bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the climate effect of unrestricted greenhouse emissions over the next 10,000 years
Authors: Kim Kwang‐Y. , Crowley Thomas J.
Published: February 2004

Although emission controls for greenhouse gases may limit their future rise, there is a finite chance that a substantial fraction of the available fossil fuel reservoir will be utilized. Geochemical models suggest that the atmospheric perturbation would then last for thousands of years. We use a well‐calibrated energy balance model, coupled to an upwelling‐diffusion deep‐ocean model, to estimate the temperature effects of such unrestricted emissions. We calculate that greenhouse warming will peak between ∼2200–2400, with a global temperature increase 4–13°C greater than present. The high‐end estimate is as much as 100% larger than estimates of the temperature increase for the ice‐free Cretaceous (100 Ma) warm period. Warming of as much as 2–5°C persists as late as 10,000 years AP. The “out‐year” projections are larger than Milankovitch effects occurring over the same interval, indicating that unrestricted emissions could lead to conditions in which anthropogenic warming dominates climate variation for the next 10,000 years.
The effect of low‐temperature oxidation on large multi‐domain magnetite
Authors: Cui Yulong , Verosub Kenneth L. , Roberts Andrew P.
Published: February 2004

Natural samples of oxidized and unoxidized magnetite have been used to study the effect of low‐temperature oxidation on magnetic domain state. All of the magnetites studied were large multi‐domain (MD) grains, ranging in size from 53 µm to at least 250 µm. Hysteresis data typical of MD grains are obtained from unoxidized magnetite samples while data from partially oxidized samples are characteristic of pseudo‐single domain (PSD) grains. Our results demonstrate that low‐temperature oxidation can seriously affect the magnetic properties of magnetite by significantly increasing the PSD‐MD threshold size. The presence of a suppressed Verwey transition at 118 K in the oxidized samples indicates that the oxidation may only be surficial and that there may exist a core of magnetite under the maghemitized surface shell. We suggest three possible mechanisms for the observed PSD‐like behavior. First, the magnetite core could be reduced sufficiently in volume to make it a PSD grain, independent of the surficial maghemite. Second, internal stress in the composite grain due to lattice mismatches between the magnetite core and maghemite rim will increase the domain wall energy and make it more difficult to add walls for a given grain size. Coupled with a reduced volume of the magnetite core, this could give rise to PSD‐like behavior. Third, the composite grain could be a mixture of SD maghemite and MD magnetite which gives rise to bulk PSD‐like properties. Our results have potentially important implications for paleomagnetic records because they provide a mechanism whereby a stable chemical remanent magnetization can be acquired by MD grains in sediments and igneous rocks.
The ionospheric signature of the cusp: A case study using Freja and the Sondrestrom radar
Authors: Nilsson Hans , Kirkwood Sheila , Eliasson Lars , Norberg Olle , Clemmons James , Boehm Manfred
Published: February 2004

Radar measurements in the cusp region, in close conjunction with the Freja satellite, show evidence of the ionospheric signature of the cusp. The intense low‐energy fluxes of ions and electrons associated with the cusp, and seen with the satellite, produce a distinct region of enhanced electron density and electron temperature in the ionospheric F‐region. The ionization due to the precipitating ions is rather weak, of the same order of magnitude, and maximizing at the same altitude, as the solar EUV ionization. That due to the electrons is much stronger, maximizes at higher altitude and is clearly identifiable in this case. This is partly because of the unusually high altitude of the cold, EUV and convection controlled F‐region, creating a distinct height difference as compared to the precipitation region, and partly because ion outflow prevents the cold daytime plasma from convecting into the precipitation region. A narrow region of high ion temperatures most likely indicating strong electric fields is seen within the precipitation region but is not coincident with the most intense precipitation. The equatorward boundary of the precipitation region is seen to move equatorward, while the convection of the plasma within the region is poleward.
Freja multiprobe observations of electrostatic solitary structures
Authors: Dovner P. O. , Eriksson A. I. , Boström R. , Holback B.
Published: February 2004

Various electrostatic solitary structures are observed by the Freja satellite in the upper ionosphere in the auroral zone. The use of multiple probes makes the determination of their propagation characteristics possible. Some of them are possibly similar to the solitary waves and weak double layers previously observed in the magnetosphere, but the Freja examples move much slower. Their size is less than 100 meters. Another type is the lower hybrid cavities, density depletions with a lower hybrid wave packet inside. The depletions are about 5%, and they have little or no speed relative to the ambient plasma in the direction perpendicular to the geomagnetic field. A third type is related to the lower hybrid cavities, but inside the density depletion there is a solitary electrostatic structure, as well as lower hybrid waves.
Use of stable sulfur isotope systematics for evaluating oxidation reaction pathways and in‐cloud‐scavenging of sulfur dioxide in the atmosphere
Authors: Tanaka Noriyuki , Rye Danny M. , Xiao Yitian , Lasaga Antonio C.
Published: February 2004

