bluuebunny/crossref_metadata_2025 huggingface dataset:
Empirical retrieval of the atmospheric air mass factor (ERA) for the measurement of water vapour vertical content using GOME data
Authors: Casadio Stefano , Zehner Claus , Pisacane Giovanna , Putz Erich
Published: September 2002

A new empirical technique for the fast retrieval of vertical concentrations of water vapour from the GOME uncalibrated spectra is described in detail. The ERA technique (Empirical Retrieval of Atmospheric air mass factor) makes maximum use of GOME's capability to measure atmospheric spectra over a broad wavelength range with high spectral resolution, by retrieving a normalisation factor for the water vapour concentrations directly from the data (oxygen slant column measurements). ERA results are compared to the ECMWF TCWV analysis (Total Column Water Vapour), showing good agreement.
Kinetics of the OH‐initiated oxidation of isoprene
Authors: Campuzano‐Jost Pedro , Williams Margaret B. , O'Ottone Luca , Hynes Anthony J.
Published: September 2002

Absolute rate coefficients have been determined for the reaction OH + C5H8 (1) and two of its isotopomeric variants. Reaction (1) was studied as a function of temperature and pressure in N2, N2/O2 and He buffer gases. At room temperature, a rate coefficient, k1, of (8.56±0.26)*10−11 cm³ s−1 independent of pressure and buffer gas identity was obtained. An Arrhenius fit to data over the temperature range 250 – 340 K gave a negative activation energy of −666±150 cal/mol. HO2 production was inferred from observations of radical regeneration in the presence of NO. The absence of a kinetic isotope effect, together with the specificity of radical regeneration, indicates that reaction proceeds via an addition channel with no significant abstraction component. Our rate coefficient for reaction (1) is 15% lower than the value currently recommenced for atmospheric modeling.
Mean Flow in composite porous media
Authors: Winter C. L. , Tartakovsky Daniel M.
Published: September 2002

We develop probabilities and statistics for the parameters of Darcy flows through saturated porous media composed of units of different materials. Our probability model has two levels. On the local level, a porous medium is composed of disjoint, statistically homogeneous volumes (or blocks) each of which consists of a single type of material. On a larger scale, a porous medium is an arrangement of blocks whose extent and location are uncertain. Using this two‐scaled model, we derive general formulae for the probability distribution of hydraulic conductivity and its mean; then we develop general perturbation expansions for mean head. We express distributions and parameters in terms of mixtures of locally homogeneous block densities weighted by large‐scale block membership probabilities.
Evidence for shear velocity anisotropy in the lowermost mantle beneath the Indian Ocean
Authors: Ritsema Jeroen
Published: September 2002

Teleseismic recordings (Δ > 87°) of a deep earthquake beneath the Banda Sea at stations in Tanzania show a difference in the arrival time of the radial (SSV) and transverse component (SSH) S wave ranging from 1–3 s. Shear velocity anisotropy in the lowermost mantle beneath the Indian Ocean is the likely cause of this signal because recordings at the same stations of closer‐in events (Δ < 80°) in the same source region do not present a comparable differential travel time. For the Banda Sea event, the SSH signals are broader than SSV signals, suggesting that a discontinuity (or strong vertical gradient) in primarily VSH marks the sudden onset of transverse isotropy in D” (with a magnitude of 1.4–2.7%) about 350 km above the core‐mantle boundary. SKKS coda, S‐to‐p converted phases at the Moho, and upper mantle heterogeneity beneath the stations obscure the onset of SSV and complicate wave shapes. It is therefore difficult to evaluate whether general anisotropy needs to be invoked into a model of shear velocity anisotropy.
The discrepancy between measured and modeled downwelling solar irradiance at the ground: Dependence on water vapor
Authors: Pilewskie P. , Rabbette M. , Bergstrom R. , Marquez J. , Schmid B. , Russell P. B.
Published: September 2002

Moderate resolution spectra of the downwelling solar irradiance at the ground in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under cloud‐free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model‐measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 Wm−2 per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.
Aseismic inflation of Westdahl Volcano, Alaska, revealed by satellite radar interferometry
Authors: Lu Zhong , Wicks Charles , Dzurisin Daniel , Thatcher Wayne , Freymueller Jeffrey T. , McNutt Stephen R. , Mann Dörte
Published: September 2002

Westdahl volcano, located at the west end of Unimak Island in the central Aleutian volcanic arc, Alaska, is a broad shield that produced moderate‐sized eruptions in 1964, 1978–79, and 1991–92. Satellite radar interferometry detected about 17 cm of volcano‐wide inflation from September 1993 to October 1998. Multiple independent interferograms reveal that the deformation rate has not been steady; more inflation occurred from 1993 to 1995 than from 1995 to 1998. Numerical modeling indicates that a source located about 9 km beneath the center of the volcano inflated by about 0.05 km³ from 1993 to 1998. On the basis of the timing and volume of recent eruptions at Westdahl and the fact that it has been inflating for more than 5 years, the next eruption can be expected within the next several years.
The 1997 fires in Kalimantan and Sumatra, Indonesia: Gaseous and particulate emissions
Authors: Levine Joel S.
Published: September 2002

