bluuebunny/crossref_metadata_2025 huggingface dataset:
Motions of the SL9 impact clouds
Authors: Sanchez‐Lavega Agustin , Lecacheux J. , Colas F. , Gomez J. M. , Laques P. , Miyazaki I. , Parker D. C.
Published: February 2004

A large number of CCD images of the SL9 impact clouds in the visible from July to October 1994 has allowed us to study the morphological changes and motions of the impact clouds. Our measurements show the existence of at least three different kind of motions: (1) Eastward expansion during the first two days of the largest impact regions (K, L, G) with velocities in the range from 36 to 60 m/s; (2) Clouds that act probably as passive tracers of the stratospheric flow (velocities in the range −15 to 20 m/s); (3) Local motions of the cloud elements with meridional components, sometimes related to the interaction with anticyclonic ovals in nearby latitudes (velocities ∼ 20 m/s). The average zonal velocity relative to System III of the cores of impacts E, A, C, W, K, L, G, R, Q1 and H was (up to 18 August) u = −1.7±1.0 m/s with an average jovicentric latitude of −43.8°±0.4°.
Collision of Schoemaker‐Levy 9 fragments A, E, H, L, Q1 with Jupiter: Mid‐infrared light curves
Authors: Lagage P. O. , Galdemard Ph. , Pantin E. , Jouan R. , Masse P. , Sauvage M. , Olofsson G. , Huldtgren M. , Nordh L. , Belmonte J. A. , Regulo C. , Espinosa J. M. Rodriguez , Vidal L. , Mosser B. , Ulla A. , Gautier D.
Published: February 2004

Light curves of the 12 µm emission following the collision of Shoemaker‐Levy 9 fragments A, E, H, L, Q1 with Jupiter are presented. Impacts F, P2, Q2, T, U were monitored, but not detected. The observations were carried out with the Saclay CAMIRAS camera mounted on the 2.56 m Nordic Optical Telescope located at La Palma (Canary Island, Spain).

Of particular interest is the light curve of the L impact (the brightest impact), where 3 different regions can be observed. A precursor flash (the debris cloud rising above the limb) is detected about 1 min 30 s after the detection from the Galileo spacecraft. Twelve minutes later, a huge infrared spot at a temperature of about 700 K appears at its peak intensity: 13 000 Jy. A new change of behaviour is observed 20 min after impact: a secondary bump appears, after which the flux decreases at a slower rate. Light curves of impacts Q1, H, E and A, up to more than one order of magnitude fainter than the L impact, are quite similar.

Ballistic re‐entry of dust‐gas in the atmosphere must be considered in the interpretation of the IR spot.
Magnetic‐quadrupole source of Neptune “high‐latitude” radio emission
Authors: Sawyer C. B. , King N. V. , Romig J. H. , Warwick J. W.
Published: February 2004

We study the occultation of the dominant X‐mode component of Neptune's smooth “high‐latitude” emission. A dipole magnetic model relates the frequency dependence of observed times of maximum emission to radio‐source locations. Dipole‐based analysis leads to seemingly convincing auroral sources. Yet multipole models of Neptune's complex magnetic field yield quite different results. Steep slopes on each constant‐field radio‐source surface explain the radio cutoff at the corresponding gyrofrequency. With the observed sense of circular polarization, the modeled radio horizon at occultation locates the radio source at a low‐latitude magnetic quadrupole rather than in the expected auroral region.
Spectral analysis of harmonic tremor signals at Mt. Semeru Volcano, Indonesia
Authors: Schlindwein Vera , Wassermann Joachim , Scherbaum Frank
Published: February 2004

A detailed spectral analysis of tremor signals recorded at Mt. Semeru volcano, Indonesia, in October 1992 by the German‐Indonesian Volcano Expedition (GIVE'92) reveals clearly harmonic spectra containing up to 11 integer harmonics. The spectral features can be explained by any rhythmically pulsating source producing a temporarily stable source signal. As one realisation of this concept we model the source as a resonating gas volume, generating seismic signals similar to the sound generated in a recorder.
Simulation of geomagnetic storms during the passage of magnetic clouds
Authors: Chen James , Slinker Steven , Fedder Joel A. , Lyon John G.
Published: February 2004

The response of the Earth's magnetosphere to the passage of interplanetary magnetic clouds is simulated using a three‐dimensional magnetohydrodynamic (MHD) model. The input solar wind condition is given by the magnetic field, particle density, and plasma flow calculated from a model magnetic cloud. The cross‐polar potential (Φp), Joule heating and electron energy precipitation into the polar cap are calculated. Synthetic magnetic indices Dst* and AE* are defined to serve as surrogates for the usual Dst and AE indices, respectively. We demonstrate that Φp² provides a good predictor of the energy deposition into the ionosphere during storm conditions and that Dst* and AE* behave qualitatively similarly to Dst and AE.
Midlatitude lidar backscatter conversions based on balloonborne aerosol measurements
Authors: Jäger Horst , Deshler Terry , Hofmann David J.
Published: February 2004

