bluuebunny/crossref_metadata_2025 huggingface dataset:
The Utopia Basin revisited: Regional slope and shorelines from MOLA profiles
Authors: McGill George E.
Published: February 2004

MOLA profiles indicate that Utopia Planitia, including the Utopia Basin, has been tilted northward by ∼0.025°since formation of the basin but no later than mid‐Late Hesperian. This tilt could be a relic of the endogenic formation of the global dichotomy in late Noachian to early Hesperian by a process involving subcrustal erosion in the lowland. The Utopia Basin survives as a deep, circular depression within Utopia Planitia. Along its south flank are several horizontal or near horizontal terraces and benches that may be shorelines of an extensive northern lowland ocean and a more restricted lake within the Utopia Basin. The large size (up to 200 km wide) of these putative shorelines represents a major geomorphic problem to be solved.
Age vs depth of glacial ice at South Pole
Authors: Price P. B. , Woschnagg K. , Chirkin D.
Published: February 2004

Knowledge of age as a function of depth in glacial ice is important for both glaciology and paleoclimatology. For sites near a ridge or dome, an ice flow model together with information on accumulation rate provides a first approximation. If the accumulation rate is high enough, annual layering of isotopes and dust measured in a solid core can provide a precise age vs depth relationship. For South Pole, the flow geometry is not simple and no deep core exists. Nevertheless, by remotely sensing peaks in scattering and absorption of light from pulsed sources buried at depths down to 2200 m, we have been able to determine age vs depth for ages up to 65,000 years. Analysis of radar isochrons by Siegert and Hodgkins provides a rough extension of the age vs depth model to ∼165,000 years near bedrock.
Satellite observations of a pacific moisture surge associated with flooding in Las Vegas
Authors: Berg Wesley K. , Anderson Donald M. , Bates John J.
Published: February 2004

A severe storm struck Las Vegas, Nevada, on July 8, 1999 causing widespread flooding and leading to a loss of life. SSM/I and GOES satellite observations reveal that this event was associated with a moisture surge originating in the tropical eastern Pacific. An evaluation of SSM/I and GOES imagery from June through September 1999 indicates that several moisture surges occurred during the North American monsoon season, seldom reaching Las Vegas, but sometimes pushing tropical moisture as far north as Lake Tahoe. The ability to identify and track these surges offers possibilities for improved understanding of the conditions leading to devastating storm events in northwestern Mexico and the southwestern United States.
Reflectivity variations off the Peru Coast: Evidence for indirect effect of anthropogenic sulfate aerosols on clouds
Authors: Kuang Zhiming , Yung Yuk L.
Published: February 2004

Using reflectivity measurements from the Total Ozone Mapping Spectrometer (TOMS), we show that over the months when stratocumulus clouds are prominent off the Peru Coast, the ultraviolet (UV) reflectance of two marine sites is consistently higher than that of the surroundings. The regions of reflectivity enhancement coincide with large anthropogenic sulfate aerosol emission sources, and the magnitude of the enhancement has a strong seasonal dependence that is related to the seasonal cloud movement. We propose the indirect aerosol effect as a plausible explanation for the reflectivity observations.
On the use of isotopic composition measurements of volatile organic compounds to determine the “photochemical age” of an air mass
Authors: Rudolph J. , Czuba E.
Published: February 2004

It is shown that stable carbon isotope ratio measurements in atmospheric volatile organic compounds can be used to determine the photochemical age of the studied compounds. This “Isotopic Hydrocarbon Clock” has several advantages compared to the conventional “Hydrocarbon Clock”. Due to the small Kinetic Isotope Effects for the reaction of hydrocarbons with OH‐radicals, the photochemical ages derived from changes in isotopic composition are the correct linearly averaged age of the studied compounds, independent of the mixing of air parcels with different photochemical ages. The uncertainties of photochemical ages derived from isotopic composition measurements of atmospheric non‐methane hydrocarbons depend primarily on the accuracy of stable carbon isotope ratio measurements, the Kinetic Isotope Effect for the reaction of hydrocarbons with OH‐radicals and the variability of isotopic composition of hydrocarbon sources. Uncertainty analysis shows that the “Isotopic Hydrocarbon Clock” is not only a theoretical possibility but a viable method to determine the photochemical age of atmospheric hydrocarbons.
Do emissions from ships have a significant impact on concentrations of nitrogen oxides in the marine boundary layer?
Authors: Kasibhatla P. , Levy H. , Moxim W. J. , Pandis S. N. , Corbett J. J. , Peterson M. C. , Honrath R. E. , Frost G. J. , Knapp K. , Parrish D. D. , Ryerson T. B.
Published: February 2004

The potential impact of ship emissions on concentrations of nitrogen oxides and reactive nitrogen compounds in the marine boundary layer is assessed using a global chemical transport model. The model predicts significant enhancements of these compounds over large regions, especially over the northern midlatitude oceans. This result is consistent with a recently published study, though the impacts predicted here are more widespread and the peak enhancements are not as large. However, comparisons of model results with recent measurements over the central North Atlantic Ocean do not provide support for these model predictions. While one cannot completely overlook the possibility that emissions of nitrogen oxides from ships may be overestimated, our analysis suggests that there may be a gap in our understanding of the chemical evolution of ship plumes as they mix into the background atmosphere in the marine boundary layer. On a related note, it is also possible that the overestimate of the impacts of ships on nitrogen oxides in the marine boundary layer by global models is due to the lack of parameterized representations of plume dynamics and chemistry in these models.
The influence of a ductile crustal zone on glacial isostatic adjustment: Geodetic observables along the U.S. East Coast
Authors: Di Donato G. , Mitrovica J. X. , Sabadini R. , Vermeersen L. L. A.
Published: February 2004

