bluuebunny/crossref_metadata_2025 huggingface dataset:
Global distribution of contrail radiative forcing
Authors: Minnis Patrick , Schumann Ulrich , Doelling David R. , Gierens Klaus M. , Fahey David W.
Published: September 2002

The global distribution of radiative forcing by persistent linear contrails has been estimated for 1992 and 2050 using global contrail cover computed for aircraft fuel consumption scenarios for the two periods, a detailed prescription of the radiative properties of the Earth's surface and the cloudy atmosphere, and flux computations with an established radiative transfer model. The computed global mean radiative forcing by line‐shaped contrails is ∼0.02 Wm−2 in 1992 and ∼0.1 Wm−2 in 2050. At northern mid‐latitudes, the zonal mean forcing is five times larger than the global mean. Diffuse contrails and indirect effects of aircraft emissions on natural cirrus are not included in this study. Thus, the results are considered a minimum estimate of contrail effects.
Laser‐spectroscopic investigation of OH‐radical concentrations in the exhaust plane of jet engines
Authors: Böckle S. , Einecke S. , Hildenbrand F. , Orlemann C. , Schulz C. , Wolfrum J. , Sick V.
Published: September 2002

Hydroxyl radical (OH) emissions are relevant for oxidation reactions in the post flame chemistry of exhaust gases emitted from jet engines. No direct measurements of OH concentrations are available to date due to the low abundance and the short lifetime of this radical species. The first application of a combined technique based on Raman scattering and laser‐induced fluorescence (LIF) spectrometry is presented here for measurements in the exhaust gases of a commercial jet engine operated in a test rig. From the measurements, upper limits for OH concentrations in the exit plane were determined in the range of 90 ppbv for take off and 80 ppbv for ap‐idle. The values are significantly below the predictions of model calculations based on HONO and HNO3 in‐flight concentration measurements presented recently. Possibilities for further increase of the detection sensitivity for OH are discussed.
Real‐time tracking of a Galician Meddy
Authors: Paillet Jérôme , Le Cann B. , Serpette A. , Morel Y. , Carton X.
Published: September 2002

We describe the properties and displacement of the northernmost Meddy that has ever been studied. This Meddy was found to the northwest of the Iberian Peninsula in April 1997. Its hydrological properties suggest that it was born offshore Galicia, the northwestern corner of Spain. It was tracked in real‐time for more than one year using recent types of deep drogued buoys and Lagrangian floats, and remained quasi‐stationary for an unusually long period of 11 months around 45°N, 12°W.
The March 25, 1998 Antarctic Plate Earthquake
Authors: Nettles Meredith , Wallace Terry C. , Beck Susan L.
Published: September 2002

The March 25, 1998, Antarctic plate earthquake (Mw=8.1) occurred ∼250 km from the nearest plate boundary, in oceanic lithosphere with an age of 35–55 my. Analysis of aftershock patterns shows that the earthquake ruptured a fault, or series of strike‐slip fault segments, nearly 300 km long. The strike of the fault(s) is nearly perpendicular to the north‐south trending fossil fracture zones which are the most marked bathymetric features of this region. Moment release during the mainshock was concentrated in two large subevents, clearly visible in the teleseismic body wave waveforms. Modeling of these body waves using a finite fault source places the first of the two subevents near the point of rupture initiation, on the eastern end of the fault, with the second large subevent occurring 220–280 km to the west. The two pulses of moment release are found to be separated in time by ∼65 s. Comparison of the relative S wave amplitudes of the first and second pulses suggests that a rotation of the focal mechanism by ∼10° occurred between the two subevents.
Agulhas Plateau, SW Indian Ocean: New evidence for excessive volcanism
Authors: Uenzelmann‐Neben Gabriele , Gohl Karsten , Ehrhardt Axel , Seargent Michael
Published: September 2002

A new set of seismic reflection and refraction lines has been interpreted regarding the basement and crustal structure of the southern Agulhas Plateau. A large number of extrusion centres were identified. Lava flows dip away from those extrusion centres and form subparallel‐stratified sequences. We interpret those extrusion centres as the result of excessive volcanism in course of the separation of the southern Agulhas Plateau from the Maud Rise. Since the sedimentary layers appear to be little affected by the volcanism, that episode obviously ceased before onset of sedimentation in Late Cretaceous times. We have not found evidence for continental fragments within overthickened, predominantly oceanic crust. We therefore propose that the Agulhas Plateau belongs to the world‐wide suite of Large Igneous Provinces (LIP) of predominantly oceanic origin.
Renormalization of earthquake aftershocks
Authors: Sornette Anne , Sornette Didier
Published: September 2002

Assume that each earthquake can produce a series of aftershock independently of its size according to its “local” Omori's law with exponent 1 + θ. Each aftershock can itself trigger other aftershocks and so on. The global observable Omori's law is found to have two distinct power law regimes, the first one with exponent p− = 1‐θ for time t < t* ∼ κ−1/θ, where 0 < 1 − κ < 1 measures the fraction of triggered earthquakes per triggering earthquake, and the second one with exponent p+ = 1 + θ for larger times. The existence of these two regimes rationalizes the observation of Kisslinger and Jones [1991] that the exponent p seems positively correlated to the surface heat flow: a higher heat flow is a signature of a higher crustal temperature, which leads to larger strain relaxation by creep, corresponding to fewer events triggered per earthquake, i.e. to a larger κ, and thus to a smaller t*, leading to an effective measured exponent more heavily weighted toward p+ > 1.
Observing plate motions in S.E. Asia: Geodetic results of the GEODYSSEA Project
Authors: Simons W. J. F. , Ambrosius B. A. C. , Noomen R. , Angermann D. , Wilson P. , Becker M. , Reinhart E. , Walpersdorf A. , Vigny C.
Published: September 2002

