bluuebunny/crossref_metadata_2025 huggingface dataset:
The variation of the plasma sheet polytropic index along the midnight meridian in a finite width magnetotail
Authors: Spence Harlan E. , Kivelson Margaret G.
Published: February 2008

We have obtained the polytropic index as a function of distance along the midnight meridian in the terrestrial magnetotail. As our purpose is to establish the effects of the finite width of the magnetotail, we use a simple theoretical model of plasma sheet convection, i.e., 2‐dimensional (2D) field structure and adiabatic inward convection of a uniform distant tail source. Particle orbits are treated independently for portions of the phase space distribution on shells of constant energy. On the midnight meridian, the moments of the distribution are parameterized by τ, the ratio of half the crosstail potential energy to the characteristic maxwellian energy of a distant downtail plasma source. We infer from the model the plasma pressure, P, and the number density, n, along the midnight meridian as a function of τ. P and n define locally an “effective” polytropic index, γ. We find that γ ranges between
and 1, depending on the value of τ and on geocentric distance. We suggest that the qualitative differences between the recent empirical determinations of the polytropic index by Baumjohann et al. [1989] and Huang et al. [1989] may be accounted for in part by this simple model.
Chaotic behaviour of ionospheric turbulence from scintillation measurements
Authors: Bhattacharyya Archana
Published: February 2008

Ionospheric amplitude and phase scintillation data have been analysed to estimate the ‘information dimension’ associated with the attractor of the system. For weak scintillations, both amplitude and phase data yield identical results which demonstrate that spatial fluctuations of electron density in the ionosphere may be characterized by a few degrees of freedom. Stronger scintillations are attributed to steepened density irregularities which cause ‘focusing’ of the incident radio wave. This results in the amplitude scintillations exhibiting higher dimensional chaos but spatial fluctuations in ionospheric density still involve low dimensional chaos.
On the dust/gas tori of Phobos and Deimos
Authors: Ip W.‐H. , Banaszkiewicz M.
Published: February 2008

The dust and gas environment in the vicinity of the orbit of the Phobos moon is assessed using both theoretical methods and observations from previous missions to Mars. It is found that a stable ring of dust particles with radii ≈ 100 μm could exist with a normal optical depth close to the upper limit determined from the Viking Orbiter 1 mission. The presence of a gas ring with neutral number density substantially higher than the hot atomic oxygen background is possible only if the Phobos moon maintains a certain level of outgassing with Qgas > 1023 molec. s−l. The narrow width (≈ 400 km) and the strong plasma perturbations sometimes observed by the Phobos 2 spacecraft at crossings of the orbit of the Phobos moon are still a puzzle to be investigated by further data analysis.
A model of the ion wake of Mars
Authors: Luhmann J. G.
Published: February 2008

Observations from the PHOBOS spacecraft suggest that, for the most part, the Martian magnetotail is induced instead of intrinsic. In this paper, test particle techniques are used to detemine how the associated ion wake might appear to detectors behind Mars if it is produced primarily by planetary ions picked up by the solar wind in the dayside exosphere. The results suggest that low energy (<10 keV) pickup ions populate the inner wake, while a more energetic component is present in the outer magnetosheath and adjacent solar wind. The latter has a finite gyroradius related spatial asymmetry controlled by the interplanetary field orientation. This asymmetry is analogous to, but stronger than, that which appears in Venus ion wake observations because of the smaller obstacle size and weaker interplanetary field at Mars.
Upstream waves at Mars: Phobos observations
Authors: Russell C. T. , Luhmann J. G. , Schwingenschuh K. , Riedler W. , Yeroshenko Ye.
Published: February 2008

The region upstream from the Mars subsolar bow shock is surveyed for the presence of MHD wave phenomena using the high temporal resolution data from the MAGMA magnetometer. Strong turbulence is observed when the magnetic field is connected to the Mars bow shock in such a way as to allow diffuse ions to reach the spacecraft. On 2 occasions this turbulence occurred upon crossing the Phobos orbit. Also weak, ∼0.15 nT, waves are observed at the proton gyro frequency. These waves are left‐hand elliptically polarized and may be associated with the pick‐up of protons from the Mars hydrogen exosphere.
Ordovician paleomagnetism of eastern Yunnan, China
Authors: Fang Wu , Van der Voo Rob , Liang Qizhong
Published: February 2008

Three magnetic components have been isolated in Ordovician formations of the Yangtze Paraplatform (South China Block). Two of these (Daqing A and Hongshiya B components) yield paleopoles that conform to the Carboniferous to Triassic segment of the apparent polar wander path for South China, and are therefore interpreted as remagnetizations. The third component (declination/inclination = 301°/+66°, N = 5 sites, k = 21.4, α95 = 17°) passes the fold test and is interpreted as primary (late Early Ordovician). The paleopole, at 39°S, 236°E, and the paleolatitude of 48°S support an Ordovician position of South China adjacent to Gondwana.
Master event relocation of Gorda Block earthquakes: Implications for deformation
Authors: Stoddard Paul R. , Woods Mark T.
Published: February 2008