We consider the influence of a 15 km thick ductile crustal layer of viscosity 1018 Pa s embedded in an elastic 80 km lithosphere on predictions of on‐going glacial isostatic adjustment (henceforth ‘GIA’) along the U.S. east coast. Crustal velocities are perturbed by 0.5 mm/yr, or more, by the inclusion of the ductile layer. Furthermore, perturbations in predictions of sea‐level rates along the U.S. east coast due to the ductile layer have a geographic pattern that is similar to residual trends evident in previous GIA corrections of tide gauge records along this coast.
Spatial slip distribution of the September 20, 1999, Chi‐Chi, Taiwan, Earthquake (MW7.6) —Inverted from teleseismic data
Authors: Ma Kuo‐Fong , Song Teh‐Ru Alex , Lee Shiann‐Jong , Wu Hsiang‐I
Published: February 2004

The teleseismic waveforms of the MW7.6 September 20, 1999 Chi‐Chi earthquake were examined to obtain the quick information on the fault rupture process. The deconvolution results show the fault ruptured from south to the north, and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane. The spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km × 15km. The maximum slip was about 8 m located at about 45 km to the north of the epicenter. The slip distributions obtained in this study have a good agreement with the observed surface breaks. The comparable static and the dynamic stress drops of about 11 Mpa in the large slip region indicate that the melting/fluid pressurization might have taken place in this earthquake. It reduces the dynamic friction and results in the large slip observed.
Solar cycle length stochastic association with Caspian sea level
Authors: Lyatkher Victor M.
Published: February 2004

Variations of the sunspot period smoothed by a special filter have been found to be strongly correlated with long‐term variations at the level of the Caspian Sea and the evaporation of the Aral Sea. The Caspian Sea's reply is delay on 10–16 years. The Aral Sea evaporation's replay interval is rather similar. It may be explained by the influence of the heat transportation by the Gulfstream flow in the Atlantic Ocean and changing the wind trend over the Caspian Sea.
Geodetic constraints on the rigidity and relative motion of Eurasia and North America
Authors: Kogan Mikhail G. , Steblov Grigory M. , King Robert W. , Herring Thomas A. , Frolov Dmitry I. , Egorov Sergei G. , Ye. Levin Vasily , Lerner‐Lam Arthur , Jones Angus
Published: February 2004

GPS observations in northeastern Asia, when combined with observations from the global network for the period 1992–1999, yield an angular rotation vector between Eurasia and North America consistent with and a factor of two more precise than estimates derived using GPS or VLBI data previously available from only western Eurasia. The new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the NUVEL‐1A global plate model, suggesting a significant change in the relative motion of Eurasia and North America over the past 3 Myr. The standard deviations of horizontal velocities from rigid plate motion for nineteen stations in Eurasia and ten in North America are less than 1 mm/yr; the observations place an upper bound of 2 mm/yr at 95% confidence for relative motion between western and eastern Eurasia.
Climate signal mapping and an application to atmospheric tides
Authors: Sherwood Steven C.
Published: February 2004

When analyzing irregularly sampled data to obtain climate signals, a typical starting point is to use spatial analysis methods to map observations onto a regular grid. Clear benefits are possible, however, from an alternative approach in which the desired signals are first estimated directly at the observing locations. The most important benefits relate to accuracy and error analysis. These principles are illustrated using the example of atmospheric tides. When properly estimated, the tides agree remarkably well with those simulated by the Goddard Earth Observing System general circulation model and, above the tropopause, are comparable to the mean meridional flow.
Rocket‐borne mesospheric measurement of heavy (m≫10 amu) charge carriers
Authors: Horányi M. , Robertson S. , Smiley B. , Gumbel J. , Witt G. , Walch B.
Published: February 2004

A rocket‐borne probe has been developed to detect charged atmospheric aerosols. The probe is a current collecting surface, shielded by a magnetic field to prevent the detection of electrons and ions below a threshold in mass. During the first test flight above White Sands, New Mexico, a narrow layer of positive charge carriers was detected at an altitude of 86.5 km with vertical extent of ≈500 m, most likely a sudden E‐layer related to the deposition of meteoric metal ions. A wide layer of negative charge carriers was observed in the altitude range of 75–86 km, consistent with the density of negative ions in this altitude range.
The diurnal cycle of convection, clouds, and water vapor in the tropical upper troposphere
Authors: Soden Brian J.
Published: February 2004

Hourly observations of the 6.7 µm water vapor radiances from geostationary satellites are used to document the diurnal cycle in upper tropospheric water vapor and its relationship to cloud cover and convection. A coherent diurnal cycle in tropical water vapor is observed which lags the variations in cloud cover by approximately 2 hours. The variations in upper tropospheric cloud and water vapor occur (roughly) in phase with changes in deep convection over land, but nearly 12 hours out of phase with those over ocean. This feature is shown to be associated with differences in the vertical structure of land and ocean convection and offers a useful test of convective parameterizations in atmospheric models.
Model and measurements show Antarctic ozone loss follows edge of polar night
Authors: Lee A. M. , Roscoe H. K. , Oltmans S.
Published: February 2004