Aerosol size distributions derived from balloon‐borne particle counter data from Laramie, WY, are used to calculate ratios of extinction, mass, and surface area to lidar backscatter at the widely used lidar wavelength of 532 nm. The results cover the range of the stratospheric aerosol layer from the tropopause to 30 km. These ratios may be used to infer particle extinction, mass, and surface area from midlatitude lidar backscatter data for the period late 1979 to 1993. This period includes the major volcanic eruptions of El Chichón and Pinatubo. The wavelength dependence of aerosol backscatter in the visible was calculated for the period 1991 to 1993 to allow conversions of the results to other lidar wavelengths. The wavelength dependence is similar to estimates from southern hemisphere midlatitude measurements indicating that these conversions may also be applied to southern hemisphere midlatitude lidar measurements.
Geoid data and thermal structure of the oceanic lithosphere
Authors: Richardson W. Philip , Stein Seth , Stein Carol A. , Zuber Maria T.
Published: February 2004

A long‐standing question is whether old oceanic lithosphere continues cooling as the boundary layer of a halfspace or approaches thermal equilibrium, as modeled by a finite thickness plate. Although the latter is the most direct inference from seafloor depths and heat flow, other explanations have been proposed. We investigate this issue using published results for the derivative of the oceanic geoid with age estimated from geoid offsets across fracture zones. Such data have not been used extensively in analyses of the thermal evolution of the lithosphere, primarily because they are inconsistent with two commonly used thermal models: a halfspace or a 125‐km‐thick plate. Recent studies, however, find that depth and heat flow data are better fit by a thinner (95 km) plate model. We thus compile published geoid slope results, and find that these data, though scattered, can discriminate between the models. Geoid slope changes with age, rather than being constant as predicted for a cooling halfspace. This variation is greater than predicted for a thick plate and is better fit by a thin plate. Geoid data should thus be useful for improving thermal models of the lithosphere.
Crustal accretion model for Iceland predicts ‘cold’ crust
Authors: Menke William , Sparks David
Published: February 2004

We present a self‐consistent crustal accretion model of Iceland that includes heat and mass transfer between an upwelling, melting mantle and an accreting, cooling crust. This models predicts sub‐solidus crustal temperatures that are consistent with seismic estimates of the maximum depth of earthquake hypocenters and mid‐crustal shear wave quality factors, and with geothermal estimates of surface heatflow.
Coronal streamers and fine scale structures of the low latitude corona as detected with Spartan 201‐01 White Light Coronagraph
Authors: Guhathakurta Madhulika , Fisher Richard R.
Published: February 2004

The solar corona was observed with an externally occulted White Light Coronagraph carried on the SPARTAN 201‐01 spacecraft for a 47 hour period beginning on April 11, 1993. At this phase of the descending solar magnetic activity cycle there were well developed coronal helmet streamers located over both the east and west limbs of the sun. Of additional interest in the SPARTAN data are the finer scale streamer structures observed in the low latitude corona which are partially resolved by the SP201‐01 instrument. The purpose of this investigation was to determine the physical and morphological characteristics of the streamers and the fine scale ray structures observed in the region between streamers. A comparison of these low latitude rays with the polar rays observed in the north and south polar holes during the same flight suggest that they have similar morphology and physical characteristics.
Velocity structure of the Northern Baikal Rift, Siberia, from local and regional earthquake travel times
Authors: Petit Carole , Déverchère Jacques
Published: February 2004

The velocity structure of the upper lithosphere in the Northern Baikal rift (NBR), Siberia, is analyzed in order to bring some constraints on the early stages of continental rifting. A simultaneous hypocenter‐velocity inversion is performed using a set of local and regional seismological data recorded in the NBR. First‐arrival times of 3,492 direct and refracted P and S waves allow to investigate the crustal velocity structure and the Moho geometry. Results of inversion reveal an unbalanced crust made of two adjacent parts of different thickness, delimited by a rather sharp discontinuity following approximately the northern edge of the rift zone. This structure is interpreted as the result of ante‐rift deformation phases, creating a weakened zone where rifting deformation may easily occur. Oblique rifting is invoked to explain the formation of sedimentary basins without significant crustal thinning at depth.
Atmospheric reactions and ultraviolet and infrared absorptivities of nitrogen trifluoride
Authors: Molina Luisa T. , Wooldridge Paul J. , Molina Mario J.
Published: February 2004

Nitrogen trifluoride is found to be stable towards photo‐oxidation reactions that limit the atmospheric lifetimes of many gaseous species. Reactions with species such as OH and HO2 are thermodynamically unfavorable. The reaction with O3, while thermodynamically favorable, is found to be too slow to be of atmospheric importance. Measurements of the NF3 absorption cross‐sections from 180 to 250 nm yield values that are smaller than those previously reported, and indicate an atmospheric lifetime against photodissociation in the stratosphere of about seven hundred years. In addition, the infrared band strengths were determined in order to enable estimates of greenhouse warming potentials. A slow reaction with aqueous Fe2+ was observed at room temperature; it could provide an additional destruction mechanism in the environment.
Observation of lump structures in the nocturnal atmospheric boundary layer with Doppler sonar and Raman lidar
Authors: Rao M. P. , Casadio S. , Fiocco G. , Lena F. , Cacciani M. , Calisse P. G. , di Sarra A. , Fuà D.
Published: February 2004

