bluuebunny/crossref_metadata_2025 huggingface dataset:
Observed stratospheric profiles and stratospheric lifetimes of HCFC‐141b and HCFC‐142b
Authors: Lee J. M. , Sturges W. T. , Penkett S. A. , Oram D. E. , Schmidt U. , Engel A. , Bauer R.
Published: February 2004

We present here the first stratospheric profile measurements of HCFC‐141b (CH3‐CFCl2) and HCFC‐142b (CH3‐CF2Cl). From the measurements we derive a stratospheric lifetime of 68±11 years for HCFC‐141b and an estimated minimum stratospheric lifetime for HCFC‐142b of 138 years relative to an N2O lifetime of 110 y. (These results increase to 104±17 y and >211 y respectively for an N2O lifetime of 168 y). Neither HCFC‐141b nor HCFC‐142b is now in equilibrium in the stratosphere, due to rapidly increasing emissions in recent years.
Wavelet analysis of velocity dispersion of elastic interface waves propagating along a fracture
Authors: Pyrak‐Nolte Laura J. , Nolte David D.
Published: February 2004

A wavelet analysis is performed on seismic waveforms of elastic interface waves that propagate along a fracture. The wavelet analysis provides a direct quantitative measure of spectral content as a function of arrival time. We find that the spectral content of the interface wave signals is not stationary, but exhibits increasing frequency content for later arrival times, representing negative velocity dispersion. The dispersion increases from −11 m/sec/MHz to −116 m/sec/MHz as the stress on the fracture is increased from 3.5 kPa to 33 MPa. The negative velocity dispersion agrees with predictions from the displacement‐discontinuity theory of the seismic response of fractures, and can be used to fit fracture stiffness.
The effect of clouds on atmospheric absorption of solar radiation
Authors: Chou Ming‐Dah , Arking Albert , Otterman Joseph , Ridgway William L.
Published: February 2004

It has long been an issue of whether clouds enhance or reduce atmospheric absorption of solar radiation. Radiative transfer calculations show that the effect of clouds on atmospheric absorption of solar radiation depends strongly on the solar zenith angle, cloud height and surface albedo. Over wide ranges of these parameters, clouds have the effect of reducing atmospheric solar heating. This result can be altered if the cloud specific absorption is amplified by a factor of 5. For the ratio of cloud forcing at the surface to that at the top of the atmosphere to reach 1.5, as suggested by recent observational analyses, cloud specific absorption would be required to increase by a factor of ≈40 beyond what has been determined by in situ aircraft measurements. Since there is no observational evidence to support such strong absorption, the excess cloud absorption, if it occurs, can only be explained by some unknown factors other than the cloud specific absorption.
Ejecta correlations with spatial crater density and Venus resurfacing history
Authors: Phillips Roger J. , Izenberg Noam R.
Published: February 2004

We examine the alternative hypotheses that on Venus (i) the spatial randomness of the crater population reflects predominantly the spatially stochastic nature of impact crater formation or (ii) a significant amount of spatial variation in crater density is due to variations in the geological rate of crater removal. Three endmember models of resurfacing are formulated: Case I assumes that a single‐age production surface accounts for the spatial distribution of craters. Case II assumes that variations in spatial crater density reflect local production surface ages, while Case III assumes that individual craters are removed regionally, so that variations in spatial crater density reflect local retention ages. These endmember models are tested by examining correlations of crater properties with crater spatial density, ρ. We analyze the distribution of embayed and tectonized craters and the relative abundances of extended ejecta deposits (termed “halos”). The three endmembers provide specific predictions as to the occurrence of halos as a function of ρ. For ρ ≲ 1.5 craters per 106 km², Case III provides the best explanation for the deficiency of halos as well as the relative abundances of modified craters. For the interval 1.5 ≲ ρ ≲ 2.5, Case II is applicable but with only a modest spread in production ages. For densities ≳2.5, Case II is the only endmember model that matches the global observations, suggesting that regions with these high densities represent a series of distinct production surfaces with ages increasing from the planetary mean retention age.
Generation of field‐aligned currents and Alfvén waves by 3D magnetic reconnection
Authors: Ma Z. W. , Lee L. C. , Otto A.
Published: February 2004

We have carried out a three‐dimensional compressible MHD simulation to study the generation of field‐aligned currents (FAC's) and Alfvén waves by magnetic reconnection for locally antiparallel magnetic fields across the current sheet. Reconnection is triggered by a localized resistivity. The results indicate that both FAC's and Alfvén waves are generated by the three‐dimensional reconnection process. Two pairs of FAC's are generated on each side of current sheet. The polarities of the resulting FAC pair in the leading bulge region are opposite to those of a FAC pair in the trailing quasi‐steady region. It is further found that a large portion of the FAC's (∼40%) is located in the closed field line region. We examine the Walén relation between FAC and parallel vorticity and find that Alfvén waves are generated and propagate away from the reconnection site. We discuss the relevance of our results to the observed Region 1 FAC's at noon.
Measurement of heavy isotope enrichment in tropospheric ozone
Authors: Krankowsky D. , Bartecki F. , Klees G. G. , Mauersberger K. , Schellenbach K. , Stehr J.
Published: February 2004

