bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloud condensation nuclei in the Amazon Basin: “marine” conditions over a continent?
Authors: Roberts Gregory C. , Andreae Meinrat O. , Zhou Jingchuan , Artaxo Paulo
Published: February 2004

Cloud condensation nuclei (CCN) are linked to radiative forcing, precipitation, and cloud structure; yet, their role in tropical climates remains largely unknown. CCN concentrations (NCCN) measured during the wet season in the Amazon Basin were surprisingly low (mean NCCN at 1% supersaturation: 267±132 cm−3) and resembled concentrations more typical of marine locations than most continental sites. At low background CCN concentrations, cloud properties are more sensitive to an increase in NCCN. Therefore, enhanced aerosol emissions due to human activity in the Amazon Basin may have a stronger impact on climate than emissions in other continental regions. In spite of the large organic fraction in the Amazonian aerosol, a detailed analysis of number distributions and size‐dependent chemical composition indicates that sulfate plays an important role in CCN activity.
Archean emplacement of eclogitic components into the lithospheric mantle during formation of the Kaapvaal Craton
Authors: Shirey Steven B. , Carlson Richard W. , Richardson Stephen H. , Menzies Andrew , Gurney John J. , Pearson D. Graham , Harris Jeffrey W. , Wiechert Uwe
Published: February 2004

Re‐Os data for selected whole‐rock eclogites and eclogitic sulfide inclusions in diamonds from seven kimberlites on the Kaapvaal‐Zimbabwe cratons yield ages around 3 Ga. The presence of such old eclogitic components in the subcontinental lithospheric mantle is more common than previously thought. Overlap of these ages with those of many cratonic peridotites demonstrates that incorporation of eclogitic materials accompanied or closely followed cratonic lithosphere stabilization. Many of these eclogitic components have fractionated C, N, O, and S isotopic compositions which could have been created at low‐temperatures, implying that some style of Archean subduction involving emplacement of oceanic lithosphere was part of craton keel development.
Regional‐scale permeability by heat flow calibration in the Powder River Basin, Wyoming
Authors: McPherson Brian J. O. L. , Lichtner Peter C. , Forster Craig B. , Cole Barret S.
Published: February 2004

Forward modeling of coupled fluid and heat flow in the Powder River basin, Wyoming, is used to explain anomalously high heat flow values observed in the southern portion of the basin. Effective basin‐scale permeabilities of selected Powder River basin aquifers and aquitards were calibrated by matching surface heat flow measurements to simulation results. Fractures associated with a large anticline in the southwestern part of the basin were found to play a major role in the basin's thermal regime. While the model results are non‐unique, they demonstrate that regional structural features play an important role in a basin's overall energy budget and fluid flow regime. With the results of the basin‐scale model it is possible to evaluate regional‐scale flow and transport processes.
A giant landslide on the southern flank of Tahiti Island, French Polynesia
Authors: Clouard Valérie , Bonneville Alain , Gillot Pierre‐Yves
Published: February 2004

We present evidence for an ancient and voluminous subaerial landslide of the southern flank of Tahiti, Society Islands. During a marine geophysical survey in 1996, submarine mass wasting deposits were mapped as far as 60 km from the southern shore of the island. Acoustic imagery reveals a surface of 2950 km² of debris avalanche and hummocky terrain. Based on bathymetric data, the volume of the debris is estimated to be 1150 km³. In comparison with Hawaiian and other oceanic island landslides, it can be classified as a giant, rapid and cataclysmic event. Tahiti morphology and the distribution of volcanic ages over the island strongly suggest that the slope failure initiated near the top of the southern island flank, between 650 and 850 ka. The landslide scar was subsequently filled by eruptions. The estimated volume of the subaerial removed material exhibits a large discrepancy with the volume of the submarine deposits that can be explained by recurrent slide events.
Ocean release of fossil fuel CO2: A case study
Authors: Drange H. , Alendal G. , Johannessen O. M.
Published: February 2004

The natural ocean uptake of the greenhouse gas CO2 can be accelerated by collecting and liquefying the gas from point sources, and by pumping it into the ocean at appropriate locations and at sufficient depths. Results from a numerical modelling system indicate that injection sites located at about 1,000 m depth in the eastern Norwegian Sea lead to efficient and long term sequestration in the abyss Atlantic. For a release rate corresponding to the CO2 emissions from a 220 MW gas power plant, it is found that the volume of the near‐source water with a pH‐reduction ≥0.1 is ∼0.5 km³. These findings, together with available technology and feasible economics, indicate that the Norwegian Sea represents a possible location for large scale demonstration of operational ocean release of CO2.
New constraints on Laurentide postglacial rebound from absolute gravity measurements
Authors: Lambert Anthony , Courtier Nicholas , Sasagawa Glenn S. , Klopping Fred , Winester Daniel , James Thomas S. , Liard Jacques O.
Published: February 2004

