bluuebunny/crossref_metadata_2025 huggingface dataset:
On the use of software beam synthesis in multiple‐receiver MF radar wind estimation
Authors: Sürücü Fahri , Franke Patricia M. , Kudeki Erhan
Published: February 2008

Multiple‐receiver MF radar data acquired during the Arecibo Initiative in Dynamics of the Atmosphere 1989 campaign are used to demonstrate the viability of wind velocity estimation with poststatistics steering (PSS) technique. PSS wind estimates are shown to compare favorably with spaced antenna (true) and interferometric wind estimates.
Transient response of a circular cylinder to an electromagnetic pulse
Authors: Ma J. , Ciric I. R.
Published: February 2008

The transient response of a perfectly conducting circular cylinder to an electromagnetic pulse of a double exponential type has been investigated, and a new analytical expression has been derived for the induced current density on the cylinder surface. The analysis performed in this paper is based on the frequency domain eigenfunction solution of the surface current density and yields an analytical expression which is theoretically valid for both the shadow and illuminated regions and for all the time ranges. Numerical calculations show that results for the entire time range after the instant the initial incident wave front has passed the cylinder axis can easily be obtained from this single analytical expression. For very large time values, only the first few terms in the expression are needed to give a satisfactory accuracy.
A high‐frequency ray analysis of the electromagnetic backscattering by a two‐dimensional ogive
Authors: Shamansky H. , Dominek A. , Wang N.
Published: February 2008

The electromagnetic backscattering from a two‐dimensional ogive is examined, including a mechanism‐by‐mechanism account for the scattered field. The uniform theory of diffraction is used in conjunction with a simple creeping wave representation to yield a solution which provides an accurate and continuous backscattering result for a wide range of ogive geometry parameters. Although not a rigorous derivation of higher‐order diffraction coefficients, this solution provides insight into the relative contributions of the various creeping waves which are generated and propagate around the two‐dimensional ogive. Comparisons with moment method (MM) calculations are used to demonstrate the range of applicability of this high‐frequency asymptotic solution.
Fade statistics and propagation events at C band for two overwater, line‐of‐sight propagation paths over a 1‐year period
Authors: Goldhirsh Julius , Dockery G. Daniel , Musiani Bert H.
Published: February 2008

We examine signal fading statistics over a 1‐year period corresponding to two overwater, line‐of‐sight, propagation links in the mid‐Atlantic coast of the United States. These links are composed of a transmitter on a tower at Parramore Island, Virginia, operating at 4.7 GHz, sending simultaneous CW signals to two receiver systems located on a lighthouse and a lookout tower on Assateague Beach, Virginia, at distances of 44 and 39 km, respectively. The receiving sites are separated by approximately 5 km. Cumulative fade distributions corresponding to yearly, monthly, and diurnal time scales were derived. The annual distributions showed fades in excess of 49 and 54 dB during approximately 7.7 hours of the year, for the lighthouse and lookout tower links, respectively. Fade duration statistics corresponding to sustained attenuation events were also derived. These events, which were arbitrarily defined as having fades relative to free space powers in excess of 20 dB for durations of 2 hours or more, are believed to be generally due to extreme subrefractive conditions. Analysis of synoptic weather conditions and nearby rawinsonde data during four sustained deep fading periods showed atmospheric conditions consistent with extreme subrefraction, where the refractivity height profiles had positive lapse rates. A measured refractivity profile, having a positive lapse rate, was injected into a propagation model based on an approximation to the scalar Helmholtz wave equation, and fade levels in the vicinity of the antenna locations were calculated. Although the refractivity profile was measured during an earlier period in the vicinity of the links, it was obtained over the water and showed an extreme positive lapse rate in refractivity, indicating that such profiles do in fact occur. Furthermore, the calculated fades were noted to have the same range of values as measured during the sustained deep fade events, showing consistency with the hypothesis that severe subrefraction may be the cause of these events.
A high‐latitude ionospheric disturbance impact assessment system
Authors: Rose Robert B.
Published: February 2008

The Disturbance Impact Assessment System (DIAS) is a computer software package designed to assess and predict the impact of solar flares on high‐latitude HF radio communications. The analysis spans the period between the flare onset (T0 hours) and the expected subsiding of its effects 5 days later (T120 hours). DIAS supports a HF communications system and when integrated into it, its operation will be entirely transparent to the user. A stand‐alone PC version was designed for tutorial purposes. Key features combine the capabilities of the algorithmic PROPHET HF signal assessment system with expert system technology. The initial system provides qualitative advice and warnings. The rule sets in DIAS cover the following types of disturbances: (1) sudden ionospheric disturbances, (2) polar cap absorption, (3) ionospheric storm, (4) auroral zone absorption, and (5) auroral sporadic E and auroral E.
Direction of arrival and amplitude fluctuations of HF transionospheric signals through field‐aligned irregularities
Authors: Montbriand L. E.
Published: February 2008

