bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytic models for the ozone radiative absorption rate at 9.6 μm in the mesosphere
Authors: Zhu Xun , Summers Michael E. , Strobel Darrell F.
Published: February 2008

Analytic models of the ozone radiative absorption rate in the 9.6 μm band were developed on the basis of negligible line overlap in the mesosphere and low thermosphere. In the first model the line intensity distribution was represented by an S−1−β tailed exponential distribution. The band escape function was calculated by an integration over a single line profile with the diffusivity effect included exactly. Because ozone absorption is weak in the mesosphere, the major contribution to the absorption rate comes mainly from the strongest lines and the distribution function reduces to exponential form. In our second model, approximations for the diffusivity effect (diffusivity factor), line profile (Voigt), and line intensity distribution (Malkmus) were introduced to obtain an analytic expression for the band escape function. Both models yield accurate results for three examples that span the range of temperatures and ozone profiles encountered in the mesosphere and lower thermosphere with the maximum fractional errors never exceeding 4%. These two models are particularly suited for non‐LTE calculations and analysis of remote sensing data of the ozone 9.6 μm band in the mesosphere and lower thermosphere.
Pressure‐induced absorption in the infrared: A data base for the modelling of planetary atmospheres
Authors: Borysow Aleksandra , Frommhold Lothar
Published: February 2008

Recent progress related to the modeling of various pressure‐induced absorption bands of binary molecular systems, involving dissimilar and like pairs of molecules such as H2, He, N2, CH4, etc., is reported. The notes include references to the existing efforts based on quantum line shape computations that reproduce the laboratory measurements of pressure‐induced absorption closely. The results may be considered a most reliable data base permitting an evaluation of pressure‐induced absorption as function of frequency, temperature, and gas density for various binary molecular systems and spectral bands in the infrared region of the spectrum.
Laboratory spectra of 13C ethane
Authors: Kurtz Joe , Reuter Dennis C. , Jennings Donald E. , Hillman John J.
Published: February 2008

The laboratory infrared spectrum of 13C mono‐substituted ethane has been obtained at high resolution (0.0025 cm−1) using the McMath Fourier transform spectrometer at Kitt Peak National Observatory in May 1990. A preliminary analysis of the ν12 rQ0 branch (substituted species) suggests that its intensity is 1.15±0.05 times stronger than the equivalent ν9 branch in the normal 12C2H6 species. This result leads to a correction of a previously published estimate for the 12C/13C ratio in the atmosphere of Jupiter from ∼94 to ∼106.
Herman‐Wallis Factors in the C2H2ν5 infrared fundamental near 14 μm
Authors: Maguire William C. , Hillman John J. , Weber Mark , Blass William E.
Published: February 2008

The presence of acetylene has been confirmed for some time in the atmospheres of the outer planets Jupiter, Saturn, Neptune, and Saturn's satellite Titan. For these atmospheres, the determination of C2H2 abundances using its strong ν5 fundamental requires laboratory line position and intensity measurements. The 1‐meter Fourier transform spectrometer at McMath solar telescope of Kitt Peak National Observatory was used to measure C2H2 at an unapodized spectral resolution of 0.0025 cm−1. Synthetic spectra are generated by convolving a Voigt line shape with an instrument function and varying intensity parameters by means of a nonlinear least squares technique. Intensities of 37 ν5 lines spanning P18 through R20 were measured using 0.123 torr of gas in a 1‐cm cell. A Herman‐Wallis intensity correction parameter A1pr = 1.3(4) × 10−3 has been derived using a least squares linear fit.
Stress analysis of Tellus Regio, Venus, based on gravity and topography: Comparison with Venera 15/16 radar images
Authors: Williams David R. , Gaddis Lisa
Published: February 2008

The tectonics of the Tellus Regio highland of Venus have been examined using Pioneer Venus altimetry and gravity data and Venera 15/16 radar images. A thin elastic shell model has incorporated the Pioneer Venus data to calculate both global, long‐wavelength and regional, shorter‐wavelength stresses for various assumed values of crust, lithosphere, and mantle thickness and modes of compensation. The effects of these parameters on the calculated stress magnitudes have been examined. The model also allows calculation of crustal thickness and mantle density anomalies. The resulting calculated stress fields have been compared to the surface morphology observed in the Venera 15/16 radar images and interpreted in terms of the stress history. The best fitting parameters are consistent with minor amounts of lithospheric flexure being necessary to produce the observed surface features. The highland region is underlain by a thick (15–20 km) crust which is responsible for most of the topographic support. A positive density anomaly exists below this crust. The denser mantle may represent the down welling portion of a flow field, in which the horizontal flow feeding the downwelling has entrained mobile crustal material, dynamically maintaining a thickened crustal root near the stagnation point of the flow below Tellus Regio. This hot crustal material may have intruded the overlying cooler crust, causing lithospheric inflation and surface volcanism. This scenario is in agreement with the available gravity and radar data and can explain the general surface morphology of Tellus Regio.
A Simulation of the behavior of the cross‐polarization discrimination in frequency‐reuse line‐of‐sight links
Authors: Costa Emanoel , Dhein Ney R.
Published: February 2008