Atmospheric lump structures were observed at Rome during two nights in the summer of 1994 by a tri‐axial Doppler sodar operating in monostatic mode. They appeared on sodar facsimile records at height ranges between 300 and 800 m for several hours each night. The vertical velocities within the lump structures ranged around ±2 m/sec. Their occurrence was found to increase as the nights progressed. A Raman lidar, which was also simultaneously operated, provided high‐resolution water vapor profiles. The sodar‐derived wind profiles confirmed the presence of sea breeze during both nights while the water vapor mixing ratio showed steep gradients at the height of lump structures. The analysis of the two data sets provided evidence that the lumps had originated, in an otherwise neutral atmosphere, from small‐scale temperature fluctuations generated in isolated regions due to thermodynamical processes of water vapor by way of condensation and re‐evaporation.
A non‐flux corrected transient CO2 experiment using the BMRC Coupled Atmosphere/Ocean GCM
Authors: Colman R. A. , Power S. B. , McAvaney B. J. , Dahni R. R.
Published: February 2004

A transient CO2 experiment has been performed with the BMRC coupled atmosphere ocean General Circulation Model (GCM). No flux corrections were used in the experiment. A roughly linear temporal increase in global surface temperature is found in response to the CO2 increase. The rate of increase is consistent with the (relatively low) equilibrium response found previously using the Atmospheric GCM and a simple ocean. Ocean surface temperatures increase more at mid latitudes than at high northern or southern latitudes where heat is sequestered into the deep ocean. Despite the secular climate drift which occurs in the model, the major patterns of atmospheric and oceanic temperature change are similar to changes noted elsewhere (from flux corrected models). This adds further support to the main conclusions drawn from transient CO2 experiments performed elsewhere with coupled GCMs.
Magnetic field observations of the 1.3‐year solar wind oscillation
Authors: Szabo Adam , Lepping Ronald P. , King Joseph H.
Published: February 2004

A 1.3‐year oscillation in the IMP‐8 and Voyager 2 solar wind plasma radial speed observations for the period of 1987–94 was recently reported [Richardson et al., 1994]. The same periodicity is identified for the same time period in the North‐South component of the interplanetary magnetic field at 1 AU when studied with a dynamic power spectrum. This observation sheds new light on the nature of these unusual oscillations.
Signature of the transition zone in the tomographic results extracted through the Eigenfunctions of the two‐point correlation
Authors: Balachandar S.
Published: February 2004

Seismic tomography (Tanimoto 1990, Su & Dziewonski 1991 and Masters et al. 1992) has provided detailed three‐dimensional map of the shear wave velocity in the Earth's mantle. These tomographic results when characterized by the radial correlation function (Jordan et al. 1993) shows no signature of the mantle transition zone. The radial correlation function and associated radial correlation length are subsets of the entire two‐point correlation and therefore here we propose an optimal characterization of the two‐point correlation in terms of its eigenfunctions. It is shown that the eigenrepresentation of the tomographic data converges rapidly and that the most energetic eigenfunctions reveal the signature of the mantle transition zone.
Effect of hydrostatic pressure on viscous remanent magnetization in magnetite‐bearing specimens
Authors: Kelso Paul R. , Banerjee Subir K.
Published: February 2004

Rocks at depth in the crust acquire a viscous (i.e., time‐dependent) magnetization under the pressure‐temperature conditions at which they reside. There have been numerous studies on the effect of temperature on viscous magnetization but little work has been performed on the effect of hydrostatic pressure. We have studied viscous remanent magnetization at 22°C in a 0.1 mT field at 0.1 and 100 MPa for natural and synthetic multidomain magnetite. The viscous remanent magnetization was found to increase nearly linearly with log(time) at both pressures. There was little change in the rate of viscous acquisition between 0.1 and 100 MPa over the multidomain grain size range studied. Thus for rocks buried at depth in the earth the enhancement of magnetic viscosity by thermal fluctuations will dominate over effects due to hydrostatic pressure.
The June 9 Bolivia and March 9 Fiji Deep Earthquakes of 1994: II. Geodynamic implications
Authors: Giardini Domenico , Lundgren Paul
Published: February 2004

The June 9, 1994 Bolivia earthquake (Mw = 8.2) occurred in the pronounced bend in the morphology of the deep South American slab, where several dynamic arguments can be put forward to explain the apparently anomalous mechanism and the horizontal fault plane; the size of the event is huge but expected when the regional seismicity of the whole century is considered. The March 9, 1994 Fiji earthquake (Fiji = 7.5) suggests that a new mode of seismic deformation is active in the northernmost termination of the Tonga‐Fiji slab, cutting across the dense cluster of seismicity of the last 30 years; the size of the event is probably close to the largest to be expected over a century in this area, having the steepest frequency‐moment distribution of all global deep seismicity.
Grain size dependence of eolian saltation lengths during snow drifting
Authors: Maeno N. , Nishimura K. , Sugiura K. , Kosugi K.
Published: February 2004