An HF crossed arm sampling array was used to investigate the effect of the ionosphere on the direction‐of‐arrival (DOA) of 9.3‐MHz transionospheric transmissions from ISIS satellites. The experimental results were compared to theoretical results obtained from a transionospheric raytrace program. The difference in elevation between the transionospheric ray and the line‐of‐sight ray, referred to as the vertical DOA error, varies with elevation angle and maximizes at the iris of the ionosphere. The theoretical results show that if the transionospheric ray passes through a horizontal gradient or blob or trough in the electron density, a refractive error occurs. This error decreases if the ray passes through an electron density enhancement which is greater above the peak of the F2 layer than below it and increases if the ray passes through an enhancement which is greater below the F2 peak than above it. Experimental data exhibit this behavior. The S4 amplitude scintillation index is essentially independent of ray elevation and aspect angle regardless of the presence or absence of magnetic field‐aligned electron density irregularities (FAIs). For times when small‐scale FAIs are clearly present, the DOA of signals from a moving satellite fluctuates both most rapidly and most slowly when the orbit is polar and passes overhead. The very rapid fluctuations occur when the DOA of the transionospheric ray is near the magnetic zenith. This may be a diffractive effect. The fluctuations are slowest, probably indicating a refractive effect, when the satellite is approaching and receeding. This behavior is dependent upon the geometry of the situation but is absent when there are no FAIs. DOA fluctuations occurred at all the invariant latitudes observable (53°–65°), with the largest fluctuations occurring more frequently north of 60° and with increasing magnetic activity. The DOA fluctuations in this area were present in the summer and absent in the winter but were negligible when FAIs were absent. The seasonal variation is believed to be due to a seasonal variation in the chemistry of the F2 layer. When large blobs of FAIs appear to be located at the expected DOA, most connecting ray paths during the satellite transit appear to be refracted from the sides of adjacent blobs. However, one could also positively identify a small number of connecting ray paths per second which arrived at the expected DOA, indicating that a few rays appeared to have woven their way among the irregularities along its path.
An empirical model of the nonauroral D Region
Authors: Friedrich M. , Torkar K. M.
Published: February 2008

An empirical model of the D region electron densities is presented, which is based on rocket‐borne wave propagation data from mid‐latitude and equatorial regions obtained during quiet conditions only. The electron densities are defined for constant neutral densities and are given as a function of solar zenith angle.
Spaced antenna diversity in temperate latitude meteor burst systems operating near 40 MHz: Variation of signal cross‐correlation coefficients with antenna separation
Authors: Cannon Paul S. , Shukla Anil K. , Lester Mark
Published: February 2008

We have studied 37‐MHz signals received over an 800‐km temperate latitude path using 400‐W continuous wave transmissions. Signals collected during a 9‐day period in February 1990 on two antennas at separations of 5λ, 10λ, and 20λ were analyzed. Three signal categories were identified (overdense, underdense, and not known (NK)) and cross‐correlation coefficients between the signals received by the two antennas were calculated for each signal category. No spatial variation, and in particular no decrease, in average cross‐correlation coefficient was observed for underdense or NK signals as the antenna spacing was increased from 5λ to 20λ. At each antenna separation the cross‐correlation coefficients of these two categories were strongly dependent on time. Overdense signals, however, showed no cross‐correlation time dependency at 5λ and 10λ, but there was a strong time dependency at 20λ. Recommendations are made in regard to the optimum antenna spacing for a meteor burst communication system using spaced antenna diversity. Our measurements support the views of Bartholomé and Vogt [1968], who suggested that a 4λ spaced antenna diversity configuration contributed to the exceptional signal throughput of the COMET meteor burst communication system.
High‐latitude seasonal variation of meteoric and nonmeteoric oblique propagation at a frequency of 45 MHz
Authors: Weitzen J. A. , Cannon P. S. , Ostergaard J. C. , Rasmussen J. E.
Published: February 2008

This paper examines the seasonal duty cycle variation of meteor and nonmeteor propagation at 45 MHz on two high‐latitude links. Software techniques for automatic data processing and analysis of the data are discussed. It is shown that for large portions of the year nonmeteoric propagation, most likely sporadic E, is the dominant propagation mechanism. Consequently, protocols for an operational meteor scatter communication network must be designed to cope with a situation in which close to an entire network may be connected for long periods of time. System duty cycles at 45 MHz in excess of 20% are common during the summer months in the high‐latitude region.
Electrostatic image method for the interaction of two dielectric spheres
Authors: Lindell Ismo V. , Sten Johan C.‐E. , Nikoskinen Keijo I.
Published: February 2008

Static image theory for a homogeneous dielectric sphere was recently formulated by on the authors to account for the reaction of the sphere to the field from any electrostatic charge distribution. The theory is applied here in the analysis of the interaction of two dielectric spheres to find their reaction to external sources. Integral equations for the line image charges are formulated in the general case and a method for their solution is given in the limiting case of two conducting spheres. A simple, approximate dipole solution for the case of weak interaction between the spheres is also discussed. The theory has a potential application in analyzing interactions of closely packed spherical particles suspended in a host medium, in terms of one‐dimensional integral equations.
Modified radiative transfer theory in second‐order backscattering coefficients of a two‐layer random medium
Authors: Mudaliar Saba , Lee Jay K.
Published: February 2008