We have used the “master‐event” technique to relocate 73 earthquakes in the northern half of the Gorda block. The revised epicenters indicate a systematic eastward bias of ∼30 km in epicenters as published in the ISC Bulletin. The new seismicity pattern reflects a more symmetric distribution of earthquakes about the Gorda Rise, and a reduced degree of seismicity within the Gorda block. Although the level of intraplate activity has apparently been reduced, a significant number of events (10–20) still appears to be related to intraplate deformation. Further relocation studies, coupled with focal mechanism determinations, are necessary to better constrain deformation models for this region.
Effect of the Loma Prieta Earthquake on surface slip along the Calaveras Fault in the Hollister area
Authors: Galehouse Jon S.
Published: February 2008

Over the past ten years we have made over 800 measurements of slip rates at 20 sites on various faults in the San Francisco Bay region. This data set enables us to compare rates and amounts of slip on these various faults before and after the Loma Prieta earthquake (LPEQ) on the San Andreas fault. No surface slip rate changes associated with the earthquake occurred at any of our sites on the San Andreas, Hayward, northern Calaveras, Concord‐Green Valley, Seal Cove‐San Gregorio, Antioch, Rodgers Creek, or West Napa faults. The LPEQ apparently triggered up to 12–14 mm of right slip on the southern Calaveras fault at our two sites in the Hollister area less than 50 km from the epicenter. Most of this slip was probably coseismic or nearly so. About the same amount of slip was triggered at these sites in 1984 by the Morgan Hill earthquake. This slip, in contrast, occurred as afterslip within about a 2.5‐month interval. The Calaveras fault in the Hollister area moves episodically, with shorter times of more rapid slip alternating with longer times of slower slip. The alternation occurs whether or not the times of faster slip are triggered by any nearby seismic event(s).
Hot‐pressing and characterization of polycrystals of β‐Mg2SiO4, for acoustic velocity measurements
Authors: Gwanmesia Gabriel D. , Liebermann Robert C. , Guyot F.
Published: February 2008

Hot‐pressing techniques have been developed for a 2000‐ton uniaxial split‐sphere apparatus (USSA 2000) to fabricate polycrystalline specimens of high‐pressure phases of mantle minerals at pressures up to 18 GPa and temperatures up to 1400°C. Cylindrical specimens (3 mm in diameter and 2–3 mm long) of the beta‐phase of Mg2SiO4 were synthesized using a NaCl cell and recovered at ambient conditions by simultaneously decompressing and cooling along a computer‐controlled P‐T path designed to preserve the high‐pressure phase and anneal strains in the polycrystalline aggregates. These specimens are single‐phased, fine‐grained (≤ 5 micron), free of microcracks and preferred orientation and have bulk densities greater than 99% of x‐ray density. Ultrasonic interferometry measurements of the P‐wave and S‐wave velocities demonstrate that the polycrystals are isotropic and exhibit velocities within 2% of the Hashin‐Shtrikman averages calculated from the single‐crystal elastic moduli. The successful fabrication of these high‐quality polycrystalline specimens makes feasible experiments to determine the pressure dependence of the acoustic velocities for high‐pressure phases of mantle minerals.
Radar characteristics of the equatorial plains of Venus from Goldstone Observations: Implications for interpretation of Magellan data
Authors: Plaut Jeffrey J. , Arvidson Raymond E. , Jurgens Raymond F.
Published: February 2008

Based on analyses of recent high resolution observations of the approximately 1000 km diameter Heng‐0 ring structure by the Goldstone Solar System Radar, we predict that the structure is a large corona. Calibrated values of radar backscatter coefficient (σ°) indicate lateral variations of a factor of 4 in Fresnel reflectivity in the vicinity of Heng‐0, as well as in other areas of the plains, at scales of tens of km. We predict that areas with very low reflectivity values, which occur in a variety of geological settings, are soil‐dominated, with bulk densities as low as 1.5 g/cm3.
Ridge belts: Evidence for regional‐ and local‐scale deformation on the surface of Venus
Authors: Zuber M. T.
Published: February 2008

We evaluate models for the formation of the ridge belt fan assemblage on Venus through consideration of the orientation, spatial distribution, topographic expression and wavelengths of observed tectonic surface features. We favor a compressional mechanism for long wavelength deformation corresponding to the spacing of ridge belts (300≤λ≤400 km). However, short wavelength ridges and grooves (10≤λ≤20 km) that are contained within belts and trend parallel to them are likely to be compressional and extensional, and to reflect both regional and local stress fields. We hypothesize that large‐scale (>> ridge spacing) early‐stage mantle downwelling is the source of regional compression responsible for the establishment of the long wavelength of deformation.
A reexamination of the spreading center hypothesis for Ovda and Thetis Regiones, Venus
Authors: Kiefer Walter S.
Published: February 2008