Repeated absolute gravity measurements have been made over a period of several years at six sites along a 3000 km‐long, mid‐continental, North American profile from the coast of Hudson Bay southward to Iowa. With the exception of the southern‐most site, the observed rates of change of gravity are significantly higher than rates predicted by current models, such as ICE‐3G and a laterally homogeneous, standard Earth. The observed gravity change rates suggest significant modifications, such as a 2 to 3‐fold increase in lower mantle viscosity or a 50% increase in Laurentide ice sheet thickness west of Lake Superior.
On the energy source for diffuse Jovian auroral emissivity
Authors: Bhattacharya B. , Thorne R. M. , Williams D. J.
Published: February 2004

Data from the Energetic Particle Detector on Galileo have been used to investigate whether the radiation belt population can act as a direct energy reservoir for Jovian auroral emissions. Energetic (E > 42 keV) ion distributions in the middle magnetosphere (9 < RJ < 26) yield peak precipitation energy fluxes comparable to a few ergs‐cm−2‐s−1, which are too weak to produce significant auroral emissivity. Detailed analysis of energetic electrons (15‐884 keV) indicates the presence of an enhanced population near the loss cone that may provide precipitation energy flux above 10 ergs‐cm−2‐s−1 over an extended region (10 ≤ RJ ≤ 25) of the middle magnetosphere. The available precipitation electron energy flux decreases at higher radial distance, falling to values below 1 erg‐cm−2‐s−1 outside 30 RJ. Additional acceleration mechanisms such as field‐aligned currents are required to account for observed auroral intensities at higher L. The precipitation flux values presented here have been calculated under the assumption of strong pitch‐angle scattering due to wave‐particle interactions in the essentially collisionless middle magnetosphere. Plasma waves with relatively modest amplitude (Bw≥ 25 pT or Ew≥ 5 mV/m) are sufficient to induce strong diffusion scattering outside 10 RJ. Such scattering can account for energy deposition over a broad latitude range (Δ λ ≥5 °) associated with the diffuse Jovian aurora.
The micrometeoroid mass flux into the upper atmosphere: Arecibo results and a comparison with prior estimates
Authors: Mathews J. D. , Janches D. , Meisel D. D. , Zhou Q ‐H.
Published: February 2004

Radar micrometeor observations at Arecibo Observatory have enabled direct estimates of the meteoroid mass flux into the upper atmosphere. We report mass flux determinations from November 1997/1998 observations that are based on the observed number of meteor events per day in the 300‐m diameter Arecibo beam and on particle mass determinations from that fraction of all particles for which deceleration is measured. The average mass of the Arecibo micrometeoroids that manifest observable deceleration is ∼0.32/0.76 µgm/particle with a resultant annual whole‐Earth mass flux of 1.6 × 106/2.7 × 106 kg/yr over the ∼10−5−10² µgm mass range for 1997/1998, respectively. The annual whole‐earth mass flux per decade of particle mass is calculated and compared with that of Ceplecha et al. [1998] (3.7 × 106 kg/yr) and with that derived by Love and Brownlee [1993] (LB) from small particle impact craters on the orbital Long Duration Exposure Facility (LDEF). We also give the LDEF results as significantly modified using the Arecibo‐determined average particle velocity of ∼50 km/sec—much larger than the effective value of 12 km/sec used by LB. This modification results in a net LDEF mass flux of 1.8×106 kg/yr—7% of the value we determined from reanalysis of the LB data using their original 12 km/sec mean impact speed. These results may provoke some debate.
Stress rates in the Central Cascadia Subduction Zone inferred from an elastic plate model
Authors: Williams Charles A. , McCaffrey Robert
Published: February 2004

GPS vectors and surface tilt and uplift rates from northwestern Oregon and southwestern Washington are inverted to estimate rates of stress changes along the Cascadia thrust fault and base of the overriding plate using a finite thickness elastic plate model. The data are fit by elevated shear stress and Coulomb Failure Function (CFF) rates within 80 km of the trench. By contrast, an elastic half‐space dislocation model does not fit as well and predicts significant amounts of locking and elevated CFF rates near the coast.
Quantification of high latitude electric field variability
Authors: Crowley Geoff , Hackert Chris L.
Published: February 2004

Variability in the high latitude electric field has been identified as a major contributor to global Joule heating. Electric field patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure are used to characterize the E‐field temporal variability over the course of 18 hours. The standard deviation of the E‐field magnitude on May 4, 1998 often exceeds the average value of the E‐field magnitude. A significant fraction of this variability arises from oscillations with period less than one hour. This confirms that Joule heating calculations based on time‐averaged E‐fields may significantly under‐predict the heating.
Comparison of Saharan dust aerosol optical depths retrieved using aircraft mounted Pyranometers and 2‐channel AVHRR algorithms
Authors: Haywood J. M. , Francis P. N. , Geogdzhayev I. , Mishchenko M. , Frey R.
Published: February 2004

