bluuebunny/crossref_metadata_2025 huggingface dataset:
Stratospheric depletion of CO on Titan
Authors: Chassefière E. , Cabane M.
Published: February 2008

A deep stratospheric depletion of CO is found in Titan's atmosphere comparing millimetric and infrared observations [Marten et al., 1988; Lutz et al., 1983]. We suggest that adsorption of CO on aerosols in the region of Titan's atmosphere where methane is expected to condense may change the vertical distribution of CO below ≈ 40 km. Aerosols slowly pervading through the methane condensation region could transport enough CO to generate the observed tropospheric enrichment provided the sticking coefficient ε (fraction of collisions yielding adsorption) is 6 10−4, assuming the same eddy diffusion coefficient K as in the Earth troposphere. In the case of a lower mixing rate, generally favoured, smaller values of ε are allowed (down to ≈ 10−6). Besides, the final radius of methane particles, just above the region where methane evaporates (below ≈ 10 km), must be 100 μm within a factor of 10. The hypothesis presented in this paper, if it is confirmed by laboratory measurements, could be an indirect evidence for large amounts of CH4 ice in the Titanian atmosphere.
Flexure of lithosphere beneath the Alberta Foreland Basin: Evidence of an eastward stiffening continental lithosphere
Authors: Wu Patrick
Published: February 2008

The flexure of the Mississippian Unconformity (MU) is used to constrain the stiffness of the lithosphere beneath the Alberta Foreland Basin (AFB). This flexure supports the sedimentological evidence for the absence of a forebulge in the AFB and implies that the peak of the forebulge lies further east of the Alberta Saskatchewan border. It is demonstrated that an eastwards stiffening lithosphere is required in order to fit the flexure of the MU. When flexural stiffness is expressed in terms of effective thickness, it varies from about 38km west of the Rocky Mountains to more than 200km underneath the North American craton. This variation of stiffness indicates that there is a strong lateral temperature and chemical variation underneath. Eastwards stiffening also implies an eastwards thickening of the elastic lithosphere. Such a model is in good agreement with recent petrological and geophysical evidences in the west and underneath the craton.
Depletion of Arctic ozone in the winter 1990
Authors: Koike M. , Kondo Y. , Hayashi M. , Iwasaka Y. , Newman P. A. , Helten M. , Aimedieu P.
Published: February 2008

Ozone mixing ratios were measured by ozonesondes on board balloons launched from Esrange, near Kiruna, Sweden (68°N, 20°E) from January 11 to February 9, 1990. The data obtained prior to a sudden warming on February 7, 1990 show that at potential temperatures between 460 and 640 K, the ozone mixing ratio just inside the polar vortex was systematically smaller than that outside, the largest difference being 29 % at around 525 K. The ozone mixing ratio at 525 K inside the vortex decreased at a rate of about 1.5 % per day between January 26 and February 4. The temperatures simultaneously observed were quite often low enough to allow for formation of nitric acid trihydrate (NAT) particles around this altitude. Depletion of ozone due to highly perturbed chemical conditions in late January and early February is strongly suggested.
Frequency dependence of QLg and its relation to crustal anelasticity in the Basin and Range Province
Authors: Mitchell Brian J.
Published: February 2008

The high observed frequency dependence of Q for 1‐hz Lg waves (f0.4–0.6) in the Basin and Range province can be explained by a frequency‐independent layered model of intrinsic Q for shear waves (Qμ) which has very low values in the upper crust and rapidly increasing values at greater depths. By contrast, earlier work in the eastern United States indicated Qμ values in the upper crust which are high and which vary with frequency. The Qμ model which best explains reported values of QLg and its frequency dependence in the Basin‐and‐Range consists of an 8‐km thick low‐Q layer (60 or less) overlying Q values as high as 1000 or more at mid‐crustal depths. This Qμ distribution is best explained by an upper crust which contains fluids in interconnected cracks overlying a lower crust where higher lithostatic pressure has closed those cracks.

These results indicate that whereas the frequency dependence of Qμ is an intrinsic property of crustal material, the frequency dependence of QLg arises from both the intrinsic frequency dependence of crustal material and its layered structure. A notation is suggested which distinguishes between the frequency dependence of QLg and Qμ.
CHEOPS III: An Ozone Research Campaign in the Arctic winter stratosphere 1989/90
Authors: Pommereau J. P. , Schmidt U.
Published: February 2008

CHEOPS ( = CHemistry of Ozone in the Polar Stratosphere) is a research project that began in 1987 as an initiative to join efforts of scientists from Germany and France combining their resources and capacities to conduct field experiments in the winter Arctic stratosphere. On the 5 February, two experiments, a cryogenic whole air sampler and an active chemical ionization mass spectrometer, were launched with a large scientific balloon from the ESA/SSC Rocket Base ESRANGE near Kiruna in Northern Sweden (68°N, 20°E∥. The scientific objective was to look for a possible latitudinal difference in the vertical distributions of various minor constituents in the lower and middle stratosphere during winter [Schmidt et al, 1991; Arnold and Knop, 1989].
Geochemical and geothermal evidence for fluid migration in the Barbados Accretionary Prism (ODP leg 110)
Authors: Vrolijk Peter , Fisher Andrew , Gieskes Joris
Published: February 2008