Crumpler, Head, and colleagues proposed that Ovda and Thetis Regiones are spreading centers. The strong positive correlation between geoid and topography observed in Ovda and Thetis is unlike that observed for terrestrial spreading centers. The maximum elevation expected for spreading centers on Venus is 1.5 km, and a cooling plate thermal model predicts a maximum geoid anomaly of 8 meters, both much less than observed. Even if a spreading center is operative in Ovda and Thetis, most of the geoid and topography must be due to other mechanisms. Crumpier et al. also proposed the existence of “cross‐strike discontinuities”, interpreted as transform fault zones, but the evidence for these structures is not conclusive.
A comparison of broadband source spectra, seismic energies, and stress drops of the 1989 Loma Prieta and 1988 Armenian earthquakes
Authors: Houston Heidi
Published: February 2008

Broadband source spectra of the 1989 Loma Prieta (MW = 6.9) and 1988 Armenian (MW = 6.7) earthquakes are computed at periods from 1 to 50 sec using digitally‐recorded teleseismic P body waves. The effects of attenuation, geometrical spreading, and radiation pattern are removed from the spectra of individual stations, which are then averaged. The source spectra of the Loma Prieta and Armenian earthquakes are higher for their seismic moments than the spectra of 11 intraplate earthquakes studied by Zhuo and Kanamori [1987], which in turn are 2 to 4 times larger than average spectra of interplate subduction zone earthquakes.

The seismically radiated energy can be computed from the source spectrum using Haskell's [1964] formulation assuming a point source with no directivity. An Orowan stress drop can be obtained from the seismic energy and moment. The Orowan stress drops for the Loma Prieta and Armenian earthquakes are both about 20 bars, significantly higher than Orowan stress drops of recent large interplate earthquakes. There is a positive correlation between the Orowan stress drops and the estimated repeat times, consistent with the notion that mechanical fault strength increases with increasing interseismic period.
Low‐frequency magnetic field measurements near the epicenter of the Ms 7.1 Loma Prieta Earthquake
Authors: Fraser‐Smith A. C. , Bernardi A. , McGill P. R. , Ladd M. E. , Helliwell R. A. , Villard O. G.
Published: February 2008

We report the results of measurements of low frequency magnetic noise by two independent monitoring systems prior to the occurrence of the MS 7.1 Loma Prieta earthquake of 17 October 1989. Our measurements cover 25 narrow frequency bands in the more than six‐decade frequency range 0.01 Hz–32 kHz, with a time resolution varying from a half hour in the ULF range (0.01–10 Hz) to one second in the ELF/VLF range (10 Hz–32 kHz). The ULF system is located near Corralitos, about 7 km from the epicenter. The ELF/VLF system is located on the Stanford campus, about 52 km from the epicenter. Analysis of the ELF/VLF data has revealed no precursor activity that we can identify at this time. However, the ULF data have some distinctive and anomalous features. First, a narrow‐band signal appeared in the range 0.05–0.2. Hz around September 12 and persisted until the appearance of the second anomalous feature, which consisted of a substantial increase in the noise background starting on 5 October and covering almost the entire frequency range of the ULF system. Third, there was an anomalous dip in the noise background in the range 0.2–5 Hz, starting one day ahead of the earthquake. Finally, and perhaps most compelling, there was an increase to an exceptionally high level of activity in the range 0.01–0.5 Hz starting approximately three hours before the earthquake. There do not appear to have been any magnetic field fluctuations originating in the upper atmosphere that can account for this increase. Further, while our systems are sensitive to motion, seismic measurements indicate that there were no significant shocks preceding the quake. Thus, the various anomalous features in our data, and in particular the large‐amplitude increase in activity starting three hours before the quake, may have been magnetic precursors.
Modeling of induced currents from electrodynamic tethers in a laboratory plasma
Authors: Urrutia J. M. , Stenzel R. L.
Published: February 2008

The presently accepted picture of the current path for electrodynamic tethers envisions a quasi‐dc current flow in a “phantom loop” consisting of the tether, two field‐aligned current channels into the ionosphere and a cross‐field dosing current in the E‐layer. Predictions are made on the establishment and maintenance of a current loop in space based on observations of time‐dependent currents between tethered electrodes in a large laboratory magnetoplasma, In addition to radiation from the contactors (“whistler wings”), the insulated tether is observed to emit waves (a “whistler wedge”). The “wedge” provides closure during loop formation by carrying cross‐field polarization currents. Whistler spread within the ray cone leads to overlapping of the current wings not far from the tether hence minimizing the role of the ionospheric closure. Maintenance of the loop requires the continuous emission of whistler waves by the entire tether thereby providing severe radiation losses.
Background magnetic spectra: ∼10−5 to ∼105 Hz
Authors: Lanzerotti L. J. , Maclennan C. G. , Fraser‐Smith A. C.
Published: February 2008