This paper presents the final geodetic results of the GEODYSSEA project. The GPS data from a 42 station network observed during two field campaigns (1994/1996) were analyzed by four groups using different software packages and analysis strategies. The precision of both campaign coordinate solutions was found to be 4–7 mm for the horizontal, and 1 cm for the vertical component. The campaign solutions were merged into one unique solution, which was accurately mapped into the ITRF‐96 reference frame. The global accuracy of this solution with respect to ITRF‐96 is ±1 cm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2–3 mm/yr. This solution was used as the basis for all scientific interpretations, which are published in separate papers. The velocity estimates of a part of the network provided the first direct measurement of a relative motion of the Sundaland block with respect to Eurasian plate.
Geochemical investigations applied to active fault detection in a volcanic area: the North‐East Rift on Mt. Etna (Sicily, Italy)
Authors: Giammanco Salvatore , Gurrieri Sergio , Valenza Mariano
Published: September 2002

Geochemical investigations were performed on the Northeast Rift of Mt. Etna, a prominent volcanic structure of this volcano. Low‐temperature fumaroles were found on the upper part of this area and the isotopic compositions of C(CO2) and He suggest a likely magmatic origin of the emitted gases. On the contrary, very low degassing was found in the lower part of the NE‐Rift, with CO2 concentrations generally very close to those in air. This pattern is probably due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing. High soil CO2 concentrations were also found in an elongated area parallel to the NE‐Rift and located immediately to the east of it. The geometry of these anomalies suggests the existence of several hidden faults, sub‐parallel to the NE‐Rift and likely connected to the Pernicana fault system. This latter structure seems to merge with the NE‐Rift at the altitude where the fumarole emissions are located. The hidden structures, together with the Pernicana system and the NE‐Rift, represent the western and northern boundaries of a large eastward collapsing sector of Mt. Etna.
Source and receiver geometry corrections for deep towed multichannel seismic data
Authors: Walia R. , Hannay D.
Published: September 2002

High resolution seismic data were collected using a Deep‐Tow Acoustics/Geophysics System (DTAGS) near ODP site 889/890, offshore Vancouver Island for deep sea gas hydrate study. The near bottom configuration and wide high‐frequency bandwidth allow much better resolution of the structures in the upper ∼400 m. However, the short 2ndash;6 m wavelengths imply accurate positioning of the source and receivers to properly determine moveout velocities and to stack the data. Consequently, a method of estimating the depths of the source and hydrophones using sea‐surface reflection times was developed. Travel time corrections based on these sea surface measurements were applied to the data by marching a time window along the seismic trace to account for the angular dependency of the reflected raypath. The need for these corrections is clearly illustrated by the results, which show non‐linear depth variations of up to 50–100 m for both the source and the hydrophone array.
Slow initial phase generated by microearthquakes occurring in the western Nagano Prefecture, Japan ‐The source effect‐
Authors: Iio Yoshihisa , Ohmi Shiro , Ikeda Ryuji , Yamamoto Eiji , Ito Hisao , Sato Haruo , Kuwahara Yasuto , Ohminato Takao , Shibazaki Bunichiro , Ando Masataka
Published: September 2002

Near‐source observations of microearthquakes occurring in the Western Nagano prefecture show that durations of recorded slows initial phases were almost constant independently of focal distance. Although a closer inspection revealed that the durations of the slow initial phases slightly increased with focal distance, they were not proportional to focal distance. Thus, it is concluded that the slow initial phases do not mainly reflect the whole path Q. If the slow initial phases were attributed to the strong anelastic attenuation in the surface layer combined with that of the whole path Q, the rise time of the P‐wave velocity pulse at the source for a M2.4 event would be estimated as about 3 ms and the source radius of the M2.4 event would be estimated as about 10 m. This value of the source radius is too small for M2.4. This suggests that the slow initial phase does not arise from the strong anelastic attenuation in the surface layer. It is likely that the slow initial phase does not mainly reflect a path effect but a source effect.
On possible scaling laws between electric earthquake precursors (EEP) and earthquake magnitude
Authors: Vallianatos F. , Tzanis A.
Published: September 2002