Measured geochemical and geothermal effects of fluid migration in the northern Barbados accretionary prism indicate that: (1) fluid flows laterally along low‐angle active faults; (2) the entire length of the Leg 110 transect is a fluid discharge zone; (3) migration results in heating of sediments across the transect but most strongly at the deformation front; and (4) migration results in dilution of pore water‐Cl and 18O enrichment more in the arcward than the seaward side of the prism, suggesting that the Cl‐poor, 18O‐rich fluids that intrude the prism are derived from smectiteillite reactions occurring arcward. These conclusions have strengthened those derived from the initial appraisal of shipboard data, modified ideas about where fluids are heated most and where the geochemistry is strongly altered, and provided new ideas about the sources of fluids and their relative contributions.
Preliminary determination of Pacfic‐North America relative motion in the southern Gulf of Calfornia using the Global Positioning System
Authors: Dixon T. H. , Gonzalez G. , Lichten S. M. , Tralli D. M. , Ness G. E. , Dauphin J. P.
Published: February 2008

Global Positioning System (GPS) data from experiments conducted in 1985 and 1989 in the southern Gulf of California, Mexico, allow a determination of relative motion between the Pacific and North American plates. The data indicate motion of Cabo San Lucas on the Pacific plate relative to North America at a rate of 47±7 mrn/yr and azimuth of 57±6° west of north (1σ errors), equivalent within uncertainties to the NUVEL‐1 global plate motion model.
Ice composition evidence of marine ice transfer along the bottom of a small Antarctic Ice Shelf
Authors: Souchez R. , Meneghel M. , Tison J.‐L. , Lorrain R. , Ronveaux D. , Baroni C. , Lozej A. , Tabacco I. , Jouzel J.
Published: February 2008

The existence of marine ice transfer along the underside of the Hell's Gate Ice Shelf ( Victoria Land), is indicated by an isotopic and chemical study of ice cores. Because of top surface ablation, the marine ice formed at the ice shelf‐ocean interface, ultimately appears at shelf surface. A succession of congelation, platelet and frazil ice is shown to occur. The combined study of stable isotope composition and of the sodium content of these different ice types proves to be a valuable tool for specifying the ice shelf‐ocean interactions in this area. Two different freezing zones separated by a melting rone exist; the parent water for the frazil ice is meltwater from congelation ice which appears in the upstream zone.
Observations of the OH Meinel (6,2) and O2 atmospheric (0,1) Nightglow emissions from Maui during the ALOHA‐90 Campaign
Authors: Hecht James H. , Walterscheid Richard L.
Published: February 2008

Observations are reported from a CCD nightglow camera deployed on Maui during ALOHA‐90. These data show that there were periods of both strong and weak gravity wave activity, that background winds in the direction of wave propogation can be derived using airglow data alone, and that there may be a connection between sporadic Na and large‐scale wave activity. These data are in fair to good agreement with models of wave induced airglow fluctuations.
Simultaneous lidar and airglow temperature measurements in the mesopause region
Authors: Yu J. R. , Latifi H. , She C. Y. , Yee J. H. , Niciejewski R. J.
Published: February 2008

A scientific flight over Fort Collins CO (40.6°N,105°W) was conducted on the night of April 15–16, 1990, during the ALOHA‐90 campaign. In this Colorado mission, a direct comparison between measured mesospheric O2 and OH rotational temperatures with the airglow instruments on board the Electra and simultaneously measured Na temperatures by a ground‐based narrowband Na lidar has been made. This first comparison resulted in general agreement in measured temperatures between different instruments.
Particle production in clouds
Authors: Hegg Dean A.
Published: February 2008

Both recent and some older field measurements reveal condensation nucleus concentrations which attain local maxima within clouds. Model calculations are presented which suggest that, if the enhanced actinic radiation flux in clouds is taken into account, homogeneous, bimolecular nucleation within clouds is a viable mechanism for production of such particles.
Observations of O2 (¹Σ) and OH nightglow during the ALOHA‐90 Campaign
Authors: Yee Jeng‐Hwa , Niciejewski Rick , Luo Ming Zhao
Published: February 2008

Two spectroscopic instruments, a 1/4 meter Ebert‐Fastie spectrometer and a Michelson interferometer, were flown aboard the NCAR Electra during the ALOHA‐90 campaign. These instruments were designed to carry out measurements of the brightnesses and rotational temperatures of the O2 Atmospheric (0–1) band and several OH Meinel bands simultaneously with sodium lidar observations. The spectrometer results taken during the nights of March 25 and March 31 are reported. Wave‐like oscillations in both O2 and OH airglow brightnesses were clearly present during both flights and a strong positive correlation of OH band brightness with sodium column density was found. A slightly weaker correlation of O2 band brightness with sodium column density was also detected. The measured brightness ratio between the OH (7–4) and (7–3) bands is found to be 11.2±0.3, which is in good agreement with the calculated ratios of 12.8 by Mies [1974] and 10.2 by Langhoff et al. [1986].
Rocket measurements of relativistic electrons: New features in fluxes, spectra and pitch angle distributions
Authors: Herrero F. A. , Baker D. N. , Goldberg R. A.
Published: February 2008