Sulfur dioxide injected into the atmosphere is most likely oxidized into sulfate. Two major oxidation pathways are possible: 1) a homogeneous pathway involving gas reaction with hydroxyl radicals and 2) a heterogeneous pathway involving aqueous dissolution or aerosol reactions (Figure 1.). The relative importance of these reaction pathways conditions is controversial. Sulfur isotope ratios can be used to quantify the relative importance of these reaction pathways. However, its application was severly hampered by the fact that the isotope fractionation factor for the homogeneous pathway was not known (Caron et. al., 1986; Nriagu et. al., 1987). A significant isotope fractionation in the homogeneous SO2 oxidation is identified for the first time using an ab initio quantum mechanical calculation. By using the sulfur isotope fractionation factors we demonstrate a technique that uses measurements of the sulfur isotope ratio in gaseous SO2, aerosol SO4 and sulfate in wet precipitation to quantify the relative importance of the homogeneous and heterogeneous reaction pathways as well as the in‐cloud scavenging of sulfur dioxide for a set of isotopic observations at New Haven, CT, USA.
Composition and freezing of aqueous H2SO4/HNO3 solutions under polar stratospheric conditions
Authors: Beyer K. D. , Seago S. W. , Chang H. Y. , Molina M. J.
Published: February 2004

The results of laboratory investigations of the freezing behavior of aqueous acid solutions indicate that in the stratosphere H2SO4/H2O aerosol droplets would not freeze at temperatures above the ice frost point in the absence of HNO3; however, in the presence of typical levels of HNO3 liquid sulfuric acid aerosols take up significant amounts of HNO3 and H2O vapors and freeze much more readily. This is a consequence of the very rapid change in composition of the liquid droplets as the temperature drops to within two to three degrees of the equilibrium temperature at which HNO3 and H2O vapors would co‐condense to form a liquid solution. In the high latitude stratosphere this HNO3/H2O ‘dew point’ is typically around 192–194 K at 100 mbar.
1991–1992 GPS measurements across the Nepal Himalaya
Authors: Jackson Michael E. , Bilham Roger
Published: February 2004

In March 1991 35 control points were measured in the collision zone between the Indian and Asian plates using the Global Positioning System (GPS). Twenty‐eight points are located in the Nepal Himalaya, and 7 in S. and E. Tibet. In October 1992, 6 of the Nepal points were remeasured together with 3 bedrock points in Bihar State, India, 5 points in E. Tibet, and one in Urumchi. The average WRMS GPS position repeatability between 1991 and 1992 improved from 8 mm to 5 mm in the north, 16 mm to 7 mm in the east, and 32 mm to 25 mm in the vertical components. Himalayan convergence rates of 20 mm/yr may be resolved to 10% accuracy within 5 years with these uncertainties. Unless improved vertical measurement techniques are introduced many decades must elapse before regional secular vertical motions may be resolved. The 1991.3–1992.8 measurements are consistent with geologically determined Himalayan convergence rates of less than 20 mm/year.
Frequency dependent crustal scattering and absorption at 5–160 Hz from coda decay observed at 2.5 km Depth
Authors: Leary Peter , Abercrombie Rachel
Published: February 2004

A triaxial 10 Hz seismometer at 2.5 km depth in the Cajon Pass borehole near the San Andreas fault in southern California records shear‐wave coda motion from small local events for over 20 seconds duration. The passband of recorded seismic motion is 5 Hz to 200 Hz. To measure the rate of coda energy decay as a function of frequency, we filter the vector velocity seismograms of seven events into five octave‐wide frequency bands (mean frequencies ≈ 7, 14, 28, 56 and 112 Hz) and square the filtered seismograms. The observed energy decay in each passband is well approximated by first and second order scattering plus intrinsic attenuation as formulated by Zeng at al. (JGR 1991). The fits determine two energy decay parameters expressed as inverse lengths, ßscat for scattering and ßintr for absorption. Because the source‐receiver distance is less than the thickness of the upper crust and the receiver is at depth, the direct body wave is uncomplicated by refracted energy and/or surface waves and allows accurate recording of coda energy relative to source pulse energy. The coda/source energy ratio directly defines the scattering attenuation parameter ßscat and voids the need for multiple offset observations. The observed frequency behavior of scattering is ßscat≈f1.3; the intrinsic attenuation parameter has frequency dependence ßintr≈f0.43. Normalized to energy lost per unit cycle (quality factor Q), intrinsic attenuation decreases with frequency, Qintr≈f0.57, while scattering attenuation increases with frequency, Qscat≈1/f0.3 with Qscat > 10Qintr at all observed frequencies.
Electrical conductivity of the continental crust
Authors: Glover Paul W. J. , Vine F. J.
Published: February 2004

Geophysical measurements indicate that the Earth's continental lower crust has a high electrical conductivity for which no simple cause has been found. Explanation usually relies on either saline fluids saturating the pores, or interconnected highly conducting minerals such as graphite, Fe/Ti oxides and sulphides, providing conducting pathways. Attempts in the laboratory to clarify the problem have, hitherto, been unable to recreate conditions likely to be present at depth by controlling the confining pressure and pore fluid pressure applied to a rock saturated with saline fluids at temperatures between 270°C and 1000°C. Here we report conductivity data obtained using a cell designed to make such measurements on rocks saturated with saline fluids. Our results show that the conductivity of saturated samples of acidic rocks is explicable entirely in terms of conduction through the pore fluid whereas the conductivity of saturated basic rocks requires the presence of an additional conduction mechanism(s). We have used the experimental data to construct electrical conductivity/depth profiles for the continental crust, which, when compared with profiles obtained from magnetotelluric observations, demonstrate that a mid to lower crust composed of amphibolite saturated with 0.5 M NaCl shows electrical conductivities sufficient to explain conductivity/depth profiles for the continental crust inferred from geophysical measurements.
Mass flux in the ecliptic plane and near the Sun deduced from Doppler scintillation
Authors: Woo Richard , Gazis Paul R.
Published: February 2004

