly separated from that level.
Cosmic‐ray scintillation at the lunar surface
Authors: Benson R. , Duller N. M. , Green P. J.
Published: February 2008

The theory of cosmic‐ray scintillations has developed rapidly over the past few years. Cosmic‐ray scintillations arise from various irregularities in the magnetic fields through which cosmic‐ray particles must travel before being observed. These scintillations are characterized by broad‐band fluctuations in intensity over time. We have undertaken a study of the cosmic‐ray background as observed with the Rice University Suprathermal Ion Detector Experiment (SIDE) that was deployed on the lunar surface during the Apollo 14 mission. The energy threshold for cosmic‐ray protons was approximately 25 MeV in one sensor and 50 MeV in another. We find that the interplanetary cosmic‐ray scintillations are observed with the SIDE and these observations are consistent with current theoretical models and with other experimental results.
UHF scintillation activity over polar latitudes
Authors: Aarons J. , Mullen J. P. , Whitney H. E. , Johnson A. L. , Weber E. J.
Published: February 2008

Polar cap ionospheric irregularities have been monitored for several years from Thule Air Base, Greenland using 250 MHz satellite beacon scintillation measurements. The seasonal pattern of the polar cap irregularities shows very high intensity levels during the winter and lower levels during the summer (sunlit) months. This behavior is similar to in‐situ polar cap electric field measurements which show larger fluctuations in the winter than in the summer, an effect which may be related to E layer conductivity changes. A striking contrast was noted between high scintillation levels observed during 1979/80, a year of high solar flux, and much lower levels observed during 1975, a year of low solar flux. This variation may be related to a corresponding solar cycle variation in polar cap F layer electron density. The data reveal little difference between periods of high and low Kp, and only a weak diurnal variation in any season. Direct optical and ionosonde measurements indicate that these scintillations are produced by ionospheric irregularities in the polar cap F‐region. Results of spaced receiver drift measurements indicate that the small scale of irregularity drift was antisunward. Intense irregularities are associated with discrete sun aligned F layer auroras. A weak background level of scintillation persisted in the high solar flux years.
HO2 in the stratosphere: Three in situ observations
Authors: Anderson J. G. , Grassl H. J. , Shetter R. E. , Margitan J. J.
Published: February 2008

Three in situ, midlatitude, midday observations of HO2 in the Earth's stratosphere were made using a chemical conversion — resonance fluorescence technique. The mean of the observed HO2 volume mixing ratios at 37, 35, 33, 31, and 29 km are respectively 4.7 × 10−10, 2.6 × 10−10, 3.9 × 10−10, ≤ 2.1 × 10−10 and ≤ 1.1 × 10−10 with an experimental uncertainty of ± 35%. Significant variability is observed among the three observations. These results are compared with a recent model of stratospheric chemistry demonstrating that while the calculated distribution falls within the band defined by the observations, the mean of the observations lies consistently above the calculation, though never by more than a factor of two. A comparison between the rate of odd oxygen production by O2 photolysis and the rate of HOx catalyzed destruction demonstrates that hydrogen‐oxygen free radicals account directly for a fractional destruction of Ox between 5 and 10 percent in the altitude interval between 29 and 37 km given current formulations of stratospheric chemistry.
Magma transport of heat on Io: A mechanism allowing a thick lithosphere
Authors: O'Reilly Thomas C. , Davies Geoffrey F.
Published: February 2008

Models indicate that the high heat flow from Io would result in a very thin (approximately 5 km) silicate lithosphere overlying a molten interior, if all heat was transported through the lithosphere via conduction. However, the presence of mountains with relief in excess of 10 km would seem to demand a thick lithosphere, at least locally. A significant fraction of Io's heat flow may be transported via advection through volcanoes. Advective heat transfer permits a thicker lithosphere than does pure conduction, possibly reconciling Io's high heat flow with the rugged topography.
Relationship between energetic particles and plasmas in the distant plasma sheet
Authors: Sarris E. T. , Krimigis S. M. , Lui A. T. Y. , Ackerson K. L. , Frank L. A. , Williams D. J.
Published: February 2008

