bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer simulations of pyroclastic flows from dome collapse
Authors: Wadge G. , Jackson P. , Bower S. M. , Woods A. W. , Calder E.
Published: February 2004

We present a method of simulating both the avalanche and surge components of pyroclastic flows generated by lava collapsing from a growing Pelean dome. This is used to successfully model the pyroclastic flows generated on 12 May 1996 by the Soufriere Hills volcano, Montserrat. In simulating the avalanche component we use a simple 3‐fold parameterisation of flow acceleration for which we choose values using an inverse method. The surge component is simulated by a 1D hydraulic balance of sedimentation of clasts and entrainment of air away from the avalanche source. We show how multiple simulations based on uncertainty of the starting conditions and parameters, specifically location and size (mass flux), could be used to map hazard zones.
The 1997 ENSO event and implication for North American Laurentian Great Lakes winter severity and ice cover
Authors: Assel Raymond A.
Published: February 2004

Mild winters and below‐average annual maximum ice cover for the Laurentian Great Lakes occur during strong warm ENSO events. During the six strongest warm ENSO events since 1950 a Great Lakes winter severity temperature index and simulated annual maximum ice cover averaged 1.2°C above and 15% below a 1950–1994 average, respectively. The observed differences between the average of the strong ENSO event years and the base period average are statistically significant.
High‐resolution bathymetry of the East Pacific Rise axial summit trough 9° 49′ ‐ 51′N: A compilation of Alvin scanning sonar and altimetry data from 1991–1995
Authors: Kurras G. J. , Edwards M. H. , Fornari D. J.
Published: February 2004

Bathymetric data acquired during six cruises to the East Pacific Rise crest 9° 49′‐51′N are compiled into a single bathymetric database and used to create high‐resolution bathymetry maps of two geologically and biologically active areas. Scanning sonar and Alvin altimetry were collected during 23 Alvin dives to the P‐vent/Bio9 and Biomarker‐141 areas during 1991–95. Bathymetry data were filtered, edited, and processed as individual dives then combined into a single database for each cruise and statistically evaluated. Cruise data sets were numerically and visually compared and cross‐correlated to known bottom features and fixed seafloor reference markers, then horizontally shifted to establish a consistent database with 3 m vertical and 5 m horizontal resolutions. The compiled and corrected bathymetry was used to produce bathymetric maps of two areas within the axial summit collapse trough; a 2 × 104 m² area around P and Bio9 vents, and a 1.1 × 10³ m² area around Biomarker 141. The resulting detailed bathymetry maps reveal topography dominated by low‐relief volcanic constructional features and post‐eruptive collapse of lobate and sheet lava surfaces.
A very broad‐band stochastic source model used for near source strong motion prediction
Authors: Berge Catherine , Gariel Jean‐Christophe , Bernard Pascal
Published: February 2004

The simulation of near‐source ground motion requires the calculation of ground motion in a very broad‐band frequency range (typically from 10 s to 0.1 s). However, the calculation of complete Green's function is too time consuming for high‐frequency simulations. We present a method to obtain very broad‐band synthetic seismograms, combining the kinematic spectral source model of Bernard et al., [1996], and an algorithm, based on the wavenumber technique of Bouchon and Aki, [1977]. High‐frequency radiations are evaluated with ray theory and a broad‐band dislocation defined on a finely discretized fault plane. The low‐frequency radiations due to the near‐ and intermediate‐fields are calculated with the complete field algorithm on a low‐wavenumber filtered dislocation. This dislocation is defined on a coarse grid over the fault, hence significantly reducing the computing time. We apply this method to compute the ground motion at a station located near an extended fault, where the near‐, intermediate‐ and far‐field radiations are important.
Observed coupling of the mesosphere inversion layer to the thermal tidal structure
Authors: Meriwether J. W. , Gao X. , Wickwar V. B. , Wilkerson T. , Beissner K. , Collins S. , Hagan M. E.
Published: February 2004

Rayleigh lidar observations of mesosphere temperature profiles obtained from 40 to ∼100 km from Logan, Utah (41.7, 111.8 W, altitude, 1.9 km) over 10 nights in late February, 1995, revealed an interesting development between 60 to 75 km of a winter mesosphere inversion layer with an amplitude of ∼20–30 K and a downward phase progression of ∼1 km/hr. The data also showed two altitude regions exhibiting significant cooling of 10–30 K in extent. These were located below and above the peak of the inversion layer, respectively, at altitudes of ∼50–55 km and ∼70–80 km. When these results were compared with the predictions of a global wave scale model (GSWM), the observed thermal mesosphere structure is similar to the computed composite tidal structure based upon the semi‐diurnal and diurnal tides with the exception that observed amplitudes of heating and cooling are ∼10x larger than predicted GSWM values. We suggest that these events over Utah are caused through a localized mechanism involving the coupling of gravity waves to the mesopause tidal structure.
A substorm model with onset location tied to an auroral arc
Authors: Lui A. T. Y. , Murphree J. S.
Published: February 2004

