bluuebunny/crossref_metadata_2025 huggingface dataset:
The global plasma environment of Io as inferred from the Galileo plasma wave observations
Authors: Louarn Philippe , Perraut S. , Roux A. , Gurnett D. , Kurth W. , Bolton S.
Published: February 2004

We take advantage of a partial and a total occultation of the jovian radio sources observed during the flyby of Io to characterize the plasma environment of this moon. We show that it presents a strong upstream / downstream asymmetry. A dense plasma structure (n > 5 × 104 cm−3) extends far from Io (at least 1000 km) in the wake direction whereas no extended dense region is found upstream. The dense region in the wake could correspond to a the stagnation region of the flow of the corotating plasma.
Interactions between mantle diapirs
Authors: Manga Michael
Published: February 2004

Experimental, theoretical, and numerical results are presented for the dynamics of interacting and deforming diapirs. The clustering of diapirs may occur as a result of the deformation induced by their mutual interactions. The time required for two diapirs in the mantle to merge can be small compared to their ascent time. The clustering of many diapirs, however, is a relatively slow process and is unlikely to significantly affect their distribution in the Earth's mantle. If coronae on Venus are produced by diapirs, diapir clustering may explain the variation of coronae size, and may be related to the observed clustering of coronae on the surface.
Ozone layer perturbation by a single blue jet
Authors: Mishin Evgeny
Published: February 2004

It was suggested that red sprites and blue jets might create long‐lived by‐products and thus have long term consequences of their occurrence in the atmosphere [Sentman and Wescott, 1996]. We have numerically evaluated a local perturbation of the ozone layer by a single blue jet, provided the jet is formed by the attachment controlled ionizing wave. The scenario of an impulse discharge in which the pulse duration is the wavefront propagation time was applied. A local perturbation of the content of nitric oxide and ozone produced by a single jet was found to be, respectively, about 10% and 0.5% at 30 km, varying with altitude (atmosphere pressure p) as ∝ p².
Testing prediction methods: Earthquake clustering versus the Poisson Model
Authors: Michael Andrew J.
Published: February 2004

Testing earthquake prediction methods requires statistical techniques that compare observed success to random chance. One technique is to produce simulated earthquake catalogs and measure the relative success of predicting real and simulated earthquakes. The accuracy of these tests depends on the validity of the statistical model used to simulate the earthquakes. This study tests the effect of clustering in the statistical earthquake model on the results. Three simulation models were used to produce significance levels for a VLF earthquake prediction method. As the degree of simulated clustering increases, the statistical significance drops. Hence, the use of a seismicity model with insufficient clustering can lead to overly optimistic results. A successful method must pass the statistical tests with a model that fully replicates the observed clustering. However, a method can be rejected based on tests with a model that contains insufficient clustering.
High‐temperature hot spots on Io as Seen by the Galileo solid state imaging (SSI) Experiment
Authors: McEwen Alfred S. , Simonelli Damon P. , Senske David R. , Klaasen Kenneth P. , Keszthelyi Laszlo , Johnson Torrence V. , Geissler Paul E. , Carr Michael H. , Belton Michael J. S.
Published: February 2004

High‐temperature hot spots on Io have been imaged at ∼50 km spatial resolution by Galileo's CCD imaging system (SSI). Images were acquired during eclipses (Io in Jupiter's shadow) via the SSI clear filter (∼0.4–1.0 µm), detecting emissions from both small intense hot spots and diffuse extended glows associated with Io‧s atmosphere and plumes. A total of 13 hot spots have been detected over ∼70% of Io–s surface. Each hot spot falls precisely on a low‐albedo feature corresponding to a caldera floor and/or lava flow. The hot‐spot temperatures must exceed ∼700 K for detection by SSI. Observations at wavelengths longer than those available to SSI require that most of these hot spots actually have significantly higher temperatures (∼1000 K or higher) and cover small areas. The high‐temperature hot spots probably mark the locations of active silicate volcanism, supporting suggestions that the eruption and near‐surface movement of silicate magma drives the heat flow and volcanic activity of Io.
Longitudinal variability of the mesopause SAO
Authors: Smith Anne K.
Published: February 2004

A longitudinal variation in the mesopause semi‐annual oscillation (SAO) is documented from wind observations made by the High Resolution Doppler Imager satellite instrument. The asymmetry is dominated by a wavenumber 1 pattern with a variable phase. During the easterly phase of the mesopause SAO (equinoxes), maximum tropical easterlies occur over eastern South America and the Atlantic Ocean in the longitude band 300°–360°. During the westerly phase (solstices), the westerly winds descend more rapidly and are larger below ∼80 km in this same (Atlantic) longitude band. To the best that can be determined with sparse data, the longitudinal asymmetries near the stratopause are weak and are in phase with those in the mesosphere.
Lagrangian flow at the foot of a shelfbreak front using a dye tracer injected into the bottom boundary layer
Authors: Houghton Robert W.
Published: February 2004

Convergent flow at the foot of the shelfbreak front in the Middle Atlantic Bight has been detected using a dye tracer, Rhodamine‐WT, injected into the bottom boundary layer. The observations substantiate model simulations by Chapman and Lentz (1994) of convergent flow in the vicinity of the front which would be very difficult if not impossible to detect with conventional moored current measurements. By following the dispersal of the dye patch over a 4 day period Lagrangian velocities of the order of 0.015 m/s with respect to the front were resolved even as the frontal boundary was displaced ∼12 km onshore. The water‐following properties of the dye tracer provides a useful technique for studying the small‐scale circulation and mixing at the frontal boundary.
Hydrocarbon ions in the ionosphere of Titan
Authors: Fox J. L. , Yelle R. V.
Published: February 2004