The modified radiative transfer theory is used to obtain the backscattering coefficients of a two‐layer random medium. Since exact solutions to the MRT equations are not available certain approximations are used. First, a first‐order approximation is made to obtain the backscattering coefficients. In an attempt to investigate the appropriateness of the first‐order approximation, higher‐order solutions are obtained. It is observed that the second‐order solution is important because it is the primary source of depolarization (cross‐polarized backscatter); besides it also helps one to estimate the error involved in settling for a first‐order approximation. Hence the second‐order backscattering coefficients are calculated and cast in a form suitable for physical interpretation. It is noticed that certain “phase” terms are absent. After exploring the reasons for this, it is suggested that the present MRT theory be further modified to accommodate these terms. Finally, with the help of numerical examples, characteristics of the second‐order solutions are studied by comparing them with the corresponding Born results and also with the first‐order solutions.
The importance of episodic events in controlling the flux of methane from an anoxic basin
Authors: Scranton Mary I. , Crill Patrick , de Angelis Marie A. , Donaghay Percy L. , Sieburth John M.
Published: February 2008

Methane distributions and fluxes were determined in the more southerly of two permanently anoxic basins at the head of the otherwise shallow and tidal Pettaquamscutt River. Fluxes out of the sediment were approximately equal to fluxes across the air‐sea interface as determined by flux chamber and were of the order of 3 ‐ 6 mg CH4 m−2 d−1. Ebullition, observed during one set of flux chamber experiments, increased air‐sea fluxes by several orders of magnitude. Methane oxidation rates within the waters of the basin were measured by using 14CH4, and a maximum in oxidation rate was observed at the oxic‐anoxic interface. Oxidation rates were about a factor of 10 lower than either measured sediment‐water or air‐sea fluxes. Fluxes across the pycnocline also were lower than sediment‐water fluxes and fell at the low end of the range of calculated air‐sea fluxes (which were lower than measured air‐sea fluxes). Therefore, on the basis of a short term survey, the system appeared to be roughly at steady state. However, in spite of the appearance of steady state, methane profiles measured over a period of several years varied dramatically suggesting that episodic events (ebullition, tidal mixing, upwelling, and intrusion events) must be major factors in the methane budget not obvious from short‐term experiments. Episodic events are probably also important for other systems such as productive coastal environments, suboxic estuaries or any other systems in which reduced gases might accumulate within or below a pycnocline. When the pycnocline is tilted or breaks down, substantial amounts of gases may be released to the atmosphere.
Biogeochemical ocean‐atmosphere transfers
Authors: Prinn Ronald , Liss Peter , Baut‐Menard Patrick
Published: February 2008

The exchange of trace gases and aerosols between the atmosphere and the ocean is an important process in the biogeochemical cycling of both biologically important elements and radiatively important compounds. This exchange process thus plays a significant role in both sustaining life in the ocean and determining the global radiative balance. These exchanges are complex involving biological and chemical processes in the sea, chemical and radiative processes in the air, and transport processes in both the atmosphere and the ocean. To give three specific examples: biological production followed by emissions of dimethyl sulfide (DMS) from the ocean leads to production of acidic cloud condensation nuclei with important implications for global marine cloud cover and thus albedo; atmospheric transport followed by deposition of iron‐containing atmospheric aerosols into the ocean leads to fertilization with possible important effects on net carbon dioxide removal through the biological planktonic pump; and, transfer of carbon compounds between atmosphere and ocean is a critical process in determining global atmospheric levels of carbon dioxide and marine atmospheric levels of reactive hydrocarbons.
Catastrophic overturn of the Earth's mantle driven by multiple phase changes and internal heat generation
Authors: Weinstein Stuart A.
Published: February 2008

The effects of phase changes and strong internal heat generation may combine to bring about brief, but extremely intense episodes of rapid thermal convection in the Earth's mantle. Numerical calculations using realistic thermodynamic properties for the exothermic Olivine → Spinel and endothermic Spinel → Perovskite + Magnesiowustite phase transitions suggest the transition region of the Earth's mantle may act as a capacitor for subducting slabs. Slab material accumulates in the transition region until a threshold level of thermal buoyancy is reached, and is then rapidly discharged into the lower mantle. In my calculations, this occurs as a catastrophic burst of convection lasting ∼10 Myr, with elevated heat transfer rates lasting ∼100 Myr. Such episodes may be analogs to superplume activity which has been hypothesized to give rise to an intense episode of intra‐plate volcanism and stabilize the geodynamo against reversals. The topography on the two phase change boundaries is found to be negatively correlated, with the correlation becoming more negative during periods of rapid convection. Furthermore, the results of this study suggest the transition region of the Earth's mantle could be ∼250 K cooler on average, and consequently more viscous, than the surrounding mantle.
H2O2 in the marine troposphere and seawater of the Atlantic Ocean (48°N – 63°S)
Authors: Weller Rolf , Schrems Otto
Published: February 2008