Two important observational constraints on substorm onset theories are that (1) substorm onset occurs on field lines of a pre‐existing auroral arc, and (2) reduction of the cross‐tail current occurs in the near‐Earth magnetotail. Recent progress in linking generation of at least some auroral arcs to field line resonances (FLRs) and current disruption to possibly the cross‐field current instability (CCI) suggests a synergistic combination of these two theories. We suggest that as the cross‐tail current sheet thins to the extent that ions become unmagnetized at the end of substorm growth phase, the equatorial electric field associated with FLRs can amplify significantly the cross‐tail current to exceed the instability threshold. This combined theory naturally accounts for the observational constraints of substorm onset starting on a pre‐existing auroral arc and linking closely with current reduction in the near‐Earth magnetotail. It is compatible with the observation of the most equatorward auroral arc being the most likely one for initial brightening because the cross‐tail current is most intense in its near‐Earth end and is therefore most likely to exceed the unstable threshold for CCI. It is also consistent with auroral precipitation fading to be a common feature before an auroral breakup. Other predictions yet to be tested are that (1) the onset is more favorable for the phase of the resonance in which the resonance‐associated field‐aligned current is directed from the ionosphere to the magnetosphere, and (2) the onset is more favorable poleward of the resonance shell or auroral arc.
Preliminary magnetostratigraphy of a thick eolian red clay‐loess sequence at Lingtai, the Chinese Loess Plateau
Authors: Ding Z. L. , Sun J. M. , Yang S. L. , Liu T. S.
Published: February 2004

Magnetic remanence and bulk susceptibility measurements are reported for a 305‐m eolian loess‐red clay sequence at Lingtai, the Chinese loess Plateau. Polarity zonation defined by about 680 remanence data yields a basal age of about 7.05 Ma for the section, which represents the oldest wind‐blown dust deposited continuously in north‐central China during the late Cenozoic. The resultant magnetostratigraphic scheme implies a nearly linear accumulation rate (about 2.98 cm/ka) of atmospheric dust on the Loess Plateau during the period of 7.05 to 2.58 Ma. Comparison of the bulk susceptibility record with the pedogenic characteristics of the red clay observed in the field suggests that magnetic susceptibility in the red clay is not as useful as in the loess‐soil sequence to indicate summer monsoon variations.
Monitoring cusp/cleft topology using Pc5 ULF waves
Authors: Ables S. T. , Fraser B. J. , Waters C. L. , Neudegg D. A. , Morris R. J.
Published: February 2004

Induction magnetometer data recorded at three closely spaced sites (∼120 Km) in Antarctica (mlat ∼ −75°) have been examined for ionospheric signatures of the cusp/cleft region of the magnetosphere. Crossphase analysis of the 1–10 mHz band, using pure‐state filtering techniques reveal diurnally varying field line resonances embedded in the spectra, while interstation phase lag measurements indicate azimuthal propagation of waves away from local magnetic noon. Using the T89 external field model crossphase measurements are put in the context of diurnally changing field line topology due to compression at the subsolar region and stretching along the dawn and dusk flanks. On six of the eight days of this study we have identify a consistent two dimensional phase pattern projected in the dayside ionosphere, indicating closed field lines thread these sites during periods of low to moderate geomagnetic activity (Kp<3).
Relationship between continuous aerosol measurements and firn core chemistry over a 10‐year period at the South Pole
Authors: Bergin M. H. , Meyerson E. A. , Dibb J. E. , Mayewski P. A.
Published: February 2004

Before ice core chemistry can be used to estimate past atmospheric chemistry it is necessary to establish an unambiguous link between concentrations of chemical species in the air and snow. For the first time a continuous long‐term record of aerosol properties (aerosol light scattering coefficient, σsp, and Ångström exponent, å) at the South Pole are compared with the chemical record from a high resolution firn core (∼10 samples per year) covering the period from 1981 to 1991. Seasonal signals in å, associated with winter minima due to coarse mode seasalt and summer maxima due to accumulation mode sulfate aerosol, are reflected in the firn core SO42−/Na+ concentration ratio. Summertime ratios of σsp and aerosol optical depth, τ to corresponding firn core sulfur concentrations are determined and the ‘calibrations’ are applied to sulfur concentrations in snowpits from a previous study. Results show that σsp estimates from snowpit sulfur concentrations are in agreement with atmospheric measurements while τ estimates are significantly different, which is likely due to the lack of understanding of the processes that mix surface air with air aloft.
Uptake coefficient of charged aerosols—implications for atmospheric chemistry
Authors: Aikin Arthur C. , Pesnell W. Dean
Published: February 2004

Gas uptake onto liquid particles is influenced by the electrical charge on the particle. This charge rearranges the spatial distribution of the dissolved reactant ions, modifying the solute‐solvent reaction at the surface and for some distance into the liquid. This results in a modification of the uptake coefficient. A general expression, applicable to laboratory and atmospheric conditions, is presented. The change in the uptake coefficient is proportional to particle charge and the square of the Debye length within the liquid. It is inversely proportional to the square of the particle radius.
Quasi‐periodic behavior of ion events and wave activity upstream from Jupiter's Bow Shock: Ulysses' observations
Authors: Anagnostopoulos G. C. , Balogh A. , Marhavilas P. K. , Rigas A. G. , Sarris E. T. , Trochoutsos P. C.
Published: February 2004