Extensive and widespread vegetation and peat fires swept throughout Kalimantan and Sumatra, Indonesia, from August 1997 through March 1998. The fires resulted from routine burning for land clearing and land‐use change. However, the severe drought conditions resulting from El Nino caused small land‐clearing fires to become large uncontrolled wildfires. Analysis of SPOT images indicate that a total of 45,600 km² burned between August and December 1997. In this paper, the gaseous and particulate emissions resulting from the 1997 fires are estimated. On a daily basis, the calculated emissions of CO2, CO, CH4, NOx, and particulates from the Kalimantan and Sumatra fires of 1997 significantly exceeded the emissions from the Kuwait oil fires of 1991.
Can Ion Cyclotron Waves Propagate to the Ground?
Authors: Johnson Jay R. , Cheng C. Z.
Published: September 2002

This paper demonstrates how ion cyclotron waves generated in the equatorial magnetosphere can propagate to the ground and resolves a discrepancy between theory and observation that has lasted over a decade. We present a full wave analysis for ion cyclotron waves propagating from the equatorial magnetosphere to the ground. Our analysis demonstrates that strong mode coupling occurs near the He+ and O+ resonance locations which allows the equatorial waves to penetrate to ionospheric altitudes with substantial amplitude and shifted polarization consistent with observational studies.
Ekman transport and upwelling during Younger Dryas estimated from wind stress from GENESIS Climate model experiments with variable North Atlantic heat convergence
Authors: Ágústsdóttir Anna María , Alley Richard B. , Pollard David , Peterson William H.
Published: September 2002

Reconstructed climatic changes during the Younger Dryas interval are similar to, but somewhat larger and more wide‐spread than, those expected based on the direct atmospheric effects of reduced North Atlantic oceanic heat transport. The paleoclimatic data show that North Atlantic cooling during the Younger Dryas was accompanied by stronger winds in many regions, suggesting that enhanced wind‐driven ocean upwelling may have served as a positive feedback on the cooling. We test this hypothesis using the GENESIS atmospheric general circulation model, and find that Younger Dryas‐age specified reduction in North Atlantic oceanic heat transport increases tropical Ekman divergence by ≈10% in regions and at times of prominent upwelling, sufficient to affect tropical temperatures.
Up‐scaling effects in passive microwave remote sensing: ESTAR 1.4 GHz measurements during SGP '97
Authors: Drusch Matthias , Wood Eric F. , Simmer Clemens
Published: September 2002

Passive microwave radiation measurements over sparsely vegetated surfaces during the Southern Great Plain Experiment are used to determine spatial up‐scaling effects. For various distributions of geophysical parameters, the differences between mean soil moisture derived from high resolution (800 by 800m²) 1.4 GHz brightness temperatures and soil moisture calculated from mean brightness temperatures at larger scales are compared. For spatial resolutions of 31.4²km², the effects of these non‐linearities in radiative transfer at 1.4 GHz do not yield differences in estimated volumetric surface soil moisture (0–5 cm) exceeding 0.02 [cm³cm−3].
A comparison of observations and model simulations of NOx/NOy in the lower stratosphere
Authors: Gao R. S. , Fahey D. W. , Del Negro L. A. , Donnelly S. G. , Keim E. R. , Neuman J. A. , Teverovskaia E. , Wennberg P. O. , Hanisco T. F. , Lanzendorf E. J. , Proffitt M. H. , Margitan J. J. , Wilson J. C. , Elkins J. W. , Stimpfle R. M. , Cohen R. C. , McElroy C. T. , Bui T. P. , Salawitch R. J. , Brown S. S. , Ravishankara A. R. , Portmann R. W. , Ko M. K. W. , Weisenstein D. K. , Newman P. A.
Published: September 2002

Extensive airborne measurements of the reactive nitrogen reservoir (NOy) and its component nitric oxide (NO) have been made in the lower stratosphere. Box model simulations that are constrained by observations of radical and long‐lived species and which include heterogeneous chemistry systematically underpredict the NOx (= NO + NO2) to NOy ratio. The model agreement is substantially improved if newly measured rate coefficients for the OH + NO2 and OH + HNO3 reactions are used. When included in 2‐D models, the new rate coefficients significantly increase the calculated ozone loss due to NOx and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircraft are also altered.
Simulation of the Quasi‐Biennial Oscillation in a general circulation model
Authors: Takahashi Masaaki
Published: September 2002

Simulation of the equatorial stratospheric quasi‐biennial oscillation (QBO) is accomplished, using a T42‐horizontal resolution, 60‐layer general circulation model (GCM), with a scheme of moist convective adjustment. In a previous paper, we succeeded in simulating a QBO in a T21 GCM using a damping time of 20 days for the maximum wavenumber in the fourth‐order horizontal diffusion. It was noted that the damping time is a factor of 10 larger than that employed in standard GCMs. In this paper, we explore whether it is possible to use a smaller damping term by going to a finer horizontal resolution. We successfully simulated a QBO using a damping time of 4 days. The period of the simulated QBO is 800 days, being almost the same as that observed. The amplitude of the zonal‐wind oscillation is 20 ms−1. However, this is achieved at the expense of much noiser precipitation and the damping time is still a factor of 7 larger than the standard values.
Delamination‐wedge structure beneath the Hidaka Collision Zone, central Hokkaido, Japan inferred from seismic reflection profiling
Authors: Tsumura Noriko , Ikawa Hidemasa , Ikawa Takashi , Shinohara Masanao , Ito Tanio , Arita Kazunori , Moriya Takeo , Kimura Gaku , Ikawa Takeshi
Published: September 2002