During the late declining phase of the solar cycle, the tilt of the solar magnetic dipole with respect to the Sun's rotation axis leads to large‐scale organization of the solar wind, such that alternating regions of high‐ and low‐speed solar wind are observed in the ecliptic plane. In this paper, we use Doppler scintillation measurements to investigate mass flux of these two types of solar wind in the ecliptic plane and inside 0.3 AU, where in situ measurements have not been possible. To the extent that Doppler scintillation reflects mass flux, we find that mass flux in high‐speed streams: (1) is lower (by a factor of approximately 2.2) than the mass flux of the average solar wind in the heliocentric distance range of 0.3–0.5 AU, (2) is lower still (by as much as a factor of about 4) than the mass flux of the slow solar wind associated with the streamer belt, and (3) appears to grow with heliocentric distance. These Doppler scintillation results are consistent with the equator to pole decrease in mass flux observed in earlier spectral broadening measurements, and with trends and differences between high‐ and low‐speed solar wind observed by in situ measurements in the range of 0.3–1.0 AU. The mass flux results suggest that the solar wind flow in high‐speed streams is convergent towards the ecliptic near the Sun, becoming less convergent and approaching radial with increasing heliocentric distance beyond 0.3 AU. The variability of mass flux observed within equatorial and polar high‐speed streams close to the Sun is strikingly low. This low variability implies that, as Ulysses currently ascends to higher latitudes and spends more time in the south polar high‐speed stream after crossing the heliospheric current sheet, it can expect to observe a marked decrease in variations of both mass flux and solar wind speed, a trend that appears to have started already.
Structural transformation in Ni‐bearing Na2Si2O5 glass and melt
Authors: Farges F. , Brown G. E. , Calas G. , Galoisy L. , Waychunas G. A.
Published: February 2004

The coordination environment around Ni at minor concentration levels (2 wt. % NiO) in Na2Si2O5 glass and melt (293–1250K) has been investigated by Ni K‐edge X‐ray Absorption Fine Structure (XAFS) spectroscopy. X‐ray Absorption Near Edge Structure (XANES) spectra indicate that both IVNi and VNi occur in the glass, whereas IVNi is dominant in the melt. The average anharmonic Ni‐O distances derived from XAFS spectra of the glass at 293 K and the melt above 1150 K are 2.00 (±0.02) and 1.97 (± 0.02) Å, respectively. The Ni‐O distance in the glass is consistent with a mixture of IVNi and VNi, whereas that in the melt is consistent with dominantly IVNi, suggesting a Ni‐coordination change during glass melting. This major change in Ni coordination indicates significant reorganization of the melt during quenching and crystallization. These observations for a compositionally‐simple melt/glass system may help explain the enrichment of Ni in early‐formed igneous minerals. They also suggest the possibility of a pressure‐induced coordination change around Ni in the mantle which may influence geochemical modeling of the deep Earth.
High‐resolution electromagnetic images of conducting zones in an upthrust crustal block
Authors: Jones Alan G. , Bailey Richard C. , Mareschal Marianne
Published: February 2004

A high‐resolution, controlled‐source, electromagnetic survey in the Kapuskasing region, over exposed deep crustal material upthrust along ramp‐and‐flat geometry faults, reveals a shallow weakly‐conductive layer (5,000–10,000 Ω·m) within a resistive host (50,000–100,000 Ω·m). This layer, at ≈1 km depth, correlates spatially with a zone of enhanced reflectivity, and coincident breaks in both conductivity and reflectivity suggest that a high‐angle fault zone offsets the layer. The cause(s) of this enhanced conductivity is conjectural until this unit is drilled, but the two probable candidates are: (1) electrolytic conduction in saline‐filled porous rocks, or (2) ionic conduction along connected grain‐boundary films of graphite. Or both conduction mechanisms may be operating with the graphite interconnectivity provided by the brines.
A three dimensional study of E region irregularity patches in the equatorial anomaly region using the Chung‐Li VHF radar
Authors: Pan C. J. , Liu C. H. , Röttger J. , Su S. Y.
Published: February 2004

Combining the Spatial and Frequency Domain Interferometry techniques, the three dimensional behavior of the E region Field Aligned Irregularity (FAI) patches are studied via Chung‐Li VHF radar. The echo patches are found to be localized within the radar beam. They are of pancake shape with dimensions in the plane containing the field line but transverse to the radar beam at least one order of magnitude greater than the dimension along the radar beam. A zonal westward drift velocity of the patches is found to be about 90 m/s at 107 km altitude in the night time. Mean Doppler (radial) velocity is about 50 m/s with a broad spectral width of 25 to 35 m/s.
Abrupt decrease of lead concentration in the Mediterranean sea: A response to antipollution policy
Authors: Nicolas E. , Ruiz‐Pino D. , Buat‐Ménard P. , Bethoux J. P.
Published: February 2004

In the Northwestern Mediterranean basin, lead concentrations in the surface waters have halved over the last 10 years. This decrease followed successive limitations of the use of lead additives in gasoline occurred in European countries since 1976 and the progressive use of unleaded fuel. The evolution of lead concentration in the Mediterranean waters is simulated by using a geochemical six‐box model and validated by measurements made since 1983. In this way, it is demonstrated that: i) previous major pollution was essentially lead gasoline derived; ii) international antipollution policy is efficient; iii) the Mediterranean Sea is an important case study area to assess the marine biosphere's response to environmental changes.
Qβ estimates from spectral ratios and multiple lapse time window Analysis: Results from an underground research laboratory in granite
Authors: Feustel Andrew J. , Young R. Paul
Published: February 2004