A simulation model of multipath propagation will be used to characterize the relationship between the cross‐polarization discrimination and the co‐polar attenuation in frequency‐reuse line‐of‐sight microwave links. The behavior of several links described in the literature will then be simulated, and the results will be compared with the corresponding measurements, to test the prediction capability of the model. A reasonable agreement between the corresponding results will be displayed. Further, it will also be shown that the cross‐polar phase patterns of the antennas could significantly affect the behavior of the cross‐polarization discrimination.
The diffraction of optic radiation by metallic bodies: Asymptotic theory
Authors: Buldyrev V. S. , Ljalinov M. A.
Published: February 2008

Results presented in this paper are the following: (1) the generalized Leontovitch conditions are obtained in the case of high or moderate conductivity of scattering body, and (2) asymptotic formulae in the problem of light diffraction are constructed on the basis of these conditions.
Total electron content obtained from ionogram data alone
Authors: Ezquer R. G. , Adler N. O. , Radicella S. M. , Gonzalez M. M. , Manzano J. R.
Published: February 2008

A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4° W), from ionogram data alone, is reported. To accomplish this, two Chapman profile expressions for the electron density (n) distribution in the F region are assumed, and a characteristic point of the n profile, called F region base point, is required. This method allows the TEC for a given particular time (not average) to be obtained. The results suggest that it could be a new method to calibrate polarimeter records used to measure TEC, and it could also allow the determination of TEC at predawn hours where only ionosounder data are available.
Length measurements of mid‐latitude scintillation irregularities
Authors: MacDougall John W.
Published: February 2008

The lengths of irregularities which produce 150‐MHz amplitude scintillations have been measured at 43°N, 81°W (geographic) using arrays of receivers with large spacings. The average length (major axis radius) of the irregularities was 6.1 km. This is much shorter than expected and implies that the measurements are of “young” irregularities, less than 1 minute old. These irregularities appear to be a large, 25–50% perturbation of the background density.
Stratigraphy and tectonic significance of Lower Paleozoic continental margin strata in northeastern Washington
Authors: Smith Moira T. , Gehrels George E.
Published: February 2008

Lower Paleozoic eugeoclinal strata in the Kootenay Arc in northeastern Washington and southeastern British Columbia are transitional between autochthonous lower Paleozoic miogeoclinal strata and outboard volcanic arc terranes of uncertain paleogeographic affinity. They provide a record of lower Paleozoic continental margin depositional and tectonic processes oceanward of the continental shelf. The southernmost stratigraphic unit, the Covada Group, is divided into two formations, the Daisy Formation, a mid fan sequence of arkosic and subarkosic wacke and arenite, and the Early Ordovician Butcher Mountain Formation, consisting of alkalic(?) pillow basalt and tuff of within‐plate affinity. Another unit, formerly part of the Covada Group, is excluded and informally named the Bradeen Hill assemblage. It contains chert, chert‐quartz arenite, quartz arenite, chert pebble conglomerate, shale, and basalt, and may be Ordovician to Devonian on the basis of stratigraphic evidence and regional correlations. The Covada Group and Bradeen Hill assemblage record (1) deposition of continentally derived sediments in a submarine fan setting, (2) relatively quiescent starved basin conditions, (3) local faulting; and (4) intermittent periods of volcanism, perhaps reflecting local extension. They can be correlated with other stratigraphic units in the Kootenay Arc and resemble units as far north as the Selwyn basin in northern Canada and as far south as the Roberts Mountains allochthon in central Nevada. This unites the stratigraphic record and implies a high degree of synchroneity of tectonic events along over 2500 km of the outer continental margin during early Paleozoic time.
Atmospheric loading of nitrogen to Alpine Tundra in the Colorado Front Range
Authors: Sievering H. , Burton D. , Caine N.
Published: February 2008

Dry deposition of atmospheric nitrogen gas and aerosol species was estimated for the alpine tundra of Niwot Ridge, 3525 m elevation in the Colorado Rockies. Comparisons, for the 4 month long growing season and the remaining 8 months of the year, were made with wet deposition and throughfall incident measurements taken during 1987‐1989. Dry deposition of N to the tundra is estimated to be equal to or slightly greater than its wet deposition. During the mid‐May to mid‐September growing season, atmospheric N deposition is >1.0 mg N m−2d−1 directly from the atmosphere with a similar amount contributed indirectly as NO3‐N in snowmelt water as a result of dry and wet deposition to the winter snowpack. The total N deposition to Niwot Ridge tundra during the growing season of about 2 mg N m−2d−1 may be compared to an earlier measurement of dry plus fog deposition (1 ‐ 2 mg N m−2d−1) to a subalpine coniferous canopy at Niwot Ridge. Nitrate yields from two small drainage basins at Niwot Ridge match these fluxes. Seven years of record from an unvegetated glacial cirque suggest an average yield from the alpine of 0.7 mg N m−2d−1. The equivalent estimate for a basin with 50% tundra vegetation cover is 0.4 mg N m−2d−1. The contrast in these two estimates of daily averaged N yields for the entire year suggests the retention of nearly 1 mg N m−2d−1 during the growing season in the more vegetated basin. The sink for this N could be the tundra soil and vegetation where biological activity is often limited by the availability of N.
Volatile biogenic halocarbons in the northwest Atlantic
Authors: Moore R. M. , Tokarczyk R.
Published: February 2008