In the Hidaka Collision Zone of Hokkaido, northern Japan, the Kuril island arc collides with the northeast Japan arc. In order to better understand the collision process, new high resolution information about lithospheric structure was obtained by means of a series of seismic reflection surveys. These seismic profiles reveal distinct zones of seismic lamination in the lower crust of the Kuril arc. The upper portion of the lower crust is characterized by numerous east‐dipping reflectors. In contrast, west‐dipping reflectors dominate the lower part of the lower crust. From this reflector configuration, the lower crust of the Kuril arc is interpreted to be delaminated by the collision. The geometry of delamination is consistent with other geophysical data, as well as the peak metamorphic grades exposed in the Hidaka mountains. As earthquakes indicate that delamination here is ongoing, the Hidaka Collision Zone represents an active model for continental growth by arc accretion with delamination of lower arc crust.
Illumination conditions at the lunar South Pole
Authors: Bussey D. Ben J. , Spudis Paul D. , Robinson Mark S.
Published: September 2002

Recent remote sensing data strongly suggest that deposits of ice occur in permanently shadowed regions at the lunar poles. Clementine, by providing the first contiguous coverage of the Moon, has enabled the production of an illumination map of the south pole. This map shows the extent of the areas of permanent darkness during winter in this region as well as identifying places on the lunar surface that receive illumination for more than 50% of the lunar day. The permanently dark areas are prime candidates for locations of ice deposits while regions that are illuminated for anomalous periods are possible sites for lunar bases. In this paper we study in detail the illumination history during a lunar day of some of these sites. While we find no area that receives permanent illumination, we do find two areas, only 10 km apart, which collectively receive sunlight for over 98% of the time.
Toluene emissions from plants
Authors: Heiden A. C. , Kobel K. , Komenda M. , Koppmann R. , Shao M. , Wildt J.
Published: September 2002

The emission of toluene from different plants was observed in continuously stirred tank reactors and in field measurements. For plants growing without stress, emission rates were low and ranged from the detection limit up to 2·10−16 mol·cm−2·s−1. Under conditions of stress, the emission rates exceeded 10−14 mol·cm−2·s−1. Exposure of sunflower (Helianthus annuus L. cv. Gigantheus) to 13CO2 resulted in 13C‐labeling of the emitted toluene on a time scale of hours. Although no biochemical pathway for the production of toluene is known, these results indicate that toluene is synthesized by the plants. The emission rates of toluene from sunflower are dependent on nutrient supply and wounding. Since α‐pinene emission rates are also influenced by these factors, toluene and α‐pinene emissions show a high correlation. During pathogen attack on Scots pines (Pinus sylvestris L.) significant toluene emissions were observed. In this case emissions of toluene and α‐pinene also show a good correlation. Toluene emissions were also found in field experiments with pines using branch enclosures.
The use of laser altimetry in the orbit and attitude determination of Mars Global Surveyor
Authors: Rowlands D. D. , Pavlis D. E. , Lemoine F. G. , Neumann G. A. , Luthcke S. B.
Published: September 2002

Altimetry from the Mars Observer Laser Altimeter (MOLA), an instrument on board the Mars Global Surveyor (MGS) spacecraft, has been analyzed for the period of the MGS Science Phasing Orbit‐1 (SPO‐1) mission phase. Altimeter ranges have been used to improve significantly the orbit and attitude knowledge of the spacecraft by the use of crossover constraint equations derived from short passes of the MOLA data. These constraint equations differ from traditional crossover constraints and exploit the small footprint associated with laser altimetry. The rationale for using this technique with laser altimetry over sloping terrain is laid out and evidence of the resulting benefit is presented.
Mesospheric electric field transients due to tropospheric lightning discharges
Authors: Pasko Victor P. , Inan Umran S. , Bell Timothy F.
Published: September 2002

A physical picture and quantitative two‐dimensional electromagnetic modeling of mesospheric electric field transients produced by cloud‐to‐ground (CG) lightning discharges with short duration currents (<0.5 ms) are presented. The range of applicability of existing quasi‐electrostatic models of sprites and the physical conditions under which relatively weak CG lightning discharges (thundercloud charge moment changes less than 50C×10 km) may initiate sprites are discussed in the context of recent experimental findings.
Aerosol silica as a possible candidate for the heterogeneous formation of nitric acid hydrates in the stratosphere
Authors: Bogdan A. , Kulmala M.
Published: September 2002

The liquid‐solid phase transitions in nanometersize HNO3/H2O solution droplets obtained on fumed silica (a counterpart of aerosol silica) have been studied with differential scanning calorimetry (DSC). “Soft” transitions, reduction in the freezing and melting temperatures, Tf and Tm, and enthalpies, ΔHf and ΔHm, are interpreted to be caused by very small size of droplets. The observed difference between ΔHf and ΔHm can serve as an evidence of temperature dependence of the enthalpy of fusion for hydrates. Freezing of droplets with stoichiometry close to nitric acid trihydrate (NAT) at temperature 4 K warmer than the ice frost point indicates that, in the stratosphere, silica particles can serve as nuclei for heterogeneous freezing of NAT.
Multiple processes causing sea‐level rise in the central Mediterranean
Authors: Di Donato G. , Negredo A. M. , Sabadini R. , Vermeersen L. L. A.
Published: September 2002