Eolian saltation, a primary process in the transport of fine granular material by wind, produces a variety of geophysical effects on Earth and other planetary surfaces. Wind‐tunnel experiments were carried out to investigate the dependence of saltation on grain size. The saltation length of snow particles was estimated at size intervals of 0.05 mm in diameter by measuring local vertical mass fluxes in 17 snow collectors arrayed at the lee end of the snow surface. The measured mean saltation length of snow particles of 0.01–1 mm in diameter ranged from 0.1 to 1.0 m at wind velocities of 5–10 m/s. Mean saltation length decreased with increasing diameter and decreasing wind speed. We suggest that the probability of the saltation length of a particle at each diameter is described by a monotonically decreasing distribution function, that is, the shorter the saltation length, the higher the frequency of its occurrence. One ramification of this distribution is that the mean saltation length does not imply the dominance of saltating particles of this length.
Recent uplift of the Alban Hills Volcano (Italy): Evidence for magmatic inflation?
Authors: Amato A. , Chiarabba C.
Published: February 2004

First‐order leveling surveyed in 1951 and 1994 along a line across the Alban Hills volcano reveals maximum vertical uplift of 30 cm (average of 7 mm/yr) in the region of geologically recent (0.020–0.030 Ma) explosive activity. The uplifted region corresponds to an area where seismic activity is concentrated, at depths of 3–6 km. Uplift exceeding 10 cm is observed over a 14‐km wide zone in the center of a 40‐km long line, with the deformation tapering to zero at both ends of the line. Data from a few sparse, older benchmarks measured in 1891 and 1927 suggest that the deformation in the first half of this century was very small compared to the period 1951–1994. The observed uplift, together with increased seismic activity, suggest that recent magma injection has occurred in the upper crust beneath the Alban Hills volcano.
Heating of the lower ionosphere electrons by electromagnetic radiation of lightning discharges
Authors: Nickolaenko A. P. , Hayakawa M.
Published: February 2004

An analysis is performed on the heating of electrons in the lower ionosphere due to the electromagnetic radiation from vertical and horizontal lightning discharges. Disturbances of the electron temperature in the daytime ionosphere may exceed 50° K for vertical strokes and 100° K for horizontal lightning discharges. The association of this analysis to some other related phenomena, is finally discussed.
Zonal wavenumber determination of the semi‐diurnal oscillation in the midlatitude upper atmosphere from single‐station optical measurements
Authors: Hernandez G.
Published: February 2004

Single station optical observations of the motions of the midlatitude upper atmosphere at Fritz Peak (39.88°N, 105.5°W), using the [OI] 17924K (557.7 nm) emission line as a tracer, are employed to experimentally determine the zonal wavenumber character and direction of travel of the observed oscillations of 12‐hr periodicity. The results show that this 12‐hr oscillation is westward traveling and of zonal wavenumber character two, and they describe a solar migrating semidiurnal tide.
The SEPAC artificial aurora
Authors: Neubert Torsten , Burch J. L. , Mende S. B.
Published: February 2004

The Space Experiments with Particle Accelerators (SEPAC) and the Atmospheric Emission Photometric Imager (AEPI) were flown on the ATLAS‐1 shuttle mission in the spring of 1992. In a series of artificial aurora experiments, SEPAC injected electron beam pulses (6.25 keV, 1.2 A) into the Earth's upper atmosphere while the AEPI camera recorded optical emissions in white light continuum and 4278 Å. The intensity, overall size, and structure of the artificial auroras have been compared to results from a two‐stream code which models collisional and transport properties of natural and artificial electron beams. Using the curvature of the magnetic field to resolve the altitude dependence of observed optical emissions, it is found that the beam reaches 110–130 km altitude and excites emissions at intensities that are consistent with model calculations (1 kR). However, it is also concluded that the near‐field intensity (5 kR) exceeds model estimates by one order of magnitude. It is argued that this unexpected enhancement is caused by emissions generated within the first 10's of kilometers of the Orbiter by suprathermal electron fluxes at levels that are orders of magnitude larger than predicted by the purely collisional model. It is suggested that the enhanced flux is due to wave‐particle interactions heating the ambient plasma.
The sliding wing crack—again!
Authors: Jeyakumaran M. , Rudnicki J. W.
Published: February 2004

We present accurate numerical calculations for the opening and extension of tensile wing cracks driven by sliding on an oblique crack with Coulomb friction. In contrast to previous analyses, the portions of the crack system that are open or closed and slipping or stuck are determined as part of the solution. Calculations reveal that reduction of the compressive normal stress accompanying opening of the wing cracks causes considerable opening of the sliding crack providing an additional component of macroscopic dilatancy. Immediately upon unloading the central portion of the planar crack is locked but there is closure of the open portions of the crack causing a decrease in inelastic volume strain as observed in laboratory experiments. Reverse slip begins near the open portion of the crack and spreads toward the center. The rate of decrease of inelastic volume strain with axial stress remains small, causing an apparent “dead band” until the axial stress is sufficiently reduced to cause reverse slip on the entire crack. This apparent “dead band” is small because opening reduces the compressive normal stress on the planar crack. These calculations demonstrate that the behavior of this model is consistent with measurements of inelastic volume strain and acoustic velocity on laboratory rock specimens.
Noctilucent cloud observations over Greenland by a Rayleigh lidar
Authors: Thayer J. P. , Nielsen N. , Jacobsen J.
Published: February 2004

