bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of tropospheric trace gases and meteorology in rural Virginia using an unattended monitoring system: Hurricane Hugo (1989), A case study
Authors: Doddridge Bruce G. , Dickerson Russell R. , Holland Joshua Z. , Cooper James N. , Wardell R. Glenn , Poulida Olga , Watkins James G.
Published: February 2008

Tropospheric trace gases such as ozone and reactive nitrogen compounds exert a strong influence on global climate, but observations of these species are limited by the necessity of having a trained observer on site to monitor instruments. A technique using modern communications technology has been developed to transport and review data collected at a remote site. The site was equipped with a PAM II station and satellite data link so that raw, real‐time data and equipment status were available for inspection readily on a workstation at the University of Maryland campus through a combination of wide and local area networks. CO, NO, NOy, O3, UV radiative flux, and meteorological parameters were measured in rural Virginia for a full year. The cleanest air observed over the year was associated with the passage of Hurricane Hugo over the mid‐Atlantic region on September 22, 1989. Hourly average data for concentrations of CO, NOy, and O3 observed during this particular case study were as low as 90 ppbv, 570 pptv, and 11 ppbv, respectively. Within this period, daytime NO was highly variable, ranging between the detection limit of the instrument, ∼ 20 pptv, and 2.4 ppbv. These concentrations are well below the hourly concentration average at this site for these species during September 1989. Equivalent potential temperature, θe, in conjunction with the trace gas concentrations and geostrophic back‐trajectories, illustrates how this hurricane influenced air parcel history; observed concentrations of CO and NOy increased with the time the air parcel spent over land. Observations at this site were consistent with current hurricane models based on mean soundings and aircraft flights. Hurricanes over land also appear to redistribute air vertically throughout the troposphere, creating the potential for substantial post‐storm tropospheric column O3 increase.
The Ozone and Aerosol Fine Structure experiment: Observing the fine structure of ozone and aerosol distribution in the atmosphere from the Salyut 7 Orbiter: 1. Introduction and the occultation experiment
Authors: Grechko G. M. , Elansky N. F. , Plotkin M. E. , Postylyakov O. V.
Published: February 2008

The Ozone and Aerosol Fine Structure (OZAFS) experiment, conducted on the Soviet Salyut 7 orbiting station in September 1985, was intended to study ozone and aerosol fine structure in the atmosphere. The experimental technique was to combine the observations of the distribution of species from the attenuation of radiation on tangent routes with photographic observations of the Earth's twilight limb. The photographic method used for measuring the vertical distribution of attenuating atmospheric components from spacecraft does not call for sophisticated instrumentation. An absorption method was used for the experiment, and a complete mathematical model of this method was constructed. The model associated directly measured values with atmospheric characteristics of interest. An algorithm of the measured data processing was used to obtain minimal errors of the ozone and aerosol retrieval on the basis of the complete model of the experiment, which contains measuring errors. This method makes it possible to reconstruct ozone profiles and aerosol extinction profiles in the stratosphere with low errors (5 to 10%),.and high spatial resolution (about 1 km).
An energy balance climate model with hydrological cycle: 1. Model description and sensitivity to internal parameters
Authors: Jentsch Volker
Published: February 2008

A thermodynamical model designed to illustrate the effect of a hydrological cycle on climate sensitivity is presented. The model contains three climatic variables: two temperatures referring to an idealized atmosphere and ocean, respectively, and atmospheric humidity. The independent variables are time and latitude. Atmosphere and ocean are coupled by radiation and convection at their interface. Some structure of the atmospheric circulation is retained by differentiating between the dynamics of a low latitude zone (0° ‐ ϕH) and that of a high latitude zone (ϕH‐90°), where ϕH ≈ 30° is the intersection of meridional temperature gradient and critical gradient for baroclinic instability. The atmospheric transport is split into an advective and a diffusive part, while the oceanic transport is approximated by pure diffusion. The coefficients associated with horizontal and vertical motion are modelled in terms of temperature gradients. The predicted water vapor gives rise to precipitation and clouds and influences (via cloud cover and greenhouse effect) the radiation balance of the system. The model is integrated for annual mean conditions until an asymptotic equilibrium is reached. The free (internal) parameters of the system are determined by optimization methods so that simulated temperature, heat flux and hydrological cycle are in close agreement with observations. The sensitivity of the model is governed by radiation parameters. Of these, the cloud albedo is the most sensitive quantity. By contrast, the model is relatively little affected by parameters associated with horizontal and vertical transport of heat.
Measurements of carbon compounds in the stratosphere using a pressure modulator radiometer
Authors: Turner D. , Drummond J. R.
Published: February 2008