Measurements of ions from three different instruments on the IMP‐7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of ∼ 100 eV to 4 MeV in the earth’s distant (∼ 30 to ∼ 40 Re) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from ∼ 10−5 to 105 (cm²sec sr keV)−1, varying smoothly over the entire energy range both when the plasma is cold (∼ 1 keV) and hot (∼ 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (≳ 50 keV) tail described well by a power law (⧜E−γ). The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. The transition between the Maxwellian and the power law occurs at E ≃ (γ + 1)kT. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.
A meteor‐ablation model of the sodium and potassium layers
Authors: Hunten Donald M.
Published: February 2008

Recent results on meteor ablation are used as input to a model in which ablation (or evaporation) is the source and deposition on dust particles is the sink. The dust comes from recondensation of the rest of the meteor vapor. An excellent match is found to the observed characteristics of the sodium layer. It is argued that the high‐latitude winter maximum of abundance (and layer height) is due to the much lower rate of ionization there and over the polar cap. The computations show the required factor of 4‐5 and also match the height variation. To keep the ion density from being too large, downward electrodynamic transport at ≃50 cm/sec must be invoked. The different behavior and low abundance of potassium require an additional sink. The one proposed is Penning ionization by inetastable excited O2. Inherent in the model is that sodium and its compounds reside almost entirely on dust particles below 80 km. Large abundances in the free form at stratospheric heights are very unlikely and are not a good explanation of observed ambient ions.
Cosmic rays and thunderstorm frequency
Authors: Lethbridge M. D.
Published: February 2008

A significant maximum in cosmic rays occurs one day before solar sector boundary crossings. Therefore, previous work showing a maximum in thunderstorm frequency one day after solar sector boundary crossings may result from high cosmic ray counts. This is evidenced by a maximum in thunderstorm frequency three days after high cosmic rays and, also, by a maximum in thunderstorm frequency three days after minimum Kp. These maxima are of higher statistical significance than those found when solar sector boundary crossings were key days.
experimental tectonophysics
Authors: Handin John , Logan J. M.
Published: February 2008

Because virtually all tectonophysical processes are masked by the overburden, or occur too slowly for adequate observation in anthropocentric time, or both, they must be studied in carefully controlled laboratory experiments that simulate the natural environment as realistically as is practicable. Extrapolations of laboratory data in space and time are invalid unless the experimental and natural phenomenologies are essentially the same. The size of conventional specimens is of the order of 10 cm, whereas the discontinuities (defects in a continuum) in real rock‐masses are often much larger, of the order of l m of more. Furthermore, such discontinuities as macrofractures (joints) may well dominate the mechanical and fluid‐transport properties in nature. Adequate sampling of rock‐mass properties will probably always require in‐situ testing, but testing machines much larger than any now available could provide useful data at least at intermediate scale.
Rock properties for which large scale tests may be necessary
Authors: Hustrulid William
Published: February 2008

The potential application of large scale geomechanical testing results to the following five mining/civil engineering problem areas; roof spans, design of rock support‐reinforcement systems, design of rock compression members, development/optimization of fragmentation systems, and design of slopes is discussed. It is concluded that such testing does have an application but to be meaningful it must be accompanied by significant field observation measurement programs.

The type of testing facility required is not universal but depends upon the problem to be examined.
Underground large scale test facility for rocks
Authors: Sundaram Panchanatham N.
Published: February 2008

This brief note discusses two advantages of locating the facility for testing rock specimens of large dimensions in an underground space. Such an environment can be made to contribute part of the enormous axial load and stiffness requirements needed to get complete stress‐strain behavior. The high pressure vessel may also be located below the floor level since the lateral confinement afforded by the rock mass may help to reduce the thickness of the vessel.
Sunlight absorption by aerosols in Jupiter's upper atmosphere
Authors: West Robert A.
Published: February 2008

The amount of sunlight deposited in the Jovian upper atmosphere is estimated from reflectivity measurements at 2400 Å by the Voyager 2 Photopolarimeter experiment and at visible and near‐IR wavelengths observed by Pioneer 10 and ground‐based instruments.