The 0.55 µm optical depth of the Saharan dust aerosol plume is determined from C‐130 pyranometer data for two different days and the results compared to those from a 2‐channel Advanced Very High Resolution Radiometer (AVHRR) retrieval algorithm. When the time difference between the C‐130 and AVHRR overpasses is small, the geographic distribution of the aerosol optical depths are similar and differ by less than +/−0.1 despite the different refractive indices, size distributions and atmospheric profiles implicit in each method. The pyranometer derived optical depth at 0.55 µm exceeds a value of 1 on one of the days, which exceeds the cloud threshold used in many satellite retrieval algorithms with implications for the accuracy of satellite derived aerosol optical depths. The difficulties in making extensive geographical comparisons between satellite and aircraft measurements owing to the differential speed of the observing platforms are also highlighted.
Initial ion equatorial pitch angle distributions from medium and high energy neutral atom images obtained by IMAGE
Authors: Perez J. D. , Kozlowski G. , C:son‐Brandt P. , Mitchell D. G. , Jahn J.‐M. , Pollock C. J. , Zhang X. X.
Published: February 2004

Examples of the extraction of equatorial ion pitch angle distributions from energetic neutral atom images taken by the HENA instrument on June 10, 2000 between 1200 and 1600 UT and MENA on August 12, 2000 at about 1000 UT on board the IMAGE satellite are presented. The extraction is performed using a method of deconvolution that expands the unknown equatorial ion pitch angle distribution in terms of tri‐cubic splines, and then finds the expansion coefficients by requiring that the result fit the data and be as smooth as possible.
Geodetic detection of active faults in S. California
Authors: Wdowinski Shimon , Sudman Yonadav , Bock Yehuda
Published: February 2004

A new analysis of velocities of geodetic markers straddling the San Andreas Fault System in southern California reveals that interseismic deformation is localized along a dozen sub‐parallel narrow belts of high shear strain rate that correlate well with active geologic fault segments and locally with concentrated zones of microseismicity. High shear strain rates (0.3–0.95 µstrain/year) are observed northward and southward of the San Andreas fault's big bend, whereas the big bend itself is characterized by a diffuse low magnitude shear strain rate. Dilatational deformation is diffuse and of relatively low magnitude (<0.2 µstrain/year), with the highest contraction rates occurring in the Ventura and Los Angeles basins. Because no prior assumptions were made regarding the geology, tectonics, or seismicity of the region, our analysis demonstrates that geodetic observations alone can be used to detect active fault segments.
Evidence that the natal pulse involves the Agulhas Current to its full depth
Authors: Lutjeharms Johann R. E. , Boebel Olaf , van der Vaart Paul C. F. , de Ruijter Wilhelmus P. M. , Rossby Thomas , Bryden Harry L.
Published: February 2004

Natal Pulses are intermittent, solitary meanders on the trajectory of the otherwise remarkably stable northern Agulhas Current. They play disparate roles in the process of inter‐ocean exchange. They have been thought to trigger the spawning of Agulhas Rings at the Agulhas Retroflection, but also to generate an upstream retroflection that prevents Agulhas water from reaching the inter‐ocean boundary. For the Natal Pulse to be such a control it has to extend to considerable depths. We present the first hard evidence that demonstrates that the Natal Pulse is indeed an inherent property of the Agulhas Current throughout its full depth. Our data comprise Eulerian current meter observations and Lagrangian float trajectories in combination with sea‐surface height and sea‐surface temperature data. The results reveal the trapping of water within the Natal Pulse, its southward advection at a phase speed of about 11–12 cm s−1, and rotation periods of 6 days.
Zonal flow driven by deep convection in the major planets
Authors: Christensen Ulrich R.
Published: February 2004

The cause of the fast zonal winds on the large gas planets is disputed. To investigate their possible origin by convection in the planets' molecular hydrogen layer, I study simple numerical models of thermal convection in a rotating sphere at low Ekman numbers for Rayleigh numbers up to 100 times critical. With stress‐free boundaries and high Rayleigh number it is possible to reproduce the observed magnitudes of the zonal and non‐zonal flow components at the surfaces of Jupiter and Saturn. While only three flow bands are found for a thick convecting shell, the number increases to seven for a shell with an inner‐to‐outer radius of 0.6.
Absorption of sunlight by dust as inferred from satellite and ground‐based remote sensing
Authors: Kaufman Y. J. , Tanré Didier , Dubovik O. , Karnieli A. , Remer L. A.
Published: February 2004

Dust absorption of solar radiation is not well known due to limitations in the accuracy of in situ measurements. Here we report two new independent remote sensing techniques that provide sensitive measurements of dust absorption. One uses satellite spectral measurements, the second ground based sky measurements. Both techniques demonstrate that Saharan dust absorption of solar radiation is several times smaller than the current international standards. For example, at wavelength of 0.64 µm the dust single scattering albedo is reported here as 0.97±0.02 rather than 0.87±0.04 in recent review.
Cloud cover variations over the United States: An influence of cosmic rays or solar variability?
Authors: Udelhofen Petra M. , Cess Robert D.
Published: February 2004