The Arrival Heights area of the Hut Point Peninsula on Ross Island has been designated the 2nd Site of Special Scientific Interest (SSSI) on the Antarctic continent. It is the only SSSI in Antarctica designated as a natural electromagnetically ‘quiet site’. As the electromagnetic noise levels of civilization increase world‐wide, such sites around the world, if preserved, will be of increasing scientific importance. We report here the determination of the amplitude and functional form of the geomagnetic fluctuations measured at Arrival Heights in June 1986. The frequency range covered is from ∼10−5 to ∼105 Hz, with a gap between ∼10−1 to ∼10¹ Hz due to instrumentation limitations. Over this frequency range, which is larger than any reported previously from any site on Earth, the magnetic field amplitude spectrum in units of
falls with increasing frequency f as ∼f−1 to ∼f−1.5, and has a value of
at f∼10−3 Hz.
Field‐aligned electric field accompanied by drift Alfvén waves in an inhomogeneous plasma
Authors: Hasegawa Akira , Maclennan Carol G.
Published: February 2008

A field‐aligned electric field, δE‖↑ which is accompanied by drift Alfvén wave perturbations in an inhomogeneous plasma, can be expressed in simple terms as

 

where ψ and δψ are the magnetic flux function and its perturbation, Te is the electron temperature, n(ψ) is the plasma density, k⟂ is the perpendicular wave number, li is the ion Larmor radius and l is the coordinate along a magnetic line of force.
Simultaneous, in situ measurements of OH, HO2, O3, and H2O: A test of modeled stratospheric HOx chemistry
Authors: Wennberg P. O. , Stimpfle R. M. , Weinstock E. M. , Dessler A. E. , Lloyd S. A. , Lapson L. B. , Schwab J. J. , Anderson J. G.
Published: February 2008

Simultaneous, in situ measurements of OH, HO2, H2O, and O3 from 37–23 km are reported. The partitioning between OH and HO2 and the total HOx concentration are compared with expected steady‐state values. The ratio of HO2 to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HOx production and loss rates. The measured HOx mixing ratio is consistent with production dominated by the reaction of O(1D) with H2O, and loss controlled by NOy below 28 km and HOx above 30 km. The steady‐state concentration of H2O2 is inferred from the measured HO2 concentration and calculated photolysis rate. The maximum H2O2 mixing ratio (at 33 km) is predicted to be less than 0.2 ppb.
A comparison of precession and obliquity effects in a Cretaceous paleocllmate simulation
Authors: Park Jeffrey , Oglesby Robert J.
Published: February 2008

A set of 36 perpetual‐season simulations with an atmospheric GCM are used to investigate the effects of precession and obliquity variations on mid‐Cretaceous climate. Climatic variables such as surface temperature, pressure and moisture transport suggest that the mid‐Cretaceous climate system is more sensitive to precession than to obliquity in most regions, even at high latitudes. Obliquity variations affect our simulations primarily by modulating the western extent of the precession‐enhanced continental monsoons. As a result, sensitivity to obliquity can be important at low, as well as high, latitudes.
Depositional history of the Celebes Sea from ODP Sites 767 and 770
Authors: Smith Randall B. , Betzler Christian , Brass Garrett W. , Huang Zehui , Linsley Braddock K. , Menill Dean , Müller Carla M. , Nederbragt Alexandra J. , Nichols Gary I. , Pubellier Manuel , Sajona Fernando G. , Scherer Reed P. , Shibuya Hidetoshi , Shyu Jih‐Ping , Solidum Renato U. , Spadea Piera
Published: February 2008

Leg 124 of the Ocean Drilling Project drilled Sites 767 and 770 in the northern Celebes Sea, reaching late middle Eocene basaltic basement at both sites. Major shifts in sediment provenance record the changing tectonic setting of the basin. From late middle Eocene into early Miocene time pelagic sedimentation prevailed, with little influence from continental or volcanic arc sources. A major continental influence is first documented in middle Miocene time as a thick sequence of quartzose, mud‐rich turbidites accumulated on the deeper basin floor, possibly in response to middle Miocene orogeny in northern Borneo. Terrigenous turbidite deposition waned during the late Miocene as active arc volcanism began to contribute significant amounts of hemipelagic sediment and ash layers, which have remained the dominant basinal sediment to the present. Although the Celebes Sea is now nearly surrounded by volcanic arc terranes, the absence of volcaniclastic sediment in the Eocene to early Miocene section suggests that the basin did not form by back‐arc spreading.
Emission rates of sulfur dioxide, trace gases and metals from Mount Erebus, Antarctica
Authors: Kyle Philip R. , Meeker Kimberley , Finnegan David
Published: February 2008

SO2 emission rates have been measured annually since 1983 at Mount Erebus, Antarctica by correlation spectrometer (COSPEC V). Following a 4 month period of sustained strombolian activity in late 1984, SO2 emissions declined from 230 Mg/day in 1983 to 25 Mg/day and then slowly increased from 16 Mg/day in 1985 to 51 Mg/day in 1987. Nine sets of filter packs containing particle and 7LiOH treated filters were collected in the plume in 1986 and analyzed by neutron activation. Using the COSPEC data and measured element/S ratios on the filters, emission rates have been determined for trace gases and metals. We infer HCl and HF emissions in 1983 to be about 1200 and 500 Mg/day, respectively. Mt. Erebus has therefore been an important source of halogens to the Antarctic atmosphere and could be responsible for excess Cl found in central Antarctica snow.
Visible light emission excited by interaction of space shuttle exhaust with the atmosphere
Authors: Murad E. , Knecht D. J. , Viereck R. A. , Pike C. P. , Kofsky I. L. , Trowbridge C. A. , Rall D. L. A. , Ashley G. , Twist L. , Elgin J. B. , Setayesh A. , Stair A. T. , Blaha J. E.
Published: February 2008

