bluuebunny/crossref_metadata_2025 huggingface dataset:
Snow cover identification through cirrus‐cloudy atmospheres using daytime AVHRR imagery
Authors: Hutchison Keith D. , Locke James K.
Published: February 2004

A technique has been developed for enhanced snow identification in cloud‐free and cirrus‐cloudy atmospheres using daytime AVHRR imagery. The procedure is based upon the strong contrast between snow and thin cirrus present in daytime 3.7 µm [albedo] data, which have been corrected for thermal emissions. Snow is identified by a strong yellow‐hue in a false‐color composite image constructed by assigning the 0.6 µm AVHRR channel to the red and green guns of a CRT and the albedo component of 3.7 µm channel to the blue gun. Surprisingly, snow becomes clearly discernible even in regions that appear to be obscured with thin cirrus clouds. This powerful image processing technique for mapping snow in cloud‐free and cirrus‐cloudy atmospheres may prove useful for a variety of applications, especially those associated with hydrological studies in regions that are frequently cloudy.
X‐ray study of iron with in‐situ heating at ultra high pressures
Authors: Dubrovinsky L. S. , Saxena S. K. , Lazor P.
Published: February 2004

We provide experimental evidence concerning the structure and the pressure‐temperature stability of a new polymorph of iron with the double hexagonal close‐packed (DHCP) structure. This experiment was performed by an in‐situ electrical heating of an iron‐wire at argon pressures of 31 and 48 GPa. The results demonstrate the stability of the new phase and the reversibility of the transformation of iron between the hexagonal close‐packed (HCP) and DHCP structures at high pressure and temperature corresponding to a depth of over 1500 km in the Earth's interior.
Strong CO2 emissions from the Arabian Sea during south‐west monsoon
Authors: Körtzinger Arne , Duinker Jan C. , Mintrop Ludger
Published: February 2004

The partial pressure of CO2 (pCO2) was measured during the 1995 South‐West Monsoon in the Arabian Sea. The Arabian Sea was characterized throughout by a moderate supersaturation of 12–30 µatm. The stable atmospheric pCO2 level was around 345 µatm. An extreme supersaturation was found in areas of coastal upwelling off the Omani coast with pCO2 peak values in surface waters of 750 µatm. Such two‐fold saturation (218%) is rarely found elsewhere in open ocean environments. We also encountered cold upwelled water 300 nm off the Omani coast in the region of Ekman pumping, which was also characterized by a strongly elevated seawater pCO2 of up to 525 µatm. Due to the strong monsoonal wind forcing the Arabian Sea as a whole and the areas of upwelling in particular represent a significant source of atmospheric CO2 with flux densities from around 2 mmol m−2 d−1 in the open ocean to 119 mmol m−2 d−1 in coastal upwelling. Local air masses passing the area of coastal upwelling showed increasing CO2 concentrations, which are consistent with such strong emissions.
Direct estimation of stomatal resistance for meteorological applications
Authors: Niyogi Devdutta S. , Raman Sethu , Prabhu A. , Kumar Udai , Joshi S. S.
Published: February 2004

Stomatal Resistance (Rs) is one of the most important parameters in the meteorological models for weather or climate analysis and hydrological scenario estimations. The information for estimating Rs is sparse particularly in the tropics limiting the development of a detailed global terrestrial biosphere‐atmosphere interaction analysis. One of the reasons for the scarcity of tropical data is the high cost of instrumentation. A hypothesis is presented to estimate Rs from plant‐nutrient status in a field study using stomatal aperture observations to develop a simple, cost‐effective technique for first‐order estimations. Comparisons with observations from a tropical field experiment are encouraging and an approach is suggested using this method for initialization of numerical models using remote sensing techniques based on nitrogen, humidity, and temperature as sufficient parameters.
GPS surveying with 1 mm precision using corrections for atmospheric slant path delay
Authors: Alber Chris , Ware Randolph , Rocken Christian , Solheim Fredrick
Published: February 2004

Multipath and atmospheric effects can limit GPS surveying precision. We surveyed a 43 km baseline using large diameter choke ring antennas to reduce multipath and pointed radiometer and barometric data to correct for atmospheric slant delay. Based on 11 daily solutions, atmospheric slant delay corrections improved vertical precision to 1.2 mm rms and horizontal precision to sub‐mm. Applications for high precision GPS surveying include deformation monitoring associated with earthquake and volcanic processes, subsidence, isostasy, and sea level measurements; monitoring of atmospheric water vapor for climate and global change research, and to improve the resolution of synthetic aperture radar; calibration of satellite altimeters; and precise satellite orbit determination.
Coronal radio sounding: Non‐Gaussian turbulence in the source regions of slow and fast solar wind
Authors: Karl J. , Pätzold M. , Bird M. K.
Published: February 2004

Structure functions of arbitrary order are analyzed using differential phase scintillation data obtained during the fourth solar conjunction of the Ulysses spacecraft in February–March 1995. The scaling features of these structure functions clearly discriminate between electron density fluctuations observed in coronal holes versus coronal streamers. The second order structure function, which is related to the power spectrum, shows essentially a scaling exponent ζ(p) = α −2, where p=2 and α is the spectral index of the three‐dimensional wavenumber spectrum of electron density fluctuations. Higher‐order structure functions provide evidence that these fluctuations are scale dependent and do not follow Gaussian statistics.
Inner core differential rotation: Facts and artefacts
Authors: Souriau Annie , Roudil Pascal , Moynot Bernard
Published: February 2004