Our analysis of a series of sea‐level records along the Italian coast of the Adriatic sea indicates a sea‐level rise not attributable to a global eustatic signal, but rather to the combined effects of active tectonics and Glacial Isostatic Adjustment (henceforth GIA). The highest predicted sea‐level rise, of the order of 0.9–1.0 mm/yr, occurs in proximity of the city of Ravenna, in the northern sector of the Adriatic sea, decreasing to 0.4–0.5 mm/yr in the northernmost and southern parts of the Adriatic sea. While GIA is the dominant mechanism of sea‐level rise in the southern sector of the Adriatic sea, active tectonics and GIA contribute a comparable amount in the north. Our results are of importance for quantitative estimates of trends of sea‐level changes in a part of the Mediterranean, the northern Adriatic sea, where the historical cities of Venice and Ravenna are severely exposed to sea‐level rise.
Some optical properties of smoke aerosol in Indonesia and tropical Australia
Authors: Gras J. L. , Jensen J. B. , Okada K. , Ikegami M. , Zaizen Y. , Makino Y.
Published: September 2002

Aerosol light‐scattering coefficient at 530 nm and its hygroscopic growth were determined in biomass‐burning smoke in the lower atmosphere over Kalimantan and northern Australia during the 1997 dry‐season fires. Both in and away from plumes, light‐scattering was considerably greater in the Indonesian region and hygroscopic growth in scattering was also consistently greater. The relative increase in scattering, from 20% to 80% relative humidity, was typically 1.37 in northern Australian and 1.65 in Kalimantan. Limited aerosol light absorption data indicate relatively small absorption in the Indonesian smoke. In part these differences can be explained by different combustion phases, mixed flaming and smoldering in the Australian savanna fires compared with predominantly smoldering in Indonesia, although these and other concurrent measurements suggest that underground peat combustion may have made a significant contribution to the Indonesian smoke.
observation of auroral emissions induced by artificial plasma jets
Authors: Erlandson R. E. , Swaminathan P. K. , Meng C.‐I. , Stoyanov B. J. , Zetzer J. I. , Gavrilov B. G. , Kiselev Yu. N. , Romanovsky Yu. A.
Published: September 2002

In this paper we present ultraviolet to near infrared spectrographic observations of high‐speed artificial plasma jet interactions with the ionosphere. The plasma jets were injected quasi‐parallel to the magnetic field at an altitude of 140 km during the Fluxus‐1 and ‐2 experiments. The jets contained aluminum ions and were generated using a shaped‐charge device known as an Explosive Type Generator (ETG). Satellite‐based spectrographic observations of the plasma jet show typical auroral emission features associated with electron impact excitation. The auroral features include emission at 135.6 nm (OI) and 557.7 nm (OI). The 135.6 nm emission was prompt while the 557.7 nm was observed for 5 seconds. The most likely source of these auroral emissions are ionospheric and magnetospheric electrons that neutralize the plasma jet.
Assessment of the impacts of the 1997–98 El Niño on the Asian‐Australia Monsoon
Authors: Lau K. M. , Wu H.‐T.
Published: September 2002

Singular Value Decomposition (SVD) analyses of rainfall and sea surface temperature (SST) are carried out globally over the entire tropics and regionally over the Asia‐Australian (AA)‐monsoon domain. Contributions to monsoon rainfall predictability by basin‐scale SST forcing and regional SST coupling are evaluated from cumulative anomaly correlation with dominant regional SVD modes. The observed 1997–98 AA‐monsoon anomalies are found to be very complex with approximately 34% of the anomalies of the Asian (boreal) summer monsoon and 74% of the Australia (austral) monsoon attributable to basin‐scale SST influence associated with El Niño. For the boreal and austral monsoon respectively, regional coupled processes contribute an additional 19% and 10%, leaving about 47% and 16% due to other factors including high frequency transients. Results suggest that in order to improve seasonal‐to‐interannual predictability of the AA‐monsoon, we need to investigate and exploit not only monsoon‐El Niño relationship, but also intrinsic monsoon regional coupled processes.
Modeling an enhancement of the lunar sodium tail during the Leonid Meteor Shower of 1998
Authors: Wilson Jody K. , Smith Steven M. , Baumgardner Jeffrey , Mendillo Michael
Published: September 2002

A region of non‐terrestrial sodium emission seen in the sky on the nights of November 18–20, 1998, has been interpreted as the Moon's distant sodium tail, possibly enhanced by micrometeor impact vaporization of the lunar regolith by the Leonid meteor shower. We show that the location and morphology of the spot can be explained by standard steady‐state models of the Moon's sodium atmosphere. Moreover, using a new time‐dependent simulation of the lunar atmosphere, we find that the Na escape rate from the Moon increased to 2 or 3 times its normal level during the most intense period of the 1998 Leonid meteor shower on November 16th and 17th.
High energy ions and electrons upstream from the Earth's bow shock and their dependence on geomagnetic conditions: Statistical results between years 1982–1988
Authors: Anagnostopoulos G. C. , Kaliabetsos G. , Argyropoulos G. , Sarris E. T.
Published: September 2002