We report new features of precipitating relativistic electron fluxes measured on a spinning sounding rocket payload at midday between altitudes of 70 and 130 km in the auroral region (Poker Flat, Alaska, 65.1°N, 147.5°W, and L=5.5). The sounding rocket (NASA 33.059) was launched at 21:29 UT on May 13, 1990 during a relativistic electron enhancement event of modest intensity. Electron fluxes were measured for a total of about 210 seconds at energies from 0.1 to 3.8 MeV, while pitch angle was sampled from 0° to 90° every spin cycle. Flux levels during the initial 90 seconds were about 5 to 8 times higher than in the next 120 seconds, revealing a time scale of more than 100 seconds for large amplitude intensity variations. A shorter time scale appeared for downward electron bursts lasting 10 to 20 seconds. Electrons with energies below about 0.2 MeV showed isotropic pitch angle distributions during most of the first 90 seconds of data, while at higher energies the electrons had highest fluxes near the mirroring angle (90°); when they occurred, the noted downward bursts were seen at all energies. Data obtained during the second half of the flight showed little variation in the shape of the pitch angle distribution for energies greater than 0.5 MeV; the flux at 90° was about 100 times the flux at 0°. We have compared the low altitude fluxes with those measured at geostationary orbit (L=6.6), and find that the low altitude fluxes are much higher than expected from a simple mapping of a pancake distribution at high altitudes (at the equator). Energy deposition of this modest event is estimated to increase rapidly above 45 km, already exceeding the cosmic ray background at 45 km.
Transport from chaotic orbits in the geomagnetic tail
Authors: Horton W. , Tajima T.
Published: February 2008

The rapid change in direction and magnitude of the magnetic field vector in crossing the quasineutral sheet in the geomagnetic tail leads to deterministic Hamiltonian chaos. The finite correlation times in the single particle orbits due to the continuum of orbital frequencies leads to well‐defined collisionless transport coefficients. The transport coefficients are derived for plasma trapped in the quasineutral sheet.
On the efficiency of solar heating in the middle atmosphere
Authors: Mlynczak Martin G. , Solomon Susan
Published: February 2008

We calculate the efficiency at which solar ultraviolet radiation absorbed in the Hartley band of ozone is directly converted to heat in the terrestrial mesosphere and lower thermosphere (50–110 km). The ozone molecule undergoes photolysis to yield the excited species O(¹D) and O2(¹Δ) with a quantum yield of about 0.9. Spontaneous emission from O2(¹Δ) and from O2(¹Σ) (excited by energy transfer from O(¹D)) significantly decreases the amount of energy available for heat. Similarly, we calculate the efficiency at which solar ultraviolet radiation absorbed by O2 in the Schumann‐Runge continuum is directly converted to heat in the lower thermosphere (95–110 km). The O2 undergoes photolysis and the excited product O(¹D) is generated. Spontaneous emission from O2(¹Σ) (excited by energy transfer from O(¹D)) reduces the amount of energy available for heat in the lower thermosphere. The consideration of these energy transfer and loss processes results in significantly reduced heating rates as compared to those conventionally calculated in models of the middle atmosphere.
Increase in the PSC‐formation probability caused by high‐flying aircraft
Authors: Peter Th. , Brühl C. , Crutzen P. J.
Published: February 2008

The saturation temperature Tsat for the formation of polar stratospheric clouds (PSC) strongly depends on the local partial pressures of nitric acid and water vapour, and thus is sensitive to NOx and H2O‐injection due to exhaust from aircraft in the stratosphere. The present paper investigates this effect, using daily stratospheric temperature data from the northern hemisphere compiled over the last 25 years by the Free University of Berlin. For Type‐I PSC the data were examined for temperatures T < Tsat ‐ 3 K, which would allow for a supercooling of about the 3 K measured in a previous arctic winter balloon mission, in effect corresponding to a large HNO3‐supersaturation. We show that this is required to overcome the heterogeneous nucleation energy barrier. We compare the analyses of both a background atmosphere and one perturbed by a fleet of 600 stratospheric aircraft flying at ∼22 km altitude. The result is that between December and March in the polar cap region there might be more than a doubling in the occurence of Type‐I PSCs and an even stronger increase of Type‐II PSCs, and accordingly a substantial enhancement in the potential ozone destruction by chlorine radicals.
CO2 transport at the air‐sea interface: Effect of coupling of heat and matter fluxes
Authors: Phillips Leon F.
Published: February 2008

Existing data on CO2 fluxes between air and sea have been calculated by assuming, incorrectly, that the thermodynamic driving force for the CO2 flux is provided solely by the CO2 partial pressure difference between the two phases. Because both heat and matter transfer occur under non‐equilibrium conditions, with finite temperature and composition differences across the interface, a proper description of transport at the air‐water interface requires the use of irreversible thermodynamics, according to which the heat and matter fluxes are coupled through the heat of solution of the gas. The present treatment shows that the driving force for CO2 transport due to the temperature difference across the interface is comparable with that arising from the partial pressure difference.
Fractal nature of the sea ice draft profile
Authors: Key J. , McLaren A. S.
Published: February 2008

The fractal dimension is examined as a descriptor of ice roughness for more than 3000 km of under‐ice draft submarine sonar data. The data can be considered to constitute a fractal set within a limited range of scales, as defined by the Hurst parameter H. It was found that 0.55 < H < 0.78 for scales of 3–15 m and 0.15 < H < 0.45 for scales of 15–75 m, beyond which H is near unity. From this it is seen quantitatively that sea ice on the large scale is smooth. The fractal dimension, D=2‐H, at the smaller scales is similar to that measured by other investigators for individual ice features such as keels. The fractal dimension did not show any changing spatial pattern across ice regions, indicating that the scaling relationship is similar even when first‐order measures such as the mean and variance of ice draft change. Therefore, D does not appear to be useful for partitioning the transect into homogeneous ice areas in the draft data examined.
On the apparent randomness of substorm onset
Authors: Lewis Z. V.
Published: February 2008