We have constructed a new model of the ionosphere of Titan that includes 67 species and 626 reactions. Although N2+ is the major ion produced over most of the ionosphere, the ionization flows to ions whose parent neutrals have lower ionization potentials and to ions formed from species with large proton affinities. In contrast to other models, which have predicted that HCNH+ should be the major ion, our calculations suggest that the major ions at and below the ion peak are hydrocarbon ions, and H, C, and N‐containing ions. Our predicted peak electron density for a solar zenith angle of 60° is about 7.5 × 10³ cm−3 at an altitude of 1040 km.
The October 9, 1995 Colima‐Jalisco, Mexico Earthquake (Mw 8): An aftershock study and a comparison of this earthquake with those of 1932
Authors: Pacheco J. , Singh S. K. , Domínguez J. , Hurtado A. , Quintanar L. , Jiménez Z. , Yamamoto J. , Gutiérrez C. , Santoyo M. , Bandy W. , Guzmán M. , Kostoglodov V. , Reyes G. , Ramírez C.
Published: February 2004

Data from portable seismographs and a permanent local network (called RESCO) are used to locate the aftershocks of the October 9, 1995 Colima‐Jalisco earthquake (Mw 8.0). The maximum dimension of the aftershock area, which is rectangular in shape, is 170 km × 70 km. Our study shows that the mainshock nucleated ∼24 km south of Manzanillo, near the foreshock of October 6, 1995 (Mw 5.8), and propagated ∼130 km to the NW and ∼40 km to SE. The aftershock area lies offshore and is oriented parallel to the coast. The observed subsidence of the coast is a consequence of this offshore rupture area. The aftershocks reach unusually close to the trench (within 20 km). This may be due to lack of sediments with high pore pressure at shallow depth. There are some similarities between this earthquake and the two great earthquakes of 1932 (3 June, Ms 8.1; 18 June, Ms 7.8) which occurred in this region. In both cases the aftershocks were located offshore and the coastline subsided. The sum of seismic moments and the rupture lengths of the 1932 events (1.8×1021 N‐m and 280 km, respectively), however, were greater than the 1995 earthquake. Also a comparison of seismograms of 1932 and 1995 earthquakes show great differences. It seems that the 1995 event is not a repeat of either June 3 or June 18, 1932 earthquakes.
Optimization of TOMS wavelength channels for ozone and sulfur dioxide retrievals
Authors: Gurevich G. S. , Krueger Arlin J.
Published: February 2004

The wavelengths of the TOMS channels can be optimized to minimize the effects of random measurement errors on simultaneous ozone and sulfur dioxide retrievals. The inversion matrix is extremely sensitive to the spectral position of the channels due to mathematical singularities related to O3 and SO2 absorption coefficients. None of the current sets of wavelengths in the TOMS instruments are optimal for the low latitude retrievals considered. Minor adjustment of the wavelengths can reduce retrieval errors by more than a factor of two.
The February 23, 1887 tsunami recorded on the Ligurian Coast, western Mediterranean
Authors: Eva Claudio , Rabinovich Alexander B.
Published: February 2004

The catastrophic Ligurian Earthquake on February 23, 1887 caused significant damage and numerous casualties in northwestern Italy and southeastern France. The first (main) shock (estimated magnitude of 6.2–6.5) produced tsunami waves observed along 250 km of the Ligurian coast from Genoa to Cannes. Typical tsunami run‐up heights were 1–2 m. The first wave was found to be negative, supporting the assumption that the earthquake was produced by release of stress along an offshore normal fault. Computed tsunami waveforms are in qualitative agreement with observed run‐ups. Unique 1887 tsunami records in Genoa and Nice harbors were found and analyzed. Numerical computations of eigenoscillations for the old (1887) Genoa harbor were made and found to be in a good agreement with the tsunami observations. The dominant observed period of 22.5 min was shown to be related to the fundamental (Helmholtz) mode of the old port. Long “ringing” and slow decay of tsunami oscillations in Genoa are associated with “pumping” of wave energy from the external basin. Several wave trains are revealed in the record that occur at 2–2.5 h intervals. They are interpreted as edge waves propagating along the Ligurian shelf and reflecting from its borders.
Thermodynamic stability and phase transitions of PSC particles
Authors: Koop Thomas , Carslaw Kenneth S. , Peter Thomas
Published: February 2004

The thermodynamic equilibrium conditions of various stratospherically relevant particles are calculated using a thermodynamic model. Due to thermodynamic constraints only certain particle combinations can exist at equilibrium in the same air mass. In particular, it is shown that liquids can coexist with solid particles over a wide range of conditions, provided that the available H2SO4 remains in the aqueous phase. Conversely, the stability of crystalline H2SO4‐containing phases is strongly affected by the formation of ice and HNO3‐containing solid phases. The results are combined with laboratory data on solid phase nucleation to construct a detailed scheme for PSC formation.
Mass balance and surface movement of the Greenland Ice Sheet at Summit, central Greenland
Authors: Hvidberg C. S. , Keller K. , Gundestrup N. S. , Tscherning C. C. , Forsberg R.
Published: February 2004