We present initial results from a statistical analysis of 2034 energetic (50–220 keV) ion events observed by the IMP‐8 spacecraft upstream from the Earth's bow shock during a 6 years period. The most important findings are the following: (1) the percentage Pe of high intensity energetic ion events accompanied by the presence of relativistic (≥ 220 keV) electrons is ∼80% (for all geomagnetic conditions), and increases significantly with increasing the index Kp of geomagnetic activity, (2) high intensity energetic ion events most often (∼93%) show spectra extending up to energies E>∼300 keV, (3) a percentage of ∼71.5% of events display non‐inverse energy dispersion of ion intensities. The above results, as well as additional results discussed in the text, suggest that a percentage as high as ∼80% of high intensity 50–220 keV ion events in our statistical sample have an origin within the magnetosphere.
Flow pattern variability in natural fracture intersections
Authors: Kosakowski Georg , Berkowitz Brian
Published: September 2002

We use numerical simulations to examine the variability of flow patterns in representative fracture intersection geometries. In contrast to existing studies of perfectly orthogonal intersections, we demonstrate that more realistic geometries lead to a rich spectrum of flow patterns. Moreover, numerical solutions of the Navier‐Stokes equations in these fracture intersections indicate that non‐linear inertial effects become important for Reynolds numbers as low as 1–100. Such Reynolds numbers often exist in naturally fractured formations, particularly in karst systems and in the vicinity of wells during pump tests.
Impacting Lunar Prospector in a cold trap to detect water ice
Authors: Goldstein David B. , Nerem R. Steven , Barker Edwin S. , Austin J. Victor , Binder Alan B. , Feldman William C.
Published: September 2002

Lunar Prospector data support the contention that water ice reservoirs exist in the permanently shaded craters near the lunar poles. Yet the question remains whether the detected hydrogen abundance is actually water ice or is hydrogen in some other form. Present plans call for a controlled impact of Lunar Prospector into a polar crater at the end of July, 1999, in an attempt to liberate a small amount of water vapor that may be detected by ground‐ and space‐based observatories. A positive spectral detection of water vapor or its photo‐dissociated byproduct, OH, would be definite proof of the presence of water ice in the regolith. The following represents both an analysis of this method of searching for water ice as well as an announcement to the observing community of the event.
Narrowband structure in HF waves above the electron plasma frequency in the auroral ionosphere
Authors: McAdams K. L. , LaBelle J.
Published: September 2002

We report high resolution measurements of the frequency‐time structure of HF waves just above the electron plasma frequency in overdense conditions in the auroral ionosphere. Short duration narrowband emissions (HF chirps) are observed whose frequencies predominantly decrease with time. Typical HF Chirp amplitudes are 1 mV/m, typical durations are 100 ms, and typical frequency‐time slopes are 50 kHz/s. The emissions often occur in flocks in which pairs of emissions appear simultaneously at frequencies 300‐2000 Hz apart and drift in parallel. The observed characteristics are consistent with propagating electromagnetic Z‐mode waves.
The barrier layer in the western tropical Atlantic Ocean
Authors: Pailler K. , Bourlès B. , Gouriou Y.
Published: September 2002

In the tropical oceans, where the temperature is roughly homogenous in the upper layer, vertical variations of salinity may be responsible for significant density stratifications. In this study on the western Tropical Atlantic Ocean, it is shown that fresh surface waters of the Amazon River discharge may induce a strong halocline in the 3–30 m depth range. This halocline induces a pycnocline that acts as a barrier for mixing between the surface and the subsurface waters. The fresh surface waters are generally associated with positive anomalies of the sea surface temperature. These positive anomalies cover a large part of the basin in boreal summer–fall, following the maximum Amazon River discharge, which may have a significant importance for the ocean‐atmosphere exchanges.
Gradient drift instability in midlatitude sporadic E layers: Localization of physical and wavenumber space
Authors: Kelley M. C. , Gelinas L. J.
Published: September 2002

Ionospheric plasmas containing density gradients are subject to a gradient drift instability under the influence of an externally applied electric field or neutral wind. In this paper we present electric field wave data from the Sudden Atom Layers sounding rocket showing a pure gradient drift instability on the topside of a 1 km thick sporadic E layer. An outer scale of 50 m was determined. Considering the local linear growth rate and the mapping of the electric field structures along magnetic field lines, we conclude that structures with scales larger than 50 m perpendicular to the magnetic field map into regions of linear stability where they are damped. The free energy is localized in wavenumber space, yielding peak fluctuating fields of 6 mV/m, corresponding to electron drifts over 190 m/s and a cascade of energy to meter scales.
On the global production rates of energetic neutral atoms (ENAs) and their association with the Dst index
Authors: Ebihara Y. , Barabash S. , Ejiri M.
Published: September 2002

This paper describes calculations of the global production rates of the energetic neutral atoms (ENAs) in the magnetosphere and their association with the Dst index on the basis of quantitative numerical simulations. We simulate an idealized moderate storm and calculate the total ENA production rates with energies between 3.8 and 160.4 keV. For energies less than 30 keV, the production rates are approximately proportional to Dst for both the storm main and the recovery phases. For energies greater than 30 keV, the total production rates do not show any clear correlation with Dst and demonstrate oscillations with the corresponding drift period and beatings.
New kinetic instability: Oblique Alfvén fire hose
Authors: Hellinger P. , Matsumoto H.
Published: September 2002