Simultaneous profiles of methane, carbon monoxide, and ozone were measured using a balloon‐borne remote sensor in August 1985. The instrument, which uses pressure‐modulated radiometers, flew over the Canadian prairies and collected data for night, sunrise, early and late morning soundings in the altitude range 20–45 km. The data processing is discussed starting from the raw radiances and finishing with the retrieval of the concentration profiles. The programs used for calculating the theoretical radiances and the retrieval process are described in detail. The factors which need to be considered in the design of future experiments, particularly with regard to the filling pressure of the modulator cells are also addressed. The methane profiles show volume mixing ratios between ≈0.7×10−6 v/v at 20 km and ≈0.8×10−6 at 45 km. The ozone profiles show mixing ratios between ≈5×10−6 v/v at 20 km and ≈7×10−6 at 45 km and the carbon monoxide profiles between ≈0.5×10−8 v/v at 20 km and ≈2×10−8 at 45 km. These profile results are compared to data sets from other authors, and the similarities and differences are briefly discussed.
Aerosol chemical components in Alaska air masses: 1. Aged pollution
Authors: Shaw Glenn E.
Published: February 2008

A 4‐year Alaska chemical data set of aerosols or “dust” in the air clearly reveals a mixture of distinct aerosol components with different and interesting chemical composition, one or two being ascribed to pollution imported to Alaska by winds all the way from other continents. Of particular note is a strong chemical contrast between what we imagine to be highly scavenged, orographically lifted, northern Pacific air (Pacific marine air mass) and stagnant Arctic air (polar air mass), the latter containing seasonal average concentrations of between 2–4 times the concentration of the former, at least for pollution markers noncrustal vanadium, noncrustal manganese, arsenic, selenium, bromine, and antimony. The findings concur our old discovery that Arctic air is persistently polluted (Arctic haze), but Pacific air is relatively clean, in spite of the fact that Alaska is downwind of major pollution sources in the Orient. This is remarkable. In this the first of a two‐part paper, we concentrate on the pollution component found primarily during incursion of Arctic polar air. Two major occurrences of visual haze with optical depths of approximately 0.2 and elevated aerosol concentration lasting about a month (spring 1985 and 1986) were affiliated with strong incoming transport of polar air, temperatures ranging from 10° to 20°C below normal (polar air) and air trajectory hindcasts leading back to industrial pollution sources in Eurasia. These long‐range transport pollution events brought metal‐rich aerosol of removal‐resistant submicron particles. The size, chemistry, and meteorology all strongly suggest the presence of a well‐aged (10–100 day) polluted air mass. An important implication is that in spring a large fraction of the Arctic polar air mass becomes charged with by‐products of industrial pollution. In this multiyear chemical data set one finds a notable summer‐winter contrast, changing by factors of 2 to 4 for pollution markers As, Se, Sb, and noncrustal manganese (NcMn) with the minima occurring in the summer months and the maxima in March and April. There is also a twofold‐threefold decrease in pollution markers between the interior or geographic center of Alaska and Barrow in Arctic Alaska, a gradient, completely in accord with the picture of a generally polluted Arctic air mass system about the size of Africa in area.
An unusual display of noctilucent clouds
Authors: Zalcik Mark S.
Published: February 2008

On the morning of July 1, 1990, an intense display of noctilucent clouds as seen from Namao, Alberta, completely disappeared in 30 min. Observations of the clouds from Slave Lake, Alberta, indicate that the display lasted only slightly longer from that site. The noctilucent clouds' rapid degeneration may have been due to induced heating of their formation zone, perhaps by a coincident aurora.
A numerical simulation of the aerosol scavenging rate by simple ice crystals
Authors: Zhang Renyi , Pitter Richard L.
Published: February 2008

Two theoretical models are presented which allow computing the efficiency with which aerosol particles are collected by simple ice crystal plates. The effect of a possible internal electric charge distribution in ice crystals on aerosol scavenging is investigated. It is shown that the capture efficiency of an ice crystal is considerably affected by such an internal charge distribution in the aerosol size range 0.05 ≤ r ≤ 1.0 μm. The present theoretical results are found to agree satisfactorily with field observations presently available.
Implications of C2H photochemistry on the modeling of C2 distributions in comets
Authors: Jackson William M. , Bao Yihan , Urdahl Randall S.
Published: February 2008

Laboratory studies of the secondary photolysis of the C2H radical are summarized and used to explain some discrepancies between models of C2 emission in comets. These studies show that several states of the C2 radicals produced in the photolysis of C2H2 at 193 nm have bimodal rotational distributions when plotted as a Boltzmann diagram. They also establish that the C2 radicals are formed with varying degrees of vibrational excitation, so that if they are formed in a similar manner in comets, the C2 radicals must start out with this initial vibrational excitation.
Collisional cooling as an environment for planetary research
Authors: Goyette Thomas M. , De Lucia Frank C. , Willey Daniel R.
Published: February 2008

A new experimental technique which provides a laboratory environment much like that of the outer planets is described. More specifically this technique, collisional cooling, allows the study of the collisional properties of molecular species at temperatures which in ordinary spectroscopic cells would result in vanishingly small vapor pressures due to condensation. In this paper the basic theory of collisions is put forth, the experimental techniques described, and the results of pressure broadening studies for a number of species described.
Sources of error in planetary photoclinometry
Authors: Jankowski David G. , Squyres Steven W.
Published: February 2008