To investigate whether galactic cosmic rays (GCR) may influence cloud cover variations, we analyze cloud cover anomalies from 1900–1987 over the United States. Results of spectral analyses reveal a statistically significant cloud cover signal at the period of 11 years; the coherence between cloud cover and solar variability proxy is 0.7 and statistically significant with 95% confidence. In addition, cloud data derived from the NCAR Climate System Model (CSM) forced with solar irradiance variations show a strong signal at 11 years that is not apparent in cloud data from runs with constant solar input. The cloud cover variations are in phase with the solar cycle and not the GCR. Our results suggest that cloud variabilities may be affected by a modulation of the atmospheric circulation resulting from variations of the solar‐UV‐ozone‐induced heating of the atmosphere.
Excitation of basin modes by ocean‐atmosphere coupling
Authors: Cessi Paola , Paparella Francesco
Published: February 2004

A conceptual model of the coupling between the upper‐ocean wind‐driven circulation and the mid‐latitude atmospheric wind‐stress illustrates that large‐scale basin‐wide oscillations with decadal period can be excited. These oceanic modes are also found in the absence of ocean‐atmosphere feedback, but they are damped. The period of the oscillation and the spatial structure of the modes are essentially the same with and without coupling. These oscillations are distinct from the coupled modes of variability arising from a delayed negative feedback between the wind‐driven flow and the wind‐stress. They are ocean‐only linear basin modes which become sustained by ocean‐atmosphere coupling.
Simulating convective clouds with sustained supercooled liquid water down to −37.5°C using a spectral microphysics model
Authors: Khain A. P. , Rosenfeld D. , Pokrovsky A.
Published: February 2004

Aircraft observations of highly supercooled water in convective clouds (1.8 gm−3 at −37.5°C) were reproduced by a numerical cloud model with explicit microphysical processes and turbulent effects. The model showed that large concentrations of small cloud droplets induced by high concentrations of CCN and a strong updraft were essential in reproducing the observations. The same model reproduced microphysically maritime clouds with fast depletion of cloud water by just changing the CCN spectrum. The constrains imposed by these extreme conditions revealed the weakness of existing cloud parameterizations, and the necessity of inclusion of very detailed explicit microphysical and turbulent cloud processes in cloud models.
Uptake of nopinone by water: Comparison between aqueous‐and gas‐phase oxidation of organic compounds in the atmosphere
Authors: Nozière B. , Longfellow C. A. , Henry B. E. , Voisin D. , Hanson D. R.
Published: February 2004

The uptake of nopinone by liquid water at room temperature has been studied in a wetted‐wall reactor coupled to a chemical ionization mass spectrometer and was found to be reversible and bulk‐specific. A Henry's law constant of H(296±3 K)=(176±50) Matm−1 was obtained. Measuring the solubility using a bubble column technique resulted in a value of H(296±1 K)=(200 ±40) Matm−1. We recommend an average value of H(296±2 K)=(195±60) Matm−1. The temperature dependence of this coefficient has been measured between 274 and 298 K and corresponds to an enthalpy of solvation of ΔsolnH=− (98±30) kJ/mol. The Henry's law coefficients measured in this work are large enough that, in the presence of clouds, aqueous‐phase sinks of nopinone might compete with its gas‐phase sinks. The possibility of such competition for other organic compounds in the atmosphere is discussed.
On the impact of gap‐filling algorithms on variability patterns of reconstructed oceanic surface fields
Authors: Sterl A.
Published: February 2004

The variability and consistency of oceanic surface fields (SST, pressure, air‐sea fluxes) from different sources are studied. The sources are reconstructions using available observations and the NCEP‐NCAR and ECMWF reanalysis. It is shown that the variabilities of different reconstructions differ widely from each other and from those of the reanalyses. Some reconstructed fields are shown to lack internal consistency. It is concluded that variability patterns inferred from gappy data have to be used with great caution. EOF‐based methods are found to yield more reliable results than those based on the method of successive correction.
Strength and elasticity of ringwoodite at upper mantle pressures
Authors: Kavner A. , Duffy T. S.
Published: February 2004

The differential stress supported by a natural iron‐bearing ringwoodite was determined using energy‐dispersive synchrotron x‐ray diffraction in a radial geometry in a diamond anvil cell. The yield strength of ringwoodite was found to increase nearly linearly from 5.8(5) GPa at a pressure of 6.2 GPa to 10.2(9) GPa at a pressure of 27.0 GPa. When scaled by the shear modulus, silicate yield strengths are systematically higher than metals, oxides, and halides at pressures up to 30 GPa. For silicates, the yield strength is 5–7% of the shear modulus in this pressure range, whereas for the other classes of solids the yield strength is typically less than 2% of the shear modulus. The results show that ringwoodite has a small postive elastic anisotropy over this pressure range.
Rocket probe observations of electric field irregularities in the polar summer mesosphere
Authors: Pfaff R. , Holzworth R. , Goldberg R. , Freudenreich H. , Voss H. , Croskey C. , Mitchell J. , Gumbel J. , Bounds S. , Singer W. , Latteck R.
Published: February 2004