Two instabilities could take place in plasma with a bi‐Maxwellian proton distribution function with Tp‖ > Tp⊥, where Tp‖ and Tp⊥ are proton temperatures, parallel and perpendicular, respectively, to the background magnetic field. The first instability is the fire hose (or whistler fire hose), generating low‐frequency whistler waves at parallel propagation. We found a new, second instability, the Alfvén fire hose, that generates zero‐frequency waves of the Alfvén branch at strongly oblique propagation. The Alfvén fire hose has a linear growth rate comparable to or even greater than that of the whistler fire hose. The two instabilities with the same initial plasma parameters are examined via one‐dimensional hybrid simulations and turn out to have behavior very different from each other. The whistler fire hose has an overall quasi‐linear evolution, while the evolution of the Alfvén fire hose is more complicated: Initially, unstable zero‐frequency waves are gradually transformed into propagating Alfvén waves; during this process the waves are strongly damped and heat protons in a perpendicular direction. Consequently, the Alfvén fire hose is very efficient at destroying proton anisotropy.
Hot oxygen profiles for incoherent scatter radar analysis of ion energy balance
Authors: Schoendorf J. , Young L. A. , Oliver W. L.
Published: September 2002

Thermospheric density and temperature are often derived from ionospheric observables measured by incoherent scatter radar (ISR) via solutions of the F region ion energy balance equation. However, this equation, consisting of an electron heat source balancing a neutral heat sink, can break down near the exobase, where the electron heat source can be too small by as much as 40%. An additional heat source is required, and theoretical and experimental studies point to a hot neutral oxygen (hot O) geocorona near the Earth's exobase to supply it. Hot O must therefore be included in the ion energy balance equation; however, its profile shape and concentration are unknown. We develop a simple method for including hot O profiles in the ion temperature fitting equation by calculating hot O concentration as a function of altitude and including the hot O heat source in the ion energy equation. The technique is tested as a function of solar cycle for March equinox conditions, and a χ2 analysis indicates that the hot O is more likely to form a layer than a concentration profile which decreases as a function of altitude.
Time‐dependent transport of field‐aligned bursts of electrons in flickering aurora
Authors: Peticolas L. , Lummerzheim D.
Published: September 2002

We have developed a time‐dependent auroral electron transport model to study emission rates caused by field‐aligned bursts of electrons (FABs) seen in flickering aurora. We simulate flickering FABs by turning on and off a downward electron intensity distribution at a given frequency. We assume this electron beam originates and is modulated at an altitude of 4000 km. We apply collisionless transport from 4000 to 600 km and solve a time‐dependent Boltzmann equation below 600 km. Because FABs have significant flux over a large energy range, dispersion has the most important effect on the resulting emission rates. We find that for a 5 Hz flickering FAB, the column emission rate varies 93% from peak to valley, whereas for 100 Hz flickering, the variation in column emission rate is only 12% from peak to valley. This variation is dependent on the frequency and source altitude. We show that with a time‐dependent transport calculation and a filtered fast photometer or imager looking in the zenith, it is possible to obtain an upper limit on the altitude from which the optical flickering originates. We also study what electron detectors on a rocket or satellite might measure in the lower ionosphere when there exists field‐aligned bursts of electrons. Velocity dispersion calculations will give source altitudes much lower than is correct if they are derived from low energy electrons (<2 keV) measured at altitudes below 150 km. Our results agree with the interpretation that field‐aligned bursts are a temporal rather than spatial feature, and from this knowledge it should be possible to reconstruct the initial electron distribution function at the source altitude.
On the stability of perpendicular electrostatic modes in stationary nongyrotropic plasmas
Authors: Romeiras Filipe J. , Brinca Armando L.
Published: September 2002

It is shown that the introduction of stationary gyrophase bunching in the electron population of a thoroughly stable magnetoplasma brings about strong growth of electrostatic waves propagating perpendicularly to the background magnetic field. We present the first derivation and analysis of the dispersion of these Bernstein‐like modes in media exhibiting stationary nongyrotropy, and we demonstrate the occurrence of solutions of the linear initial‐value problem with growth rates of the order of the associated real frequencies.
Characteristics of pseudobreakups and substorms observed in the ionosphere, at the geosynchronous orbit, and in the midtail
Authors: Aikio A. T. , Sergeev V. A. , Shukhtina M. A. , Vagina L. I. , Angelopoulos V. , Reeves G. D.
Published: September 2002