A new insight into the ways that the Jovian magnetosphere influences the near Jupiter interplanetary space becomes possible thanks to Ulysses' collection of magnetic field, plasma and energetic ion (HI‐SCALE) data during its inbound trajectory (d22–d34, 1992). The most striking new results from the analysis of those data are the following: a) presence of large amplitude (ΔB⟂/B≈1) near plane polarized Alfvén waves upstream from the Jovian bow shock with a period equal to the planet's rotation (∼10h) at times when the Interplanetary Magnetic Field (IMF) was in contact with the bow shock/magnetopause and lay well outside the ecliptic; b) observation of ∼10h quasi‐periodic variation in the ion plasma and energetic ion data up to energies of ∼2 MeV, c) existence of a variation with a period 2.5 h ≤T ≤6.5 h in the magnetic field and the ion data, in several cases, d) detection of magnetic waves and charged particle modulation with a period of ∼40min, e) observation of an ∼10 h inward/outward motion of the Jovian magnetopause. The observations are consistent with generation of the low frequency upstream (Alfvén) waves through periodic injection of plasma/energetic ions from within the magnetosphere into the upstream region.
Electron impact excitation of nitric oxide under auroral conditions
Authors: Cartwright D. C. , Brunger M. J. , Campbell L. , Mojarrabi B. , Teubner P. J. O.
Published: February 2004

Excitation of the ground vibrational levels and nine excited electronic states in NO has been simulated for an IBC II aurora. New electron impact excitation cross sections for NO were combined with a measured IBC II auroral secondary electron energy distribution and the electronic‐vibrational populations were determined for conditions of statistical equilibrium. This model predicts an extended vibrational distribution in the NO ground electronic state produced by radiative cascade from the many higher lying doublet excited electronic states. In addition to energy storage in the vibrational population of the ground electronic state, both the a 4Π and L′ ²Φ excited electronic states are predicted to have relatively high number densities in aurora. This extended ground state vibrational distribution is predicted to emit infrared [IR] radiation from 1.3 to 8.2 µm and most IR bands are predicted to be stronger than band emission from any of the electonic transitions.
Particle entry through reconnection grooves in the magnetopause with a dawnward IMF as simulated by a 3‐D EM Particle Code
Authors: Nishikawa K.‐I.
Published: February 2004

We report progress in the long‐term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three‐dimensional electromagnetic particle code. After a quasi‐steady state is established with an unmagnetized solar wind we gradually switch on a northward interplanetary magnetic field (IMF), which causes a magnetic reconnection on the magnetopause tailward of the dayside cusps and makes the magnetosphere dipolarized. In the case that the northward IMF is switched gradually to dawnward, there is no signature of reconnection in the near‐Earth magnetotail in contrast to the case with the southward turning. On the contrary analysis of magnetic fields in the magnetopause confirms a signature of magnetic reconnection at both the dawnside and duskside. The plasma sheet in the near‐Earth magnetotail clearly thins as in the case of southward turning. Arrival of dawnward IMF to the magnetopause creates a reconnection groove which causes particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. This deep connection is more fully recognized tailward of Earth. The flank weak‐field region joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross‐tail S that structurally integrates the magnetopause and the tail interior. This structure might contribute to direct entry between the magnetosheath plasma to plasma sheet, in which the entry process heats the magnetosheath plasma to plasma sheet temperatures. In spite of strong plasma entry into the inner magnetosphere, the dawnward IMF prevents the reconnection in the near‐Earth magnetotail due to the penetrated IMF By component. Therefore, the onset of substorms may not take place. However, it is still possible that this particle entry causes pseudo‐substorm onsets.
Ozone production efficiencies of acetone and peroxides in the upper troposphere
Authors: Folkins Ian , Chatfield R. , Singh H. , Chen Y. , Heikes B.
Published: February 2004

HOx concentrations in the upper tropical troposphere can be enhanced by the presence of acetone and the convective injection of peroxides. These enhancements in HOx might be expected to increase ozone production by increasing the rate of the HO2+NO reaction. We show however that the convective enhancements of hydrogen peroxide (H2O2) and methyl hydroperoxide (CH3OOH) above steady state during the PEM West B campaign were largely restricted to air parcels of marine boundary layer origin in which the mean NO concentration was 8 pptv. The ozone production efficiencies of the two peroxides at such low NO concentrations are very small. Their impact on the ozone budget of the upper tropical troposphere during PEM West B was therefore probably modest. Unlike the peroxides, acetone in the upper tropical troposphere during PEM West B exhibited a positive correlation with NO. It also has a much larger ozone production efficiency than either H2O2 or CH3OOH. It therefore has a much greater potential for significantly increasing ozone production rates in the upper tropical troposphere.
Propagation directions of gravity wave patterns observed in OH CCD images during the SEEK Campaign
Authors: Nakamura Takuji , Tsuda Toshitaka , Miyagawa Hirohisa , Matsushita Yoshihito , Fukunishi Hiroshi , Takahashi Yukihiro , Yamada Yoshinori
Published: February 2004

OH airglow (about 87 km altitude) was observed with a CCD imager at Shigaraki (34.9°N, 136.1°E) in August 1996, during the SEEK campaign period. From nine night observations, the characteristics of the gravity wave modulation of the OH airglow layer were extracted and analyzed. The distributions of the horizontal wavelength, observed wave period and horizontal phase speed were 10–30 km, 5–30 min and 20–60 m/s, respectively. The horizontal propagation direction was mainly north‐eastward. This preferential direction is similar to previous MU radar observations of mesospheric gravity waves (68–80km) in summer months, but different from the propagation direction of gravity waves expected from FAI theories and observations in the E‐region.
Empirical determination of depth‐distance corrections for mb and Mw from global seismograph network stations
Authors: Nolet Guust , Krueger Steve , Clouser Robert M.
Published: February 2004

Using P wave amplitudes from 52 deep earthquakes, recorded by the Global Seismograph Network (GSN) between 1991 and 1996, we empirically determined depth‐distance corrections for body wave magnitude mb and moment magnitude Mw. After correcting vertical, broadband records from stations of the GSN for instrument response and source radiation factors, P wave amplitudes from velocity records were read for the case of mb and the surface area under the displacement pulse of the P wave for Mw. Amplitudes were then normalized to a scalar moment M0=1018 Nm, or mb=5.7, Mw=5.9. Using the generic logarithmic relationship for each magnitude, correction factors Q(Δ, h) were determined.