Tropospheric ozone samples collected during a twelve‐month period in urban air show an enrichment of about 9% in the heavy isotope 50O3 consistent with predictions from laboratory measurements. The enhancement of about 7% observed in 49O3 is still within the uncertainty of the expected value. These measurements confirm that the isotope effect, repeatedly found in laboratory experiments, is also produced in the atmosphere during the ozone formation process.
Prediction of single phase transport parameters in a variable aperture fracture
Authors: Keller Arturo A. , Roberts Paul V. , Kitanidis Peter K.
Published: February 2004

A single variable aperture fracture plane is the microscopic scale equivalent of a pore in a porous medium, with the advantage that it can be more easily characterized using a deterministic or stochastic description of the fracture aperture. Fracture aperture distributions can be measured in the laboratory for small fractured cores using Computed Tomography (CT) X‐ray scanning to a resolution of about 50 µm. Using the small perturbation analysis developed by Gelhar (1987) based on a stochastic description of the fracture aperture distribution, we predict the breakthrough curve of a dissolved contaminant in an aqueous phase flowing through a single natural fracture, from the knowledge of the geostatistical description of the fracture aperture. The results of the stochastic analysis are compared to experimental results from the actual breakthrough curve of a nonsorbing solute flowing through a single fracture plane in a granite core at different flow rates, with a fracture aperture characterized using CT scanning. The measured effective transmissivity is 13% larger than the estimated value, and the measured dispersivity is 33% larger than the estimated value. Errors introduced by the boundary conditions, the first order approximation and heterogeneities not sampled by the CT scanner may account for the difference. The estimation method may be useful for predicting solute breakthrough at field sites if the required statistics are obtained from hydraulic and tracer tests at similar sites.
Potential flow downstream of the heliospheric terminal shock: A non‐spherical shock
Authors: Nerney Steven , Suess S. T.
Published: February 2004

We have solved for the potential flow down‐stream of the terminal shock of the solar wind in the limit of small departures from a spherical shock due to a latitudinal ram pressure variation in the supersonic solar wind. The solution connects anisotropic streamlines at the shock to uniform streamlines down the heliotail because we use a non‐slip boundary condition on the heliopause at large radii. The rotational velocity about the heliotail in the near‐field solution decays as the fourth power of distance from the shock. The polar divergence of the streamlines will have consequences for the previously discussed magnetic pressure ridge that may build‐up just inside the heliopause.
Calar Alto observations of Shoemaker Levy 9: Characteristics of the H and L impacts
Authors: Hamilton D. P. , Herbst T. M. , Richichi A. , Böhnhardt H. , Ortiz J. L.
Published: February 2004

We describe data obtained at Calar Alto's 3.5‐meter and 2.2‐meter telescopes during the impacts of SL9 fragments H and L with Jupiter. Both the H and L impact lightcurves display three major features which we call 1) the first precursor, 2) the second precursor, and 3) the main event. The peak of the first precursor occurs before the onset of the Galileo PPR signal for each impact. We identify these three features with 1) the bolide entry into the jovian atmosphere, 2) the rising impact fireball, and 3) reimpacting ejecta. We also identify faint spots that appear near the H and L impact sites just before the respective events and suggest that the pre‐L spot was caused by the J fragment which vanished in December 1993.
Fine structure in the spectra of low latitude field line resonances
Authors: Samson J. C. , Waters C. L. , Menk F. W. , Fraser B. J.
Published: February 2004

The power spectra of low latitude (L<3), ground‐based recordings of dayside geomagnetic pulsations in the 10‐100 mHz band indicate that these pulsations come from discrete, driven field line resonances which are coupled to compressional, magnetohydrodynamic, cavity or waveguide modes. The spectral bands of individual harmonics of the field line resonances seen by the magnetometers have envelopes which are typically 10's of mHz wide but also show a fine scale structure of almost equispaced peaks with separations of about 3 to 5 mHz. A WKB analysis of a cavity or waveguide model shows that the fine structure is likely due to field line resonances driven by waveguide modes with turning points within the plasmasphere and reflection at the dayside magnetopause.
Observations of an upward‐directed electron beam with the perpendicular temperature of the cold ionosphere
Authors: Boehm M. H. , Clemmons J. , Wahlund J.‐E. , Eriksson A. , Eliasson L. , Blomberg L. , Kintner P. , Höfner H.
Published: February 2004

The Freja TESP electron spectrometer has repeatedly observed ∼100 eV ‐ 1 keV upward‐directed, anti‐field‐aligned electron beams near 1700 km altitude in the auroral zone. A particularly intense event, at energies up to 2 keV, is described. The beam perpendicular temperature T⟂ e was as low as 0.1–0.2 eV at 100–200 eV parallel energy. The 10–15 s period of upward fluxes was coincident with a low density (∼10 cm−3) period and a ∼5 keV ion conic. Strong low frequency waves and the lack of any downward motion in the simultaneously observed ion conic suggest a strong element of wave acceleration, while electric field and ion loss cone measurements provide limited evidence of potential acceleration to a fraction of the observed energies.
Maximum Langmuir fields in planetary foreshocks determined from the electrostatic decay threshold
Authors: Robinson P. A. , Cairns Iver H.
Published: February 2004