A differential rotation of the inner core with respect to the mantle has been recently detected from the variations in time of the inner core anisotropy symmetry axis. This detection relies on the assumption that the anisotropy axis is tilted with respect to the rotation axis. We show that such a tilt cannot be reliably detected with the presently available data. In addition, we observe an apparent correlation between the differential travel time residuals of the core phases used to infer inner core rotation, and the magnitude of the events. This correlation, which could result from the analysis method of the data and from their varying frequency content, may partly bias the observations. Although these results do not rule out the possibility of an inner core differential rotation, they question whether it has actually been detected.
Reproducing the velocity and stress fields in the aegean Region
Authors: Cianetti S. , Gasperini P. , Boccaletti M. , Giunchi C.
Published: February 2004

Recent satellite geodetic measurements help to clearly define the velocity field in the Aegean‐Anatolian area. The velocity field can be broadly characterized by anticlockwise rotation of this region relative to Eurasia, around a pole located at Lat. 32.73, Long. 32.03, north of the Egyptian shoreline. Studies of the fault kinematics in the region also provide information on the time evolution of the stress field. In this work, we model deformation in the Aegean‐Anatolian region to better understand the tectonic origin of the observed stress and velocity fields. We found that the observed deformation pattern can be well reproduced by imposing simple boundary conditions including: (1) northward displacement of the Arabian plate, (2) locking of eastward motion in northwestern Greece and (3) suction force at the Hellenic trench. The observed variation in the stress field occurred at 0.9 Ma can be partially explained by a change in the activity of the North Anatolian fault.
Accurate analytic representations of solar time and seasons on Mars with applications to the Pathfinder/Surveyor missions
Authors: Allison Michael
Published: February 2004

Efficient analytic recipes are presented for a moderately accurate, closed‐form calculation of the areocentric longitude (Ls), analemmic “equation of time,” and solar hour angles on Mars, along with an approximate recovery of the Viking “Local Lander Time.” The adopted fit to the fictitious mean sun implies a Mars tropical orbit period of 686.9725d.
Ultrasonic velocities of opaline rocks undergoing silica diagenesis
Authors: Chaika Caren , Dvorkin Jack
Published: February 2004

Experimental results of laboratory measurements at ultrasonic frequencies on dry opaline rocks are documented from the Monterey Formation, a siliceous unit in the San Joaquin basin. In these samples the silica is primarily biogenic opal‐A in origin, but progressively alters to opal‐CT and then quartz with depth. The diagenetic transitions are accompanied by a marked porosity reduction. Compressional and shear wave velocities were measured on core plugs at effective reservoir pressure. Experimental results on samples from the opal‐A/opal‐CT transition and the opal‐CT/quartz transition show very little pressure‐dependence of elasticwave velocities. When their elastic moduli are normalized by those of the solid phase, the moduli‐porosity trend is very close to that of chalk and, in the lower‐porosity domain, of some clean sandstones.
Mesospheric standing waves near South Pole
Authors: Hernandez G. , Smith R. W. , Kelley J. M. , Fraser G. J. , Clark K. C.
Published: February 2004

Optical measurements of mesospheric winds near South Pole, during August 1996, show the presence of large‐scale standing waves with periods of 51.3‐hr and 107‐hr, respectively. In addition, a 11.6‐hr period zonal wavenumber‐one oscillation with a westward phase progression was also observed. The direction of the observed mean wind has changed nearly 60° westward from the typical wind direction observed during the same month in previous years. The direction of the presently observed mean wind is nearly parallel to wind direction of the 51.3‐hr standing oscillation, suggesting an interaction between the mean wind field and the wave during this observation. Based on the simultaneous observation at Scott Base of an uncommon wave with 11.53‐hr periodicity with short (∼20 km) vertical wavelength of propagation, the 11.6‐hr wave observed from South Pole can be identified as a zonal wavenumber one inertio‐gravity mode of oscillation. Because of the transience of this wave and its closeness to the inertial period, we also discuss another approach to the interpretation of such waves as possible forced oscillations.
On the dissociative ionization of SO2 in Io's atmosphere
Authors: Michael M. , Bhardwaj A.
Published: February 2004

Unattenuated ionization rates for the dissociative photoionization of SO2 producing SO2+, SO+, S+, O+, and O2+ ions are reported during solar minimum and maximum conditions. It is found that in the atmosphere of Io the photo‐dissociation‐ionization of SO2 could be an important source of the production of SO+, S+, O+, and O2+ ions and that its contribution is much greater (factor of 5–10) compared with that due to direct photoionization of, respectively, SO, S, O, and O2 gases. Role of photoelectron impact ionization of SO2 in producing SO2+, SO+, S+, O+, and O2+ ions in the Io's atmosphere is investigated using a Monte Carlo model. It is recommended that the models of Io's ionosphere‐atmosphere should include the dissociative ionization of SO2.
Ramp thickness and ion heating in 1D simulations of laminar quasi‐perpendicular shocks
Authors: Wilkinson William P.
Published: February 2004

