bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave activity in the neighborhood of the bowshock of Mars
Authors: Sagdeev R. Z. , Shapiro V. D. , Shevchenko V. I. , Zacharov A. , Király P. , Szegó K. , Nagy A. F. , Grard R. J. L.
Published: February 2008

Plasma wave activity in the neighborhood of the Martian bow shock were measured for the first time by the Soviet spacecraft Phobos‐2 in a wide frequency range from dc to 150 kHz. The wave activity varied in character as the spacecraft moved across different plasma regions: in the neigborhood of the Martian bow shock, inside the magnetosheath and in the tail region.

In this paper we provide suggestions for the processes responsible for these plasma waves. The most interesting peculiarities of the wave activity around Mars is the sharp increse of wave intensity in the magnetosheath region. This increase is attributed to two different physical mechanisms. High frequency waves are excited at the shock front due to currents flowing along the front; these ion acoustic waves are convected inside by the solar wind. The low frequency waves (∼100 Hz) close to the inside boundary were, we believe, generated by heavy Martian ions diffusing through the planetopause into the magnetosheath.
Evidence for local and nonlocal barotropic responses to atmospheric forcing during BEMPEX
Authors: Luther Douglas S. , Chave Alan D. , Filloux Jean H. , Spain Peter F.
Published: February 2008

The coherence between single bottom pressure and barotropic velocity records collected in the North Pacific during BEMPEX and air pressure, wind stress, and stress curl derived from FNOC products are examined over the 200‐1 day period band. Strong coherence between the bottom pressure and all atmospheric variables is seen, nonlocal coherence (maximum up to 1000 km to the southeast) dominating at periods longer than ≈10 d and coherence being prevalent at shorter periods, consistent with predictions from existing models of atmospherically‐forced barotropic motion. The azimuth of the nonlocal coherence maximum relative to the ocean station is a function of frequency, which is not expected from the models. The coherence between the barotropic velocity (as measured by the electric field) and the atmospheric variables is weaker, but nonlocal coherence with the wind stress and wind stress curl at periods greater than a week, and local coherence with the wind stress at shorter periods, is statistically significant.
Sensitivity of the equilibrium surface temperature of a GCM to systematic changes in atmospheric carbon dioxide
Authors: Oglesby Robert J. , Saltzman Barry
Published: February 2008

The equilibrium response of surface temperature to atmospheric CO2 concentration, for six values between 100 and 1000 ppm, is calculated from a series of general circulation model experiments. This response is nonlinear, showing greater sensitivity for lower values of CO2 than for the higher values. It is suggested that changes in CO2 concentration of a given magnitude (e.g., 100 ppm) play a larger role in the Pleistocene ice age type temperature variations, than in causing global temperature changes due to anthropogenic increases.
The Loma Prieta Earthquake of October 18, 1989: Results of teleseismic mantle and body wave inversion
Authors: Romanowicz Barbara , Lyon‐Caen Hélène
Published: February 2008

We present the results of an analysis of teleseismic mantle and body wave data observed on digital very broad band stations for the Loma Prieta earthquake of 10/18/1989. Both datasets yield consistent mechanisms with first motion and geodetic measurements. An interesting result of the mantle wave analysis is the realization of a special relation of the geographical position of this event, its source mechanism and the upper mantle degree 2 heterogeneity. Bodywave modelling indicates that the mechanism may be a double shock and could correspond to partitioning of the fault into thrust and strike slip motion. The available teleseismic data in the appropriate distance range are unfortunately not sufficient to lead, to firm conclusions on this point, which should be tested by local observations.
Aftershock slip behavior of the 1989 Loma Prieta, California Earthquake
Authors: Oppenheimer David H.
Published: February 2008

An analysis of 745 aftershocks of the M7.1 Loma Prieta earthquake of 17 October, 1989 reveals a wide variety of focal mechansims. At the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the San Andreas fault. At the southeastern end the mechanisms exhibit right‐lateral motion on near‐vertical planes, suggesting that these aftershocks involve slip on the San Andreas fault. Few of the aftershock mechanisms in the central zone resemble the main shock mechanism (strike N130°E, dip 70°SW, rake 140°), but instead exhibit reverse, right‐lateral, left‐lateral, and normal motion on planes subparallel to the main shock rupture plane. The dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter. However, the lack of agreement between of the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane. This behavior is consistent with observations of aftershock sequences for other dip‐slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic. If the stress drop for the main shock relieved most of the tectonic stress, the mechanisms could reflect the heterogeneity of the near‐field stress redistribution. Alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane.
Preliminary velocity and resistivity models of the Loma Prieta Earthquake region
Authors: Eberhart‐Phillips Donna , Labson Victor F. , Stanley William D. , Michael Andrew J. , Rodriguez Brian D.
Published: February 2008

