bluuebunny/crossref_metadata_2025 huggingface dataset:
GEOTAIL observations of total pressure and electric field variations in the near and mid‐distant tail associated with substorm onsets
Authors: Miyashita Y. , Machida S. , Nishida A. , Mukai T. , Saito Y. , Kokubun S.
Published: September 2002

Selecting 263 substorm events with Pi 2 pulsation, we have statistically investigated temporal variations in the total pressure and the electric field (E = −V × B) in the near‐Earth magnetotail with GEOTAIL data. It was found that a total pressure decrease occurs first in the premidnight region around (X, Y) ∼ (−18, 7)RE in the GSM coordinates about 1 or 2 min before onset, and propagates to the surrounding regions successively. The dawn‐to‐dusk electric fields around X ∼ −10RE and X ∼ −28RE have the same magnitudes and develop considerably about 1 min after onset, while that around (X, Y) ∼ (−20, 5)RE is smaller. These results strongly suggest that the magnetic reconnection takes place at least 2 min earlier than the dipolarization, and that, on the average, the center of the energy release is initially located around the premidnight region of (X, Y) ∼ (−19, 6)RE.
Peru Basin sediments: Diagenetic implications of a low coercivity overprint of the NRM
Authors: Urbat Michael , Dekkers Mark J.
Published: September 2002

Two coexisting populations of magnetite that vary by at least 320 kyr in age characterize the magnetomineralogy in oxic through suboxic Peru Basin sediment (7°04′S / 88°28′W). 1) Primary magnetite barely underwent post‐depositional alteration and yields a straightforward magnetostratigraphy (Brunhes Chron ‐ top of Olduvai Subchron). 2) A stable, low‐coercivity overprint of the NRM resides in secondary, slightly oxidized SD magnetite that recorded the Brunhes Chron direction. The secondary magnetite appears at the modern Fe‐redox boundary (2.6 mbsf) and continues downhole to abruptly disappear at 5.3 mbsf in the Matuyama Chron. It can be discerned by combined analyses of directional data and the Verwey transition in low‐temperature remanence measurements (20–300 K) that appears concomitant with the overprint.
Chemical ozone depletion during Arctic winter 1997/98 derived from ground based millimeter‐wave observations
Authors: Langer J. , Barry B. , Klein U. , Sinnhuber B. ‐M. , Wohltmann I. , Künzi K. F.
Published: September 2002

We present ground based millimeter‐wave measurements of Arctic stratospheric ozone at Ny‐Ålesund, Spitsbergen (79N, 12E), for winter 1997/98. Vortex averaged chemical ozone depletion rates around the 475 K isentropic level were derived from our observations using measured ozone trends for 20 day periods and calculations of diabatic descent inside the vortex. Back trajectory calculations for air‐parcels crossing Ny‐Ålesund show that measurements at Ny‐Ålesund were representative for vortex air‐masses. Significant chemical ozone depletion was observed during one period at the end of February 1998 with loss rates of 32 ppb/day around the 475 K isentropic level. During this period the loss rate was higher than in February 1997. Due to the early breakup of the polar vortex, the chemical ozone depletion stopped in March and the accumulated loss is found to be 0.64±0.2 ppm in 1997/98.
On the relationship between turbulent internal energy and available energy in local formulation
Authors: Herbert Fritz , Kucharski Fred
Published: September 2002

The interdependence between the turbulent internal energy (as it was introduced in Herbert and Kucharski [1998]) and the atmospheric shallow fluid available energy is analytically investigated in conformity with the corresponding local energy balance differential equations that are imposed as central physical criteria. It is shown that the available and turbulent internal energy forms do well combine together under the assumption of a further thermal energy function coupled with appropriate substantial simplifications.
Local time dependence of Jovian radio emissions observed by Galileo
Authors: Menietti J. D. , Gurnett D. A. , Kurth W. S. , Groene J. B.
Published: September 2002

Galileo has been in orbit around Jupiter since December 1995. All the orbits are equatorial and elliptical, with apogees between 60 RJ–142 RJ and perigees from 8–12 RJ. Since orbit injection, the plasma wave instrument (PWS) has been collecting data over specific intervals of each of the orbits at all local times and a range of different radial distances. We present the results of a survey of the data for the frequency range 300 kHz to 5.6 MHz, which includes the hectometric (HOM) and low‐frequency decametric (DAM) emissions. The results indicate that both the HOM and DAM emission are more intense and occur more frequently in the midnight sector of Jupiter. This is in analogy to Earth and consistent with a magnetic substorm source for a portion of the radio emissions in this frequency range. Another peak in the power levels is observed on the Jovian dayside in the local time range 11 hrs.<LT<12 hrs. This peak does not have a terrestrial counterpart. We speculate that this dayside peak may be a result of sampling near perigee, but we cannot rule out the possibility that this is not the case.
Fullerenes found in the Permo‐Triassic mass extinction period
Authors: Chijiwa Takuya , Arai Toshinari , Sugai Toshiki , Shinohara Hisanori , Kumazawa Mineo , Takano Masao , Kawakami Shin‐iti
Published: September 2002