A total of 973 observed values of Q in the plane of distance Δ vs. depth h were smoothed by local averaging, as well as fitted by a parameterized smooth surface. These empirical Q(Δ, h) surfaces differ in important detail from those historically established by Gutenberg and Richter, and markedly from the theoretical curves predicted by Veith and Clawson (1971). We present a first empirical correction factor for the determination of Mw from P wave displacements.
Sn velocities in western and eastern North America
Authors: Nolet Guust , Coutlee Craig , Clouser Robert
Published: February 2004

We have investigated the use of the new delay time data set of Engdahl et al. [1997] for the construction of tomographic images of Sn velocity in North America. The delays show a significant difference in average delay between paths located west and east of 105°W. This difference is larger when paths longer than 10° are included, indicating a positive gradient for the S velocity in eastern North America. Discarding outliers, two separate regions in the western and eastern United States and Canada where imaged. Low velocities were found under the Colorado Plateau, extending westwards towards the Gulf of California. In the eastern U.S. the Michigan Basin stands out with low Sn velocity, and the Grenville province is characterized by a positive anomaly.
Low ferric iron content of (Mg,Fe)O at high pressures and temperatures
Authors: McCammon Catherine , Peyronneau Jean , Poirier Jean‐Paul
Published: February 2004

New results from high‐pressure multi‐anvil and diamond anvil cell experiments show that the Fe3+ content of (Mg,Fe)O is low at high pressures and temperatures, and relatively independent of oxygen fugacity. At 18 GPa and 1000°C, the maximum solubility of Fe3+ in Mg0.8Fe0.2O ranges from approximately 2% Fe3+/ΣFe at the Fe‐FeO buffer to 3–7% Fe3+/ΣFe at the Re‐ReO2 buffer. These low values are likely due to a high‐pressure phase transition in the system Fe3O4‐MgFe2O4, resulting in preferential partitioning of Fe3+ into the high‐pressure phase. (Fe,Mg)Fe2O4 would be exsolved in (Mg,Fe)O depending on the oxygen fugacity, which could have significant effects on transport properties. Exsolved (Fe,Mg)Fe2O4 could also be useful as an oxygen barometer.
Ascending subducted oceanic crust entrained within mantle plumes
Authors: Yasuda Atsushi , Fujii Toshitsugu
Published: February 2004

Upward migration of subducted oceanic crust from deep in the upper mantle is discussed based on high‐pressure experimental data. Numerical calculation reveals that a subducted oceanic crust, which is negatively buoyant in the present upper mantle, can ascend from the transition zone and be observed as a discrete magma source at the surface only when it has been broken into fragments comparable in dimension with its thickness and involved in a solid diapir of heated peridotite. For example, a solid diapir of heated peridotite with a temperature excess of 200°C can contain up to 15∼20 vol% of fragments of oceanic crust when it passes through the upper mantle, and it may cause extensive basaltic volcanism at the surface.
The 1997 PMSE season ‐ Its relation to wind, temperature and water vapour
Authors: Kirkwood S. , Barabash V. , Chilson P. , Réchou A. , Stebel K. , Espy P. , Witt G. , Stegman J.
Published: February 2004

Factors determining the onset and decay of the Polar Mesosphere Summer Echo (PMSE) season in 1997 are examined. PMSE from the ESRAD radar at 68°N, 20°E are compared with simultaneous observations of stratospheric winds, upper‐mesosphere temperature, upper mesosphere water vapour and noctilucent clouds. There was a 3‐week delay from the start of summer, defined by temperature or stratospheric winds, to the start of PMSE. At the end of the summer, the return to winter conditions was simultaneous in all three parameters. Noctilucent clouds at 55–60°N were confined to the period of lowest temperatures, when PMSE were also present throughout the day. Water vapour observations show an increase during the summer, possibly taking place in late May, at about the time PMSE first appeared. It seems likely that the start of the PMSE season is determined by water vapour availability, while the end of the season is determined by temperature.
The impact of subvisible cirrus clouds near the tropical tropopause on stratospheric water vapor
Authors: Rosenfield Joan E. , Considine David B. , Schoeberl Mark R. , Browell Edward V.
Published: February 2004