Concentrations of H2O2 in gas phase and seawater have been measured in pristine regions of the Atlantic Ocean during the RV Polarstern expedition ANT X‐1 from 11/15/91 to 01/02/92. A broad maximum of gaseous H2O2 mixing ratio in the troposphere was found between the tropic of cancer and the tropic of capricornus with peak values around 1.8 ppbv. The observed ratio of organic peroxides/total amount of peroxides was 0.2–0.35, in contrast to the remarkably lower ratio of 0.05–0.10 measured in the continental troposphere by other groups. In the Atlantic surface seawater the H2O2 concentrations were determined to be around 0.1 μmol/L, decreasing with increasing water depth to a value below the detection limit at approximately 100 m. We observed low H2O2 concentrations (≈ 0.03 μmol/L) in surface water in coastal shelf regions and in the partly ice covered Weddell Sea.
Second flight of the Spacelab Grille Spectrometer during the ATLAS‐1 mission
Authors: De Maziere M. , Muller C. , Lippens C. , Vercheval J. , Fonteyn D. , Armante R. , Camy‐Peyret C. , Achard V. , Besson J. , Marcault J. , Henry D. , Papineau N. , Meyer J. P. , Frimout D.
Published: February 2008

The SPACELAB grille spectrometer on its second space flight during the ATLAS‐1 mission (March 24 ‐ April 2, 1992) took advantage of the favorable timeline and of the extra day to perform more than 65 successful solar occultation runs. It succeeded in obtaining spectra pertinent to its ten target molecules in the full range of altitudes available to the solar infrared occultation technique. These ten molecules are H2O, CO, CO2, CH4, NO, NO2, N2O, HCl, HF and O3. The preliminary analysis of the sunset observation presented here adds new information to the available database on HCl vertical profiles, for assessing long‐term trends of this important stratospheric species.
Observations of terrestrial far UV emissions by the Faust Telescope
Authors: Chakrabarti Supriya , Sasseen Timothy P. , Lampton Michael , Bowyer Stuart
Published: February 2008

The FAUST telescope was developed to provide precise photometry of extended astronomical objects in the 1400–1800 Å wavelength interval, and has a field of view of 7.6° and an angular resolution of 2 arc minutes. It was carried into orbit by the space shuttle Atlantis in March 1992 as part of the ATLAS‐1 mission. During this flight, on several occasions it was pointed at the Earth to provide an estimate of the terrestrial nightglow, auroral and shuttleglow emissions. Our preliminary findings on these non‐astronomical measurements are that auroral precipitation activity dominates in the high magnetic latitude, and that outside the high magnetic latitude region we consistently see diffuse emission of .005 to .02 Rayleighs/Å, slowly varying over the nightside. We explore interpretations of this emission as terrestrial nightglow and shuttleglow, and find a possible explanation as NO chemiluminescent nightglow.
An amorphous phase on the anorthite hugoniot
Authors: Campbell Andrew , Heinz Dion
Published: February 2008

Compressional wave velocities as a function of pressure have been measured in pressure‐amorphized anorthite to 14 GPa at room temperature. A weighted linear fit to the data gives a zero‐pressure value of Vp = 6.35±0.12 km s−1, with a slope of 0.154±0.016 km s−1 GPa−1. It is shown that these compressional wave velocities compare well with bulk sound speeds inferred from shock‐wave experiments on anorthite above the phase transition at 30 GPa, assuming a value of Poisson's ratio in the range of 0.15 to 0.20. All crystalline assemblages which have been suggested as high‐pressure phases of anorthite are shown to possess zero‐pressure bulk sound speeds in the range 6.9 km s−1 to 8.1 km s−1, well above the value of 5 km s−1 extrapolated from the shock‐wave data. It is therefore proposed that the shock Hugoniot of anorthite above 30 GPa represents the properties of the pressure‐amorphized phase, rather than those of the equilibrium high‐pressure phases.
Spurious changes in the ISCCP dataset
Authors: Klein Stephen A. , Hartmann Dennis L.
Published: February 2008

A long‐term decrease in mean cloud optical depth and mean cloud top temperature exists in the International Satellite Cloud Climatology Project (ISCCP) dataset for the July 1983 to December 1990 time period equatorward of 50° latitude. The decrease in optical depth of 2 is large compared to its mean of 4.6 for this period. The nature of this decrease suggests that it is not real, but rather an artifact of incomplete normalization of the visible channel on successive polar orbiters used as the calibration standard for ISCCP. This decrease has large impacts on the amounts of different cloud types defined by ISCCP, especially for cloud types whose mean amount is small. The decrease in mean cloud top temperature of 5 K has a smaller effect on the amounts of various cloud types. More accurate calibration techniques are needed in order to establish long‐term climate trends from ISCCP.
The upper atmosphere research satellite (UARS)
Authors: Reber Carl A.
Published: February 2008

The Upper Atmosphere Research Satellite (UARS) was launched by the Space Shuttle on September 12, 1991 into a near circular orbit at 585 km altitude inclined 57 degrees to the Equator. Measurements were initiated a few days later, including solar energy inputs to the atmosphere and vertical profiles of temperature, important minor gas species, and wind fields. The orbital parameters, combined with the sensor measurements characteristics, yield a measurement pattern that produces near global coverage with a duty cycle that periodically favors the Northern or the Southern hemispheres. A few spacecraft and instrument anomalies have impacted the total amount of data obtained to date, but the overall performance of the mission has been very good.
Auroral currents during the magnetic storm of November 8 and 9, 1991: Observations from the Upper Atmosphere Research Satellite Particle Environment Monitor
Authors: Anderson B. J. , Potemra T. A. , Bythrow P. F. , Zanetti L. J. , Holland D. B. , Winningham J. D.
Published: February 2008