A three‐dimensional chemical‐transport model of the stratosphere has been used to study the 1996 austral winter and spring. Both the model and ozonesonde measurements show that ozone depletion associated with the Antarctic ozone hole follows the edge of polar night: very little ozone‐depleted air mixes ahead of the terminator as it sweeps poleward, until the terminator reaches 80°S. Other details of the model ozone field show very good agreement with measurements.
Modeling climate shift of El Nino variability in the Holocene
Authors: Liu Zhengyu , Kutzbach J. , Wu Lixin
Published: February 2004

A coupled ocean‐atmosphere general circulation model is used to investigate climatic shift of El Nino in the Holocene. The model simulates a reduced ENSO intensity in the early and mid‐ Holocene, in agreement with paleoclimate record. The ENSO reduction is proposed to be caused by both an intensified Asian summer monsoon and a warm water subduction from the South Pacific into the equatorial thermocline.
Effect of burning C3 and C4 plants on the magnetic susceptibility signal in soils
Authors: Lu Houyuan , Liu Tungsheng , Gu Zhaoyan , Liu Baozhu , Zhou Liping , Han Jiamao , Wu Naiqin
Published: February 2004

To understand the origin of the ultrafine pedogenic components responsible for the magnetic susceptibility (MS) enhancement remains a major challenging problem, in linking the magnetic signal with paleoclimatic conditions. Here we examine the influence of natural fires on the MS signal of both plants and modern soils and in particular the MS difference between C3 and C4 plant ashes and their influence possibly on soil magnetic susceptibility. We demonstrate that burning of C3 and C4 plants can enhance MS signal of modern soils. We show that C4 plants have greater potential to enhance the MS signal. The average MS value of C4 plant ashes is (532±61)×10−8m³ kg−1, much higher than the average MS value of (120±65)×10−8m³ kg−1 of C3 plant ashes. The Fe2O3 concentration in C4 plant is two to four times higher than that in C3 plant. One burning of the grassland, mainly consisting of C4 plants, can enhance MS value of the surface soil up to about 30–40%.
Postglacial rebound in a non‐Newtonian spherical Earth
Authors: Giunchi Carlo , Spada Giorgio
Published: February 2004

Using finite‐elements we study the postglacial rebound in an axisymmetric Earth with a non‐Newtonian rheology. Our approach allows for the first time a self‐consistent study of the effect of a power‐law creep on the long‐wavelength deformations, which cannot be performed using flat models. We show that, for a non‐Newtonian upper mantle, the time‐variations of the low‐degree Stokes coefficients become largely insensitive to the viscosity of the lower mantle. This is in contrast with previous evidence based on Newtonian models, which emphasized the importance of the low degree signatures for constraining the lower mantle viscosity.
The effect of elastic strain on the microstructure of free surfaces of stressed minerals in contact with an aqueous solution
Authors: den Brok S. W. J. , Morel J.
Published: February 2004

The influence of gradients in bulk elastic strain energy on the dissolution and growth behaviour of minerals in rocks is commonly considered negligible. We experimentally observed, however, that regular arrays of macroscopically visible etch grooves may develop on the originally smooth free surfaces of soluble crystals held in an undersaturated aqueous solution if the crystals are only elastically stressed. These grooves are oriented perpendicular to the compressive stress. They disappear soon after the stress is taken off. The formation of the grooves is well explained by recent theories on the instability of the surface of stressed solids. Development of such instabilities could significantly affect the grain boundary structure in rocks, and have a major effect on dissolution and growth processes.
Observations of VHF source powers radiated by lightning
Authors: Thomas R. J. , Krehbiel P. R. , Rison W. , Hamlin T. , Harlin J. , Shown D.
Published: February 2004

Three‐dimensional lightning mapping observations have been used to estimate the peak source powers radiated by individual VHF events of lightning discharges. The peak powers vary from minimum locatable values of about 1 W typically up to 10–30 kW or more in the 60–66 MHz passband of the receivers. An energetic positive bipolar event radiated in excess of 300 k W peak power. The strongest radiation sources tended to be observed in the upper part of storms, corresponding to the upper positive charge region, where the breakdown is of negative polarity. The results illustrate the bidirectional nature of intracloud discharges, with the largest source powers being along the negative portion of the discharge and an order of magnitude greater than the source powers along the positive portion. Overall, the source powers follow an approximate P−1 distribution for powers above about 100 W. The radiation sources indicate the location of the main charge regions in a storm; sample comparisons with radar data show that the main negative charge coincided with the precipitation core
Poroelastic coupling between the 1992 Landers and Big Bear Earthquakes
Authors: Masterlark T. , Wang H.
Published: February 2004

A three‐dimensional finite element model was constructed to investigate the significance of poroelastic coupling between the 1992 Landers and Big Bear earthquakes in southern California. The homogeneous poroelastic model predicted a maximum increase in left lateral slip potential (change in shear stress less the change in effective fault normal stress scaled by a coefficient of friction) along the southwest part of the Big Bear fault, consistent with the epicentral location. In contrast, slip potential calculated for a weak fault zone in a state of isotropic stress for drained conditions, indicated a maximum increase along the northeast part of the Big Bear fault.
Along strike variations in the electrical structure of the San Andreas Fault at Parkfield, California
Authors: Unsworth Martyn , Bedrosian Paul , Eisel Markus , Egbert Gary , Siripunvaraporn Weerachai
Published: February 2004