A preliminary three‐dimensional velocity model of the Loma Prieta epicentral region in the Santa Cruz Mountains of California has been derived using raypaths from aftershocks recorded by the U.S.G.S. seismic network. In addition, a magnetotelluric sounding profile was completed prior to the earthquake and a two‐dimensional resistivity model computed. The velocity and resistivity models include a low‐resistivity (3–10 ohm‐m), low‐velocity (3.3–5.8 km/s) wedge of material between the Zayante and San Andreas faults that extends to depths of over 8 km and is interpreted to be largely Tertiary marine sedimentary rocks. A high‐resistivity (>1000 ohm‐m), high‐velocity (6.4–6.7 km/s) zone between the San Andreas and Sargent faults may represent largely mafic intrusive rocks.
A shear‐wave polarization study in the Wellington Region New Zealand
Authors: Gledhill K. R.
Published: February 2008

A month of digital data from two three component seismograph stations near Wellington, New Zealand, was analysed as part of a feasibility study for a major project to investigate shear‐wave splitting. Although the total number of earthquakes studied was small (14), some suggestive results were obtained. Almost all events recorded within the shear wave window showed a phase reversal of the horizontal components after one or two shear wave cycles, suggesting that there are actually two shear‐wave arrivals. The measured polarization of the first shear wave arrivals was N (31 +/−11) E. This polarization alignment cannot be explained by focal mechanisms, and it is unlikely to be due to topography because of the station‐to‐station correlation. The present evidence suggests the most likely cause is crustal anisotropy due to the geological structure at shallow depth, rather than stress aligned micro‐cracks.
Large‐scale patterns of eolian sediment transport on Venus: Predictions for Magellan
Authors: Saunders R. S. , Dobrovolskis Anthony R. , Greeley Ronald , Wall Stephen D.
Published: February 2008

The atmosphere of Venus is likely to exert a major influence on the surface. Arecibo and Venera 15/16 observations of the population of impact craters with bright halos give direct evidence of surface modification, on the scale of centimeters, to smooth the surface on time scales of 50 ‐ 250 my. Both chemical and mechanical modifications probably occur. Diurnal winds in the planetary boundary layer can transport particles. Using boundary layer theory, including the effects of topography, surface stresses and resulting transport and deposition of sand‐size particles are calculated. Regional slopes are sites of largest surface stresses. Sand will be generally transported downhill, although there is a preferential net transport from east to west, in the same direction as the atmospheric superrotation. It is predicted here that streaks may be seen in the Magellan radar images which will indicate directions of net eolian transport on the surface of Venus.
Fault kinematics in the 1989 Loma Prieta rupture area during 20 years before that event
Authors: Seeber Leonardo , Armbruster John G.
Published: February 2008

The Loma Prieta (LP) compressional bend of the San Andreas fault zone (SAF) appears to be multi‐stranded and vertically segmented; thus, faults in this segment other than the one that ruptured in 1989 may: 1) be the source of prior large events associated with this portion of the SAF and 2) be highly stressed after the 1989 LP event. The fault that ruptured in 1989 was remarkably aseismic during the preceding 20 years; seismicity occurred on some of the neighboring faults of the system, but others remained aseismic. The Lake Elsman burst of seismicity within 1.6 years of the main shock is on a set of secondary faults within the foot‐wall of the rupture. The shallow (≤5 km) portion of the SAF, morphologically and structurally characterized as steep and predominantly strike‐slip, and the imbricate thrust zone to the northeast were also quiescent. These upper crustal faults may partition the oblique motion accomplished by LP‐like ruptures in the lower crust into fault‐parallel (transcurrence) and fault‐normal motion (convergence), respectively. While the overall level of seismicity in the region around LP increased over the 20 years before 1989, the level of seismicity (number of events) on the creeping portion of the SAF next to the LP segment decreased. Moreover, the level of background seismicity on this and other fault segments varied dramatically, both up and down, in conjunction with major regional earthquakes on other segments. Thus, improved models for precursory patterns of seismicity should account for mechanistically more realistic changes than simple seismicity increase or decrease everywhere around an impending rupture.
The CaCO3 profile in a recent Ionian sea core and the tree ring radiocarbon record over the last two millennia
Authors: Castagnoli G. Cini , Bonino G. , Caprioglio F. , Serio M. , Provenzale A. , Bhandari N.
Published: February 2008

The calcium carbonate (CaCO3) profile of a recent sediment core, drilled in the Ionian Sea in 1979, is studied. The CaCO3 content of the sediment has been measured at regularly spaced intervals of Δd=0.25 cm corresponding to Δt=3.87 yr from AD 170 to the present. The CaCO3 profile of the core closely resembles the radiocarbon time series as deduced from tree ring data. The two records have a correlation coefficient of about 0.8 and show strikingly similar long‐term variations. This result presumably follows from the fact that both systems take part in the carbon cycle. The spectral analysis of the CaCO3 time series reveals the presence of the well known periodicity with period ca: 200 years, characteristic of the Δ14C record. Since the CaCO3 content of sea sediments is governed by biological, physical and chemical processes in surface sea waters, which in turn are strongly influenced by climatic conditions, and since the ≈200 yr Δl4C wave is known to be governed by solar modulation of galactic cosmic rays, the tuning of these two records on the same frequencies suggests a strong sun‐climate relationship.
Gravity wave spectra in the middle atmosphere as observed by Rayleigh lidar
Authors: Wilson R. , Hauchecorne A. , Chanin M. L.
Published: February 2008