One‐dimensional hybrid simulations are used to investigate the effect of the shock ramp's width on the heating of the transmitted ions at low Mach number nearly perpendicular shocks. The suitability of the hybrid code for such a study is established by considering the correlation between precursor wavelength and ramp thickness as a function of θBn, the angle between the upstream magnetic field and upstream‐pointing shock normal. The simulated shocks are found to preserve their dispersive character at geometries close to perpendicular, becoming rapidly narrower as θBn approaches 90°. The effect of shock thickness on the transmitted ions is examined by comparing their heating at three shocks with θBn = 83°, 86° and 88°, respectively, which are successively thinner by a factor of 2. The results are discussed in the light of recent theoretical studies on the subject.
Seismic and electrical anisotropy in the Mornos Delta, Gulf of Corinth, Greece, and its relationship with GPS strain measurements
Authors: Bernard P. , Chouliaras G. , Tzanis A. , Briole P. , Bouin M.‐P. , Tellez J. , Stavrakakis G. , Makropoulos K.
Published: February 2004

Shear‐wave splitting studies on seismograms from local earthquakes at the site of the Mornos delta (Gulf of Corinth, Greece) has revealed a clear seismic anisotropy, with a fast S polarization striking N55 ± 25°. Magneto‐telluric soundings in the frequency range 0.01 to 100 Hz on the delta showed a clear electric anisotropy, with a N55° ± 10° direction for the highest frequency. This anisotropy spans through the whole layer of sediments, about 1 km thick. Comparison of the 1966–1972 triangulations and the 1991–1995 GPS positions of geodetic points in and around the delta showed rapid extension strain (2 × 10−6/year) in the direction N340° ± 30°, perpendicular to the fast S and the highest conductivity directions, suggestive of a causal relationship between these observations. We thus propose that this strain controls the two reported anisotropies, by the formation and maintaining of fluid filled, steeply dipping antithetic faults and fractures, and fluid filled vertical cracks, all striking N55° ± 20°. The source of strain is likely to be active normal faulting near and under the delta, as independently evidenced by the recent discovery of nearby offshore faults, striking about N60°, significantly different from the dominant E‐W strike of the major faults of the Gulf.
Wave characteristics of daytime and nighttime Pi 2 pulsations at the equatorial and low latitudes
Authors: Shinohara M. , Yumoto K. , Yoshikawa A. , Saka O. , Solovyev S. I. , Vershinin E. F. , Trivedi N. B. , Da Costa J. M.
Published: February 2004

Peculiarities of daytime and nighttime Pi 2 pulsations at the dip equator are examined by using multipoint measurements from the 210° magnetic meridian (MM) magnetometer network. We found that during daytime the amplitude of Pi 2 pulsations at the dip equator is enhanced, and the phase lags ∼ 34° behind those at low‐latitude (magnetic latitude Φ = 19.5‐46.2°) stations. On the other hand, during nighttime the amplitude of Pi 2 pulsations at the dip equator is depressed, and the phase lags ∼ 18° behind those at the lower latitudes. Because the zonal ionospheric conductivity at the dip equator is much higher than that at the off‐dip equator region, Pi 2 signals are expected to be distorted more effectively at the dip equator. The observations imply that the daytime and nighttime Pi 2 pulsations in the equatorial and low‐latitude regions can be explained by invoking an instantaneous penetration of electric field variations from the nightside polar ionosphere to the dayside equatorial ionosphere, and a direct incidence of compressional oscillations from the nightside inner magnetosphere, respectively.
Freezing of polar stratospheric clouds in orographically induced strong warming events
Authors: Tsias A. , Prenni A. J. , Carslaw K. S. , Onasch T. P. , Luo B. P. , Tolbert M. A. , Peter Th.
Published: February 2004

Results from laboratory experiments and microphysical modeling are presented that suggest a potential freezing nucleation mechanism for polar stratospheric cloud (PSC) particles above the water ice frost point (Tice). The mechanism requires very high HNO3 concentrations of about 58 wt% in the droplets, and leads to the freezing of nitric acid dihydrate (NAD) in a highly selective manner in the smallest droplets of an ensemble. In the stratosphere such liquid compositions are predicted to occur in aerosol droplets which are warmed adiabatically with rates of about +150 K/h from below 190 K to 194 K. Such rapid temperature changes have been observed in mountain leewaves that occur frequently in the stratosphere, clearly demonstrating the need for a stratospheric gravity wave climatology.
Fluid flow triggered migration of events in the 1989 Dobi Earthquake sequence of central Afar
Authors: Noir J. , Jacques E. , Békri S. , Adler P. M. , Tapponnier P. , King G. C. P.
Published: February 2004

During the August 1989 sequence of earthquakes beneath the Dobi graben in Central Afar, principal events (including 10 shocks with ML≥5.5) propagated ∼50 km north‐westwards in ∼50 h. The sequence is analyzed in terms of triggering by propagation of a critical pore pressure wave in a compressible fluid through a fractured medium. The macroscopic fluid diffusion tensor D in the crust beneath the graben is estimated. Its principal eigenvector strikes ∼N115°E nearly parallel to the graben axis. With a value
, it is about 10 times larger than the other two, consistent with fissure anisotropy in the graben. The order of magnitude of the permeability (∼10−8 m²) is compatible with characteristic fissure widths ranging from 1 mm to 3 cm. Estimating such parameters in other extensional regions might help to understand better the temporal evolution of seismic swarms.
CUPRI observations of pre‐sunrise vertical type‐I echoes from the equatorial electrojet above Alcântara, Brazil
Authors: Swartz Wesley E.
Published: February 2004