Photoclinometry has become a popular technique for the extraction of topography from digital images of planetary surfaces. The technique, however, is subject to a number of error sources that can degrade results significantly. We present here a quantitative analysis of error sources in one‐dimensional planetary photoclinometry. The technique is affected by at least seven error sources, which can be broken down into three categories: those arising from (1) the spacecraft image, (2) the planetary body, and (3) the scan line orientation. Spacecraft image error sources include noise, background offset, and quantization. Errors deriving from the planetary body include those induced by variations in photometric properties, such as albedo, by incorrectly compensated atmospheric effects, and by an incorrectly determined photometric function. Finally, errors will result for scan lines which do not lie perpendicular to topographic strike. We calculate slope errors for each of these sources, using the examples of Voyager imaging of Ganymede and Viking orbiter imaging of Mars. Slope errors are investigated for a variety of viewing and lighting geometries, slope angles, and slope orientations. The results can be broken down into nonsystematic and systematic errors. Nonsystematic errors are introduced by image noise and quantization and affect the slope calculation for each picture element independently. Other error sources are systematic; these errors are more insidious, since they may retain the general appearance of the topography while approximately scaling all relief by a multiplicative constant. We present derivations that allow the calculation of photoclinometric slope errors for any photometric function and also briefly discuss the implications of our results for two‐dimensional photoclinometric techniques.
Polarization of the impulsive signals observed in the nightside ionosphere of Venus
Authors: Strangeway R. J.
Published: February 2008

The impulsive plasma wave bursts detected by the Pioneer Venus Orbiter electric field detector in the nightside ionosphere of Venus have been attributed to atmospheric lightning. However, it has also been argued that the wave bursts are generated locally by plasma instabilities. The waves associated with local instabilities are most probably electrostatic in nature, while lightning‐generated waves should be whistler mode waves, at least at the lowest frequencies. It may be possible to identify the wave modes through analysis of the wave polarization. We show that for typical ionospheric parameters the whistler mode wave electric field should be polarized predominantly perpendicular to the ambient magnetic field. However, the signals are often impulsive in nature, with durations much less than the spacecraft spin period, and an individual wave event is likely to be aliased since the event may occur at arbitrary spin phase and arbitrary intensity. Statistical analysis of the wave polarization using data acquired in the third nightside periapsis season shows that the 100‐Hz data suffer from interference, which may be due to the interaction of the spacecraft with the ambient plasma. The interference is removed through visual inspection of the data, and we show that the 100‐Hz waves are polarized perpendicular to the ambient magnetic field provided we restrict the data to those intervals in which the magnetic field is sufficiently far from horizontal to allow vertical propagation within the whistler mode resonance cone. The 100‐Hz waves detected outside of the resonance cone are polarized parallel to the magnetic field, as are the waves at higher frequency. The waves consequently fall into two classes: whistler mode waves which are most likely due to atmospheric lightning, since the low phase speed of the whistler mode argues against an in situ instability, and a mode that is polarized parallel to the ambient field. This latter mode may be analogous to the anomalous parallel polarized wave fields detected in the terrestrial ionosphere above thunderstorms.
The Sudbury structure: Controversial or misunderstood?
Authors: Grieve Richard A. F. , Stöffler Dieter , Deutsch Alex
Published: February 2008

The origins of the Sudbury Structure and associated Igneous Complex have been controversial. Most models call for a major impact event followed by impact‐induced igneous activity, although totally igneous models are still being proposed. Much of the controversy is due, in our opinion, to a misunderstanding of the size of the original Sudbury Structure. By analogy with other terrestrial impact structures, the spatial distribution of shock features and Huronian cover rocks at the Sudbury Structure suggest that the transient cavity was ∼100 km in diameter, which places the original final structural rim diameter in the range of 150–200 km. Theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in ∼104 km3 of impact melt, more than sufficient to produce a melt body the size of the Igneous Complex (present volume 4–8 × 103 km3). For the Igneous Complex to be an impact melt sheet it must have a composition similar to that of the target rocks. Evidence for this has been presented previously for Sr and Nd isotopic data, which suggest a crustal origin. Here, we also present new evidence from least squares mixing models that the average composition of the Igneous Complex corresponds to a mix of Archean granite‐greenstone terrain, with possibly a small component of Huronian cover rocks. This is a geologically reasonable mix, based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size. The Igneous Complex is differentiated, which is not a characteristic of previously studied terrestrial impact melt sheets. This can be ascribed, however, to its great thickness and slower cooling. That large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted. If this working hypothesis is accepted, namely, that both the Sudbury Structure and the Igneous Complex are impact in origin, then previous hybrid impact‐igneous hypotheses can be discarded and the Sudbury Structure can be studied specifically for the constraints it provides to large‐scale cratering and the formation of basin‐sized (multiring?) impact structures.
Shoaling of the Eastern Mediterranean Pycnocline due to reduction of excess evaporation: Implications for sapropel formation
Authors: Rohling Eelco J.
Published: February 2008