A suite of naturally produced volatile halomethanes which are potential sources of gaseous halogens to the atmosphere have been measured in the water column of the NW Atlantic Ocean. Bromoform, chlorodibromomethane, dichlorobromomethane, dibromomethane, and methyl iodide all showed higher concentrations in coastal waters than in the pelagic zone. Such a distribution is consistent with known sources of these compounds in macro‐algae. Chloroiodomethane alone showed elevated concentrations in surface open ocean waters, and its distribution is interpreted as indicating production by phytoplankton, either directly or through an intermediate such as di‐iodomethane. The latter explanation is supported by post‐cruise estimates of the di‐iodomethane distribution. Whereas most of the compounds measured in this study have higher concentrations in the upper water column, both dibromochloromethane and bromodichloromethane showed increases with depth which would be consistent with a slow reaction of surface‐derived bromoform with chloride.
Factors affecting methane production under rice
Authors: Delwiche C. C. , Cicerone R. J.
Published: February 2008

To understand why atmospheric methane is increasing worldwide, accurate estimates are needed of the global input from rice fields. We report greenhouse and laboratory studies over three growing seasons to isolate and control factors that might affect methane emission from rice paddies, including soil texture, added exogenous organic matter (OM), nitrogen and sulfate ion, and water management. Without added OM, methane production was relatively low, increasing during the growing season, and continuing after harvest, provided the soil remained water‐logged. If ground rice straw was added to the soil prior to planting, methane production began shortly after flooding, with an initial burst of the gas after 3 to 5 weeks, and then a gradual increase to a second peak later in the season (and after harvest), with rates considerably higher than in treatments without added OM.
Spectral characterstics of fluctuations in laboratory plasma simulating features of bottom side of equatorial spread‐F
Authors: Prasad G. , Bora D. , Saxena Y. C.
Published: February 2008

Spectral characteristics of fluctuations in laboratory plasma under conditions similar to those obtained in equatorial F‐region plasma, are presented. Essential characteristics of the bottom side of the night time equatorial F‐region plasma, viz., density gradient antiparallel to gravity and perpendicular to the magnetic field, and magnetized electrons and ions are simulated in a toroidal laboratory plasma, where curved magnetic field produces effective gravity. Low frequency (ω < Ωi,kpi « 1) waves travelling in E × B direction are observed. The one dimensional k‐spectrum (S(k) ∝ kn) of density fluctuations exhibits two marked slopes with indices n = −2.3 ± 0.3 and −4.4 ± 0.2. Results are similar to the in‐situ measurements in F‐region and support theoretical predictions and numerical simulations based on Rayleigh‐Taylor and universal drift instabilities.
The abundance of O++ in the Jovian magnetosphere
Authors: Bagenal F. , Shemansky D. E. , McNutt R. L. , Schreier R. , Eviatar A.
Published: February 2008

From a synthesis of data from the Plasma Science and Ultraviolet Science instruments on the Voyager 1 spacecraft we present a radial profile of O++ abundance between 4.9 and 42 RJ. We observe a sharp rise in O++ mixing ratio near 7.5 RJ, coincident with a sharp rise in effective electron temperature at the outer boundary of the Io plasma torus. Beyond 8.5 Rj the O++ mixing ratio is found to be roughly constant which indicates freezing of the ionization prevailing at the outer edge of the hot torus.
Accurate determination of Cartesian coordinates at geodetic stations using the global positioning system
Authors: Soler Tomás , Strange William E. , Hothem Larry D.
Published: February 2008

Comparison of Cartesian coordinates determined at collocated sites using two independent space techniques, very long baseline interferometry (VLBI) and Global Positioning System (GPS), shows remarkable agreement even when the points in question span transcontinental distances. The results corroborate the capabilities of commercial dual‐frequency GPS receivers to perform geodetic work at the highest available accuracy. Adjusted geocentric coordinates of a configuration of GPS stations well distributed along the eastern half of the United States were accurately determined (better than 10−8) in the rigorously defined International Earth Rotation Service (IERS) terrestrial reference frame ITRF 89.
Unusual radio and plasma wave phenomena observed in March 1991
Authors: Reiner M. J. , Stone R. G. , Fainberg J.
Published: February 2008

During the intense solar flare activity in March 1991 a number of unusual radio emission and Langmuir wave phenomena were observed by the radio and plasma wave (URAP) experiment on the Ulysses spacecraft. These phenomena were associated with unusual conditions in the interplanetary medium (IPM) presumably resulting from intense solar activity. Some of these URAP observations cannot be explained by mechanisms usually attributed to interplanetary (IP) radio emissions and Langmuir wave activity and require other interpretations.
Observation of high‐N hydroxyl pure rotation lines in atmospheric emission spectra by the CIRRIS 1A Space Shuttle Experiment
Authors: Smith D. R. , Blumberg W. A. M. , Nadile R. M. , Lipson S. J. , Huppi E. R. , Wheeler N. B. , Dodd J. A.
Published: February 2008