Ground‐based video photography of firings of Space Shuttle Primary Reaction Control System (PRCS) engines show optical emissions extending nearly 4 km from the vehicle after steady state is reached. The total intensity and spatial distribution of these emissions depend on the angle between the spacecraft velocity vector and the engine exhaust axis. Candidate sources for this radiation are reviewed and the conclusion is reached that it is most likely due to vibrationally excited OH, formed by the reaction of fast ambient O atoms and H2O molecules in the exhaust.
Observational signatures of nonlinear magnetotail particle dynamics
Authors: Chen James , Burkhart Grant R. , Huang Cheryl Y.
Published: February 2008

It has been predicted that the nonlinear particle dynamics in the magnetotail leads to a class of resonance structures in the quiet‐time ion distribution functions in the Central Plasma Sheet. These structures exhibit a scaling law of
. In this letter, we report the first identification of such a scaling law in quiet‐time CPS distribution functions obtained aboard ISEE 1. We propose a method which uses the observed resonance structures to determine the quiet‐time current sheet thickness based on a measurement of the distribution function and magnetic field obtained by one satellite.
Upstream waves at mercury, Venus and earth: Comparison of the properties of one Hertz waves
Authors: Orlowski D. S. , Crawford G. K. , Russell C. R.
Published: February 2008

Previous studies have shown that the Venus foreshock region contains low‐frequency upstream waves similar to those in the terrestrial foreshock, but perhaps with different amplitudes than at Earth. Herein, we compare the properties of a second class of upstream waves, analogous to the so‐called 1 Hz waves at Earth. The waves observed at Mercury, Venus, and Earth have very similar properties, i.e., propagation angles less than 55 degrees to the magnetic field and less than 35 degrees to the solar wind flow direction. The waves occur exclusively on the field lines connected to the bow shock. They are most commonly left‐hand elliptically polarized with similar fractional amplitudes, approximately 0.1 of the background field strength. Their amplitudes decrease with increasing distance from the shock. The observed frequencies are similar for Mercury, Venus and Earth when scaled by the interplanetary magnetic field. If, as generally assumed at Earth, these waves arise in regions of backstreaming electrons, these results imply that similar electron foreshocks occur at Earth, Venus and Mercury despite differences in bow shock size and the nature of the obstacle to the solar wind.
Equilibrium structure of the plasma sheet boundary layer‐lobe interface
Authors: Romero H. , Ganguli G. , Palmadesso P. , Dusenbery P. B.
Published: February 2008

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential (e ф ∼ 2 κTe, where e and Te are the charge and electron temperature, respectively) is established in order to maintain quasineutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.
Comparison of ozone profiles from ground‐based laser heterodyne spectrometer and ozonesonde measurements
Authors: Taguchi M. , Okano S. , Fukunishi H. , Sasano Y.
Published: February 2008

To evaluate the accuracy of the vertical profiles and total column densities obtained by a ground‐based laser heterodyne spectrometer, four ozonesonde measurements were performed at Sendai, Japan in November 28–December 2, 1989. The altitudes, widths and maximum values of the peaks in the ozone vertical distributions obtained by the laser heterodyne observations agreed well with those obtained by the ozonesondes, though the fine structures in the ozone distributions can not be resolved by this remote sensing method. The total column densities and their temporal variation obtained by the laser heterodyne observations were also consistent with the ozonesonde data and the Dobson spectrophotometer data at Sapporo and Tateno.
The pressure dependence of the reaction between ClO and OClO at 226K
Authors: Parr A. D. , Wayne R. P. , Hayman G. D. , Jenkin M. E. , Cox R. A.
Published: February 2008

The reaction between ClO and OClO (1),

 

has been studied using the molecular modulation technique at 226K over the pressure range 4.8 – 29.0 torr. The reaction has a strong pressure dependence and the termolecular rate constant obtained at this temperature is

 

The importance of the reaction is discussed in the context of the large ozone depletions observed in the Antarctic springtime. An explanation for the unexpected behaviour observed in earlier studies of the OClO/N02 system is also given.
Near absence of lightning in torrential rainfall producing Micronesian thunderstorms
Authors: Takahashi Tsutomu
Published: February 2008

The near absence of lightning in the torrential rain producing, tall, convective clouds at Ponape, Micronesia was studied by the use of special radiosondes. A unique rainwater accumulation process involving frozen raindrop‐hail formation was found to take place in a narrow layer of altitude just above the freezing level. However, the concentration of frozen particles, including graupel, was one order of magnitude less than that required to trigger lightning. This may be the reason for the weakness of electrical activity in Micronesian thunderstorms.
DSM complete synthetic seismograms: SH, spherically symmetric, case
Authors: Cummins Phil R. , Geller Robert J. , Hatori Tomohiko , Takeuchi Nozomu
Published: February 2008