During the GRIP deep drilling in Central Greenland, the ice sheet topography and surface movement at Summit has been mapped with GPS. Measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25–60 km from the GRIP site. Some results are: The GRIP site is located approximately 2 km NW of the topographic summit; the surface velocity at the GISP 2 site is 1.7 m/yr in the W direction. The present mass balance at Summit is calculated to be −0.03±0.04 m/yr, i.e. close to steady state. This result is the best now available for Summit. A small thinning rate might be a transient response of the Greenland Ice Sheet due to the temperature increase at the Wisconsin‐Holocene transition.
Transient decreases of Earth's far‐ultraviolet dayglow
Authors: Frank L. A. , Sigwarth J. B.
Published: February 2004

Ten years ago transient decreases in Earth's far‐ultraviolet dayglow were reported for global images acquired with the high‐altitude, polar‐orbiting spacecraft Dynamics Explorer 1. These decreases were observed primarily in the atomic oxygen emissions at 130.4 nm. The diameters of these dark spots, or “atmospheric holes”, were in the range of 50 to 100 km. Recently a sophisticated camera for imaging Earth's far‐ultraviolet dayglow, with far greater spatial and temporal resolutions than its predecessor, was launched with the Polar spacecraft. The images from this spacecraft provide irrefutable evidence that these atmospheric holes are a geophysical phenomenon.
Detection of atomic oxygen trails of small comets in the vicinity of Earth
Authors: Frank L. A. , Sigwarth J. B.
Published: February 2004

Transient trails of emissions at far‐ultraviolet wavelengths have been detected by the Earth Camera on board the Polar spacecraft. These emissions are interpreted in terms of resonantly scattered solar radiation from atomic oxygen at 130.4 nm. The temporal durations of the emission trails are typically tens of seconds. The maximum brightnesses of the shorter trails are usually lesser than those of the longer trails which indicate that the shorter trails are farther from the spacecraft. The rate of occurrence of these trails is approximately 5 to 10 each day. These events are interpreted as the signatures of the disruption and rapid dissipation of small comets in the vicinity of Earth.
Interaction of Io with its torus: Does Io have an internal magnetic field?
Authors: Khurana Krishan K. , Kivelson Margaret G. , Russell Christopher T.
Published: February 2004

Galileo observed a large depression in the background magnetic field during its flyby through Io's plasma wake. Two hypotheses have been put forward to explain the observed magnetic field perturbation. Kivelson et al. [1996a, b] have suggested that although plasma currents are present, Io must possess an internal field in order to explain the large field depression. Frank et al. [1996] on the other hand have suggested that the observed field depression was caused purely by plasma currents generated by Io's interaction with its torus. We present a combined analysis of field and particle data from the flyby. Under certain assumptions, we develop models of Io's interaction with the plasma to calculate the magnetic field resulting from the diamagnetic and non‐diamagnetic effects of the Io‐plasma interaction. If the assumptions are valid, then it must be concluded that the plasma effects can account for only a fraction (< 30%) of the observed depression and that the principal cause of the reduction in the field strength observed along the trajectory of Galileo is a source inside of Io.
CCl2F2 mixing ratio profiles in the 1995 late winter Arctic vortex from balloon‐borne spectra
Authors: Hartmann J.‐M. , Kochel J.‐M. , Payan S. , Camy‐Peyret C. , Engel A.
Published: February 2004

The vertical profile of CCl2F2 has been retrieved in the altitude range 15 to 22 km from solar occultation spectra recorded with a balloon‐borne Fourier transform spectrometer (0.013 cm−1 resolution) launched on 22 March 1995 from Kiruna (Sweden, 67°N, 22°E). The choices of the grid of retrieval altitudes, of the spectral range, and of the absorption cross‐section data used for the retrievals are studied carefully. The vertical distribution obtained is characteristic of conditions pertaining to the late winter Arctic vortex. The measured mixing ratio profile of CCl2F2 is discussed in connection with the N2O profile also retrieved with the same instrument. These remote sensing measurements of CCl2F2 are compared with in situ results obtained from the same location and during the same period with balloon‐borne grab or cryosamplers. These data are analyzed in terms of diabatic descent in the polar vortex.
The circulation south of Australia derived from an inverse model
Authors: Schodlok Michael P. , Tomczak Matthias
Published: February 2004

An inverse model is used to determine circulation and volume transports in the Australian sector of the southern Indian Ocean from observations during WOCE. Water movement in the upper 1000 m is westward along the continental slope and eastward in the Subantarctic Front (SAF). The Subtropical Front is not associated with continuous eastward flow; however, such flow appears to build up between 120°E and 132°E, where it dominates the region between 37°S and 42°S. Antarctic Intermediate Water is found to move from the Pacific into the Indian Ocean, except in the region of the SAF where it moves from the Indian to the Pacific Ocean. Circumpolar Deep Water exhibits weak flow which can only be reliably resolved in the upper part, where it is predominantly westward. Antarctic Bottom Water enters the Australian Basin through two depressions in the Australian‐Antarctic Discordance at 125°37′E and at 126°30′E.
Violent silicate volcanism on Io in 1996
Authors: Stansberry J. A. , Spencer J. R. , Howell R. R. , Dumas C. , Vakil D.
Published: February 2004