Pure rotation line emissions from highly rotationally excited OH have been observed between 80 and 110 km tangent height under both nighttime and daytime quiescent conditions. Data were obtained using the cryogenic CIRRIS 1A interferometer, operated on the Space Shuttle. Transitions from OH(v=0–2, N′≤33) were identified between 400 and 1000 cm−1, corresponding to states with energies as high as 23000 cm−1. These are the first definitive observations of OH pure rotation transitions in the air glow, and by far the highest N levels observed in any type of OH airglow emission spectrum. The present observations of highly excited rotational states of OH parallel those made during recent field studies of NO and laboratory studies of OH, NO, and CO.
Meridional currents during equatorial geomagnetic disturbances
Authors: Rastogi R. G.
Published: February 2008

The annual average solar daily variations of the eastward component of the geomagnetic field, Y, at the equatorial stations, Kodaikanal and Huancayo indicate an increase on disturbed than on quiet days. With increasing daily mean geomagnetic activity index Ci, there is a systematic increase of daily mean value of Y and the systematic decrease of the daily mean value of H, (northward component) at both the stations. The storm‐time variations of the Y field are in opposite to the corresponding variations of the H field at both the stations. It is suggested that with increasing geomagnetic activity, the development of equatorial ring current is associated with corresponding increase of meridional currents at low latitudes.
Nonlinear magnetosonic waves and mirror mode structures in the March 1991 Ulysses interplanetary event
Authors: Tsurutani Bruce T. , Southwood David J. , Smith Edward J. , Balogh Andre
Published: February 2008

In examining the March 23–25, 1991 Ulysses (2.2 AU) high speed solar wind events, we find two distinct plasma wave modes: steepened magnetosonic waves with whistler precursors and mirror mode structures. These two modes are locally generated by plasma instabilities, presumably associated with anisotropies existing in the energetic shock particles and solar wind plasma, respectively. The magnetosonic waves are generated by a right‐hand resonant instability associated with a ∼ 40 keV ion beam.

By an extrapolation of the results presented here, assuming microflares and nanoflares at the Sun generate shocks in the lower corona and these shocks accelerate energetic ions, we suggest that the ions, via the right‐hand resonant instability, generate magnetosonic waves which steepened to form “microshocks” (such as shown here). These shocks could, in turn, accelerate more energetic ions, leading to a shock/energetic ion/magnetosonic wave cascade. These newly formed magnetosonic waves and shocks presumably could propagate in a broad range of directions, leading to energy dissipation over a large region of the outer corona.
Material transport in laser‐heated diamond anvil cell melting experiments
Authors: Campbell Andrew J. , Heinz Dion L. , Davis Andrew M.
Published: February 2008

Olivine from San Carlos, Arizona, Fa0.093 was compressed in a diamond anvil cell and melted under the action of a Nd: YAG laser. Stripes of melted material were formed by scanning the sample under the laser. Scanning electron microscopy and x‐ray microanalysis of the recovered samples reveal large‐scale (∼100 μm) transport of material through the sample, caused by the laser‐induced melting. Early‐crystallizing phases form at the beginning of the laser‐melted stripe; incompatible elements and late‐crystallizing phases are concentrated at the end of the stripe. This behavior is exploited to determine melting behavior of high‐pressure silicate assemblages of olivine composition. At pressures where β‐spinel is the phase melted, relative strengths of partitioning can be estimated for the incompatible elements studied. Iron was found to partition into the melt from β‐spinel less strongly than calcium, and slightly more strongly than manganese. At higher pressures, where a silicate perovskite/magnesiowüstite assemblage is melted, it is determined that silicate perovskite is the liquidus phase, with iron‐rich magnesiowüstite accumulating at the end of the laser‐melted stripe.
Evidence for Langmuir wave collapse in the interplanetary plasma
Authors: Kellogg Paul J. , Goetz K. , Howard R. L. , Monson S. J.
Published: February 2008

With the Fast Envelope Sampler part of the URAP experiment on Ulysses, we have observed much rapidly varying structure in plasma waves in the solar wind. Here we discuss extremely narrow (1 ms) structures observed together with electrostatic Langmuir waves, as well as some broader Langmuir wave packets
Evidence for anomalous earthquake size distributions in regions of minimal strain
Authors: Westaway Rob
Published: February 2008

Some regions have no earthquakes above magnitude ∼5.5, and thus apparently contain only small active faults, with length less than the thickness of the brittle upper crust. Britain and SSW Turkey are examples, with strain rates ∼3×10−20 and ∼3×10−17 s−1. Their seismicity has Gutenberg‐Richter parameter b ∼1.5, larger than ∼1 typical elsewhere, sufficient for equal strain to be associated with each order‐of‐magnitude of fault length present. These regions deform by increasing lengths and number densities of small faults. When strain reaches ∼0.01, these faults will be so closely‐spaced that they may interact, forming large faults that cut the brittle layer and take up most later deformation. Deformation involving only small faults will last <1 Myr in regions with strain rate ∼10−15 s−1, and is unlikely to be observed.
Adsorption of HCL on ice under stratospheric conditions: A computational study
Authors: Kroes Geert‐Jan , Clary David C.
Published: February 2008