Fullerenes have been identified by high‐performance liquid chromatography with UV‐visible spectroscopic analysis of toluene extracts of deep sea claystones from Permo‐Triassic (P/T) boundary sections in the Inuyama area, central Japan. The analysis reveals the presence of 10–20 parts per trillion of C60 only in the dark‐colored rock samples, suggesting the anoxia at the time of the P/T boundary 250 million years ago, when the greatest Phanerozoic mass extinction occurred. The fullerenes were likely synthesized within locally anoxic zone in the extensive wildfires on the supercontinent Pangea and deposited on an anoxic deep‐sea floor of the superocean Panthalassa.
The global nature of solar cycle variations of the solar wind dynamic pressure
Authors: Richardson John , Wang Chi
Published: September 2002

The solar wind dynamic pressure measured near the ecliptic varies over the solar cycle. A major unanswered question has been whether this variation is a global feature or restricted to low latitudes and thus perhaps a consequence of the changing heliospheric current sheet configuration. We use plasma data from IMP‐8, Ulysses and Voyager 2 to show that the large‐scale variation of the solar wind dynamic pressure is the same at all latitudes. Thus the solar wind source varies globally over the solar cycle, with important implications for the source mechanism and motions of the heliospheric boundaries.
Meteor trail advection and dispersion; Preliminary lidar observations
Authors: Grime Brent W. , Kane Timothy J. , Collins Stephen C. , Kelley Michael C. , Kruschwitz Craig A. , Friedman Jonathan S. , Tepley Craig A.
Published: September 2002

Sodium resonance lidar observations of meteor ablation trails at the Arecibo Observatory (18.30°N, 66.75°W) are presented. Of particular interest is the event of 23 March 1998, during the Coqui II sounding rocket campaign. On this date, the lidar was operating with two beams probing different volumes of the sodium layer separated zonally by 15.7±0.8 km. A single meteor trail was observed near 89 km altitude in both lidar field‐of‐views with a 310±50 s temporal displacement. This observational separation suggested a westward zonal wind of 50±10 m/s, while trail dispersion yielded an upper bound for the total diffusion coefficient of 2.6±0.5 m²/s which is consistent with dispersion seen in other trails. The data supports the need for future observation with systems specialized for meteor detection.
Estimating the hydrologic induced signal in geodetic measurements with predictive filtering methods
Authors: Braitenberg Carla
Published: September 2002

The high precision achieved with continuous geodetic instruments makes it necessary to take ambient factors into account. Among these, one of the most disturbing is the hydrologic agent. After giving a characterization of the induced signals in the specific case of subsurface tilt and extensometric measurements, the techniques of predictive filtering are shown to solve the problem of modeling the induced signals. The results obtained here may be applied also to other continuous geodetic and gravity measurements.
Monthly stable isotope records in an Australian coral and their correspondence with environmental variables
Authors: Bian Huisheng , Druffel Ellen R. M.
Published: September 2002

Monthly skeletal stable isotope measurements of a Porites australiensis coral from Abraham Reef, Australia, spanning the period from 1981 to 1991, are compared with monthly averaged SST (sea surface temperature) from satellite collected AVHRR (Advanced Very High Resolution Radiometer) and monthly downward surface short‐wave insolation (SSI) measurements. We found that the δ18O values varied as a function of the change in seawater temperature. There were anomalously high δ18O values in coral that grew during the summer season of the three El Niño events 1982–83, 1987, and 1991. Advection of seawater with higher salinity (and higher δ18O values) to our site or discrepancies between ocean skin temperature and mixed layer SST are likely reasons for the reduced resolution of δ18O‐based SST. Increased coral δ13C values occurred simultaneously with increases in SSI. During most El Niño events the maximum and minimum δ13C values were lower than during normal years.
In situ measurement of the aerosol size distribution in stratospheric solid rocket motor exhaust plumes
Authors: Ross M. N. , Whitefield P. D. , Hagen D. E. , Hopkins A. R.
Published: September 2002

The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB‐57F aircraft. Aerosol size distribution in the 0.01 µm to 4 µm diameter size range was measured using a two component sampling system. The measured distributions display a trimodal form with modes near 0.005 µm, 0.09 µm, and 2.03 µm and are used to infer the relative mass fractionation among the three modes. While the smallest mode has been estimated to contain as much as 10% of the total mass of SRM exhaust alumina, we find show that the smallest mode contains less than 0.05% of the alumina mass. This fraction is so small so as to significantly reduce the likelihood that heterogeneous reactions on the SRM alumina surfaces could produce a significant global impact on stratospheric chemistry.
Ozone and temperature profiles measured above Kiruna inside, at the edge of, and outside the Arctic Polar Vortex in February and March 1997
Authors: Kreher K. , Bodeker G. E. , Kanzawa H. , Nakane H. , Sasano Y.
Published: September 2002

Ozone depletion above Kiruna (67.9°N, 21.1°E), Sweden, was investigated using daily ozone and temperature measurements by ozonesondes between 1 February and 25 March 1997. Using UKMO Ertel's potential vorticity (EPV) and wind fields, three dynamically distinct regions were defined on a grid of isentropic surfaces viz.: the polar vortex boundary region characterized by steep EPV gradients, the area poleward of the boundary region (inside the polar vortex), and the area equatorward of the boundary region (outside the polar vortex). Due to dynamically induced displacements of the vortex, measurements were made in all three regions. By calculating the isentropic EPV at each measurement point and comparing it with the values defining the equatorward and poleward edges of the vortex boundary region, all ozone and temperature measurements could be binned according to their position relative to the vortex edge. Since the data outside the polar vortex were highly variable, mean ozone profiles and their standard deviations were calculated and compared only for the two other regions. To investigate whether differences between these mean profiles were indicative of ozone loss, the temporal evolution of ozone mixing ratios measured along several isentropic surfaces was examined, taking into account the diabatic descent of airmasses. Finally, ozone loss rates were calculated for six potential temperature surfaces and loss rates of up to 0.63ppm/month were found inside the Arctic vortex at surfaces descending from approximately 475 K (1 February) to 460 K (25 March).
Polar cap optical observations of topside (>900 km) molecular nitrogen ions
Authors: Romick G. J. , Yee J‐H. , Morgan M. F. , Morrison D. , Paxton L. J. , Meng C‐I.
Published: September 2002