We monitored Io's volcanic thermal emission from 1.7 to 4.8 µm in 1995/96. The data reveal a number of brightenings when Io's thermal emission increased several‐fold. We use a model of emission from lava flows to understand observations of two brightenings in 1996. The brightenings were caused by eruptions ≃ 3km² in extent, with eruptive rates of 104‐106 m²s−1 and with maximum lava temperatures ≥ 1400 K. These events were probably lava lakes and/or fire fountains.
Regulation of algal blooms in Antarctic Shelf Waters by the release of iron from melting sea ice
Authors: Sedwick Peter N. , DiTullio Giacomo R.
Published: February 2004

During summer 1995–96, we measured iron in the water column and conducted iron‐enrichment bottle‐incubation experiments at a station in the central Ross Sea (76°30′S, 170°40′W), first, in the presence of melting sea ice, and 17 days later, in ice‐free conditions. We observed a striking temporal change in mixed‐layer dissolved iron concentrations at this station, from 0.72–2.3 nM with sea ice present, to 0.16–0.17 nM in ice‐free conditions. These changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal (diatom) biomass. Our incubation experiments suggest that conditions were iron‐replete in the presence of sea ice, and iron‐deficient in the absence of sea ice. We surmise that bioavailable iron was released into seawater from the melting sea ice, stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer, until iron‐limited conditions developed. These observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production, particularly ice‐edge blooms, in seasonally ice‐covered Antarctic waters.
The angular distribution of auroral kilometric radiation observed by the GEOTAIL spacecraft
Authors: Kasaba Y. , Matsumoto H. , Hashimoto K. , Anderson R. R.
Published: February 2004

We examine the angular distribution of auroral kilometric radiation (AKR) based on a 38‐month data set of GEOTAIL plasma wave observations. We show that the AKR illumination pattern becomes narrower with increasing frequency above 300 kHz. The difference is more evident in the duskside zone and when geomagnetic conditions become more disturbed. We also show that AKR is more active on the winter hemisphere especially for the higher frequency range.
A first comparison of POLAR magnetic field measurements and magnetohydrodynamic simulation results for field‐aligned currents
Authors: Fedder J. A. , Slinker S. P. , Lyon J. G. , Russell C. T. , Fenrich F. R. , Luhmann J. G.
Published: February 2004

This letter presents comparisons between POLAR magnetic field measurements and results from a global numerical simulation of the Earth's magnetosphere using WIND measurements of the solar wind parameters as input. The comparison shows that the simulation provides a good representation for the magnetic perturbation associated with an upward Region 1 field‐aligned current (FAC) in the prenoon sector. This current system is caused by the interplanetary magnetic field (IMF) negative By component and also features downward current on open field lines at higher latitudes. The results also show effects caused by a gradual rotation of the IMF northward and a sudden return to its initial dawnward direction. The self‐consistent simulation Birkeland current pattern at ionospheric altitudes is also presented, and its evolution caused by the IMF rotations is discussed.
Hot spots on Io: Initial results from Galileo's near infrared mapping spectrometer
Authors: Lopes‐Gautier Rosaly , Davies A. G. , Carlson R. , Smythe W. , Kamp L. , Soderblom L. , Leader F. E. , Mehlman R.
Published: February 2004

The Near‐Infrared Mapping Spectrometer on Galileo has monitored the volcanic activity on Io since June 28, 1996. This paper presents preliminary analysis of NIMS thermal data for the first four orbits of the Galileo mission. NIMS has detected 18 new hot spots and 12 others which were previously known to be active. The distribution of the hot spots on Io's surface may not be random, as hot spots surround the two bright, SO2‐rich regions of Bosphorus Regio and Colchis Regio. Most hot spots seem to be persistently active from orbit to orbit and 10 of those detected were active in 1979 during the Voyager encounters. We report the distribution of hot spot temperatures and find that they are consistent with silicate volcanism.
Geology and topography of Ra Patera, Io, in the Voyager era: Prelude to eruption
Authors: Schenk Paul M. , McEwen Alfred , Davies A. G. , Davenport Trevor , Jones Kevin , Fessler Brain
Published: February 2004

Voyager era stereo images are used to map the geology and topography of Ra Patera (a major active volcanic center and possible site of sulfur eruptions on Io). The summit of Ra Patera reaches only ∼1 km above the surrounding plains. Pre‐Voyager‐era lava flows occur on slopes of 0.1–0.3°, comparable to the lunar mare. These flows were emplaced at either low viscosities, high eruption rates, or both. A 600‐km‐long ridged mountain unit (rising to ∼8 km near Carancho Patera) forms a 60 by 90 km wide plateau ∼0.5 km high 50 km east of Ra Patera. The new lava flows observed by Galileo flowed around the southern edge of this plateau.
Antarctic circumpolar waves: An Indication of ocean‐atmosphere coupling in the extratropics
Authors: Qiu Bo , Jin Fei‐Fei
Published: February 2004

Recent observational studies have detected coherent oceanic and atmospheric Antarctic circumpolar waves (ACWs) which propagate eastward at speeds of 6–8 cm s−1 with a circumpolar wavenumber of 2. Analysis of global wind data suggests that the ACWs are not remotely forced by tropical El Niño activity through atmospheric teleconnection. Rather, a coupled instability of the Antarctic Circumpolar Current and its overlying atmospheric motion is proposed to be responsible for the generation of the ACWs. The phase relationship among the observed oceanic and atmospheric variables supports the coupled instability theory. This study provides one clear example that extratropical ocean‐atmosphere dynamical coupling is essential in generating climate variations on time scales of several years and longer.
Ventilation processes and water mass ages in the thermocline of the southeast Indian Ocean
Authors: Karstensen Johannes , Tomczak Matthias
Published: February 2004