A simple two‐layered model is applied to assess the relation between variations in the depth of the permanent pycnocline and changes in the excess of evaporation over freshwater input, in the eastern Mediterranean. This study is performed to estimate the magnitude of the excess evaporation at times of sapropel formation in the eastern Mediterranean. Pycnocline shoaling, from a depth below the euphotic layer to a depth within that layer at times of sapropel formation, has been inferred from the planktonic foraminiferal record by Rohling and Gieskes (1989). The model suggests that a decrease in the eastern Mediterranean excess evaporation, defined as evaporation minus total freshwater input, by about 8.5 × 1011 m³ yr−1 would suffice to invoke shoaling of the pycnocline to a depth within the euphotic layer. A consideration of the effects exerted by concomitant changes in the thermal balance suggests that the necessary decrease of excess evaporation may even be smaller than the above estimate.
On three‐dimensional propagation and dispersion of wave packets described by spatial moments
Authors: Dong B. , Yeh K. C.
Published: February 2008

In this paper we study the three‐dimensional propagation of a vector wave packet in a lossless, homogeneous but anisotropic medium. By using the superposition principle and Fourier transform theory a general formulation of wave packet propagation theory is developed. We prove that the square magnitude of the complex amplitude of the wave packet over the whole space integrates to a constant. The conservation of this integral merely reflects the lossless nature of the medium. This integral can be considered as the zeroth spatial moment. Upon this foundation the first and second spatial moments are introduced. The first moment determines the position vector of the centroid of a wave packet. It is a linear function of time, showing the motion of the centroid at a spectrum weighted average of the gradient of frequency in wave number space. Thus the concept of group velocity is extended to the wide banded wave packets. The second moment of the wave packet describes the property of dispersion. It reflects the anisotropic nature of the propagating medium and reveals the fact that the length of the wave packet expands with time in the form of time squared.
Calculation and verification of antenna temperature for Earth‐based reflector antennas
Authors: Lambert Kevin M. , Rudduck Roger C.
Published: February 2008

This paper describes an application of the classical convolution integral for the calculation of antenna temperature to Earth‐based microwave antennas. The Ohio State University‐Reflector Antenna Code has been implemented to provide the radiation pattern of antennas in the calculation. Use of the code allows the full volumetric pattern of the antenna, including all sidelobes, backlobes, and cross‐polarized response, to be included in the calculation. Additionally, the contribution to the antenna temperature from various regions of the pattern can be calculated separately and analyzed. Examples of the calculations are given along with a description of an experiment which was performed to verify the accuracy of the technique.
On some problems of the theory of radio wave propagation in a randomly inhomogeneous ionosphere
Authors: Tinin M. V. , Afanasyev N. T. , Mikheev S. M. , Pobedina A. P. , Fridman O. V.
Published: February 2008

In considering HF propagation in a random inhomogeneous ionosphere it is necessary to take into account regular and random caustics. Regular caustics connected with regular refraction of radio waves in the ionosphere form a skip zone and determine the maximum usable frequency (MUF) and the maximum of the oblique incidence backscatter sounding (OBS) signal. Random fluctuations of ionospheric radio rays “wash out” field enhancement in the vicinity of MUF and the maximum OBS signal. The presence of random caustics results in strong intensity fluctuations of ionospheric radio waves. The above mentioned problems are considered by the interference integral method. A scintillation index formula for strong fluctuations of oblique ionospheric radio waves is obtained. Average intensity and average pulse signal which form in the vicinity of MUF are investigated. The peculiarities of oblique multihop radio wave propagation, taking into account random ionospheric inhomogeneities, terrestrial surface roughness, and caustics focusing in skip distance are discussed.
On the growth of normal faults and the existence of flats and ramps along the El Asnam active fold and thrust system
Authors: Avouac J. P. , Meyer B. , Tapponnier P.
Published: February 2008

The combination of detailed topographic leveling on the southwest segment of the El Asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps. The fault appears to be growing along strike toward the southwest end, where the main shock initiated in 1980. From a depth of about 10 km, the main thrust appears to ramp to the basement‐Cenozoic cover interface on a plane striking N40°E and dipping 50°–55° to the northwest. Along the southwest segment where folding has not yet developed, the thrust continues steeply through the Cenozoic cover to the near surface where it flattens, causing normal faulting. Along the central and northeast segments, which display a more evolved fold structure, the deep thrust probably flattens at a depth of 5–6 km, into a decollement along the Cenozoic‐Jurassic interface before ramping to the surface. The Sara El Marouf and Kef El Mes anticlines have thus formed as fault propagation folds. Normal faults at Beni Rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement. The greater separation (∼7 km) between the normal faults at Beni Rached and the thrust where it crosses Oued Cheliff than along the southwest segment (∼1 km) reflects the greater depth of the ramp to flat bend. We infer that the September 9, 1954, earthquake activated only the central deep segment of the main thrust together with the Beni Rached normal faults, while that of October 10, 1980, activated the whole system of flat decollements, ramp thrusts and compatibility normal faults. Further complexities of the faulting in map view are related to changes of strike of the thrust (in particular north of Oued Cheliff).
Arctic haze: Patterns and relationships to regional signatures of trace gases
Authors: Khalil M. A. K. , Rasmussen R. A.
Published: February 2008