Modelling surface adsorption of HCl on type II PSC's, we have performed computer simulations of adsorption of HCl on single crystal ice. For stratospheric conditions, the maximum surface coverage of ice by HCl is calculated to be 10−7 monolayer. This value was obtained by taking surface disorder into account. It is much too low for the reaction of HCl with chloronitrate to proceed rapidly on ordinary ice in one step. The calculated value of the surface coverage is much lower than recent experimental values for the uptake of HCl by polycrystalline ice, and the validity of the interpretation of the uptake of HCl by polycrystalline ice as being due to surface adsorption is questioned.
Long‐term winter total ozone changes at MacQuarie Island
Authors: Lehmann P. , Karoly D. J. , Newman P. A. , Clarkson T. S. , Matthews W. A.
Published: February 2008

Measurements of total ozone at Macquarie Island (55°S, 159°E) reveal statistically significant reductions of approximately twelve percent during July to September when comparing the mean levels for 1987–90 with those in the seventies. A back‐correction of 1963–79 Macquarie Island monthly mean ozone data is described which enabled this comparison.
Observational support for the current sheet catastrophe model of substorm current disruption
Authors: Burkhart G. R. , Lopez R. E. , Dusenbery P. B. , Speiser T. W.
Published: February 2008

It has recently been found that a one‐dimensional current sheet equilibrium with a non‐zero confection electric field, Ey, and a non‐zero normal magnetic field component, Bn, can reach a point of catastrophe through either the reduction of the drift velocity, υD = cEy/Bn or the increase of Bn. This point of catastrophe coincides with a value of κA ≃ 0.7, where κA is the self‐consistent value of κ = (Rmin/ρA max)½ corresponding to ions of average energy. (Here Rmin is the minimum field‐line radius of curvature and ρA max is the maximum gyroradius for ions of average energy.) The point of catastrophe was found to be preceded by a twisting of the current sheet field‐lines into the dawnward direction, i.e. by the development of a y‐component of B, with odd symmetry in z, and a sign opposite Bx, where positive x is earthward, positive y is in the dawn‐to‐dusk direction and positive z is northward. Since the loss of the current sheet would cause the local configuration to become more dipolar, it was suggested that the catastrophic loss of the local current sheet equilibrium could correspond to local current disruption and dipolarization. In this paper, observations of some of the signatures predicted by theory are presented.
The shedding of an anticyclonic eddy from the Alaskan stream as observed by the Geosat altimeter
Authors: Okkonen Stephen R.
Published: February 2008

The evolution of a meander into an anticyclonic eddy which separates from the Alaskan Stream in the vicinity of the central Aleutian Islands is observed in two years of sea surface height anomalies computed from GEOSAT Exact Repeat Mission altimeter data. The trajectory of the center of mass is estimated using a modified perpendicular bisector method. Eddy separation is inferred to occur where the trajectory makes a distinct turn to the southwest. The observed region of meander growth, and eddy separation agrees with that predicted by theory. The evolution of meander/eddy height and radius is estimated from least squares fits of the data to an axially symmetric Gaussian profile. The heights and radii are used to calculate the strength (vorticity) and energetics of the meander/eddy. Ekman dynamics are assumed to govern the eddy decay. Spin down times based on vorticity are much longer than those based on energetics. This is consistent with an eddy's ability to maintain its integrity as it decays. Representative height, diameter, and velocity scales of the eddy are characteristic of rings spawned by other current systems. Assuming a ring structure for this eddy the estimated ring volume represents a 21% transport anomaly referenced to the mean annual transport into the Bering Sea.
Occurrence of particle‐bound polysulfides and significance of their reaction with organic matters in marine sediments
Authors: Vairavamurthy Appathurai , Mopper Kenneth , Taylor Barrie F.
Published: February 2008

Inorganic polysulfides (Sn2−, where n > 1) contribute to the incorporation of sulfur into organic matter in reducing sediments, especially when conditions exist for partial oxidation of sulfide. Inorganic polysulfides have been assumed previously to exist only in the aqueous phase. Our results suggest that a significant fraction of inorganic polysulfides is bound to the particulate‐phase of sediments and can react with carbon‐carbon unsaturated bonds in organic matter, thereby attaching it to the particulate phase through polysulfide linkages. This mechanism may affect the bioavailability of the reactive organic matter in sediments and hence may play an important role in the preservation of organic matter in anoxic marine sediments.
Xenon critical velocity releases from the acitvny satellite: Discussion of attempted optical observations
Authors: Wescott E. M. , Stenbaek‐Nielsen H. C. , Hampton D. L.
Published: February 2008

The ACTIVNY satellite launched on Sept. 30, 1989 was a platform for a suite of active plasma experiments, including releases of Xe gas to test Alfvén's critical velocity effect. Three releases were done over Alaska and three over Utah, all fully illuminated by sunlight. We attempted optical observations from ground stations in the dark, using various low light level imagers and spectrographs, with narrow bandpass filters on XeI and XeII lines and also in white light. Viewing conditions were very good on several releases, the satellite could be tracked easily, but we saw no optical evidence of the releases from any wavelength. We discuss the reasons why optical diagnostics in the visible and near infrared failed to detect emissions from the releases.
Absolute positioning using Doris tracking of the SPOT‐2 satellite
Authors: Watkins M. M. , Ries J. C. , Davis G. W.
Published: February 2008