The Ballistic Missile Defense Organization's (BMDO) Midcourse Space Experiment (MSX) has obtained the first optical observations of molecular ions at very high altitudes above the northern polar cap. Spectra over geomagnetic latitudes ∼ 80°N, at 1300 MLT of the N2+ 1st Negative Bands are identified with a total band intensity of 2.5 kR and an implied number density of 10³ ions cm−3 at 900 km. Additional N2+ transitions from the Meinel bands were also observed. No other permitted optical emissions were observed above 450 km indicating that the source must be solar resonance fluorescence of the N2+ ion. The presence of heavy molecular ions at high altitudes is an indication of the upward flow of ions from the ionosphere into the magnetosphere. These optical observations suggest a new technique for the study of the global structure and temporal variation of plasma energization and transport between the ionosphere and magnetosphere in the polar regions.
Electrokinetic and magnetic fields generated by flow through a fractured zone: A Sensitivity study for La Fournaise Volcano
Authors: Adler Pierre M. , Le Mouel Jean‐Louis , Zlotnicki Jacques
Published: September 2002

A number of electric and magnetic signals have been observed on La Fournaise volcano, attributed to electrokinetic effects. A simple model is proposed here to check this hypothesis. The volcano is idealized as a 2d heterogeneous structure composed of a fractured zone located between two porous zones through which meteoritic waters flow downwards; flow occurs predominantly in the fractured zone and induces electromagnetic fields. Correct orders of magnitude are obtained for the measured surface fields. The importance of the heterogeneous character of the underground medium is demonstrated; local measurements of various quantities are recommended.
“Skewness” of S‐wave velocity in the mantle
Authors: Yanagisawa Takatoshi , Hamano Yozo
Published: September 2002

We analyze tomographic models of the S‐wave velocity in the mantle. The depth variation of laterally heterogeneous structure is parametrized in terms of the “skewness,” which yields information on mantle convection. Recent models show negative skewness in the lower half of the mantle. Assuming that the velocity anomaly is related to the temperature anomaly, this suggests that there is significant heat flow from the core.
Source distributions of substorm ions observed in the near‐Earth magnetotail
Authors: Ashour‐Abdalla M. , El‐Alaoui M. , Peroomian V. , Walker R. J. , Raeder J. , Frank L. A. , Paterson W. R.
Published: September 2002

This study employs Geotail plasma observations and numerical modeling to determine sources of the ions observed in the near‐Earth magnetotail near midnight during a substorm. The growth phase has the low‐latitude boundary layer as its most important source of ions at Geotail, but during the expansion phase the plasma mantle is dominant. The mantle distribution shows evidence of two distinct entry mechanisms: entry through a high‐latitude reconnection region resulting in an accelerated component, and entry through open field lines traditionally identified with the mantle source. The two entry mechanisms are separated in time, with the high‐latitude reconnection region disappearing prior to substorm onset.
Northern hemisphere summer ozone variability observed by POAM II
Authors: Hoppel Karl W. , Bowman Kenneth P. , Bevilacqua Richard M.
Published: September 2002

Zonal asymmetry in ozone mixing ratio was observed by POAM II during the 1994–1996 summers between 55°N and 65°N and between 21 km and 28 km in altitude. The zonal variance can be described as persistent large‐scale ozone patterns that move approximately with the zonal mean wind. The histories of air parcels observed by POAM are deduced from 20‐day back trajectories using UKMO winds which have been corrected for stationary anomalies. The ozone mixing ratio is found to correlate with the average latitude of the back trajectory throughout the summer, indicating that the zonal variance is a result of meridional transport. The meridional transport appears to be caused by breaking of westward‐propagating waves that are evanescent in the summer easterly flow.
Simulation of the κ−5/3 mesoscale spectral regime in the GFDL SKYHI General Circulation Model
Authors: Koshyk John N. , Hamilton Kevin , Mahlman J. D.
Published: September 2002

Data from very high horizontal resolution simulations with the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model are used to calculate the kinetic energy spectrum as a function of horizontal wavenumber, κ, in the upper troposphere. The spectrum shows the familiar ∼ −3 slope at scales longer than ∼ 1000 km, in agreement with previous general circulation model and observational studies. At shorter scales, the spectrum becomes shallower with a slope ∼ −5/3, also in agreement with available observations. The −5/3 slope spans about a decade of the resolved scales and this result represents the first successful simulation of such a broad range of the mesoscale regime by a global model. Partitioning of the flow between rotational and divergent components shows that the rotational part dominates at large scales and that there is approximate equipartition between rotational and divergent parts at mesoscales. Analysis of the parameterized kinetic energy dissipation shows that vertical diffusion dominates horizontal diffusion for a wide range of wavenumbers extending well into the κ−5/3 regime.
Electron acceleration in the auroral current circuit
Authors: Rönnmark Kjell
Published: September 2002