Electric field wave measurements gathered on a sounding rocket flown in the presence of polar mesospheric summer echoes reveal a distinct layer of irregularities between 83–86 km with broadband amplitudes of > 10 mV/m rms. The waves are characterized by bursty, spiky waveforms with lower frequencies (∼ 10 Hz) dominant in the upper portion of the layer near 85 km and broader band emissions, extending to higher frequencies (∼ 1000 Hz) dominant in the lower portion of the layer near 83.5 km. The lower altitudes correspond to a region of weak optical emissions associated with a noctilucent cloud. The waves appear in and around regions where charged/neutral aerosols (1–10 nm) and large electron density depletions were observed. The irregularities likely result from a variety of processes including space charge inhomogeneities, mixed neutral and plasma motions, and complex effects associated with charged aerosols of varying sizes.
Large amplitude perturbations in mesospheric OH Meinel and 87‐Km Na lidar temperatures around the autumnal equinox
Authors: Taylor M. J. , Pendleton W. R. , Liu H.‐L. , She C. Y. , Gardner L. C. , Roble R. G. , Vasoli V.
Published: February 2004

Two high‐precision CEDAR instruments, an OH Mesospheric Temperature Mapper (MTM) and a Na Temperature Lidar, have been used to investigate seasonal variability in the mid‐latitude temperature at ∼87 km altitude over the western USA. Here we report the observation of a large perturbation in mesospheric temperature that occurs shortly after the autumnal equinox in close association with the penetration of planetary‐wave energy from the troposphere into the mesosphere. This perturbation has been observed on three occasions and exhibits a departure of up to ∼25–30 K from the nominal seasonal trend during a disturbed period of ∼2 weeks. Such behavior represents a dramatic transient departure from the seasonal trend expected on the basis of current empirical models. These novel results coupled with a recent TIME‐GCM modeling study [Liu et al., 2000] provide important insight into the role of planetary waves in mesospheric variability during the equinox periods.
A test of magnetospheric radio tomographic imaging with IMAGE and WIND
Authors: Cummer S. A. , Reiner M. J. , Reinisch B. W. , Kaiser M. L. , Green J. L. , Benson R. F. , Manning R. , Goetz K.
Published: February 2004

Theoretical studies have shown the potential scientific value of multi‐spacecraft radio tomographic imaging of the magnetosphere. The <10 RE WIND perigee passes during August 2000 afforded a unique opportunity to test and verify the capabilities of radio tomography by measuring interspacecraft electromagnetic wave propagation parameters using the Radio Plasma Imager (RPI) on IMAGE as the transmitter and the WAVES instrument on WIND as the receiver. The primary goal of this experiment was to measure Faraday rotation variations in the RPI signal and interpret them in terms of the path‐integrated magnetic field and electron density. A special 6 W linearly‐polarized 828 kHz RPI signal was clearly detected by WAVES more than 6 RE away and showed a distinct signature of time‐varying Faraday rotation. We show how changes in the path‐integrated electron density/magnetic field product can be unambiguously measured from this continuous, low signal to noise ratio, single frequency measurement.
Evidence for charged aerosols and associated meter‐scale structure in identified PMSE/NLC regions
Authors: Mitchell John D. , Croskey Charles L. , Goldberg Richard A.
Published: February 2004

Evidence for the existence of negatively charged aerosols/dust in PMSE/NLC regions has been obtained by the unique combination of rocket probes flown during the DROPPS Program. Simultaneous current measurements of charged aerosols, ions, and electrons were accomplished by using a configuration of blunt probes, Gerdien condenser, and DC Langmuir probe. The two blunt probes, with different fixed‐bias voltages to discriminate the collection of mobile charge carriers, consistently demonstrated the presence of impacting negatively charged aerosols. Their occurrence coincided with an electron bite‐out, thus confirming the associated loss process as aerosol attachment.
Photochemically‐induced alteration of stable carbon isotope ratios (δ13C) in terrigenous dissolved organic carbon
Authors: Opsahl Stephen P. , Zepp Richard G.
Published: February 2004

Exposure of riverine waters to natural sunlight initiated alterations in stable carbon isotope ratios (δ13C) of the associated dissolved organic carbon (DOC). Water samples were collected from two compositionally distinct coastal river systems in the southeastern United States‐the Satilla River which has high DOC concentrations (10–35 mg/l), and the Altamaha River which has relatively low DOC concentrations (3–9 mg/1). Approximately 21–26% of the DOC was remineralized to DIC. The δ13C of remineralized DIC was isotopically “light” (δ13C = −28.8 to −33.2‰), relative to the initial DOC (δ13C = −27.4‰), leaving a residual fraction of isotopically “heavy” (δ13C = −25.8 to −26.6‰) DOC. Photochemically‐induced fractionation of 13C results from selective degradation of certain biochemical constituents including lignin phenols. These results are consistent with shifts in δ13C of DOC observed during mixing of river and marine waters, suggesting that photochemically‐induced alterations are a factor in determining these changes.
Interdecadal variability in dissolved oxygen in the intermediate water layer of the Western Subarctic Gyre and Kuril Basin (Okhotsk Sea)
Authors: Andreev Andrey G. , Kusakabe Masashi
Published: February 2004

