bluuebunny/crossref_metadata_2025 huggingface dataset:
The coseismic geodetic signature of the 1999 Hector Mine earthquake
Authors: Hurst Kenneth J. , Argus Donald F. , Donnellan Andrea , Heflin Michael B. , Jefferson David C. , Lyzenga Gregory A. , Parker Jay W. , Smith Mark , Webb Frank H. , Zumberge James F.
Published: February 2004

The M = 7.1 Hector Mine earthquake ruptured the Lavic Lake fault near Twentynine Palms, CA at 09:46 UTC October 16, 1999. Because it occurred near the eastern edge of the Southern California Integrated GPS Network (SCIGN), a network of permanent, continuously recording GPS receivers for measuring the crustal deformation field around Los Angeles, CA, it was possible to determine the deformation associated with the earthquake with unprecedented speed and reliability. Thirty‐four stations recorded displacements over the 3‐sigma level. The displacements measured with GPS can be modeled by a fault 46.2±2.6 km long, 8.2±1.0 km wide, striking 330°, dipping 84° east, with 301±36 cm right lateral strike‐slip, and 145±36 cm of east‐up dip‐slip, yielding a potency of 1.3 km³ and geodetic moment of 3.8 × 1026 dyne‐cm. The trace and dip of the model fault is consistent with the observed ground rupture and seismic focal mechanisms.
A coral δ18O record of ENSO driven sea surface salinity variability in Fiji (south ‐western tropical Pacific)
Authors: Le Bec Nolwenn , Julliet‐Leclerc Anne , Corrège Thierry , Blamart Dominique , Delcroix Thierry
Published: February 2004

The role of salinity in the dynamics and thermodynamics of El Niño ‐ Southern Oscillation (ENSO) events is increasingly being investigated. However, instrumental records of salinity are scarce and short in the tropical Pacific, and there is a clear need for a reliable salinity proxy to extend our knowledge of ENSO through time. Here, we present 40 years of δ18O data from a Fiji coral (16°48′S–177°27′E). The coral δ18O signal integrates both sea surface temperature (SST) and sea surface salinity (SSS) variations. On a seasonal timescale, δ18O is mainly driven by SST changes whereas on an interannual ENSO timescale, it is almost exclusively affected by SSS variability. Since interannual fluctuations of SSS are rather well correlated to the Southern Oscillation Index in Fiji, coral δ18O can be used to reconstruct paleo‐salinity data with some level of confidence. This may help for tracking ENSO influences back in time.
1738 years of Mongolian temperature variability inferred from a tree‐ring width chronology of Siberian pine
Authors: D'Arrigo Rosanne , Jacoby Gordon , Frank David , Pederson Neil , Cook Edward , Buckley Brendan , Nachin Baatarbileg , Mijiddorj R. , Dugarjav Chultamiin
Published: February 2004

1738 years (AD 262–1999) of temperature variability are inferred from tree‐ring widths of Siberian pine at Solongotyn Davaa (Sol Dav), a timberline (2420 m) site in Mongolia. This chronology can account for 33% of the temperature variance from 1882–1993. The warmest conditions over the past millennium are during the 20th century. The 1999 ring width has the highest index value over the past millennium. Both warmer and colder intervals are inferred during the “Medieval Warm Epoch”. The most severe cold occurred in the 19th century. Unusual cold and frost in AD 536–545 coincide with extremes in other proxies and historical accounts, confirming a widespread, catastrophic event. Trends resemble those of other Eurasian paleoseries, and hemispheric‐scale reconstructions over the past millennium. More chronologies such as Sol Dav are essential to improve coverage in the uncertain earlier centuries of these reconstructions and their estimates of natural variability relative to recent anthropogenic change.
An improved estimate of the isotopic air‐sea disequilibrium of CO2: Implications for the oceanic uptake of anthropogenic CO2
Authors: Gruber Nicolas , Keeling Charles D.
Published: February 2004

We reevaluate the isotopic air‐sea disequilibrium of CO2 on the basis of a new high‐quality global data set of surface observations of the reduced isotopic ratio (δ13C) of dissolved inorganic carbon (DIC). We find a global mean isotopic air‐sea disequilibrium of 0.62±0.10 permil for 1990. Inserting our estimate into an anthropogenic 13C budget for the period from 1985 to 1995 yields an oceanic uptake of 1.5±0.9 Pg C yr−1, within the range of most other estimates. The large uncertainty of this estimate could be reduced with (i) better characterization of the surface ocean variability in δ13C, (ii) improved knowledge of the air‐sea gas exchange coefficient, and (iii) a significant reduction in the uncertainty associated with the air‐land biosphere disequilibrium.
Arctic climate and atmospheric planetary waves
Authors: Cavalieri Donald J. , Häkkinen Sirpa
Published: February 2004

Analysis of a fifty‐year record (1946–1995) of monthly‐averaged sea level pressure data provides a link between the phases of planetary‐scale sea level pressure waves and Arctic Ocean and ice variability. Results of this analysis show: (1) a breakdown of the dominant wave 1 pattern in the late 1960's, (2) shifts in the mean phase of waves 1 and 2 since this breakdown, (3) an eastward shift in the phases of both waves 1 and 2 during the years of simulated cyclonic Arctic Ocean circulation relative to their phases during the years of anticyclonic circulation, (4) a strong decadal variability of wave phase associated with simulated Arctic Ocean circulation changes. Finally, the Arctic atmospheric circulation patterns that emerge when waves 1 and 2 are in their extreme eastern and western positions suggest an alternative approach for determining significant forcing patterns of sea ice and high‐latitude variability.
The scaling of hydraulic conductivity in rock fracture zones
Authors: Odling Noelle E.
Published: February 2004