We took measurements of up to 30 gases in Arctic haze and in clean Arctic air. These data were obtained from some 500 flask samples taken on three expeditions of the Arctic Gas and Aerosol Sampling Program (AGASP 1, 2, and 3) during the spring of 1983, 1986, and 1989. Concentrations of many gases are significantly higher in the haze layers compared to outside the haze. To look for the possible origins of the haze, we used cluster analysis to derive regional signatures of trace gases at ground‐based sites in middle and high northern latitudes. Comparison of the regional signatures with concentrations observed in Arctic haze suggest that there are no significant contributions from North America but possible influences from Russia and eastern Europe. These conclusions complement results derived from the analysis of the Arctic aerosol chemistry. It is possible, however, that Arctic haze originates from the military, industrial, and mining activities within the Arctic circle, particularly from the Russian Koala peninsula.
The transverse coherence function at NORSAR over a wide range of separations
Authors: Flatté Stanley M. , Xie Xiao‐Bi
Published: February 2008

We have used data from the 80‐km‐diameter NORSAR array and the 3‐km‐diameter NORESS array to determine the Transverse Coherence Function (TCF) of arrival time for spatial separations ranging from a few hundred meters to 80 km. To accomplish our objective, we have devised a method to combine data from arrays of different aperture. The procedure is based on information about rms fluctuations and rms tilts on each array. Synthetic fluctuation fields with different statistical properties were generated to test the combination method. Our results for the TCF from NORSAR and NORESS are in reasonable agreement with the predictions of the Flatté‐Wu model of heterogeneities under NORSAR.
Search for lower mantle high‐velocity zones beneath the deepest Kuril and Mariana earthquakes
Authors: Okano Kenta , Suetsugu Daisuke
Published: February 2008

We perform travel time analyses for the Kuril and the Mariana subduction zones to investigate whether a lower mantle high‐velocity zone exists immediately beneath the deepest earthquakes in these regions. We use P and PKIKP wave arrival time data read directly and accurately from WWSSN short‐period vertical component records and corrected for the effect of lateral heterogeneity far from the source regions using a differential residual sphere technique. The corrected residuals for the deep Kuril events show that a high velocity zone extends in the down‐dip direction of the Kuril slab in the lower mantle. On the other hand, the residuals for the deep Mariana events show no evidence for a high‐velocity zone in the down‐dip direction beneath the deepest earthquakes. A reasonable interpretation of these results is that the Kuril slab penetrates into the lower mantle (h≥670 km) but that the Mariana slab does not extend vertically into the lower mantle.
Mesospheric oh airglow temperature fluctuations: A spectral analysis
Authors: Dewan E. M. , Pendleton W. , Grossbard N. , Espy P.
Published: February 2008

A field campaign under Project MAPSTAR was conducted in Colorado during May‐July 1988. As part of this effort ground based measurements of OH airglow rotational temperatures at 85 km were made by means of an infrared Fourier spectrometer (IRFWI of USU). These measurements employed a least squares spectral fitting technique involving the 3–1 Meinel band. These data and their estimated PSD's will be presented. The latter will be interpreted by means of the relations between gravity wave temperature fluctuations and vertical displacement fluctuations given by Makhlouf et al (1990).

The results will be compared with the predictions of the gravity wave model of Dewan (1990, 1991) and shown to be in reasonable agreement thus lending further support to the local wave‐cascade hypothesis.
Experiments on convection in rotating hemispherical shells: Transition to a quasi‐periodic state
Authors: Cordero S. , Busse F. H.
Published: February 2008

Convection driven by thermal buoyancy in the presence of the Coriolis force occurs in planetary atmospheres and interiors. In order to model convection subject to nearly spherically symmetric distributions of gravity and temperature, a hemisphere has been constructed which can be rotated about its axis of symmetry. The angular velocity is selected such that the paraboloidal surfaces of equal potential match closely surfaces of constant radius within the hemispherical fluid shell. While the baroclinicity of the fluid state is still noticeable, quantitative measurements can be obtained which can be compared with the theoretical calculations for the spherically symmetric case. The drift of the convection columns has been measured and a transition from the singly periodic state of convection to a modulated state has been visualized and determined quantitatively.
‘Skidding’ of the CRRES G‐9 barium release
Authors: Huba J. D. , Mitchell H. G. , Fedder J. A. , Bernhardt P. A.
Published: February 2008