Using dissolved oxygen (DO) concentration at isopycnal surfaces we have observed an oscillation in the intermediate water layer of the Western Subarctic Gyre (WSG) and the Kuril Basin of the Okhotsk Sea with a period of about 20 years. The interdecadal oscillation in DO is strongly correlated with the intensity of the Aleutian Low pressure cell with a 2‐year time lag. The interdecadal variations in DO in the intermediate water layer of the WSG and the Okhotsk Sea may be a result of oscillation in the atmospheric forcing, leading to variations in the isopycnal fluxes of DO at the boundaries of the Okhotsk Sea‐Western Subarctic Gyre‐subtropical region, the isopycnal‐ surface replacement in the WSG, and in changes in the intermediate water formation rate in the Okhotsk Sea.
Mesospheric planetary waves at northern hemisphere fall equinox
Authors: Liu H.‐L. , Roble R. G. , Taylor M. J. , Pendleton W. R.
Published: February 2004

Northern hemisphere planetary waves are strong in the winter and weak in the summer, and they go through a fast transition around equinox. This transition is studied here using NCAR Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics general circulation model (TIME‐GCM) simulations with 1997 National Centers for Environmental Prediction (NCEP) analysis. The planetary wave variability during the transition and its effect on the temperature and winds in the mesosphere are examined. The simulated planetary wave structure agrees with climatological studies, and the fast transition of the planetary waves is captured by the model. The wave variability produces large temperature changes in the upper atmosphere above local stations in middle and high latitudes. The qualitative behavior of the model is in excellent agreement with recent observations of a major perturbation in OH mesospheric temperatures from Ft. Collins (Taylor et al., 2001), although the smaller calculated magnitude suggests that the planetary wave amplitude might be underestimated by the model.
Meridional transport of the North Pacific Intermediate Water in the Kuroshio‐Oyashio Interfrontal Zone
Authors: Yoshinari Hiroshi , Yasuda Ichiro , Ito Shin‐ichi , Firing Eric , Matsuo Yutaka , Katoh Osamu , Shimizu Yugo
Published: February 2004

Meridional transport and origin of the North Pacific Intermediate Water (NPIW) in the Kuroshio‐Oyashio interfrontal zone (K/O zone) were examined using hydrographic and velocity data with LADCP (Lowered Acoustic Doppler Current Profiler) along 37°N in the northwestern Pacific. Dominant northward transports were observed west of the Shatsky Rise (coast‐157°E) in both upper (26.6–27.0σθ) and lower NPIW (27.0–27.5σθ). In the upper NPIW, northward transports of 4.3 Sv which consist of the dominant Kuroshio (3.2 Sv) and small Oyashio component (1.1 Sv) were observed, suggesting that the upper NPIW in the K/O zone was formed by the mixing between the southward Oyashio water across the Oyashio Front and the Kuroshio water bifurcated from the Kuroshio Extension. In the lower NPIW, 9.4 Sv of northward transports (Kuroshio 5.5 Sv and Oyashio 3.9 Sv) were observed, suggesting that the lower NPIW in the K/O zone was maintained by the northward transport of the NPIW formed near the Kuroshio Extension.
Are we exceeding the limits of the Great Circle Approximation in global surface wave tomography?
Authors: Spetzler Jesper , Trampert Jeannot , Snieder Roel
Published: February 2004

The ray theoretical great circle approximation in global surface wave tomography is found to be limited to Earth models with a maximum degree l ≤ 30 for surface waves at 40 s and l ≤ 20 for surface waves at 150 s. This result holds for both phase velocity and group velocity maps. The highest resolution in present‐day global surface wave tomography is close to these limits of ray theory. In order to obtain higher degree resolution models of the Earth in future surface wave tomography, it is necessary to take the scattering of surface waves into account. Increasing the data coverage in seismological networks will not improve the details of tomographic images if ray theory is still applied. It is essential to include the finite‐frequency effects as well.
Variation of the exponential and power law creep parameters with strain for Carrara Marble deformed at 120° to 400°C
Authors: Covey‐Crump S. J.
Published: February 2004

Reliable extrapolation of flow laws for geological materials from laboratory to natural conditions depends upon a sound micromechanical interpretation of the values of the material parameters in those flow laws. In practice, such interpretations require the experimentally determined values of the material parameters to be close to those applying during steady state deformation and/or at given material structure (mechanical state). Using an especially detailed mechanical data set for Carrara marble and a description of flow properties incorporating an explicit structure dependence, the variation of the constant strain and constant structure values of the material parameters in the exponential and power law creep equations is determined as a function of strain. The large variation that is observed underscores the need both for the acquisition of mechanical data to large strains and for further work investigating the structure dependence of flow properties, if flow law extrapolation is to be performed with confidence.
Role of meteoric dust in sprite formation
Authors: Zabotin N. A. , Wright J. W.
Published: February 2004

We show that ubiquitous small conducting particles of meteoric origin in the mesosphere and stratosphere may explain some features of sprite occurrence and fine structure. The main processes involved are: electrostatic field amplification by microspires on the dust surface, “cathode‐like instability” in their vicinity, autoemission and explosive emission of electrons. Additional observations, theoretical development and perhaps laboratory experiments are warranted.
Cirrus climatological results from lidar measurements at OHP (44°N, 6°E)
Authors: Goldfarb L. , Keckhut P. , Chanin M.‐L. , Hauchecorne A.
Published: February 2004