The onset of the expansion phase of substorms is currently unpredictable, that unpredictability being related to the nonlinear nature of the solar wind‐magnetosphere interaction. Using the mathematics of catastrophe theory it is possible to describe the substorm phenomenon in terms of a fundamental singularity of the solar wind‐magnetosphere interaction. The apparently random nature of substorm onset can then be explained as the result of an unfolding of the singularity of the cusp catastrophe which is in principle predictable. Substorm expansions are triggered when two features of the solar wind‐magnetosphere interaction are critically functionally related.
A PAN analog from isoprene photooxidation
Authors: Bertman Steven B. , Roberts James M.
Published: February 2008

Peroxymethacrylic nitric anhydride (MPAN), a potential atmospheric photoproduct, was synthesized and characterized in the laboratory for the first time. The compound was identified by FT‐IR, GC‐MS, GC/ECD, and decomposition studies. Purification of synthetic mixtures provided a sample suitable for calibration of instruments for ambient atmospheric sampling. Possible field identification of MPAN is reported, and the role of MPAN in the chemistry of the rural troposphere is discussed.
Evidence for chaotic behaviour in seismic wave scattering
Authors: McCloskey John , Bean C. J. , Jacob A. W. B.
Published: February 2008

Scattering of seismic waves by lithospheric heterogeneities produces seismic coda which typically look random. Consequently stochastic modelling methods are usually applied to these coda [1–6]. Here, we introduce a technique, based on previous work [7], for evaluating the predictability of time‐series data as an indicator of underlying determinism. When analyzed using this method both earthquake and explosive source seismic coda display strong short term predictability which is not consistent with a random generation mechanism.
Jupiter's dayglow H Ly α emission line profile
Authors: Clarke John T. , Gladstone G. Randall , Ben Jaffel Lotfi
Published: February 2008

IUE spectra of Jupiter's low latitude H Ly α emission line profile have been obtained on and off the “Ly α bulge” at the longitude of the central meridian (CML), near the limb of the planet, and at midlatitudes on the CML. All equatorial locations show line broadening beyond the IUE resolution of 0.14 Å. The equatorial lines are significantly broader than at midlatitudes on the CML, and near the limb the lines are broader than on the CML, both on and off the bulge. The observed line shapes are not consistent with pure resonant scattering of solar Ly α by upper atmospheric H atoms with a variable H abundance: calculated profiles near the limb have much less intense cores. The broadening of the bulge line profiles on the CML and limb compared with off‐bulge regions demonstrates that the bulge effect is a broadening of the line, not an increase in the line core flux. We propose that there is either a substantial broadened internal source and/or the upper atmosphere has considerable Doppler broadening (winds or turbulence) to increase the resonant scattering line width.
Development of magnetic soil from ferroan dolomite
Authors: Moukarika A. , O'Brien F. , Coey J. M. D. , Resende Mauro
Published: February 2008

An occurrence of maghemitic soil in association with ferroan dolomite in Minas Gerais is characterized by X‐ray diffraction, magnetization measurements and Mössbauer spectroscopy. Altered layers on outliers of dolomite, which has composition (Ca1.04Mg0.83Fe0.11Mn0.02)(CO3)2 indicate the weathering sequence: ferroan dolomite → calcite + poorly‐crystallized ferric hydroxide → maghemite + hematite + goethite. The spontaneous magnetization of the maghemitic soil (65 wt% Fe2O3) is 8.8 JT−1kg−1; the magnetization of the soil maghemite itself is estimated to be 25±5 JT−1kg−1, which is greatly reduced from the value for pure maghemite because of isomorphous substitution.
The electric field changes and UHF radiations caused by the triggered lightning in Japan
Authors: Kawasaki Zen‐Ichiro , Kanao Tadashi , Matsuura Kenji , Nakano Minoru , Horii Kenji , Nakamura Koh‐Ichi
Published: February 2008

The electric field changes, the magnetic field changes, and UHF radiation were observed during the rocket‐triggered lightning experiment in winter storms. A remarkable discrepancy is noticed between electromagnetic field changes of flashes triggered with a rocket and an isolated wire that struck a power tower and flashes with a rocket and a grounded wire. Flashes to tower have a distinguishable first pulse of a large amplitude, which, we speculate, occurs at the moment of attachment of a downward leader to the tower. The UHF radiation measurements indicate that the triggered lightning process starts with a pulse series resembling a negative stepped leader. The electric field change records of rockettriggered lightning in winter storms do not show the presence of rapid field variations typical for return strokes in natural cloud‐to‐ground flashes.
An improved concept of the equivalent displacement height for curved traced profiles
Authors: Röth Ernst‐Peter
Published: February 2008

A method is presented to improve the concept of the equivalent displacement height (EDH). The EDH is the normalized variance of an atmospheric tracer. When the tracer's altitudinal profile exhibits a strong curvature or possesses a vanishing slope, the EDH of the earlier definitions was governed by the normalization factor, namely the slope, rather than by the tracer's variance. This may lead to misinterpretations of the EDH. The introduction of the profile's curvature into the definition of the equivalent displacement height overcomes the former difficulties and allows to derive more accurate transport parameters from the EDH.
Temperature variability in the Gulf of California during the last century: A record of the recent strong El Niño
Authors: Juillet‐Leclerc A. , Labeyrie L. D. , Reyss J. L. , Schrader H.
Published: February 2008