Experimental data and a simulation study of the CRRES G‐9 ionospheric barium release are presented. Comparison of optical images of the release at times t ≈ 0 and 21 sec indicate that the cloud ‘skidded’ ∼ 9 km. The simulation study is based upon a 2D electrostatic code which incorporates time‐dependent coupling to the background plasma. We find that the densest portion of the barium ion cloud ‘skids’ ∼ 15 km within the first 3 sec following the release, consistent with analyses of the optical data.
Line‐tying effects on the Kelvin‐Helmholttz instability
Authors: Miura Akira , Kan J. R.
Published: February 2008

A three‐dimensional linear analysis of the line‐tied Kelvin‐Helmholtz (K‐H) instability is carried out. The line‐tying by the conducting ionospheres has a stabilizing influence on all unstable modes, but the ionospheric stabilization of the instability can be insignificant when the eigenmode of the flow perturbation has nodes at the ionospheric boundaries.
The paleomagnetic record of Uppermost Permian, Lower Triassic rocks from the South China Block
Authors: Enkin R. J. , Courtillot V. , Leloup Ph. , Yang Z. , Xing L. , Zhang J. , Zhuang Z.
Published: February 2008

In order to constrain better the paleogeography of the blocks that now make up China, we collected paleomagnetic samples from Uppermost Permian to Middle Triassic limestones from two localities in the Sichuan Basin (South China Block). A low inclination component which passes both the fold test and the reversal test was found in five sites (D=46.1°, I=11.9°, k=83.6, α95=8.7°). We review corresponding remanences found in other studies of Permo‐Triassic rocks from the Sichuan Basin, and show that the component is probably characteristic of the Lower Triassic. We then review paleomagnetic results from the Uppermost Permian Emeishan Basalt. Despite small local rotations, the difference between the Emeishan Basalts and the Sichuan Basin poles is interpreted to be the result of motion of the whole South China Block around the time of the Permo‐Triassic boundary rather than of strain within the block.
Background velocity inversion with a genetic algorithm
Authors: Jin Side , Madariaga Raul
Published: February 2008

We propose a method for the non‐linear inversion of the velocity field from reflection profiles. The inverse problem is separated into a linear and a nonlinear domain. Linearized inversion is applied to the retrieval of the short wavelength features of the velocity or impedance field. This problem has a huge number of degrees of freedom but it can be solved by an efficient asymptotic migration‐inversion method. The low frequency part of the velocity field — the background — is inverted using a non‐linear genetic algorithm applied to an objective functional defined in migrated data space. Computer time is significantly reduced using this objective function instead of straightforward waveform fitting. We apply our method to the inversion of a 1‐D background velocity model from a reflexion profile of the North Sea. For this problem, we found that the genetic algorithm is more reliable and efficient than other velocity analysis methods.
A self‐consistent model for the particles and fields upstream of an outgassing comet: 2. A time‐dependent description
Authors: Flammer K. , Birmingham T. E. , Mendis D. A. , Northrop T. G.
Published: February 2008

In a previous paper [Flammer et al., 1991], we determined the global variation of the magnetic field and solar wind flow parameters in the unshocked region upstream of an outgassing comet using a kinetic treatment for the cometary ions. Two different assumptions were made concerning the cometary ion distribution function: the pickup cometary ions formed either a velocity space gyrotropic ring distribution or a velocity space isotropic shell distribution in the solar wind frame of reference. In the present paper we consider the general case wherein the newly picked up ions are elastically pitch angle scattered from the initial ring distribution to a shell with some characteristic time scale τ. Using theoretically determined parameters which reflect the conditions expected at comet Kopff (a typical short‐period comet and a possible target for the CRAF/Cassini mission) for various heliocentric distances, we determine how the pitch angle scattering rate affects the global morphology.
Observations of the effects of ionospheric heating on the amplitude of low‐power diagnostic radio waves at Arecibo
Authors: Stocker A. J. , Robinson T. R. , Jones T. B.
Published: February 2008

The effects of ionospheric heating on low‐power diagnostic radio waves at Arecibo are reported. During O mode heating it was found that the signal strengths of the diagnostic waves were reduced by up to approximately 7 dB. The diagnostic signals are only significantly attenuated during heating at full power (effective radiated power of 80 MW). During X mode heating, no amplitude effects could be detected. The maximum attenuation of the diagnostic signals measured at Arecibo is lower than those typically observed at Tromsø, which is consistent with the predictions of theory. These results are discussed in the context of theoretical calculations of the anomalous absorption due to mode coupling caused by small‐scale field‐aligned irregularities. From observations of the effects of heating on the amplitudes of several low‐power diagnostics, the length of these irregularities along the geomagnetic field is estimated.
Energy distribution of energetic O+ precipitation into the atmosphere
Authors: Ishimoto M. , Romick G. J. , Meng C. ‐I.
Published: February 2008

