bluuebunny/crossref_metadata_2025 huggingface dataset:
Borehole instabilities in the KTB main borehole
Authors: Borm G. , Engeser B. , Hoffers B. , Kutter H. K. , Lempp C.
Published: February 2004

Borehole instability has been a central problem for drilling operations and borehole measurements within the German Continental Deep Drilling Project (KTB) main borehole, which has been drilled entirely through crystalline rocks, mostly paragneisses and metabasites. The types of borehole instabilities observed were drilling‐induced tensile fractures, breakouts, and convergence zones. These were strongly dominated by foliate, graphitic gneisses with sometimes very low and anisotropic rock strength, unfavorably high and nonuniform horizontal stresses, and the effects of hydraulic interactions of the drill mud and formation fluids. The instability problems encountered in the KTB main borehole have clearly demonstrated that undergauge sections, which first appeared at depths below 7500 m and probably resulted from time‐dependent convergence of wet crystalline rocks, had a much greater impact on the drilling operations than all the breakouts or drilling‐induced tensile fractures.
Geochemistry of Mesozoic Pacific mid‐ocean ridge basalt: Constraints on melt generation and the evolution of the Pacific upper mantle
Authors: Janney Philip E. , Castillo Paterno R.
Published: February 2004

We present major and trace element and Sr‐Nd‐Pb isotope results on Mesozoic (130–151 Ma) mid‐ocean ridge basalt (MORB) recovered from five Deep Sea Drilling Project sites in the central and northwestern Pacific Ocean. Seawater alteration is responsible for much of the major element variability in these basalts, but magmatic variations are still discernible. Major element modeling of the least altered samples indicates that the basalts were generated by degrees and pressures of melting identical to those of modern Pacific MORB, and this, in addition to the similarity in spreading rates between the East Pacific Rise and Mesozoic Pacific ridges, suggests that the style of mantle upwelling and melting at spreading centers is spreading rate dependent. In general, the five Mesozoic MORB units, like Jurassic Pacific MORB from Ocean Drilling Program Site 801, are depleted in highly incompatible elements relative to average N‐MORB and display a wide range in Nd and Pb isotopic ratios (εNd(T) = 8.4–11.6; 206Pb/204Pbi = 17.9–18.6) but have a low and uniform Sr isotopic composition (87Sr/86Sri = 0.7023–0.7026). This isotopic variation can be explained by mixing a depleted mantle source with small amounts of recycled oceanic crust (HIMU). In contrast to the older MORB, mid‐Cretaceous Pacific MORB (≈115–100 Ma) are moderately to strongly enriched in highly incompatible elements with an “enriched mantle” isotopic affinity. The shift in MORB composition coincides with the onset of effusive mid‐Cretaceous intraplate volcanism in the Pacific and reflects widespread contamination of the Pacific upper mantle with materials derived from the plumes or plume heads responsible for mid‐Cretaceous oceanic plateaus and seamount chains.
Polar motion of a viscoelastic Earth due to glacial cycle mass loading
Authors: Bills Bruce G. , James Thomas S.
Published: February 2004

The growth and decay of ice sheets can change the symmetry axis of the global mass distribution and thus excite motion of the rotation axis of the Earth. We develop a simple, normal mode expansion of the operator which converts surface load histories into polar motion histories, and use it to characterize the polar motion response to arbitrary surface loading excitation, in terms of gain and phase, for a wide range of Earth models and excitation time scales. Uncertainties in loading history presently limit the utility of constraints on mantle rheology which can be obtained from matching the present direction and rate of motion of the pole. Because of its magnitude and distance from the pole, the Laurentide ice sheet alone can induce motion of the rotation pole by over 100 km. This will influence the pattern of incident radiation on continents and oceans, and may play a significant role in limiting ice sheet growth. Differential motion of the mantle and core, on a glacial timescale, may also influence the geomagnetic field.
Intraplate versus ridge volcanism on the Pacific‐Antarctic Ridge near 37°S–111°W
Authors: Hekinian Roger , Stoffers Peter , Devey Colin , Ackerman Dietrich , Hémond Christophe , O'Connor John , Binard Nicolas , Maia Marcia
Published: February 2004