Indian Central Water (ICW) and Subantarctic Mode Water (SAMW) are the two major sources for the ventilation of the permanent thermocline in the Indian Ocean. ICW is formed by subduction in the region of negative wind stress curl, while SAMW is formed by convective overturning at the Subantarctic Front. SAMW contributes to the depth range of ICW, but is not easily identified, because most hydrographic properties (temperature, salinity and nutrients) of SAMW do not differ much from those of ICW. This study identifies ICW and SAMW in a zonal section near 32°S and evaluates the relative importance of convection vs. subduction for the ventilation process. Oxygen and nutrient data from the eastern part (50–114°E) of WOCE section 15 are used with temperature and salinity to determine water mass fractions of subducted ICW and of SAMW from water mass mixing analysis. The individual age fields of the two water mass components are then derived from a combination of the fractions obtained with a linear oxygen/CFC mixing model. Unlike earlier studies, which derive an uncalibrated apparent age, our results express water mass age in true units of time (years). The core of the SAMW near 114°E is about 5 years old, while the core of the subducted ICW (at 60–80°E) shows an increase of age with depth, in agreement with the subduction process. ICW moves eastward with the South Indian Current, reaching an age of 35 years at 114°E. SAMW spreads westward against the mean flow through turbulent diffusion, reaching an age of 25 years at 50°E.
A new fracturing mechanism for granular media
Authors: Bessinger Brad A. , Liu Zhong , Cook Neville G. W. , Myer Larry R.
Published: February 2004

Borehole breakout experiments are performed on sintered glass bead bricks and a new microscale fracturing mechanism is described that results in a macroscopic fracture plane oriented perpendicular to the uniaxial compressive loading stress. Scanning Electron Microscopy (SEM) is used to inspect the fracture surfaces and it is found that fracture propagation occurs through a process of grain debonding and ejection from the sample. A two‐dimensional boundary integral simulation models the effect of grain removal on subsequent fracturing by reducing the Young's modulus of failed grains, thereby allowing the compressive loading stress to be transferred to adjoining grains and grain contacts. It is found that this stress concentration is sufficient to induce additional grain failure and macroscopic fracture growth perpendicular to the applied load.
Contrasting lithospheric structure between the Colorado Plateau and Great Basin: Initial results from Colorado Plateau ‐ Great Basin PASSCAL Experiment
Authors: Sheehan Anne F. , Jones Craig H. , Savage Martha Kane , Ozalaybey Serder , Schneider Jeffrey M.
Published: February 2004

The Colorado Plateau ‐ Great Basin (CPGB) PASSCAL experiment provides broadband seismic data that allow us to determine crustal and upper mantle structure in the Colorado Plateau and eastern Great Basin. Twelve portable broadband seismometers throughout Utah and Nevada are supplemented by permanent broadband stations in the region. Receiver functions indicate an average crustal thickness of 35 ± 5 km in the Great Basin (GB) with a strong P‐to‐S (Ps) conversion from the Moho. The crust in the transition between the Great Basin and Colorado Plateau (CP) produces a strong intracrustal conversion. The CP has somewhat thicker crust (42 ± 5 km) and weaker Moho conversion. BR surface wave phase velocities are 3–4% higher than CP phase velocities in the 20–35 s range, consistent with a thinner crust under the GB. The phase velocities at periods greater than 40 s are indistinguishable between the two provinces, indicating that differences between upper mantle velocities are minor. Shear wave splitting yields fast polarizations that parallel the western and northern boundaries of the CP, with delay times decreasing towards the center of the Plateau.
Measuring regional atmospheric water vapor using the Swedish Permanent GPS Network
Authors: Elgered Gunnar , Johansson Jan M. , Rönnäng Bernt O. , Davis James L.
Published: February 2004

We investigate the application of a geodetic network of ground‐based GPS receivers in Sweden to the measurement of atmospheric water vapor. Using data acquired during four days in December 1993, we show that it is possible to study the detailed motions of air mass systems. Estimates of water vapor from GPS data agree with those from radiosonde and microwave radiometer data to within 1 mm RMS.
Variability and anisotropy of mesospheric wind spectra
Authors: Hocke K. , Igarashi K.
Published: February 2004

The winter mesosphere over Japan was observed with the new MF radars at Wakkanai (45.4°N, 141.7°E) and Yamagawa (31.2°N, 130.6°E). The wind spectra show dominance of different tidal waves at the two sites at the same time. The temporal evolution of the wind spectra is suggestive of resonant nonlinear interactions between planetary waves, tides, and gravity waves. At Wakkanai, the decay of the 24‐h and 12‐h waves was observed in the spectra of the zonal wind component. It is remarkable that the 12‐h wave of the meridional wind component remained strong while the zonal 12‐h wave disappeared. Further anisotropies of the meridional and zonal frequency spectra are described, as well as the slopes of the wind power spectra.
A new type of mid‐latitude multi‐path whistler trains including a non‐ducted whistler
Authors: Ohta K. , Kitagawa T. , Hayakawa M. , Dowden R. L.
Published: February 2004