We present a new technique, based on the Direct Solution Method (DSM) [Geller et al., 1990; Hara et al., 1991; Geller and Ohminato, 1994], for calculating SH (toroidal) synthetic seismograms for spherically symmetric, isotropic, media. No asymptotic approximations are used and the synthetics, which fully include both body and surface waves, can be computed for a broad range of frequencies. Our algorithm accurately handles sources that require discontinuities in the vertically dependent part of the displacement. We use matrix operators that minimize the numerical error of the solutions. An example synthetic profile is presented for a 600km deep source in the IASP91 model for the period range 4‐5000s.
Cosmic ray induced neutron background sources and fluxes for geometries of air over water, ground, iron, and aluminum
Authors: O'Brien K. , Sandmeier H. A. , Hansen G. E. , Campbell J. E.
Published: February 2008

The work reported here has applications in neutron detection and 14C dating. In detection, one wants to measure a signal in the presence of the natural neutron background created by primary cosmic ray particles incident on the atmosphere. Neutron sources created by these cosmic rays and resulting fluxes are calculated as a function of depth in air, seawater, ground, iron, and aluminum. What is new here is the analytical generation of cosmic ray neutron sources as a function of depth in various materials. Good agreement is obtained with experimental data for both neutron spectra and fluxes in the air over ground geometry. The air/seawater geometry has the lowest cosmic ray induced interface neutron flux (3.1 × 10−3 neutrons/(cm2 s)) followed by air/ground (6.4 × 10−3), air/aluminum (2.1 × 10−2), and the highest interface value for air/iron (7.7 × 10−2 neutrons/(cm2 s)).
Origin of annual and subannual periodicities in F region ionization
Authors: Shirke J. S. , Degaonkar S. S.
Published: February 2008

The monthly median values of maximum electron density NmF2 in the F region are harmonically analyzed for a number of high‐latitude and auroral zone stations for each hour of the day during 1958 and 1964. In the high‐activity year 1958 the annual maximum appears in December around 70°N (geographic latitude) for a few hours around noon. The December excess diminishes gradually toward the south, though the duration over which it lasts increases toward the dip equator. By 70°S a slight June enhancement is seen around noon. During the remaining hours of the day a December phase is seen around 70°S, having a large amplitude which decreases toward the north, reaching a slight June excess by 70°N. A 6‐monthly component with equinoctial maximums exists at all stations for all hours of the day, the amplitude being somewhat larger in the south than it is in the north. In the low‐sunspot year 1964 the December phase of the annual component is present in the north with low amplitude for a few hours around noon. The same phase prevails in the south. This is followed in local time by a large‐amplitude June phase in the north and a December phase in the south. The 6‐monthly component is predominant during daytime only and has equinoctial maximums. The current theories are shown to be inadequate to explain these results.
A determination of F region convective electric fields from rocket measurements of ionospheric thermal ion spectra
Authors: Morgan B. G. , Arnoldy R. L.
Published: February 2008

A detector package designed to measure the bulk flow of heavy ions was developed for sounding rocket studies of the lower ionosphere. The unit was first flown on board Electron Echo 3, which was launched eastward from Poker Flat Research Range on April 17, 1974. From least squares fits of a shifted, drifting Maxwellian distribution to direct measurements of the ionospheric particles' thermal energy spectra, average values of rocket payload potential, ion temperature, and bulk plasma flow were obtained. By interpreting the bulk flow velocity transverse to the local magnetic field as convective drift the strength of convective electric fields was inferred. Parameters determined from the data support an ion temperature of 1500 ± 94°K, a payload potential of 1.2 V, and convective field values of 6 ± 4 mV/m east and 25 ± 4 mV/m north. These values compare with an ion temperature of 1000°K, a northward field of 21 mV/m and an eastward field of O mV/m as measured by the auroral backscatter radar at Chatanika, Alaska. Results from the electron echo experiment are also consistent with these electric field values.
Chatanika Radar observations of ionospheric and field‐aligned currents
Authors: Kamide Y. , Horwitz J. L.
Published: February 2008