Magnetotelluric exploration has been used to image along strike variations in the electrical resistivity structure of the San Andreas Fault at Parkfield, California. A low resistivity wedge extending to a depth of several kilometers is continuous over a horizontal distance of 8 km. The base of the wedge is coincident with the shallowest microearthquakes. A change in the electrical and fluid connection of the San Andreas Fault with a low resistivity zone in the Franciscan formation is observed along the Parkfield segment.
Introducing probabilistic aftershock hazard mapping
Authors: Wiemer Stefan
Published: February 2004

Aftershocks to large earthquakes pose a significant hazard, a fact that was highlighted by damaging aftershocks to the 1999 Turkey and Taiwan mainshocks. A new approach is introduced to quantify this hazard in terms of physical parameter maps that forecast the probabilistic aftershock hazard based on the observed spatially varying aftershock activity. For two case studies, the Landers and Northridge mainshocks, probabilistic aftershock hazard maps are shown to improve conventional aftershock hazard assessment.
Warm core ring velocities inferred from NSCAT
Authors: Cornillon Peter , Park Kyung‐Ae
Published: February 2004

The NASA scatterometer, NSCAT, was designed to estimate from space the wind velocity relative to the ocean surface velocity. Assuming that the spatial scale of the meteorological forcing giving rise to the wind is large compared with the diameter of a warm core ring, it should be possible to obtain information about the currents in the ring from the demeaned scatterometer winds. To test this hypothesis, 14 NSCAT passes obtained within three days of clear AVHRR‐derived sea surface temperature images showing a warm core ring were analyzed for evidence of circulation in the rings. The residual wind vectors for the 14 scatterometer passes were binned and averaged by radial distance from ring center. The mean azimuthal component of the speed compares well with ADCP data collected in one of the rings: a maximum of ≈ 0.89 m/s ≈ 50 km from ring center compared with 0.88 m/s and 1.0 m/s for the two ADCP transects, both also at 50 km from ring center.
Propagation of North Pacific interdecadal subsurface temperature anomalies in an ocean GCM
Authors: Nonaka Masami , Xie Shang‐Ping
Published: February 2004

Propagation of subsurface North Pacific interdecadal variations is investigated with an ocean general circulation model forced by observed sea surface temperature anomalies. Subsurface temperature anomalies subducted in the central subtropical North Pacific take a more westward pathway than a passive “temperature” tracer and reach the western boundary to the north of the bifurcation latitude. This prevents them from extending into the equator. On the boundary between the subtropical and the subarctic gyres, on the other hand, the upper 500 m heat content anomaly is found to propagate eastward as high vertical modes of Rossby waves advected by the mean eastward current. This notion is supported by a sign reversal in temperature anomaly underneath.
The effect of spatial and temporal accumulation rate variability in west Antarctica on soluble ion deposition
Authors: Kreutz K. J. , Mayewski P. A. , Meeker L. D. , Twickler M. S. , Whitlow S. I.
Published: February 2004

Annually‐dated snowpit and ice core records from two areas of West Antarctica are used to investigate spatial accumulation patterns and to evaluate temporal accumulation rate/glaciochemical concentration and flux relationships. Mean accumulation rate gradients in Marie Byrd Land (11–23 gcm−2yr−1 over 150 km, decreasing to the south) and Siple Dome (10–18 gcm−2yr−1 over 60 km, decreasing to the south) are consistent for at least the last several decades, and demonstrate the influence of the offshore quasi‐permanent Amundsen Sea low pressure system on moisture flux into the region. Local and regional‐scale topography in both regions appears to affect orographic lifting, air mass trajectories, and accumulation distribution. Linear regression of mean annual soluble ion concentration and flux data vs. accumulation rates in both regions indicates that 1) concentrations are independent of and thus not a rescaling of accumulation rate time‐series, and 2) chemical flux to the ice sheet surface is mainly via wet deposition, and changes in atmospheric concentration play a significant role. We therefore suggest that, in the absence of detailed air/snow transfer models, ice core chemical concentration and not flux time‐series provide a better estimate of past aerosol loading in West Antarctica.
Effect of grain size on the distribution and transport of deep‐seated fluids and melts
Authors: Wark David A. , Watson E. Bruce
Published: February 2004

Because permeability increases with the square of the grain size for a given fluid fraction, it is commonly assumed that porous flow of fluids and melts is more effective in coarse‐grained domains of deep‐seated rocks. This relative behavior is accurate, however, only as a description of two systems operating in isolation. We demonstrate that if coarse‐ and fine‐grained domains are in chemical communication, then equilization of pore‐wall curvature across the system results in concentration of fluid or melt in domains of finer grain size. Because of this localization of fluid, the permeability of the finer‐grained domains will match or exceed that of domains with coarser grains. Fluid focussing due to differences in grain size has potentially important implications for grain‐scale transport of metamorphic fluids — including those released from subducting slabs into the sheared mantle wedge — and also for partial melts in the mantle and deep crust.
The global flux of carbon dioxide into groundwater
Authors: Kessler Toby J. , Harvey Charles F.
Published: February 2004