Zero to about one percent of the incident energy is absorbed at altitudes above the 100 mbar level in models with mean values for haze optical depth and single scattering albedo. Several percent of the incident energy could be absorbed, if limiting values are used, and if an additional absorbing layer is incorporated below the high altitude haze in Pioneer models. Maximum absorption occurs at the edge of the polar regions near ±65° latitude. Most of the absorbed energy is derived from visible and near‐IR radiation rather than UV radiation.
A local dust storm in the Chryse Region of Mars: Viking Orbiter observations
Authors: James Philip B. , Evans Nancy
Published: February 2008

A local dust storm was observed near the Viking Lander 1 site by Viking orbiter l in September, 1977, when the areocentric longitude of the sun, Ls, was 340° (shortly before vernal equinox). The orbiter observations, which consisted of a time sequence of pictures, show that the storm moved at about 50 m/sec to the ENE from the Lunae‐Planum region into the Chryse basin. Both baroclinic waves and topography may have been associated with the generation of the storm.
Cosmic‐ray scintillations observed from space
Authors: Owens A. J.
Published: February 2008

A theoretical calculation is given for the "scintillations" or fluctuations of cosmic rays expected to be observed during quiet times by a detector in interplanetary space or on the lunar surface. Interplanetary scintillations caused by fluctuations in the interplanetary magnetic field are not sufficient to explain the power spectrum recently reported by Benson et al. (1981) from a detector on the moon. Their inferred cosmic‐ray fluctuations are considerably larger than observed during undisturbed periods by ground‐based and satellite experiments.
Some remarks on the thermal consequences of ridge subduction
Authors: Hsui Albert T.
Published: February 2008

A simple model has been developed to study the thermal consequences of ridge subduction. The geological process is modeled as a flat plate moving over a finite line heat source. Effects of plate velocity, ridge length and the oblique angle between ridge and trench axes have been investigated. Calculated results indicate that the depth of thermal perturbation of a ridge is inversely proportional to plate velocity. Thermal effects will penetrate deeper into a plate for longer ridges if the ridge axis is parallel to the direction of plate motion. However, depth of thermal disturbance is found to be independent of ridge length if ridge axis is normal to plate motion direction.
Greenhouse effect of trace gases, 1970‐1980
Authors: Lacis A. , Hansen J. , Lee P. , Mitchell T. , Lebedeff S.
Published: February 2008

Increased abundances were measured for several trace atmospheric gases in the decade 1970‐1980. The equilibrium greenhouse warming for the measured increments of CH4, chlorofluorocarbons and N2O is between 50% and 100% of the equilibrium warming for the measured increase of atmospheric CO2 during the same 10 years. The combined warming of CO2 and trace gases should exceed natural global temperature variability in the 1980's and cause the global mean temperature to rise above the maximum of the late 1930's.
Correlations between solar wind parameters and auroral kilometric radiation intensity
Authors: Gallagher D. L. , D'Angelo N.
Published: February 2008

The relationship between solar wind properties and the influx of energy into the nightside auroral region, as indicated by the intensity of auroral kilometric radiation, is investigated. Fluctuations, as large as three orders of magnitude and with periods related to the solar rotation period, are found in the observed intensity of auroral kilometric radiation. Correlations are made with solar wind ion density, bulk flow speed (Vsw), total IMF strength (Bsw), |Vsw × Bsw| electric field, solar wind VswBs (where Bs is the southward component of the IMF Bz), solar wind Vsw²Bsw and VswBsw², and the substorm parameter ϵ (= VswBsw²sin4(θ/2)Lo²). The best correlation is between the solar wind bulk flow speed and the intensity of auroral kilometric radiation. For the 203 daily averages examined, a linear correlation coefficient of 0.78 is found.
Seasonal dependence of large‐scale Birkeland currents
Authors: Fujii R. , Iijima T. , Potemra T. A. , Sugiura M.
Published: February 2008