The Cornell University Portable Radar Interferometer (CUPRI) made high resolution vertical radar measurements of the equatorial electrojet above Alcântara, Brazil from mid‐August to mid‐October, 1994, as part of the Guará Dip Equator Campaign. Spectra obtained during the period of a few hours before sunrise show the usual nighttime persistence asymmetry wherein there is a preponderance of downward type‐I phase velocities as a function of time. These are the first high resolution measurements in South America of this effect at a location other than Jicamarca, Peru. Furthermore the CUPRI interferometer phase data clearly indicate that when changes in the sign of the dominate type‐I peaks occur, they are tied to the normal phase progressions of the large scale waves. No reversal of the asymmetry (as does occur in the daytime) was seen in this nighttime period.
Synthetic aperture radar interferogram of the 1995 Kobe Earthquake and its geodetic inversion
Authors: Ozawa Shinzaburo , Murakami Makoto , Fujiwara Satoshi , Tobita Mikio
Published: February 2004

Crustal deformation from the Mw=6.9 January 17 (JST), 1995, Kobe, Japan earthquake was detected by synthetic aperture radar interferometry (SAR) More than four fringes with ellipsoidal shape were observed surrounding the Nojima fault on northern Awaji island, suggesting a shortening in the range of more than 11.75 × 4 cm on the east side of this fault. The SAR sensor shows ellipsoidal fringes with an uplift zone in the Rokko mountain range and sharp subsidence around the Kobe area. In addition to SAR interferometry, leveling and GPS surveys were conducted by the Geographical Survey Institute of Japan (GSI). The permanent GPS observation sites of the GSI monitored ground displacements from this earthquake with daily updates. Based on these geodetic data, we estimated the faulting mechanism of the earthquake. The analytical procedure was an iterative linearized least squares method. A multi‐fault system consisting of six subfaults was constructed. The locations of the estimated model faults were close to those of the active faults in this area, running from the Nojima fault on Awaji island to the Rokko faults in the Kobe area with a change in strike angle near the Ohtsuki fault in the Kobe area. The slip vectors of the Nojima fault on Awaji island had a large component of reverse dip‐slip of about 2 m and strike slip of about 2 m. In the Kobe area, the amount of slip ranged from 0.3 to 1.2 m and was small compared with the slip on the Nojima fault. The results of these slip vectors agreed well with the results of other seismic, geodetic, and field studies.
Temporal evolution of very strong Trimpis observed at Darwin, Australia
Authors: Dowden Richard L. , Brundell James B. , Rodger Craig J.
Published: February 2004

Very strong phase and amplitude perturbations (Trimpis) of the very strong VLF transmission from NWC received in Darwin, Australia, enabled accurate measurement of the amplitude and phase of the scattered signal and of the time variation of these. The amplitude of the scattered signal decays as the logarithm of time, quite at odds with the exponential decay observed on classic Trimpis. During the amplitude decay, the phase of the scattered signal decreased at a decreasing rate. This is shown to be consistent with scattering from a bundle of sprite‐like, conducting columns extending some 50 km below the base of the ionosphere.
Global lightning and climate variability inferred from ELF magnetic field variations
Authors: Füllekrug Martin , Fraser‐Smith Antony C.
Published: February 2004

We report characteristics of global lightning activity on a seasonal time scale as inferred from two independently operating instruments measuring magnetic field variations in the lower ELF range. In this picture, the strongest source of lightning activity is centered on the North American continent. We reduce the source proximity effect to the observing sites experimentally with a simple differential technique and reconfirm the conclusion of Holzer and Deal (1956) that wave propagation conditions in the lower ELF range are of minor importance. The resulting mean seasonal variations of continental lightning in mid‐ and tropical latitudes are found to be related to surface temperature variations in moderate‐ and tropical rain forest climates and they support the view of Williams (1992) that monitoring of global lightning activity may provide a thermometer‐independent measure of temperature changes associated with climate variability.
Neural network prediction of AE data
Authors: Takalo Jouni , Timonen Jussi
Published: February 2004

Neural network (NN) models were constructed to study prediction of the AE index. Both solar wind (vBz) and previous observed AE inputs were used to predict AE data for different numbers of time steps ahead. It seems that prediction of the original unsmoothed AE data is possible only for 10 time steps (25 min) ahead. The predicted time series of the AE data for 50 time steps (125 min) ahead was found to be dynamically different from the original time series. It is possible that the NN model cannot reproduce the turbulent part of the power spectrum of the AE data. However, when using smoothed AE data the prediction for 10 time steps ahead gave an NMSE of 0.0438, and a correlation coefficient of 0.98. The predictive ability of the model gradually decreased as the lead time of the predictions was increased, but was quite good up to predictions for 30 time steps (75 min) ahead.
Io: Galileo evidence for major variations in regolith properties
Authors: Simonelli Damon P. , Veverka Joseph , McEwen Alfred S.
Published: February 2004

Galileo SSI images taken at different times early in the Jupiter orbital tour show striking, widespread changes in Io's color and albedo patterns that result from observing the satellite's surface at different lighting and viewing geometries. Such changes indicate significant variations in the photometric or light‐scattering behavior of the Ionian surface from region to region, and thereby provide strong evidence for major lateral variations in regolith properties. In particular, the regolith particles in Io's bright equatorial band appear to be larger than, or have a higher density of internal scatterers than, those in the satellite's higher‐latitude regions. Such heterogeneity is not surprising on Io, given the rapid rate of volcanic resurfacing.
Opposite ion dispersions observed quasi‐simultaneously in the polar cusp by the DE‐2 and AUREOL‐3 satellites
Authors: Escoubet C. P. , Bosqued J. M. , Hoffman R. A. , Berthelier A. , Anderson P. C.
Published: February 2004