Exploration of the Foundation Volcanic Chain (33°S–131°W; 37°S–111°W) revealed the existence of different magmatic provinces with relation to their geological settings. (1) The Pacific‐Antarctic Ridge (PAR) is made up of several en echelon segments where both glassy midocean ridge basalts (MORBs) with low incompatible elements (K2O<200 ppm, Zr<120 ppm and Ce<20 ppm) as well as andesites and dacites have erupted, (2) Oblique Ridges located up to 300 km from the PAR axis are topped with seamounts made up essentially of transitional (T) and enriched (E) MORBs with intermediate incompatible elements (K2O=0.11–0.40%, Zr=70–140 ppm and Ce =15–30 ppm), (3) the Foundation Seamounts (FS) consisting essentially of isolated volcanoes which have erupted alkalic lavas (alkali basalt, trachybasalt and trachyandesite) with high incompatible elements (K2O (0.50–1.1%, Zr (>150 ppm) and Ce (>48 ppm)) at about 306–1300 km from the PAR axis, (4) The Old Pacific Seamounts built on a crust older than 23 m. y. located west of longitude 124°W (>1300 km from the PAR axis) consist of T and EMORB. On the PAR axis, extensive crystal fractionation (>65%) produced the silicic lavas. On the basis of Pacific plate reconstruction using a half spreading rate of about 50 mm/yr and integrating the observed compositional changes with respect to the structural settings, it is inferred that the last volcanic events giving rise to the FS took place at about 110 km from the PAR axis about 5 m. y. ago. The Oblique Ridges built between 5 m. y. and <1 m. y. are believed to represent ancient leaky transforms and/or large discontinuities between accreting ridge segments filled by volcanic cones during the interaction (mixing) of the enriched plume components of the FS with PAR depleted (MORB type) magmatism. The Old Pacific Seamounts built on ancient crust (>23 m. y.) with MORB volcanics comparable to those of the the Oblique Ridge‐PAR provinces, could also have been formed by an interaction between the Foundation Seamount (dredge site 28) hotspot magmatism and that of an ancient accreting ridge magmatism precursor of the PAR.
Frequency of occurrence of moderate to great earthquakes in intracontinental regions: Implications for changes in stress, earthquake prediction, and hazards assessments
Authors: Triep Enrique G. , Sykes Lynn R.
Published: February 2004

We investigate the departure of shallow intracontinental earthquakes from the frequency‐magnitude relationship log (n(M)) =a‐bM. We consider seven large continental regions but exclude subduction zones. In each, “active” and “stable” areas are differentiated. Within active areas we separately categorize earthquakes on faults with high slip rates. We use data sets from 1978–1994 and 1900–1994, which are complete for moment magnitudesMw≥5.3 and ≥7.0, to calculate changes inbvalue withMw. For all active intracontinental regions combined except Asia,bchanges at 98% confidence from 0.90 to 2.1 at a corner magnitudeMcof 6.9 to 7.0. The distribution for stable regions indicates a similar change. Values ofMcare associated with downdip widths of rupture of about 23 to 27 km, which are smaller than those for subduction zones. In each case,Mcmarks a transition from unbounded to bounded earthquakes. In Asia, events from 1958 to 1994 also delineate a similar change nearMc7.0. Earthquakes in Asia of 7.0≤Mw≤8.1 from 1900 to 1957, however, define abvalue of 1.0 and a moment release rate 5.6 times higher than that from 1958 to 1994. Those anomalous values indicate that a large region of Asia was close to failure, i.e., near a self‐organized critical state, during the earlier period. We associate those changes with the giant Himalayan earthquake in 1950 ofMw8.6. Regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries. Extrapolating rates of activity of the past 95 years toMw≥8.0 indicates that such events should be very rare in stable areas.
Continuous monitoring of surface deformation at Long Valley Caldera, California, with GPS
Authors: Dixon Timothy H. , Mao Ailin , Bursik Marcus , Heflin Michael , Langbein John , Stein Ross , Webb Frank
Published: February 2004

Continuous Global Positioning System (GPS) measurements at Long Valley Caldera, an active volcanic region in east central California, have been made on the south side of the resurgent dome since early 1993. A site on the north side of the dome was added in late 1994. Special adaptations for autonomous operation in remote regions and enhanced vertical precision were made. The data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber. Measurement precisions (1 standard error) for “absolute” position coordinates, i.e., relative to a global reference frame, are 3–4 mm (north), 5–6 mm (east), and 10–12 mm (vertical) using 24 hour solutions. Corresponding velocity uncertainties for a 12 month period are about 2 mm/yr in the horizontal components and 3–4 mm/yr in the vertical component. High precision can also be achieved for relative position coordinates on short (<10 km) baselines using broadcast ephemerides and observing times as short as 3 hours, even when data are processed rapidly on site. Comparison of baseline length changes across the resurgent dome between the two GPS sites and corresponding two‐color electronic distance measurements indicates similar extension rates within error (∼2 mm/yr) once we account for a random walk noise component in both systems that may reflect spurious monument motion. Both data sets suggest a pause in deformation for a 3.5 month period in mid‐1995, when the extension rate across the dome decreased essentially to zero. Three dimensional positioning data from the two GPS stations suggest a depth (5.8±1.6 km) and location (west side of the resurgent dome) of a major inflation center, in agreement with other geodetic techniques, near the top of a magma chamber inferred from seismic data. GPS systems similar to those installed at Long Valley can provide a practical method for near real‐time monitoring and hazard assessment on many active volcanoes.
Continuous dust concentration profile of pre‐Holocene ice from the Greenland Ice Sheet Project 2 ice core: Dust stadials, interstadials, and the Eemian
Authors: Ram Michael , Koenig Gerson
Published: February 2004