Beyond the scale of a few meters, fracture traces as viewed on aerial photographs represent fracture zones. Thus for bulk fractured rock permeability, the hydraulic properties of fracture zones are important. Here, observations on joint zones in sandstones from western Norway are used to build a quantitative model relating joint zone length and effective hydraulic conductivity. Using simple rules for hydraulic conductors in series and parallel applied to joint zone geometry, the ‘effective’ hydraulic aperture (the aperture of a single parallel‐walled channel that conducts the same flow) is estimated for 72 joint zones of known length. A power law relation between trace length, l, and effective hydraulic aperture, be, with an effective exponent of around 0.27 is found which may extend to km scales. This exponent contrasts with values of 0.5 to 2.0 reported for veins.
Mercury cycling in boreal ecosystems: The long‐term effect of acid rain constituents on peatland pore water methylmercury concentrations
Authors: Branfireun Brian A. , Bishop Kevin , Roulet Nigel T. , Granberg Gunnar , Nilsson Mats
Published: February 2004

Sulphate‐reducing bacteria have been identified as primary methylators of mercury (Hg) in the laboratory and in field investigations. However, no studies have investigated the effect of long‐term deposition of sulphate on methylmercury (MeHg) dynamics in peatlands, which are known to be significant sources of MeHg to downstream waters in the boreal forest zone. As an ancillary experiment to a larger project investigating the effects of acid rain constituents on peatland carbon dynamics, the influence of experimentally elevated Na2SO4 and/or NH4NO3 deposition on peat pore water MeHg concentrations was determined using a simple mesocosm experimental design. After three years, additions of S in amounts equivalent to the 1980s dry and wet deposition in Southern Sweden resulted in peat pore water MeHg concentrations up to six times above background levels. Elevated N loads had no effect on pore water MeHg concentrations.
Mean annual temperature trends and their vertical structure in the tropical Andes
Authors: Vuille Mathias , Bradley Raymond S.
Published: February 2004

Mean annual temperature trends in the tropical Andes were determined over the last six decades (1939–1998), to investigate the apparent inconsistency between the observed glacier retreat and the reported slight cooling trend in the lower tropical troposphere after 1979. Our results indicate that temperature in the tropical Andes has increased by 0.10°–0.11°C/decade since 1939. The rate of warming has more than tripled over the last 25 years (0.32°–0.34°C/decade) and the last two years of the series, associated with the 1997/98 El Niño, were the warmest of the last six decades. Temperature trends vary with altitude and show a generally reduced warming with increasing elevation. However, despite the lower rate of warming, the trend toward increased temperatures is still significant at the 95% confidence level, even at the highest elevations. Clearly high elevation surface stations in the Andes do not reflect the slight cooling trend observed in the tropical lower‐troposphere.
The origin of Bahamian Whitings revisited
Authors: Broecker W. S. , Sanyal A. , Takahashi T.
Published: February 2004

Two schools of thought exist regarding the origin of the aragonite needles which make up the milky patches of water prominent on the Bahama Banks. One school views these so‐called whitings as spontaneous precipitates [Cloud, 1962; Shinn et al.,1989; Robbins et al.,1997] and the other views them as stirred up bottom sediment [Broecker and Takahashi, 1966; Morse et al.,1984]. In the paragraphs which follow we summarize what we consider to be iron‐clad radiocarbon and chemical evidence that whitings are dominated by re‐suspended sediment. We offer a new and highly speculative mechanism for this re‐suspension. Black‐tipped sharks which inhabit whitings purposefully stir up the sediment in order to create a trap for fish, much as spiders construct webs as traps for insect prey.
High‐resolution image of the oceanic moho in the subducting Nazca Plate from P‐S converted waves
Authors: Bock Günter , Schurr Bernd , Asch Günter
Published: February 2004

Short‐period P‐S converted waves outline the oceanic Moho of the descending Nazca plate in northern Chile at 24°S. Comparison with hypocentral locations obtained with temporary local seismic networks show that earthquakes inside the subducting oceanic lithosphere of the Nazca plate are located predominantly in the oceanic crust at depths between 70 and 120 km, and probably in the upper mantle at depths below 120 km. The results suggest that dehydration embrittlement as mechanism for intermediate‐depth earthquakes is active both in the former oceanic crust and upper mantle of subducting lithosphere.
FAST observations of ULF waves injected into the magnetosphere by means of modulated RF heating of the auroral electrojet
Authors: Robinson T. R. , Strangeway R. , Wright D. M. , Davies J. A. , Horne R. B. , Yeoman T. K. , Stocker A. J. , Lester M. , Rietveld M. T. , Mann I. R. , Carlson C. W. , McFadden J. P.
Published: February 2004