On 26 August 1982 the satellites Dynamics Explorer 2 (DE‐2) and Aureol‐3 (A‐3) crossed around the same time the southern polar cusp. DE‐2 detected the cleft in the prenoon sector (11.5 H MLT) constituted by a poleward ion dispersion with two steps at around 50 and 1.5 keV, respectively. Around 1.5 H MLT eastward, A‐3 detected a diffuse ion precipitation, immediately followed by an equatorward dispersion (energy increases when the latitude increases). The convection pattern detected by DE‐2 was directed westward in the cleft with a maximum, around 1600 m/s, centred on the low energy step. The convection velocity measured by A‐3 had a component directed poleward where the diffuse ion precipitation was observed and a convection with an equatorward component where the ion dispersion is observed. The IMP‐8 IMF data showed a gap at the time of the cusp crossings, however using the IMF‐Bz component around that time and the AE index we infer that the IMF‐Bz would have been positive during the cusp crossings. We are explaining the observations by the merging of the interplanetary magnetic field with the geomagnetic lobe field lines which produces the dispersion observed at high latitude on A‐3 and the low energy step observed by DE‐2. At the same time a viscous diffusion on the frontside of the magnetosphere produces the diffuse ion precipitation observed by A‐3 and the high energy step observed by DE‐2.
Current‐voltage characteristic of the TSS‐1R satellite: Comparison with isotropic and anisotropic models
Authors: Vannaroni G. , Dobrowolny M. , Lebreton J. P. , Melchioni E. , De Venuto F. , Harvey C. C. , Iess L. , Guidoni U. , Bonifazi C. , Mariani F.
Published: February 2004

In this paper we present an analysis of the satellite current‐voltage (I‐V) characteristics observed during the TSS‐IR mission. The satellite I‐V curves were compared with the predictions by two theoretical models: the first one [Parker and Murphy, 1967] considers the channeling effect of the terrestrial magnetic field as the dominating process in the current collection, whereas the second one [Alpert et al., 1965] neglects the magnetic field and assumes an isotropic spherical geometry. Even though neither of the two theories reproduces rigorously the TSS experimental situation, as they neglect both the motion of the body and possible anomalous collisions, we find that both the models, in certain conditions, could reproduce theoretical curves in agreement with the data. However we suggest that, when the effect of the plasma turbulence is considered, the data could be better interpreted on the basis of the Alpert formulation.
A history of high‐temperature Io volcanism: February 1995 to May 1997
Authors: Spencer John R. , Stansberry John A. , Dumas Christophe , Vakil David , Pregler Randy , Hicks Michael , Hege Keith
Published: February 2004

Ground‐based observations of Io's infrared thermal emission between February 1995 and May 1997 show several discrete brightenings for which we can constrain locations, fluxes, and durations. Several of these were brief high‐temperature events, with temperatures up to at least 1500 K, similar to but often smaller than the rare “outbursts” seen previously. Loki, Io's most powerful volcano, was relatively active before and probably during Galileo's December 1995 Io flyby, was faint during most of 1996, and began a major, long‐lived brightening between February 20 and March 12 1997. Thermal emission was not seen from Ra Patera, site of an active plume in Galileo images. Major outbursts were seen on March 2nd and September 27 1995.
Crustal deformation at Long Valley Caldera, eastern California, 1992–1996 inferred from satellite radar interferometry
Authors: Thatcher Wayne , Massonnet Didier
Published: February 2004

Satellite radar interferometric images of Long Valley caldera show a pattern of surface deformation that resembles that expected from analysis of an extensive suite of ground‐based geodetic data. Images from 2 and 4 year intervals respectively, are consistent with uniform movement rates determined from leveling surveys. Synthetic interferograms generated from ellipsoidal‐inclusion source models based on inversion of the ground‐based data show generally good agreement with the observed images. Two interferograms show evidence for a magmatic source southwest of the caldera in a region not covered by ground measurements. Poorer image quality in the 4 year interferogram indicates that temporal decorrelation of surface radar reflectors is progressively degrading the fringe pattern in the Long Valley region.
Causes of equatorial asymmetry in sea surface temperature over the eastern Pacific
Authors: Xie Shang‐Ping , Seki Mieko
Published: February 2004

It is a long‐standing mystery that the climatological equator departs from the geographical one and is located around 10°N over the eastern Pacific. Key to maintaining the Northern Hemisphere position of the atmospheric intertropical convergence zone (ITCZ) is a hemispheric asymmetry in sea surface temperature (SST) with higher SSTs north of the equator (Fig. 1A). Using ship and satellite observations, we show that the scalar wind speed difference across the equator, through latent heat flux, is the main cause of this SST asymmetry while the sun‐shielding effect of precipitating clouds at the ITCZ is largely offset by the effect of high relative humidity. In the far eastern Pacific, non‐precipitating stratiform clouds also play a role in cooling the Southern Hemisphere. Surface air‐sea temperature difference field displays a distribution that acts to reduce the observed latitudinal asymmetry of SST.
The interaction of viscous heating with grain‐size dependent rheology in the formation of localized slip zones
Authors: Kameyama Masanori , Yuen David A. , Fujimoto Hiromi
Published: February 2004