A technique for estimating field‐aligned current densities from Chatanika (64.9° invariant latitude) incoherent scatter radar measurements is presented and used to examine characteristics of ionospheric and field‐aligned currents at auroral latitudes as functions of magnetic local time and substorm activity. The field‐aligned current densities are obtained as the divergence of height‐integrated ionospheric currents measured at different latitudes. In this paper the one‐dimensional divergence of the horizontal currents is taken to approximate the current density of a field‐aligned current sheet with variations of the horizontal current parallel to the current sheet assumed to be negligible. It is found that the field‐aligned current densities thus deduced from the Chatanika radar data agree with those obtained from simultaneous magnetic observations by the Triad satellite, when the divergence for the radar estimates is taken either perpendicular to the direction of the field‐aligned current sheet inferred from the Triad data or simply along the electric field direction. The following are general features of the estimated field‐aligned currents: (1) Downward (or upward) field‐aligned currents with densities of 10−6–10−5 A/m² are typically obtained in the evening (or morning) sector, particularly equatorward of Chatanika. The observations thus correspond to the equatorward portion of the field‐aligned current system normally observed by more direct methods. (2) During periods of increased geomagnetic activity the observed densities are enhanced, and at times the current directions are reversed. The latter feature presumably occurs during expansion of the auroral oval, when the poleward portion of the current system (in which the current directions are the opposite of those of the equatorward half) moves within the region probed by the radar.
The interplanetary scattering mean free path from 1 to 3 × 10³ MV
Authors: Zwickl R. D. , Webber W. R.
Published: February 2008

We have made a statistical study of published intensity‐time profiles of proton and electron solar particle events from 1967 to 1974 in an attempt to examine systematically the temporal and rigidity dependence of the interplanetary scattering mean free path from ∼1 to 3 × 10³ MV. The observed tmax, the time from the release at the sun to the time of maximum flux at the spacecraft, from solar particle events that complied with a stringent selection criterion were interpreted in terms of a propagation model, with Kr = K0, to obtain the average radial scattering mean free path λr. We find that (1) λr appears to be species independent when it is derived from proton and electron solar particle events, (2) λr varies less than a factor of 2 from solar maximum to solar minimum, and (3) λr is nearly rigidity independent below ∼500 MV. The values of λr that we obtain at low rigidities are inconsistent with all current theoretical models that derive λr from the interplanetary magnetic field fluctuations.
On the observation of a flare‐generated shock wave at 9.7 AU by Pioneer 10
Authors: Dryer M. , Shea M. A. , Smart D. F. , Collard H. R. , Mihalov J. D. , Wolfe J. H. , Warwick J. W.
Published: February 2008

The period March 15 to May 15, 1976, was declared in advance to be the internationally recognized Study of Travelling Interplanetary Phenomena Interval II. A variety of ground‐ and space‐based equipment was requested to make coordinated studies during this part of the minimum of solar cycle 20. Following an absence of solar activity for a long period, several type II radio bursts on March 20, 1976, produced by two solar flares behind the east limb heralded a series of solar, interplanetary, and terrestrial events. These solar radio astronomical observations were followed by non‐Io‐associated radio emission from Jupiter and solar wind plasma detection at Pioneer 10 at 9.7 AU of an apparent shock wave on March 30 and April 9, 1976, respectively. In view of the fact that the solar flares on March 20 were essentially at central meridian with respect to Jupiter and Pioneer 10 and also that the sun was extremely inactive prior to that date we consider the circumstantial evidence that at least one solar‐flare‐generated shock wave propagated to the position of Pioneer 10. The average velocities of this shock wave, together with the inferred type II velocity, support previous observations and theory concerning the rapid deceleration and survival of interplanetary shock waves to distances at least as large as ∼10 AU. It is therefore believed that dissipation (other than that within shocks themselves) plays an insignificant role in shock wave dynamics within the solar wind.
Interplanetary scintillation measurements of the electron density power spectrum in the solar wind
Authors: Coles W. A. , Harmon J. K.
Published: February 2008

The Spatial spectrum of electron density in the solar wind is estimated over the frequency range 2 × 10−3 to 3 × 10−2 km−1 by using 74 MHz observations of interplanetary scintillation. The inversion technique by which the spatial spectrum is estimated from the observed temporal spectrum requires weak scattering. Hence at 74 MHz it can only be applied for solar elongations greater than 40°. The shape of the spectrum is best described by a two‐component power law (P(q) ∝ q−α) where α ≅ 2.7 at low wave numbers and α ≅ 3.2 at higher wave numbers. Occasionally, a single α ≅ 3.0 gives a satisfactory description. The shape of the spectrum varies significantly from day to day, but no mean variation with solar distance has been observed.
Rapid scan Doppler velocity maps of the UHF diffuse radar aurora
Authors: Moorcroft D. R. , Tsunoda R. T.
Published: February 2008

This paper presents the first results of rapid scan Doppler spectra of the diffuse radar aurora obtained with the Homer 398‐MHz phased array radar. Each spectrum was obtained from three consecutive 1‐ms radar pulses spanning an interval of 0.04 s. The spectral resolution obtainable with these short samples was improved by using a maximum entropy method of spectral analysis. Most of the results were obtained from the postmidnight period and were characterized by relatively narrow spectra having Doppler velocities which were nearly constant over an extended azimuth sector (referred to as a Doppler velocity plateau). Typically, there is a positive plateau to the west and a negative plateau to the east, separated by a small or nonexistent transition region; this situation exactly parallels the observations in the equatorial electrojet of ‘Type 1’ irregularities, and it is likely that these velocity plateaus arise from the same mechanism. In addition, transition spectra are observed which tend to be broader and have Doppler shifts intermediate between those of the positive and negative plateaus. In contrast to previous observations of the evening diffuse radar aurora these transition spectra were not localized in one azimuth sector. A unique feature of the observations was the occurrence of double‐peaked spectra, the Doppler velocities of the two peaks usually corresponding to the positive and negative plateau velocities. These last two observations, and also other evidence, can be understood as a consequence of an irregular auroral electrojet.
Rigidity‐independent coronal propagation and escape of solar protons and α particles
Authors: Perron C. , Domingo V. , Reinhard R. , Wenzel K. ‐P.
Published: February 2008