An experiment to measure quality factor (Q) in‐situ was carried out at the Underground Research Laboratory in Manitoba, Canada using the Spectral Ratio technique and a form of the Mulitple Lapse Time Window Analysis technique. The volume of rock examined measures approximately 30 × 30 × 30 m at a depth of 420 m in Lac Du Bonnet Granite. The site encompases 16 triaxial accelerometers grouted in the bottom of boreholes drilled from access tunnel walls. The source for the seismic pulses was a mechanical hammer placed at the bottom of specially located boreholes. Results from the Spectral Ratio experiment gave S‐wave quality factor (Qβ) of 114 ± 18. Based upon the short duration of the first arrival pulses and low scattered wave energy in the signal coda, we conclude that the Spectral Ratio technique measured the intrinsic attenuation of the rock mass. Further analysis using the more recently developed Multiple Lapse Time Window Analysis gave results for intrinsic Qβ (Qi) of between 85 and 100. Conversely, values for scattering Qβ (Qs) were greater than 800. The high correlation for Qi values between the two methods help to confirm the nature and absolute values of the attenuation, and also support the use of the later technique where spectral ratios cannot be applied.
Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate
Authors: Jensen E. J. , Toon O. B.
Published: February 2004

We have investigated the processes that control ice crystal nucleation in the upper troposphere using a numerical model. Nucleation of ice resulting from cooling was simulated for a range of aerosol number densities, initial temperatures, and cooling rates. In contrast to observations of stratus clouds, we find that the number of ice crystals that nucleate in cirrus is relatively insensitive to the number of aerosols present. The ice crystal size distribution at the end of the nucleation process is unaffected by the assumed initial aerosol number density. Essentially, nucleation continues until enough ice crystals are present such that their deposition growth rapidly depletes the vapor and shuts off any further nucleation. However, the number of ice crystals nucleated increases rapidly with decreasing initial temperature and increasing cooling rate. This temperature dependence alone could explain the large ice crystal number density observed in very cold tropical cirrus.
A simple model of magnetic moment scattering in a field reversal
Authors: Delcourt D. C. , Martin R. F. , Alem F.
Published: February 2004

We examine the nonadiabatic motion of charged particles in a field reversal using a simple centrifugal impulse model. It is shown that, though this model cannot account for long term behaviors, it accurately describes the abrupt magnetic moment change experienced by the particles between two consecutive adiabatic (magnetic moment conserving) sequences. Good agreement is obtained between analytical estimates and trajectory computations. Our analysis also suggests a new pitch angle dependent parameter to characterize the jumps in magnetic moment. Application to particle motion in a cusped field geometry demonstrates that magnetic moment damping and subsequent particle escape can be adequately modeled by means of such centrifugal impulses.
Hybrid simulation of comet Shoemaker‐Levy 9 interaction with Jovian bow shock
Authors: Lipatov A. S. , Sharma A. S.
Published: February 2004

The interaction of the solar wind with comet Shoemaker‐Levy 9 leading to the formation of the cometary magnetosphere and its interaction with the Jovian bow shock is simulated using a one dimensional hybrid code. The mass loading of the solar wind by the cometary ions leads to the formation of a bow shock behind which the plasma density is 2–3 cm−3 and the electron temperature is 4 eV. The interaction of this system with the Jovian bow shock yields local enhancements of the magnetic field and the plasma density by factors of 4‐5 and the electron temperature by 2‐3.
the thickness of upper mantle discontinuities, as inferred from short‐period J‐array data
Authors: Yamazaki Akira , Hirahara Kazuro
Published: February 2004

The thickness of upper mantle discontinuities (at depths around 410 km and 660 km) provides a critical clue to our understanding of deep earth. Since the amplitude of reflected or S‐P converted waves is controlled by the thickness of discontinuities, short‐period studies of such waves may give a fine constraint on the thickness of upper mantle discontinuities. In this study, we analysed short‐period and vertical waveform data from 14 deep events in the Fiji‐Tonga region. The data were obtained from J‐Array, a short‐period and large‐aperture seismic array in Japan. With slant stack analyses of these data, we detected short‐period reflections or S‐to‐P conversions from 410 km and 660 km discontinuities near sources, which implies that both discontinuities are quite sharp. To directly measure the frequency content of these waves, linear slant stacks were made with various frequency pass‐bands (0.2–0.5, 0.5–1.0 and 1.0–2.0 Hz). Synthetic traces were generated for the models with various thicknesses of the 410 km and the 660 km discontinuities. Comparison of slant stacks with synthetic traces indicates that the thickness of both discontinuities is at most 5 km.
Volatility of elemental carbon
Authors: Jennings S. G. , O'Dowd C. D. , Cooke W. F. , Sheridan P. J. , Cachier H.
Published: February 2004