Maximum electric fields of Langmuir waves at planetary foreshocks are estimated from the threshold for electrostatic decay, assuming it saturates beam‐driven growth, and incorporating heliospheric variation of plasma density and temperature. Comparison with spacecraft observations yields good quantitative agreement. Observations in type III radio sources are also in accord with this interpretation. A single mechanism can thus account for the highest fields of beam driven waves in both contexts.
Electron dynamics and whistler waves at quasi‐perpendicular shocks
Authors: Krauss‐Varban D. , Pantellini F. G. E. , Burgess D.
Published: February 2004

The collisionless, supercritical, quasi‐perpendicular fast shock is investigated on sub‐ion scales using an implicit, two‐dimensional (2‐D) full particle code. For the first time, simulations are carried out with realistic characteristic frequencies and sufficiently high mass ratio between the protons and electrons. As a result, there is relatively little scattering of the electrons, i.e., they behave largely adiabatically as previously suggested based on spacecraft observations at the Earth's bow shock. The large mass ratio also allows for a realistic description of the whistler mode dispersion. Phase‐standing whistlers with propagation along the shock normal appear as transients. The dominant whistlers found at late times in the simulations have upstream directed group velocity but propagate at oblique direction between the shock normal and the ambient magnetic field. Their properties match those of the ubiquitous observed upstream whistlers (“one‐Hertz waves”).
Hierarchical organization as a diagnostic approach to volcano mechanics: Validation on Piton de la Fournaise
Authors: Grasso J. R. , Bachèlery P.
Published: February 2004

Self‐organized systems are often used to describe natural phenomena where power laws and scale invariant geometry are observed. The Piton de la Fournaise volcano shows power‐law behavior in many aspects. These include the temporal distribution of eruptions, the frequency‐size distributions of induced earthquakes, dikes, fissures, lava flows and interflow periods, all evidence of self‐similarity over a finite scale range. We show that the bounds to scale‐invariance can be used to derive geomechanical constraints on both the volcano structure and the volcano mechanics. We ascertain that the present magma bodies are multi‐lens reservoirs in a quasi‐eruptive condition, i.e. a marginally critical state. The scaling organization of dynamic fluid‐induced observables on the volcano, such as fluid induced earthquakes, dikes and surface fissures, appears to be controlled by underlying static hierarchical structure (geology) similar to that proposed for fluid circulations in human physiology. The emergence of saturation lengths for the scalable volcanic observable argues for the finite scalability of complex naturally self‐organized critical systems, including volcano dynamics.
Auroral fading in ionosphere‐magnetosphere coupling model: Implications for possible mechanisms
Authors: Janhunen P. , Pulkkinen T. I. , Kauristie K.
Published: February 2004

Sudden fading of the growth phase auroral arc and precipitation is sometimes observed just prior to substorm expansive phase onset. We can see a very similar phenomenon in a numerical ionosphere‐magnetosphere coupling model. In the numerical simulation, the fading occurs because the region of hot and dense magnetospheric plasma moves towards the Earth. At the same time, the plasma that maps to the poleward part of the fading area is cooled, which reduces precipitation there. The hot and dense plasma near geostationary orbit continues to precipitate, but to a lesser extent because it resides in a more dipolar field. Thus the fading phenomenon appears to to occur because the hot and dense plasma is temporarily “hidden” from the ionosphere. A few minutes later it moves tailward which causes the auroral brightening.
“Strong” Ground motions in North America from the Bolivia Earthquake of June 9, 1994 (Mw=8.3)
Authors: Anderson John G. , Savage Martha , Quaas Roberto
Published: February 2004

The Bolivia earthquake was remarkable for being felt in North America, as far as 8680 km from the epicenter. This paper examines the characteristics of ground motions in North America from the perspective of strong motion seismology. Data on ground motions is mostly from high‐gain stations, but we also have two strong motion accelerograms. The largest accelerations and highest frequencies are associated with the P and PcP phases, which also correlate with the felt reports in several instances. Felt locations are associated with a combination of favorable factors. Most are in a distance range where P‐wave amplitudes tend to be relatively high, as observed in the empirical correction factors for body wave magnitude, and in regions with relatively high values of Q in the lithosphere. In addition, site effects, structural amplification, or both, seem to contribute to the selective detection of the earthquake in the regions where some people noticed it. Motions were far below design spectra for earthquake resistant design, and far below levels likely to be associated with damage.
Gravity wave momentum flux in the lower stratosphere over convection
Authors: Alexander M. Joan , Pfister Leonhard
Published: February 2004

This work describes a method for estimating vertical fluxes of horizontal momentum carried by short horizontal scale gravity waves (λx = 10–100 km) using aircraft measured winds in the lower stratosphere. We utilize the in situ wind vector and pressure altitude measurements provided by the Meteorological Measurement System (MMS) on board the ER‐2 aircraft to compute the momentum flux vectors at the flight level above deep convection during the tropical experiment of the Stratosphere Troposphere Exchange Project (STEP‐Tropical). Data from Flight 9 are presented here for illustration. The vertical flux of horizontal momentum in these observations points in opposite directions on either side of the location of a strong convective updraft in the cloud shield. This property of internal gravity waves propagating from a central source compares favorably with previously described model results.
Close in ScS and sScS reverberations from the 9 June 1994 Bolivian Earthquake
Authors: Clarke Timothy J. , Silver Paul G. , Yeh Yu‐Lien , James David E. , Wallace Terry C. , Beck Susan L.
Published: February 2004