The global flux of dissolved inorganic carbon (DIC) downward into groundwater is estimated to be ∼0.2 GtC/y. The flux is mapped over the earth's land surface by combining existing global maps of groundwater recharge, soil water pH and average temperature with a global map of soil vapor PCO2 estimated from evapotranspiration. The estimated total flux of DIC into groundwater is significantly increased if larger, but reasonable, estimates of groundwater recharge are used, and the flux could potentially be much larger for higher soil moisture pH. The residence time of DIC in groundwater is at least as long as the residence time of groundwater, which may be on the order of hundreds to thousands of years.
Joint inversion of InSAR and teleseismic data for the slip history of the 1999 Izmit (Turkey) Earthquake
Authors: Delouis B. , Lundgren P. , Salichon J. , Giardini D.
Published: February 2004

The slip history of the Izmit earthquake is investigated by jointly inverting SAR and teleseismic data with a multi‐segment, variable‐slip, finite fault model. Surface offsets are used as an added constraint. The highest slip values (5 to 7 m of right‐lateral displacement) are associated with a strong central asperity surrounding the hypocenter. The bilateral breaking of this main asperity, which lasted about 10 sec, dominates the source time function. From the Gölcük‐Izmit area to Lake Sapanca, a relatively good correspondence is observed between slip at depth and at the surface, but farther to the West and to the East slip tends to be confined to the near surface. Slip in the easternmost part of the rupture (Düzce segment) is not well resolved. Our analysis finds the InSAR and teleseismic data to be compatible and complementary. This study shows the potential of the joint inversion of both data sets for a rapid determination of the spatio‐temporal history of large earthquakes.
The subglacial cavity and implied dynamics under Nioghalvfjerdsfjorden Glacier, NE‐Greenland
Authors: Mayer Christoph , Reeh Niels , Jung‐Rothenhäusler Frederik , Huybrechts Philippe , Oerter Hans
Published: February 2004

Seismic depth soundings on Nioghalvfjerdsfjorden Glacier (NFG), NE Greenland, reveal an overdeepened trough under the floating glacier. The maximum depth of the trough reaches more than 900 m below sea level. Mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8 m a−1. The geometry of the cavity and water mass characteristics from CTD measurements suggest the existence of a well defined regional circulation system. Warm, saline and rather dense water follows the inward inclining basal slope through the deep valley of Dijmphna Sund towards the grounding line. Shallow ridges at the eastern glacier front prevent this water mass entering from that direction. The comparatively cold, fresh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east. The abundance of subglacial melt water east of NFG is most probably one of the main reasons for the semi permanent sea ice cover in this region. Cold water masses upwelling in the Northeast Water Polynia and detected by satellite remote sensing are very likely influenced and modified by the subglacial melt water production.
A physical‐model‐based, field‐wise and self‐contained algorithm for removing directional ambiguities of ocean surface winds retrieved from scatterometer measurements
Authors: Kim Young‐Joon
Published: February 2004

An algorithm is introduced to remove the directional ambiguities in ocean surface winds measured by scatterometers, which requires scatterometer data only. It is based on two versions of PBL (planetary boundary layer) models and a low‐pass filter. A pressure field is first derived from the median‐filtered scatterometer winds, is then noise‐filtered, and is finally converted back to the winds, respectively, by an inverted PBL model, a smoothing algorithm, and a PBL model. The derived wind field is used to remove the directional ambiguities in the scatterometer data. This new algorithm is applied to Hurricane Eugene and produces results comparable to those from the current standard ambiguity removal algorithm for NASA/JPL SeaWinds project, which requires external numerical weather forecast/analyses data.
Decline in Mediterranean rainfall caused by weakening of Mediterranean cyclones
Authors: Trigo Isabel F. , Davies Trevor D. , Bigg Grant R.
Published: February 2004

Wet season (October–March) rainfall over the Northern Mediterranean has decreased over the last four decades. The decline is being forced locally by a decrease in the intensity of cyclogenesis events in the region. The forcing is subtle, since overall cyclone frequency exhibits no significant trend over time. The reduction in strength of the most intense cyclones is driven by recent trends observed in the coupled ocean‐atmospheric circulation over the Northern Atlantic, in particular by the northwards migration of the main Atlantic storm‐tracks.
First profile measurements of tropospheric BrO
Authors: Fitzenberger R. , Bösch H. , Camy‐Peyret C. , Chipperfield M. P. , Harder H. , Platt U. , Sinnhuber B. ‐M. , Wagner T. , Pfeilsticker K.
Published: February 2004

Tropospheric BrO profiles (about 0.6±0.2 ppt, and 2.0±0.8 ppt at profile maximum) were measured for the first time. Our measurements add new information to recent speculations—based on indirect evidence— of BrO possibly being ubiquitous in the free troposphere [Harder et al., 1998; Frieß et al., 1999; Van Roozendael et al., 1999; Pundt et al., 2000]. Our study relies on a detailed comparison of BrO slant column densities (BrO‐SCD) measured in the troposphere from the LPMA/DOAS (Laboratoire de Physique Moléculaire et Applications and Differential Optical Absorption Spectroscopy) gondola by direct Sun absorption, and BrO‐SCD values subsequently measured in the lowermost stratosphere during balloon ascent. The difference in total atmospheric BrO‐SCDs measured in the troposphere and lowermost stratosphere—after a suitable correction for the change in BrO due to photochemistry and the observation geometry—is then attributed to tropospheric BrO.
The in situ stress field of the Perth Basin, Australia
Authors: Reynolds S. D. , Hillis R. R.
Published: February 2004