The formation of localized shear zones is important for understanding many local and global processes in geodynamics. We have developed a self‐consistent thermal‐mechanical model together with a rheology which depends on temperature, strain‐rate and grain‐size distribution. The grain‐size distribution has contributions from both dynamic recrystallization and grain‐growth processes, and is governed locally by a nonlinear ordinary differential equation. A one‐dimensional model with 104 points is employed to resolve all of the scales involving grain‐size and temperature. We found that grain‐growth inhibits the development of shear zones, and that there is a delicate interplay between viscous heating and grain‐growth process in determining whether narrow fault zones are developed quickly. For realistic parameters of rheology and grain‐boundary processes for wet olivine, the magnitude of the rate of grain‐growth is crucial to determine whether shear zones are stable or unstable at temperature T ≃ 1000 K or shear stress σ ≃ 100 MPa.
The BrO + Ch3O2 reaction: Kinetics and role in the atmospheric ozone budget
Authors: Aranda Alfonso , Le Bras Georges , La Verdet Gérard , Poulet Gilles
Published: February 2004

Using the discharge flow method with detection of species by mass spectrometry and laser‐induced fluorescence, the kinetics of the reaction BrO + CH3O2 → products has been studied at 298 K. The rate constant obtained is (5.7±0.6) × 10−12 cm³ molecule−1 s−1. The mechanism of the reaction has been also investigated. These laboratory data are used to discuss the possible impact of this reaction on the ozone budget in different parts of the atmosphere. The reaction is likely to be negligible in the stratosphere, but is potentially significant in the remote marine boundary layer. The BrO+CH3O2 reaction, together with other BrO+RO2 reactions, may also significantly contribute to the ozone loss events observed in the Arctic troposphere in spring.
Western Pacific tropospheric ozone and potential vorticity: Implications for Asian pollution
Authors: Newell Reginald E. , Browell Edward V. , Davis Douglas D. , Liu Shaw C.
Published: February 2004

Tropospheric ozone (O3) cross sections measured with lidar from a DC‐8 aircraft over the western Pacific correspond closely with potential vorticity (PV). Both are transported from the middle latitude stratosphere, although this is not the only source of O3, and both have sinks in the tropical boundary layer. O3 and PV are good indicators of photochemical and transport process interactions. In summer, some Asian pollution, raised by convection to the upper troposphere, passes southward into the tropics and to the Southern Hemisphere. In winter, subsidence keeps the pollution at low altitudes where it moves over the ocean towards the ITCZ, with photochemical destruction and secondary pollutant generation occurring en route. Convection raises this modified air to the upper troposphere, where some may enter the stratosphere. Thus winter Asian pollution may have a smaller direct influence on the global atmosphere than it would if injected at other longitudes and seasons.
Motorization of China implies changes in Pacific air chemistry and primary production
Authors: Elliott Scott , Blake Donald R. , Duce Robert A. , Lai C. Aaron , McCreary Iain , McNair Laurie A. , Rowland F. Sherwood , Russell Armistead G. , Streit Gerald E. , Turco Richard P.
Published: February 2004

The People's Republic of China, the world's most populous nation, is considering extensive development of its automotive transportation infrastructure. Upper limits to the associated pollution increases can be defined through scenarios with Western style vehicles and vehicle‐to‐person ratios. Here we construct estimates of fundamental changes to chemistry of the Pacific ocean/atmosphere system through simple budgeting procedures. Regional increases in tropospheric ozone could reach tens of parts per billion. Observations/experiments suggest that enhanced nitrogen oxides will react with sea salt aerosols to yield chlorine atoms in the marine boundary layer. Nitrate deposition onto the open sea surface would support several percent of exported North Pacific carbon production. Transport of biologically active iron to surface waters may follow from increases in mineral dust and acid sulfate aerosols. Altered plankton ecodynamics will feed back into climate processes through sea to air flux of reduced sulfur gases and through carbon dioxide drawdown.
Decay of a vertical plasma column: A model to explain VLF sprites
Authors: Dowden Richard L. , Rodger Craig J.
Published: February 2004

VLF sprites are identified by high angle scattering of VLF transmissions by the conducting plasma columns which appear as the luminous columns of “red sprites”. VLF sprites are “early/fast Trimpis” and probably vice versa. Recently discovered properties of early/fast Trimpis are the logarithmic decay of the amplitude of the scattered signal and monotonic variation of its phase. These properties are explained in terms of scattering from a vertical column or set of columns extending from 50 km (or lower) altitude to about 80 km.
12C/13C kinetic isotope effects in the reactions of CH4 with OH and Cl
Authors: Gupta Mohan L. , McGrath M. P. , Cicerone R. J. , Rowland F. S. , Wolfsberg M.
Published: February 2004

In qualitative agreement with previous MP2 level calculations of the 12C/13C kinetic isotope effects (KIEs) for H‐abstraction of CH4 by OH and Cl, higher level calculations yield KIEs at 300 K that differ from the corresponding experimental values, but in different directions. At QCISD(T)/6‐311+G(2df,p), the theoretical KIE for CH4+Cl is 32‰ less than the measured value, while for CH4+OH, the theoretical KIE is greater than the measured value, but only by 5‰. Noticeable differences in atmospheric model simulation studies can occur if the measured KIEs are replaced by the analogous theoretical values. For example, the effect of carbon isotopic fractionation from the CH4 + Cl reaction on stratospheric δ13CH4 will be significantly lower than that obtained by Bergamaschi et al. [1996]. It is suggested, for the CH4+OH reaction and especially for the CH4+Cl reaction, that additional KIE measurements are needed.
Rate parameter uncertainty effects in assessing stratospheric ozone depletion by supersonic aviation
Authors: Dubey Manvendra K. , Smith Gregory P. , Hartley W. Seth , Kinnison Douglas E. , Connell Peter S.
Published: February 2004