Recordings of the Bolivian Earthquake of 9 June, 1994 from two portable experiments were analyzed for ScS and sScS reverberations. These stations span the distance range 6°–22°, sampling the mantle beneath South America along an EW line from the central Andes to the Brazilian Craton. We used the CORE method to obtain path‐averaged locations of the Moho and 400 and 660 km discontinuities. The average depth for D400 is 410km for the BANJO stations and 395km beneath Brazil, and the value for D660 is 700km for BANJO and 675km for BLSP, while the difference D660–D400 ≡ ΔD is 290km and 280km respectively. These values are much larger than the global average (around 245km) and suggest 200°–300° colder temperatures in the region sampled. This is most plausibly explained by the reduced temperatures in the slab and surrounding region. We also detect a significant discontinuity at 210 km depth, with a shear wave impedance increase of at least 5%. Finally, we observe systematic variations in duration between P, ScS and sScS that can only be attributed to source finiteness. These observations constrain the inclination of an equivalent unilateral rupture velocity vector to be −17° (positive up from horizontal). Our rupture model is consistent with models derived from subevent analysis of the P wave arrivals, and implies a source extent of 72 km.
The band of solar wind variability at low heliographic latitudes near solar activity minimum: Plasma results from the Ulysses rapid latitude scan
Authors: Gosling J. T. , Bame S. J. , Feldman W. C. , McComas D. J. , Phillips J. L. , Goldstein B. , Neugebauer M. , Burkepile J. , Hundhausen A. J. , Acton L.
Published: February 2004

Near solar activity minimum large variations in the quiescent solar wind flow are confined to a narrow latitude band centered near the heliographic equator. During Ulysses' recent rapid latitude scan this band was ∼43° wide. Flow parameters poleward of the band in the opposite solar hemispheres were nearly the same. Main entry into the band of variable solar wind was via a shock disturbance most likely associated with over‐expansion of a coronal mass ejection event. Wind variability within the band was associated primarily with longitudinal structure in the solar corona and solar rotation; high‐speed streams observed there were associated with locations where the polar coronal holes extended equatorward toward the Ulysses orbit. Observations indicate that the polar coronal holes at this time occupied only ∼13% of the low corona, yet a nearly uniform high‐speed wind (average speed ∼750 km s−1) filled ∼63% of the heliosphere. This indicates the holes expanded by a factor of ∼4.8 from the low corona to interplanetary space. Much of this lateral expansion occurred beyond 1.74 solar radii from Sun center.
Nonlinear coupling of lower hybrid waves to the kinetic low‐frequency plasma response in the auroral ionosphere
Authors: Sanbonmatsu K. Y. , Goldman M. V. , Newman D. L.
Published: February 2004

A hybrid kinetic‐fluid model is developed which is relevant to lower hybrid spikelets observed in the topside auroral ionosphere [Vago et al., 1992; Eriksson et al., 1994]. In contrast to previous fluid models [Shapiro et al., 1995; Tam and Chang, 1995; Seyler, 1994; Shapiro et al., 1993] our linear low frequency plasma response is magnetized and kinetic. Fluid theory is used to incorporate the nonlinear wave coupling. Performing a linear stability analysis, we calculate the growth rate for the modulational instability, driven by a lower hybrid wave pump. We find that both the magnetic and kinetic effects inhibit the modulational instability.
Maximum altitude penetration of atmospheric gravity waves observed during ALOHA‐93
Authors: Swenson G. R. , Gardner C. S. , Taylor M. J.
Published: February 2004

Atmospheric Gravity Waves (AGWs) are subject to altitude propagation limits which are governed by the diffusion processes. Diffusion times and scales which exceed the wave period and wavelength define the limiting domain for AGWs. An expression is presented which defines the upper altitude limit to which AGWs can propagate given vertical diffusion constraints of the atmosphere. Airglow, lidar, and radar measurements are combined to characterize the intrinsic AGW parameters in the 80–105 km altitude region. A subset of AGWs (17) observed by airglow imagers during the ALOHA‐93 were made when simultaneous wind measurements were available and intrinsic wave parameters were calculated. The limiting altitude of propagation for these measured monochromatic waves is calculated to range from 110–150 km (with a mean limiting altitude of 130 km). The altitude limit is necessarily lower for waves with short vertical wavelengths and longer intrinsic periods. This observation is important for a large number of issues including energetic considerations regarding thermospheric heating in models which consider upward propagating AGWs (and energy flux) of tropospheric origin. This limited data base should be expanded for statistical significance in future work.
Measurements of stratospheric carbon dioxide and water vapor at northern midlatitudes: Implications for troposphere‐to‐stratosphere transport
Authors: Boering K. A. , Hintsa E. J. , Wofsy S. C. , Anderson J. G. , Daube B. C. , Dessler A. E. , Loewenstein M. , McCormick M. P. , Podolske J. R. , Weinstock E. M. , Yue G. K.
Published: February 2004