The magnetic storm of November 8 and 9, 1991, lead to expansion of the auroral oval below 45° magnetic latitude (MLAT) and auroral phenomena were sampled by the Upper Atmosphere Research Satellite (UARS). The attitude precision and stability of UARS allow monitoring of Birkeland and ionospheric currents via magnetic field measurements from the Particle Environment Monitor (PEM) magnetometer. This paper reports the development of the intensity and location of Birkeland currents associated with this storm. Two principle results are obtained: (1) total Birkeland currents exceed 30 MA, more than 6 times nominal values, indicating Joule heating of about 3×1012 W; (2) Birkeland currents below 50°, polar cap currents indicative of anti‐sunward convection, and cusp particle signatures of southward IMF all persist at least eight hours into recovery phase of the storm.
Self‐consistent electrostatic potential due to trapped plasma in the magnetosphere
Authors: Miller Ronald H. , Khazanov George V.
Published: February 2008

A steady state solution for the self‐consistent electrostatic potential due to a plasma confined in a magnetic flux tube is considered. A steady state distribution function is constructed for the trapped particles from the constants of the motion, in the absence of waves and collisions. Using Liouville's theorem, the particle density along the geomagnetic field is determined and found to depend on the local magnetic field, self‐consistent electric potential, and the equatorial plasma distribution function. A hot anisotropic magnetospheric plasma in steady state is modeled by a bi‐Maxwellian at the equator. The self‐consistent electric potential along the magnetic field is calculated assuming quasineutrality, and the potential drop is found to be approximately equal to the average kinetic energy of the equatorially trapped plasma. The potential is compared with that obtained by Alfvén and Fälthammar [1963].
The evolution of ozone observed by UARS MLS in the 1992 late winter southern polar vortex
Authors: Manney G. L. , Froidevaux L. , Waters J. W. , Elson L. S. , Fishbein E. F. , Zurek R. W. , Harwood R. S. , Lahoz W. A.
Published: February 2008

The evolution of ozone (O3) observed by the Microwave Limb Sounder on board the Upper Atmosphere Research Satellite is described for 14 Aug through 20 Sep 1992, in relation to the polar vortex. The development of an ozone hole is observed in column O3, and a corresponding decrease is seen in O3 mixing ratio in the polar lower stratosphere, consistent with chemical destruction. The observations also suggest that poleward transport associated with episodes of strong planetary wave activity is important in increasing O3 in the mid‐stratosphere.
CLAES observations of CLONO2 and HNO3 in the Antarctic stratosphere, between June 15 and September 17, 1992
Authors: Roche A. E. , Kumer J. B. , Mergenthaler J. L.
Published: February 2008

The Cryogenic Array Etalon Spectrometer (CLAES) on the NASA Upper Atmosphere Research Satellite (UARS) began viewing the stratosphere in October 1991. This paper presents preliminary retrievals of ClONO2 and HNO3 from the CLAES measurements for selected days in June, July, August, and September of 1992 for the southern hemisphere. The data shows that by July 10, lower stratospheric ClONO2 and HNO3 have developed high “collar” regions surrounding the polar vortex, and low values inside the vortex. This general structure is sustained through September 17, although the ClONO2 values inside the vortex increase significantly by this date. The data suggests that substantial sequestration of gaseous HNO3 in polar stratospheric clouds occurs in the early winter Antarctic stratosphere, accompanied by the conversion of ClONO2 to reactive chlorine through heterogeneous processes on the PSCs.
Monitoring changes in mean‐sea‐level to millimeters using GPS
Authors: Ashkenazi V. , Bingley R. M. , Whitmore G. M. , Baker T. F.
Published: February 2008

The fiducial GPS technique is now well established in geodesy and geophysics, for determining horizontal and vertical land movements. In particular, the technique is used in crustal dynamics and in monitoring changes in mean‐sea‐level. The main limiting factor to achieving accuracies of a few millimeters is the reference frame (or datum), as defined by the adopted coordinates of the fiducial stations. This paper summarises a series of tests which have been carried out to assess the quality of alternative global reference frameworks, in order to achieve the highest accuracies for tide gauge heights in the UK.
Source mechanisms for morning auroral features
Authors: Connors Martin , Rostoker Gordon
Published: February 2008

Examination of Viking UV images of the morning auroral oval at times of high activity has shown three distinct types of auroral feature. Moving spots at the equatorward border of the oval are found to be associated with Ps 6 magnetic disturbances observed from the ground. Discrete, periodically spaced, features at high latitude are also observed. A variable but stationary emission feature is seen near the dawn terminator. The discrete features are manifestations of the Kelvin‐Helmholtz instability (KHI) on shear layers created by high speed flow between them, based on quantitative estimates of phase velocity, wave number, and growth rate. The terminator feature may arise from precipitating electrons forming the upward electrical current in part of the large‐scale driven system. This part of the driven system is caused by the conductivity gradient at dawn and has been previously detected by other means.
A numerical method for characterizing the time‐dependent diffusion of radon in a porous material
Authors: Tsai Shih‐Chin , Hsu Chun‐Nan
Published: February 2008