Measurements of ring current ion densities by the Active Magnetospheric Particle Tracer Explorers CCE satellite suggest that a large flux of energetic (tens of keV) O+ precipitates in the mid‐latitude atmosphere during major geomagnetic storms. The mass spectrometer (>30 keV) on board the NOAA 6 satellite measured an ion flux of 30 ergs cm−2 s−1 at 52° invariant latitude during a very large geomagnetic storm. To calculate atmospheric response to precipitation of the energetic O+ fluxes, we have revised an O+ transport model to include energies up to 200 keV. The model's sensitivity to the estimated cross sections and model atmospheres for various monoenergetic O+ fluxes are presented in this paper. Calculation of the atmospheric response to O+ precipitation shows that (1) most of the incident energy is immediately transformed into atmospheric heating, (2) the total number of escape particles is smaller than the total number of incident particles, in contrast to the results of previous models, and (3) the peak heating and ionization altitudes vary from 104 to 300 km depending on the incident energy. The results are most sensitive to the estimated differential scattering cross sections at large scattering angles. The use of forward scattering cross sections at both extremes of the possible range results in very different energy allocations and altitudes of peak ionization and heating (a difference of as much as 80 km). The MSIS‐86 model atmosphere with extreme parametric values caused little change in the energy allocation, but the large variation in the model atomic oxygen density (F10.7 index = 70 and 210) alters the peak heating and ionization altitude for low‐energy incident O+ (a few keV) by 50 km.
The complete UV spectrum of SO2 by electron impact, 2, The middle ultraviolet spectrum
Authors: Ajello Joseph M. , James Geoffrey K. , Kanik Isik
Published: February 2008

We have measured the middle ultraviolet (MUV) electron impact induced fluorescence spectrum of SO2 from 200 to 430 nm in a crossed beam experiment. The spectrum is dominated by two features at the experimental resolution of 0.5 nm. These two features are referred to as MUV1 and MUV2. MUV1 is the SO(A3∏ → X3 ∑‐) band system extending from 240 to 265 nm produced by dissociative excitation. MUV2 is a blend of the
molecular band systems in the range 264‐430 nm. In addition, the excitation function measurements of MUV2 indicate that low‐energy electrons effectively prepare SO2 in one or more electronically excited triplet states that involve the SO2 (ā(3B1)) state by direct excitation and/or cascading. A candidate triplet band system for this emission process is the
electronic transition. This emission process is the largest contributor to the MUV2 emission cross section at low electron impact energy. The peak cross section for MUV1 occurs at 20 eV with a value of 25.0 ± 5.5 × 10‐19 cm2. The peak cross section for MUV2 arises at 9 eV with a value of 368 ± 81 × 10‐19 cm2. The laboratory measurements of the excitation functions of both MUV features were made from 0 to 1 keV. The emission cross sections are an important part of the total inelastic cross section of SO2 needed in modeling the Io atmosphere. The laboratory results give a plausible explanation of the Io auroral hot spots observed by Voyager 2.
The complete UV spectrum of SO2 by electron impact, 1, The vacuum ultraviolet Spectrum
Authors: Ajello Joseph M. , James Geoffrey K. , Kanik Isik , Franklin Brian O.
Published: February 2008

We have measured the vacuum ultraviolet (VUV) emission cross sections of SO2 from 40 to 200 nm in the laboratory in a crossed beam experiment. The wavelength range comprised the extreme ultraviolet (EUV) spectrum, from 40 to 120 nm, and the far ultraviolet (FUV) spectrum, from 120 to 200 nm. The EUV and FUV emission spectra induced by electron impact consist of atomic multiplets of S I, II, and III and O I, II, and III. The studies included the measurement of excitation functions of the strongest multiplets from 0 to 1 keV impact energy and the identification of dissociation processes from the analysis of the threshold excitation function. The O I (98.9 nm) resonance multiplet (g3 P‐3D) is the strongest EUV feature from electron impact induced fluorescence of SO2 with a peak cross section of 7.82 ± 1.59 × 10‐19 cm2 at 125 eV electron impact energy. The O I (130.4 nm) multiplet (g3P‐3S) resonance transition is the strongest feature in the FUV, with a peak cross section of 1.98 ± 0.44 × 10‐18 cm2 at 90 eV. The strongest feature of S I in the VUV is the S I (147.9 nm) multiplet (g3 P‐3D) resonance transition, with a peak cross section of 1.52 ± 0.33 × 10‐18 cm2 at 90 eV. Dissociation‐excitation cross sections of SO2 are important contributors to the total inelastic cross section of SO2 gas interacting with electrons. These cross sections are used in neutral cloud theory models of the Io atmosphere. The laboratory spectrum at low energy (~22 eV) matches a recently obtained IUE FUV spectrum of Io. The comparison represents evidence of a thin or intermediate atmosphere of SO2 that is directly impacted by the plasma torus. The existence of an atmosphere on Io embedded in the corotating torus plasma is an important remote sensing target for the Hubble Space Telescope, Goddard High Resolution Spectrograph and Faint Object Spectrograph, and Galileo EUV and FUV spectrometers, among other present and planned VUV studies of the Jovian system.
Comparison of dayside current layers in Venus' Ionosphere and Earth's equatorial electrojet
Authors: Cole Keith D.
Published: February 2008