Simultaneous in situ measurements of CO2 and water vapor in the lower stratosphere were obtained in November 1992 and May 1993 up to 21 km at midlatitudes. Seasonal changes in both species were observed up to pressure‐altitudes of 19 km (∼440 K), a result of vertical propagation of seasonal oscillations in CO2 and H2O mixing ratios for air entering the stratosphere in the tropics followed by horizontal transport to midlatitudes. The inferred phase difference between their seasonal cycles at the tropical tropopause (2 months) remained coherent at midlatitudes, although the amplitudes were reduced, implying a mean transport time of 4–6 months from the tropical tropopause (∼16 km) to ∼18.5–19 km at midlatitudes in both November and May. The measurements indicate that air enters the stratosphere throughout the year and suggest that vertical propagation of the seasonal minimum in water vapor, rather than deep convective overshoot, is both sufficient and necessary to explain the minimum in water (“hygropause”) observed several kilometers above the tropopause.
Optical properties of atmospheric aerosols from moments of the particle size distribution
Authors: McGraw Robert , Huang Peter I. , Schwartz Stephen E.
Published: February 2004

The method of moments is a powerful tool for directly calculating the lower‐order moments of an aerosol size distribution without full knowledge of the distribution itself. These moments can be tracked in space and time to represent the effects of nucleation, evaporation and growth, coagulation, and complex flowfield dynamics. This letter applies quadrature methods for efficient estimation of aerosol optical properties directly from a known moment sequence. The approach is demonstrated using particle size distributions obtained from fits to field measurements. Comparison of light‐scattering phase functions and other integral optical properties calculated from the moments with those obtained from the full distributions shows that the lower‐order moments lead to an efficient and accurate parametrization for these properties.
A two‐dimensional spectral analysis of short period gravity waves imaged in the OI(557.7 nm) and near infra red OH nightglow emissions over Arecibo, Puerto Rico
Authors: Taylor M. J. , Garcia F. J.
Published: February 2004

In January 1993 an extensive set of radar and optical data was gathered from various key sites around the world during a coordinated “10 Day Run” designed to investigate the coupled dynamic behavior of the upper atmosphere on a large, medium and small scale. As part of this campaign an all‐sky CCD imaging system was operated at Arecibo Observatory, Puerto Rico, to help quantify the response of the low latitude mesosphere‐thermosphere system to short period (<1 hour) gravity waves. Measurements of the OI(557.7 nm) and near infrared OH nightglow emissions were made in conjunction with photometric and ISR radar soundings and revealed an abundance of small‐scale structure in the 80–100 km range. In this letter we apply two‐dimensional spectral analysis techniques to aid in the interpretation of a complex set of image data that consisted of two intersecting quasi‐monochromatic gravity wave patterns progressing on approximately orthogonal headings. An investigation of the spectral content and temporal evolution of these wave motions at each emission altitude is presented.
Glacial‐interglacial migration of an upwelling field in the Western Equatorial Pacific recorded by sediment 15N/14N
Authors: Nakatsuka Takeshi , Harada Naomi , Matsumoto Eiji , Handa Nobuhiko , Oba Tadamichi , Ikehara Monoru , Matsuoka Hiromi , Kimoto Katsunori
Published: February 2004

Nitrogen isotope ratios (δ15N) of surface sediment in the equatorial ocean reflect the mode of upper water circulation pattern. We applied this knowledge to reconstruct glacial‐interglacial variations of an upwelling field in western equatorial Pacific using δ15N from sediment cores. Distinct minima in δ15N values were found corresponding to glacial periods on the northern and eastern edges of the upwelling field (Mindanao Dome), indicating glacial enlargement of upwelling due to enhanced winter monsoon activity. However, at a site on southern side of the upwelling region, minima in δ15N values were obtained during interglacial periods. These opposing variations in δ15N values could be interpreted as a northward shift of the upwelling zone, during glacial periods. The glacial‐interglacial migration of the circulation pattern in this region may reflect a modal change in the global thermohaline circulation (conveyor belt) during glaciation.
Rate of NO2 photolysis from the surface to 7.6 km altitude in clear‐sky and clouds
Authors: Kelley Paul , Dickerson Russell R. , Luke Winston T. , Kok Gregory L.
Published: February 2004

The photolysis of NO2 by solar UV radiation produces ozone in the troposphere. Radiative transfer models predict an increase in actinic UV flux with altitude, but this has never been well documented experimentally. This paper presents direct airborne measurements of both upwelling and downwelling flux (2π sr each) from 0.2 to 7.6 km for clear‐sky conditions and 58° solar zenith angle. The downwelling flux increases by 33% and upwelling flux increases by a factor of four going from the surface to 7.6 km. Excellent agreement was found with models using detailed solutions to the radiative transfer equation or the six‐stream approximation, while a number of two‐stream computer models agreed within 10 to 25%. Compared to clear‐sky measurements, in‐cloud enhancement of up to 58% was also observed.
Simultaneous observations of the Saturnian aurora and polar haze with the HST/FOC
Authors: Gérard J. C. , Dols V. , Grodent D. , Waite J. H. , Gladstone G. R. , Prangé R.
Published: February 2004