A total of 17 wells in the Perth Basin were interpreted to have 114 breakouts covering a combined length of 3.2 km and a mean σHmax orientation of 108°N. The inferred mean orientation of σHmax in the Perth Basin is broadly consistent with that in the adjacent basement, Yilgarn Block. The new data confirm that σHmax orientation in the region is consistent with other stress indicators, different depths and different geological provinces. The new data also confirm that the orientation of σHmax does not parallel the NNE direction of absolute plate velocity. Anomalous north‐south σHmax orientations identified in a number of wells in the Perth Basin can be attributed to local structural effects.
Accurate GPS orientation of a long baseline for Neutrino Oscillation Experiments at Fermilab
Authors: Soler Tomás , Foote Richard H. , Hoyle Dixon , Bocean Virgil
Published: February 2004

Recent research in elementary particle physics is concentrating a great amount of effort on neutrino oscillation experiments. These studies require the accurate pointing of neutrino beams between two distant points. The Fermi National Accelerator Laboratory (Fermilab) intends to build a new particle beamline to direct a beam of muon neutrinos from its Main Injector toward a far‐off (735 km away) underground detector capable of searching for non‐zero neutrino mass by looking for neutrino oscillations. This paper describes the GPS work carried out to accurately position the reference ground marks at the two sites from which the spatial orientation of the baseline can be accurately determined. The effect of plate rotations on the absolute orientation of the baseline was also investigated.
Evolution and biological effects of the 1997–98 El Niño in the upwelling ecosystem off northern Chile
Authors: Ulloa Osvaldo , Escribano Ruben , Hormazabal Samuel , Quiñones Renato A. , González Rodrigo R. , Ramos Marcel
Published: February 2004

During the 1997–98 El Niño event, the temperature and oxygen contents of the coastal waters off northern Chile were noticeably higher than during non‐El Niño conditions, but phytoplankton and Zooplankton biomasses were not dramatically altered. In contrast, the herbivorous copepod Calanus chilensis, which showed a limited tolerance to low‐oxygen conditions, exhibited greater abundances, higher growth rates, and a significant reduction in adult body size. These results indicate a positive effect of the changes in oceanographic conditions due to El Niño on Zooplankton growth and production, and provide evidence for lack of food limitation on secondary production in the coastal region during this period.
Intensified Asian Summer Monsoon and its variability in a coupled model forced by increasing greenhouse gas concentrations
Authors: Hu Zeng‐Zhen , Latif Mojib , Roeckner Erich , Bengtsson Lennart
Published: February 2004

The Asian summer monsoon response to global warming is investigated by a transient green‐house warming integration with the ECHAM4/OPYC3 CGCM. It is demonstrated that increases of greenhouse gas concentrations intensify the Asian summer monsoon and its variability. The intensified monsoon results mainly from an enhanced land‐sea contrast and a northward shift of the convergence zone. A gradual increase of the monsoon variability is simulated from year 2030 onwards. It seems to be connected with the corresponding increase of the sea surface temperature variability over the tropical Pacific.
GCM response to Late Precambrian (∼590 Ma) ice—covered continents
Authors: Baum Steven K. , Crowley Thomas J.
Published: February 2004

Recent coupled energy balance/ice sheet modeling studies indicate that ice‐covered continents can be simulated for the Late Precambrian with 6% solar constant reduction. We examine the ocean mixed layer response to such an ice sheet with the GENESIS 2 general circulation model and CO2 levels varying from 0.5–2.5 times present. The ocean ices over completely at 0.5–1.0X present levels, with the final phase of sea ice growth occurring within a single model year. A qualitatively different 2.5X CO2 solution is close to equilibrium and yields open water between ∼25 °N and ∼25 °S paleolatitude. The prevailing wind patterns suggest that an equatorial Pacific‐type circulation may have developed in part of the Neoproterozoic ocean.
Seismic Source characterization using a neighbourhood algorithm
Authors: Kennett B. L. N. , Marson‐Pidgeon K. , Sambridge M. S.
Published: February 2004

The full characterization of a seismic source requires the specification of the hypocentre location and the source mechanism. The non‐linear inversion is accomplished in two stages using the Neighbourhood Algorithm (NA), a direct search method in parameter space which is able to preferentially sample those regions with least data misfit; there are just two control parameters and no differentiation is employed. The first step is hypocentre location using a 4‐D search space and a focussed search strategy. The second step is waveform inversion of the early part of P and S wavetrains to refine source depth and extract the source mechanism. With a moment tensor representation, this second stage explores an 8‐D parameter space. For both the hypocentre and source mechanism inversion the NA method provides rapid and effective results with information from just a few stations, as illustrated with an event in southern Xinjiang.
A method for the separation of source and site effects and the apparent Q structure from strong motion data
Authors: Petukhin Anatoly , Irikura Kojiro
Published: February 2004