In this paper, we present and discuss the pre‐Holocene dust profile of the Greenland Ice Sheet Project 2 (GISP2) ice core retrieved from central Greenland measured using laser/light scattering (LLS) from ice and compare it with the electrical conductivity method and oxygen isotope profiles. We describe how we dated the pre/Holocene ice using the annual dust peaks observed with LLS (starting from the accepted chronology to 2250 m) and obtained a chronology in substantial accord with the gas‐age dating of the ice. We also show that the GISP2 ice core penetrated the Eemian and that a record of a 10.2‐kyr penultimate glaciation is present in the GISP2 core.
Seasonal and interannual variability of atmospheric convergence zones in the tropical Pacific observed with ERS‐1 scatterometer
Authors: Zheng Quanan , Yan Xiao‐Hai , Liu W. Timothy , Tang Wenqing , Kurz Dragan
Published: February 2004

Monthly images of atmospheric convergence zones in the tropical Pacific were produced with 1992–1994 ERS‐1 scatterometer wind vectors. From the images, the position, width, and intensity of the convergence zones can be determined. Latitude‐time sections of ocean surface wind divergence show that the summer position of the ITCZ in the eastern Pacific during the observed period exceeded the normal position northward by 3°–6° latitude, and the annual cycle in the western Pacific for 1994 was quite weak, implying a persistently unusual case.
Bistatic HF radar diagnostics induced field‐aligned irregularities
Authors: Yampolski Y. M. , Beley V. S. , Kascheev S. B. , Koloskov A. V. , Somov V. G. , Hysell D. L. , Isham B. , Kelley M. C.
Published: February 2004

In late March and early April of 1995, an experimental campaign involving the modification of the F2 ionospheric layer took place in Russia and Ukraine. HF pulsed and CW Doppler radar observations of field‐aligned irregularities within the region over the Sura heater were made with the UTR‐2 radio telescope serving as the receiver. In this paper, some preliminary results of our bistatic radar observations of the modified region are presented. These results include measurements of the drift, evolution, and decay of inhomogeneities and turbulence contained within the modified region and evidence of interactions between the ionospheric plasma, Alfvén waves, and free geomagnetic pulsations.
Hot protons in the inner corona and their effect on the flow properties of the solar wind
Authors: Esser Ruth , Habbal Shadia R. , Coles William A. , Hollweg Joseph V.
Published: February 2004

Following recent observations which indicate the presence of extremely high flow speeds in the inner corona, 700 – 800 km s−1 below 10 RS, and the possible presence of very high proton temperatures, 3 × 106 ≤ Tp ≤ 8.5 × 106 K, we present a parameter study which shows that if the high proton temperatures in the inner corona are genuine, then flow speeds of 700 to 800 km s−1 can readily be achieved at 10 RS or even closer to the coronal base. If one allows for both heat and momentum deposition in the inner corona, the rapid acceleration close to the coronal base can be achieved with proton temperatures well below the upper limit placed by the observations.
Low‐energy (<1.6 MeV) particle counting rates and solar magnetic activity: A study of the 1980 anomaly
Authors: Rodríguez‐Pacheco J. , Sequeiros J. , del Peral L. , Medina J. , Wenzel K.‐P.
Published: February 2004

We present a study of the relation between the solar magnetic activity (centered in sunspots, flares types N and B, and long‐duration X class flares) and the counting rates of particles in interplanetary space with energies below 1.6 MeV obtained from the Low‐Energy Proton Experiment (DFH‐EPAS) onboard International Sun‐Earth Explorer spacecraft, during the period 1978–1982. Our study shows that the particle counting rates are neither correlated with sunspots number nor with flares type N, but they are correlated with flares type B and mainly with long‐duration X class flares. The origin of the low counting rates of particles detected during the years 1979–1980 is investigated as well. The disappearance of the strongest interplanetary shocks during that period can explain this phenomenon, at least within the energy range studied. The absence of any anomalous behavior in the flares type B and in the long‐duration X class flares during this period suggests that this shock behavior can be produced by anomalous conditions of the interplanetary magnetic field during the Sun's polar magnetic field reversal.
Density in the magnetosphere inferred from ISEE 1 spacecraft potential
Authors: Escoubet C. P. , Pedersen A. , Schmidt R. , Lindqvist P. A.
Published: February 2004

The potential of ISEE 1 spacecraft has been used to derive the plasma density in the magnetosphere and its environment. First, we show that using the equilibrium of currents flowing in and out of a spacecraft, we could numerically derive a relation between the spacecraft potential and the density of the surrounding plasma. After verifying that this relation was in good agreement with the measurement of the density made by other instruments during selected periods of time, we apply this relation to the spacecraft potential measured continuously from 1977 to 1984 on ISEE 1. An image of the plasma density in the magnetosphere and its environment is obtained as a result. All principal magnetospheric regions are clearly identified: the solar wind with a density around 5 cm−3, the magnetosheath with a density around 50 cm−3, the magnetosphere with a density around 1 cm−3, the plasma sheet with a density around 0.5 cm−3, and finally, the more tenuous tail lobes with a density below 0.1 cm−3. The plasma density was observed slightly higher on the dawnside than on the duskside of the magnetosphere. In addition, the magnetosheath was closer to the Earth on the dawnside than on the duskside. When the magnetic activity increased (recorded by the AE index), the dayside magnetosphere was compressed/eroded by about 1 to 2 RE while the plasmasphere/inner magnetosphere became quite irregular and expanded in the dawn‐midnight and in the dusk‐noon sectors. In addition, during high magnetic activity, the plasma sheet at YGSM = 0 was thicker and slightly denser than at low‐activity. On the other hand, the flanks of the plasma sheet were thinner and slightly less dense during high‐activity than during low‐activity.
Geocoronal hydrogen Balmer‐α line profiles obtained using Fabry‐Perot annular summing spectroscopy: Effective temperature results
Authors: Nossal S. , Roesler F. L. , Coakley M. M. , Reynolds R. J.
Published: February 2004