Rayleigh lidar offers the unique ability to make routine measurements of temperature (or density) mesoscale fluctuations in the 30 to 75 km altitude range. Power spectra of density and temperature fluctuations, versus vertical wavenumber and (apparent) frequency, are derived from lidar measurements. These spectra are interpreted in the framework of the gravity wave theory. Power spectral density increases from the stratosphere to the mesosphere in the entire accessible spectral range. Comparison with vertical spectra obtained with various sounding systems indicates a dispersion of the temperature power spectra in the stratosphere as an increase with altitude of the ratio of potential to kinetic energy.
Three‐dimensional simulation study of ionospheric plasma clouds
Authors: Zalesak S. T. , Drake J. F. , Huba J. D.
Published: February 2008

We present the results of fully three‐dimensional numerical simulations of ionospheric plasma cloud evolution. We first consider the evolution of the plasma cloud considered by Drake and Huba [1987] in the limit of vanishingly small ion compressibility. The simulations support the results of the analytical theory: finite plasma temperature, combined with fully three‐dimensional plasma dynamics, is a stabilizing influence on plasma cloud evolution. This stability is associated with sheared azimuthal ion flows in the vicinity of the cloud surface. We then consider cloud evolution using realistic values of ion compressibility. We find that the cloud rapidly diffuses to a state in which the sheared azimuthal flow is substantially reduced; subsequently, the cloud becomes unstable and structures.
Optical observations on the CRIT‐II Critical Ionization Velocity Experiment
Authors: Stenbaek‐Nielsen H. C. , Wescott E. M. , Haerendel G. , Valenzuela A.
Published: February 2008

A rocket borne Critical lonization Velocity (CTV) experiment was carried out from Wallops Island at dusk on May 4, 1989. Two barium shaped charges were released below the solar terminator (to prevent photoionization) at altitudes near 400 km. The ambient ionospheric electron density was 5×105 cm−3. The neutral barium jet was directed upwards and at an angle of nominally 45 degrees to B which gives approximately 3×1023 neutrals with super critical velocity. Ions created by a QV process in the region of the neutral jet would travel up along B into sunlight where they can be detected optically. Weïï defined ion clouds (max. brightness 750 R) were observed in both releases. An ionization rate of 0.8%s−1 (125s ionization time constant) can account for the observed ion cloud near the release field line» but the ionization rate falls off with increasing distance from the release. It is concluded that a CIV process was present in the neutral jet out to about 50 km from the release, which is significantly further than allowed by current theories.
Simulation study of ion two‐stream instability in the auroral acceleration region
Authors: Gray Perry C. , Hudson Mary K. , Bergmann Rachelle , Roth Ilan
Published: February 2008

Particle in cell plasma simulation technique has been used to study the effect of the ion two‐stream instability on hydrogen and oxygen distributions at small relative drifts (vH+−vo+<2cH, the hydrogen sound speed). We investigate whether heating due to parallel modes which are unstable at low drifts might be sufficient to quench oblique modes which are unstable at higher drifts. We find that this is not the case and that the oblique modes contribute significantly to heating.
Comment on ‘Single station ocean current vector measurement: Application of the spaced antenna (SA) technique’
Authors: Barrick Donald E.
Published: February 2008

A “spaced antenna” (SA) technique for HF ocean‐surface current measurement was introduced by May et al. [1989]. It was stated that the SA technique can measure transverse surface current speed from a single HF radar station, in addition to the radial speed that is conventionally obtained; it is claimed, therefore, that a single station can thereby measure the total current vector, eliminating the need for two radars. This sequel presents the derivation showing that the SA technique actually measures the radial speed's angular variation with respect to bearing, rather than the transverse current speed. The former is equal to the transverse speed only when there is no curvature in the current streamlines. Using reported voracities, we show that neglect of the resulting curvature in attempting to deduce the transverse speed produces errors too large to allow accurate single‐site current mapping based on SA measurements for normal coastal operation. We consider applications where the SA should prove advantageous, and give limits on radial variation for required transverse speed accuracy.
Distributed coma sources and the CH4/CO ratio in Comet Halley
Authors: Boice D. C. , Huebner W. F. , Sablik M. J. , Konno I.
Published: February 2008

Early analyses of the Ion Mass Spectrometer (IMS) data from the Giotto flyby of Comet P/Halley indicated significant abundances of CHn+ (n=1 to 4). The source of these ions was assumed to be frozen CH4 in the nucleus. An abundance of about 2% CH4 was consistent with this interpretation, resulting in a ratio of CH4/CO that is greater than the predicted limits for interstellar clouds or the solar nebula. However, subsequent analyses of data from the Giotto Neutral Mass Spectrometer (NMS) indicate distributed sources of CO and H2CO in the coma that are most likely associated with organic (CHON) particles, rich in CH‐bearing compounds that decay and produce CHn+ species. We present a model that qualitatively accounts for the measured spatial distribution of CO and H2CO and indicates that most of the CH4+ deduced from the Giotto IMS data may originate from organic compound in the coma dust and not from volatiles released directly from the nucleus. As a consequence, the absence of CH4 in the icy phase of the nucleus is consistent with the observations with an upper limit of about 0.5% to the ratio CH4/CO. This is an important criterion for theories of comet formation.
Models for the hotspot distribution
Authors: Jurdy Donna M. , Stefanick Michael
Published: February 2008