We present a comprehensive study of a sequence of two substorms and multiple pseudobreakups using optical, magnetic and incoherent scatter radar measurements, energetic particles from two geosynchronous satellites and particle and field data from the Geotail spacecraft located at Xgsm ∼ −86 RE. Following conventional nomenclature, we classified as pseudobreakups those auroral breakups which did not exhibit significant poleward expansion (< 2° magnetic latitude). Auroral intensifications following substorm breakups were also observed, and were classified separately. Pseudobreakups were found not to differ from substorm breakups in longitudinal extent (from 1.3 to 6.1 hours of magnetic local time), or in duration (from 5 to 16 minutes). In general, the ionospheric currents producing ground magnetic disturbances were more intense during substorms than pseudobreakups. We found that pseudobreakups are associated with the same magnetospheric processes as substorm breakups which involve current wedge formation, midlatitude magnetic Pi2 pulsations and energetic particle injections at the geosynchronous altitude. Moreover, pseudobreakups are associated with magnetic reconnection in the near‐Earth region, evidenced by the typical subsequent detection of a plasmoid at Geotail. This implies that the magnetotail volume influenced by a pseudobreakup is quite large in radial distance. We conclude that there is no definitive qualitative distinction between pseudobreakups and substorms but there is a continuum of states between the small pseudobreakups and large substorms.
Galileo plasma observations at Europa: Ion energy spectra and moments
Authors: Paterson W. R. , Frank L. A. , Ackerson K. L.
Published: September 2002

Observations from the Galileo plasma analyzer (PLS) recorded during two near encounters with Europa are reported. The measured ion energy spectra show that the ions near Europa are a mix of thermalized torus plasmas with approximately Maxwellian ion velocity distributions and partially thermalized pickup ions with ring distributions. The measurements are used to determine plasma moments including ion number densities, bulk flow velocities, and ion temperatures. These parameters provide information concerning the interaction that occurs as corotating torus plasmas sweep past this moon. The first encounter on December 19, 1996, took the spacecraft through the wake of the moon with the altitude at closest approach approximately 700 km. The trajectory for the second encounter on February 20, 1997, was on the upstream side of the moon with closest approach at an altitude approximately 600 km. Features of the interaction are found to include (1) deflection of plasma flow away from the moon on the upstream side and into the wake on the downstream side, (2) evidence of boundaries in the near wake that indicate a structured wake, and (3) maximum heavy‐ion densities near closest approach ∼40/cm3 that place a limit on the density of a high‐altitude ionosphere at Europa.
Energy spectrum and charge composition of a new, long‐lived, unstable electron radiation belt
Authors: Galper A. M. , Koldashov S. V. , Mikhailov V. V. , Voronov S. A. , Maslennikov L. V. , Shvetz N. I.
Published: September 2002

An experimental study of a long‐lived unstable electron belt created on March 24, 1991 is presented. The new belt occupied the slot region between the inner and outer radiation belts. Electrons, positrons, and protons with 20–200 MeV/c momenta were measured with the Mariya‐2 magnetic time‐of‐flight spectrometer‐telescope on board the orbital station Mir. The unstable belt turned out to consist solely of electrons (the positron fraction is less than 1%). The electron energy spectrum of this unstable belt has been analyzed throughout its 2‐year lifetime. Within the energy range 10–50 MeV, the spectrum agreed well with a power law E−α with α = 13±5. This spectrum is very soft compared with the spectrum of the stable electron belt located in the inner zone.
Solar wind input between substorm onsets during and after the October 18–20, 1995, magnetic cloud
Authors: Freeman M. P. , Farrugia C. J.
Published: September 2002

We study an aspect of substorm occurrence during Earth passage of the October 1995 magnetic cloud and the corotating stream overtaking it. The substorms were identified primarily by five latitudinal arrays of ground‐based magnetometers around the globe and the interplanetary observations were from the Wind spacecraft. The aspect we study is the energy and magnetic flux accumulated in the geomagnetic tail between successive substorm onsets, which we calculate by integrating different theoretical and empirical expressions for the solar wind‐magnetosphere coupling rates. These coupling functions, which depend strongly on the interplanetary magnetic field (IMF) north‐south component, Bz, have all been proposed previously as appropriate measures of solar wind input into the magnetosphere and indeed most correlate well with the cross‐polar cap potential. We contrast the effect on magnetospheric substorms of three solar wind states: A 14 hour long period of continuous and strong IMF Bz < 0 and a 16 hour long period of continuous and strong IMF Bz > 0, both states due to the magnetic cloud; and a 22 hour long period of intermittent IMF Bz polarity of large, but weaker amplitude, due to Alfvén waves in the faster stream. We find that (1) the average rate of substorm onset occurrence during the Bz < 0 phase in the cloud is higher than during the intermittent Bz polarity in the wake, by about a factor of 1.4. (2) The long Bz > 0 phase of the cloud elicited no substorm onsets. (3) The total time for which Bz is negative between substorm onsets is less variable than the interonset interval itself, but still varies between ∼ 0.5 hour and ∼ 4 hours. (4) The integral of any individual solar wind‐magnetosphere coupling function between successive substorm onsets is also variable. (5) The interonset integral varies differently for different coupling functions, even for those which measure the same quantity (energy or magnetic flux). (6) For all energy and magnetic flux coupling functions we find a positive correlation between the interonset integral and the value of the coupling function around the time of the preceding substorm onset. The correlation is best for the ε and υBs functions. This result is consistent with those substorm models in which substorm onset occurs at some fixed energy or magnetic flux threshold and where the amount of energy or magnetic flux lost following each substorm onset is proportional to the solar wind input rate at the time of onset.
Intercomparison of NEAR and Wind interplanetary coronal mass ejection observations
Authors: Mulligan T. , Russell C. T. , Anderson B. J. , Lohr D. A. , Rust D. , Toth B. A. , Zanetti L. J. , Acuna M. H. , Lepping R. P. , Gosling J. T.
Published: September 2002