A volatility technique whereby aerosol particles are heated to the relatively high temperature of 860 °C is used to infer the presence of elemental carbon in polluted air masses in the vicinity of the west coast of Ireland. The volume of elemental carbon for submicrometre sized particles contained in the aerosol is estimated from the fall off in number concentration at a critical onset temperature of about 730–735 °C, as also obtained for laboratory carbon ink aerosol. The technique permits determination of the elemental carbon volume percentage of the total fine aerosol volume, and an estimation of the abundance of elemental carbon contained within the black carbon fraction of the atmospheric aerosol. Supplementary black carbon mass concentration measurements were obtained using a thermal method and an aethalometer absorption method. The work suggests that elemental carbon can be identified using the volatility technique and that it can yield size‐segregated information on the fraction of elemental carbon in atmospheric aerosol.
Pioneer and Voyager observations of solar cycle variations in the outer heliosphere
Authors: Gazis P. R.
Published: February 2004

Solar wind measurements from the Pioneer 10, Pioneer 11, and Voyager 2 spacecraft are now available through mid‐1993. These measurements extend our knowledge of the outer heliosphere to heliographic latitudes that range between −10° and 17.5°, and provide insight into the variation with solar cycle of the structure of the distant solar wind. The average temperature, mass flux density, dynamic pressure, and kinetic and thermal energy flux densities varied strongly with solar cycle at the latitude of Pioneer 11 (10° to 17° N), but were almost constant in the vicinity of the solar equator. These parameters may have increased with latitude between the solar equator and 17° N. There was also a short‐term variation in average solar wind parameters near the time of the 1986 solar minimum, when the inclination of the heliospheric current sheet dropped below the latitude of Pioneer 11.
Radiative signatures from impact of comet Shoemaker‐Levy‐9 on Jupiter
Authors: Ahrens Thomas J. , Takata Toshiko , O'Keefe John D. , Orton Glenn S.
Published: February 2004

The visible optical power emitted from the expansion plumes from 0.4 and 2 km diameter fragments of Shoemaker‐Levy are expected to be, ∼25% and comparable to, the visible solar flux reflected from Jupiter, respectively, for several minutes, and could be easily observed by sensors on the Galileo spacecraft. Earth‐based observers can detect these plumes as these expand over the SW limb of Jupiter and come into earth view some minutes after impact!
Mass and penetration depth of Shoemaker‐Levy 9 fragments from time‐resolved photometry
Authors: Boslough Mark B. , Crawford David A. , Robinson Allen C. , Trucano Timothy G.
Published: February 2004

Computational simulations of the first 100 seconds of interaction of Shoemaker‐Levy 9 fragments with the Jovian atmosphere have revealed a potential method for estimating the masses and penetration depths of the individual objects. For sufficiently large fragments, impact‐generated fireballs will rise into line‐of‐sight over the Jovian limb (less than one minute after impact for a 3‐km diameter fragment). It is possible that time‐resolved radiometric measurements from Earth‐ and orbital‐based observatories may detect two different arrivals for each impact: first the shock wave and, a few seconds later, a debris front (fireball). Measurements of one or both arrival times with time resolutions of better than one second will provide information that would place strong restrictions on the range of values of equivalent explosive yield (from which fragment mass can be extracted) and effective penetration depth. We believe that time‐resolved photometry measurements of impact‐induced light emission (impact‐flash signatures) will provide the best means by which Shoemaker‐Levy 9 fragment masses can be determined if they are greater than about 5×1015 g (corresponding to a 1‐km diameter ice sphere).
One‐dimensional hybrid simulations of current sheets in the quiet magnetotail
Authors: Cargill P. J. , Chen J. , Harold J. B.
Published: February 2004

Hybrid simulations (kinetic ions, massless fluid electrons) have been performed of the magnetotail current sheet for parameters characteristic of the quiet magnetotail (υD, bn < 1). Here bn = Bn/B0,υD = (cEy/Bn)/υi,Bn is the north / south (z) magnetic field, B0 the asymptotic value of the tailward (x) field and υi the ion thermal speed, where the magnetospheric coordinate system is used. It is shown that the current sheet is more stable than in previously examined cases with high υD and / or large bn. A clear single reversal in Bx persists over the entire simulation and a By component is created, with a slow rate of growth (hundreds of Ωi−1, where Ωi = eB0/miC). This is many minutes in real time. It is suggested that the waves are due to an electromagnetic instability of the cross‐field ion current.
Moist convective clouds in Titan's atmosphere
Authors: Awal M. , Lunine J. I.
Published: February 2004

We examine moist convection as a plausible mechanism for driving large vertical motions and mixing in the troposphere of Titan. The model used here is based on that ofStoker[1986] for Jupiter — a one dimensional diagnostic model of cumulus clouds developed to calculate cloud temperature and vertical velocity profiles ‐ incorporating an improved treatment of the drag effect of condensate on the buoyancy of the plumes. We find that under conditions plausible for the near surface of Titan, moist convection can occur with vertical velocity in excess of 1–13 m/s but that such plumes occupy only a very small fraction of the surface area of Titan. Nonetheless, we also find that such plumes may be the primary means of moving methane and other trace species from the surface into Titan's upper troposphere.
A global radiative‐convective feedback
Authors: Fowler Laura D. , Randall David A.
Published: February 2004