We assume, without reference to any particular electrification mechanism, that a pre‐seismic, time dependent polarization appears in a number of spherical volumes distributed in some earthquake preparation zone embedded in a half space of constant resistivity. We estimate the resulting transient electric and magnetic fields in the quasi‐static approximation. On assuming that the number of polarized spheres N is scaling with their radii l as N∝1/lD, we show that at some distance r from the zone, the electric field and the magnitude of the earthquake are related as LogE=αM+C, where α=(3‐D)/2 and similarly for the magnetic field. Fragmentation experiments and theoretical simulations indicate that 2.2 ≤ D ≤2.6, yielding 0.4>α>0.2. The lower fractal dimensions correspond to the case of dynamic crack propagation. Letting D≈2.3, yields α≈0.35 which is comparable to the experimental value of 0.35 given by Varotsos and Alexopoulos, (1984) on the basis of a few earthquake sequences in Greece. This indicates that electric and magnetic earthquake precursors may obey scaling laws that are direct consequence of the fractal distribution of their generators and also implies that transient precursors may result from microfracturing and fragmentation processes in the earthquake preparation zone.
A new light on arresting mechanism of dynamic earthquake faulting
Authors: Kame Nobuki , Yamashita Teruo
Published: September 2002

Classic analyses have shown that dynamic growth of a shear crack cannot be arrested in a uniformly stressed elastic medium with homogeneously distributed fracture strengths. This leads to a general supposition that earthquake rupture growth is arrested by inhomogeneities in the distributions of strengths or stresses. We propose a novel idea for arresting mechanism of dynamic crack growth in the simulation with no constraints on the crack geometry. Our analysis shows that the arresting occurs spontaneously soon after crack bending even in the homogeneous medium and that inhomogeneities are indispensable not for stopping crack growth, but for its promotion.
Oblique convergence in the Himalayas of western Nepal deduced from preliminary results of GPS measurements
Authors: Jouanne F. , Mugnier J. L. , Pandey M. R. , Gamond J. F. , Le Fort P. , Serrurier L. , Vigny C. , Avouac J. P.
Published: September 2002

A GPS network consisting of 29 sites was installed in central and western Nepal, with measurements taken in 1995 and partial remeasurements in 1997. Data suggest 15 +/−5 mm/yr of N180° convergence between the Higher Himalayas and India, a result that is consistent with N‐S shortening across the arcuate shape of the Nepalese Himalayas and an oblique underthrusting of the Indian crust below the High Himalayas of western Nepal. A 4 +/−3 mm/year E‐W extension and deviation of the principal shortening axes are inferred east of 83°E, where Quaternary faults (Darma‐Bari Gad fault system and Thakkhola graben) delineate a crustal wedge. This wedge is located on the SE projection of the Karakorum fault and may segment the Himalayan thrust belt. The convergence between the outer belt of western Nepal and India is less than 3 mm/yr, an attenuation consistent with creep on a dislocation locked beneath the Lesser Himalayas. A preliminary model suggests that this N 120°E striking dislocation is affected by a 19 mm/yr thrust component and a 7 mm/yr right lateral component.
Nonlinear energy dissipation in a cellular automaton magnetotail field model
Authors: Takalo J. , Timonen J. , Klimas A. , Valdivia J. , Vassiliadis D.
Published: September 2002

A magnetic field model of the magnetotail current sheet based on cellular automaton (CA) is presented. The present isotropic model is a continuously driven, two‐dimensional running CA. The model has a physical interpretation in terms of magnetohydrodynamic (MHD) equations, and features self‐organized critical (SOC) behavior with power‐law scalings both in durations and sizes of instabilities (avalanches). The model has nonlinear energy dissipation, and shows avalanches with and without an external trigger. Thus the model reproduces some of the statistical features recently observed in the magnetotail.
Mixing on the Black Sea Shelf north of the Bosphorus
Authors: Gregg Michael C. , Özsoy Emin
Published: September 2002

Microstructure observations over the Black Sea shelf and slope north of the Bosphorus reveal a very small turbulent diapycnal diffusivity, Kρ ≈ 10−6 m² s−1 in the Cold Intermediate Water during late summer, when winds are at their seasonal minimum. Recent modeling by Oğuz et al. [1998] shows that only with such low diffusivity can the observed separation between dissolved oxygen, O2 and hydrogen sulfide, H2S, be maintained. The measurements also provide a reference for mixing over continental shelves where tides are negligible and when winds are light.
Nonlinear two‐stream instabilities as an explanation for auroral bipolar wave structures
Authors: Goldman M. V. , Oppenheim M. M. , Newman D. L.
Published: September 2002

The evolution of two counter‐streaming electron beams is shown by means of 2‐D kinetic simulations to lead to electron distributions and coherent localized bipolar plasma wave structures with features similar to those measured by the FAST satellite in the auroral ionosphere. Electrostatic whistler waves are generated at later times when the bipolar structures begin to lose coherence and break up in the dimension transverse to the geomagnetic field.
Observations of systematic temporal evolution in elemental composition during gradual solar energetic particle events
Authors: Tylka Allan J. , Reames Donald V. , Ng Chee K.
Published: September 2002

The WIND/EPACT experiment offers a ∼100 fold increase in collecting power over instruments flown in previous solar cycles, thus allowing unprecedented detailed studies of temporal evolution in gradual solar energetic particle (SEP) events. We present hourly WIND/EPACT observations at ∼2–10 MeV/nuc from the 20 April 1998 and 26 August 1998 SEP events. These observations show striking patterns in elemental composition which evolve in a systematic fashion throughout the events' several‐day durations. These data, combined with theoretical modeling in a companion Letter [Ng et al. 1999], suggest that a dynamic Alfvén wave field, generated primarily by streaming energetic protons, is responsible for the complex behavior which is observed.
Effect of proton‐amplified waves on the evolution of solar energetic particle composition in gradual events
Authors: Ng Chee K. , Reames Donald V. , Tylka Allan J.
Published: September 2002