Published hotspot catalogues all show a hemispheric concentration beyond what can be expected by chance. Cumulative distributions about the center of concentration are described by a power law with a fractal dimension closer to 1 than 2. Random sets of the corresponding sizes do not show this effect. A simple shift of the random sets away from a point would produce distributions similar to those of hotspot sets. The possible relation of the hotspots to the locations of ridges and subduction zones is tested using large sets of randomly‐generated points to estimate areas within given distances of the plate boundaries. The probability of finding the observed number of hotspots within 10° of the ridges is about what is expected.
Lower mantle inhomogeneities inferred from PcP precursors
Authors: Weber M. , Körnig M.
Published: February 2008

A search of phases arriving between P and PcP, the reflection from the core‐mantle boundary (CMB), was performed in the Bulletins of the International Seismological Center (BISC). The distribution of the turning/reflection points of anomalous waves in the lowermost mantle indicates the areas which are possibly anomalous regions. The regions exhibiting these anomalies cover only a small fraction of the lowermost mantle sampled. The areas which can be associated with anomalous arrivals are the lowermost mantle under the North Pole region, northern Siberia, central Siberia, western Mongolia, Afghanistan, northeastern China/Korea and the North Atlantic Ridge. These are the regions which should be studied in more detail by analyzing the seismograms, i.e., the amplitude and waveform information, at the corresponding stations in addition to the travel time information reported to the ISC.
Leg 124 of the Ocean Drilling Program
Authors: Silver Eli A. , Rangin Claude
Published: February 2008

Leg 124 of the Ocean Drilling Program drilled five sites in the Sulu and Celebes Seas (Figure 1). The papers presented in this issue provide an overview of some of the preliminary results of the shipboard science. They represent a team effort, and all are co‐authored by the entire scientific party. Our objectives were to determine the age and origin of these basins, and their stratigraphic histories, as indicators of the complex tectonic and paleoceanographic events that have affected the western Pacific region during the Cenozoic. Numerous competing hypotheses have been put forward to explain the array of marginal basins and island arcs in the western Pacific, and these basins are all potential recorders of the complex history of the western Pacific history.
Heterogeneous production of cloud condensation nuclei in the marine atmosphere
Authors: Hegg Dean A.
Published: February 2008

Model calculations are presented which indicate that newly created particles in the marine atmosphere will commonly only be able to achieve sizes, by means of gas‐phase processes, sufficient to activate in cumuliform clouds. Aqueous sulfate production in such clouds will be generally necessary to grow them large enough to activate in marine stratus clouds.
A simple inertial model for Neptune's zonal circulation
Authors: Allison Michael , Lumetta James T.
Published: February 2008

Voyager imaging observations of zonal cloud‐tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m·s−1 and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid‐latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale LD≈3000 km.
A three‐dimensional simulation of a coronal streamer
Authors: Linker Jon A. , Van Hoven Gerard , Schnack Dalton D.
Published: February 2008

We have used a time‐dependent magnetohydrodynamic (MHD) simulation to investigate the magnetic topology of an idealized streamerlike configuration in three dimensions. Starting from an initially current‐free multipole field and a transonic flow, a quasi‐steady, streamerlike configuration forms. The simulated streamer exhibits a closed magnetic field region bounded by a current layer and surrounded by open fields. This helmet region is surmounted by a current layer, with an enhanced density in the closed field and current sheet regions. The simulated streamer has a finite longitudinal extent, with the closed field region primarily confined to the center of the structure.
Thermal bending stresses and vertical motion on oceanic transform fault
Authors: Wessel Pål
Published: February 2008

The conductive cooling of new oceanic lithosphere causes both horizontal and vertical contraction. Along transform faults and fracture zones, the contraction of material on each side of the fault leads to differential subsidence since juxtaposed seafloor of different ages subside at different rates. Horizontal contraction causes accumulation of thermal bending stresses, which are partly relieved by flexural bending along the transform. The relative vertical motion implied by plate flexure at the transform is more important than that predicted by differential subsidence; when combined this net vertical slip rate may exceed 5 % of the full spreading rate for slow spreading ridges. The high vertical to horizontal slip ratios implied may explain anomalously high subsidence rates for seafloor in the proximity of ridge‐transform intersections. Departure from horizontal strike‐slip inferred from transform fault focal mechanisms may possibly be used to put additional constraints on the isotherm controlling the transition from brittle to ductile failure in the oceanic lithosphere.
Stability of (Mg,Fe)14Si5O24 AT 17 GPa and 1800°C and its partitioning behavior of transition elements
Authors: Urakawa Satoru , Kato Manabu
Published: February 2008

Stability of an anhydrous analogue of phase B (AnhB) was investigated at 17 GPa and 1800°C using an MA8 type apparatus. Fe/(Mg+Fe) ratio in AnhB is restricted to within ∼0.1. The divalent transition elements such as Ni and Co are preferentially accommodated in AnhB than in modified spinel (β).
Ground observations of waves at 2.96 MHz generated by an 8‐ to 40‐keV electron beam in the ionosphere
Authors: Monson S. J. , Kellogg P. J.
Published: February 2008