Results are reported from an experiment in which the HF high power facility at Tromsø was utilised to inject artificial ULF waves into the magnetosphere by means of modulated heating of the auroral electrojet. Local electric field oscillations associated with the artificially stimulated ULF waves were detected on board the FAST spacecraft, at an altitude of 2550 km. In addition, a modulated downward flux of electrons was also detected. The artificially excited waves, together with these energised downward electrons, were observed in a narrow region only a few tens of km across the geomagnetic field, which mapped down the geomagnetic field line to the heated volume in the ionosphere. Furthermore, the downward flux exhibited energy dispersion in a manner that was consistent with the artificially excited waves having followed the geomagnetic field line out beyond the spacecraft, where they appear to have stimulated electron precipitation back down the field line.
Traveling ionospheric disturbances detected in the FRONT Campaign
Authors: Saito A. , Nishimura M. , Yamamoto M. , Fukao S. , Kubota M. , Shiokawa K. , Otsuka Y. , Tsugawa T. , Ogawa T. , Ishii M. , Sakanoi T. , Miyazaki S.
Published: February 2004

The F‐region Radio and Optical measurement of Nighttime TID (FRONT) campaign was conducted to clarify the non‐classical features of traveling ionospheric disturbances (TIDs) at mid‐latitudes in May, 1998 and August, 1999. A cluster of all‐sky CCD cameras and a GPS receiver network observed a wide area of the ionosphere over Japan to detect the spatial structure and temporal evolution of TIDs. The propagation direction of the nighttime TID detected during the FRONT campaign periods is restricted to the southwest. The time evolution of their amplitude indicates that the TID structure is intensified as it travels from high‐latitudes to low‐latitudes. The significant coincidence between the structures of 630 nm band airglow and total electron content indicates that the perturbations take place in the bottomside of the ionospheric F region. Coherent echoes from the field‐aligned irregularities were observed by the MU radar in the nights when the TID activity was high.
Focusing of eruptions by fracture wall erosion
Authors: Hieronymus Christoph F. , Bercovici David
Published: February 2004

Lithospheric flexural stresses beneath volcanic loads are horizontally strongly compressive towards the top of the lithosphere. Thus, while magma transport through the brittle lithosphere occurs via fractures, the fracture paths under the volcanic center are predicted by stress trajectories to be horizontal and thus unable to supply melt to the volcanic edifice where eruptions are observed. Moreover, the magnitude of the compressive stresses under large loads would close down any vertical magma paths. Both problems may be resolved by additional stresses due to melting or thermomechanical erosion of fracture walls developing over the life‐span of the volcano. Fractures form and close frequently in the seismogenic zone of the lithosphere, with each fracture eroding away a small amount of material. The total amount of material removed makes the stress field more tensile, thereby facilitating the long‐lived and vertically oriented magma pathways necessary to build discrete volcanic structures.
Pitch angle distribution of relativistic electrons in the inner radiation belt and its relation to equatorial plasma wave turbulence phenomena
Authors: Morioka Akira , Misawa Hiroaki , Miyoshi Yoshizumi , Oya Hiroshi , Iizima Masahide , Nagai Tsugunobu
Published: February 2004

The pitch angle distribution of relativistic electrons in the inner radiation belt and its relation to local plasma waves were investigated using the data from the Akebono satellite. It was found that energetic electrons (>1 MeV) in the inner radiation belt showed an unexpected dumbbell distribution near the magnetic equator. This feature was commonly observed both in magnetically disturbed and undisturbed conditions. It was also found that this anomalous pitch angle distribution of energetic electrons was always accompanied with the enhancement of local UHR waves around the magnetic equator. These newly found features indicate the existence of an unknown wave‐particle interaction process between the relativistic electrons and quasi‐electrostatic plasma waves in the equatorial region of the plasmasphere.
Determination of semi‐diurnal ocean tide loading constituents using GPS in Alaska
Authors: Khan Shfaqat Abbas , Tscherning Carl Christian
Published: February 2004

During the past years, the accuracy of relative positioning using differential GPS (DGPS) has been improved significantly. The present accuracy of DGPS allows us to directly estimate the differential amplitudes and Greenwich phase lags of the main semi‐diurnal ocean tide loading constituents (S2, K2, M2 and N2). For this purpose a test is carried out using two GPS stations in Alaska. One station, Chi3, is located on an island in the Gulf of Alaska, while the second station, Fair, is located far away from the coastal areas. Processing hourly GPS solutions for the baseline between Fair and Chi3 during 49 days gives differential amplitudes of 23.21 mm and 4.71 mm for M2 and N2, respectively, while the theoretically differential amplitudes of M2 and N2 are 20.90 mm and 4.21 mm, respectively (using the GOT99.2 ocean tide model). The diurnal ocean tide loading constituents are not considered, because unmodeled troposphere effects increase the noise level near the diurnal frequency band and prevent us from obtaining significant results.
A new satellite deep convective ice index for tropical climate monitoring: Possible implications for existing oceanic precipitation data sets
Authors: Robertson Franklin R. , Spencer Roy W. , Fitzjarrald Daniel E.
Published: February 2004