We present a model of the coupled evolution of energetic ions and Alfvén waves, incorporating magnetic focusing, pitch‐angle diffusion, wave amplification, and a traveling ion source. Ion transport through proton‐amplified waves with non‐Kolmogorov spectra produces the contrasting three‐stage evolution of Fe/O and He/H ratios at several MeV/amu observed by Wind/EPACT in the 20 April 1998 gradual solar energetic particle event [Tylka et al., 1999].
Rupture directivity of the major shocks in the 1997 Umbria‐Marche (central Italy) sequence from regional broadband waveforms
Authors: Alessandro Pino Nicola , Mazza Salvatore , Boschi Enzo
Published: September 2002

We derive the relative moment rate function for the main shocks in the Fall 1997 Central Italy seismic sequence (Mw=5.7; 6.0; 5.6) by applying an empirical Green function method. By using three conveniently placed broad‐band MedNet stations we obtain clear source time functions indicating directivity effects for all of the three earthquakes, with southeastward rupture propagation for the two southernmost events and an opposite direction for the other and largest one. Taking a simple source model, forward modeling is utilized for determining fault parameters such as length, rupture propagation velocity and direction and slip distribution.
Impact of cirrus cloud ice crystal shape and size on multiple scattering effects: Application to spaceborne and airborne backscatter lidar measurements during LITE Mission and E LITE Campaign
Authors: Chepfer Hélène , Pelon Jacques , Brogniez Gérard , Flamant Cyrille , Trouillet Vincent , Flamant Pierre H.
Published: September 2002

Forward scattering in cirrus clouds can significantly affect backscatter lidar signal. Its contribution can be estimated numerically knowing the size and shape of the crystals. Contemporary airborne and space‐borne lidar measurements collected during the European Lidar In‐space Technology Experiment (E‐LITE) field campaign (in the framework of the NASA/LITE mission) are used to show that forward scattering reduces the optical depth derived from space‐borne measurements by at least a factor of 2 with respect to the true value. This reduction factor is discussed in terms of crystal size and shape (i.e. forward scattering, and measurement configuration). It is shown that cirrus backscatter‐to‐extinction ratios derived from airborne and space‐borne lidar measurements can be used to illustrate the sensitivity of multiple scattering effects the ice crystal size and shape.
Heat flow variations in a deep borehole near Sept‐Iles, Québec, Canada: Paleoclimatic interpretation and implications for regional heat flow estimates
Authors: Mareschal Jean‐Claude , Rolandone Frédérique , Bienfait Gérard
Published: September 2002

A deep (> 2000m) borehole in the Sept‐Iles intrusion, on the north shore of the Saint Lawrence River, in Québec, Canada, was repeatedly logged for temperature. Systematic variations of the temperature gradient with depth are not correlated with the thermal conductivity. We interpreted the temperature profile as follows:

(1) During the last glacial maximum, the temperature at the base of the ice sheet was cold (≈−5°C); (2) When the region was below sea level, between 10 and 5ky B.P., the ground surface temperature was warm (≈ 6°C); (3) The average ground surface temperature dropped to ≈ 2°C at 5ky B.P. when the region rebounded above sea level; (4) The long time averaged ground surface temperature before the last glacial maximum was ≈0 ‐ 1°C; (5) The reference heat flow (36 – 37mW m−2) is 4–5mW m−2 higher than estimated from the upper 1000m of the heat flow profile.

This interpretation can not be extrapolated to the entire region covered by the Laurentide ice sheet. Except for extremely deep (> 1500m) boreholes, the small uncertainty (< 15%) affecting heat flow estimates can not be eliminated.
Evidence for deformation associated with the 1998 eruption of Axial Volcano, Juan de Fuca Ridge, from acoustic extensometer measurements
Authors: Chadwick William W. , Embley Robert W. , Milburn Hugh B. , Meinig Christian , Stapp Michael
Published: September 2002

Acoustic extensometer instruments capable of making precise daily measurements of horizontal distance were deployed across the north rift zone of Axial Volcano in June 1996 and were in place when a submarine eruption began on Axial's south rift zone in January 1998. The instruments recorded a gradual 9‐cm extension over a 405‐m baseline leading up to the eruption, and then an abrupt, 4‐cm contraction at the time of the eruption. An elastic point‐source deformation model shows that deflation of Axial's summit can explain both the 4‐cm distance decrease at the extensometer array and a 3.2‐m subsidence measured by another instrument in the caldera, if the pressure source is located at a depth of 3.8 km below the center of the caldera. The 9‐cm distance increase may represent pre‐eruption spreading across the rift zone.
Simultaneous atomic and ion layer enhancements observed in the mesopause region over Arecibo during the Coqui II Sounding Rocket Campaign
Authors: Friedman J. S. , González S. A. , Tepley C. A. , Zhou Q. , Sulzer M. P. , Collins S. C. , Grime B. W.
Published: September 2002