Near simultaneous observations of the Saturnian H2 north ultraviolet aurora and the polar haze were made at 153 nm and 210 nm respectively with the Faint Object Camera on board the post‐COSTAR Hubble Space Telescope. The auroral observations cover a complete rotation of the planet and, when co‐added, they reveal the presence of an auroral emission near 80°N with a brightness of about 150 kR of total H2 emission. The maximum vertical optical depth at 210 nm is found to be located ∼5° equatorward of the auroral emission zone. The haze particles are presumably formed by hydrocarbon aerosols initiated by H2+ auroral production. In this case, the 3 × 1010 W of H2 emission observed with the FOC, combined with the deduced haze optical depth requires an efficiency of aerosol formation of about 7%. This result indicates that auroral production of hydrocarbon aerosols is a viable source of high‐latitude haze.
Monument motion and measurements of crustal velocities
Authors: Johnson Hadley O. , Agnew Duncan Carr
Published: February 2004

It is usually assumed in geodetic studies that measurement errors are independent from one measurement to the next and that the rate of deformation (velocity) is constant over the duration of the experiment. Any temporal correlation between measurements can substantially affect the uncertainty in this velocity estimate when it is determined from the time series of measurements. One source of possible long‐term correlation is motion of the geodetic monument with respect to the “deep” crust. Available measurements suggest that this motion introduces errors that have the form of a random walk process. We show how such errors affect the uncertainty of velocity estimates. For a geodetic experiment of set duration we calculate the velocity uncertainty as a function of the number of observations and of the relative amount of correlated and uncorrelated noise. We find that 1) neglecting long‐term temporal correlations makes the uncertainty in the estimated velocities much too small, and that 2) when the correlated and independent noise sources are of similar magnitude, the expected improvement in uncertainty from having more measurementis not realized; there is almost no improvement in some cases. We have also examined the effect of outliers (“blunders”) on the velocity uncertainty; for a frequency of outliers typical of geodetic field campaigns, the previous two conclusions remain unchanged. These results suggest that long‐term correlations have a large effect on estimating deformation rates; unless these correlations are small, frequent observations give little advantage. If frequent observations are planned, the amount of correlated noise due to monument instability must be kept small if the full capabilities of the measurement technique are to be realized.
Submarine analogs to Venusian pancake domes
Authors: Bridges Nathan T.
Published: February 2004

The morphology and dimensions of the large diameter, steep‐sided, flat‐topped “pancake domes” on Venus make them unlike any type of terrestrial subaerial volcano. Comparisons between images of Hawaiian seamounts and pancake domes show similarities in shapes and secondary features. The morphometry of pancake domes is closer to that of Pacific seamounts than subaerial lava domes. Considering both morphology and morphometry, seamounts seem a better analog to the pancake domes. The control of volatile exsolution by pressure on Venus and the seafloor can cause lavas to have similar viscosities and densities, although the latter will be counteracted by high buoyancy underwater. However, analogous effects of the Venusian and seafloor environments alone are probably not sufficient to produce similar volcanoes. Rather, Venusian lavas of various compositions may behave like basalt on the seafloor if appropriate rates and modes of extrusion and planetary thermal structure are also considered.
Anthropogenic impact on global geodynamics due to reservoir water impoundment
Authors: Chao Benjamin Fong
Published: February 2004

Water impounded in artificial reservoirs since ∼1950 is by far the largest anthropogenic hydrological change in terms of the mass involved. This mass redistribution contributes to geodynamic changes in the Earth's rotation and gravitational field that have been closely monitored by modern space geodetic techniques. We compute the effect of 88 major reservoirs on length‐of‐day, polar motion, and low‐degree gravitational coefficients. On an individual basis much smaller than geophysical signals in scale and magnitude, these anthropogenic effects prove to be non‐negligible cumulatively, especially when considering the fact that our results represent underestimates of the reality. In particular, reservoir water has contributed a significant fraction in the total observed polar drift over the last 40 years.
Introduction to ALOHA/ANLC‐93: The 1993 airborne lidar and observations of the Hawaiian Airglow/Airborne Noctilucent Cloud Campaigns
Authors: Gardner Chester S.
Published: February 2004

The middle atmosphere is a region of rich photochemical and dynamical interactions. A variety of interesting and important structures are found in the middle atmosphere including the airglow layers, the meteoric metal layers, and noctilucent clouds. Recent modeling studies have suggested that the expected increases in atmospheric CO2 and CH4 during the next century may result in significant changes in middle atmosphere temperatures, densities, and composition. Studies of this important region are now receiving considerable attention because of the interest in global change problems.
An improved estimate of the oceanic lifetime of atmospheric CH3Br
Authors: Yvon Shari A. , Butler James H.
Published: February 2004

Previous estimates of the partial atmospheric lifetime of CH3Br with respect to degradation in the ocean have not fully accounted for co‐variation of sea‐surface and boundary layer properties. Here we substantially reduce uncertainty in this calculation by using a coupled, ocean‐atmosphere box model and a tightly gridded data set of oceanic and atmospheric properties. The best estimate of the partial atmospheric lifetime of CH3Br with respect to the ocean is 2.7 y with a possible range, due mainly to the choice of computational procedures for critical terms, of 2.4 to 6.5 y. This range is about one‐third of that estimated previously. The total atmospheric lifetime, based upon oceanic, atmospheric, and proposed soil losses with all of their uncertainties, is 0.8 (0.6 to 1.4) y. Only 28% of this total uncertainty is attributable to the uncertainty in oceanic loss.
The subducted Rivera‐Cocos Plate Boundary: Where is it, what is it, and what is its relationship to the Colima Rift?
Authors: Bandy W. , Mortera‐Gutierrez C. , Urrutia‐Fucugauchi J. , Hilde T. W. C.
Published: February 2004