The oxygen isotopic ratio of diatom silica from a box core collected on the eastern slope of the Guaymas Basin (Gulf of California) has been analyzed. This core covers the last 90 years. The isotopic record indicates a progressive and continuous temperature increase of about 8°C from the end of the last century until 1980 with superimposed, rapid temperature fluctuations of 2 to 4°C. Although the Gulf of California is not directly under the influence of El Niño, short temperature increases may be associated with the El Niño events described by Quinn et al. (1987). The longer term changes are attributed to a decrease of upwelling intensity linked to weakening of the trade winds in the Northern Hemisphere.
Upper crustal resistivity structure of the East Pacific Rise near 13°N
Authors: Evans R. L. , Constable S. C. , Sinha M. C. , Cox C. S. , Unsworth M. J.
Published: February 2008

An active source electromagnetic (EM) sounding has been conducted on the axis of the East Pacific Rise (EPR) at 13° 10′N. 1D inversion and modelling techniques, seeking resistivity as a function of depth, have been applied to 8 Hz amplitude data collected along the ridge crest. Resistivity is seen to increase monotonically between 50 m and 1 km below the seafloor, increasing from ∼1Ωm to around 90Ωm. We observe no intrinsic difference in upper crustal resistivity structure between the rise axis and 100,000 year old crust. Inferred surface porosities of 20% are larger than those recorded in 5.9 my old crust in DSDP hole 504B. Our data do not require, and lack sufficient information for, the reliable inclusion of a conductive termination to the model below 1.2 km.
Evidence for denitrification in the 1990 Antarctic spring stratosphere: I, Lidar and temperature measurements
Authors: Gobbi Gian Paolo , Deshler Terry , Adriani Alberto , Hofmann David J.
Published: February 2008

Lidar soundings of the lower stratosphere were made between August 30 and October 11, 1990, at McMurdo Station, Antarctica (78S–167E). Polar stratospheric clouds (PSCs) were observed in only two periods: between September 5 and 10, and on October 7. During these days McMurdo was well within the polar vortex, and temperatures in the lower stratosphere reached seasonal minima. Temperature soundings and two water vapor measurements were also made in the same period. The water vapor content between 11 and 20 km was found to be between 2 and 3 ppmv. Using these values for water vapor, condensation temperatures for water and nitric acid trihydrate were calculated and compared with the temperature measurements. Analysis of these comparisons together with the lidar observations indicated that PSCs appeared only when temperatures were below the threshold condensation point for an air mass containing approximately 1 ppbv nitric acid. This was observed from the beginning of measurements on August 30, and suggests that the Antarctic lower stratosphere was highly denitrified both at the end of winter and during the early spring of 1990.
UV absorption spectrum and absorption cross sections of COF2 at 296 K in the range 200 – 230 nm
Authors: Nölle Andreas , Heydtmann Horst , Meller Richard , Schneider Wolfgang , Moortgat Geert K.
Published: February 2008

The UV spectrum and the absorption cross sections of carbonyl fluoride (COF2) have been measured in the wavelength range 200 – 230 nm at 296 K with a resolution of 0.03 nm by diode array spectroscopy. Preliminary results of the determination of the quantum yield of COF2 at 193 nm and 296 K are presented. The new absorption cross sections and the new estimate of the quantum yield were used to calculate photodissociation rate constants at solar zenith angles ranging from 0° to 86° as a function of height (0 – 55 km).
Libration in the Earth's rotation
Authors: Chao B. F. , Dong D. N. , Liu H. S. , Herring T. A.
Published: February 2008

External luni‐solar torque exerted on the difference (B‐A) of the Earth's two equatorial principal moments of inertia gives rise to two types of librational motions in the Earth's rotation: the semidiurnal libration in spin and the prograde diurnal libration in polar motion. Formulas for the librations considering a realistic Earth model and their tidal decompositions are derived and evaluated. The spin libration has a maximum peak‐to‐peak amplitude of 0.09 milliarcseconds, that of the polar libration is 0.06 milliarcseconds. Implications concerning their detectability and role in the tidal variation of Earth rotation are discussed.
On the ELF generation efficiency of the Tromsø Heater Facility
Authors: Barr Richard , Stubbe Peter
Published: February 2008

Using amplitude modulation derived from repetitive pulses of varying duty cycle with the Tromsø heater facility, we determine the ratio of the heating to cooling time constants of ELF currents generated in the D‐region. This ratio is found to decrease from 1.03±0.07 at 510 Hz to 0.28±0.03 at 6010 kHz. These results, which were obtained using an effective radiated power of 240 MW, suggest that future heater facilities designed to optimise ELF radiation efficiency using the technique of ‘beam painting’ will have to operate at considerably higher power levels than the Tromsø facility if any practical advantages are to be gained.
Identification of the aurorals O(¹S) precursor in photometric time sequences of pulsating aurora
Authors: Shepherd G. G. , Paulson K. V. , Brown S. , Gault W. A. , Moise A. , Solheim B. H.
Published: February 2008