We have investigated the sensitivity of the intensity of convective activity and atmospheric radiative cooling to radiatively thick upper‐tropospheric clouds using a new version of the Colorado State University General Circulation Model. The model includes a bulk cloud microphysics scheme to predict the formation of cloud water, cloud ice, rain, and snow. The cloud optical properties are interactive and dependent upon the cloud water and cloud ice paths. We find that the formation of a persistent upper tropospheric cloud ice shield leads to decreased atmospheric radiative cooling and increased static stability. Convective activity is then strongly suppressed. In this way, upper‐tropospheric clouds act as regulators of the global hydrologic cycle, and provide a negative feedback between atmospheric radiative cooling and convective activity.
The possible reflection of mantle discontinuities in Pacific geoid and bathymetry
Authors: Wessel Pål , Bercovici David , Kroenke Loren W.
Published: February 2004

Geoid anomalies over the Pacific plate show lineated undulations approximately oriented in the direction of absolute plate motion. Conventional spectral analyses have revealed a broad range of dominant wavelengths, but as filtering is direction‐dependent, results are difficult to interpret. Here, we present a new approach designed to quantify the correlation between the geoid undulations and Pacific plate motion. We calculate the spatial correlation between geoid lineations and arbitrarily oriented, axisymmetric sinusoidal undulations of given wavelength. The pole ( i.e., the orientation) of the sinusoid which maximizes the correlation is determined. The distance between this pole and the Pacific hotspot pole is calculated and represents a measure of how well a geoid lineation of a given wavelength aligns with Pacific plate motion. This distance varies with undulation wavelength and has discrete minima for several wavebands. These minima, moreover, occur at wavelengths whose values are remarkably close to the depths of seismically inferred mantle discontinuities. A similar analysis of available bathymetry corroborates these findings. If these correlations are significant, they suggest that geoid (and bathymetry) undulations are influenced by mantle structure and thus are likely to reflect mantle dynamics.
A Coulomb collision algorithm for weighted particle simulations
Authors: Miller Ronald H. , Combi Michael R.
Published: February 2004

A binary Coulomb collision algorithm is developed for weighted particle simulations employing Monte Carlo techniques. Charged particles within a given spatial grid cell are pair‐wise scattered, explicitly conserving momentum and implicitly conserving energy. A similar algorithm developed by Takizuka and Abe [1977] conserves momentum and energy provided the particles are unweighted (each particle representing equal fractions of the total particle density). If applied as is to simulations incorporating weighted particles, the plasma temperatures equilibrate to an incorrect temperature, as compared to theory. Using the appropriate pairing statistics, a Coulomb collision algorithm is developed for weighted particles. The algorithm conserves energy and momentum and produces the appropriate relaxation time scales as compared to theoretical predictions. Such an algorithm is necessary for future work studying self‐consistent multi‐species kinetic transport.
Meridional distributions of NOx, NOy, and other species in the lower stratosphere and upper troposphere during AASE II
Authors: Weinheimer A. J. , Walega J. G. , Ridley B. A. , Gary B. L. , Blake D. R. , Blake N. J. , Rowland F. S. , Sachse G. W. , Anderson B. E. , Collins J. E.
Published: February 2004

The meridional distribution of NOx in the lower stratosphere and upper troposphere is inferred from 10 flights of the NASA DC‐8 in the northern winter of 1992, along with like distributions of NOy, NOx/NOy, CO, and C2Cl4. In the lowest few km of the stratosphere there is little vertical gradient in NOx over the range of latitudes measured (40°–90°N). There is a substantial latitudinal gradient, with 50 pptv above the pole and 120 pptv near 40°N. In the uppermost few km of the troposphere, background values range from 30 pptv over the pole to 90 pptv near 40°N. On two occasions higher values, up to 140 pptv in the mean, were seen 2–3 km below the tropopause in association with frontal systems. The meridional distributions of CO and C2Cl4 show the same feature, suggesting that the source of the elevated NOx is near the earth's surface.
The procession constant of the Earth: Variations through the Ice‐Age
Authors: Peltier W. R. , Jiang Xianhua
Published: February 2004

We directly calculate the history of variations in Earth's precession constant H that are forced by variations in surface mass associated with late Pleistocene ice‐age glaciation and deglaciation events. Our analyses show that the magnitude of ΔH/H0 is lower than that required to cause the recently hypothesized resonant reduction of the precession period.
Right‐handed ion/ion resonant instability in the plasma sheet boundary layer: GEOTAIL observation in the distant tail
Authors: Kawano H. , Fujimoto M. , Mukai T. , Yamamoto T. , Terasawa T. , Saito Y. , Machida S. , Kokubun S. , Nishida A.
Published: February 2004

An excellent example of an onset of the right‐handed ion/ion resonant instability is observed on October 8, 1993, when the Geotail was in the distant tail of XGSM = −142RE. Preceding and following a passage of a plasmoid, magnetic noises having a right‐hand circular polarity with the frequencies around the proton cyclotron frequency are detected. Especially, the event after the passage lasted for more than 10 min., and the ion plasma in this boundary layer was composed of a tailward streaming cold dense plasma and a warm tailward beam coming presumably from the plasma sheet, drifting at 1000 km/s relative to the former along the field line. We have used this distribution as a source function for a linear Vlasov analysis, and confirmed that the generation mechanism of the waves can well be explained in terms of the resonant interaction with the beam.
Auroral myriametric radiation observed By GEOTAIL
Authors: Hashimoto K. , Matsumoto H. , Kojima H. , Murata T. , Nagano I. , Okada T. , Tsuruda K. , Iyemori T.
Published: February 2004