The radiative impact of subvisible cirrus ice clouds at and just below the tropical tropopause has been studied using a zonally averaged interactive chemistry‐radiation‐dynamics model. Model runs have been performed with and without the inclusion of the radiative heating of these thin ice clouds, and with and without sedimentation. Near‐infrared optical depths of 0.005–0.08 were computed for assumed log‐normal size distributions of spherical particles having mode radii of 2–10 µm. Particles with 6 µm mode radii have computed scattering ratios of 3–15 at 603 nm, in good agreement with lidar observations. The increased radiative heating of these clouds, 0.1–0.2 K/day, results in temperature increases of 1–2 K and vertical velocity increases of 0.02–0.04 mm/s. As a consequence of the warmer tropopause, lower stratosphere water vapor increases by as much as 1 ppmv. The dehydration resulting from sedimentation was found to be a much smaller effect.
Seasonal evolution of total and gravity wave induced laminae in ozonesonde data in the tropics and subtropics
Authors: Grant William B. , Pierce R. Bradley , Oltmans Samuel J. , Browell Edward V.
Published: February 2004

ECC ozonesonde ozone and potential temperature profile data for several stations from 25.05°S to 19.6°N were processed to look for the type, seasonal behavior, and vertical distribution of the laminar structure in the troposphere and lower stratosphere. The fractions of ozone laminae associated with Rossby and gravity wave induced laminae were determined from correlations between ozone and potential temperature structure. Gravity‐wave‐induced laminae in the stratosphere were found to be associated with deep convection in the winter months and winds form the southwest in the summer months for the Hilo station, and orographic wave activity for the Pretoria station in September. No significant Rossby wave activity was found for these stations. Lower tropospheric laminae of mixed characteristics were found to be prevalent at the Hilo, related to transport from the northeast, and the continental tropical stations in the June–August period, which are associated with biomass burning.
Petrologic evidence for pre‐eruptive pressure‐temperature conditions, and recent reheating, of andesitic magma erupting at the Soufriere Hills Volcano, Montserrat, W.I.
Authors: Devine J. D. , Murphy M. D. , Rutherford M. J. , Barclay J. , Sparks R. S. J. , Carroll M. R. , Young S. R. , Gardner J. E.
Published: February 2004

The recent eruption of the Soufriere Hills Volcano in Montserrat (July, 1995, to present; September, 1997) has produced an andesitic dome (SiO2 ∼ 59–61 wt.%). The eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region (P ∼ 130 MPa; ≥5 km depth). The composition of the andesite has remained essentially constant throughout the eruption, but heating by the mafic magma increased the andesite temperature from ≤830°C to ≤880°C. Prior to being heated, the stable mineral assemblage in the andesite was plagioclase + amphibole + orthopyroxene + titanomagnetite + ilmenite + quartz. The rise in temperature from ≤830°C to ≤880°C (fO2 ∼ 1 log unit above NNO) has caused quartz to become unstable, and has also caused changes in silicate and Fe‐Ti oxide mineral compositions. The andesitic magma is likely saturated with an H2O‐rich vapor phase in the upper part of the magma storage region. Melt H2O content is ∼4.7 wt.%.
The cusp/magnetosheath interface on May 29, 1996: Interball‐1 and Polar observations
Authors: Savin S. P. , Romanov S. A. , Fedorov A. O. , Zelenyi L. , Klimov S. I. , Yermolaev Yu. I. , Budnik E. Yu. , Nikolaeva N. S. , Russell C. T. , Zhou X‐W. , Urquhart A. L. , Reiff P. H.
Published: February 2004

On May 29, 1996, under steady strong northward IMF and high solar wind dynamic pressure conditions both Polar and Interball cross field lines that pass through the northern cusp and apparently close to the post‐cusp reconnection site. The magnetopause current observed by Interball consists of two quite distinct layers, an inner broad current that is quite turbulent and another current that is quite abrupt and quiet. Polar also crosses current layers, similar to the Interball inner one. These observations support a model in which cusp field lines experience essentially stochastic behavior but on average provide topological connection between the cusp and magnetosheath.
Wet and dry sizes of atmospheric aerosol particles: An AFM‐TEM Study
Authors: Pósfai Mihály , Xu Huifang , Anderson James R. , Buseck Peter R.
Published: February 2004

We studied the hygroscopic behavior of atmospheric aerosols by using a novel approach, the combination of atomic force microscopy (AFM) with transmission electron microscopy (TEM) imaging of the same individual particles. By comparing the dimensions of hydrated and dry ammonium sulfate particles collected above the North Atlantic Ocean, we determined that particle volumes are up to four times larger under ambient conditions (as determined by AFM) than in the vacuum of a transmission electron microscope. We interpret these changes as resulting from the loss of water. Organic films on the particles may be responsible for the relatively large water uptake at low relative humidities.
Seasonal evolution of Rossby and gravity wave induced laminae in ozonesonde data obtained from Wallops Island, Virginia
Authors: Pierce R. Bradley , Grant William B.
Published: February 2004

A method for evaluating the seasonal evolution of ozone laminae using ozonesonde data is discussed. The method uses the correlation between small‐scale ozone and potential temperature variations to distinguish between laminae generated by quasi‐isentropic filamentation by Rossby waves and by vertical displacements of material surfaces by gravity waves. Data from Wallops Island, Virginia show that Rossby wave induced ozone laminae are most frequently encountered at Wallops during the winter months near 15 km while statistically significant gravity wave induced laminae occur above 15 km during the early winter and at the tropopause from late winter through early spring.
The orientation of plasma structure in the solar wind
Authors: Richardson J. D. , Paularena K. I.
Published: February 2004