Previous studies of photometric time sequences from pulsating aurora have established that the O(¹S) metastable leading to the emission of the auroral green line is excited by two processes, one direct, the other indirect, with the indirect precursor having a lifetime of about 0.1s. In this paper we report on new high time‐resolution measurements which extend the observations of precursor lifetime down to about 0.01s. Simultaneous observations of pulsations in the Vegard‐Kaplan band system were also made in order to obtain direct measurements of the lifetimes of the N2(A³∑u+) metastable; these were found to be essentially equal to those of the precursor over the lifetime range from 0.01s to 0.1s, and less well‐correlated for longer lifetimes. This result identifies the O(¹S) precursor as N2(A³∑u+), at least over the altitude range 97 to 125 km.
The Apollo lunar surface water vapor event revisited
Authors: Freeman J. W. , Hills H. K.
Published: February 2008

On March 7, 1971, the first sunrise following the Apollo 14 mission, the Suprathermal Ion Detector Experiment (SIDE) deployed at the Apollo 14 site reported an intense flux of ions whose mass per charge was consistent with water vapor. We examine the amount of water and discuss the various acceleration processes responsible for accelerating ions into the SIDE. We conclude that during most of the event the observed water vapor ions were accelerated by the negative lunar surface electric potential and secondly that this event was probably the result of mission associated water vapor, either from the LM ascent and descent stage rockets or from residual water in the descent stage tanks.
Effect of anthropogenic aerosols on biologically active ultraviolet radiation
Authors: Liu S. C. , McKeen S. A. , Madronich S.
Published: February 2008

Aerosols from anthropogenic sources contribute significantly to the scattering of solar radiation in the atmosphere over most populated areas. By using observed values of visual range we estimate that in non‐urban areas of the industrialized countries the amount of biologically active solar radiation (UVB, 280 to 315 nm) reaching the surface has decreased by a range of 5 to 18% since the industrial revolution, primarily due to aerosols formed from emissions of sulfur dioxide (SO2). The UVB reduction in the industrialized countries may have offset partly or fully the UVB increases associated with current stratospheric ozone depletion at NH continental mid‐latitudes. However, this offset is not expected to continue because the SO2 emissions are leveling off in the industrialized countries.
Prompt ionization in the CRIT II barium releases
Authors: Torbert R. B. , Kletzing C. A. , Liou K. , Rau D.
Published: February 2008

Observations of electron and ion distributions inside a fast neutral barium jet in the ionosphere show significant fluxes within 4 km of release, presumably related to beam plasma instability processes involved in the Critical Ionisation Velocity (CIV) effect. Electron fluxes exceeding 5 × 1012/cm2‐str‐sec‐keV were responsible for ionizing both the streaming barium and ambient oxygen. Resulting ion fluxes seem to be consistent with 1–2% ionization of the fast barium, as reported by optical observations, although the extended spatial distribution of the optically observed ions is difficult to reconcile with the in‐situ observations. When the perpendicular velocity of the neutrals falls below critical values, these processes shut off. Although these observations resemble the earlier Porcupine experimental results [Haerendel, 1982], theoretical understanding of the differences between these data and that of earlier negative experiments is still lacking.
High latitude pulsating aurorae revisited
Authors: Wu Q. , Rosenberg T. J.
Published: February 2008

Dayside auroral pulsations (10–40 s periods) have been studied for different levels of geomagnetic disturbance with N2+ 427.8 nm emission data obtained at South Pole station, Antarctica (−74.2° MLAT). The occurrence distribution exhibits a single peak at magnetic noon under geomagnetically quiet conditions (0 ≤ Kp < 1). With increased Kp, the distribution shifts to earlier times, the peak occurring at 1000–1030 MLT for 1 ≤, Kp < 4. At these higher Kp levels a secondary occurrence peak is evident in the afternoon sector between 1400 and 1600 MLT, occurring earlier as Kp increases. These results are compared with those obtained separately for pre‐noon pulsations observed at Ny Alesund and post‐noon pulsations observed at Davis, northern and southern hemisphere sites at approximately the same magnetic latitude as South Pole. South Pole and Ny Alesund observe morning peaks at the same time and with a similar lack of Kp dependence; South Pole and Davis observe afternoon peaks with similar Kp dependence, though the peak occurs earlier at Davis. In contrast to the results from the earlier studies, the South Pole observations show larger pulsation amplitudes in the morning sector and significantly higher occurrence rates overall.
The relationship between erythemal UV and ozone, derived from spectral irradiance measurements
Authors: McKenzie R. L. , Matthews W. A. , Johnston P. V.
Published: February 2008

Spectral measurements of solar ultraviolet (UV) radiation received at the ground at Lauder, New Zealand (45°S) during 1990 are used in conjunction with ozone total column measurements to investigate the relative importance to erythemally active UV radiation of variations in solar zenith angle, ozone, and cloud cover. At this site solar zenith angle variations are the dominant factor, but clouds frequently attenuate the clear sky irradiances by more than 50%. Ozone reductions of 1% typically cause an increase in erythemally active UV irradiance of 1.25±0.20%.
High temperature viscous magnetization of oceanic deep crustal‐ and mantle‐rocks as a partial source for MAGSAT magnetic anomalies
Authors: Pozzi Jean Pierre , Dubuisson Gilles
Published: February 2008