The tropical atmosphere is continually overturning, with deep moist convective cloud systems exporting energy from the subcloud layer and depositing it in the upper troposphere. A new satellite index of this deep convective activity is based upon measurements of large ice particles in the upper portions of tropical convective complexes. This 20‐year record reveals a strong signal of the El Niño Southern Oscillation (ENSO), with 10 to 15% upward (downward) swings in the deep convective index during El Niño (La Niña). Warming of tropical sea surface temperatures (SST), whether from anthropogenically‐produced greenhouse gases or natural climate variability, is expected to be associated with more convective overturning of the atmosphere. While other tropical precipitation climatologies vary dramatically in their support of this relationship, the present deep convective ice (DCI) index shows a strong correlation between interannual variations of tropical convection and SST.
New studies of the visible and near‐infrared absorption by water vapour and some problems with the HITRAN database
Authors: Belmiloud Djedjiga , Schermaul Roland , Smith Kevin M. , Zobov Nikolai F. , Brault James W. , Learner Richard C. M. , Newnham David A. , Tennyson Jonathan
Published: February 2004

New laboratory measurements and theoretical calculations of integrated line intensities for water vapour bands in the near‐infrared and visible (8500–15800 cm−1) are summarised. Band intensities derived from the new measured data show a systematic 6 to 26% increase compared to calculations using the HITRAN‐96 database. The recent corrections to the HITRAN database [Giver et al., J. Quant. Spectrosc. Radiat. Transfer, 66, 101–105, 2000] do not remove these discrepancies and the differences change to 6 to 38%. The new data is expected to substantially increase the calculated absorption of solar energy due to water vapour in climate models based on the HITRAN database.
The ring effect in skylight polarisation
Authors: Aben I. , Stam D. M. , Helderman F.
Published: February 2004

Skylight reflectivity and polarisation spectra across the ultraviolet (UV) and visible (VIS) wavelength range show abundant features coinciding with solar Fraunhofer lines. Although the appearance of these features in reflectivity spectra has been shown to be caused by rotational Raman scattering by atmospheric molecules, quantitative modelling of this so‐called Ring effect as observed in polarisation spectra of scattered sunlight is still lacking. Accurate modelling of UV‐VIS radiances and polarisation at high‐spectral resolution has, however, become increasingly important because of the increased use of high‐spectral resolution spectrophotometers, that are often highly polarisation sensitive. In this paper, we present high‐spectral resolution skylight polarisation spectra and show that the Ring effect in these spectra can be simulated using a radiative transfer program that includes rotational Raman scattering up to the second order of scattering.
Fault zone amplified waves as a possible seismic hazard along the Calaveras Fault in central California
Authors: Spudich P. , Olsen K. B.
Published: February 2004

The Calaveras fault lies within a low velocity zone (LVZ) 1–2 km wide near Gilroy, California. Accelerographs G06, located in the LVZ 1.2 km from the Calaveras fault, and G07, 4 km from G06, recorded both the M 6.2 1984 Morgan Hill and the M 6.9 1989 Loma Prieta earthquakes. Comparison of the ground motions shows that a large 0.6–1.0 Hz velocity pulse observed at G06 during the Morgan Hill event may be amplified by focussing caused by the LVZ. Such amplified waves might be a mappable seismic hazard, and the zone of increased hazard can extend as much as 1.2 km from the surface trace of the fault. Finite‐difference simulations of ground motions in a simplified LVZ model show a zone of amplified motion similar to the observations.
The effects of variable thermal conductivity on mantle heat‐transfer
Authors: van den Berg Arie P. , Yuen David A. , Steinbach Volker
Published: February 2004

We have examined the styles of steady‐state convective heat transfer for two kinds of mantle thermal conductivity models in an aspect‐ratio one box. We have employed the phonon portion of the thermal conductivity model of Hofmeister (1999) and varied the radiative component in this model. We have also considered a second model which emphasizes radiative heat transfer and has a high contribution in the lower mantle. We have conducted constant viscosity calculations out to a surface Ra of 1010. Variable conductivity enhances in most cases the surface heat flow. The smallest deviation from the constant conductivity model comes from the phonon model with the parameters associated with oxides. Larger heat flow is obtained with silicates and increasing radiative contributions associated with the values of Shankland et al. (1979). The highest heat flow values are obtained for the radiatively dominated model, where the thermal conductivity in the deep mantle can be a factor of 50 greater than the surface conductivity value.
Vertical correlations of water vapor in GCMs
Authors: Sun De‐Zheng , Covey Curt , Lindzen Richard S.
Published: February 2004

Correlations of tropical mean water vapor with its surface values have been calculated for all AMIP1 models and some of the AMIP2 models. The previously noted discrepancy between the GFDL model and rawinsonde data also exists for other models: the interannual correlations of water vapor with its surface values decline to smaller values in observations than in the models. This discrepancy is reduced somewhat after the data from the models were sampled at the same locations where observational data were collected, but remains significant even at low levels. Significant discrepancy between models and observations also exists in the regressions of water vapor on temperature, suggesting something other than differences in the noise level as the main cause for the discrepancy in the vertical correlations between model and rawinsonde observations.
How northward turnings of the IMF can lead to substorm expansion onsets
Authors: Russell C. T.
Published: February 2004