The French DORIS doppler satellite tracking/positioning system has been operational on the SPOT‐2 satellite since 1990. We have analyzed 80 days of data from 42 ground beacons and determined three dimensional site coordinates which agree with a set of SLR/VLBI positions at the 20–30 millimeter level in each coordinate after removal of common rotations, translations, and a scale difference. The accuracy of the vertical component is comparable to that of the horizontal components, indicating that residual troposphere error is not a limiting factor. The translation parameters indicate that the DORIS network realizes a geocentric frame to about 50 mm in each component. The considerable amount of data provided by the nearly global, all‐weather DORIS network allowed this complex parameterization required to reduce the unmodelled forces acting on the low Earth satellite. The positioning results obtained from tracking using essentially the same ground network and the higher altitude TOPEX/POSEIDON spacecraft should be superior to those obtained for SPOT‐2.
The uptake of HNO3 onto ice, NAT, and frozen sulfuric acid
Authors: Hanson David R.
Published: February 2008

The uptake of HNO3 onto ice, HNO3‐H2O layers, and solid H2SO4/H2O solutions were studied in a cylindrical flow tube in conjunction with a chemical ionization mass spectrometer detection system. An efficient loss of HNO3 from the gas‐phase to these surfaces was observed and the uptake coefficient was ≥0.3. The HNO3‐H2O layers formed, however, had HNO3 vapor pressures significantly in excess of the expected values for NAT (nitric acid trihydrate). Supersaturations in HNO3 of at least a factor of three and up to ten were observed suggesting a hindrance to the formation of NAT. These results imply that the condensation temperatures of Type I PSCs are 2–3 K colder than that expected for NAT.
The Lyman alpha bulge of Jupiter: Effects of non‐thermal velocity field
Authors: Ben Jaffel Lotfi , Clarke John T. , Prangé Renée , Gladstone G. Randall , Vidal‐Madjar Alfred
Published: February 2008

In this preliminary study, we outline for the first time the effect of non‐thermal line broadening processes (turbulence, random waves, convection ,...) on the shape and intensity of the H Ly‐α line resonance scattered from the atmosphere of Jupiter and we show how a non‐thermal velocity field, confined to the bulge region, in the upper atmosphere of Jupiter, may account for most of the H Ly‐α bulge features. Both the shape and the brightness of the Ly‐α line from the bulge region as reported by the IUE instrument and the Voyager UV Spectrometer can be recovered assuming resonant scattering with a total atomic hydrogen [H]∼ 4 × 1017 cm−2, and a non‐thermal component [H]∼ 2 × 1015 cm−2 above the thermopause.
Formation of model polar stratospheric cloud films
Authors: Middlebrook Ann M. , Koehler Birgit G. , McNeill Laurie S. , Tolbert Margaret A.
Published: February 2008

Fourier transform infrared spectroscopy was used to examine the competitive growth of films representative of polar stratospheric clouds. These experiments show that either crystalline nitric acid trihydrate (β‐NAT) or amorphous films with H2O:HNO3 ratios close to 3:1 formed at temperatures 3–7 K warmer than the ice frost point under stratospheric pressure conditions. In addition, with higher HNO3 pressures we observed nitric acid dihydrate (NAD) formation at temperatures warmer than ice formation. However, our experiments also show that NAD surfaces converted to β‐NAT upon exposure to stratospheric water pressures. Finally, we determined that the net uptake coefficient for HNO3 on β‐NAT is close to unity, whereas the net uptake coefficient for H2O is much less.
components of interannual ozone change based on NIMBUS 7 TOMS data
Authors: Hood Lon L. , McCormack John P.
Published: February 2008

A multiple regression statistical model is applied to estimate the latitude and seasonal dependences of the solar cycle, quasi‐biennial oscillation (QBO), and anthropogenic trend components of stratospheric total ozone change using 13.2 years of Nimbus 7 TOMS data. The characteristics of the linear trend component are in agreement with earlier studies. The QBO regression coefficient is significantly different from zero at high southern latitudes in the Austral spring supporting earlier evidence that the Antarctic ozone depletion is modulated by the QBO. The existence of a solar cycle component is indicated by empirical studies of model residuals and by the approximate agreement of the derived global mean solar coefficient amplitude with photochemical calculations. Initial estimates for the latitude dependence of the solar coefficient suggest higher amplitudes with increasing latitude, especially in the southern hemisphere in spring. The statistical model predicts a return to more rapid ozone depletions during the next 4 years as solar minimum is approached.
P‐wave image of the crust and uppermost mantle in southern California
Authors: Zhao Dapeng , Kanamori Hiroo
Published: February 2008

We have determined a P‐wave tomographic image of the crust and uppermost mantle in southern California by using 131,372 P‐wave arrival times from 6,437 local earthquakes recorded by the Caltech‐USGS Southern California Seismic Network in the past twelve years. The obtained image has a spatial resolution of 25 km in the horizontal direction and 8–11 km in depth. The tomographic image is found to correlate well with major surface geological features. In the shallow crust, sedimentary basins such as the Los Angeles Basin, Ventura Basin and Santa Maria Basin are well imaged as low velocities, while batholiths such as the Peninsular Ranges and San Gabriel Mountains are imaged as high velocities. In the deeper crust, the velocity is low beneath the Mojave Desert, Coso volcanic area and Salton Trough, while it is high beneath the Great Valley, Continental Borderland and the major basins. A high‐velocity layer exists in the mid‐crust beneath the Salton Trough, in good agreement with a previous study using seismic explosions and gravity data. In the uppermost mantle, the velocity is low beneath southeastern Sierra Nevada and the volcanic areas while it is high beneath the Mojave Desert and along the Pacific coast.
A temperature dependent kinetic study of the reaction of the hydroxyl radical with CH3Br
Authors: Zhang Zhengyu , Saini Rameshwar D. , Kurylo Michael J. , Huie Robert E.
Published: February 2008

Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH3Br over the temperature range 250 to 400 K. The Arrhenius expression k = 5.79 × 10−12 exp(‐1560/T) cm3 molecule−1 s−1 was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH3Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years.
Precursors to SS and structure of transition zone of the north‐western Pacific
Authors: Petersen N. , Gossler J. , Kind R. , Stammler K. , Vinnik L.
Published: February 2008

In the records of the Gräfenberg observatory and of a few other stations we have detected long‐period SH reflections at the underside of mantle discontinuities. The bounce points of the reflections are located in the northwestern margins of the Pacific. The data are used to evaluate S660S ‐ S410S differential times which are directly related to the thickness of the layer between the two discontinuities. Most of the bounce points are in the area of the Japan and Kuril ‐ Kamchatka subduction zones where a large‐scale depression of the 660‐km discontinuity was previously found and attributed to a cooling effect of subduction [Shearer & Masters, 1992]. According to our data the differential time in this region is 3 s less than in the IASP91 model. This anomaly suggests a thinning of the layer between the two discontinuities instead of thickening which is expected from depression of the lower discontinuity. Our analysis also indicates that there is a strong reflector in the study region at a depth of 900 km.
The thickness of resistive‐dispersive shocks
Authors: Hau L. ‐N. , Sonnerup B. U. Ö.
Published: February 2008

The purpose of this paper is to examine the thickness of slow, intermediate, and fast shocks described by the resistive‐dispersive plasma model, which contains two scale lengths: the resistive length λr and the ion inertial length λi. It is found that for the case where λr ≪ λi, i.e., for small resistivity, slowly damped wave trains dominate the structure yielding an effective shock thickness much greater than the ion inertial length. When λr ≫ λi, i.e., for large resistivity, the shock structure has a thickness of the order of the resistive length so that it is again much larger than λi. Thus a minimum thickness is predicted by the resistive‐dispersive model and occurs for intermediate resistivity: it is found to be a few λi for the slow shocks in distant magnetotail as well as for subcritical bow shocks and about 20λi for intermediate shocks with typical magnetopause parameters. It is shown that the shock thickness also depends critically on the upstream plasma beta, β1 = 2μop1/B1², small β1 values leading to smaller thickness. The effect of regular Newtonian viscosity on the shock thickness is also examined briefly.
The distribution of nitrate content in the surface snow of the Antarctic Ice Sheet along the route of the 1990 International Trans‐Antarctica Expedition
Authors: Dahe Qin , Zeller Edward J. , Dreschhoff Gisela A. M.
Published: February 2008

Previous work showed that nitrate measured at very high resolution (1.5 cm) in snow depositional sequences in Antarctica could be correlated with short‐term phenomena such as solar proton events (Dreschhoff and Zeller, 1990). It was clear that deposition of the ionization products in the snow is strongly dependent upon precipitation and atmospheric conditions during and immediately after the event. Information about the geographic distribution of the nitrate fallout over Antarctica was limited to only a few sites, however. A unique opportunity to examine this aspect of the nitrate distribution and to test more fully the hypothesis that atmospheric ionization from solar‐charged particles is responsible for a significant portion of nitrate was presented to us by a set of surface snow samples collected by the International Trans‐Antarctica Expedition foot traverse. The set of 95 samples of the upper 25 cm was collected by one of us (Qin) at roughly equal distances along the 5736‐km route from July 27, 1989, to March 3, 1990. Samples are distributed along a track from 65°05′S, 59°35′W, through 90°S, to 66°33′S, 95°39′E, which represents geomagnetic latitudes 50°S, west longitude, to 77°S, east longitude. The profiles of nitrate concentration and flux along the route were plotted and indicate that (especially at the higher elevation of the polar plateau) the distribution may be affected by electron precipitation.
H I Lyman alpha emission from Saturn (1980‐1990)
Authors: McGrath Melissa A. , Clarke John T.
Published: February 2008