The NASA Coqui II sounding rocket campaign in Puerto Rico provided the opportunity to obtain a large number of lidar and incoherent scatter radar observations of atomic sodium and ion layers in the upper mesosphere and lower thermosphere. Sodium layer enhancements, coupled with ion layers, were frequently observed in the range of 90–105 km altitude. We found that above 97 km all of the enhanced Na layers were observed to have an associated ion layer, and below that altitude some Na enhancements could occur in their absence. Finally, we show one extraordinary case of a sporadic Na layer that grew to near its peak concentration before the associated ion layer appeared at its altitude.
A global MHD solar wind model with WKB Alfvén waves: Comparison with Ulysses data
Authors: Usmanov Arcadi V. , Goldstein Melvyn L. , Besser Bruno P. , Fritzer Johannes M.
Published: September 2002

We use a steady state global axisymmetric MHD model to reproduce quantitatively the Ulysses observations during its first fast latitude traversal in 1994–1995. In particular, we are able to account for the transformation of a surface dipole magnetic field near the Sun into the configuration observed at large heliocentric distances. The MHD equations are solved by combining a time relaxation numerical technique with a marching‐along‐radius method. We assume that Alfvén waves, propagating outward from the Sun, provide additional heating and acceleration to the flow. Only solutions with waves reproduce the plasma parameters observed in the high‐latitude fast solar wind. We show that the meridional distribution of solar wind plasma and magnetic field parameters is dominated by two processes. First, inside ∼24 R⊙ both the plasma velocity and magnetic field relax toward a latitude‐independent profile outside the equatorial current sheet (where magnetic forces dominate over thermal and wave gradient forces). Second, outside ∼24 R⊙ there is another meridional redistribution due to a poleward thermal pressure gradient that produces a slight poleward gradient in the radial velocity and an equatorward gradient in the radial component of the magnetic field. We reproduce the observed bimodal structure and morphology of both fast and slow wind and show that computed parameters are generally in agreement with both in situ data and conditions inferred to be characteristic of the solar corona.
Evaluation of the tail current contribution to Dst
Authors: Turner N. E. , Baker D. N. , Pulkkinen T. I. , McPherron R. L.
Published: September 2002

The Dst index is produced using low‐latitude ground magnetic field measurements and frequently is used as an estimate of the energy density of the ring current carried mainly by energetic (∼ 10 – 200 keV) ions relatively close to the Earth. However, other magnetospheric current systems can cause field perturbations at the Earth's surface: for example, dayside magnetopause currents are known to contribute to the Dst index. It has also been suggested that the nightside tail current sheet can significantly affect the Dst index during high magnetic activity periods when the currents are intense and flow relatively close to the Earth. In this study, several disturbed periods are input into Tsyganenko magnetic field models. From the time series of the external and internal fields an artificial Dst index is computed using the same procedure followed in the actual Dst calculation. A tail region in the magnetosphere is explicitly defined and the T96 and T89 models are used to calculate the effect of current within this tail region on ground measurements and therefore on Dst. The results are then compared with the measured Dst to determine the tail current contribution to Dst. It is found that for a geomagnetic storm and a storm‐time substorm with Dst of ∼ 80 nT the tail current contribution is between 22 and 26 nT. The same analysis is also applied to several isolated non‐storm‐time substorms, yielding a nearly linear relationship between Dst and the tail current contribution. This contribution is approximately one quarter of Dst.
On the relative importance of convection and temperature to the behavior of the ionosphere in North America during January 6–12, 1997
Authors: Richards P. G. , Buonsanto M. J. , Reinisch B. W. , Holt J. , Fennelly J. A. , Scali J. L. , Comfort R. H. , Germany G. A. , Spann J. , Brittnacher M. , Fok M.‐C.
Published: September 2002

This paper is primarily concerned with the causes of the large density and temperature enhancements that are often observed during magnetically quiet periods on winter nights at mid‐latitudes in the North American sector. Measurements from a network of Digisondes and an incoherent scatter radar are compared with the field line interhemispheric plasma (FLIP) model for January 6–12, 1997, in order to examine the temporal evolution and geographical extent of the enhancements in eastern North America. Postsunset measurements at Millstone Hill show high electron temperatures accompanied by rapid density decay until midnight followed by a rapid temperature decay accompanied by a pronounced density enhancement in the early morning hours. The FLIP model reproduces the nighttime density enhancement well, provided the model is constrained to follow the topside electron temperature and also that the overlying plasmaspheric flux tube is full. The dramatic reduction in plasmaspheric heat flux near midnight results in a sharp decrease in ionospheric temperature, inducing a large downward flow of plasmaspheric ions which creates the nighttime enhancement in ionospheric density. We find that the nighttime plasmaspheric heat flux variation drives the nighttime ionospheric density variation, which is opposite to conclusions in previously published work. Although the plasmaspheric heat flux variation can explain the ionospheric density variation, the reasons for this heat flux variation are not understood. Convection of plasma from higher magnetic latitudes is now included in the FLIP model but is not needed to produce the observed nighttime density maximum. We have found that the fraction of light ions in the topside ionosphere at 500 km altitude in the model is very close to that obtained from chemical equilibrium and agrees well with the measured fraction. The model generally reproduces the daytime electron density very well at all stations except Bermuda, where the difference is as much as 50%.
A test of the Dessler‐Parker‐Sckopke relation during magnetic storms
Authors: Greenspan M. E. , Hamilton D. C.
Published: September 2002