The Magsat data have yielded a global cartography of long‐wavelength anomalies of lithospheric origin. The magnetizations needed to model these anomalies are much higher than those measured on samples by laboratory experiments. An enhancement of both induced and viscous magnetization at high temperature has often been put forward to account for the “missing magnetization”. Experimental measures of viscous magnetization Mv at high temperature are presented for oceanic deep crustal‐ and mantle‐rocks. At room temperature, Mv hereafter defined in experiments as the magnetization acquired after 400 s in a weak field, is negligible in comparison with the room temperature induced magnetization Mk0. At higher temperatures, between 200°C and 450°C, Mv represents about 20% of Mk0 and is further enhanced near 500°C, ranging from 25 to 130% of Mk0. An extrapolation of these results to geological times shows that the viscous magnetization acquired since the last reversal of the Earth magnetic field may be of the order of magnitude of the induced magnetization Mk0, above 200°C and possibly predominant near 500°C. However, a magnetic uppermost mantle is still needed to explain the magnetizations of oceanic lithosphere derived from Magsat data.
Modes of interannual variability in the stratosphere
Authors: Dunkerton Timothy J. , Baldwin Mark P.
Published: February 2008

During 1964–91, stratospheric temperature and circulation in northern hemisphere winter varied interannually on time scales from 2 to ∼12 years. A substantial percentage of December‐February (DJF) interannual variance was correlated with the quasi‐biennial oscillation (QBO). Additional monthly variance could be accounted for by quasi‐decadal oscillation and QBO/low‐frequency modulation. The QBO was the largest and most consistent of these signals, and its decadal modulation explains an apparent correlation with the solar cycle depending on the sign of the QBO ‐ an interpretation supported by principal component analysis.
Initial duct growth determined from cold‐start plasma‐line data recorded at Arecibo
Authors: Muldrew D. B.
Published: February 2008

Recent high‐resolution height observations of the HF‐induced plasma line have been made by Djuth et al. [1990]. The plasma line is first observed after 3 ms very close to the HF‐reflection height and not at the height expected from weak‐turbulence theory in a uniformly varying ionosphere. Natural field‐aligned ducts exist in the ionosphere. Those with a diameter of a few meters or more can trap Langmuir waves (L waves) generated by the parametric decay instability and propagating nearly parallel to the magnetic field B. The ponderomotive force of the trapped L waves near the highest HF interference maximum causes electrons to be expelled parallel to B and ions to be expelled perpendicular to B. The ion gyroradius is comparable to the smallest duct diameter that can trap L waves. Since it only takes a few milliseconds for the ions to move at their thermal velocity across the duct, the duct can grow in a few milliseconds to a level where L waves capable of backscattering the Arecibo radar can be trapped. Duct growth is eventually limited by Landau damping and/or escape of the ducted L waves. These control the lower‐height limit of the plasma line and terminate the overshoot.
Cloud‐to‐stratosphere lightning discharges: A radio emission model
Authors: Farrell W. M. , Desch M. D.
Published: February 2008

Recent observations of rare cloud‐to‐stratospheric lightning discharges suggest the events are inherently “slow‐rising”, with the emitted energy reaching peak values in about 10 milliseconds. Applying a dipole radiation model, we demonstrate that the emitted radio wave energy from such slow‐rising events is strongest below about 50 Hz, and possesses a significant rolloff at higher frequencies. In the analysis, various current distributions are considered in order to determine the effect on the radio spectrum. Near 10 kHz, the emission from cloud‐to‐stratospheric lightning is significantly reduced as compared to the typical cloud‐to‐ground return stroke, with amplitudes as much as 50 dB lower. This result may explain the lack of detection of VLF signals from recently observed long‐lasting discharge events.
Nonresonant low‐frequency instabilities in multibeam plasmas: Applications to cometary environments and plasma sheet boundary layers
Authors: Verheest Frank , Lakhina G. S.
Published: February 2008

Low‐frequency electromagnetic fluctuations dominate the wave spectrum observed during strong plasma flows in the region upstream of a cometary nucleus and in the plasma sheet boundary layer of the Earth's magnetotail. A theoretical framework is established in the long‐wavelength limit for nonresonant instabilities in a multibeam plasma, for any number of beams. Both the growth rates of the instabilities and the ultimate levels of magnetic field turbulence are given. A two‐beam plasma models the contamination of the upstream solar wind by cometary material, whereas a three‐beam model is invoked for the plasma sheet boundary layer, with two counterstreaming proton beams in the presence of an oxygen beam. If the two proton beams by themselves already excite a low‐frequency instability, the injection of oxygen at rest in the center‐of‐mass frame does not change the instability characteristics. Where the two proton beams alone are stable, a sufficient amount of oxygen with a sufficient velocity offset in the center‐of‐mass frame can render the plasma sheet boundary layer unstable. In both cases, the theoretical levels of low‐frequency turbulence are in good agreement with observations and/or numerical simulations.
The three‐dimensional raman's distribution as a non‐Maxwellian model and the ionospheric ion outflows into the magnetosphere revisited
Authors: Hubert D. , Kinzelin E.
Published: February 2008

The three‐dimensional Raman's distribution as a model for fitting non‐Maxwellian distributions, and the consequences for the hydrodynamic mirror force due to coupling between pressure anisotropy and the inhomogeneous geomagnetic field are revisited. We demonstrate that the three‐dimensional Raman's model is unable to quantitatively predict the Post‐Rosenbluth or ion cyclotron instability threshold. The application of this model to deduce ion temperature anisotropy from only one radar spectra measurement is shown to be restricted to specific aspect angles and small electric field intensities. This model provides the line‐of‐sight temperature and then the thermodynamical temperature for aspect angle equal to 54.7°. The hydrodynamic upwelling force is shown to be greatly affected by the ion‐neutral interaction process. This additional force represents an important amount of the gravity in the presence of large electric fields. The upwelling force is overestimated to a great extent, when using the three‐dimensional Raman's model to fit non‐Maxwellian distribution functions observed in the auroral ionosphere.
A model for the disc Lyman alpha emission of Uranus
Authors: Ben Jaffel L. , Prangé R. , Emerich C. , Vidal‐Madjar A. , McConnell J. C.
Published: February 2008