Data from the ISEE 3, IMP 8, and WIND spacecraft are used to find the average east‐west orientation of plasma structures in the solar wind. We determine the lags which, after radial propagation effects are removed, give the best correlations between data sets. These lags, when combined with the spacecraft positions and solar wind speeds, are then used to calculate the front angles of the propagating plasma. The average front normals are neither radial nor perpendicular to the magnetic field, but are roughly halfway between. Front angle distributions peak at lower angles near solar maximum than at solar minimum. These results may indicate that time‐dependent changes in the solar wind source are as important as longitudinal variations of the source in producing the solar wind structure observed near Earth.
The relationship between P/Fe and V/Fe ratios in hydrothermal precipitates and dissolved phosphate in seawater
Authors: Feely Richard A. , Trefry John H. , Lebon Geoff T. , German Christopher R.
Published: February 2004

A strong positive relationship between the molar P/Fe ratio in fresh hydrothermal Fe ferrihydrite precipitates and seawater‐dissolved phosphate has been demonstrated using samples from the Atlantic and Pacific Oceans. We ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal Fe‐rich particles above hydrothermal vents. In contrast, molar V/Fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate. These results indicate that inter‐ocean variations in dissolved phosphate control the P/Fe and V/Fe ratios in hydrothermal Fe precipitates, one of the precursors of metalliferous sediment.
The Aleutian Earthquake of June 10, 1996 (Mw 7.9) ruptured parts of both the Andreanof and Delarof Segments
Authors: Tanioka Yuichiro , Gonzalez Frank I.
Published: February 2004

The epicenter of the Aleutian earthquake of June 10, 1996, is located in the Delarof segment where a large subduction earthquake is expected. However, the aftershock area of the earthquake is not only in the Delarof segment but also in the Andreanof segment where the 1986 Andreanof earthquake occurred previously. We estimate the fault parameters of the 1996 earthquake by numerically computing the tsunami and comparing the waveforms with that recorded at Adak. The fault width is 30 km or less, and the average slip is about 4 m. The observed far‐field tsunamis around the Pacific are also explained by the synthetic tsunami computed using the above fault parameters. The results indicate that the 1996 earthquake ruptured parts of both the Delarof and Andreanof segments. However, the 1996 earthquake did not rupture the region of the largest moment release by the 1986 earthquake.
Comparison of the dynamics of the AU and PC indices
Authors: Takalo J. , Timonen J.
Published: February 2004

The properties of AU and PC data were analyzed with different methods. It is shown that the dynamical behavior of the AU and PC time series, as analyzed by the structure function (SF), are very similar, while the SF of the AL time series shows different behavior. The SF of the AL data has a slope of 0.5 up to about 2 hours, after which it quickly decreases to about 0.1. On the other hand the slope of the SFs of AU and PC data continuously decreases to about 0.2, and in a longer time scale. It is suggested that the dissipative auroral electrojet currents have a characteristic time scale of 2 hours, and this underlies the AL dynamics. In contrast with this, the nondissipative Hall currents that most influence the AU and PC dynamics, do not seem to have a distinct characteristic time scale. However, the cross‐correlation between the PC and AL indices is higher than that of the PC and AU indices, especially during wintertime. This is argued to result from the polar cap currents being more interconnected with the westward electrojets than with the eastward electrojets, in spite of the difference in their dynamic behaviors.
Natural electromagnetic pulses in the ELF range
Authors: Nickolaenko Alexander P. , Hayakawa Masashi
Published: February 2004

We analyze the propagation of electromagnetic waves in the ELF. We apply the modal solution for the spherical Earth‐ionosphere cavity and obtain the time domain fields using the FFT algorithm. The Schumann resonance amplitude over the frequency‐distance plane consists of summits and depressions exhibiting separate extended zones. When the source‐observer distance is small, the field maximum is found at some hundred hertz. This component rapidly decays with the distance. The time domain ELF pulse travels with a constant velocity and “bounces” from the source antipode. Its width increases along the path due to absorption of the high frequency component. The distance dependence of the pulse amplitude depends on both the geometrical focusing and the high frequency absorption.
Stationary anomalies in stratospheric meteorological data sets
Authors: Bowman Kenneth P. , Hoppel Karl , Swinbank Richard
Published: February 2004

Several northern hemisphere stratospheric meteorological data sets are shown to contain stationary anomalies. We consider four possible explanations for the anomalies: 1) real stationary‐wave features; 2) biases in the analysis and assimilation methods; 3) errors in data input into the analysis and assimilation systems; and 4) tidal signals that are undersampled in the daily analyses. Because the easterly flow in the summer stratosphere is not consistent with stationary waves and the anomalies are present in multiple analyses, we conclude that the anomalies are a combination of biases in the input data and tidal signals that are aliased to zero frequency by daily sampling. Because the anomalies are large, they can have significant impacts on many applications of the data, including trajectories and chemical transport calculations.
Interstation Pc3 coherence at cusp latitudes
Authors: Szuberla C. A. L. , Olson J. V. , Engebretson M. J. , Fraser B. J. , Ables S. , Hughes W. J.
Published: February 2004