We report on the detection of noctilucent clouds (NLCs) by a Rayleigh lidar system located on the west coast of Greenland during operations in July and August 1994. The lidar detected NLCs in the zenith on three nights (July 28–29, July 31–August 1, and August 4). The lidar measurements are presented at temporal (1 minute) and spatial (192 meter) resolutions exceeding previously reported lidar measurements of NLCs and reveal significantly more structure in the clouds. Unique cloud features are observed for each night NLCs were detected. Because of the large backscatter ratio associated with NLCs, the volume backscatter coefficient for the cloud particles can be determined more accurately from the lidar signal than the backscatter ratio as the upper mesospheric molecular number density is negligible in the volume backscatter coefficient calculation. The volume backscatter coefficient values determined from the three nights of NLC observations would be classified by current models as moderate to extreme. The extreme backscatter from NLC measurements on August 4 tests the assumptions used in existing models.
The June 9 Bolivia and March 9 Fiji deep earthquakes of 1994: I. Source processes
Authors: Lundgren Paul , Giardini Domenico
Published: February 2004

We examined the source characteristics of the 1994 deep earthquakes of Bolivia (June 9) and Fiji (March 9) over a period range of 1–1000 s using moment tensor and body wave analyses. Moment tensor inversions from 100–1000 s reveal that these two earthquakes were essentially point sources at very long period with insignificant isotropic and non‐double couple components with scalar moments Mo = 2.56 × 1021 Nm for the Bolivia and Mo = 0.26 × 1021 Nm for the Fiji earthquakes. Body wave analysis for the Bolivia event reveals a 45 s duration, a nearly linear E‐NE 1 km/s rupture on the subhorizontal focal mechanism plane giving a stress drop Δσ = 114 MPa. For the Fiji earthquake we find a change in focal mechanism and a linear 3 km/s rupture plunging shallowly to the north on the steep dipping nodal plane with a duration of at least 20 s and Δσ = 14 MPa. Both ruptures propagated parallel their null (σ2) axis and suggests that their width is controlled by the thickness of the seismogenic volume in deep slabs.
Rupture history of the Great Bolivian Earthquake: Slab interaction with the 660‐km discontinuity?
Authors: Estabrook Charles H. , Bock Günter
Published: February 2004

Teleseismic body waves of the great Bolivian earthquake of June 9, 1994 are analyzed to determine the focal parameters and rupture history. Broadband seismograms reveal a complex rupture process: A small initial event (Mw 7.2) was followed about 10 s later by a large moment release pulse of about 40 s duration. Focal mechanisms determined for the mainshock indicate normal faulting with one very shallow NE dipping plane. Azimuthal variation in body‐wave displacement pulse widths suggest northward rupture. From master event and body‐wave inversion, the main moment release is located 25–50 km NE of the initiation point at about 650‐km depth with only small depth variations between the initial and main event. This suggests that rupture was N directed on the near‐horizontal plane. Because the slab along other parts of the Andean arc at about 600‐km depth dips steeply, a sub‐horizontal plane may imply shearing perpendicular to slab dip. Downdip compression on a sub‐horizontal plane would then imply that the slab does not penetrate the 660‐km seismic discontinuity, but rather, is being sheared out to the NE. This interpretation is not unique as other scenarios are also possible. Such an event immediately above the 660‐km discontinuity suggests massive deformation above the discontinuity with no smooth slab penetration into the lower mantle.
Optical determination of the vertical wavelength of propagating 12‐hour period upper atmosphere oscillations
Authors: Hernandez G. , Wiens R. , Lowe R. P. , Shepherd G. G. , Fraser G. J. , Smith R. W. , LeBlanc L. M. , Clark M.
Published: February 2004

Vertical wavelengths of propagation of the 12‐hour oscillation of the upper atmosphere have been optically determined from measurements of horizontal motions derived from the Doppler shifts of [OI] at 557 nm and OH(6–2) at 840 nm and from the [OI] and OH(8,3) heights of emission measured by the WINDII experiment. These determinations, at 43.98°S, 170.42°E, have established the existence of a large, brief, yet persistent, enhancement in the vertical wavelength of propagation near the austral autumn equinox. The typical vertical wavelengths of oscillation during the year are in the range 20 km to 40 km, except during the brief period near the austral autumn equinox when they increase to about 100 km. These findings indicate a change in the atmospheric structure at those heights, favoring the presence of longer vertical wavelength modes near the austral autumn equinox.
Antarctic bottom water formation and the global cadmium to phosphorus relationship
Authors: Frew Russell D.
Published: February 2004

Near‐surface waters close to the Antarctic continent are found to have high cadmium concentrations with respect to phosphorus. These waters have been shown to be the major component in the local formation of Antarctic Bottom Water in this region. It is demonstrated that Antarctic Bottom Water so formed would have a high preformed cadmium to phosphorus ratio. The ventilation of the abyssal ocean with this water would contribute to the observed kink in the global cadmium to phosphorus relationship. This is an important conclusion for paleochemical studies and may account for part of the discrepancy between cadmium and carbon‐13 paleochemical tracers observed in the Southern Ocean.
Near‐IR emissions in the upper Jovian atmosphere after SL‐9 impact: Indications of possible northern counterparts
Authors: Schulz R. , Encrenaz Th. , Stüwe J. A. , Wiedemann G.
Published: February 2004