A new/modified technique for the separation of source, path and site effects from strong motion records is proposed. To do this we made two extensions of the method developed in [Iwata and Irikura, 1988]. (1) We allow the Q‐value to be variable with depth and subregion in a block model of the medium with constant Q in each block. Path lengths within blocks are calculated using ray approximation. (2) To estimate the absolute site effect at reference station (and source effects respectively) we can use the H/V spectral ratio method for the S‐wave group to determine the spectral correction at the reference station. Our new method was applied to a set of KNET data in the Tohoku area of Japan. Preliminary results of Q structure inversion show that Q has minor variations with depth, and slightly decreases in the deepest layer. Source effects clearly show the existence of fmax phenomena (fmax=13Hz).
Enhanced Mantle Conductivity from Sulfide Minerals, Southern Sierra Nevada, California
Authors: Ducea Mihai N. , Park Stephen K.
Published: February 2004

Petrographic studies of peridotitic xenoliths entrained in late Quaternary basalts from beneath the southern Sierra Nevada have revealed the presence of accessory sulfide minerals along grain boundaries and fractures. Equilibration temperatures from the xenoliths are sufficiently high that the molten sulfides coexist with the basaltic melt. Sulfides are extremely conductive relative to the solid matrix or the basaltic melt, so a small fraction can increase the bulk conductivity of the mantle appreciably. Previous estimates of 2–5% partial melt from magnetotelluric measurements can be plausibly reduced to less than 1%. Such low melt percentages have longer residence times in the mantle and are more consistent with the volumetrically minor late Quaternary basalt flows and the primitive basalt compositions.
The SLR secular gravity variations and their impact on the inference of mantle rheology and lithospheric thickness
Authors: Devoti R. , Luceri V. , Sciarretta C. , Bianco G. , Di Donato G. , Vermeersen L. L. A. , Sabadini R.
Published: February 2004

A long history of SLR (Satellite Laser Ranging) observations of the geodetic satellites LAGEOS‐I, LAGEOS‐II, Starlette and Stella have been analyzed in order to estimate the time series of the low degree zonal coefficients in the Earth gravity field, up to degree six, and derive their secular drifts. The paper will point out the critical aspects of the analysis process and will compare the estimated zonal rates with other published results. Comparison of these zonal rates with the results of global, viscoelastic Earth models forced by Pleistocenic deglaciation, shows that the SLR retrieved zonals and the lumped odd zonals can be used to infer the upper mantle viscosity and lithospheric thickness. Discrepancies in the viscosity profiles, required to reproduce the different zonals, seem to indicate ongoing mass redistribution over the Earth.
Ozone profiles from 30 to 110 km Measured by the Occultation Radiometer Instrument during the period Aug. 1992–Apr. 1993
Authors: Fussen Didier , Vanhellemont Filip , Bingen Christine , Chabrillat Simon
Published: February 2004

We present ozone volume mixing ratio profiles obtained by the ORA instrument during the period Aug. 1992–Apr. 1993. They have been retrieved by applying a specific inversion algorithm to a radiometric UV channel contaminated by Rayleigh scattering. The results compare reasonably well with other instruments up to the mesopause and are probably the first extended ozone data in the lower thermosphere (90–110 km).
A global albedo data set derived from AVHRR data for use in climate simulations
Authors: Strugnell Nicholas C. , Lucht Wolfgang , Schaaf Crystal
Published: February 2004

We present a global 1‐km albedo dataset derived from Advanced Very High Resolution Radiometer (AVHRR) satellite remote sensing data, a global land cover classification and field observations of typical land surface bidirectional reflectance distribution functions (BRDFs). There is a clear need for such a global albedo map for use in atmospheric radiative transfer models. A land cover classification based on surface structure is employed and class correspondences used to generate a structural class map from an existing ecological global land classification. Representative field measurements of BRDF are assigned to each of the structural classes allowing us to retrieve BRDF shape parameters and albedo for each class using a semiempirical model. These parameters were adjusted using global AVHRR data to account for intra‐class variations of surface reflectance. Albedos were calculated from the adjusted parameters and summarised by land cover type, continent and season.
Seasonal temperature variations influence isoprene emission
Authors: Pétron G. , Harley P. , Greenberg J. , Guenther A.
Published: February 2004

Isoprene (2‐methyl‐1,3‐butadiene) emission from plants is highly temperature dependent. The influence of long‐term variations in growth temperature on isoprene emission rates from bur oak (Quercus macrocarpa) leaves was investigated under controlled environmental conditions. Trees were installed in a growth chamber and exposed to a series of daytime temperatures that were varied after a period of 3–6 weeks. Emission capacity (measured at leaf temperature of 25°C and photosynthetic photon flux density of 900 µmol m−2 s−1) doubled when growth temperature was increased from 25 to 30°C. Ten days after the growth temperature was decreased to 20°C, isoprene emission capacity fell to 25 to 50% of its peak value. When growth temperature was returned to 30°C, emission capacity doubled within 5 hours and continued to increase over several days. The observed behavior can be described by modifying existing algorithms.
Pn wave velocities beneath the Tanzania Craton and adjacent rifted mobile belts, east Africa
Authors: Brazier Richard A. , Nyblade Andrew A. , Langston Charles A. , Owens Thomas J.
Published: February 2004