This paper reports on a new type of midlatitude multi‐path whistlers based on the observations at Hobart, Australia and Dunedin, New Zealand. Though a majority of whistler elements are ducted, this new type includes a non‐ducted whistler as well. The study is based on the detailed comparison of the field‐analysis direction finding results with the nose‐extension ones. Important findings have emerged from this study and are summarized as follows. (1) A majority of whistler elements are ducted, (2) the duct dimension is highly likely to be less than 50km in diameter, (3) the ducts are likely to be extended well down to the ionospheric region, (4) the whole life of ducts seems to be of the order of 6 hours, with including cyclic occurrence and decay, and (5) at least one whistler element was experimentally convinced to be a non‐ducted PL whistler.
Late‐phase acceleration of energetic ions in corotating interaction regions
Authors: Reames D. V. , Ng C. K. , Mason G. M. , Dwyer J. R. , Mazur J. E. , von Rosenvinge T. T.
Published: February 2004

We report on new high‐sensitivity measurements from the WIND spacecraft of the spatial distributions of 30 keV/amu to 10 MeV/amu ions from corotating interaction regions (CIRs) that extend far beyond the confines of the parent high‐speed solar‐wind stream. Not only do late‐phase MeV ions persist far into the declining solar wind, but they also show a continual gain in energy, even after sector boundary passage, until the next small increase in solar wind speed occurs. These ions are accelerated in the distant heliosphere as the reverse shock from the CIR propagates completely across the rarefaction region produced by the declining solar wind, growing in acceleration efficiency as it propagates. Energetic ions from a single CIR event are seen for a period of 17 days and ∼225° in solar longitude. The observed energy spectra can be fit to the theory of Fisk and Lee [1980] only if shock compression increases with time so that the spectra harden significantly.
Broadband seismic observations at Satsuma‐Iwojima Volcano, Japan
Authors: Ohminato Takao , Ereditato Davide
Published: February 2004

This paper reports the results of preliminary analysis of broadband seismic observations conducted at Satsuma‐Iwojima volcano, Japan. The recorded broadband data show a wide variety of seismic features. Small (M∼0), short‐period volcanic earthquakes characterized by a long (∼5 s) emergent phase and by nearly identical waveforms are located at the very shallow part of the summit crater. Long‐period seismic pulses synchronized with a regular amplitude modulation of volcanic tremor have an interval of approximately 46 to 50 min. Each of the long‐period pulses has almost identical waveform. Polarization of the long‐period events suggests a very shallow source which can be interpreted as a result of a volume expansion mechanism. The correlation between the long‐period seismic pulses and volcanic tremor seems to be associated with magma convection and the degassing process inside the conduit of the volcano.
Broad band interferometric measurement of rocket triggered lightning in Japan
Authors: Ushio Tomo‐o , Kawasaki Zen‐Ichiro , Ohta Yasuhisa , Matsuura Kenji
Published: February 2004

A broad band interferometer to investigate the location of radio sources due to lightning flashes in two dimension has been manufactured and evaluated during the Rocket Triggered Lightning Experiment in Japan. Having high digitization rate, a broad band interferometer is not able to record the entire radiation process emitted by a lightning discharge. Therefore, we introduced a method of sequential triggering for each electromagnetic pulse that allows to record as long periods of radiation as we need. We obtained several data sets of upward stepped leaders for both negative polarity and positive one during the experiment. The apparent speed of an upward negative leader is estimated at 6 × 105 m/sec. The time intervals between successive electromagnetic pulses are from 11 to 93 microseconds with a mean of 22 microseconds. A triggered lightning to an experimental power transmission tower, normally it is called an altitude triggered lightning, is also conducted. One of the altitude triggered lightning lowered negative charges to the tower. In this case both the negative downward leader and the positive upward one can be generated. Some isolated pulses emitted by the downward negative stepped leader which attaches to the transmission tower are observed and located. Pulses emitted by the positive upward leader penetrated into a negatively charged region of a thundercloud are also observed. The location of radiation sources are distributed within a few degrees of azimuth. The time intervals between successive pulses are from 14 to 188 microseconds with a mean of 78 microseconds.
The effect of hyperviscosity on geodynamo models
Authors: Zhang K. , Jones C. A.
Published: February 2004

Some fundamental difficulties in the construction of an Earth‐like dynamo model and the role of hyperviscosity in attempting to overcome these difficulties are discussed. An Earth‐like convection model influenced by an imposed toroidal magnetic field is investigated both with and without the effect of hyperviscosity. It is shown that hyperviscosity affects the dynamics of convection significantly; the effect is similar in some respects to that of a strong magnetic field. The effective Ekman number, a key parameter for an Earthlike dynamo model, is substantially increased when hyperviscosity is employed.
Acetone in the upper troposphere and lower stratosphere: Impact on trace gases and aerosols
Authors: Arnold F. , Bürger V. , Droste‐Fanke B. , Grimm F. , Krieger A. , Schneider J. , Stilp T.
Published: February 2004

Upper tropospheric and lower stratospheric acetone measurements have been performed in summer and winter 1994 through 1996 at latitudes between 30°N and 75°N using ion‐molecule reaction mass spectrometry. We observed very high acetone volume mixing ratios of up to 3000 pptv (parts per trillion by volume) in extended air masses and in summer when acetone destruction by photodissociation is fast. This indicates efficient transport of acetone and photochemical acetone precursors to the upper troposphere and efficient upper tropospheric formation of acetone products, especially HOx radicals and PAN. Our data indicate large HOx production from acetone which has important implications for other trace gases and aerosols.
New insights on OH: Measurements around and in clouds
Authors: Mauldin R. L. , Madronich S. , Flocke S. J. , Eisele F. L. , Frost G. J. , Prevot A. S. H.
Published: February 2004