The evolution of the Jovian atmosphere as a result of the impact of SL‐9 was monitored in the near‐IR at the 3.5‐m New Technology Telescope at ESO, La Silla, from July 22–31, 1994. At the beginning of the observational run the spectra around 3.5 µm show enhanced H3+ emissions at −44° and +44° latitude, which are distributed similarly in longitude. Later, most of the H3+ emission is present in the northern polar region while it has faded at −44°. In the 2.1 µm range all spectra obtained at −44° lat. show a continuum associated to the impact sites on which in some cases the H2 quadrupole line is indicated. The spatial distribution of the H2 emission in the northern hemisphere does not show a clear correlation to the impact sites.
Photooxidation of CS2 in the near‐ultraviolet and its atmospheric implications
Authors: Goss Lisa M. , Frost Gregory J. , Donaldson D. J. , Vaida Veronica
Published: February 2004

Sequential two photon photolysis of CS2 is discussed. Experiments in our lab and others have shown that photolysis of CS2 and O2 mixtures with light of energies below the SC‐S bond dissociation energy produces OCS and SO2. We explain these results by the two photon sequential absorption and subsequent dissociation of CS2 to CS+S. The implications of this mechanism for the oxidation of CS2 in the atmosphere are discussed. Comparison to the currently accepted OH‐initiated oxidation mechanism suggests that the sequential two‐photon mechanism is too slow to be important in the atmosphere.
Missing chemistry of reactive nitrogen in the upper stratospheric polar winter
Authors: Kawa S. R. , Kumer J. B. , Douglass A. R. , Roche A. E. , Smith S. E. , Taylor F. W. , Allen D. J.
Published: February 2004

Data from the CLAES on UARS indicate that a significant mechanism for production of HNO3 in the middle to upper stratosphere is missing from the chemical reaction set currently used by atmospheric models. Measured HNO3 in the polar vortex is strongly enhanced relative to the extra‐vortex at 1200 K potential temperature (near 3 mbar) in January, 1992. The HNO3 vertical profile shows this enhancement forms a secondary altitude maximum from about 10 to 2 mbar (800‐1500 K). A chemistry/transport model (CTM) simulation of this period produces no increase of HNO3 in the vortex near 3 mbar and no secondary maximum in the HNO3 profile. Furthermore, the CTM produces relatively high N2O5 in the vortex, with a vertical peak near 3 mbar, while both CLAES and ISAMS show a shallow minimum there. The implication of this comparison is that some unmodeled process is acting to enhance HNO3 and reduce N2O5 at high latitudes in the winter middle and upper stratosphere. Heterogeneous conversion of N2O5 to HNO3 on hydrated ion clusters is proposed as a possibility for the missing mechanism.
Automated near‐realtime CMT inversion
Authors: Kawakatsu Hitoshi
Published: February 2004

The Earthquake Research Institute (ERI) of the University of Tokyo has completely automated the process of determining source mechanisms of earthquakes using waveform data. The solutions are automatically distributed using the Internet without being checked. The process is initiated by receipt of e‐mail giving the origin time and location of an earthquake. To determine the source mechanism, we apply the Harvard centroid moment tensor (CMT) inversion method to long‐period body wave data (the portion of the seismogram from the first arrival to the initial surface wave). The method has been successfully applied since October 1993 to all of the major earthquakes in the world for which we received event e‐mail. 108 of the 242 CMT solutions in 1994 were determined within 6 hours of the event, with an average delay of 3.8 hours. For local events (e.g., events around Japan), it is also possible to determine CMT solutions within 30 minutes from the occurrence of the earthquakes, using an efficient dialup data retrieval system operated by ERI.
A modified thermal conductivity for low density plasma magnetic flux tubes
Authors: Comfort R. H. , Craven P. D. , Richards P. G.
Published: February 2004

In response to inconsistencies which have arisen in results from a hydrodynamic model in simulations of high ion temperatures (1–2 eV) observed in low density, outer plasmasphere flux tubes, we postulate a reduced thermal conductivity coefficient in which only particles in the loss cone of the quasi‐collisionless plasma contribute to the thermal conduction. Other particles are assumed to magnetically mirror before they reach the topside ionosphere and therefore not to remove thermal energy from the plasmasphere. This concept is used to formulate a mathematically simple, but physically limiting model for a modified thermal conductivity coefficient. When this modified coefficient is employed in the hydrodynamic model in a case study, the inconsistencies between simulation results and observations are largely resolved. The high simulated ion temperatures are achieved with significantly less heat input, and result in substantially lower ion temperatures in the topside ionosphere. We suggest that this mechanism may be operative under the limited low density, refilling conditions in which high ion temperatures are observed.
Annual and semi‐annual temperature oscillations in the upper mesosphere
Authors: Niciejewski R. J. , Killeen T. L.
Published: February 2004

Fourier transform spectrometer observations of the mesosphere have been performed at the University of Michigan (latitude: 42½ N) on a long term basis. A database of near infrared Meinel hydroxyl spectra has been accumulated from which rotational temperatures have been determined. Harmonic analysis of one‐day averaged temperatures for the period 1992.0 to 1994.5 has shown a distinct annual and semi‐annual variation. Subsequent fitting of a five term periodic function characterizing the annual and semi‐annual temperature oscillations to the daily averaged temperatures was performed. The resultant mean temperature and the amplitudes and phases of the annual and semi‐annual variations are shown to coincide with an emission height slightly above 85 km which is consistent with the mean rocket derived altitude for peak nocturnal hydroxyl emission.
A comparison of the thermal characteristics of active lava flows and forest fires
Authors: Flynn Luke P. , Mouginis‐Mark Peter J.
Published: February 2004