Understanding the mechanism supporting the potential drops that accelerate electrons into discrete auroral arcs has been an outstanding problem in space physics for decades. A few thousand kilometers above auroral arcs the electron density often is well below 106 m−3, and the parallel current density into discrete auroral arcs is often a few µA/m². To carry this current in such a low density plasma, the electrons must be accelerated to high energies, and kV potential drops can be supported by electron inertia alone. We describe how an equatorial MHD generator sets up the auroral current system and creates the parallel potential drop that accelerates auroral electrons to keV energies.
Seismic‐based estimate of hydraulic parameters at Vesuvius Volcano
Authors: Ventura Guido , Vilardo Giuseppe
Published: September 2002

We analyzed the seismicity of the Vesuvius volcano in order to estimate the hydraulic diffusivity α, the permeability κ, the pore‐fluid pressure and the stress magnitude in the seismogenetic volume. Vesuvius seismicity develops within the caldera volume and an events clustering occurs at about 2 km of depth. α has been estimated with two independent methods based on (a) the analysis of time history of earthquake occurrence combined with rainfall data of the last 25 years and (b) the progressive migration of earthquake foci observed during the February‐April 1996 seismic sequence. The obtained value (α = 0.25 m²s−1) has been utilized to calculate the permeability of the Vesuvius lavas (κ = 5.3 · 10−14 m²). Assuming a Coulomb criterion of failure, we performed a stress analysis of focal mechanisms in order to estimate the values of the ratio λ between the pore fluid pressure and the vertical stress for which the nodal planes have sufficiently resolved shear stress to slip. We found λ=0.6. We conclude: (a) the caldera volume is affected by an intense hydrothermal fluid circulation; (b) the spatio‐temporal features of the seismic activity are governed by increases in pore‐pressure; (c) the maximum rock strength weakening occurs at the transition between the sedimentary rocks of the volcanic basement and the intra‐caldera volcanics.
The 1997 Umbria‐Marche (Italy) earthquake sequence: Relationship between ground deformation and seismogenic structure
Authors: Cinti F. R. , Cucci L. , Marra F. , Montone P.
Published: September 2002

A field survey performed during the 1997 Umbria‐Marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks (Mw ≥ 5.7). The ruptures are concentrated in narrow bands that, in part, are on and near previously mapped high‐angle normal faults. The geometry of the ground deformation is consistent with the NE‐trending extension indicated by CMT focal solutions of the mainshocks. The distribution of aftershocks suggests that the three mainshocks occurred on ∼40° SW‐dipping normal faults. Geological investigations, modelling of expected coseismic elevation changes, and seismic data, suggest that the surface deformation is not the direct result of primary rupture of faults at depth.
Broadband microtremor observation of basin resonance in the Mississippi Embayment, central US
Authors: Bodin Paul , Horton Steve
Published: September 2002

We report systematic variations in the fundamental period of seismic site resonance within the Mississippi embayment. The resonance periods are revealed by peaks in horizontal to vertical (H/V) spectral ratios of microtremor measurements, and increase with the depth to the sediment/basement interface. The sediment depth varies slowly enough spatially that at any site it can be modeled as a one‐dimensional problem, revealing structural details of the sedimentary column. The strong impedance contrast and gentle dip of the base of the embayment sediments may trap seismic energy within the soft sediments, increasing durations and amplitudes of strong ground motions. Broadband recordings of microtremor within the Mississippi embayment provide a simple method to study the seismic response of the basin.
Ab initio study of the elastic behavior of MgSiO3 ilmenite at high pressure
Authors: Da Silva Cesar R. S. , Karki Bijaya B. , Stixrude Lars , Wentzcovitch Renata M.
Published: September 2002

We investigate the athermal high pressure behavior of the elastic properties of MgSiO3 ilmenite up to 30 GPa using the ab initio pseudopotential method. Our results at zero pressure are in good agreement with single‐crystal elasticity measurements. The elastic anisotropy is shown to decrease slightly under compression and hence to remain substantial (25 to 20% shear wave anisotropy and 16 to 10% longitudinal wave anisotropy) over the pressure regime studied. The directions of fastest and slowest wave propagation are found to change slightly with pressure as determined by the pressure dependence of c14 and c25. Comparisons with the elastic behavior of other deep transition zone phases such as ringwoodite and garnet show that ilmenite is likely to be the fastest and most anisotropic mineral in this region. Large contrasts (≈ 10%) in velocities and densities between ilmenite and garnet are suggested to be significant for the interpretation of lateral structure in the transition zone.
Fault fragment control in the 1997 Umbria‐Marche, central Italy, Earthquake Sequence
Authors: Meghraoui Mustapha , Bosi Vittorio , Camelbeeck Thierry
Published: September 2002

The Umbria‐Marche region in central Italy experienced a sequence of shallow earthquakes in late 1997, including three mainshocks on September 26th (Ms 5.5 and 5.9) and October 14th (Ms 5.5). This seismic sequence illustrates the relationships between small‐scale active faults and moderate‐magnitude earthquakes. We suggest that a small‐scale active fault corresponds to a “fault fragment” and that it refers to the fault area required for producing a coseismic deformation at the ground surface. The seismic activity and related three mainshocks occurred along three fault fragments which total ∼25 km in length and show a listric geometry at depth. Fault fragments are laterally controlled by pre‐existing transverse fold‐and‐thrust structures and may constitute a major component of the seismic strain release in active continental regions.
Evidence for volcanic influence on Mexico City aerosols
Authors: Raga G. B. , Kok G. L. , Baumgardner D. , Báez A. , Rosas I.
Published: September 2002