A Fabry‐Perot annular summing spectroscopy technique has been used at the University of Wisconsin's Pine Bluff Observatory to acquire geocoronal Balmer‐α line profile data with significantly improved precision and height resolution. The double‐etalon Fabry‐Perot interference pattern is imaged onto a Photometries PM512 charge‐coupled device (CCD) chip, thus enabling light to be gathered in multiple spectral bins simultaneously. In comparison with scanning systems we used earlier, the high quantum efficiency of the CCD and the multichannel detection associated with the Fabry‐Perot annular summing technique have enabled us to save a factor of about 10 in the integration time required for studies of the line profile. As a result, we are now able to both more precisely observe the line shape of the very faint (1–10 R) Balmer‐α emission and obtain data using shorter integration times. Our data illustrate the scientific potential for using this technique for the study of very faint extended emission line sources. We present exospheric effective temperatures obtained from line profile data acquired during the period of 1992–1993. When these data are compared with predictions from the Anderson et al. [1987] and MSIS90 models, there are points of agreement as well as some discrepancies. Included in this paper are discussions of both technical issues associated with applying annular summing spectroscopy for geocoronal Balmer‐α observations and results of data obtained using this technique.
Geotail measurements compared with the motions of high‐latitude auroral boundaries during two substorms
Authors: Maynard N. C. , Burke W. J. , Erickson G. M. , Nakamura M. , Mukai T. , Kokubun S. , Yamamoto T. , Jacobsen B. , Egeland A. , Samson J. C. , Weimer D. R. , Reeves G. D. , Lühr H.
Published: February 2004

Geotail plasma and field measurements at −95 RE are compared with extensive ground‐based, near‐Earth, and geosynchronous measurements to study relationships between auroral activity and magnetotail dynamics during the expansion phases of two substorms. The studied intervals are representative of intermittent, moderate activity. The behavior of the aurora and the observed effects at Geotail for both events are harmonized by the concept of the activation of near‐Earth X lines (NEXL) after substorm onsets with subsequent discharges of one or more plasmoids down the magnetotail. The plasmoids must be viewed as three‐dimensional structures which are spatially limited in the dawn‐dusk direction. Also, reconnection at the NEXL must proceed at variable rates on closed magnetic field lines for significant times before beginning to reconnect lobe flux. This implies that the plasma sheet in the near‐Earth magnetotail is relatively thick in comparison with an embedded current sheet and that both the NEXL and distant X line can be active simultaneously. Until reconnection at the NEXL engages lobe flux, the distant X line maintains control of the poleward auroral boundary. If the NEXL remains active after reaching the lobe, the auroral boundary can move poleward explosively. The dynamics of high‐latitude aurora in the midnight region thus provides a means for monitoring these processes and indicating when significant lobe flux reconnects at the NEXL.
Waves and turbulence in high Mach number nearly parallel collisionless shocks
Authors: Scholer M. , Kucharek H. , Jayanti V.
Published: February 2004

We have performed a number of one‐dimensional hybrid simulations (massless electrons, macroions) of almost parallel collisionless shocks (angle between the upstream magnetic field and shock normal of 5°) for medium and high Mach number shocks. One of the key questions we address is whether downstream convected upstream waves or waves locally generated at the interface of the incoming solar wind and the partially thermalized plasma are the main source of the downstream turbulence. In the medium, supercritical Mach number regime the small‐wavelength interface waves are damped in a transition region and contribute to downstream dissipation [Krauss‐Varban, 1995]. These waves are right‐hand polarized and propagate in the downstream rest frame toward the shock. In an Alfvén Mach number regime around MA ∼ 8 we find behind the shock ramp right‐hand polarized waves with both helicities. These are interpreted in terms of both the ion/ion resonant and the ion/ion right‐hand nonresonant instability occurring in the shock transition region. The latter occurs, according to linear theory, when the beam density is high and when the relative speed between the ion beam and the ambient ions is large. In this Mach number regime the shock‐produced waves have larger wavelengths and are less strongly damped. We suggest that they are subject to a parametric decay instability, resulting in an inverse cascade of short‐wavelength waves to longer ones farther downstream. In the very high Mach number regime, damping as well as decay of the shock‐produced waves is slow in comparison with the transit time from the shock to the magnetopause. The shock‐generated waves are then the dominant source of the downstream turbulence.
Association of waves with narrow particle dropouts in the outer radiation belt
Authors: Imhof W. L. , Mobilia J. , Voss H. D. , Collin H. L. , Walt M. , Anderson R. R. , Wygant J. R.
Published: February 2004