Gravity data, the geometry of the Wadati‐Benioff zone beneath western Mexico, and the seafloor morphology of the Rivera‐Cocos plate boundary west of the Middle America trench suggest that the subducted part of this boundary lies directly beneath and is oriented parallel to the Southern Colima rift. Thus, the Southern Colima rift likely formed in response to divergence between the subducting Rivera and Cocos plates due to direct coupling between these two plates and the overriding North American plate. In contrast, the subducted plate boundary lies east of and oblique to the Northern Colima and Central Colima grabens. East of the Central Colima graben a low density zone overlies the boundary and underlies surface exposures of Cretaceous granitoids and associated thermal springs and shallow focus earthquakes; characteristics that are explained by thermal convection induced in the upper mantle by divergence between the subducted Rivera and Cocos plates. These characteristics along with the adjacent locations of the low density upper mantle and the Central Colima graben are consistent with crustal extension produced by the uniform‐sense normal simple shear mechanism.
Ocean‐load tides at the South Pole: A validation of recent ocean‐tide models
Authors: Agnew Duncan Carr
Published: February 2004

Small diurnal and semidiurnal gravity tides are seen at the South Pole because of the loading by and attraction of the ocean tides. These data provide a check on the quality of ocean‐tide models, especially in the southernmost ocean, which has historically been the most lacking in tidal data. Ocean‐tide models developed in the 1980's did not predict the gravity tides at this location very well. Recently‐developed models based on the Topex/Poseidon altimetric data and improved hydrodynamical modeling agree much better with the observations, provided that the tides beneath the ice shelves are included. The level of agreement at this remote location suggests that, loads from very local tides aside, the new generation of ocean‐tide models can predict the loading tides to very high accuracy.
Fault healing inferred from time dependent variations in source properties of repeating earthquakes
Authors: Marone Chris , Vidale John E. , Ellsworth William L.
Published: February 2004

We analyze two sets of repeating earthquakes on the Calaveras fault to estimate in‐situ rates of fault strengthening (healing). Earthquake recurrence intervals tr range from 3 to 803 days. Variations in relative moment and duration are combined to study changes in stress drop, rupture dimension, rupture velocity, and particle velocity as a function of tr. Healing rates and source variations are compared with predictions of laboratory‐derived friction laws. Two interpretations of event duration τ are used: one in which τ is given by the ratio of slip to particle velocity and one in which it scales as rupture dimension divided by rupture velocity. Our data indicate that faults strengthen during the interseismic period. We infer that source dimension decreases with tr due to aseismic creep within the region surrounding the repeating events. Stress drop increases 1–3MPa per decade increase in tr, which represents an increase of a factor of 2–3 relative to events with tr between 10 and 100 days. This rate of fault healing is consistent with extrapolations of laboratory measurements of healing rates if fault strength is high, on order of 60MPa, and stress drop is roughly 10% of this value.
Three‐dimensional Vp and Vp/Vs structure at Loma Prieta, California, from local earthquake tomography
Authors: Thurber Clifford H. , Atre Shashank R. , Eberhart‐Phillips Donna
Published: February 2004

P and S‐P times from local earthquakes and P times from explosions at seismic stations in the vicinity of the 1989 Loma Prieta earthquake are inverted simultaneously to produce three‐dimensional images of Vp and Vp/Vs structure along the rupture zone. The results confirm the presence of the major heterogeneities identified in previous studies using P waves only, including high Vp along the rupture in areas of significant slip and a low‐velocity wedge along the San Andreas at the SE edge of the rupture. A change in rock properties evidenced by a significant Vp/Vs increase (equal to a 30% Poisson's ratio increase) from the middle crust to the upper crust may have been responsible for the upward termination of the main shock rupture. We speculate that the deep high‐Vp body that lies along the SE portion of the rupture zone consists of two bodies, based on model results indicating that the SW part of the body has relatively high Vp/Vs while the NE part has relatively low Vp/Vs.
Spherical‐spline parameterization of three‐dimensional earth models
Authors: Wang Zheng , Dahlen F. A.
Published: February 2004

We propose a spherical surface‐spline method that parameterizes a two‐dimensional model on a sphere in terms of a local cubic B‐spline basis on a triangular grid of knots with approximately equal interknot spacing. Numerical results show that such a parameterization can represent a model on a sphere with an accuracy equal to that of the spherical‐harmonic parameterization of the corresponding nominal degree. Furthermore, it significantly reduces the computational time needed to calculate surface‐wave synthetic seismograms on a laterally heterogeneous Earth, and makes it feasible to apply JWKB theory to surface‐wave inversion studies.
Evidence of high‐latitude reconnecting during northward IMF: Hawkeye observations
Authors: Kessel R. L. , Chen S.‐H. , Green J. L. , Fung S. F. , Boardsen S. A. , Tan L. C. , Eastman T. E. , Craven J. D. , Frank L. A.
Published: February 2004