The frequent triggering of the expansion phase of substorms by northward turnings of the interplanetary magnetic field (IMF) can be understood in terms of the existence of two neutral points. The distant neutral point produces a plasma sheet on closed field lines that resupplies the magnetized plasma surrounding the near‐Earth neutral point. As long as the near‐Earth neutral point reconnects in moderately dense plasma, the reconnection rate is low. When the IMF turns northward, reconnection at the distant neutral point ceases but reconnection at the near‐Earth neutral point continues and soon reaches open, low density magnetic field lines where the rate of reconnection is rapid, and a full expansion phase occurs. This model is consistent with the observations of substorms with two onsets: an initial one at low invariant latitudes when reconnection at the near Earth neutral point first begins and the second when reconnection reaches low density field lines at the edge of the plasma sheet and continues into the open flux of the tail lobes. It is also consistent with the occurrence of pseudo breakups in which reconnection at the near Earth neutral point begins but does not proceed to lobe field lines and a full expansion phase.
Comparison of global distributions of zonal‐mean gravity wave variance inferred from different satellite instruments
Authors: Preusse Peter , Eckermann Stephen D. , Offermann Dirk
Published: February 2004

Gravity wave temperature fluctuations acquired by the CRISTA instrument are compared to previous estimates of zonal‐mean gravity wave temperature variance inferred from the LIMS, MLS and GPS/MET satellite instruments during northern winter. Careful attention is paid to the range of vertical wavelengths resolved by each instrument. Good agreement between CRISTA data and previously published results from LIMS, MLS and GPS/MET are found. Key latitudinal features in these variances are consistent with previous findings from ground‐based measurements and some simple models. We conclude that all four satellite instruments provide reliable global data on zonal‐mean gravity wave temperature fluctuations throughout the middle atmosphere.
Multi‐point observation of short‐period mesospheric gravity waves over Japan during the FRONT Campaign
Authors: Shiokawa K. , Ejiri M. K. , Otsuka Y. , Ogawa T. , Kubota M. , Igarashi K. , Saito A. , Nakamura T.
Published: February 2004

Simultaneous observations of short‐period gravity waves were carried out using three all‐sky cooled‐CCD imagers of OH airglow at Moshiri (northern edge of Japan) and at Shigaraki and Bisei (middle part of Japan) during the FRONT campaign of May 1998. These stations were separated by horizontal distances of 250–1300 km, and they offered a unique opportunity to investigate the spatial extent of gravity waves in the mesopause region. The images from Shigaraki and Bisei showed short‐period gravity waves (horizontal wavelength: 20–40 km, phase front: ∼east‐west aligned) moving northward (phase velocity: 20–40 m/s) on May 19, 21 and 22. At Moshiri, similar east‐west waves moving northward were observed on May 19 and 21, indicating a broad horizontal extent of the gravity waves. Waves at Moshiri were not evident on May 22, however. The horizontal wind measured by the MF radar at Wakkanai (near Moshiri) showed height profiles that were similar to those at Yamagawa (southern edge of Japan) on May 19 and 21 but quite dissimilar on May 22. On the basis of these data, we suggest that short‐period gravity waves in the mesopause region can have a broad spatial extent of more than 1000 km. The generation and propagation of internal gravity waves are discussed as a cause of the spatial extent of the waves.
Electron temperature control of PMSE
Authors: Rapp Markus , Lübken Franz‐Josef
Published: February 2004

Recently an artificially induced modulation of polar mesosphere summer echos (PMSE) was observed when the electrons at PMSE altitudes were heated by a ground based heating facility [Chilson et al., 2000]. The PMSE disappeared within a few seconds when the heater was switched on and reappeared within a few seconds when the heater was switched off again. We explain these observations employing a model of electron diffusion in the environment of positive ions and negatively charged aerosols which takes into account enhanced electron temperatures. If the electron temperature equals the neutral gas temperature, electron diffusion is efficiently inhibited due to the multipolar electric field between the aerosols, positive ions, and electrons. If the electron temperature is enhanced, however, the electron diffusivity is increased which compensates the effect of charged aerosols such that spatial structures in the electron gas at scales as small as the radar half wavelength are efficiently destroyed by diffusion. Furthermore, an enhanced electron temperature increases the aerosol charge which supports the decay of electron disturbance through plasma interference effects. The heating experiment has demonstrated that the reduction of electron diffusivity by charged aerosol particles is the underlying physical mechanism for the existence of PMSE.
Antarctic ice streams and outflow channels on Mars
Authors: Lucchitta Baerbel K.
Published: February 2004

New sonar images of the Antarctic sea floor reveal mega‐scale glacial lineations that are strikingly similar to longitudinal flutes in martian outflow channels. The analogs suggest that ice moved through the martian channels in places and carved the flutes. The ice in martian channels may have moved like Antarctic ice streams on deformable debris saturated with water under high pore pressure. On Mars, water at the base of ice‐filled channels may have come from residual water or melt water liberated during past warmer climates or higher heat flows.
Opening‐mode fracture in siliceous mudstone at high homologous temperature—effect of surface forces
Authors: Eichhubl Peter , Aydin Atilla , Lore Jason
Published: February 2004

In analogy to high‐temperature sintering of ceramics and metal powder compacts, the formation of opening‐mode fractures in siliceous mudstone during natural in‐situ combustion of hydrocarbons is attributed to contractile surface forces between mineral grains and an interstitial melt phase. A comparison between bulk density increase during sintering and created fracture space indicates that fracturing resulted from contraction of the rock matrix due to porosity reduction, grain‐scale mass transfer, and high‐temperature mineral formation. It is suggested that contractile surface forces between mineral grains and between mineral grains and pore fluid contribute to subcritical fracture formation under a wide range of subsurface conditions.
Modification of daytime compressional waves by the ionosphere: First results from OERSTED
Authors: Jadhav Geeta , Rajaram Mita , Rajaram R.
Published: February 2004