An investigation has been made of the association of plasma waves with narrow dropouts (<30‐min observation time) in the fluxes of trapped energetic electrons and protons within the radiation belts. The experiment, conducted with instruments on the CRRES satellite, indicates that 5 Hz < frequency < 1 kHz waves are nearly always produced at the times and positions of narrow energetic electron flux dropouts. The waves may be produced at the positions of steep particle flux gradients. This phenomenon is best studied during short‐duration events that provide measurements on both sides of a boundary in a relatively quiescent state. In addition to an investigation of the waves associated with narrow dropouts the data presented here show the general correlations between waves and particle fluxes, particularly after new injections or plasmapause crossings. In some cases, energetic proton dropouts also occur and may contribute to the generation of waves.
Nonlinear whistlers: Implications for 100 Hz electric fields observed in the Venus ionosphere
Authors: Cole K. D. , Hoegy W. R.
Published: February 2004

Conditions on the electric field of an electromagnetic wave in a plasma are found which make the wave magnetic field comparable in strength to the ambient field. The conditions arise from higher‐order forces than are used in linear theory. It is found that the strong 100‐Hz signals observed at night by the Pioneer Venus orbiter in the Venus ionosphere at 129 km and a large fraction of the signals observed at 160 km, if interpreted as whistlers, would meet these conditions. The observations would represent highly nonlinear states for whistlers. Previous analyses of the 100‐Hz signal interpreted as due to “linear” whistlers could therefore be flawed. This supports our contention [Cole and Hoegy, 1996a, b], arrived at by an independent argument, that the whistler hypothesis for the 100‐Hz signal is invalid. In addition, in a new contribution to linear theory of the dispersion relationship, it is found that in the Venus ionosphere, in the high collision frequency region near 130 km altitude, linear whistlers would propagate freely in any direction, contrary to assumptions otherwise in the literature. They are critically damped there. At 160 km, normal linear‐limit theory applies and manifests normal guidance by the ambient magnetic field, subject to ω<p cosθ, with little damping.
Recurrent geomagnetic storms and relativistic electron enhancements in the outer magnetosphere: ISTP coordinated measurements
Authors: Baker D. N. , Li X. , Turner N. , Allen J. H. , Bargatze L. F. , Blake J. B. , Sheldon R. B. , Spence H. E. , Belian R. D. , Reeves G. D. , Kanekal S. G. , Klecker B. , Lepping R. P. , Ogilvie K. , Mewaldt R. A. , Onsager T. , Singer H. J. , Rostoker G.
Published: February 2004

New, coordinated measurements from the International Solar‐Terrestrial Physics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth's magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X‐ray data are also used to identify the solar coronal holes that produce the high‐speed solar wind streams which, in turn, cause the recurrent geomagnetic activity. It is concluded that even during extremely quiet solar conditions (sunspot minimum) there are discernible coronal holes and resultant solar wind streams which can produce intense magnetospheric particle acceleration. As a practical consequence of this Sun‐Earth connection, it is noted that a long‐lasting E>1MeV electron event in late March 1996 appears to have contributed significantly to a major spacecraft (Anik E1) operational failure.
Ion cyclotron modes in a two‐ion‐component plasma with transverse‐velocity shear
Authors: Gavrishchaka Valeriy V. , Koepke Mark E. , Ganguli Gurudas I.
Published: February 2004

Electrostatic ion cyclotron fluctuations driven by combination of a magnetic‐field‐aligned electron current and a localized transverse electric field in two‐ion‐component plasmas are investigated through the use of nonlocal linear theory for a collisionless plasma. The emphasis is on the stability properties of these modes as a function of relative concentration of plasma components. For various characteristic parameters, such as the spatial dimension of the inhomogeneous electric field profile, magnitude of the E × B velocity, magnitude of the field‐aligned current, and temperature ratio τ = Ti/Te, it is shown that in contrast to the homogeneous case of the current‐driven ion cyclotron mode, the ion cyclotron modes in the presence of a transverse‐velocity shear can be unstable in a significantly wider range of relative concentration ratios. Moreover, positive growth rates are possible for relatively small and even zero values of field‐aligned current in the inhomogeneous electric field case. The mode characteristics in the two cases differ significantly. For example, in the inhomogeneous case, the frequency spectrum is broadband including frequencies much smaller than ion gyrofrequency. The relevance of these results to ionospheric observations is discussed.
Correlation between core ion energization, suprathermal electron bursts, and broadband ELF plasma waves
Authors: Knudsen David J. , Clemmons James H. , Wahlund Jan‐Erik
Published: February 2004