Magnetic fluctuations in the 22–100 millihertz (Pc3) band are a consistent indicator of the presence of the cusp in the overhead ionosphere at high latitudes. Correlation of the signals from a variety of instruments have shown that the sources of these pulsations are local (ionospheric) rather than distant (magnetospheric) [Engebretson et al., 1990]. Modulated electron precipitation is presumed to be the source of the fluctuations through the modulations in ionospheric conductivity that they produce. Olson and Szuberla [1997] used data from a pair of cusp stations to deduce the scale size of the precipitating beams using a simple model in which the beams were assumed to have circular cross section. They obtained an upper bound for the coherence length of the order of 200 km. In this paper we extend the analysis of Olson and Szuberla by incorporating data from the Magnetometer Array for Cusp and Cleft Studies (MACCS) magnetometer array and the Australian ANARE antarctic sites to give a broader range of station separations. Using a statistical approach we computed the cumulative distribution function of the interstation coherence and from that distribution we established a measure of coherence, CL. The result of this analysis is a coherence that diminishes with inter‐station distance as CL ≈ 1.4 exp(−S/250) where S is the station separation in km. When this result is interpreted in the context of the simple model mentioned above we find a coherence length of 140–180km.
Natural CF4 and SF6 on Earth
Authors: Harnisch Jochen , Eisenhauer Anton
Published: February 2004

The occurrence of CF4 and SF6 in natural fluorites (CaF2) is reported. Contents are found to be typically 200–2000 ppt‐mass for CF4 and 50–100 ppt‐mass for SF6. CF4 and SF6 were also detected in granites where fluorite is an accessory mineral. CF4 and SF6 thus possess a large reservoir in the continental crust that by degassing can sustain natural atmospheric background levels of 40 ppt‐mole and up to 0.01 ppt‐mole, respectively. The article also discusses how natural SF6 may cause interference in hydrological tracer studies.
Ionospheric absorption on October 24, 1995 solar eclipse
Authors: Abraham Saji , Dhaka S. K. , Nath N. , Baluja K. L.
Published: February 2004

The ground based vertical radio wave propagation experiment was conducted at the frequency of 2.5 MHz to study variations in ionospheric radio wave absorption during partial solar eclipse that occurred on October 24, 1995 at Delhi (28.6°N, 77.2° E). It was observed that the minimum in absorption data was four minutes earlier than the ground level eclipse totality, and an anomaly was accompanied by an abnormal sharp rise (shock‐like wave structure) in absorption data around 30 minutes after the eclipse totality. Absorption during post‐eclipse control days was higher compared to those on pre‐eclipse control days.
The chemical kinetics of HONO formation resulting from heterogeneous interaction of NO2 with flame soot
Authors: Gerecke Andreas , Thielmann Axel , Gutzwiller Lukas , Rossi Michel J.
Published: February 2004

Uptake experiments at ambient temperature of NO2 on ethylene, acetylene and toluene soot resulted in significant amounts of HONO. The initial uptake coefficient γ0 of NO2 on ethylene soot decreased from 0.12 to 0.03 with increasing NO2 concentration in the range 8×1010 to 1.4×1013 molecule s−1. The HONO yields relative to NO2 taken up were in the range 50 to 93% and were consistent with a mechanism in which either soot or hydrogen contained in it was the reducing agent. The branching ratio of the yield of HONO and NO was a function of the sampling spot at which the soot was collected within a diffusion flame and ranged from 23 to 2.2 with increasing distance from the flame base and thus age. The total amount of HONO generated in one uptake experiment was 1.2×1016 molecules per mg of soot. Heating cycles bring back the ability of soot to generate HONO, but at diminishing yields.
Heterogeneous processes involving sodium halide particles and ozone: Molecular bromine release in the marine boundary layer in the absence of nitrogen oxides
Authors: Hirokawa J. , Onaka K. , Kajii Y. , Akimoto H.
Published: February 2004

Heterogeneous reactions involving sodium halide particles and gaseous ozone were investigated by reaction‐chamber experiments in order to explore the possible role of sea‐salt particles as a source of reactive halogen species in the troposphere. In the studies of sodium bromide and ozone, it was found that gaseous bromine molecules were produced in the presence of water vapor with which the salts were almost deliquesced. This preliminary result suggests that reactive bromine species can be released from sea‐salt to the atmosphere of the marine boundary layer in the absence of nitrogen oxides.
Particle composition of a young condensation trail and of upper tropospheric aerosol
Authors: Kuhn M. , Petzold A. , Baumgardner D. , Schröder F. P.
Published: February 2004

Aerosol and contrail particles in a young exhaust plume of an Airbus A310‐300 were characterized with respect to size distribution and refractive index at plume ages ≤ 2 sec. The instrumentation included standard particle spectrometers (PCASP‐100X, FSSP‐300) and a new instrument (Multiangle Aerosol Spectrometer Probe, MASP) for simultaneous measurement of particle size and refractive index. The particle size distributions as measured with the standard FSSP‐300 and the new MASP showed good agreement. The observed refractive indices indicated a mixture of pure ice particles, black carbon aerosol, and an internal mixture of these components in the contrail, while black carbon and sulfate‐containing compounds dominated the upper tropospheric background aerosol.
Corehole seismometer development for low‐noise seismic data in a long‐term seafloor observatory
Authors: Stakes D. , McClain J. , VanZandt T. , McGill P. , Begnaud M.
Published: February 2004