The Dessler‐Parker‐Sckopke relation (DPS) predicts a linear dependence of the perturbation magnetic field at the surface of the Earth on the total ring current kinetic energy. In this paper, we test DPS by using measurements of the major ring current ion species made by the charge‐energy‐mass spectrometer on the Active Magnetospheric Particle Tracer Explorers CCE spacecraft. We use spectra from passes through the equatorial storm time ring current near the maximum phase of 80 magnetic storms between 1984 and 1989 to estimate the global ring current energy content ERC and compare it with the average value for Dst during each pass. Our work shows that DPS holds well on average. In particular, there is a strong linear correlation between ring current energy estimated from nightside ion measurements and the Dst index, and the slope of the least squares fit line giving Dst as a function of nightside ERC is in good agreement with the prediction of DPS. In contrast, day side measurements of ERC do not yield a robust correlation with Dst. Although we cannot rule out the possibility that currents other than the ring current (for example, tail currents and the magnetopause current) may cause large magnetic perturbations, we conclude that these perturbations, if they exist, must be largely compensating. By examining how the ratio of Dst to ERC varies with the local time sector of the in situ ion measurements, we obtain statistical information on the anisotropy of the storm time ring current. We find that the largest values of ERC/Dst result from nightside measurements and the smallest values result from measurements in the 0600 to 1200 LT region, as would be expected for an ion population injected on the nightside that must drift westward around the Earth, undergoing losses, to reach the dayside morning sector.
Bidirectional particle flows at cosmic ray and lower (∼1 MeV) energies and their association with interplanetary coronal mass ejections/ejecta
Authors: Richardson I. G. , Dvornikov V. M. , Sdobnov V. E. , Cane H. V.
Published: September 2002

We demonstrate a close relationship between bidirectional flows of galactic cosmic rays measured by the worldwide neutron monitor network and bidirectional flows of solar/shock‐accelerated particles at much lower energies (∼ 1 MeV) observed by near‐Earth spacecraft, during January–September 1982. We find that ∼ 80% of bidirectional cosmic ray flows are accompanied by bidirectional low energy ion flows. The observations indicate a close association between BCRFs and interplanetary coronal mass ejections/ejecta. The bidirectional flows suggest that particles of a wide range of energies are trapped on expanding, looped magnetic field lines, providing that their gyroradii are much smaller than the ∼ 0.1 to few AU scale sizes of ejecta. Unidirectional flow components are less well correlated at ∼ 1 MeV and cosmic ray energies, presumably because they reflect gradients in different particle populations. We discuss several events in detail and illustrate how changes in particle flows may be related to substructures within these ejecta.
Determination of vertical plasma drift and meridional wind using the Sheffield University Plasmasphere Ionosphere Model and ionospheric data at equatorial and low latitudes in Brazil: Summer solar minimum and maximum conditions
Authors: Souza J. R. , Abdu M. A. , Batista I. S. , Bailey G. J.
Published: September 2002

The F region critical frequency foF2 and peak height hmF2, measured simultaneously at the equatorial location Fortaleza (4°S, 38°W, magnetic latitude = 3.5°S) and at the low‐latitude location Cachoeira Paulista (22°S, 45°W, magnetic latitude = 15°S), are compared with their values calculated by the Sheffield University Plasmasphere‐Ionosphere Model (SUPIM) to determine the vertical (E × B) drift velocity at the equator and the magnetic meridional wind velocity over the two locations. The calculated and observed values of foF2 are then matched at both Fortaleza and Cachoeira Paulista to obtain the magnetic meridional winds over their respective conjugate locations. To account for the observed foF2 diurnal variation pattern over Cachoeira Paulista, it was found necessary to include a small source of ionization, attributable to energetic particle precipitation in the South Atlantic anomaly region. The vertical drift velocity and magnetic meridional wind velocity derived for summer months during both solar minimum and solar maximum are compared with their values given by other published models. While the diurnal variation of the modeled vertical drift velocity shows general agreement with the values based on Jicamarca radar measurements (the exception being during the sunset‐midnight period at solar maximum and between 2000–2300 LT at solar minimum), the magnetic meridional wind shows significant differences with respect to the Horizontal Wind Model 1990 (HWM90) [Hedin et al., 1991] during both solar minimum and solar maximum at Fortaleza and at locations conjugate to Fortaleza and Cachoeira Paulista.
The 30‐MHz radar interferometer studies of midlatitude E region irregularities
Authors: Hysell D. L. , Burcham J. D.
Published: September 2002