The seasonal dependence of large‐scale Birkeland currents has been determined from the analysis of vector magnetic field data acquired by the TRIAD satellite in the northern hemisphere. Statistical characteristics of single sheet (i.e., net currents) and double sheet Birkeland currents were determined from 555 TRIAD passes during the summer, and 408 passes during the winter (more complicated multiple‐sheet current systems were not included in this study). The average Kp value for the summer events is 1.9 and for the winter events is 2.0. The principal results include the following: (1) The single sheet Birkeland currents are statistically observed more often than the double sheet currents in the dayside of the auroral zone during any season. The single sheet currents are also observed more often in the summer than in the winter (as much as 2 to 3 times as often depending upon the MLT sector). (2) The intensities of the single and double sheet Birkeland currents on the dayside, from approximately 1000 MLT to 1800 MLT, are larger during the summer (in comparison to winter) by a factor of about 2. (3) The intensities of the double sheet Birkeland currents in the nightside (the dominant system in this local time) do not show a significant difference from summer to winter. (4) The single and double sheet currents in the dayside (between 0600 and 1800 MLT) appear at higher latitudes (by about 1° to 3°) during the summer in comparison to the winter. These characteristics suggest that the Birkeland current intensities are controlled by the ionospheric conductivity in the polar region. The greater occurrence of single sheet Birkeland currents during the summertime supports the suggestion that these currents close via the polar cap when the conductivity there is sufficiently high to permit it. Since the intensities of Birkeland currents are larger during periods of greater ionospheric conductivity, an important source (but perhaps not the only source) of these currents must be a voltage generator in the magnetosphere, possibly related to the convective electric field.
Study of a subsurface fracture zone by vertical seismic profiling
Authors: Stewart Robert R. , Turpening Roger M. , Toksoz M. Nafi
Published: February 2008

Remotely estimating the properties of subsurface fracture zones is important in characterizing the structure of the shallow earth. We present a vertical seismic profiling (VSP) technique to make this fracture zone estimation and discuss the results of a VSP experiment performed in the upper 770 m of the Michigan Basin. Both P and SH waves were used to observe an explosively‐fractured volume of Antrim shale. The experiment was divided into two parts: a "before" survey run on the unaltered rock, then an identical "after" survey executed across the fractured volume. A seismic velocity structure of the basin was calculated from the "before" survey. Comparison of the "after" observations to the "before" data, elucidated the fracture volume and its effective elastic parameters. From travel‐time delays, amplitude attenuation, converted and scattered waves, we estimated the depth (395 m), shape (ellipsoidal), size (10 m × 20 m × 30 m) and porosity (20%) of the fracture zone.
Sequential development of grooved terrain and polygons on Ganymede
Authors: Golombek Matthew P. , Allison M. Lee
Published: February 2008

Grooves on Ganymede have been interpreted as fractures that result from extensional tectonics which, accompanied by some type of resurfacing, changed relatively low‐albedo, heavily cratered terrain to higher‐albedo, less cratered grooved terrain. The formation of grooves involved initial fracturing of cratered terrain, resurfacing confined within these fractures, and subsequent fracturing of resurfacing material. Crosscutting and terminating, or "T" structural relationships among grooves, groove sets, and cratered terrain indicate that grooved terrain developed in three stages. The formation of primary grooves marks the initial breakup of cratered terrain. Secondary grooves generally terminate against primary grooves and complete the breakup of cratered terrain into polygons that are mechanically isolated from adjacent polygons. In the final stage (3), polygons of cratered terrain are fractured, resurfaced, and the resurfacing material is subsequently fractured by a set of closely spaced, parallel to subparallel grooves that terminate against the older primary and/or secondary grooves. In each of these stages, the groove‐forming process occurs in the same sequence: fracturing, resurfacing, and subsequent fracturing of resurfacing material, but most of the area of grooved terrain is resurfaced during stage 3. The process may stop during any of the three stages yielding areas of fractured cratered terrain, polygons of cratered terrain, polygons which have been resurfaced but not subsequently fractured (smooth terrain), or completely grooved terrain. Regardless of place or time of development, grooved terrain appears to have evolved according to the same sequential order of stages. Because the development of grooves within each stage created smaller isolated polygons out of larger areas, this process has resulted in the break‐up of the surface of Ganymede into progressively smaller and more equidimensional mechanical units.
A new iterative method for finding the normal modes of a laterally heterogeneous body
Authors: Kawakatsu Hitoshi , Geller Robert J.
Published: February 2008

We present a new iterative method for finding the normal modes of a laterally heterogeneous body. The number of operations used by our method is proportional to the square of the number of basis functions used, while the effort required by the variational method increases as the cube of the number of basis functions. A numerical example shows that, at least for lower order modes, our iterative method yields results which are as accurate as the variational method.
NOx in the mid‐Pacific troposphere
Authors: Noxon J. F.
Published: February 2008