Longstanding problems unique to marine seismology (in contrast to land‐based studies) include high levels of environmental noise, unpredictable instrument placement, short measurement duration, and limited numbers of instruments. Traditional instruments are deployed and recovered from a surface ship with no capability to verify data acquisition until the end of the experiment. They are often poorly sited and usually poorly coupled to the seafloor. Experiments have typically been short in duration with only a minimum number of instruments. The result of these logistical problems is high background noise, sparse data recovery (compared to continental stations), and low fidelity data. In an effort to solve many of these problems, we have developed and deployed “corehole seismometers” (1–90 Hz) into small boreholes drilled by an underwater drilling system, using a tethered Remotely Operated Vehicle (ROV). The results are seismic data with a significantly lower background noise level, a lower threshold for recognition of small events, well‐oriented (and useable) horizontal seismograms, and a much longer deployment capability. We present new data from these instruments and compare them with data from two types of traditional instruments deployed from a surface ship. These contemporaneous deployments were conducted during 1996 and 1997 in Monterey Bay.
Rates of volcanic CO2 degassing from airborne determinations of SO2 Emission rates and plume CO2/SO2: test study at Pu′u ′O′o Cone, Kilauea Volcano, Hawaii
Authors: Gerlach Terrence M. , McGee Kenneth A. , Sutton A. Jefferson , Elias Tamar
Published: February 2004

We present an airborne method that eliminates or minimizes several disadvantages of the customary plume cross‐section sampling method for determining volcanic CO2 emission rates. A LI‐COR CO2 analyzer system (LICOR), a Fourier transform infrared spectrometer system (FTIR), and a correlation spectrometer (COSPEC) were used to constrain the plume CO2/SO2 and the SO2 emission rate. The method yielded a CO2 emission rate of 300 td−1 (metric tons per day) for Pu′u ′O′o cone, Kilauea volcano, on 19 September 1995. The CO2/SO2 of 0.20 determined from airborne LICOR and FTIR plume measurements agreed with the CO2/SO2 of 204 ground‐based samples collected from vents over a 14‐year period since the Pu′u ′O′o eruption began in January 1983.
Ultrafine aerosol particles in aircraft plumes: In situ observations
Authors: Schröder F. P. , Kärcher B. , Petzold A. , Baumann R. , Busen R. , Hoell C. , Schumann U.
Published: February 2004

Measurements of ultrafine particles in the near field of the DLR research aircraft ATTAS using low (0.02 g/kg fuel) and high (2.7g/kg) fuel sulfur contents (FSCs) are presented. Soot emissions of ∼ 1015/kg show no significant dependence on FSC. Strong evidence is found that ∼ 1/3 of the soot particles must be involved in ice nucleation in contrails, in addition to freezing of newly formed volatile particles. In the absence of contrails, numbers of volatile particles with diameters D > 5 nm reach ∼ 1017/kg for high FSC, and still reach ∼ 1016/kg for low FSC. A clear contribution of H2SO4 to volatile particle growth is observed. If growth is exclusively linked to H2SO4, the S to H2SO4 conversion efficiency increases with decreasing FSC. Depletion of ultrafine particles is observed in contrails, very likely due to scavenging by contrail ice crystals.
Tropical entrainment time scales inferred from stratospheric N2O and CH4 observations
Authors: Herman R. L. , Scott D. C. , Webster C. R. , May R. D. , Moyer E. J. , Salawitch R. J. , Yung Y. L. , Toon G. C. , Sen B. , Margitan J. J. , Rosenlof K. H. , Michelsen H. A. , Elkins J. W.
Published: February 2004

Simultaneous in situ measurements of N2O and CH4 were made with a tunable diode laser spectrometer (ALIAS II) aboard the Observations from the Middle Stratosphere (OMS) balloon platform from New Mexico, Alaska, and Brazil during 1996 and 1997. We find different compact relationships of CH4 with N2O in the tropics and extra‐tropics because mixing is slow between these regions. Transport into the extra‐tropics from the tropics or the polar vortex leads to deviations from the normal compact relationship. We use measured N2O and CH4 and a simple model to quantify entrainment of mid‐latitude stratospheric air into the tropics. The entrainment time scale is estimated to be 16 (+17, −8) months for altitudes between 20 and 28 km. The fraction of tropical air entrained from the extra‐tropical stratosphere is 50% (+18%, −30%) at 20 km, increasing to 78% (+11%, −19%) at 28 km.
Evidence of two regimes of easterly waves over West Africa and the tropical Atlantic
Authors: Diedhiou Arona , Janicot Serge , Viltard Alain , de Felice Pierre
Published: February 2004

Synoptic‐scale easterly waves at 700 hPa have been studied over West Africa and the tropical Atlantic for the summers of 1979–1995. Spectral analyses (Fast Fourier and Wavelet Transforms) of 700 hPa meridional wind component along 17.5°N enable to point out two band‐periods, between 3 and 5 days and between 6 and 9 days. An example of each wave is shown. Composite analysis confirms the evidence of two such regimes of easterly waves during summer over West Africa and the tropical Atlantic. The 6–9‐day wave regime differ from the 3–5‐day wave regime by larger anticyclonic cells originated from the Libyan and the Azores areas, and by more northern tracks.
Local heating/cooling of the mesosphere due to gravity wave and tidal coupling
Authors: Liu Han‐Li , Hagan Maura E.
Published: February 2004

Numerical experiments in this study show that the tidal wind may have strong impacts on the stability of the gravity wave and therefore significantly affects the breaking of the gravity wave. This enhances the local dynamical cooling and turbulence heating, and produces descending heating/cooling structures, which are similar to recent lidar observations. The propagating phase of such structures is dependent on the descending phase of the tidal wave and the gravity wave breaking level. The maximum heating corresponds closely with a negative or positive shear of the accelerated flow, depending on the gravity wave propagation direction.