The 30‐MHz radar observations of coherent scatter from midlatitude E region plasma irregularities are presented and interpreted. Our analysis indicates that quasiperiodic (QP) echoes can be interpreted as quasi‐point target scatterers drifting through the radar beam at approximately constant altitude. Interferometry data collected with multiple baselines show that the patchy scatterers are not organized along wave fronts but instead form drift and decay independently of one another. An analysis of the intensity of the echoes versus range reveals that the morphology of the QP echo striations is consistent with expectations for drifting field‐aligned irregularities with finite aspect angle sensitivity. An analysis of the effects of refraction, aspect sensitivity, and scattering geometry shows that the plasma irregularities in question reside at altitudes between 95 and 120 km. Type I echoes observed on one occasion imply the existence of strong zonal polarization electric fields with magnitudes of about 20 mV/m. A numerical model of the E region current system demonstrates how such electric fields can be generated by elongated, patchy sporadic E layers electrically coupled to the F region dynamo.
Cosmic radiation in the heliosphere at successive solar minima: 4. Modulation of galactic cosmic rays during the three consecutive solar minimum periods of 1977/1978, 1987 and 1997
Authors: Reinecke J. P. L. , McDonald F. B. , Moraal H.
Published: September 2002

Extensive data sets have been measured for galactic and anomalous cosmic rays during the past three solar minimum modulation periods of 1977, 1987, and 1997 by various spacecraft at distances ranging from 1 to 66 AU from the Sun. In this paper we investigate the radial, latitudinal, and rigidity dependence of the diffusion mean free paths (λ) deduced from galactic helium and hydrogen in the heliosphere and compare these values with those from earlier studies by Reinecke et al. [1993, 1996] and from theoretical calculations by Zank et al. [1997, 1998].
Products of the reaction of 8 km/s N(4S) and O2
Authors: Caledonia G. E. , Krech R. H. , Oakes D. B. , Lipson S. J. , Blumberg W. A. M.
Published: September 2002

Reactions involving fast nitrogen atoms are of importance both in the upper atmosphere and in defining the near‐field environment around orbiting spacecraft. We present the first quantitative study of the distribution of vibrationally excited ground state NO produced in the reaction of 8 km/s N atoms with O2. A pulsed beam of energetic nitrogen atoms was interacted with thermal oxygen molecules under single‐collision conditions in a crossed beam configuration. The fundamental and first overtone band emissions of the reaction product NO (X2Π) were measured using both band‐pass‐filtered radiometers and a circular variable filter. The spectrally resolved emissions were analyzed to determine the nascent NO vibrational distribution and the vibrational state‐specific reaction cross sections. The present results are compared with earlier measurements performed at thermal energies and contrasted with theoretical predictions.
Ionospheric total electron content response to solar eclipses
Authors: Tsai H. F. , Liu J. Y.
Published: September 2002

On October 24, 1995, and March 9, 1997, two solar eclipse events occur. It is therefore of interest to investigate how the ionosphere responded to the eclipses. Five global positioning system (GPS) ground‐based receivers are specifically designed to observe large‐scale ionospheric variations over the geomagnetic equatorial, equatorial anomaly crest, and midlatitude regions. Two‐dimensional images of ionospheric total electron content (TEC) during the two eclipse periods are constructed. The deviations in the TEC images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large‐scale changes. Four features of the TEC deviations, pre‐ascension (PA), major depression (MD), sunset ascension (SA), and secondary depression (SD) have been observed. A detailed study shows that in geomagnetic low latitudes, PAs are possibly related to the locations of the equatorial anomaly crest. The latitudinal location, amplitude, and occurrence time of MDs suggest that the fountain effect is essential. SAs and SDs occurring in geomagnetic equatorial and low latitudes and appearing respectively before/around and after local sunset indicate that the prereversal enhancement plays an important role.
Solar cycle dependence of the heliospheric shape deduced from a global MHD simulation of the interaction process between a nonuniform time‐dependent solar wind and the local interstellar medium
Authors: Tanaka T. , Washimi H.
Published: September 2002

The global structure of the solar wind/very local interstellar medium interaction is studied from a fully three‐dimensional time‐dependent magnetohydrodynamic model, in which the solar wind speed increases from 400 to 800 km/s in going from the ecliptic to pole and the heliolatitude of the low‐high‐speed boundary changes from 30° to 80° in going from the solar minimum to solar maximum. In addition, the interplanetary magnetic field (IMF) changes its polarity at the solar maximum. As a whole, the shapes of the terminal shock (TS) and heliopause (HP) are elongated along the solar polar axis owing to a high solar wind ram pressure over the poles. In the ecliptic plane, the heliospheric structure changes little throughout a solar cycle. The TS in this plane shows a characteristic bullet‐shaped structure. In the polar plane, on the other hand, the shape of the TS exhibits many specific structures according to the stage of the solar cycle. These structures include the polygonal configuration of the polar TS seen around the solar minimum, the mesa‐ and terrace‐shaped TSs in the high‐ and low‐speed solar wind regions seen around the ascending phase, and the chimney‐shaped TS in the high‐speed solar wind region seen around the solar maximum. These structures are formed from different combinations of right‐angle shock, oblique shock, and steep oblique shock so as to transport the heliosheath plasma most efficiently toward the heliotail (HT). In the HT, the hot and weakly‐magnetized plasma from the high‐heliolatitude TS invades as far as the ecliptic plane. A weakly time‐dependent recirculation flow in the HT is a manifestation of invading flow. Distributions of magnetic field in the HT, which are a pile‐up of the compressed IMF over several solar cycles, are modified by the flow from high‐heliolatitude.
Radio signatures of a fast coronal mass ejection development on November 6, 1997
Authors: Maia D. , Vourlidas A. , Pick M. , Howard R. , Schwenn R. , Magalhães A.
Published: September 2002