The major physical aspects of the equatorial electrojet of Earth and the dayside ionospheric current layers of Venus are compared, viz., the electric current intensity and total current, roles of electric field, pressure and gravity, diffusion time scales, and the Bemouille effect. The largest potential differences, of the order of 10 volts, horizontally across the dayside ionosphere of Venus, have important implications for possible dynamo action in the Venus ionosphere and the application of an electric field from the lower atmosphere or from the solar wind. An upper limit to the horizontal scale of vertical magnetic fields in the Venus ionosphere is estimated thereby for the first time. New upper limits on the velocity in, and thickness of, a possible S layer at Venus (Cloutier et al., 1987) are presented. If an S layer exists, it is only for extreme conditions of the solar wind. A mechanism for formation of magnetic ropes in the Venus ionosphere is also proposed.
Propagation and amplification of auroral kilometric radiation in finite width auroral cavities
Authors: Gaelzer R. , Ziebell L. F. , Schneider R. S.
Published: February 2008

We investigate amplification of the auroral kilometric radiation over the geomagnetic poles. The physical parameters needed for the calculation are obtained from a particular model that approximately reproduces the conditions in the auroral zone, taking into account density gradients perpendicular to the geomagnetic field and also the parallel magnetic field gradient. The components of the dielectric tensor are calculated in the locally homogeneous plasma approximation, and the dispersion relation is exactly solved with all harmonics and powers of the Larmor radius needed for the convergency of the solution. We also make a ray tracing study in the geometrical optics approximation, using the method of Poeverlein. The ray tracing study shows that the spatial scale of inhomogeneity, perpendicular to the magnetic field, is a very important factor in the amplification and that the distance to obtain a given amplification can be substantially reduced when the density gradient is increased.
Substorm‐associated radar auroral surges
Authors: Freeman M. P. , Southwood D. J. , Lester M. , Yeoman T. K. , Reeves G. D.
Published: February 2008

We report a recurrent convection signature observed in the E region ionosphere within ∼2 hours of the dusk meridian by the SABRE radar facility. In a typical event, the irregularity drift speed in the SABRE field of view is seen to increase from about 300 m s−1 to of the order of 1 km s−1 in the space of about 10 min. The speed subsequently remains at the enhanced level for 10 min or longer before declining as rapidly as its onset. The total event duration ranges between 30 min and 1 hour. As the irregularity drift speed increases the direction of the drift velocity changes, rotating poleward. At the same time, the radar backscatter power decreases. The onset of the drift speed enhancement crosses the SABRE field of view as a front moving from east to west. Detailed study of individual events indicates that the events are associated with increases in the |AL| index and with the injection of energetic particles into geosynchronous orbit. We thus suggest that the events are part of the magnetospheric response to the onset of a geomagnetic substorm. However, while each event appears to be associated with a substorm onset, not every substorm onset is associated with an event, at least not at SABRE. We estimate the speed at which the substorm‐initiated ionospheric flow enhancement moves from the nightside to be 1–4 km s−1, a figure that is consistent with the rate at which the drift velocity front crosses the SABRE field of view. Although the front is associated with a rotation in the drift velocity, we see little evidence of strong vertical vorticity as the front passes. However, shears in the flow do develop subsequently which seem likely to correspond to field‐aligned current. Although associated with substorm onset, we argue that these events are distinct from westward traveling surges and appear to differ from the midlatitude phenomenon known as subauroral ion drifts. We thus call this new‐found signature a substorm‐associated radar auroral surge or SARAS event.
Energy spectrum of particles accelerated near a magnetic x line
Authors: Bruhwiler D. L. , Zweibel Ellen G.
Published: February 2008

We study the acceleration of test particles near a static magnetic x line with a uniform electric field and a strong component of the magnetic field, B∥, parallel to the x line. The energy spectrum of the accelerated particles is found analytically in the nonrelativistic limit, showing good agreement with numerical simulations. At high energies, the spectrum decays exponentially with a characteristic energy very different from that found in studies assuming B∥ = 0.
Nonlinear dynamics of charged particles in the magnetotail
Authors: Chen James
Published: February 2008

An important region of the Earth's magnetosphere is the nightside magnetotail, which is believed to play a significant role in energy storage and release associated with substorms. The magnetotail contains a current sheet which separates regions of oppositely directed magnetic field. Particle motion in the collisionless magnetotail has been a long‐standing problem. Recent research from the dynamical point of view has yielded considerable new insights into the fundamental properties of orbits and of particle distribution functions. A new framework of understanding magnetospheric plasma properties is emerging. Some novel predictions based directly on nonlinear dynamics have proved to be robust and in apparent good agreement with observation. The Earth's magnetotail may serve as a paradigm, one accessible by in situ observation, of a broad class of boundary regions with embedded current sheets. This article reviews the nonlinear dynamics of charged particles in the magnetotail configuration. The emphasis is on the relationships between the dynamics and physical observables. At the end of the introduction, sections containing basic material are indicated.