A statistical study of 42 solar proton and α particle events has been performed in the energy range of 9–36 MeV/nucleon (nuc) as measured by the Space Science Department/European Space Agency experiment on Heos 2 during 1972–1974. From one event to another there is a high variability of the p/α ratio at equal energy per nucleon ranging from about 4 to 1000 at 10 MeV/nuc. It is found that the lower value of the p/α ratios increases with azimuthal distance from the flare site. We show that this is not the result of rigidity‐dependent coronal processes but that the increase follows rather as a consequence of two observations: (1) the p/α ratio is correlated with the size of the particle event (Van Hollebeke, 1975) and (2) the number of observed particle events decreases to the east as is found by numerous authors. A model calculation based on these observations is in good agreement with the data. The conclusion of rigidity‐independent coronal propagation and escape also follows from other observations. First, the p/α ratios simultaneously measured by the University of Chicago experiment on board Pioneer 10 and 11, which have different connection longitudes, are generally the same as the Heos 2 values. Second, no systematic variation of the p/α ratio is found for the few cases of large individual events, when the p/α ratio can be followed over an extended time period, i.e., over an extended range of connection longitudes. Third, the proton and α particle spectral exponents show no systematic variation with heliolongitude. It is concluded that the observed large variations of the p/α ratio from event to event are essentially due to different acceleration or storage conditions at the flare site.
Variance and spectra of angle‐of‐arrival and Doppler fluctuations caused by ionospheric scintillation
Authors: Crane Robert K.
Published: February 2008

The variance and spectra of angle‐of‐arrival and Doppler fluctuations were estimated by using 150‐ and 400‐MHz transmissions from the low‐orbiting U.S. Navy navigation satellites observed at the Millstone Hill radar facility. A theoretical model for the variance and spectra was also constructed by using the Rytov approximation and a power law power spectrum model for the electron density fluctuations. The model provided a means for the estimation of both the axial ratio and the location of the lower edge of the irregularity region, using only angle‐of‐arrival and Doppler observations made at a single location. Good agreement was obtained between the model estimates and observations. Analysis of data from two magnetic storms revealed simultaneous occurrences of E region and F region irregularities at invariant latitudes north of 56°.
Detection of stimulated brillouin scattering by the Jicamarca Radar
Authors: Fejer J. A. , Rinnert K. , Woodman R.
Published: February 2008

Observations of weak stimulated Brillouin scattering with the 50‐MHz incoherent scatter radar at Jicamarca are described. The nonlinear interaction of the upgoing radar wave with the downcoming waves, incoherently backscattered from greater heights, causes an asymmetry in the incoherent ‘ion’ backscatter spectrum. For a given antenna aperture this asymmetry increases with increasing power and decreasing frequency of the radar. The theoretically predicted effect was unambiguously verified, using 3‐ms pulses and long integration time. Model calculations based on the theory presented show good agreement with the observations.
low‐altitude plasma line anisotropy
Authors: Oran Elaine S. , Palmadesso Peter J. , Ganguly Suman
Published: February 2008

Plasma line observations obtained from incoherent radar backscatter have been used as a ground‐based method for deriving information about the size and anisotropy of the ionospheric photoelectron fluxes. In the past, data interpretation has been confined to altitudes above the F2 peak. Measurements below the F2 peak consistently show an anisotropy in the ratio of the downshifted to upshifted amplitudes of 20–50% when it is generally assumed that diffusion processes dominate. We describe calculations of the plasma line intensity which use a multiangle multienergy calculation of the photoelectron distribution function. The calculated electron flux exhibits a small low‐altitude low‐energy anisotropy which is reflected in the plasma line measurements. Given anisotropic elastic electron‐neutral cross sections, the flux anisotropy arises when the local mean free path is of the order of the local scale height. The net effect is conversion of a spatial density inhomogeneity into a velocity distribution anisotropy.
Diurnal and seasonal effects in E region low‐latitude nitric oxide
Authors: Stewart A. I. , Cravens T. E.
Published: February 2008

Measurements of nitric oxide in the lower E region made by the ultraviolet nitric oxide experiment on Atmosphere Explorer C during 1974 are used to demonstrate diurnal and seasonal effects at low latitudes. At the equator, NO increases by about a factor of 2 between sunrise and the early afternoon; this is followed by a small decline toward sunset. Seasonally, NO shows an asymmetry about the equator with more NO on the summer side than on the winter side; at equinox the asymmetry vanishes. These effects are in qualitative accord with the current theoretical understanding of thermospheric nitric oxide.