Measurements of NO2 in spectra of the rising and setting sun from Mauna Loa, Hawaii, gave a mean of 30 ppt for NOx at 3 ± 0.5 km altituge in the mid‐Pacific troposphere. Natural variations of ∼ 50 percent occurred about this mean together with the systematic nocturnal decay expected from the reaction of NO2 with ozone. The tropospheric column abundance of NO2 exhibited a correlation with the variation of NO2 density at 3 km; the changes in both appear related to the strength of the trade winds and may reflect an overall rising or sinking motion in the lower troposphere. The measured NOx appears to be free of any anthropogenic influence and low enough in density that in the lower mid‐Pacific troposphere the source of ozone is downward diffusion from above and not local photochemical production.
Analysis of total ozone data for the detection of recent trends and the effects of nuclear testing during the 1960's
Authors: Reinsel Gregory C.
Published: February 2008

Time series modeling of total ozone data is considered for the detection of changes in ozone due to the possible effects of nuclear weapons testing in the early 1960's and more recent effects of the release of chlorofluromethanes (CFMs). Based on ozone data from a network of Dobson stations over the period 1958‐1979, the results of this analysis are consistent with a maximum decrease in ozone in the northern hemisphere of approximately 2 to 4.5% due to nuclear testing effects in the early 1960's. In addition, our findings show little evidence of any significant trend in global total ozone occurring in the 1970's, with the global change during 1970‐1979 estimated as (.488 ± 1.354)%.
Stratospheric aerosol and condensation nuclei enhancements following the eruption of Alaid in April 1981
Authors: Hofmann D. J. , Rosen J. M.
Published: February 2008

A significant enhancement of the stratospheric aerosol and condensation nuclei levels was observed at Laramie, Wyoming beginning in May 1981, following the eruption of the volcano Alaid (50.8°N, 155.5°E) on April 28. Observations to mid‐July suggest that in terms of effects on the stratosphere, the eruption was similar to that of Mt. St. Helens in May 1980.
Anomalous resistivity on auroral field lines
Authors: Rowland H. L. , Palmadesso P. J. , Papadopoulos K.
Published: February 2008

Conditions that exist along auroral field lines (δni/no > .25, Ωe/ωe > 1) act to break the adiabatic invariance of the electron magnetic moment, cause strong anomalous dc resistivity, and generate electron distributions in good agreement with observations.
The variability of mesospheric water vapor
Authors: Gibbins C. J. , Schwartz P. R. , Thacker D. L. , Bevilacqua R. M.
Published: February 2008

Measurements of the H2O emission line at 22.2 GHz show that the concentration in the mesosphere of water vapor molecules can be highly variable, ranging from nearly constant mixing ratios of 2‐4 ppmv, up to a layer near 65 km altitude with peak values around 12 ppmv. Results above 70 km altitude have been used to deduce a value for the vertical eddy diffusion coefficient of (4.4 ± 0.7)×105 cm²sec−1.
Initial vector magnetic anomaly map from MAGSAT
Authors: Langel R. A. , Schnetzler C. C. , Phillips J. D. , Horner R. J.
Published: February 2008

Global magnetic component anomaly field maps have been derived from the MAGSAT vector magnetometer data obtained from November 1979 through May 1980. The amplitude of variations of the components over the maps are between 10 and 15 nT, well above the noise in the data. Averaged data, in 2° by 2° blocks, exhibit standard errors of the mean of about 1 nT over most of the X and Z maps, and about 2 nT over most of the Y maps. Errors rise to about twice these amounts near the auroral belts. Most of the anomalies in the component data are consistent with a crustal magnetization model which incorporates dipoles aligned only in the direction of the main field. However, there appear to be some regions which require dipoles aligned in some other direction (i.e. remanent magnetization).
Detection of uncharted seamounts using satellite altimetry
Authors: Lazarewicz Andrew P. , Schwank David C.
Published: February 2008

The topography of the marine geoid (and corresponding sea surface) contains characteristic local features caused by seamounts. These features can be successfully detected and located using matched filters to process single tracks of satellite altimeter data. Comparison of detected seamount features with the SYNBAPS and Scripps bathymetric data bases can reveal uncharted seamounts. This technique has been applied to 33 Seasat tracks in a region of the western Pacific bounded by 0 to 15 degrees North and 160 to 165 degrees East. From this analysis, we find three uncharted seamounts in this region. In all three cases, a detailed examination of the bathymetry shows no known bathymetric feature consistent with the detected signature. The method used to estimate the size and location of these uncharted seamounts is discussed.
Trajectory parameterization ‐ A new approach to the study of the cosmic ray penumbra
Authors: Cooke David J.
Published: February 2008