A climatology of cirrus clouds over the Observatoire de Haute Provence in France has been constructed from the analysis of ground‐based lidar measurements taken from 1997 to 1999. During this period the high‐resolution Rayleigh/Mie lidar collected 384 nights of measurements and cirrus profiles are observed in about half of these cases. We find subvisible cirrus (tau < 0.03) constitute ∼20% of cirrus cloud occurrences and that the mean thickness of a subvisible cirrus cloud layer is less than 1 km. A discussion of the error associated with these determinations is also presented.
Precipitation forecast skill of different convective parameterization and microphysical schemes: Application for the cold season over Greece
Authors: Kotroni V. , Lagouvardos K.
Published: February 2004

Since March 2000, the MM5 model is running operationally at the National Observatory of Athens. For the definition of the model setup, namely the selection of the convective parameterization and the microphysical schemes, sensitivity of meso‐β‐scale simulations to different schemes has been investigated. This work focuses on the detailed comparison of MM5 simulations of eight precipitation events that occurred over the Greece during the cold period 1999–2000. Model results are compared against observations using statistical methods, in order to assess the agreement of predicted with observed precipitation amounts, the agreement of the areal coverage of precipitation and the correct placement of maxima and minima. Although all combinations showed a considerable forecast skill, the combination of the Kain‐Fritsch convective parameterization scheme with the Shultz microphysical scheme demonstrated the best forecast skill and the more consistent behaviour.
The interaction of HCl with water‐ice at tropospheric temperatures
Authors: Hynes Robert G. , Mössinger Juliane C. , Cox R. Anthony
Published: February 2004

The uptake of HCl on frozen film ice surfaces was studied as a function of temperature and HCl partial pressure (PHCl) in a flow reactor. The temperatures ranged from 205 to 230 K, and PHCl was (0.4–2.0) × 10−6 Torr. The initial uptake coefficients, γ, and the HCl surface coverage are reported. It was observed that the coverage varied from 3.0 × 1014 molecules/cm² at 205 K to 1.0 × 1014 molecules/cm² at 230 K. At 205 K the coverage showed no dependence on PHCl; the average surface coverage was ∼ (2.0±0.7) ×1014 molecules/cm² at saturation. This value is consistent with other studies on similarly prepared ice films. It was found that γ ∼0.1 at 205 K, but decreased substantially when the temperature increased; however, γ was insensitive to PHCl.
Th‐234 applied to particle removal rates from the surface ocean: A mathematical treatment revisited
Authors: Alleau Y. , Colbert D. , Covert P. , Haley B. , Qiu X. , Collier R. , Falkner K. , Hales B. , Prahl F. , Gordon L.
Published: February 2004

It has been recognized since the 1950's that radioisotopic disequilibrium between naturally occurring parent‐daughter isotope pairs in seawater can provide information on the rate of processes segregating them. In the surface ocean, the U‐238: Th‐234 parent‐daughter pair tends to display measurable disequilibrium that is attributable to the effects of scavenging on particle reactive thorium. A range of approaches has been applied to deriving quantitative information on particle scavenging and sinking rates from U‐238:Th‐234 measurements. Here, we review the mathematical underpinnings of a very basic conceptual model of the removal process in order to correct a misunderstanding that has arisen in recent literature.
Equatorial inertia‐gravity waves observed in TOPEX/Poseidon sea surface heights
Authors: Gilbert Sherryl A. , Mitchum Gary T.
Published: February 2004

We report an evaluation of the ability of the TOPEX/Poseidon altimeter to observe equatorial inertia‐gravity waves in the central Pacific. Aliasing problems limit us to examining meridional mode two, but this mode is an energetic one in the Pacific basin. These estimates of the temporal potential energy modulations are compared with estimates from tide gauges in the tropical Pacific, and we find that the time series obtained at these points show good agreement.
Reaction and desorption of HCl and HBr following collisions with supercooled sulfuric acid
Authors: Behr Peter , Morris John R. , Antman Melissa D. , Ringeisen Bradley R. , Splan Jennifer R. , Nathanson Gilbert M.
Published: February 2004

Gaseous HCl and HBr react with sulfuric acid at rates that depend strongly on acid concentration over a range of acidities typical of stratospheric aerosols. We monitor the competition between immediate desorption and H→D exchange after HCl and HBr thermalize upon collision with the surface of deuterated sulfuric acid: the exchange probabilities decrease from 0.7 to 0.1 (HCl) and 0.9 to 0.2 (HBr) as the acid concentration is increased from 55 to 70 wt% D2SO4 at 213 K. These measurements imply that HCl and HBr desorb faster than they dissociate at higher acidities, impeding the formation of Cl− and Br− in more acidic aerosols. Residence time measurements of HCl molecules that do enter the acid, however, indicate that HCl is more soluble than expected at high sulfuric acid concentrations.
An oxygen isotope record of lacustrine opal from a European Maar indicates climatic stability during the Last Interglacial
Authors: Shemesh Aldo , Rietti‐Shati Miri , Rioual Patrick , Battarbee Rick , de Beaulieu Jacques‐Louis , Reille Maurice , Andrieu Valerie , Svobodova Helena
Published: February 2004