Ionospheric modulation of compressible hydromagnetic waves has been examined using the scalar magnetic field data obtained from the Oersted satellite and ground magnetic data from the Japanese sector. It is shown that the day side ionosphere introduces significant phase delays for frequencies in excess of about 20 mHz. The phase delay increases with frequency and with increase in the conductivity of the ionosphere. There is also an increase in the amplitude of the wave above equatorial day side ionosphere. The uniformly excellent coherence between the satellite and ground oscillations and systematically good correlation between the filtered time series at the two levels suggests that the compressible hydromagnetic waves are phase coherent over a wide range of latitudes.
Measuring postglacial rebound with GPS and absolute gravity
Authors: Larson Kristine M. , van Dam Tonie
Published: February 2004

We compare vertical rates of deformation derived from continuous Global Positioning System (GPS) observations and episodic measurements of absolute gravity. We concentrate on 4 sites in a region of North America experiencing postglacial rebound. The rates of uplift from gravity and GPS agree within one standard deviation for all sites. The GPS vertical deformation rates are significantly more precise than the gravity rates, primarily because of the denser temporal spacing provided by continuous GPS tracking. We conclude that continuous GPS observations are more cost efficient and provide more precise estimates of vertical deformation rates than campaign style gravity observations where systematic errors are difficult to quantify.
Lower ionospheric modification by lightning‐EMP: Simulation of the night ionosphere over the United States
Authors: Rodger Craig J. , Cho Mengu , Clilverd Mark A. , Rycroft Michael J.
Published: February 2004

It has recently been suggested that successive intense lightning‐electromagnetic pulse (EMP) events could cause significant large‐scale changes to the properties of the nighttime lower ionosphere. In order to examine this quantitatively, data on lightning detected over the United States are combined with the output from a simulation code. During the course of a night strong lightning‐EMP events can lead to significant (∼100% or even greater) increases in the electron density of the lower ionosphere, with the largest increases at ∼90 km altitude. Regions with significant decreases in electron density are also possible. It is shown that changes in the electron temperature of the lower ionosphere are unlikely to be significant. The time required to produce large‐scale changes of ionospheric electron density above an active thunderstorm may explain the observation of a thunderstorm “modification time” before red sprite activity is initiated.
First detection of global dawn‐dusk ionospheric current intensities using Ampère's integral law on Ørsted orbits
Authors: Stauning Peter , Primdahl Fritz
Published: February 2004

The magnetic measurements by the Ørsted satellite in noon‐midnight orbits have enabled the derivation of the global dawn‐dusk oriented ionospheric currents from an Ampère's law closed loop line integral of the geomagnetic vector field along the satellite track. The globally integrated dawn‐to‐dusk ionospheric current is found to be proportional to the geo‐effective solar wind electric field and is around 1 million ampère for a typical solar wind electric field of 2 mV/m. Dividing the Ampère integral into semi‐orbit parts has enabled us to show that the hemispherical total current intensities depend on the respective polar cap conductivities, which relate to the daily and seasonally varying solar illumination. The more illuminated hemisphere conveys up to three times more current from dawn to dusk than does the less illuminated.
Formation of intense nose structures
Authors: Ganushkina Natalia Yu. , Pulkkinen Tuija I. , Bashkirov Vladimir F. , Baker Daniel N. , Li Xinlin
Published: February 2004

We examine one well‐observed event on November 3, 1997, when clear signatures of intense nose structures were observed during substorm activity on three subsequent inner magnetosphere crossings by Polar and Interball Auroral probe. Tracing particles numerically in stationary electric (Volland‐Stern) and magnetic (T96) field models shows that the inward displacement of the intense nose structure in this case could not be formed only by convection in a time‐stationary electric field. We add time varying electric and magnetic fields to the tracing procedure which propagate toward the Earth and represent the dipolarization process at a substorm onset. These results show that particles could be moved into the inner magnetosphere within some tens of minutes, consistent with the observations.
Measurements of NOx emissions from the Antarctic snowpack
Authors: Jones A. E. , Weller R. , Anderson P. S. , Jacobi H.‐W. , Wolff E. W. , Schrems O. , Miller H.
Published: February 2004

It has been shown that NOx is produced photochemically within the snowpack of polar regions. If emitted to the atmosphere, this process could be a major source of NOx in remote snowcovered regions. We report here on measurements made at the German Antarctic station, Neumayer, during austral summer 1999, aimed at detecting and quantifying emissions of NOx from the surface snow. Gradients of NOx measured, and fluxes calculated using local meteorology measurements. On the 2 days of flux measurements, the derived fluxes showed continual release from the snow surface, varying between ∼0 and 3 × 108 molecs/cm²/s. When not subject to turbulence, the variation was coincident with the uv diurnal cycle, suggesting rapid release once photochemically produced. Scaling the diurnal average of Feb. 7th (1.3 × 108 molecs/cm²/s) suggests an annual emission over Antarctica of the order 0.0076TgN.
Wavelet identification of the spatial distribution of fractures
Authors: Sahimi Muhammad , Hashemi Mehrdad
Published: February 2004