The nonthermal continuum radiation or Terrestrial Myriametric Radiation (TMR) has been widely received by spacecraft. Some of the TMR are, however, intensified and broadened in frequency in good correlation with the Auroral Kilometric Radiation (AKR). We call such radiation Auroral Myriametric Radiation (AMR), because this is well correlated with the AKR. Correlations between the AMR and the AKR, difference between the AMR and the TMR, and the intensity and the frequency bandwidth of the AMR are discussed. Although the lower cutoff frequencies of the TMR has been widely used to estimate the local plasma frequency, evidence is presented that the two frequencies do not coincide in some cases.
Extra‐tropical QBO signals in angular momentum and wave forcing
Authors: Baldwin Mark P. , Tung Ka Kit
Published: February 2004

Although the period of the equatorial stratospheric quasi‐biennial oscillation (QBO) is approximately 30 months, quasi‐biennial modulation of the extratropical annual cycle may be expected to produce additional spectral peaks at approximately 8.6 and 20 months in the extratropics. Using Northern Hemisphere data for 1964–78 and global data for 1978–93 it is shown that these spectral peaks are robust in both angular momentum and Eliassen‐Palm flux divergence. This spectral signature represents a circulation anomaly in both hemispheres, and implies a dynamical origin to the previously observed similar spectral peaks in column ozone in the extratropics.
Evolutionary conditions in the dissipative MHD system: Stability of intermediate MHD shock waves
Authors: Hada Tohru
Published: February 2004

The evolutionary conditions in the dissipative magnetohydrodynamic (MHD) system are discussed, and the results are applied to argue stability of MHD intermediate shock waves. When dissipative wave modes are included, arbitrary perturbations given to the shock can be expressed as a superposition of outgoing wave modes from the shock: thus, intermediate shocks are evolutionary in dissipative MHD. The matching conditions of incoming and outgoing wave modes at the shock give an under‐determined set of equations, which defines a unique solution when the minimum dissipation principle is imposed.
The uptake of N2O5 onto small sulfuric acid particles
Authors: Hanson D. R. , Lovejoy E. R.
Published: February 2004

The probabilities for N2O5 loss onto sulfuric acid aerosol (60–80 wt % H2SO4, 0.1–0.2 um radius, 230–300K) were measured using a laminar flow reactor coupled to a sulfuric acid aerosol source and a chemical ionization mass spectrometer. The aerosol morphology was extracted from measurements of the aerosol extinction of ultraviolet light (200–370nm) by using Mie theory. The reaction probabilities, γ, are large (0.06–0.12) and are comparable to probabilities measured previously under similar conditions on bulk sulfuric acid surfaces and small aerosol. These measurements confirm that the overall reaction of N2O5 with H2O in/on 60–80% sulfuric acid is fast and the uptake is due to loss very close to the liquid surface.
Correlation of ozone loss with the presence of volcanic aerosols
Authors: McGee Thomas J. , Newman Paul , Gross Michael , Singh Upendra , Godin Sophie , Lacoste Anne‐Marie , Megie Gerard
Published: February 2004

Statistically significant reductions of ozone compared to a climatological profile have been measured above the Observatoire de Haute Provence (OHP) in Southern France (43.9°N, 5.7°E) during the months of July and August, 1992. Lidar profiles of ozone, temperature and aerosols were recorded on 25 separate nights during that time. The change in the ozone profile is correlated with the presence of volcanic aerosols from the eruption of Mt. Pinatubo. The total ozone loss amounts to approximately a 10% reduction in the total ozone column over OHP.
Hydrothermal event plumes from the coaxial seafloor eruption site, Juan de Fuca Ridge
Authors: Baker Edward T. , Massoth Gary J. , Feely Richard A. , Embley Robert W. , Thomson Richard E. , Burd Brenda J.
Published: February 2004

The episodic magmatic intrusions that accompany seafloor spreading can profoundly affect the discharge of hydrothermal heat and fluid. A rapid field response to the acoustic detection of seismic activity on the CoAxial segment of the Juan de Fuca Ridge, June/July 1993, provided the opportunity to conduct a unique series of observations of hydrothermal event plumes. Between July 3 and 26 we detected at least three event plumes ranging in plume volume from 1.3 to 4 × 1010 m³, and in excess heat from 2.2 to 12.4 × 1015 J. Two were discovered directly above a new lava extrusion. One of these was first sampled within days of its release, as evidenced by its asymmetric shape, complex structure, and a steadily increasing light attenuation anomaly apparently generated by ongoing precipitation of hydrothermal Fe. We hypothesize that event plumes were produced intermittently in response to successive volcano‐tectonic events that produced pulses in seismic activity between June 28 and July 14.
Effects of two dust storms on solar radiation in the Beijing‐Tianjin area
Authors: Zhou Mingyu , Chen Zhi , Huang Runheng , Wang Qimao , Arimoto Richard , Parungo Farn , Lenschow Donald , Okada Kikuo , Wu Peiming
Published: February 2004

AVHRR albedo data obtained from the NOAA‐11 satellite and chemical data for aerosol particle samples collected in Beijing were interpreted together with meteorological data to study the radiative effects of Asian dust. Compared with the clear‐sky background, the albedo values for the Beijing area during two dust storms in April 1993 increased by 20 to 125%; the direct solar radiation flux at the surface decreased; and the scattered radiation flux at the surface increased. The total solar radiation flux at the ground during the two dust storms decreased by 40% and 10% respectively. Furthermore, the extent of the changes was related to the strength of the dust storms. This paper demonstrates the feasibility of using satellite data to study the radiative forcing of dust storms.
Observation of a monthly variation in global surface temperature data
Authors: Best Clive H.
Published: February 2004