A new approach to the examination of the structure of the cosmic ray penumbra has been developed, which, while utilizing the speed, efficiency and "real" geomagnetic field modeling capabilities of the digital computer, yields an analytical insight equivalent to that of the earlier and elegant approaches of Stormer, and of Lemaitre and Vallarta. The method involves an assigning of parameters to trajectory features in order to allow the structure and properties of the penumbra to be systematically related to trajectory configuration by means of an automated set of computer procedures. Initial use of this "trajectory parameterization" technique to explore the form and stability of the penumbra has yielded new and important knowledge of the penumbra and its phenomenology. Among the new findings is the discovery of isolated forbidden penumbral "islands."
Statistics of cold cumulonimbus anvils based on enhanced infrared photographs
Authors: Danielsen Edwin F.
Published: February 2008

Infrared photographs from the Atlantic Geosynchronous Satellite, enhanced to resolve cold anvil temperatures of tropical clouds, are analyzed statistically to determine their spatial‐temporal variability during the NASA‐U2 Flight Experiment of 1980. Diurnal dependence varies regionally, indicating topographic control via low level convergence and release of convective instability. Anvil growth rates, area covered and duration are discussed for individual and merging anvil systems. Gradients of anvil temperatures implied by infrared photographs are shown to be caused, in part, by radial decrease in anvil depth, i.e., to emissivities less than 1. An error in cloud top temperature of 10C is caused by 10% reduction in emissivity. Errors are near zero in dense, actively growing portions of the anvil.
Cosmic rays near the heliospheric current sheet
Authors: Kota J. , Jokipii J. R.
Published: February 2008

We present a discussion of full, three‐dimensional model simulations of the solar modulation of galactic cosmic rays, including drift. Our particular emphasis is on the variation of the cosmic‐ray intensity near the heliospheric current sheet. We show that the model quite naturally produces a negative gradient away from a wavy current sheet as seen by an observer on the Earth. We conclude that recent observations of Newkirk and Lockwood are not in conflict with these model results, and hence are consistent with modulation models in which drift plays an important role.
Synthetic aperture radar measurements of ocean surface currents
Authors: Lyzenga D. R. , Shuchman R. A. , Rufenach C. L.
Published: February 2008

The data recorded by a synthetic aperture radar (SAR) can in principle be analyzed to obtain the radial velocity of moving objects in the scene relative to the flight path of the SAR platform. The application of this concept for measuring ocean surface currents has been evaluated using data from SAR systems mounted in aircraft and spacecraft platforms. This paper summarizes the results of these experiments and describes the system effects which can influence the measurement accuracy. Considerations involved in the design of optimum systems for this application are also discussed.
A new concept of plasma motion and planetary magnetic field for Venus
Authors: Knudsen William C. , Banks Peter M. , Miller K. L.
Published: February 2008

We show that the magnetohydrodynamic conditions of the Venus ionosphere near the terminator favor convection of magnetic field rather than diffusion. Consequently, any planetary magnetic field which Venus may possess will be strongly affected by the global antisunward flow of the ionosphere which has been revealed by the Pioneer‐Venus retarding potential analyzer. The magnetic flux from an internal magnetic field will accumulate in the night hemisphere. Details of the structure and dynamics of such accumulations depend on particular details of the magnetic field source and the time‐dependent plasma flow pattern, but a simple interpretation of observational data yields a magnetic dipole moment of 7 × 1020 G cm³ directed along the planet spin vector.
Variation of amplitude of PKP from underground explosions in the southcentral Pacific
Authors: Massot J. P. , Rocard Y.
Published: February 2008

Taking advantage of the French nuclear test site in Southcentral Pacific for the analysis of PKP seismic waves, a systematic study around amplitude and arrival times was untertaken. A peak in the amplitude versus distance curves at 145°5 was observed with amplitudes up to 20 times larger than observed amplitudes in the 130‐140° distance range. This peak, together with six secondary maxima in the 142‐147° distance range is in good agreement with theoretical amplitude versus distance curves computed from interference phenomena and Airy diffraction theory. Some variation of blast site epicenter and energy provides the best check of the amplitude oscillations versus frequency and distance.