In situ measurements of sulfur dioxide (SO2), carbon monoxide (CO) and sulfate mass provide evidence that aerosol composition in Mexico City is affected by emissions from the neighboring volcano, Popocatepetl. The data collected over a two‐week period in November 1997 suggest that there are two distinct pathways by which SO2 is incorporated into particulates. Periods of high humidity, fog, and rain are accompanied by elevated sulfate mixing ratios, attributed to aqueous chemistry. Similarly, elevated sulfate concentrations in low humidity periods appear to be a result of adsorption onto existing particles. These two mechanisms are important for understanding the processes associated with particle formation in this highly polluted urban area. Under the influence of volcanic emissions, SO2 concentration can reach more than four times the monthly mean daily average (20ppbv) and particulate sulfate can be a factor of 2 larger.
Solubilities of CH3C(O)O2NO2 and HO2NO2 in water and liquid H2SO4
Authors: Leu Ming‐Taun , Zhang Renyi
Published: September 2002

In this paper we analyze literature values of the Henry's law constants of peroxyacetyl nitrate (CH3C(O)O2NO2, PAN) and peroxynitric acid (HO2NO2) in water and liquid sulfuric acid, and derive correlative expressions to predict the solubilities of PAN and HO2NO2 in liquid H2SO4 over a wide range of temperature and acidic composition. To a first‐order approximation, the results indicate that the Henry's law constants (in units of mol kg−1 atm−1) are ln(H) = 1.07 ‐ mH2SO4 × (0.69 ‐ 152/T) ‐ 5810 × (1/T0 ‐ 1/T) for PAN and ln(H) = 3.69 ‐ mH2SO4 × (− 0.25 + 65/T) ‐ 8400 × (1/T0 ‐ 1/T) for HO2NO2 where mH2SO4 is the molality of sulfuric acid, T is the temperature of solutions, and T0 = 298.15 K. The activity coefficients of PAN and HO2NO2 in aqueous H2SO4 are found to have a simple relationship with the molality of H2SO4.
Contrasting geophysical and geochemical signatures of a volcano at the axis of the Wharton Fossil Ridge (N‐E Indian Ocean)
Authors: Hébert Hélène , Villemant Benoît , Deplus Christine , Diament Michel
Published: September 2002

The Styx volcano is a prominent seamount (20–30 km diameter, 2500 m high) located at the axis of the Wharton fossil spreading center (N‐E Indian Ocean), where seafloor spreading stopped 40 Ma ago. Gravity modeling shows that it was emplaced on a weak lithosphere, in agreement with an on axis origin when seafloor spreading was active. The rocks dredged at the summit of the volcano are extreme typical alkaline basalts, indicating a deep enriched mantle source. We show here that most of this seamount was emplaced during the final stage of the seafloor spreading in the Wharton Basin. We then discuss how alkaline magmatism can be emplaced at the summit of the Styx.
Partitioning of NOy species in the summer Arctic stratosphere
Authors: Osterman G. B. , Sen B. , Toon G. C. , Salawitch R. J. , Margitan J. J. , Blavier J. ‐F. , Fahey D. W. , Gao R. S.
Published: September 2002

Volume mixing ratio profiles of the quantitatively significant NOy species NO, NO2, HNO3, HNO4, ClNO3 and N2O5 were measured remotely from 8 to 38 km by the JPL MkIV FTIR solar absorption spectrometer during balloon flights from Fairbanks, Alaska (64.8°N, 147.6°W) on May 8 and July 8, 1997. The observed ratio of NOx (NO + NO2) to NOy (total reactive nitrogen) is 10 to 30% greater than calculated by a steady state model using standard photochemistry constrained by MkIV measurements of long lived precursors (e.g., H2O, CH4, CO and N2O) and SAGE II aerosol surface area. The persistence of this discrepancy to 38 km altitude suggests that processes involving aerosols, such as the reduction of HNO3 on the surface of soot particles, cannot be the sole explanation. The most likely resolution to this discrepancy is that the rate of NO2 + OH + M → HNO3 + M (the dominant sink of NOx in the Arctic stratosphere during times of near continuous solar illumination) is significantly slower than the currently recommended rate.
Stratospheric clouds over England
Authors: Hervig Mark
Published: September 2002

Aerosol measurements from the Halogen Occultation Experiment show stratospheric clouds over England on March 3 and 4, 1996. The measured cloud volume density profiles were compared to equilibrium volumes computed for nitric acid trihydrate (NAT) and liquid ternary H2SO4‐H2O‐HNO3 aerosols. The measurements on March 4 are confidently identified as NAT, and isentropic back‐trajectories show that conditions were favorable for ice formation roughly 11 hours upwind of the observed cloud. These results support the suggestion that ice formation could be a necessary precursor to NAT nucleation.
Response of the equatorial Indian Ocean to an unusual wind event during 1994
Authors: Vinayachandran P. N. , Saji N. H. , Yamagata Toshio
Published: September 2002