An analysis of global surface temperature data is described. The data originates from the European Centre for Medium Range Weather Forecasting, and covers the period 1986–1991 with a spatial resolution of 1.125 degrees. A global average temperature, Tav, defined as the area weighted average of local temperatures, has been calculated for each day in this time period. In addition to clear seasonal variations, a small monthly oscillation is visible. The data for each year has been fitted to the form Tav=A+Bx+Ccos(Dx+E), where x is the day within the year. Subtracting the fitted seasonal variation from the data isolates the remaining monthly oscillations. The magnitude of this oscillation is about 0.2°K. A Fourier analysis shows the time period to be 30±3 days, and an anti‐correlation between southern and northern hemispheres is observed. The oscillation is found to be stronger towards the polar regions and absent in the tropics. Possible physical and model effects are considered.
A comparison of GCM sensitivity to changes in CO2 and solar luminosity
Authors: Marshall Susan , Oglesby Robert J. , Larson Jay W. , Saltzman Barry
Published: February 2004

We evaluate the equilibrium response of the atmospheric climate to a wide range of systematic variations in carbon dioxide (100 to 1000 ppm) and solar luminosity (±5% of today's value) using the NCAR CCM1. The quantitative responses of each set of simulations are compared using a formal sensitivity analysis. Although the forcings on the climate are different, both temporally and spatially, similarities appear in the climatic response. The results of this analysis have broader implications for the use of simulations of past climates as a guide for possible future climatic change.
Morphological studies of the Ayu Trough, Philippine Sea – Caroline Plate Boundary
Authors: Fujiwara T. , Tamaki K. , Fujimoto H. , Ishii T. , Seama N. , Toh H. , Koizumi K. , Igarashi C. , Segawa J. , Kobayashi K. , Kido M. , Seno T. , Kinoshita H.
Published: February 2004

The Ayu Trough lies on the southern boundary between the Philippine Sea Plate and Caroline Plate. Although this trough may be the best place to study the evolution and kinematics of the Philippine Sea Plate, the origin and evolution of this trough are poorly understood. Our geophysical and morphological surveys in the northern part of the Ayu Trough revealed that the trough shares morphological similarities with slow‐spreading mid‐ocean ridges. The seafloor ages and an average spreading rate of the trough were inferred from the average length of the ridge segments, distribution of sediment thickness, and basement subsidence. Based on the seismic section at 3°30′N, the opening of the trough started about 25 Ma with an average half‐spreading rate 4.1 mm/yr. This spreading rate is much slower than some previous estimates. The present magma production rate and activity of the trough is estimated to be even lower than the 25 m.y. average. The seafloor depth of the trough axis and relief of the axial valley are approximately twice as deep as that of active mid‐ocean ridges. The trough axis valley is covered with sediment in contrast with the axial valleys of active mid‐ocean ridges. Sedimentation at the trough axis shows that the spreading rate has been quite slow for the last 2.5 Ma.
Total sulfur dioxide emissions and pre‐eruption vapor‐saturated magma at Mount St. Helens, 1980–88
Authors: Gerlach T. M. , McGee K. A.
Published: February 2004

SO2 from explosive volcanism can cause significant climatic and atmospheric impacts, but the source of the sulfur is controversial. TOMS, COSPEC, and ash leachate data for Mount St. Helens from the time of the climactic eruption on 18 May 1980 to the final stages of non‐explosive degassing in 1988 give a total SO2 emission of 2 Mt. COSPEC data show a sharp drop in emission rate that was apparently controlled by a decreasing rate of magma supply. A total SO2 emission of only 0.08 Mt is estimated from melt inclusion data and the conventional assumption that the main sulfur source was pre‐eruption melt; commonly invoked sources of “excess sulfur” (anhydrite decomposition, basaltic magma, and degassing of non‐erupted magma) are unlikely in this case. Thus melt inclusions may significantly underestimate SO2 emissions and impacts of explosive volcanism on climate and the atmosphere. Measured CO2 emissions, together with the H2O content of melt inclusions and experimental solubility data, indicate the Mount St. Helens dacite was vapor‐saturated at depth prior to ascent and suggest that a vapor phase was the main source of sulfur for the 2‐Mt of SO2. A vapor source is consistent with experimental studies on the Mount St. Helens dacite and removes the need for a much debated shallow magma body.
Simultaneous spectroradiometry: A study of solar UV irradiance at two altitudes
Authors: Blumthaler M. , Webb A. R. , Seckmeyer G. , Bais A. F. , Huber M. , Mayer B.
Published: February 2004

Spectrally resolved measurements of solar ultraviolet (UV) radiation were made at adjacent mountain top and valley sites, vertically separated by 1 km. Data was collected over a period of 4 days in August 1993 providing simultaneously measured spectra for a range of zenith angles with both sites in direct sunlight and less than 2 octas of cloud cover. As there was no snow cover the local albedo was similar at both sites. Irradiances at the mountain site were 9% higher than the valley at 370 nm, increasing gradually to 11% at 320 nm. Across the UVB waveband the altitude effect increased dramatically to 24% at 300 nm. The magnitude of the altitude effect was independent of zenith angle, within the measurement accuracy, for the range z = 30°–70°. These measured differences between the mountain and valley station can be interpreted by model calculations using the corresponding differences in air pressure, column ozone and aerosol content.