Box model sensitivity‐uncertainty calculations for O3 depletion from supersonic aircraft emissions were performed at the most perturbed locale using localized outputs of the LLNL 2‐D diurnally averaged assessment model. Processes controlling N2O5, catalytic O3 loss steps O+NO2 and HO2+O3, HOx sink reactions OH+ HNO3/HNO4, and the O+O2 recombination that forms O3 are identified as the dominant photochemical uncertainty sources. Guided by local sensitivities, 2‐D model runs were repeated with 9 targeted input parameters altered to 1/3 of their l‐σ uncertainties to put error‐bounds on the predicted O3 change. Results indicate these kinetic errors can cause the predicted local O3 loss of 1.5% to be uncertain by up to 3% in regions of large aircraft NOx injection.
Trans‐ionospheric pulse pairs (TIPPs): Their geographic distributions and seasonal variations
Authors: Zuelsdorf R. S. , Strangeway R. J. , Russell C. T. , Casler C. , Christian H. J. , Franz R. C.
Published: February 2004

Since November 1993 the Blackbeard instrument aboard the ALEXIS satellite has detected pairs of pulses in the VHF band, known as Trans‐Ionospheric Pulse Pairs (TIPPs). These pulses exhibit dispersion consistent with a source of sub‐ ionospheric origin. As of January 1997 over 850 TIPPs have been detected. The source of these emissions still remains a mystery, although it is believed that TIPPs are in some way related to thunderstorms as such storms provide a strong sub‐ionospheric source and produce radiation in the same frequencies observed by Blackbeard. In an attempt to establish this connection we compare the geographic occurrence of TIPPs to that of lightning flashes observed from space by the Optical Transient Detector (OTD) on the Microlab‐1 spacecraft. TIPP data run from 2 November 1993 to 19 November 1996. OTD data run from 1 May 1995 to 30 November 1996. The geographical occurrence of TIPPs and that of lightning flashes is strongly correlated. TIPPs occur less frequently during the winter months and their region of production moves southward in the North American sector similar in behavior to lightning activity.
Interchange and kink modes in the near‐Earth plasma sheet and their associated plasma flows
Authors: Pritchett P. L. , Coroniti F. V.
Published: February 2004

Three‐dimensional (3‐D) particle simulations are used to investigate the response of the near‐Earth plasma sheet to the imposition of an external convection electric field for the case where magnetic flux is blocked from leaving the region. Under these conditions an interchange mode with characteristic wavelength of 1–2 RE (determined by the ion gyroradius) in the east‐west direction is excited before the plasma sheet is severed by the formation of a neutral line. The nonlinear growth of the interchange mode produces a strong (10–20 mV/m), localized ( ≲ 0.5 RE) Ey field which drives earthward flows of both electrons and ions. These flows pinch off regions of southward Bz which eventually are expelled tailward in narrow fingers around the edges of the earthward flow bursts.
Global Positioning System constraints on fault slip rates in the Death Valley Region, California and Nevada
Authors: Bennett R. A. , Wernicke B. P. , Davis J. L. , Elósegui P. , Snow J. K. , Abolins M. J. , House M. A. , Stirewalt G. L. , Ferrill D. A.
Published: February 2004

We estimated horizontal velocities at 15 locations in the vicinity of Yucca Mountain, Nevada, from Global Positioning System surveys conducted between 1991 and 1996. We used these velocity estimates to infer slip rates on two major Quaternary faults within the eastern California shear zone (ECSZ), the Hunter Mountain and Death Valley faults. The sum of slip rates across the two faults is well determined at 5 ± 1 mm/yr (1‐σ). Between 3 to 5 mm/yr of this motion appears to be accommodated along the Death Valley fault, implying 30–50 m of strain accumulation over the next 10,000 yr. If so, there is potential for 5 to 10 Mw 6.5–7.5 earthquakes during this period, a finding consistent with paleoseismological studies of the fault zone. Yucca Mountain, which lies 50 km east of the ECSZ, is the proposed location for the disposal of high‐level nuclear waste in the United States.
The current‐voltage characteristics of a large probe in low Earth orbit: TSS‐1R results
Authors: Thompson D. C. , Bonifazi C. , Gilchrist B. E. , Williams S. D. , Raitt W. J. , Lebreton J.‐P. , Burke W. J. , Stone N. H. , Wright K. H.
Published: February 2004

Measurements of the current collected by the Tethered Satellite System (TSS) satellite as a function of voltage and ambient plasma parameters are presented. The satellite current is found to vary approximately with the square root of the potential from below 10 to nearly 1200 V. The collected current exceeded premission expectations, based on the Parker and Murphy [1967] collection model, by factors of two to three. Possible reasons for discrepancies between the measurements and model are briefly discussed.
A possible role of weak zone at plate margin on secular mantle cooling
Authors: Honda S.
Published: February 2004