Reconnection is accepted as an important process for driving the solar wind/magnetospheric interaction although it is not fully understood. In particular, reconnection for northward interplanetary magnetic field (IMF) at high‐latitudes tailward of the cusp, has received little attention in comparison with equatorial reconnection for southward IMF. Using Hawkeye data we present the first direct observations of reconnection at the high‐latitude magnetopause (75°) during northward IMF in the form of sunward flowing protons. This flow is nearly field aligned, approximately Alfvénic, and roughly obeys tangential momentum balance. The magnetic field shear is large at the magnetopause and there is a non‐zero BN component suggesting the existence of a rotational discontinuity and reconnection. The Hawkeye observations support several recent simulations at least qualitatively in terms of flow directions expected for high‐latitude reconnection during northward IMF.
Stealth plumes on Io
Authors: Johnson Torrence V. , Matson Dennis L. , Blaney Diana L. , Veeder Glenn J. , Davies Ashley
Published: February 2004

We suggest that Io's eruptive activity may include a class of previously undetected SO2 geysers. The thermodynamic models for the eruptive plumes discovered by Voyager involve low to moderate entropy SO2 eruptions. The resulting plumes are a mixture of solid and gas which emerge from the vent and follow essentially ballistic trajectories. We show that intrusion of silicate magma into buried SO2 deposits can create the required conditions for high entropy eruptions which proceed entirely in the vapor phase. These purely gaseous plumes would have been invisible to Voyager's instruments. Hence, we call them “stealth” plumes. Such eruptions could explain the “patchy” SO2 atmosphere inferred from recent UV and microwave spectral observations. The magma intrusion rate required to support the required gas production for these plumes is a negligible fraction of estimated global magma intrusion rates.
On the relationship between total ozone and solar ultraviolet radiation at St. Petersburg, Russia
Authors: Varotsos C. , Kondratyev K. Ya. , Katsikis S.
Published: February 2004

Daily total ozone observations made with the Total Ozone Mapping Spectrometer (TOMS) flown on the satellite Nimbus‐7 during 1978–1992, have been used in order to investigate the increase in the daily broad‐band and spectral solar ultraviolet radiation reaching the ground through a recently developed parametric model. Total ozone reductions of 3.0% during summer time and 11% during winter time per decade, at St. Petersburg (60°N, 30°E), Russia, cause an increase in erythematically active ultraviolet irradiance of at least 7% and 22%, respectively.
Properties of magnetohydrodynamic turbulence in the solar wind as observed by Ulysses at high heliographic latitudes
Authors: Goldstein B. E. , Smith E. J. , Balogh A. , Horbury T. S. , Goldstein M. L. , Roberts D. A.
Published: February 2004

The Ulysses mission provides an opportunity to study the evolution of magnetohydrodynamic (MHD) turbulence in pure high‐speed solar wind streams. The absence at high heliocentric latitudes of the strong shears in solar wind velocity generally present near the heliocentric current sheet allows investigation of how fluctuations in the magnetic field and plasma relax and evolve in the radially expanding solar wind. We report results of an analysis of the radial and latitudinal variation of the turbulence properties of the fluctuations, especially various plasma‐field correlations, in high latitude regions. The results constrain current theories of the evolution of MHD turbulence in the solar wind. Compared to similar observations at 0.3 AU by Helios, we find spectra that are similar in having a large frequency band with an f¹ power spectrum in the outward traveling component of the waves, followed at higher frequencies by a steeper spectrum. Ulysses observations establish that at high latitudes the turbulence is less evolved (i.e., has a smaller inertial range) than it is in the ecliptic at the same heliocentric distance, apparently due to the absence of strong velocity shear. Once Ulysses is in the polar coronal hole, properties of the turbulence appear to be determined by the heliocentric distance of the spacecraft rather than by its helio‐latitude.
Measurement of stratospheric HBr using high resolution far infrared spectroscopy
Authors: Carlotti M. , Ade P. A. R. , Carli B. , Ciarpallini P. , Cortesi U. , Griffin M. J. , Lepri G. , Mencaraglia F. , Murray A. G. , Nolt I. G. , Park J. H. , Radostitz J. V.
Published: February 2004

Far infrared spectral features of HBr have been observed in the stratospheric emission spectrum using a balloon borne high resolution Fourier transform spectrometer equipped with a high sensitivity detector specially designed for this purpose. The value of 1.6±0.6 parts per trillion in volume for the HBr mixing ratio has been retrieved, from the global‐fit analysis of 121 spectra, in the 25–36.5 km altitude range. The result is briefly compared with models and previous assessments.
Observations of plasma waves in magnetic holes
Authors: Lin Naiguo , Kellogg P. J. , MacDowall R. J. , Balogh A. , Forsyth R. J. , Phillips J. L. , Buttighoffer A. , Pick M.
Published: February 2004

We report the first observations of Langmuir waves excited within magnetic holes, which are characterized by a depression of magnetic field strength. This phenomenon is very common in the solar wind. In addition to Langmuir waves, waves at a few kHz, which are typical of Doppler‐shifted ion acoustic frequencies in the solar wind, and low frequency electromagnetic waves (below the electron cyclotron frequency) are sometimes observed simultaneously within the holes. In the holes with directional discontinuities at the boundary, the above plasma waves may occur at the edges of the holes. Possible physical mechanisms of the wave excitation are discussed.