The Oporto radiospectrograph and the Nançay radioheliograph recorded a radio event on November 6, 1997, closely related in time with a flare on National Oceanic and Atmospheric Administration (NOAA) active region 8100. At the beginning of the event the radio sources are located on a rather small volume in the vicinity of the flare site. In a timescale of only a few minutes the radio emission sites spread over a large volume in the corona, covering a range of 100° in heliolatitude. During the period of the radio event the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) observed an extremely fast coronal mass ejection (CME), with a velocity around 2000 km s−1. This CME presents the particularity of having a fast lateral expansion, giving it a shape reminiscent of a “coat hanger.” There is a very good association between the latitudinal extent and time development of the CME seen by LASCO and the radio sources recorded by the radio instruments.
Relationships between coronal mass ejection speeds from coronagraph images and interplanetary characteristics of associated interplanetary coronal mass ejections
Authors: Lindsay G. M. , Luhmann J. G. , Russell C. T. , Gosling J. T.
Published: September 2002

With an eye toward space weather forecasting and the planned Solar Terrestrial Relations Observatory mission, a combination of Solwind and SMM coronagraph data and Helios‐1 and Pioneer Venus Orbiter interplanetary field and plasma data are used to study statistical relationships between the speeds of coronal mass ejections (CMEs) observed near the Sun and key characteristics of the associated interplanetary disturbances (interplanetary coronal mass ejections (ICMEs)) detected near the ecliptic at ≤ 1 AU. When confident associations can be made between the coronagraph observations and interplanetary observations, a predictable relationship is found between observed coronagraph CME speeds and subsequently observed ICME bulk plasma speeds. Consistent with earlier work, the CMEs, regardless of their speed, produce ICMEs moving at least as fast as the minimum solar wind speed. As a rule, the CMEs observed at speeds below the average solar wind speed produce ICMEs that travel faster than the associated CME, implying acceleration, while CMEs with coronagraph speeds above the average solar wind speed produce ICMEs that travel slower than the associated CME, implying deceleration of initially fast low‐heliolatitude ejecta. A formula is provided for estimating ICME speed from CME speed. As also previously found, faster CMEs tend to produce ICMEs with larger internal magnetic field magnitudes. While the size and occurrence of southward Bz in an ICME are not generally related to the observed CME speed, Bz in the sheath region preceding the ICME shows some positive correlation. These observations confirm that while the occurrence of large interplanetary magnetic field magnitudes and high bulk plasma speeds associated with ICME passage may be predictable from coronagraph‐derived CME speeds, other important ICME features like large‐magnitude southward Bz require other diagnostics and tools for forecasts.
Compressional MHD waves in the magnetosphere: A new approach
Authors: Lee Dong‐Hun , Kim Kihong
Published: September 2002

Dynamics of compressional MHD wave propagation is theoretically studied in the dayside and nightside magnetosphere. In order to analytically examine the MHD wave equation, we adopt the quantum mechanical approach which is often used in the problem of the Schrödinger's equation. The wave solutions are obtained for dayside and nightside Alfven speed profiles, respectively, without any arbitrary boundary condition at the magnetopause or the bow shock. The result shows that the previous cavity/waveguide models are found to be inappropriate for studying compressional wave properties in the magnetosphere. We discuss the role of virtual resonances which generally represent any possible compressional modes in the magnetosphere.
Altitude dependencies in the solar activity variations of the ionospheric electron density
Authors: Su Y. Z. , Bailey G. J. , Fukao S.
Published: September 2002

In this study, 7 years (1986–1992) of measurements from the Japanese middle and upper atmosphere (MU) radar have been analyzed to investigate the solar activity variations of the ionosphere. The observations show strong altitude dependencies in the solar activity variations of the electron density. Below 300 km altitude, the electron density increases nonlinearly with F10.7, with the rate of increase being much lower when F10.7 is greater than 150. This nonlinear variation becomes weaker with increasing altitude. Above 450 km altitude, the electron density increases almost linearly with F10.7 when F10.7 lies in the range 100 to 250. For values of F10.7 less than 100, the electron density at low altitudes increases with increasing F10.7, while at higher altitudes (above about 400 km) the electron density remains almost constant. Mechanisms to explain the observed behavior have been investigated using the Sheffield University Plasmasphere Ionosphere Model. The model calculations show that while the variations with F10.7 of the solar EUV flux and neutral gas densities play important roles in the nonlinear variations of the electron density with F10.7, the correlation of the plasma loss rate with temperature being negative at low temperatures and positive at high temperatures is an important mechanism for the nonlinear variations at low altitudes. Model results also suggest that vibrationally excited N2 strengthens the nonlinear variations of electron density with F10.7. The disappearance of the nonlinear variations at high altitudes, for values of F10.7 above 100, results from the altitude dependencies of the neutral gas variation on F10.7 and of the relative importance of plasma loss, production, and diffusion processes. At high altitudes, the plasma loss processes, which play an important role in the nonlinear variations at low altitudes, are unimportant when compared with the effects arising from plasma production and diffusion. The altitude dependencies of the electron density variations with F10.7, for values of F10.7 less than 100, are due mainly to the altitude dependencies of the neutral gas densities with F10.7.