Observations of Saturn made with the International Ultraviolet Explorer (IUE) satellite over the past decade have been analyzed to determine the characteristics of the H I Ly α dayglow and auroral emissions. The dayglow emission shows significant long‐ (years) and short‐term (days‐months) variability, with peak emissions in excess of 2 kR observed in 1980 and again in 1989; the disk brightness decreased after 1980 to its lowest value of ∼1 kR in January 1984; it then rose steadily and also exhibited increased short‐term variability between 1987 and 1989. The dayglow emission is strongly correlated (r>0.7) with the solar Ly α flux, the solar He 10,830 Å equivalent width (EQW), and the solar 10.7‐cm radio flux. The amplitude of the long‐term variation best matches that of the solar 10.7‐cm radio flux, while the short‐term variability is more closely proportional to the solar Ly α flux and the He 10,830 Å EQW. Unless the interplanetary medium hydrogen density is larger than the majority of published values, a large discrepancy of more than a factor of 2 exists between the Ly α brightnesses measured by IUE and Voyagers 1 and 2 on nearly the same dates that cannot be explained by solar variability. Current models suggest that resonant scattering can account for less than one‐half of the observed dayglow emission. In addition, the ratio of solar maximum to solar minimum brightnesses is larger than can be explained by resonant scattering from hydrogen produced by solar extreme ultraviolet (EUV) processes. We conclude, based on current models, that the Saturn Ly α dayglow is not dominated by resonant scattering but nonetheless varies in direct proportion to solar activity. Postulations of a significant collisional source for the emission therefore remain plausible. Intermittent outbursts of up to 1 kR in auroral emission above disk brightness have also been observed over the past decade. Neither the dayglow nor the auroral emission exhibits any dependence on magnetic longitude. Several attempts to observe Saturn aurora associated with a major solar flare that produced unprecedented geomagnetic activity in March 1989 were unsuccessful.
The dynamics of low‐β plasma clouds as simulated by a three‐dimensional, electromagnetic particle code
Authors: Neubert T. , Miller R. H. , Buneman O. , Nishikawa K. ‐I.
Published: February 2008

The dynamics of low‐β plasma clouds moving perpendicular to an ambient magnetic field in vacuum and in a background plasma is simulated by means of a three‐dimensional, electromagnetic, and relativistic particle simulation code. The simulations show the formation of the space charge sheaths at the sides of the cloud with the associated polarization electric field which facilitate the cross‐field propagation, as well as the sheaths at the front and rear end of the cloud caused by the larger ion Larmor radius, which allows ions to move ahead and lag behind the electrons as they gyrate. Results on the cloud dynamics and electromagnetic radiation include the following: (1) In a background plasma, electron and ion sheaths expand along the magnetic field at the same rate, whereas in vacuum the electron sheath expands much faster than the ion sheath. (2) Sheath electrons are accelerated up to relativistic energies. This result indicates that artificial plasma clouds released in the ionosphere or magnetosphere may generate optical emissions (aurora) as energetic sheath electrons scatter in the upper atmosphere. (3) The expansion of the electron sheaths is analogous to the ejection of high‐intensity electron beams from spacecraft: a stagnation point is reached where the expansion is halted, allowing only a fraction of the electrons to escape. These electrons may have energies exceeding the initial beam energy (sheath electrostatic potential energy). (4) Second‐order and higher‐order sheaths are formed which extend out into the ambient plasma. These sheaths are curved, the curvature increasing with the order of the sheath. (5) The formation of the sheaths and the polarization field reduces the forward momentum of the cloud. Furthermore, as the cloud moves across the field, sheath particles are peeled off and left behind, while fresh particles continue to drift into the sheaths in order to maintain these. This process requires continued energy supply which further decelerates the cloud. (6) The coherent component of the particle gyromotion (the particles are born with a coherent component at t=0) is damped in time as the particles establish a forward directed drift velocity. In addition, particles undergo orbital phase mixing associated with the establishment of the polarization electric field. For a dense cloud in vacuum the damping occurs very quickly, while for clouds in a background plasma the polarization fields are shorted, leaving the particles to gyrate as single particles. In this case, the coherent component is almost undamped. (7) The coherent particle gyrations generate electromagnetic radiation. The simulations indicate that artificial plasma clouds released in space will radiate close to the cloud electron or ion cyclotron/upper hybrid frequencies.
Particle simulations of driven collisionless magnetic reconnection at the dayside magnetopause
Authors: Ding D. Q. , Lee L. C. , Swift D. W.
Published: February 2008

Basic plasma processes associated with driven collisionless magnetic reconnection at the Earth's dayside magnetopause are studied on the basis of particle simulations. A two‐and‐one‐half‐dimensional (2½‐D) electromagnetic particle simulation model with a driven inflow boundary and an open outflow boundary is developed for the present study. The driven inflow boundary is featured with a driving electric field for the vector potential, while the open outflow boundary is characterized by a vacuum force‐free condition for the electrostatic potential. The major findings are as follows: (1) the simulations exhibit both quasi‐steady single X line reconnection and intermittent multiple X line reconnection (MXR); the MXR process is characterized by repeated formation and convection of magnetic islands; (2) particle acceleration in the reconnection process results in a power law energy spectrum of ƒ(E) ∼ E−4 for energetic ions with E > 40 keV and energetic electrons with E > 3 keV, where E is the particle energy; particles are accelerated to high energy near magnetic O line regions as particles are trapped within magnetic islands; (3) field‐aligned particle heat fluxes and intense plasma waves associated with the collisionless magnetic reconnection process are also observed; typical power spectra of fluctuating magnetic and electric fields are found to be PB ∼ f−3.6 and PE ∼ f−1.8, respectively, where f is the wave frequency; (4) when applied to the dayside magnetopause, simulation results show that the MXR process tends to generate a simultaneous magnetic field perturbation on both sides of the dayside magnetopause, resembling the observed features of two‐regime flux transfer events (FTEs); and (5) an intrusion of magnetosheath plasma bulge into the magnetosphere due to the formation of magnetic islands may lead to the layered structures observed in magnetospheric FTEs. Simulation results are applied to the dayside magnetopause to provide an explanation for some features associated with dayside magnetic reconnection and FTEs.