The diffusion coefficient of radioactive radon (Rn) in a porous medium was determined in this study by measuring the time‐dependent diffusion of radon through a thin slab of the material. The diffusion process was required to reach a steady state so as to obtain a good estimate of the diffusion coefficient. A numerical method using the nonlinear least‐squares and Marquardt's method (NLSM) was proposed for characterizing the diffusion coefficient of Rn so as to determine whether the process has reached steady‐state or not. Zeolite 4A was selected as testing porous material. The NLSM method was shown by the results to be able to agree well with the results by the conventional method while the process had already reached steady‐state. The results show that the apparent diffusion coefficient of zeolite 4A of porosity 0.62 is 8.31×10−6m²s−1 from NLSM calculation. The Rn adsorption coefficient for this porous matrix is about 6.9×10−4m³kg−1 derived on the basis of linear adsorption isotherm assumption. The method could be applied toward other porous materials, i.e., soils and building materials that are the primary sources of indoor radon.
Reexamination of the relation between depth of the Antarctic Ozone Hole, and equatorial QBO and SST, 1962–1992
Authors: Angell J. K.
Published: February 2008

The relation between depth of the Antarctic ozone hole, and equatorial QBO and SST, is reexamined for the interval 1962–1992, using Dobson total‐ozone data at the South Pole, Singapore 50 mb zonal wind, and average SST in the El Nino region 12S–2N, 180–90W. During this interval the correlation between October–November values of South Pole total ozone, and south polar 100 mb temperature from radiosondes, is 0.93. In 23 of 27 cases, South Pole springtime (October–November) total ozone decreased from one year to the next when the Singapore 50 mb zonal wind averaged from the east during the intervening 3 seasons and increased when this wind averaged from the west. Owing to the high serial correlation of the wind and total‐ozone data, this distribution is only significant at the 5% level according to the Chi‐square test, but basically supports the conclusions of Garcia and Solomon (1987) and Lait et al. (1989) regarding the relation between equatorial QBO and depth of the ozone hole. The tendency for a deeper ozone hole when equatorial SST warms (El Nino) yields a relation between depth of the Antarctic ozone hole, and equatorial QBO and SST, significant at the 1% level only by the subjective drawing of a smooth line which separates springtime total‐ozone increases and decreases from one year to the next in 24 of 25 cases with 2 cases on the line of separation. The Singapore 50 mb wind has been from the west during the first half of 1993, suggesting a less deep ozone hole in 1993 than in 1992, especially if the current prolonged El Nino finally abates in mid 1993.
The effects of shallow rheological boundaries in the upper mantle on inducing shorter time scales of diapiric flows
Authors: van Keken Peter E. , Yuen David A. , van den Berg Arie P.
Published: February 2008

We have studied the effects of rheological boundaries in the upper mantle on the dynamics of inducing pulsating diapiric plumes. We have compared the effects due to shallower rheological interfaces in the upper mantle on the timescales of the pulsations. Comparing with a basic model with a rheological interface at 670 km depth, we find that timescales between pulsations can be reduced considerably down to a few million years by adding another rheological boundary at 400 km depth. These results suggest that short timescale diapiric flows may be generated from relatively stationary upwellings from the lower mantle because of the presence of rheological boundaries in the shallow upper mantle.
Continental water recycling and H218O concentrations
Authors: Koster Randal D. , de Valpine D. Perry , Jouzel Jean
Published: February 2008

Using a GCM fitted with tracer diagnostics, we examine how continental moisture recycling affects the stable water isotope content of precipitation, focusing on its contribution to the “noise” in the well‐established relationship between temperature and δ18O. On a global basis, for temperatures between −30° and 15°C, continental recycling explains more than a third of the variability in annual δ18O that is not explained by temperature. Recycling appears almost as important as temperature in defining δ18O distributions during northern hemisphere summer.
Processes associated with ocean crustal formation: The Juan De Fuca Ridge
Authors: Johnson H. Paul
Published: February 2008

Recent geophysical, geological and geochemical studies on the Juan de Fuca Ridge have been gathered into a special collection of manuscripts that demonstrate the interdisciplinary nature of the crustal formation and evolutionary processes. On the ridge axis, these new studies include long‐term sea floor and water column measurements that indicate ‘real‐time’ changes due to volcanic activity and related hydrothermal flux, sea floor measurements of seismic activity detecting swarms of earthquakes near the axial zone, and submersible observations of a 2‐km along‐strike spacing of large‐scale hydrothermal fields. Detailed sampling of axial basalts show that, in spite of abundant evidence of ‘excess’ volcanic activity, the Juan de Fuca Ridge is not a traditional hot spot. On a larger scale, geophysical surveys of the ridge flanks show that the upper crust can vary in thickness by a factor of two, that crustal porosity systematically decreases with age, and the topographic forcing is the dominant control of off‐axis hydrothermal circulation. Finally, the Juan de Fuca Ridge has long been a testing ground for innovative survey techniques, and this issue includes reports on the development of acoustic backscatter as a quantitative measure of basement roughness and as an indicator of the presence of lithified sediments overlying zones of fluid upwelling.
Wavelet analysis of a bathymetric profile reveals anomalous crust
Authors: Little Sarah A. , Carter Patricia H. , Smith Deborah K.
Published: February 2008