Landsat TM data of active lava flows from Kilauea Volcano Hawaii (7/23/91) and forest fires within Yellowstone National Park (9/8/88) are compared to show the differences in the spectral and spatial distribution of radiance. At visible wavelengths, smoke from forest fires obscures terrain features, while active eruptions show little degassing at breakouts (ruptured lava tubes). Lava flows exhibit a gradual increase in infrared radiance (>2 µm) from the edge of an emplaced flow to the central breakout. The hottest parts of the forest fire (which radiate similar amounts of energy to flow breakouts) are located within 90 m of the edge of the burn scar with the interior portions exhibiting sharp decreases in infrared radiance. The radiance measured at 10.4–12.4 µm relative to that at near‐infrared wavelengths (2.08–2.35 µm) suggests that the surface cracks exposing molten lava anneal proportionately with the progressive thickening of the flow crust, while burn scars, produced by forest fires, cool to pre‐burn background temperatures rapidly with only small areas of high‐temperature embers remaining. These differences will be important for the implementation of an automatic thermal‐anomaly detection system using satellite data.
Recovery of ozone in the lower stratosphere at the South Pole during the spring of 1994
Authors: Hofmann D. J. , Oltmans S. J. , Johnson B. J. , Lathrop J. A. , Harris J. M. , Vömel H.
Published: February 2004

During 1994, springtime Antarctic ozone measured at the south pole did not reach the record lows recorded during the 1993 ozone hole period when a value of 91±5 DU was observed. A low value of 102 DU was recorded on October 5, 1994, but such values were not sustained as in 1993. The recovery of total ozone in 1994 was mainly the result of moderation of ozone destruction in the 10–14 km region, probably related to diminishing stratospheric aerosol from the Pinatubo eruption, and may have also been partially related to disturbance of the vortex earlier than normal. As in 1993, ozone profiles at the minimum showed nearly complete destruction of ozone between 15 and 20 km in 1994. In this region, the rate of decline of ozone in September was at least as fast or somewhat faster than in 1992 and 1993 indicating continuing saturation of the ozone destroying chemistry, which is expected as stratospheric chlorine amounts continue to rise. As in 1993, ozone was again observed to be reduced in the 22–24 km region, suggesting that the ozone hole has now probably extended to a region unaffected prior to 1992.
Solar UV irradiance variability during the declining phase of the solar cycle 22
Authors: Chandra Sushil , Lean Judith L. , White Oran R. , Prinz Dianne K. , Rottman Gary J. , Brueckner Guenter E.
Published: February 2004

The SUSIM (Solar Ultraviolet Spectral Irradiance Monitor) and the SOLSTICE (Solar Stellar Irradiance Comparison Experiment) instruments on the UARS (Upper Atmosphere Research Satellite) have been making continuous measurements of the solar UV flux in the spectral range 115–420 nm since October 1991. This period, characterized as the declining phase of solar cycle 22, shows a transition from near maximum to near minimum solar activity levels. During this period, the solar UV flux at Lyman α decreased by about 45% from a mean solar maximum value of about 9 mW/m², and the integrated solar flux between 200–205 nm decreased by about 5% from a mean value of about 47 mW/m². Using the MgII index as a proxy of solar UV irradiance variability, it is shown that the temporal relationship of the UARS solar Lyman α irradiance and the MgII index during solar cycle 22 is significantly different than during solar cycle 21, inferred from the SME (Solar Mesosphere Explorer) Lyman α measurements. Moreover, during solar cycle 22, the scale factor for solar Lyman α irradiance (% change for 1% change in MgII index) is about 1.5 times larger for long term changes than for changes over the time scale of a solar rotation. Unlike Lyman α, the scale factor for the UV flux in the 200–205 nm wavelength range, is close to unity both for the rotational and longer time scales. The spectral dependence of the two scale factors in the 120–200 nm range is derived from the SOLSTICE data which may be used with the MgII index to estimate the UV irradiance variability in this spectral range for both short and long time scales.
Climate response to radiative forcings by sulfate aerosols and greenhouse gases
Authors: Cox Stephen J. , Wang Wei‐Chyung , Schwartz Stephen E.
Published: February 2004

The annual, global mean radiative forcing for the troposphere‐surface system has been used to rank the global warming influences of atmospheric trace gases. The approach was also used recently to compare the cooling influence of tropospheric sulfate aerosols with the warming influence of greenhouse gases. However, the spatial inhomogeneity of sulfate aerosols (concentrated mainly in the continental Northern Hemisphere) may induce climate responses which differ other than just in sign from those induced by increased concentrations of the more homogeneously distributed greenhouse gases. Here we use a general circulation model to further examine the suitability of global mean radiative forcing as a predictor of differences in global, hemispheric, and regional climate responses to differing spatial and temporal forcing patterns. The calculated responses indicate that changes of the global and annual mean surface air temperature depend only on global average net forcing and are not highly sensitive either to the details of the spatial and seasonal patterns in forcing or to the nature of the forcing (shortwave vs. longwave). Thus in global and annual mean the negative aerosol forcing may be viewed as a scaleable anti‐greenhouse forcing. However substantial responses to nonuniformly distributed aerosol forcing were observed at hemispheric and regional scales. Further, the patterns of response differ from the patterns of forcing, leading to the conclusion that the spatial distribution of all significant forcings must be accurately represented when studying regional climate changes.
Mid stratospheric ozone minima in polar regions
Authors: Austin John , Hofmann David J. , Butchart Neal , Oltmans Sam J.
Published: February 2004