Electromagnetic waves at 2.96 MHz, associated with a beam of 8‐ to 40‐keV electrons in the ionosphere, were observed during the Electron Echo 4 rocket experiment in January 1976. Over 1000 electron pulses were emitted during the rocket experiment, and about 20% of these produced observable signals on the ground. Waves were generated under three different sets of conditions. One set of conditions led to maximum amplitude at 190 km; 2.96 MHz is the second harmonic of the electron cyclotron frequency at an altitude of 160–170 km, so the frequency was about 1% above the local gyrofrequency at the rocket. The second set of conditions led to peak signal amplitude in the 110‐ to 130‐km range, at twice the relativistic cyclotron frequency of the 8‐ to 16‐keV beam. The third set of conditions required that the beam be fired downward. Observations were also made at 0.161, 1.11, 1.25, 1.39, and 5.73 MHz, but no signals were detected at those frequencies.
Time variations of HF‐induced plasma waves
Authors: Showen Robert L. , Kim Dae M.
Published: February 2008

Intense plasma waves are generated by an HF pump wave in an ionospheric heating experiment at the Arecibo Observatory. These plasma waves can be observed as enhancements to the ion and plasma lines of the incoherent backscatter echo. The enhancements can be 3 or 4 orders of magnitude more intense than the unenhanced lines and tend to fluctuate wildly. Both the purely growing and the decay mode parametric instabilities are present. When the pump wave is turned on abruptly, the enhancements develop in time in a repeatable manner. A rather remarkable feature on time scales of seconds is an overshoot in instability power. Overshoots occur frequently but not universally and last for 1–6 s. They can have a magnitude from 10 to hundreds of times the average instability level. The growth of field‐aligned irregularities may be the cause of the overshoots. The overshoots appear to be definitely related to an unusually rapid rise in measured electron temperature that cannot be understood in terms of ohmic energy deposition. On time scales of milliseconds there is a ‘miniovershoot’ before the growth of the instability to a large value. The spectral details also change in a striking manner. The instabilities can first be detected 2–4 ms after pump wave turn‐on. The decay mode is present as well as a broad featureless ‘noise bump,’ which partially sharpens into a line as time progresses. These changes of the spectra in time seem to run counter to the currently accepted theories of plasma wave saturation.
Self‐consistent particle and parallel electrostatic field distributions in the magnetospheric‐ionospheric auroral region
Authors: Chiu Y. T. , Schulz Michael
Published: February 2008

The variation of the self‐consistent electrostatic potential along the magnetic field is calculated by application of the principle of quasi‐neutrality to the plasma components distributed along an auroral field line. The equilibrium plasma consists of hot anisotropic magnetospheric plasma, ionospheric plasma evaporated or extracted upward by the parallel electrostatic field, and backscattered electrons. It is shown that the above charged particle populations can support a potential difference of up to several Kilovolts between the equator and the ionosphere along an auroral field line. Moreover, the corresponding parallel electric field has the proper signature to account for electron precipitation characteristics. Comparisons between theoretical and observed electron precipitation fluxes lead to estimates for the various physical parameters in the model.
A steady three‐fluid coronal expansion for nonspherical geometries
Authors: Joselyn JoAnn , Holzer Thomas E.
Published: February 2008

A steady three‐fluid model of the solar coronal expansion, in which 4He++ ions (alphas) are treated as a nonminor species, is developed for nonspherically symmetric flow geometries of the general sort thought to be characteristic of coronal holes. It is found that the very high mass fluxes in the low corona, which are associated with rapidly diverging flow geometries, lead to a locally enhanced frictional coupling between protons and alphas and consequently to a significant reduction of the He/H abundance ratio in the lower corona from that normally predicted by multifluid models. In the models considered, the frictional drag on the protons by the alphas (a process neglected in most studies) is found to play an important role near the sun. Heavy ions, other than alphas, are treated as minor species and are seen to exhibit varying responses to the rapidly diverging flow geometries, depending on the ion mass and charge. As for the protons, the frictional effect of the alphas on the heavier ions is found to be significant in the models considered.
The sizes of particles in noctilucent clouds: Implications for mesospheric water vapor
Authors: Gadsden M.
Published: February 2008

The amount of water vapor involved in the formation of noctilucent clouds may be a considerable fraction of the water vapor available in the mesosphere. If the cloud particles consist principally of ice, estimates of the amount of water in the clouds will correspond critically with the size of the particles assumed to be involved. The evidence for the typical radius being no greater than 0.1 µm is reviewed and found to be not as strong as might be thought.
Oscillating echoes from the polar E layer
Authors: Bratteng Ove , Leer Egil
Published: February 2008

Radio waves with a frequency of 4 MHz transmitted vertically into the polar ionosphere and reflected in the E layer occasionally show very stable oscillations in intensity. This phenomenon, which occurs mainly in the evening sector under quiet conditions, has been studied at Ny‐Ălesund, Spitzbergen, by using a 4‐MHz transmitter and four spaced receiving antennas. The observed oscillations can be explained as interference of waves reflected from a pair of enhanced ionization regions some 30 km apart and moving with a horizontal velocity of the order of 100 m/s. The low drift velocity is consistent with low magnetic activity.
Arecibo Ionospheric Modification Experiments—Correlation of 630.0‐nm intensity suppressions and enhancements with backscatter radar data
Authors: Sipler Dwight P. , Biondi Manfred A.
Published: February 2008