A 200 km anomalous topographic zone was discovered using wavelet scale analysis in a 1600 km linear bathymetric profile taken northeast of Hawaii. A spectral analysis of the zone shows that the power in wavelengths shorter than 25 km averages 5–10 times lower than the surrounding topography. Conversely, wavelengths longer than 25 km have 2–3 times greater power than nearby topography. Further research reveals that this low‐frequency zone correlates with the eastern flank of a regional bathymetric high which has been described by J. Mammerickx [1981]. Details of the features suggest that this zone is a small, abandoned, slow‐spreading rift overprinted by a regional thermal swell. The magnitude of the feature is smaller than other, known, abandoned spreading centers, making it easy to overlook without the application of the wavelet transform.
Kinetics of the reaction of CH3O2 with ClO at 293 K
Authors: Kenner R. D. , Ryan K. R. , Plumb I. C.
Published: February 2008

The reaction of CH3O2 with ClO has been studied at 293 K using a flow reactor sampled by a mass spectrometer. Under conditions where [ClO] » [CH3O2], the CH3O2 decayed under pseudo‐first‐order conditions giving a rate coefficient of (1.9±0.4)×10−12 cm³ s−1. CH3OCl was detected as a reaction product. The implications of the measurements for the chemistry of the stratosphere are discussed briefly.
Self‐consistent current sheet structures in the quiet‐time magnetotail
Authors: Holland Daniel L. , Chen James
Published: February 2008

The structure of the quiet‐time magnetotail is studied using a test particle simulation. Vlasov equilibria are obtained in the regime where υD = Ey c/Bz is much less than the ion thermal velocity and are self‐consistent in that the current and magnetic field satisfy Ampere’s law. Force balance between the plasma and magnetic field is satisfied everywhere. The global structure of the current sheet is found to be critically dependent on the source distribution function. The pressure tensor is nondiagonal in the current sheet with anisotropic temperature. A kinetic mechanism is proposed whereby changes in the source distribution results in a thinning of the current sheet.
A kinetic description of electron beam ejection from spacecraft
Authors: Khazanov George V. , Neubert Torsten , Gefan Grigorii D. , Trukhan Aleksander A. , Mishin Evgeni V.
Published: February 2008

A model based on the Boltzmann kinetic equation describing electron beam ejection from spacecraft is presented. Results are shown for steady‐state, beam‐atmosphere interaction (BAI) and for beam‐plasma interaction (BPI). The BPI considered is that of elastic scattering of beam electrons with strong, short‐scale Langmuir turbulence. This mechanism has been suggested for prompt echoes of beam electrons observed in sounding rocket experiments. It is shown that the interaction is sufficiently strong to account for observations of back‐scattered electrons at the beam accelerator energy. However, it is clear from observations that particles undergo diffusion in energy at a rate exeeding levels expected for BAI. Inelastic scattering in BPI must therefore also be important.
Mesospheric 12‐hour oscillation near South Pole, Antarctica
Authors: Hernandez G. , Fraser G. J. , Smith R. W.
Published: February 2008

A 12‐hour oscillation in the horizontal motion of the neutral mesosphere near the South Pole has been determined from optical measurements of the Doppler shift of the OH emission in this region of the upper atmosphere. The measurement of this wave's phase progression with longitude shows this wave to be a westward‐traveling zonal wavenumber one mode. The absence of significant oscillation at this periodicity in the simultaneously measured mesospheric temperature is consistent with the zonal wavenumber one determination. Tentative assignment of this oscillation to an inertio‐gravity wave has been made based on these findings. The observation of this 12‐hour periodicity oscillation as a zonal wavenumber one motion precludes its identification as a zonal wavenumber two semidiurnal tide.
Geoid anomalies from Cenozoic subduction in semi‐dynamical flow models including a phase boundary
Authors: Zhang Shuxia , Christensen Ulrich
Published: February 2008

In order to investigate the relationship between the geoid and plate subduction, we develop a 3‐D spherical shell model in which the circulation is driven by both buoyancy forces and an imposed surface velocity, taken from plate reconstruction for the past 65 Ma. To avoid numerical resolution problems, we use an enhanced value of thermal diffusivity, which leads to an overly thick lithosphere. The correct amount of buoyancy is re‐established by using a reduced value of thermal expansion coefficient. First, we calculate the present temperature field in the mantle due to the Cenozoic plate motions for models with and without a phase transition at 660 km depth, which is approximated by a locally modified effective thermal expansion coefficient. In a second step the geoid anomalies are determined subject to a stress‐free upper boundary condition. When the thermodynamic parameters of the boundary at 660 km allow slab penetration into the lower mantle, the medium wavelength (ℓ=4–11) geoid agrees well with the observed geoid if there is a moderate increase of viscosity from the upper to the lower mantle. When the Clapeyron slope is sufficiently negative to prevent slab penetration, the agreement is poor.
The 7 March 1988 North Pacific Intraplate Earthquake
Authors: Padmos L. , VanDecar J. C.
Published: February 2008