We study a simple 2‐D model of secular mantle cooling by convection in which the viscosity depends exponentially on the temperature. To understand the effects of weak zones near the sinking and rising areas, their position and viscosity are imposed. The heat transport efficiency is measured by introducing local Rayleigh (Ral) and Nusselt (Nul) numbers defined at each thermal boundary layer. We find that the Nul ‐ Ral relationship for the bottom boundary layer is similar to that of the steady‐state convection with constant viscosity in a rectangular box. The existence of weak zones predicts a higher Nul for the top thermal boundary layer, suggesting that this will enhance the heat transport of the top layer. If we change Ral of the top layer into the higher of the two Rals, which is usually that of bottom layer, the resultant Nul ‐ Ral approaches that of steady‐state constant viscosity convection. This may imply that the heat transport of convection with secular cooling may be controlled by the boundary layer which has higher Ral. We also suggest that the commonly used parameterization, in which the convecting medium is treated as having a constant viscosity equal to that of its isothermal core, may overestimate the heat transport efficiency.
Conductive heat loss in recent eruptions at mid‐ocean ridges
Authors: Johnson Paul , Hutnak Michael
Published: February 2004

A new technique for measuring conductive heat flow from unsedimented volcanic rocks on the sea floor has been tested on two new eruption sites in the NE Pacific. This technique consists of isolating the surficial rocks from sea water using water‐saturated urethane foam as an insulating thermal blanket. The thermal gradient transferred from the outcrop to the thermal blanket is a quantitative measurement of the conductive heat flow that takes place in unsedimented volcanic areas. We deployed two thermal blankets at 13 sites on the 1993 and 1996 Juan de Fuca/Gorda Ridge flows and found (1) a factor of 10 decrease in heat flow over a period of 12 months on the 1993 CoAxial flow, (2) a value of 6950 mW/m² on the 8 month old Gorda flow, and (3) measurements of heat flow versus age‐since‐eruption indicate that newly extruded volcanic units are quite permeable to fluid circulation and cool rapidly by convection in only a few years. These new heat flux data confirm that the extrusive volcanic layer is not the primary heat source for long‐lived, high temperature hydrothermal systems, which must instead rely on a more isolated thermal reservoir within the lower crustal rocks.
Observations of reflected ions and plasma turbulence for satellite potentials greater than the ion ram energy
Authors: Wright K. H. , Stone N. H. , Sorensen J. , Winningham J. D. , Gurgiolo C.
Published: February 2004

During the TSS‐1R mission, the behavior of the ions flowing from the forward hemisphere of the Tethered Satellite System (TSS) satellite was examined as the potential on the satellite was changed from below to above 5 V. The ram energy of the ambient atomic oxygen ions is ∼5 eV. For satellite potentials <5 V, no ions were observed on the ram side of the satellite. When the satellite potential was raised >5 V, ions were observed to be flowing from the forward region of the satellite. In the region sampled, the ion flux was a few percent of the ambient with energies of ∼5 eV. The temperature of the out‐flowing ions was observed to be enhanced, relative to the ambient ionosphere. The net current to the probe package became much more noisy for satellite potentials >5 V as compared with satellite potentials <5 V, indicating a more disturbed plasma environment.
Topographically generated gravity waves in the Brooks Range, Alaska
Authors: Lynch Amanda H.
Published: February 2004

Amplified wind events are identified over the Brooks Range in Alaska, with observed wind speed increasing from calm to 5 ms−1 over 24 to 36 hours. In simulations using an limited area climate system model, the wind events are captured consistently, although generally display greater strength than observed. Cooling associated with the wind events lead to an identification of the NE region of the North Slope of Alaska, below the inversion, as the source region for the air flow. Analysis of the wind event of 7th January 1992 supports the nonlinear hydraulic model of gravity waves.
Enhanced electrodynamic tether currents due to electron emission from a neutral gas discharge: Results from the TSS‐1R Mission
Authors: Gilchrist B. E. , Bonifazi C. , Bilén S. G. , Raitt W. J. , Burke W. J. , Stone N. H. , Lebreton J. P.
Published: February 2004

During the reflight of the first electrodynamic Tethered Satellite System (TSS‐1R) mission, the unplanned separation of the tether at the Orbiter end resulted in the highest tether current during the mission. In the moments just prior to the tether separation with 19.7 km of tether deployed and a generated electromotive force (EMF) of 3482 V, currents reaching approximately 0.97 A were shunted through the tether to the Orbiter electrical ground, which was in contact with the ionosphere primarily through its main engine surfaces. This current level was nearly twice as large as observed during any nominal operating period. As the failure point of the tether entered into the ambient plasma, the current increased to 1.1 A and maintained this level even after the break for approximately 75 s. The principal surprise in these results was that the broken end of the tether, with only a few short strands of copper wire, could support higher currents than the much larger Orbiter conducting surface areas. Analysis of possible current enhancement mechanisms revealed that only a gas‐enhanced electrical discharge, providing an electron emission source, was plausible. Ground plasma chamber tests confirmed this analysis. The TSS‐1R results thus represent the highest electron current emission from a neutral plasma source yet demonstrated in a space plasma. This is of interest for current collection processes in general and plasma contactor development in particular.
A persistent imbalance in HOx and NOx photochemistry of the upper troposphere driven by deep tropical convection
Authors: Prather Michael J. , Jacob Daniel J.
Published: February 2004

Convection in the tropics turns over the upper troposphere at rates (0.08 d−1) comparable to photochemical processes controlling the absolute abundance of HOx (OH + HO2) and the abundance of NOx (NO + NO2) relative to HNO3. Here we identify convection of boundary‐layer CH3OOH as a primary source of HOx to the upper troposphere. Turnover of NOx leads to NO/HNO3 ratios much higher than predicted for local photochemical steady‐state. Through convective transport the upper troposphere is more photochemically active in producing O3, an important greenhouse gas.