Observations of the lowest energy or core ions provide a particularly sensitive measure of the early stages of auroral ion energization. Freja satellite observations of 0–20 eV core ions in the topside auroral ionosphere and cusp/cleft show signs of heating within both regions of VLF hiss and broadband ELF plasma waves. However, heating to several eV or more is associated predominantly with the ELF waves. A correlation analysis of wave and core ion data formed from orbital segments shows that, on average, correlations are highest for wave frequencies below several hundred Hz, and less at VLF hiss frequencies. A similar analysis shows a higher correlation between electron precipitation and ion heating for electron energies below several hundred eV (i.e., the energies associated with suprathermal electron bursts) and a lower correlation above the 1 keV energies associated with auroral inverted‐V's. Signs of core ion heating begin to appear when wave power at the O+ gyrofrequency exceeds about 10−3 (mV m−1)2/Hz, and when the integrated field‐aligned electron flux exceeds a few times 107 cm−2 s−1 sr−1. This electron energy flux threshold is at least an order of magnitude lower than previously inferred from earlier studies comparing suprathermal electron fluxes and energetic ions. Almost all observed heating events occur during enhanced or active geomagnetic conditions; i.e., Kp ≥ 4. While the most intense core ion heating is correlated with broadband ELF waves, we also present one example of weak ion heating of a few eV in a region of VLF auroral hiss.
Theory of quasi‐monochromatic whistler wave generation in the inner plasma sheet
Authors: Villalón Elena , Burke William J.
Published: February 2004

Nonlinear interactions between plasma sheet electrons and nearly monochromatic whistler wave packets are studied. The theory applies to the generation of chorus emissions from quasi‐monochromatic wavelets observed in the plasma sheet at the top of the ELF/VLF hiss band. The hiss‐triggered chorus is produced by step‐like deformations that develop in distribution functions at the boundaries between resonant and nonresonant electrons. Equations are obtained describing the wave amplitudes and frequency‐time characteristics for propagation at small angles with respect to the geomagnetic field. The linear resonant interactions leading to wavelet generation are investigated. The resonant wave frequencies change along the field lines to compensate for geomagnetic field inhomogeneities. If the electric fields exceed the amplitudes of those in the background plasmapheric hiss (≫ 10−6 V/m), electrons become trapped in phase space, and their distribution functions develop plateaus whose extents are proportional to the square roots of electric field amplitudes. Nonlinear currents generated by the trapped electrons are studied to obtain analytical representations of the growth rates and frequency spreads. Numerical examples are presented to illustrate our theoretical analysis.
N2 triplet band systems and atomic oxygen in the dayglow
Authors: Broadfoot A. L. , Hatfield D. B. , Anderson E. R. , Stone T. C. , Sandel B. R. , Gardner J. A. , Murad E. , Knecht D. J. , Pike C. P. , Viereck R. A.
Published: February 2004

New spectrographic observations of the Earth's dayglow have been acquired by the Arizona Airglow Experiment (GLO) flown on the space shuttle. GLO is an imaging spectrograph that records simultaneous vertical profiles of prominent Earth limb emissions occurring at wavelengths between 115 and 900 nm. This study addresses the measured emissions from the N2 triplet states (first positive, second positive, and Vegard‐Kaplan band systems) and their excitation by the local photoelectron flux. The triplet state population distributions modeled for aurora by Cartwright [1978] are modified for dayglow conditions by changing to a photoelectron‐flux energy distribution and including resonance scattering by the first positive system. Modeled and observed intensities are in excellent agreement, in contrast to the well‐studied auroral case. This work concentrates on dayglow conditions at 200 km altitude near the subsolar point. Parameters to infer the local photoelectron flux from the emission band intensities are provided. Several atomic oxygen dayglow emission features were analyzed to complement the N2 analysis. The photoelectron‐excited O I(135.6, 777.4 nm) lines were found to be 3 to 4 times weaker than predicted while the O I(630.0, 844.6 nm) lines were in close agreement with the model prediction.
MHD drift ballooning instability near the inner edge of the near‐Earth plasma sheet and its application to substorm onset
Authors: Pu Z. Y. , Korth A. , Chen Z. X. , Friedel R. H. W. , Zong Q. G. , Wang X. M. , Hong M. H. , Fu S. Y. , Liu Z. X. , Pulkkinen T. I.
Published: February 2004

The MHD drift ballooning mode (DBM) instability near the inner edge of the near‐Earth plasma sheet is studied by using both the one‐fluid generalized progressing wave expansion method and the two‐fluid approach. It is found that in the frame of reference at rest relative to the bulk plasma the DBM may become a purely growing mode in two distinct circumstances, which, for convenience, are called the DBM1 and DBM2, respectively. The β threshold for the DBM1 is identical with that derived by Ohtani and Tamao [1993] and Southwood and Kivelson [1987], while the criterion of the DBM2 covers that of Miura et al. [1989]. Comparisons of the theory with GEOS 2 data show that the DBM2 is more easily excited in the late substorm growth phase. There is considerable evidence that the DBM is generated at expansion onsets. The characteristic features of magnetic field dipolarization can be interpreted in terms of the development of the DBM. The extremely thin current sheet cases should be studied with approaches other than those used in this work.
Particle entry into the magnetosphere with a southward interplanetary magnetic field studied by a three‐dimensional electromagnetic particle code
Authors: Nishikawa K.‐I.
Published: February 2004