A detailed analysis is made of an unusual North Pacific intraplate event that occurred on 7 March 1988 approximately 500 km off the coast of the Japanese island of Hokkaido. It is the largest event recorded in the seismically quiet area by nearly an order of magnitude and has an anomalous mb/Ms ratio (mb=5.8, Ms=5.1). The short‐period response recorded at the Washington Regional Seismograph Network (WRSN) contains strong water‐layer multiples that appear to suggest a source depth on or above the ocean floor. This can be explained, however, as the sampling of a node of the P‐wave radiation pattern. The modeling of short‐period seismograms recorded worldwide gives a focal mechanism with fault planes (340°, 69°, 72°) and (202°, 27°, 129°) (strike, dip, slip) and a source depth of 10 km below sea level. The observed low amplitude first arrival at WRSN and the fact that the signals observed at the other stations are modeled well indicates an almost pure double‐couple source for this strong intraplate event.
Theory of kilometer‐size density waves in the nightside Venus ionosphere
Authors: Huba J. D.
Published: February 2008

Quasi‐sinusoidal density waves were frequently observed during the end of the Pioneer Venus Orbiter (PVO) mission when the orbiter was at low periapsis [Brace, this issue]. These waves occur at altitudes ∼145–155 km and have wavelengths ∼1 km. It is suggested that a radial, ambipolar electric field E0, directed downward, is established in the Venus ionosphere during electron pressure enhancements above ∼160 km. This field generates an electron E × B drift VE; the ions move radially and do not E × B drift because they are unmagnetized (i.e., νin » Ωi). This drift is shown to drive a collisional drift wave instability for sufficiently large values of VE, nominally, VE > υi where υi is the ion thermal velocity. For parameters typical of the nightside Venus ionosphere, this instability generates plasma fluctuations with wavelengths ∼1 km, consistent with observations.
A new interpretation on the origin of enhanced ion acoustic fluctuations in the upper ionosphere
Authors: Forme F. R. E.
Published: February 2008

Enhanced ion acoustic fluctuations have been recently observed by incoherent scatter radars in the upper ionosphere. Here it is suggested that these fluctuations can be due to the Langmuir wave decay L→L’+S. In this process the “pump” Langmuir waves (L) are produced by a beam instability due to streaming soft electrons. Those waves then produce backscattered Langmuir waves (L’) and ion acoustic waves (S). Estimations of the required electron beam energy and flux, as well as the beam number density are given. It is found that satellite and rocket observations support this interpretation.
Static compressibility of magnesite to 20 GPa: Implications for MgCO3 in the lower mantle
Authors: Redfern S. A. T. , Wood B. J. , Henderson C. M. B.
Published: February 2008

The bulk modulus of MgCO3 magnesite has been measured to 20 GPa at room temperature using X‐ray powder diffraction. Since the response to pressure is primarily compression of the MO6 octahedron, magnesite is substantially less compressible than Ca‐carbonates of similar structure type. Using the Birch equation of state, with KT′ of 4.0, we obtain KT of 142 (±9) GPa at room temperature. The full Birch‐Murnaghan equation of state yields KT of 151 (±7) GPa and KT′ of 2.5.

These results, together with other thermodynamic data, have been applied to calculate the stability of magnesite under lower mantle conditions. Assuming lower‐mantle saturation in (Mg,Fe)O, magnesite should be stable to temperatures well in excess of 6000 K at the core‐mantle boundary, i.e. at least up to the solidus of peridotitic or pyroxenitic compositions. This confirms that magnesite is a stable host for carbon in the mantle.
Observation of nitric oxide rovibrational band head emissions in the quiescent airglow during the Cirris‐1A Space Shuttle Experiment
Authors: Smith D. R. , Ahmadjian M.
Published: February 2008

Band head emissions from highly rotationally excited NO (v,J) (J≈90) have been observed in the quiescent atmosphere at tangent heights between approximately 115 and 190 km for both sunlit and nighttime conditions. The data were obtained by the cryogenic CIRRIS‐1A interferometer which was operated on‐board the space shuttle between 28 and 30 April 1991. Up to ten emission features between 2020 and 1744 cm−1 in the earthlimb spectra have been identified as the R‐branch band heads of the NO Δv=1 sequence for the vibrational states v′ = 1 – 10. The presence of these band heads requires a very high degree of rotational excitation corresponding to rotational energy in excess of 1.4 eV. These are the first observations of emissions from highly rotationally excited NO in the quiescent airglow and they parallel the recent discovery of highly excited pure rotational transitions of OH in the airglow for both nighttime and daytime quiescent conditions.
Evolution of large amplitude Alfvén waves in the solar wind with β∼1
Authors: Hada Tohru
Published: February 2008

A new set of equations is obtained which describes evolution of finite amplitude, dispersive, elliptically polarized quasi‐parallel Alfvén waves, when the plasma and the wave amplitude satisfy the condition, |1‐CS2/CA2| < δB/B0, where CA and Cs are the Alfvén and the sound speed, respectively, and δB/B0 is the Alfvén wave amplitude normalized to the background magnetic field. When this condition is satisfied, the sound wave as well as the right‐ and left‐hand polarized Alfvén waves are nearly all degenerated. The solar wind plasma is a typical medium for the obtained set of equations to apply, since the plasma β is high, and the solar wind Alfvén waves have large amplitude. Modulational instability of a circularly polarized parallel Alfvén wave is discussed.