A new efficient radiative transfer algorithm for inhomogeneous atmospheres has been used to simulate the limb to limb Lyman α reflectivities observed with the Voyager ultraviolet spectrometer during the flyby of Uranus. It was shown that complete frequency redistribution should be adequate to describe the disc emissions. The model atmosphere used was derived using a combination of Voyager measurements and modeling. Atomic H densities calculated had sources derivable directly from solar FUV and EUV fluxes. To fit the observations, four contributions are evaluated: (1) the resonance scattering of solar Lyman α radiation, (2) Rayleigh‐Raman scattering of solar Lyman α radiation, (3) the resonance scattering of interplanetary Lyman α radiation, and (4) a possible internal source of unknown origin. From comparison with the observations, and provided that the published Voyager calibrations are correct, it is shown that only atmospheres with low eddy diffusion coefficients (KH ≤ 100 cm² s−1) and an internal source could simulate both the shape and the strength of the measured disc emission. The main results are then that the direct solar Lyman α scattering contribution (type 1 plus type 2) is of the order of 760 R, the scattering of interplanetary Lyman α contributes about 320 R, and a small additional internal source providing about 100–500 R is needed to match the measurements. Further, the analysis of the disc intensities suggests that there is no strong variation of K with latitude.
On large‐scale rotational motions and energetics of auroral shear layers
Authors: Lotko W. , Shen M.‐M.
Published: February 2008

The stability, dynamics and energetics of an auroral shear layer are considered in the framework of incompressible, one‐fluid magnetohydrodynamics, under conditions where current flow through the system is limited by the finite Pedersen conductivity and an enhanced field‐aligned resistivity. The model includes a magnetospheric region where currents resulting from polarization electric fields and viscous forces are important, an ionospheric substrate of uniform conductivity, and a force‐free acceleration region, characterized by a linear current‐voltage relation and located at an intermediate altitude between the magnetospheric viscous/polarization layer and the ionosphere. It is assumed that the Alfvén wave transit time across the viscous/polarization layer is small compared with the eddy time. Neutral stability of the model system is determined for a class of one‐dimensional equilibria in which a specified current distribution at the upper boundary of the viscous/polarization layer produces a potential structure with convergent, localized reversals in the transverse (E×B) electric field. The calculated neutral curves depend on three nondimensional parameters related to the intensity of the imposed field‐aligned current, the shear layer scale size, and the ratio of resistive to viscous drag at equilibrium. Numerical simulations of unstable configurations show that (1) two‐dimensional quasi‐steady rotational states arise when the equilibrium is weakly unstable; (2) eddy shedding turbulent states can arise when the equilibrium is strongly unstable; and (3) the flow kinetic energy and energy input/dissipation rates in the model system are reduced as a consequence of the instability. Power spectral densities for the electric and magnetic fields are also evaluated along sample “satellite” cuts through the shear layer. An application to postnoon auroral forms confirms the tendency for 2D rotational motion and periodic bright spots, although the observed intensity of the upward field‐aligned current suggests that the effective resistivity of the system is not sufficient to suppress inductive fields in the vortex dynamics.
Proxy studies of energy transfer to the magnetosphere
Authors: Scurry L. , Russell C. T.
Published: February 2008

The transfer of energy into the magnetosphere is studied using as proxy the Am geomagnetic index and multilinear regressions and correlations with solar wind data. In particular, the response of Am to the reconnection mechanism is examined in relation to the orientation of the interplanetary magnetic field as well as the upstream plasma parameters. A functional dependence of Am on clock angle, the orientation of the IMF in the plane perpendicular to the flow, is derived after first correcting the index for nonreconnection effects due to dynamic pressure and velocity. An examination of the effect of upstream magnetosonic Mach number shows the reconnection mechanism to become less efficient at high Mach numbers. The reconnection mechanism is shown to be slightly enhanced by higher dynamic pressures.
Upper atmospheric infrared radiance from CO2and NO observed during the SPIRIT 1 Rocket Experiment
Authors: Adler‐Golden S. M. , Matthew M. W. , Smith D. R.
Published: February 2008

Spectral limb radiance data on CO2ν2and NO 5.3‐μm emissions obtained in the Spectral Infrared Interferometric Telescope rocket experiment have been analyzed. The data cover auroral intensities from several kilorayleighs to over 100 kR at 391.4 nm, and tangent heights of ∼70–200 km at high latitudes (60°–65°N). Volumetric emission and kinetic temperature profiles have been obtained using linear least squares inversion procedures. The CO2ν2radiance profile is found to be similar to previous observations. The NO 5.3‐μm emission is somewhat weaker than that typically measured; this is ascribed mainly to below‐average thermospheric temperatures. Auroral enhancement of NO hot bands was not observable with the available sensitivity. An approximate thermospheric temperature profile derived from the NO band shape compares reasonably with the mass spectrometer/incoherent scatter 86 model.