We report progress in the long‐term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three‐dimensional electromagnetic particle code. A new run that includes an interplanetary magnetic field yields results that are encouragingly consistent with established features of the solar wind‐magnetosphere interaction. After a quasi‐steady state is established with an unmagnetized solar wind we switch on a southward interplanetary magnetic field (IMF), which causes the magnetosphere to stretch and allows particles to enter the cusps and nightside magnetosphere. Analysis of magnetic fields near the Earth confirms a signature of magnetic reconnection at the dayside magnetopause, and the plasma sheet in the near‐Earth magnetotail clearly thins. Later magnetic reconnection also takes place in the near‐Earth magnetotail. Arrival of southward IMF near the front of the magnetosphere causes a sunward velocity in the dayside magnetosphere, as required to feed flux tubes into the dayside reconnection process. Sunward flow near the equatorial plane of the magnetosphere implies a dawn‐to‐dusk electric field. Initially, the velocity in the distant tail is not much affected by the southward turning. Therefore the dawn‐dusk electric field increases in the sunward direction, which causes Bz to decrease with time in the near‐Earth magnetotail. The cross‐field current also thins and intensifies, which excites a kinetic (drift kink) instability along the dawn‐dusk direction. As a result of this instability the electron compressibility effect appears to be reduced and to allow the collisionless tearing to grow rapidly with the reduced Bz component. At the same time the nightside magnetic fields are dipolarized and a plasmoid is formed tailward. We find that due to the reconnection particles were injected toward the Earth from the neutral line (X line). Consistent with this dawn‐dusk electric field and magnetic reconnection at the dayside magnetopause, both ions and electrons enter the magnetospheric interior easily. In our simulations, kinetic effects self‐consistently determine the dissipation rate in the magnetopause associated with reconnection.
Progress on relating optical auroral forms and electric field patterns
Authors: Johnson M. L. , Murphree J. S. , Marklund G. T. , Karlsson T.
Published: February 2004

Ultraviolet auroral imagery and in situ electric field measurements from Freja are presented and used to identify signatures of the perpendicular electric field associated with three basic arc configurations. The auroral imagery is essential in identifying the two‐dimensional characteristics of the discrete auroral forms for which electric field signatures are examined. The high‐resolution data show the differences between the electric field signatures of the quiet and disturbed arcs (spirals) occurring as a single arc or as a part of a series of parallel arcs within the dusk and premidnight auroral distribution. The scale size of the arcs is given by their thickness, typically ∼ 100 km. Common electric field signatures, such as a reduction in the convection electric field in the region of the arc and enhancements of the convection electric field at the boundaries of the arc, are observed. The electric field reductions dominating the signatures of quiet arcs occurring as a single arc indicate that these arcs are characterized with a weak field‐aligned current. As inferred from the electric field enhancements dominating the signature of quiet arcs which are a part of a series of arcs, these arcs are characterized with a strong field‐aligned current. Features which distinguish the quiet arcs from the disturbed arcs are the quasi‐periodic fluctuations in the disturbed arc's electric field signature. The turbulence in the electric field indicates that shear structures and shear‐driven plasma instabilities are involved in the formation of auroral spirals.
High‐latitude ionospheric transient events in a global context
Authors: Korotova G. I. , Sibeck D. G. , Rosenberg T. J. , Russell C. T. , Friis‐Christensen E.
Published: February 2004

This paper presents a comprehensive global study of bow shock motion, magnetosheath dynamic pressure variations, dayside magnetospheric magnetic field perturbations, and cosmic noise absorption events attending a sequence of transient events observed in high‐latitude global ground magnetograms on February 14, 1986. ISEE 2 spacecraft observations indicated that most of the transient ground magnetometer events were associated with abrupt inward and outward motions of the dawn bow shock during a prolonged period of strongly northward and orthospiral interplanetary magnetic field orientation. Geosynchronous GOES 5 and 6 magnetometer observations provide evidence for corresponding compressions and expansions, which propagated duskward through the prenoon magnetosphere. The magnetopause moved inward past the CCE spacecraft during some of the compressions. The compressions scattered magnetospheric particles and thereby produced quasi‐periodic oscillations in the cosmic noise absorption recorded by high‐latitude ground riometers. We infer that (unobserved) strong transient variations in the solar wind dynamic pressure produced the various phenomena and that the ground magnetometer signatures are best explained in terms of the pressure pulse model of Southwood and Kivelson [1990], in which a single sharp change in the solar wind dynamic pressure generates a pair of field‐aligned currents.
Modeling the ionospheric response to traveling atmospheric disturbances
Authors: Bauske R. , Prölss G. W.
Published: February 2004