We propose a novel and efficient method for identifying the spatial distribution of fractures and faults of field‐scale porous media, such as oil reservoirs and groundwater aquifers. The method is based on wavelet transformation of the porosity logs, and is demonstrated by its applications to synthetic as well as real data.
Influence of a stochastic moist convective parameterization on tropical climate variability
Authors: Lin Johnny Wei‐Bing , Neelin J. David
Published: February 2004

Convective parameterizations used in general circulation models (GCMs) generally only simulate the mean or first‐order moment of convective ensembles and do not explicitly include higher‐order moments. The influence of including unresolved higher‐order moments is investigated using a simple stochastic convective parameterization that includes a random contribution to the convective available potential energy (CAPE) in the deep convective scheme. Impacts are tested in an tropical atmospheric model of intermediate complexity. Adding convective noise noticeably affects tropical intraseasonal variability, suggesting inclusion of such noise in GCMs might be beneficial. Model response to the noise is sensitive not only to the noise amplitude, but also to such particulars of the stochastic parameterization as autocorrelation time.
Chance encounter with a stratospheric kerosene rocket plume from Russia over California
Authors: Newman P. A. , Wilson J. C. , Ross M. N. , Brock C. A. , Sheridan P. J. , Schoeberl M. R. , Lait L. R. , Bui T. P. , Loewenstein M. , Podolske J. R.
Published: February 2004

A high‐altitude aircraft flight on April 18, 1997, detected an enormous aerosol cloud at 20 km altitude near California (37°N). Not visually observed, the cloud had high concentrations of soot and sulfate aerosol, and was over 180 km in horizontal extent. The cloud was probably a large hydrocarbon‐fueled rocket vehicle, most likely burning liquid oxygen and kerosene. One of two Russian Soyuz rockets could have produced the cloud: a launch from the Baikonur Cosmodrome, Kazakhstan on April 6; or one from Plesetsk, Russia on April 9. Parcel trajectories and long‐lived trace gas concentrations suggest the Baikonur launch as the cloud source. Cloud trajectories do not trace the Soyuz plume from Asia to North America, illustrating the uncertainties of point‐to‐point trajectories. This cloud encounter is the only stratospheric measurement of a hydrocarbon‐fueled rocket.
Massive positive and negative ions in the wake of a jet aircraft: Detection by a novel aircraft‐based large ion mass spectrometer (LIOMAS)
Authors: Wohlfrom K.‐H. , Eichkorn S. , Arnold F. , Schulte P.
Published: February 2004

Negative and positive chemiions (CI) were measured by an aircraft‐based large ion mass spectrometer (LIOMAS) in the wake of a jet aircraft (ATTAS) at an altitude of 8 km and at plume ages between 0.6 and 6.2s. CI mass distributions were measured for mass numbers m up to 8500 atomic mass units, and additionally total fractional CI abundances fM for CI with m > 8500 were obtained. Very massive CI were observed even when nearly sulfur free jet fuel was burnt in the ATTAS engines (fuel sulfur content FSC = 2mg/kg). This indicates that a CI growth process was operative which did not involve sulfur, but more likely low volatility organic compounds (LVOC). However, when fuel with an FSC = 118mg/kg was used a significant additional negative CI growth was observed which must be due to sulfur‐bearing molecules, probably sulfuric acid which is formed by oxidation of fuel sulfur. Use of the fuel with higher FSC did not change the size distribution of positive ions significantly. For both FSC the negative ions had a larger mean m compared to the positive ions.
A tentative chronology for the EPICA Dome Concordia Ice Core
Authors: Schwander Jakob , Jouzel Jean , Hammer Claus U. , Petit Jean‐Robert , Udisti Roberto , Wolff Eric
Published: February 2004

A tentative age scale (EDC1) for the last 45 kyr is established for the new 788‐m EPICA Dome C ice core using a simple ice flow model. The age of volcanic eruptions, the end of the Younger Dryas event, and the estimated depth and age of elevated 10Be, about 41 kyr ago were used to calibrate the model parameters. The uncertainty of EDC1 is estimated to ±10 yr for 0 to 700 yr BP, up to ±200 yr back to 10 kyr BP, and up to ±2 kyr back to 41 kyr BP. The age of the air in the bubbles is calculated with a firn densification model. In the Holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum.
The impact of polynyas on the stability of the thermohaline circulation as simulated in a coupled ocean‐atmosphere‐sea ice box model
Authors: Grigg Sian B. , Holbrook Neil J.
Published: February 2004

This study uses a box model of the North Atlantic Ocean to test the stability of the thermohaline circulation under two different climatic regimes: a warmer regime where deepwater formation occurs through open ocean convection; and a cooler regime where deepwater formation occurs with the aid of brine rejection from sea ice formation. We find that the brine rejection mechanism produces a more stable modeled thermohaline circulation than the open ocean convection mechanism, i.e. a circulation which is able to withstand a larger high latitude freshwater perturbation. These results demonstrate that the effects of leads and polynyas on brine rejection rates are important and suggest that the presence of open water within modeled sea ice contributes significantly to the sensitivity of the climate response and cannot easily be ignored.
Polar cap X‐rays and electrons under low density solar wind conditions: Coordinated PIXIE and DMSP observations on 11 May 1999
Authors: Anderson P. C. , McKenzie D. L. , Datlowe D. W. , Hawley J. D. , Petrinec S. M. , Schulz M. , Larson D. E.
Published: February 2004