Nearly 4 months of continuous interplanetary magnetic field measurements September 1997 through December 1997 have allowed us to compare four interplanetary coronal mass ejection (ICME) events seen by the NEAR and Wind spacecraft. When the spacecraft are in close proximity (separated by 1° in azimuth relative to the sun) the ICMEs seen by Wind and NEAR have similar signatures as expected for structures with dimensions along the solar wind flow of ∼0.2 AU. When the NEAR spacecraft is separated by ∼5.4° in azimuth from the Earth the vector signature of ICMEs seen at NEAR begins to differ from those seen at Wind even though the magnitude of the field in the events and the background solar wind show similarities at the two spacecraft. When the spacecraft are separated by 11.3° the magnetic signatures are quite different and sometimes ICMEs are seen only at one of the two locations. Nevertheless, in all cases the magnetic helicity of the cloud structures seen at NEAR is the same as at Wind. The radial speeds of the shock and ICME leading edge as they cross Wind and the time delays of those events, for which we have some assurance that they also arrived at NEAR, indicate that the ICMEs decelerate measurably as they travel near 1 AU.
Alfvén wings and electromagnetic induction in the interiors: Europa and Callisto
Authors: Neubauer Fritz M.
Published: September 2002

The recent evidence for the importance of magnetic fields due to electromagnetic induction in the conducting interiors of the satellites Europa and Callisto has motivated this extension of the Alfvén wing model to include induction effects. These are due to the temporal variations of the Jovian magnetospheric field at the satellite positions. We show that the maximum strength of the induction effects in a satellite during a Jovian synodic rotation increases as a function of distance from Jupiter because of the increasing significance of the current sheet. For the modified Alfvén wings we obtain the following results which also order the recent Galileo results: (1) For very small Alfvén Mach numbers the maximum Alfvén wing currents are reduced by the induction effects. This behavior is favored by a small distance between the conducting satellite interior and outer ionospheric boundary. (2) During a Jovian synodic rotation past a satellite the Alfvén wings are strongest at crossings of the central current sheet, whereas induction magnetic fields are most significant at maximum magnetic latitude. This result may be important for satellite footprint observations. (3) The maximum Alfvén wing current in item 1 also applies for somewhat larger Alfvén Mach numbers, if the ionospheric conductivity distribution is symmetric between the upstreamside and the downstreamside. For a dominating conductivity on the downstreamside the maximum Alfvén wing current is enhanced and vice versa for the opposite conductivity distribution. (4) Magnetic field measurements from satellite orbiters can be used to probe their conducting interiors, for examples any salty oceans.
Local variations of interplanetary magnetic field at Earth's bow shock
Authors: Kessel R. L. , Quintana E. , Peredo M.
Published: September 2002

We present interplanetary magnetic field (IMF) observations from Geotail and Wind in which the IMF was not uniform over spatial scales relevant to the magnetosphere. Geotail. at the dawn flank of the Earth's bow shock, measured magnetic field directions 60° to 120° different from the magnetic field measured by Wind on the duskside ∼30 RE upstream, during a 2‐hour interval. If there is a global connection between these observations, one possible explanation is a kink in the magnetic field near the Sun‐Earth line. The different orientations of IMF at Wind and Geotail (and thus the kink) change during the 2‐hour interval. Multiple shock crossings may have resulted from the changing orientations driving small surface waves on the shock surface. During this interval the bow shock does not fit a standard dawnside‐quasi‐parallel‐duskside‐quasi‐perpendicular picture. Instead, both sides of the bow shock may have been locally quasi‐perpendicular. The question of where a quasi‐parallel bow shock and/or foreshock could form needs to be explored. Both before and after the 2‐hour time interval, the IMF was close to uniform as measured by Wind. Geotail. and IMPS.
A very large scale flow burst observed by the SuperDARN radars
Authors: Nishitani Nozomu , Ogawa Tadahiko , Pinnock Mike , Freeman Mervyn P. , Dudeney John R. , Villain Jean‐Paul , Baker Kile B. , Sato Natsuo , Yamagishi Hisao , Matsumoto Haruhisa
Published: September 2002

We examined the dynamics of the ionospheric plasma in the dayside sector by using the HF radar data at Iceland West and at Finland from 1100 to 1230 UT on September 5, 1995. During that period, the solar wind density was high and the IMF was strongly southward. The dayside magnetopause was highly compressed nearly to the geosynchronous orbit. The two radars simultaneously detected a poleward flow burst in the noon sector which, assuming uniformity of flow in the region of the data gap (1.5 MLT) between the two radars, showed a magnetic local time extent of 5 hours. This local time extent is 2 to 3 hours wider than previous results. The maximum poleward plasma velocity of the flow burst is ∼750 m/s, and the latitudinal size of the flow burst region is ∼100 to 200 km. This flow burst region initially expanded in longitude up to 5 hours, and then shifted poleward with a phase speed of 400 to 670 m/s. The flow burst has a duration of ∼20 min. This large‐scale poleward flow burst is likely to be due to large‐scale reconnection occurring at the dayside magnetopause and subsequent convection as the magnetic field lines are transported across the polar cap.