Simultaneous filter photometer and backscatter radar measurements during RF heating of the ionosphere (ionospheric modification) at Arecibo, Puerto Rico, in 1975 are used to relate 630.0‐nm nightglow intensity modifications to F region changes. The observed ohmic heating of the F region electrons accounts for the measured 630.0‐nm intensity suppression resulting from reduced O(¹D) production by O2+ ion‐electron recombination. The 630.0‐nm intensity enhancements caused by impact excitation of oxygen atoms by fast electrons are associated with the presence of strong plasma instabilities, as is manifested by large backscattered power from the heating wave absorption region. The variability in the RF heating wave‐ionospheric plasma coupling is demonstrated by observations of suppression, no change, and enhancement of 630.0‐nm nightglow intensity during similar heating cycles over a 2‐hour period.
Ionospheric heating by radio waves: Predictions for Arecibo and the satellite power station
Authors: Perkins F. W. , Roble R. G.
Published: February 2008

The effect of resistive heating by radio waves on ionospheric temperatures, electron densities, and airglow emissions is examined by using numerical ionospheric structure and heat balance codes. Two cases are studied: (1) a 3‐GHz, 10‐GW microwave beam from a proposed satellite power station and (2) 1‐MW and 3‐MW beams of 15‐MHz radio waves launched by the Arecibo antenna. By intent, these two cases have similar intensities and geometries of resistive heating. The most dramatic heating effects are predicted to occur in the E region, where a thermal runaway will take place. The E region electron temperature will increase from 200°K to roughly 1000°K, and the E region electron density will increase by a factor of about 3. In the F region, where thermal conductivity plays an important role, temperature increases of 200°–500°K will appear along magnetic field lines passing through the radio wave beams. Enhanced emissions in airglow and molecular infrared lines will also occur. Radio wave heating, when combined with the diagnostic capabilities of the Arecibo incoherent scatter radar, will generate new opportunities to measure the rates of atomic physics processes and neutral atmosphere temperatures and composition at D and E region altitudes.
Nonlinear mixing as a plasma density probe
Authors: Dysthe K. B. , Mjølhus E. , Trulsen J.
Published: February 2008

Nonlinear mixing of two electromagnetic waves, ω± and k±, in an inhomogeneous isotropic and collisionless plasma in the parameter range β2/3(KL)1/3 ≪ 1 is studied. Here β is the ratio of electron thermal velocity to speed of light, K = Ω/c, Ω = ω+ − ω−, and L is a local characteristic length for electron density variation. Langmuir waves, Ω and kL, are found to be excited in two different ways. When (Δk/ K)β2/3(KL)1/3 ≫ 1, where Δk = k+ − k−, resonant wave mixing occurs in which the generated Langmuir waves satisfy kL ≈ Δk. When (Δk/K)β2/3(KL)1/3 ≪ 1, nonlinear conversion takes place at the critical surface where Ω equals the local plasma frequency, the Langmuir waves propagating antiparallel to the density gradient and not along Δk. Coherent scattering of electromagnetic waves off the density perturbations associated with the excited Langmuir waves is studied.
Injun 5 observations of low‐energy plasma in the high‐latitude topside ionosphere
Authors: Burke William J. , Donatelli Delia E. , Sagalyn Rita C.
Published: February 2008

The two Air Force Geophysics Laboratory low‐energy spherical electrostatic analyzers aboard Injun 5 have provided observations which are used in conjunction with simultaneous Lepedea observations to study the energetic and ambient thermal plasmas in the evening sector topside ionosphere. Significant thermal electron flux enhancements are observed in the vicinity of the inverted V structures which could be due to either auroral return currents or ionospheric scale height changes. Enhanced hyperthermal (E > 28 eV) fluxes of positive ions, as well as vehicle potential modulations, are observed as the satellite passes through inverted V events. At 2500 km the polar cap electron density, temperature, and energy density were 89 ± 41 cm−3, 2234 ± 480°K, and 16.2 ± 5.8 eV/cm³, respectively. Higher energy densities were found during times of magnetic disturbance. Persistent fluxes of hyperthermal electrons are identified with the polar rain observed with Isis 2 experiments. Finally, evidence is cited for the existence of small‐scale (20 km) structures within the region of plasma sheet precipitation.
The latitudinal distributions of auroral zone electric fields and ground magnetic perturbations and their response to variations in the interplanetary magnetic field
Authors: Horwitz J. L. , Doupnik J. R. , Banks P. M. , Kamide Y. , Akasofu S. ‐I.
Published: February 2008