The first airborne measurements of OH performed in the lower free troposphere are presented. Measurements performed above clouds yielded large [OH], with values of 8–15 × 106 molecule cm−3, compared with values of 3–5 × 106 molecule cm−3 measured in cloud free regions. Measurements performed inside a cloud also yielded relatively high [OH], with values of 7.5 × 106 molecule cm−3, yet a factor of 2 lower than 15 × 106 molecule cm−3 measured just above the cloud. Steady state model calculations using Eppley scaled photolysis rates underestimate [OH] above clouds and overestimate [OH] inside clouds. Actinic fluxes of 2.5 times clear sky values (obtained from theoretical calculations) bring model values into agreement with those measured above clouds, while OH loss onto cloud droplets needs to be included for calculations inside clouds.
Does the UVI on polar detect cosmic snowballs?
Authors: Parks G. , Brittnacher M. , Chen L. J. , Elsen R. , McCarthy M. , Germany G. , Spann J.
Published: February 2004

If 20 to 40 ton cosmic snowballs pelt Earth as claimed by Frank and Sigwarth [1997a], dark pixels will be produced in the 130.4 nm images of dayglow obtained by the Ultraviolet Imager (UVI) on the Polar spacecraft. Examination of the UVI images has revealed that dayglow images are indeed spotted with single and multiple dark pixels. But is a snowball the only explanation for these dark pixels? To learn more about the dark pixels, we have examined the calibration images obtained from the same camera just before the instrument was launched. We find that dark pixels similar to those in dayglow images also exist in calibration images. This strongly indicates that the source of the dark pixels is instrumental. For further verification, a statistical analysis found the dark pixels from dayglow and calibration images have nearly identically shaped occurrence patterns. We have also looked for evidence of spacecraft “wobble” which demonstrates that the source of a bright or dark feature in the images is external to the camera, but found none for dark pixels. Finally, we studied the bright streaks that frequently appear in UVI images, sometimes comet‐like in appearance. These trails are ionization tracks produced by cosmic rays or other penetrating energetic particles interacting with our camera. We conclude that the source of the dark pixels in dayglow images is internal to the camera system and there is no scientific evidence from UVI that snowballs pelt Earth.
Rapid response of greenhouse gas emission to early spring thaw in a subarctic mire as shown by micrometeorological techniques
Authors: Friborg T. , Christensen T. R. , Søgaard H.
Published: February 2004

Most studies of soil/atmosphere greenhouse gas exchange in Arctic and Sub‐Arctic wetlands have been conducted by the use of small scale chamber techniques during the growing season. To improve the knowledge about the processes in the transition period from winter to growth season, an experiment is presented here showing measurements of CH4, CO2 and H2O using both chambers (only CH4) and eddy correlation technique from the thaw period in early spring and during mid summer. The emphasis is on a comparison between eddy correlation and chamber measurements of methane fluxes during spring thawing in a subarctic mire near Abisko, northern Sweden. Methane exchange as measured by the two techniques is compared and evaluated in relation to temperature variations and atmospheric conductance. During the thaw period, integrated daily net fluxes of CH4 flux showed emission rates increasing from 2.6 mg m−2 d−1 to 22.5 mg m−2 d−1 within four days; the later rate corresponding to approximately 25% of the mid‐summer flux. A profound diurnal cycle was observed in the release of methane, emphasising the importance of continuous measurements when calculating integrated fluxes.
Meteor decay times and their use in determining a diagnostic mesospheric Temperature‐pressure parameter: Methodology and one year of data
Authors: Hocking W. K. , Thayaparan T. , Jones J.
Published: February 2004

Ambipolar diffusion coefficients in the meteor region have been measured using meteor decay times determined with the CLOVAR radar [Hocking, 1997]. This parameter may then be used to infer information about atmospheric temperatures or pressures in that region. In particular, we show annual variations in the parameter
. Our procedures, together with the underlying assumptions, are described, and our results are compared to the CIRA (1986) empirical model as well as other experimental data. These successful measurements have been possible because of our use of a new 5‐element interferometer which has minimal inter‐element coupling and has an angular location accuracy of better than ±2°, together with new algorithms which introduce important corrections to the decay time height profile. We concentrate in this paper on monthly averages, but higher temporal resolutions are possible.
Global energetic neutral atom (ENA) measurements and their association with the Dst index
Authors: Jorgensen A. M. , Spence H. E. , Henderson M. G. , Reeves G. D. , Sugiura M. , Kamei T.
Published: February 2004

We present a new global magnetospheric index that measures the intensity of the Earth's ring current through energetic neutral atoms (ENAs). We have named it the Global Energetic Neutral Index (GENI), and it is derived from ENA measurements obtained by the Imaging Proton Spectrometer (IPS), part of the Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment on the POLAR satellite. GENI provides a simple orbit‐independent global sum of ENAs measured with IPS. Actual ENA measurements for the same magnetospheric state look different when seen from different points in the POLAR orbit. In addition, the instrument is sensitive to weak ion populations in the polar cap, as well as cosmic rays. We have devised a method for removing the effects of cosmic rays and weak ion fluxes, in order to produce an image of “pure” ENA counts. We then devised a method of normalizing the ENA measurements to remove the orbital bias effect. The normalized data were then used to produce the GENI. We show, both experimentally and theoretically the approximate proportionality between the GENI and the Dst index. In addition we discuss possible implications of this relation. Owing to the high sensitivity of IPS to ENAs, we can use these data to explore the ENA/Dst relationship not only during all phases of moderate geomagnetic storms, but also during quiescent ring current periods.
Geometry, kinematics and rates of deformation in a normal fault segment boundary, central Greece
Authors: Morewood N. C. , Roberts G. P.
Published: February 2004