Unusual westward wind anomalies were observed in the Indian Ocean during 1994. The response of the ocean to these anomalies is studied using an ocean general circulation model forced with interannual winds. Model results show that the eastward equatorial jets in the Indian Ocean were weak during 1994. Consequently, the sea level in the eastern Indian Ocean was unusually low, the thermocline and the mixed layer were shallow, and the subsurface flow remained eastward throughout the year. Anomalies of sea surface temperature (SST) and sea level in the eastern Indian Ocean were enhanced by upwelling favorable winds along the coast of Indonesia. The model results agree with observations and TOPEX/POSEIDON data. We suggest that the dynamical response of the ocean to wind anomalies played a role in generating the SST anomalies during 1994 and enhanced the large‐scale air‐sea interaction, independent of the El Niño Southern Oscillation.
Huascaran δ18O as an indicator of tropical climate during the Last Glacial Maximum
Authors: Pierrehumbert R. T.
Published: September 2002

The interpretation of the isotopic composition of Andes tropical mountain glaciers is reconsidered using a simple Rayleigh distillation model. It is shown that Andes snowline depression and Huascaran ice core δ18O are consistent with a 3°C drop in sea surface temperature during the Last Glacial Maximum, accompanied by an increase from 40% at present to 60% during the LGM in the annual mean proportion of atmospheric water lost to continental runoff. Broecker's interpretation of Huascaran δ18O as a paleo‐hygrometer is discussed.
The temporal evolution of the ratio HNO3/NOy in the Arctic lower stratosphere from January to March 1997
Authors: Schneider J. , Arnold F. , Curtius J. , Sierau B. , Fischer H. , Hoor P. , Wienhold F. G. , Parchatka U. , Zhang Y. C. , Schlager H. , Ziereis H. , Feigl Ch. , Lelieveld J. , Scheeren H. A. , Bujok O.
Published: September 2002

Aircraft‐based measurements of HNO3, NOy, N2O, and O3 have been performed in the Arctic lower stratosphere in January (POLSTAR I) and March (STREAM III) of 1997. The two projects employed different aircraft platforms. In addition, NOy and O3 were measured using different instruments in the two campaigns. HNO3 and NOy were found strongly correlated with correlation coefficients of 0.84 (POLSTAR I) and 0.69 (STREAM III), respectively. The fraction of HNO3 within NOy decreased from 96% in January to 59% in March. The decrease is consistent with the lifetime of HNO3 due to photolysis after polar sunrise. The relationship of NOy and HNO3 with N2O shows that in January NOy and HNO3 values were markedly higher than expected, which may indicate nitrification by PSC‐II particle sedimentation and evaporation. Contradictory, the ratios NOy/O3 observed in January are only slightly elevated. In March, NOy‐N2O and NOy‐O3 relations agree well with others reported in the literature. The difference between the NOy‐O3 and NOy‐N2O relationships is partly explained by an observed O3 decrease of about 30% between January and March.
Phase‐space electron holes along magnetic field lines
Authors: Muschietti L. , Ergun R. E. , Roth I. , Carlson C. W.
Published: September 2002

Recent observations from satellites crossing active magnetic field lines have revealed solitary potential structures that move at speeds substantially greater than the ion thermal velocity. The structures appear as positive potential pulses rapidly drifting along the magnetic field. We interpret them as BGK electron holes supported by a population of trapped and passing electrons. Using Laplace transform techniques, we analyse the behavior of one phase‐space electron hole. The resulting potential shapes and electron distribution functions are self‐consistent and compatible with the field and particle data associated with the observed pulses. In particular, the spatial width increases with increasing amplitude. The stability of the analytic solution is tested by means of a two‐dimensional particle‐in‐cell simulation code with open boundaries. We also use our code to briefly investigate the influence of the ions. The nonlinear structure appears to be remarkably resilient.
Effects of pore pressure on compressional wave attenuation in a young oceanic basalt
Authors: Tompkins Michael J. , Christensen Nikolas I.
Published: September 2002

Laboratory data are reported for ultrasonic compressional wave attenuation (αp) as a function of pore pressure in a Juan de Fuca Ridge dredge basalt. Four experiments have been made to determine the relationships between attenuation and quality factor (Qp) and confining and pore pressures in the shallow ocean crust. Attenuation was measured at 1) a constant differential pressure of 40 MPa; 2) confining pressures to 120 MPa and atmospheric pore pressures; 3) a constant confining pressure of 50 MPa while varying pore pressures; 4) a constant confining pressure of 100 MPa while varying pore pressures. For atmospheric pore pressures, αp ranges from 1.64 dB/cm to 7.08 dB/cm (Qp = 24 to 10). In addition, attenuation increases systematically with increasing pore pressure and decreasing differential pressure (confining pressure ‐ pore pressure). Results from DSDP and ODP downhole packer experiments suggest that the hydrostatic pore pressure regime may best approximate in situ conditions for young oceanic crust. Hydrostatic pore pressures (@ 5000 meters depth) reduce Qp as much as 35% from normal atmospheric pressure conditions; therefore, pore pressures generated in the upper oceanic crust may be responsible in part for the observed low seismic Qp within layer 2A. Qp measurements at elevated pore pressures agree well with seismic Qp data.
Characteristic modes of isotopic variations in atmospheric chemistry
Authors: Manning Martin R.
Published: September 2002