Anomalous increases of the ionization density at middle latitudes (positive ionospheric storms) are often a prominent feature of upper atmospheric storms. One of their possible causes are traveling atmospheric disturbances (TADs) which propagate from polar to equatorial latitudes, carrying along equatorward‐directed meridional winds. At middle latitudes, these winds cause an increase in the height of the F2 layer which in turn will lead to an enhancement of the ionization density. Using a simple description of a TAD and an ionospheric model, we are able to reproduce the basic properties of such perturbations. We also attempt to simulate an actually observed storm period. Rough agreement is obtained when the wind speed is derived from the height of the F2‐layer peak. A more detailed simulation of the initial phase of the storm requires a more refined TAD model with time‐dependent height gradients in the wind field.
Analytical representation of g factors for rapid, accurate calculation of excitation rates in the dayside thermosphere
Authors: Strickland D. J. , Majeed T. , Evans J. S. , Meier R. R. , Picone J. M.
Published: February 2004

An algorithm has been developed that rapidly and accurately calculates altitude profiles of volume excitation rates for many species of aeronomic interest. These rates may be specified as functions of solar activity (specific to the Hinteregger et al. [1981] model in this phase of the work) and solar zenith angle (SZA). The algorithm relies on an analytical expression for the g factor as a function of total vertical column density. The g factor for a given state and excitation process can be defined as the direct volume excitation rate for this process divided by the density of the species involved in the direct excitation. Modeling results from this work show that g, when expressed as a function of total vertical column density, is independent of model atmosphere within a small error illustrated in the text. The dependence within g then reduces to solar activity (characterized by F10.7) and SZA. Extensive photoelectron transport calculations have been performed that provide numerical g factors for 22 excitation processes, 3 F10.7 values (75, 150, and 250), and 8 solar zenith angles (0°, 45°, 60°, 70°, 80°, 85°, 87°, and 90°). The results have been fitted with a 10 coefficient analytical expression comprised of a function based on an analytical solution to a simplified photoelectron transport equation and two Gaussian functions needed for structure because of soft X ray energy deposition. The resulting coefficients are used to calculate g factors for user‐specified pairs of F10.7 and SZA by two‐dimensional interpolation. By inputting a model atmosphere the corresponding volume excitation rates may also be specified. For photoionization excitation the analytic expression for the g factor is much simpler. Results presented herein include comparisons between numerical g factors and their fits, along with examples of both g factors and corresponding volume excitation rates for the purpose of showing the effects of changing solar activity and SZA. Tables are included that identify excitation processes, identify additional processes that must be considered to derive emission rates, and provide cross‐section information for the electron impact processes addressed in this work.
Solar wind stream interfaces in corotating interaction regions: SWICS/Ulysses results
Authors: Wimmer‐Schweingruber Robert F. , von Steiger Rudolf , Paerli Raoul
Published: February 2004

Motivated by the well‐known differences in charge state and even elemental composition of the slow solar wind as compared to high‐speed streams, we have analyzed observations made by the Solar Wind Ion Composition Spectrometer (SWICS)Ulysses mass spectrometer of the series of corotating interaction regions (CIRs) encountered by Ulysses in 1992/1993 at 4.5–5.4 AU from the Sun. Stream interfaces (SIs) are first identified within each CIR using the kinetic parameters (density and thermal speed) of the main components, protons and alpha particles. We then show that SIs are also the location of the expected compositional changes in the heavy ion components, such as the freezing‐in temperatures of C and O and the strength of FIP fractionation as given by the Mg/O abundance ratio, to within the time resolution with which these parameters may be obtained by SWICS. The changes in freezing‐in temperatures are so clear that they in turn may be used as a robust indicator of the SI location and even reveal that some of the SI crossings were in fact multiple. We conclude that the heavy ion composition of the solar wind changes abruptly at the SI and remains well preserved out to large heliocentric distances.
An analytic approach to toroidal eigen mode
Authors: Sinha A. K. , Rajaram R.
Published: February 2004

It has been shown that the failure of the classical WKB approach in reproducing the correct frequency spectrum and spatial structures of field line resonances should be attributed to the inability of the method to provide a natural solution close to the turning points. A direct analytic solution has been formulated to derive the toroidal field line resonance structure. Finally, the solutions thus obtained have been compared with the numerically found exact solutions in order to test the authenticity of the formalism.
Alfven wave generation by disturbance of ionospheric conductivity in the field‐aligned current region
Authors: Kozlovsky A. E. , Lyatsky W. B.
Published: February 2004

A fundamental problem of the Alfven wave generation from a region of disturbed ionospheric conductivity in the ambient field‐aligned current area is investigated. It is shown that the field‐aligned current of the outgoing Alfven wave appears not only at the boundary but also inside the region of enhanced (or diminished) conductivity. If the ionosphere conductivity increases, the additional field‐aligned current of the outgoing Alfven wave inside the region of disturbed conductivity is directed in the same way the background field‐aligned current. For a circular region of disturbed conductivity the electric field of the outgoing Alfven wave can be presented as the sum of electric fields of the two‐dimensional dipole, quadrupole, and screened monopole sources. For a strip‐like region of disturbed conductivity the electric field of the outgoing Alfven wave appears only inside the strip and can be presented as the sum of homogeneous and linearly varying electric fields.