Chatanika observations of latitudinal distributions of convection electric fields (E⊥) are compared with isointensity ΔH contours in latitude and time from the Alaskan magnetometer chain and with the north‐south component of the interplanetary magnetic field (IMF Bzm) from Imp‐J. As expected, northward electric fields were generally observed within latitude and time regions where ΔH was positive, while southward electric fields were observed within negative ΔH regions. However, correlation between the magnitudes of the electric fields and of the ΔH perturbations was not strong, owing to variability in ionospheric conductivities produced by precipitation and solar illumination. In the midnight sector the northward‐to‐southward transition in the electric field and positive‐to‐negative ΔH transition were roughly collocated (to within 1 hour in local time) as signatures of the Harang discontinuity. The most important findings are that (1) southward (northward) IMF Bzm transitions caused rapid equatorward (poleward) shifts of the electric field and ΔH patterns and (2) southward IMF Bz transitions, magnetospheric substorms, and local time transitions of the Harang discontinuity can all lead to northward‐to‐southward transitions of the electric field in the midnight sector. Due to the interlaced phasing of each of these three causal mechanisms a highly complex temporal pattern of electric fields results.
The polarization, frequency, and wavelengths of high‐latitude turbulence
Authors: Temerin Michael
Published: February 2008

A new feature of electric field frequency‐time spectrograms observed on the S3‐3 satellite, the resonance fingerprint, is used to determine the polarization, frequency, and wavelengths of high‐latitude turbulence. It is found that in the rest frame of the plasma the frequency is approximately zero, the wavelength may be as small as 5 m, and the electric field is polarized in the plane normal to the magnetic field. Consequently, the power spectrum below a few hundred hertz as measured by a satellite is dominated by the Doppler shift of zero frequency turbulence. The resonance fingerprint is a characteristic pattern of bite‐outs in the electric field power spectrum which repeats at twice the spin frequency of the satellite. The bite‐out, an interference effect, is a consequence of the fact that a double probe is insensitive to wavelengths such that the double‐probe separation is an integral multiple of wavelength.
Injun 5 low‐energy plasma observations during a major magnetic storm
Authors: Rao Lalitha D. V. , Burke William J. , Kanal Madhoo , Sagalyn Rita C.
Published: February 2008

Electron densities and temperatures as well as omnidirectional fluxes of hyperthermal positive ions (E > 28 eV) were measured by means of spherical Langmuir probes aboard Injun 5 at altitudes of >2000 km during a major geomagnetic storm. The electron density in the mid‐latitude trough decreased and the temperatures increased during the early phases of the storm. As the storm progressed, the trough's position moved equatorward, plasma depletions being observed to an invariant latitude of 40° during the early recovery phase. Hyperthermal ions detected in the vicinity of the trough were ring current particles reaching to the satellite's altitude. The minimum thermal electron densities in the trough were found to be within 1° of latitude of the maximum ring current flux. Maximum electron temperatures were measured several degrees equatorward of this position. Injun 5 electron temperatures are compared with those measured by Alouette 2 over the reported positions of stable auroral red arcs. The observations are also used to evaluate further a method developed by Cole (1970) for calculating the position of the ring current by using ground magnetic fluctuations.
Radio aurora in the dayside auroral oval, 1, Spatial relationship with field‐aligned currents and energetic particles
Authors: McDiarmid D. R. , McNamara A. G.
Published: February 2008

The location of radio aurora in the dayside (sunlit) auroral oval has been compared to the location of the field‐aligned currents and energetic particles observed by Isis 2. The following have been observed in the period after geomagnetic noon: Diffuse radio aurora occurs under the region 2 (downward) field‐aligned current sheet and also under a region of >3‐keV proton precipitation. However, this precipitation does not account for the field‐aligned current. The relationship between the proton precipitation and the radio aurora remains, at present, morphological. In contrast, there is an indication that discrete radio aurora, when it occurs, does so under the region 1 (upward) field‐aligned current. The situation prior to geomagnetic noon is confused and requires further observations for clarification.
The Echo 4 Electron Beam Experiment: Television observation of artificial auroral streaks indicating strong beam interactions in the high‐latitude magnetosphere
Authors: Hallinan T. J. , Stenbaek‐Nielson H. C. , Winckler J. R.
Published: February 2008

Ten artificial auroral streaks produced by the Echo 4 rocket‐borne electron accelerator were recorded with an image orthicon television system. The streaks were viewed normal to their direction along the magnetic field, and the threshold accelerator power necessary for optical imaging was found to be near 1 kW. The observed streaks were all produced by beams injected downward from the rocket directly into the atmosphere. Upward‐injected beams of up to 2‐kW power did not produce optically observable echo auroras after the hemisphere‐to‐hemisphere round trip, although echoes were observed by particle counters on the rocket. The failure to observe the echo auroras optically may be the result of strong pitch angle scattering. The positions, orientations, altitudes, and vertical extents of the observed streaks are in satisfactory agreement with model calculations. Some of the streaks had diameters of ∼5 times the electron gyroradius. This is the expected collisional spreading for a beam that, above the atmosphere, is confined to a single gyrodiameter. Other streaks, injected from rocket apogee (215 km), exhibited substantial fluctuations in width that are interpreted as evidence for strong beam interactions with the ambient ionosphere.
Excede 2 Test, an artificial auroral experiment: Ground‐based optical measurements
Authors: O'Neil R. R. , Shepherd O. , Reidy W. P. , Carpenter J. W. , Davis T. N. , Newell D. , Ulwick J. C. , Stair A. T.
Published: February 2008