Interacting chemical systems can be analyzed using the structures and lifetimes of characteristic modes of variation about a quasi‐steady state. For the atmospheric CH4‐CO‐OH system, characteristic modes of concentration variation involve predominantly a single species, but their lifetimes differ from the dominant species turnover times. Here a species turnover time is the species amount divided by its removal rate, whereas the characteristic mode lifetime is the amplitude of a perturbation pattern divided by its rate of change and includes feedback effects. Characteristic mode analysis is used here to consider variations in both concentrations and isotopic ratios for such systems. New ‘isotopic modes’ are identified which are only weakly affected by feedbacks and have lifetimes very close to species turnover times. This raises the possibility that analysis of variations in both concentration and isotopic ratios may provide a unique tool for resolving turnover times and chemical feedbacks in atmospheric chemistry.
Cirrus detrainment‐temperature feedback
Authors: Chou Chia , Neelin J. David
Published: September 2002

In considering the role of cirriform clouds in climate change, it is important to distinguish among the relationships of different high cloud types to large‐scale atmospheric dynamics. While cirrostratus and cirrocumulus (CsCc) have a clear relation to deep convective sources, the ensemble behavior of cirrus is more subtle. An empirical relation is found between cirrus fraction and deep cloud top temperature that points to detrainment temperature as a dominant factor governing tropical and subtropical cirrus. This cirrus‐detrainment‐temperature (CDT) relation provides a target for modelers, and suggests an additional cloud‐climate feedback. As surface temperatures warm, detrainment temperatures cool as deep cloud top height increases. The CDT relation implies that cirrus fraction increases. Because cirrus are optically thinner than CsCc, the competition between longwave feedbacks and cloud albedo feedbacks leads to a hypothesized positive climate feedback by cirrus fraction.
Are revised models better models? A skill score assessment of regional interannual variability
Authors: Sperber Kenneth R. , Participating AMIP Modelling Groups
Published: September 2002

Various skill scores are used to assess the performance of revised models relative to their original configurations. The interannual variability of all‐India, Sahel and Nordeste rainfall and summer monsoon windshear is examined in integrations performed under the experimental design of the Atmospheric Model Intercomparison Project. For the indices considered, the revised models exhibit greater fidelity at simulating the observed interannual variability. Interannual variability of all‐India rainfall is better simulated by models that have a more realistic rainfall climatology in the vicinity of India, indicating the beneficial effect of reducing systematic model error.
Fractal behavior of ozone, wind and temperature in the lower stratosphere
Authors: Tuck A. F. , Hovde S. J.
Published: September 2002

We apply a measure from fractal geometry to time series of airborne observations of ozone and meteorological quantities in the lower stratosphere. The Hurst exponent measure demonstrates that the lower stratospheric ozone, wind and temperature obey single exponent power law scaling to a high degree of fidelity. As a result, we suggest that ozone and horizontal windspeed behave as random, self‐affine fractals, that vertical wind speed behaves antipersistently and that horizontal wind direction and temperature behave persistently. The persistent variables are candidates for multifractality.
Further evaluation of waves and turbulence encountered by the Galileo Probe during descent in Jupiter's atmosphere
Authors: Seiff Alvin , Kirk Donn B. , Mihalov John , Knight Tony C. D.
Published: September 2002

Data from the Galileo Probe in Jupiter descent indicated descent velocity oscillations as large as ±5 m/s on a height scale of a few km, which suggested gravity waves in the atmosphere between 4 and 20 bars (Seiff et al., 1998), an important observation for atmospheric stability and dynamics. But we now find these velocity fluctuations to be inconsistent with simultaneous measurements of mean accelerations, which were relatively steady. This conflict is resolved in favor of the accelerometers. The velocity fluctuations can be explained from digital uncertainties in the slow rate of pressure rise. However, the accelerometers did record higher frequency perturbations of up to 0.1g. Attributed to turbulence, these imply turbulent velocities from 0.3 to 5 m/s at scales of 10 to 40 m. However, they were at least partly a result of unsteady parachute aerodynamics.
Enhanced O3 and NO2 in thunderstorm clouds: Convection or production?
Authors: Winterrath Tanja , Kurosu Thomas P. , Richter Andreas , Burrows John P.
Published: September 2002

Ground based zenith sky measurements of O3 and NO2 slant optical thickness (SOT) from a field campaign at the Observatoire de Haute Provence in June 1996 are reported. Differential optical absorption spectroscopy in the 450–497 nm region was used to derive SOT for both species under clear sky, cloudy and thunderstorm conditions. SOT enhancements of 62% for O3 and up to 320% for NO2 are found in a thunderstorm cloud. Interpretation of the measurements was carried out using a radiative transfer model. To explain the measurements a mean increase of 38 ppbv of the in‐cloud concentration of O3 has to be assumed. This amount leads to a mean in‐cloud concentration of more than 100 ppbv of O3. The corresponding increase in NO2 is 3 ppbv, resulting in an in‐cloud concentration of 3.2 ppbv. The NO2 enhancements are in large part explained by lightning processes. In contrast, the enhanced O3 appears to be induced by intrusion of stratospheric air and possibly ozone production by non‐lightning discharge mechanisms.
Physical‐statistical retrieval of water vapor profiles using SSM/T‐2 Sounder data
Authors: Rieder Markus J. , Kirchengast Gottfried
Published: September 2002