P wave travel times from regional earthquakes recorded by the Tanzania Broadband Seismic Experiment have been inverted for long wavelength (>100 km) Pn velocity variations beneath Tanzania using a generalized inverse algorithm. Pn velocities, on average, are 8.40 to 8.45 km/s beneath the center of the Tanzania Craton, 8.30–8.35 km/s beneath the terminus of the Eastern Branch of the rift system, and 8.35–8.40 km/s beneath the Western Branch. These velocities indicate that there are no broad (>100 km wide) thermal anomalies in the uppermost mantle beneath areas of rifting in Tanzania, and suggest that thermal anomalies present deeper in the mantle have not yet reached the base of the crust.
On Steady Rate Coupling Between an Elastic Upper Crust and a Viscous Interior
Authors: Zatman Stephen
Published: February 2004

Although it is commonly accepted that the upper (seismogenic) layer of the Earth's crust deforms elastically except in localized zones (faults) where deformation is discontinuous, the sub‐seismogenic layer is not as well understand. Possibilities for the rheology include viscous or viscoelastic behavior, and localization of shear to relatively thin zones (that can sometimes be >1 km in width). If the sub‐seismogenic layer is viscous or viscoelastic, then during interseismic periods a steady rate of deformation will be achieved after transients associated with viscoelastic relaxation have decayed away (for sufficiently long earthquake cycles). I find that in this situation the motion in the elastic layer is decoupled from that deep within the viscous layer, and they may be very different from each other. This implies that one can not use contemporary geodetic data to infer steady motion in a viscous sub‐seismogenic layer (although it may be used to study viscoelastic relaxation).
Interannual mean sea level change and the Earth's water mass budget
Authors: Chambers Don P. , Chen Jianli , Nerem R. Steven , Tapley Byron D.
Published: February 2004

The relationship between interannual global mean sea level change and the Earth's water mass budget is examined between 1993 and 1998 by removing the steric (thermal) component from mean sea level computed with TOPEX/Poseidon (T/P) altimetry. The steric component is calculated from subsurface temperatures measured by expendable bathythermographs and interpolated to a global grid by empirical orthogonal function (EOF) reconstruction. Results indicate that from late‐1995 to early‐1998, the thermal expansion of sea level was significantly higher than the total sea level change measured by T/P, suggesting that fresh water mass was lost from the ocean. The size of the maximum water mass lost is equivalent to about 18 mm of sea level. An error analysis indicates that this value is significant at the 95% confidence level. Results from numerical models show similar magnitudes of water mass change in the ocean at interannual periods, but at different phases.
African dust and the demise of Caribbean Coral Reefs
Authors: Shinn Eugene A. , Smith Garriet W. , Prospero Joseph M. , Betzer Peter , Hayes Marshall L. , Garrison Virginia , Barber Richard T.
Published: February 2004

The vitality of Caribbean coral reefs has undergone a continual state of decline since the late 1970s, a period of time coincidental with large increases in transatlantic dust transport. It is proposed that the hundreds of millions of tons/year of soil dust that have been crossing the Atlantic during the last 25 years could be a significant contributor to coral reef decline and may be affecting other ecosystems. Benchmark events, such as near synchronous Caribbean‐wide mortalities of acroporid corals and the urchin Diadema in 1983, and coral bleaching beginning in 1987, correlate with the years of maximum dust flux into the Caribbean. Besides crustal elements, in particular Fe, Si, and aluminosilicate clays, the dust can serve as a substrate for numerous species of viable spores, especially the soil fungus Aspergillus. Aspergillus sydowii, the cause of an ongoing Caribbean‐wide seafan disease, has been cultured from Caribbean air samples and used to inoculate sea fans.
Initiation of Martian outflow channels: Related to the dissociation of gas hydrate?
Authors: Max Michael D. , Clifford Stephen M.
Published: February 2004

We propose that the disruption of subpermafrost aquifers on Mars by the thermal‐ or pressure‐induced dissociation of methane hydrate may have been a frequent trigger for initiating outflow channel activity. This possibility is raised by recent work that suggests that significant amounts of methane and gas hydrate may have been produced within and beneath the planet's cryosphere. On Earth, the build‐up of overpressured water and gas by the decomposition of hydrate deposits has been implicated in the formation of large blowout features on the ocean floor. These features display a remarkable resemblance (in both morphology and scale) to the chaotic terrain found at the source of many Martian channels. The destabilization of hydrate can generate pressures sufficient to disrupt aquifers confined by up to 5 kilometers of frozen ground, while smaller discharges may result from the water produced by the decomposition of near‐surface hydrate alone.
Eruption conditions of Pele Volcano on Io inferred from chemistry of its volcanic plume
Authors: Zolotov Mikhail Yu. , Fegley Bruce
Published: February 2004

We use thermodynamic models and published 1996 Hubble Space Telescope (HST) observations of SO2, SO, and monatomic sulfur gas in the Pele volcanic plume on Jupiter's moon Io to evaluate the temperature (1440 K) and oxidation state (3.3 log fO2 units below the Ni‐NiO buffer) of Pele's magma and exsolved volcanic gas. Combination of these results with 1999 HST data on the SO2/S2 ratio in the Pele plume allows us to calculate pressures (10−4.7–10−5.4 bar) in the vicinity of volcanic vent and to present a detailed chemical model for the plume. Our model indicates that the Pele plume represents volcanic gas, which last equilibrated at magmatic temperature and was not significantly altered in the plume. Finally, the redox state of Pele plume indicates that Io is differentiated and has an oxidized, Fe‐metal free mantle.