The geometry, kinematics and rates of deformation within a fault segment boundary between the ends of two major active normal fault segments have been investigated through examination of a faulted 126 ka marine terrace. Slip‐vector azimuths defined by striations on the faults indicate N‐S extension on c. E‐W faults, sub‐parallel to those from earthquake focal mechanisms, together with significant and contemporaneous E‐W extension on c. N‐S faults. Summed rates of E‐W extension along a c. 550 m transect (0.17 mm/yr) are comparable with those for N‐S extension (0.20 mm/yr) along a c. 350 m transect. Our observations show that distributed non‐plane strain extension occurs in fault segment boundaries and this should be noted when studying fault‐tip fracture toughness and regional deformation rates.
Red sprites: Lightning as a fractal antenna
Authors: Valdivia J. A. , Milikh G. , Papadopoulos K.
Published: February 2004

A new and improved model of red sprites is presented. Emphasis is placed in accounting for the puzzling observation of the spatial structure in the red sprite's optical emissions. The model relies upon a horizontal fractal lightning discharge, which generates the EMPs that excites the optical emissions in the lower ionosphere. It is shown that the fractal model may account for the observed sprite's spatially structured optical pattern, while reducing the typical charge threshold to approximately 100 C.
Seismological evidence for the existence of anisotropic zone in the metastable wedge inside the subducting Izu‐Bonin Slab
Authors: Iidaka Takashi , Obara Kazushige
Published: February 2004

The mechanism of deep earthquakes has been a puzzle since their discovery almost 70 years ago. Experimental observations at high‐pressure have reported faulting caused by spinel‐filled anti‐cracks in metastable olivine and suggesting that the anticrack mechanism is responsible for deep earthquakes. We compared the shear‐wave splitting of earthquakes from the upper and lower planes of the double seismic zone to detect anisotropy caused by the faultings inside the metastable wedge. We detected the anisotropic zone inside the metastable wedge at the depth of about 340–390 km, which corresponds to the depth range of a second peak on the histogram of earthquakes. The observed polarization direction, east‐west, is almost parallel to the direction of subduction, which can be explained by a view that the shear‐wave splitting is caused by the en echelon arrays of spinel‐filled anti‐cracks and anticrack‐associated faultings.
Hydrostatic pore fluid pressure to 9 km depth ‐ Fluid inclusion evidence from the KTB deep drill hole
Authors: Grawinkel Andrea , Stöckhert Bernhard
Published: February 2004

The KTB drill hole (Germany) provides a unique opportunity to study the pore fluid pressure as a function of depth in metamorphic continental crust to 9101 m depth and to ambient temperatures of ca. 265°C. Open fissures identified in cuttings and cores along the entire profile are partially coated by minerals crystallized from the pore fluid. The fluid inclusions in these minerals reflect pore fluid composition and pressure. A NaCl‐dominated aqueous fluid with low salinity is encountered to ca. 4 km depth, whereas the fluid is CaCl2‐dominated with a higher salinity of ca. 4 to 24 wt.‐% NaCl equiv. between 4 and 9 km depth, consistent with analyses of the free fluid (available to 6 km depth) and hydraulic tests. The densities of the fluid inclusions invariably indicate a hydrostatic pore fluid pressure to 9 km depth and thus confirm the predictions based on rock strength.
Measurements of wave‐cloud microphysical properties with two new aircraft probes
Authors: Gerber H. , Twohy Cynthia H. , Gandrud Bruce , Heymsfield Andrew J. , McFarquhar Greg M. , DeMott Paul J. , Rogers David C.
Published: February 2004

Measurements of ice water content (IWC) and mean ice‐crystal size and concentration made by two in‐situ probes, CVI and PVM, were compared on the DC‐8 aircraft during SUCCESS flights in orographic ice clouds. The comparison of IWC in these wave clouds, that formed at temperatures of about −38 °C on April 30 and −62 °C on May 2, 1996, showed good agreement. The comparison of ice crystal concentrations agreed better for the April‐30 clouds than for the May‐2 clouds; and the effective radius compared for both probes and for remote retrievals from aircraft and satellite for a segment of the Berthoud wave cloud (May 2) agreed within 30%. The measured parameters of the ice crystals were similar to earlier measurements and recent modeling of cold wave clouds.
Quantum yields of O(¹D) in the photolysis of ozone between 289 and 329 nm as a function of temperature
Authors: Talukdar Ranajit K. , Longfellow Cheryl A. , Gilles Mary K. , Ravishankara A. R.
Published: February 2004

The quantum yields for O(¹D) production in O3 photolysis between 203 and 320 K, and 289 to 329 nm were measured. A portion of the observed O(¹D) quantum yields at wavelengths greater than 310 nm is attributed to a spin‐forbidden channel and the variation of quantum yield with temperature is ascribed to photodissociation of vibrationally (or rotationally) excited ozone. Our results yield atmospheric O(¹D) production rates larger than those obtained from current recommendations, especially at high solar zenith angles, low temperatures, and large overhead ozone columns.