The feasibility of retrieving water vapor profiles from downlooking passive microwave sounder data is demonstrated by usage of a retrieval algorithm which extends Bayesian optimal estimation. Special Sensor Microwave T‐2 (SSM/T‐2) downlooking sounder data, consisting of brightness temperature measurements sensitive to water vapor, are used together with total water vapor content data for computing tropospheric water vapor profiles. The significant nonlinearity in the cost function, an implication of the corresponding (nonlinear) radiative transfer equation, necessitates several extensions of the well‐known optimal estimation inversion scheme. We supplemented the scheme by simulated annealing and iterative a priori lightweighting and obtained a powerful physical‐statistical hybrid algorithm. Retrievals based on SSM/T‐2 data were compared to atmospheric analyses of the European Centre for Medium‐Range Weather Forecasts (ECMWF). A statistical validation of the retrieved profiles is presented. The comparisons indicate an approximate accuracy of about 15 to 20 percent for relative humidity.
Joint statistics of photon pathlength and cloud optical depth
Authors: Min Qilong , Harrison Lee
Published: September 2002

A mean pressure‐ and temperature‐weighted photon pathlength in the atmosphere can be inferred from moderate resolution measurements in the O2A‐band. We show a pathlength retrieval method and calibration results for measurements from a Rotating Shadowband Spectroradiometer (RSS), and present the joint statistics of pathlength and cloud optical depth for cloudy skies observed at the Southern Great Plains (SGP) site from Sept. 30 to Dec. 22, 1997. Two different population branches are apparent in the scattergram of the pathlength vs. cloud optical depth; we attribute these to 1) single layer cases exhibiting small variations of pathlength enhancement over large optical depth ranges; 2) multiple layer cases with large variances of enhanced photon pathlengths.
BrCl production in NaBr/NaCl/HNO3/O3 solutions representative of sea‐salt aerosols in the marine boundary layer
Authors: Disselkamp R. S. , Chapman E. G. , Barchet W. R. , Colson S. D. , Howd C. D.
Published: September 2002

Atomic bromine and chlorine liberated from sea‐salt aerosol is thought to play an important role in chemistry of the marine boundary layer. Despite numerous modeling studies, no prior experimental investigations of the oxidation of halide species contained in simulated, or actual, sea‐salt solutions have been performed. We present laboratory data that examines chemistry in NaBr/NaCl/HNO3/O3 solutions at 290 K. Ozonation experiments were performed by flowing ozone in air through a nitric acid/salt solution and monitoring pH with time using an ion‐sensitive electrode. The rate of oxidation was observed to be first order in ozone concentration and to have a non‐first order bromide concentration dependence. Ion Chromatography was used to measure both bromide disappearance as well as oxidation products formed during the course of the reactions studied. Our measurements of the oxidation rate versus ion concentration indicate that the high ionic strength present in sea‐salt aerosol will possess unique kinetics different from dilute solution behavior. In addition, our results are consistent with the reaction sequence O3 + H+ + Br− → O2 + HOBr and HOBr + Cl− + H+ → BrCl + H2O. These observations support the HOBr mediated Cl− oxidation process proposed previously (Vogt et al., 1996).
Essential characteristics of the Antarctic‐Spring Ozone Decline: Update to 1998
Authors: Uchino Osamu , Bojkov Rumen D. , Balis Dimitris S. , Akagi Kazuaki , Hayashi Motowo , Kajihara Ryoichi
Published: September 2002

Using both ground‐based and satellite data up to December 1998, the intensity, duration, appearance at both horizontal and vertical scales and ozone‐mass deficiency (O3MD) of the severe ozone decline observed over the southern polar region are presented. Over the last six years: the depletion within the ozone hole area (i.e. total ozone amounts <220 m atm‐cm) is almost three times more severe than in the early 1980s, the ozone hole (O3h) area has exceeded 22 million km² at its maximum, and the lowest total ozone was ∼100 m atm‐cm. However, during the 1998 season for the first time for nearly 20 days the O3h area exceeded 25 million km², and the integrated O3MD during September‐October, poleward of 60°S, exceeded the average value of the 1990s by ∼25%. At the beginning of the 1980s, ozone hole values were observed mostly in October, but more recently, they frequently continue until mid‐December. The depletion was most severe in the 12–20 km layer over Antarctica: ∼70% in September, ∼90% in October and ∼80% in November. Related to this, the monthly mean lower stratospheric temperatures between 70–90°S have declined by ∼10°C in October, ∼12°C in November and by ∼5°C in December. Taking the last six years seasonally integrated O3MD over the area poleward of 60°S (average ∼6.300 Mt) is about a third greater than the O3MD over the northern polar region winter‐springs. Over the southern mid‐latitudes O3MD is about a third less than the deficiency observed between 35–55°N.
Differences in near‐mesopause summer winds, temperatures, and water vapor at northern and southern latitudes as possible causal factors for inter‐hemispheric PMSE differences
Authors: Huaman Mercedes M. , Balsley Ben B.
Published: September 2002

We report the results of a recent study to examine possible causal factors that could explain the observed differences in PMSE intensity in the northern and southern hemispheres. A variety of satellite data, models and ground‐based radar observations in the two hemispheres during local summer have been examined in this attempt. We will show results of inter‐hemispheric comparisons of temperatures, winds, and water vapor. The primary conclusions that can be drawn from these studies are that, while water vapor differences in the two hemispheres are difficult to interpret at near‐mesopause altitudes, the inter‐hemispheric temperature comparisons show clearly that the southern hemispheric mesopause is indeed a few degrees warmer. Moreover, southern summer mesospheric mean winds are considerably weaker than they are in the north. These results provide support for earlier speculations that were made to explain the observed inter‐hemispheric difference in PMSE occurrence.