Recent springtime measurements of ozone vertical profiles in polar regions have revealed local ozone depressions of about 25% at altitudes near 30 km. Similar features are also identified in three‐dimensional photochemical model results. The modeled ozone depressions are local and temporary, often associated with stratospheric warming events which transport air from low latitudes, altering its photochemical history. The feature may be a component of the climatology of the region, but occurs less frequently in the model, possibly because of the long‐standing problem of the underprediction of upper stratospheric ozone.
Further evidence of fractal structure in hydraulic conductivity distributions
Authors: Molz Fred J. , Boman Gerald K.
Published: February 2004

Past rescaled range analyses of porosity and hydraulic conductivity (K) distributions have indicated the presence of long‐range correlations in the data typical of the related stochastic functions known as fractional Gaussian noise and fractional Brownian motion [Hewett, 1986; Molz and Boman, 1993]. New K data analyzed herein lend further support to this notion. Horizontal processes that mimic fBm will display a power‐law variogram. The Mandelbrot‐Weierstrass random fractal function is introduced as an analytical model for fBm and used to illustrate several concepts. With the exception of the Hurst coefficient value (H), our analysis supports the existence of fractal‐like K fields similar to those visualized by Neuman [1990, 1994]. Past studies which produced H values greater than or less than 0.5 appear to differ mainly because of the underlying model, fractional motion or fractional noise, that was assumed in the respective analyses.
An heuristic model for sea level rise due to the melting of small glaciers
Authors: Wigley T. M. L. , Raper S. C. B.
Published: February 2004

Ice melt from glaciers and small ice caps (GSICs) is an important component of past and future sea level rise. Projections made to date of future GSIC‐derived sea level rise have used a simple model that has conceptual weaknesses, calibrated using data that have since been revised. Here we devise a more satisfactory model that accounts for regional variations in the altitudinal ranges of the world's glaciers, calibrate it using recent data, and consider the implications for future sea level rise. Because of compensating factors, the new projections are similar to the earlier ones, but their methodological basis is far more sound. Wide uncertainties still remain.
Radial gradients of ion densities and temperatures derived from SWICS/Ulysses observations
Authors: Liu S. , Marsch E. , Livi S. , Woch J. , Wilken B. , von Steiger R. , Gloeckler G.
Published: February 2004

Mean density and temperature gradients of solar wind protons and α particles are derived from SWICS/Ulysses observations between 1.2 and 5.4 AU in the ecliptic plane during declining solar activity. All parameters are sorted in solar wind speed classes. The radial gradients show a similar behavior for both ion species. In the slow solar wind protons as well as α particles are found to expand adiabatically all the way out to many AUs, while in the fast wind ions evolve non‐adiabatically and are heated by interplanetary sources. The α particle to proton temperature and density ratios are also determined. They do not show any clear radial dependence.
The Ulysses south polar pass: Transient fluxes of energetic ions
Authors: Bothmer V. , Marsden R. G. , Sanderson T. R. , Trattner K. J. , Wenzel K.‐P. , Balogh A. , Forsyth R. J. , Goldstein B. E.
Published: February 2004

Using Ulysses low energy telescope (LET) measurements of protons and alpha particles with energies of ∼1–5 MeV/n, we present first observations of transient energetic particle events in the high latitude heliosphere. Three transient particle events with gradual onsets and time durations of several days have been identified in the LET data at heliographic latitudes as high as ∼60°S, at radial distances from the Sun between 3.3–3.6 AU. No transient increases were observed polewards of 60°S. All three of the events were associated with passage of a coronal mass ejection (CME) over Ulysses, and two were associated with the newly identified type of forward/reverse shock pairs in the solar wind caused by over‐expanding CMEs. The largest of the three transient events has also been observed at Earth's orbit, i.e. in the ecliptic. The observations show that energetic particles can be convected into the high latitude heliosphere through CMEs.
The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere
Authors: Forsyth R. J. , Balogh A. , Smith E. J. , Murphy N. , McComas D. J.
Published: February 2004

Between April and November 1994 the Ulysses spacecraft explored heliographic latitudes above 60°S in the southern polar heliosphere and had returned to 20°S by February 1995. We have used hourly averages of the magnetic field measurements made by Ulysses to study the underlying heliospheric field direction. In contrast to data previously reported from lower latitudes, we find that above 60°S neither the mean nor the most probable azimuthal angle of the magnetic field agree with that predicted by the Parker model, the most probable angle being of the order of 24° more tightly wound than expected. The distribution of azimuth angles retains the high degree of asymmetry previously found at lower latitudes causing the mean angle to remain slightly less tightly wound than the prediction. In this high latitude region, the distribution of the meridional (north‐south) angle is found to be symmetric with mean and most probable values close to the Parker prediction.