X‐ray images from 11 May 1999 typically show emissions filling a region above about 75°–80° magnetic latitude with the emitting region centered a few degrees toward mid‐morning from the magnetic pole during a period when the solar wind reached unusually low values. Ionospheric particle measurements show the entire northern polar cap illuminated by precipitating electrons during much of this time, while the southern polar cap was mostly “dark.” The precipitating electrons had multicomponent spectra, one component with characteristic energy ∼200 eV throughout the observation period, and others with time‐varying characteristic energies ranging between ∼3.5 keV and 10 keV, all components with spatial characteristics common to polar rain. Measurements in the solar wind also show similar multicomponent spectra and are relatively well correlated with observations of solar radio bursts and the polar‐cap x‐ray flux. We conclude that the higher energy components were associated with electrons accelerated in solar flares or coronal flare‐like events.
Radar reflections and water content estimation of aeolian sand dune
Authors: Bano Maksim , Girard Jean‐François
Published: February 2004

Many Ground‐penetrating radar (GPR) profiles acquired on the dry aeolian environment have shown a strong reflectivity inside the present‐day dunes. Changes in water content are believed to be the origin of this reflectivity. In this paper we try to model the radar reflections coming from the bottom of a dry aeolian dune by using the 1D wavelet modeling method. The principle of this method is to calculate the effects of the propagation (absorption, dispersion and geometrical spreading) and reflection on a reference wavelet for different values of various parameters, and the best fit between the observed and calculated data leads to the optimum set of parameters. By combining the wavelet modeling method with a semi‐empirical mixing formula for the bulk permittivity of moist sandy soils we estimate the water content and explain the importance of this latter parameter on reflection coefficient and on wavelet modeling.
Propagation of 10–50 mHz ULF waves with high spatial coherence at high latitudes
Authors: Howard T. A. , Menk F. W.
Published: February 2004

We used the IMAGE high latitude magnetometer array from two weeks in March 1996 to study 10–50 mHz (Pc3–4) pulsations that exhibit high coherence over an extended spatial region. These are a small sub‐class of daytime Pc3 activity at high latitudes. Nine of eleven events did not show evidence of field line resonance harmonics. Instead, the observed amplitudes decreased equatorward, and phase relationships indicate poleward propagation. The results suggest that the pulsations are due to incoming fast mode waves driving forced field line oscillations or are propagating direct to the ionosphere. Coherence scale lengths at the ground are of order 1 × 10³ km, and the pulsation frequency often appears to be predicted by the ion‐cyclotron mechanism in the upstream solar wind.
Non‐adiabatic response of relativistic radiation belt electrons to GEM magnetic storms
Authors: McAdams K. L. , Reeves G. D.
Published: February 2004

The importance of fully adiabatic effects in the relativistic radiation belt electron response to magnetic storms is poorly characterized due to many difficulties in calculating adiabatic flux response. Using the adiabatic flux model of Kim and Chan [1997a] and Los Alamos National Laboratory geosynchronous satellite data, we examine the relative timing of the adiabatic and non‐adiabatic flux responses. In the three storms identified by the GEM community for in depth study, the non‐adiabatic energization occurs hours earlier than the adiabatic re‐energization. The adiabatic energization can account for only 10–20% of the flux increases in the first recovery stages, and only 1% of the flux increase if there is continuing activity.
Calibration changes in the isotopic thermometer for snow according to different climatic states
Authors: Holdsworth Gerald
Published: February 2004

Bore hole thermometry indicates that the estimated temperature shift at Summit (Greenland) from the Last Glacial to Holocene times was ∼50% higher than the value obtained using the traditional isotopic δ (T) thermometer calibrated with today's data. A mechanism offered by Boyle [1997] to explain the anomalous ice core δ shift is examined. The mechanism, called the Boyle Effect, is theoretically possible but if it operated at Summit, it appears to be only capable of accounting for slightly more than half of the Summit δ 18O anomaly of ∼4.3‰. A new semi‐quantitative mechanism is proposed that could account for the remaining part of the anomaly. Other mechanisms have been advanced but they are not so amenable to quantitative application and testing.
A new type of sea bed waves
Authors: Knaapen Michiel A. F. , Hulscher Suzanne J. M. H. , de Vriend Huib J. , Stolk Ad
Published: February 2004

Sandy beds of shallow tidal seas often exhibit a range of rhythmic patterns, from small‐scale ripples a few metres long to large tidal sandbanks with a wavelength of kilometres. For example, on the access route to Rotterdam harbour ships cross a field of sandwaves. The crests of these sandwaves determine the effective navigation depth. To warrant navigability, the North Sea Directorate of the Netherlands Ministry of Transport, Public Works and Water Management continually monitors the bathymetry in the sandwave area, originally using echo sounding. Our analysis of these data has revealed a new rhythmic pattern, in addition to the well‐known sandwaves and tidal sandbanks. The wavelength of this new pattern, labelled here as long bedwaves, is three times the one of sandwaves, and the crest orientation is different. Interference of the three modes leads to the rather complex bathymetry revealed by echo soundings.