On April 13, 1975, a rocket‐borne electron accelerator was launched from the Poker Flat Research Range near Fairbanks, Alaska. The launch, the second effort in the Excede series of artificial auroral experiments, was designated Excede 2 test. The pulsed accelerator operated for approximately 100 s in the altitude range 106–135 km, providing a 3‐kV electron beam with maximum currents of 10 A. A rocket‐borne retarding potential analyzer indicated that the charge buildup on the electron‐emitting payload never exceeded a positive potential of 200 V. Ground‐based television systems and a dual channel telephotometer recorded the optical emissions induced in the night atmosphere by the rocket‐borne accelerator. The ground‐based telephotometer measured the time dependent emission profiles of the N2+ (B²Σu+ → X²Σg+) first negative (0‐0) band at 3914 Å and the O(¹S) emission at 5577 Å produced by the pulsed rocket‐borne electron source. The fluorescent or luminous efficiency for the production of the N2+ 1 N (0‐0) band at 3914 Å by energetic electrons at altitudes of approximately 110 km was determined to be equivalent to or greater than 3.2 × 10−3. A value of 1.1 was measured for the steady state photon emission ratio of the O(¹S) 5577‐Å to N2+ 1 N (0‐0) 3914‐Å emissions induced in the atmosphere at 110 km by the rocket‐borne electron source. The ground‐based telephotometer measurements have been corrected for the effects of atmospheric extinction by measuring the apparent stellar radiance of Vega.
A quantitative technique for modeling ionospheric and magnetospheric current distributions
Authors: Oldenburg D. W.
Published: February 2008

Linear inverse theory has been used to generate specific height‐integrated current distributions which recreate observed ground‐based magnetometer data. The current distributions are found by minimizing functional forms subject to the condition that the observations are reproduced to within a desired accuracy. A theoretical example shows that the ‘flattest’ model might be particularly insensitive to random errors in the observations.
Monte Carlo modeling of exospheric bodies: Mercury
Authors: Smith Gerald R. , Shemansky D. E. , Broadfoot A. Lyle , Wallace L.
Published: February 2008

Previous model calculations of the helium exospheres of Mercury and the moon have been based on a regime in which each helium atom impact with the surface results in the selection of a new particle chosen from a given source distribution. The particular velocity space distribution in the source particles was chosen with the implied intent that the resulting atmosphere would be barometric under ideal conditions. In effect, two particle source distributions have been used in the published calculations, which we describe here as Maxwell‐Boltzmann (M‐B), and Maxwell‐Boltzmann flux (M‐B‐F). In the instances in which the atmospheric distribution has been calculated for regions above the surface, the resulting model atmosphere represents a mixture of the M‐B and M‐B‐F sources. We suggest that none of the published exospheric calculations for the two bodies represent atmospheres produced by a barometric source of particles. Although a barometric source of particles cannot be justified in terms of surface physics, an exosphere produced by such a source is a valuable point of reference for calculations based on more realistic conditions. According to the analysis presented below, the appropriate source distribution should be M‐B‐F if the particles in the distribution are to be treated as components of flux. Monte Carlo calculations with an M‐B‐F source are compared with Mariner 10 ultraviolet spectrometer data. The comparison suggests that present models are incapable of fitting the observed Mercury exosphere.
Plasma flows and magnetic field vectors in the plasma sheet during substorms
Authors: Lui A. T. Y. , Frank L. A. , Ackerson K. L. , Meng C. ‐I. , Akasofu S. ‐I.
Published: February 2008

Simultaneous observations of plasma flow and the magnetic field in the plasma sheet from the Imp 6 satellite during magnetospheric substorms are examined to assess whether plasma flow is predominantly perpendicular or along the magnetic field line. For the period from September 1971 to December 1972, simultaneous magnetic field data are available for a total of 119 measurements of plasma flow during plasma sheet thinnings and expansions within the downstream distance of XSM ≃ ‐32 RE. It is found that the observed plasma flow has a large component along the magnetic field line and is not simply the
drift (steady or transient convection flow) nor any cross‐field flow. In general, the higher the flow speed, the closer the observed plasma flow direction is aligned with the magnetic field line. Further, there is no clear association between the plasma flow direction and the sign of the BZSM component of the magnetic field. These results suggest that in general the rapid plasma flows observed in the magnetotail during substorms are predominantly field‐aligned flows and are likely to be due to a magnetic‐field‐aligned pressure gradient or magnetic‐field‐aligned electric field.
Carbon dioxide concentrations in the lower thermosphere
Authors: Trinks H. , Fricke K. H.
Published: February 2008

Carbon dioxide number densities were measured for the first time in the sunlit lower thermosphere on June 29, 1974, above Wallops Island (38°N). The CO2 concentrations were obtained with a mass spectrometer that employed a cryo‐cooled ion source. Below the turbopause the CO2 densities correspond to the ground level mixing ratio; above the turbopause the observed n(CO2)/n(Ar) ratio decreases more rapidly with altitude than is expected for diffusive equilibrium. Photolysis and reactions with the O+ ion alone remove sufficient amounts of CO2 to explain the observed deviation from a pure diffusive equilibrium separation.