The penultimate temperate period, 127–110 ka before present (BP), bracketed by abrupt shifts of the global climate system initiating and terminating it, is considered as an analogue of the Holocene because of a similar low global ice‐volume. Ice core records as well as continental and marine records exhibit conflicting evidence concerning the climate variability within this period, the Last Interglacial. We present, for the first time, a high‐resolution record of oxygen isotopes in diatom opal of the Last Interglacial obtained from the Ribains Maar in France (44°50′09″N 3°49′16″E). Our results indicate that the Last Interglacial in southwestern Europe was generally a period of climatic stability. The record shows that the temperate period was initiated by an abrupt warm event followed midway by a minor climatic transition to a colder climate. An abrupt isotopic depletion that occurs simultaneously with abrupt changes in pollen and diatom assemblages marks the end of the temperate period, and is correlative with the Melisey I stadial. Variations in the isotopic composition of lake‐water related to the isotopic composition of precipitation and evaporation dominate the biogenic opal oxygen isotope record.
The Pacific Ocean Subtropical cell surface limb
Authors: Johnson Gregory C.
Published: February 2004

The subtropical cells (STCs) cycle subtropically subducted water to the equator, where it upwells and flows pole ward at the surface, exchanging heat and freshwater with the atmosphere. Pacific STC surface flow is analyzed using drifter data. Mean surface velocities are estimated. The mean divergence reveals substantial equatorial upwelling. Off‐equatorial downwelling around ±4° latitude suggests that about half the upwelled water may recirculate in shallow tropical cells. Pathways and time scales for the poleward surface limb of the STC are estimated. Mean streamlines reach ±9° latitude after half a year and ±22° after 2 years, taking a more convoluted path in the northern hemisphere. They reenter the subtropics in the western half of the basin, far from the subduction regions feeding the equatorward limbs of the STCs, reinforcing the point that the STCs are intrinsically linked with the global ocean circulation.
Compositional structure within the lunar crust as constrained by Lunar Prospector thorium data
Authors: Warren Paul H.
Published: February 2004

Lunar Prospector gamma‐ray spectrometer data for surface thorium indicate that craters greater than about 60 km in diameter tend to excavate into materials less Th‐rich than the surface regolith. For the largest 12 craters and basins amenable to this type of analysis (diameters between 90 and 930 km), the ratio of crater (or basin) Th concentration to regional background Th averages 0.76±0.13. This trend implies a pronounced diminution in average Th concentration with increasing depth (down to roughly 30 km deep) in the lunar crust. Assuming deep‐origin Orientale ejecta was strongly diluted by turbulent basin‐modification mixing, an even more pronounced depth‐Th anticorrelation would be indicated by extrapolation of the trend of the 30–300 km craters to higher diameters, i.e., deeper excavations. In any case, the overall lunar crust, and by extension the bulk Moon, is probably far less Th‐rich than a simple averaging of surface compositions would suggest.
The anomalous diffusion of meteor trails
Authors: Dyrud Lars P. , Oppenheim Meers M. , vom Endt Axel F.
Published: February 2004

Radars frequently detect meteor trails created by the ablation of micro‐meteoroids between 70 and 120 km altitude in the atmosphere. Plasma simulations show that density gradients at the edges of meteor trails drive gradient‐drift instabilities which develop into waves with perturbed electric fields often exceeding hundreds of mV/m. These waves create an anomalous cross‐field diffusion that can exceed the cross‐field (⟂ B) ambipolar diffusion by an order of magnitude. The characteristics of the instabilities and anomalous diffusion depend on the trail altitude, latitude, and density gradient. A simple relation defines the minimum altitude at which meteor trail density gradients drive plasma instabilities and anomalous diffusion. These results impact a number of meteor radar studies, including those that use diffusion rates to determine trail altitude, and atmospheric temperature.
Deep roots sustain amazonian rainforest in climate model simulations of the Last Ice Age
Authors: Kleidon Axel , Lorenz Stephan
Published: February 2004

We show with a series of climate model simulations of the last glacial maximum that the extent of humid regions in Amazonia depends considerably on the ability of vegetation to recycle soil moisture. When deep roots and the associated large soil water storages are included in the simulations, enhanced transpiration leads to enhanced continental moisture recycling and a cooler surface climate. These differences are similar in magnitude to those introduced by the glacial conditions. As a result, the extent of humid regions is considerably enlarged, in particular for the Amazon basin. A series of indications support the consequences of this effect, suggesting that the Amazonian biogeography during glacial periods may not have been drastically different from today.
Air‐sea interaction and spatial variability of the surface evaporation duct in a coastal environment
Authors: Brooks Ian M.
Published: February 2004

Aircraft observations are presented of the horizontal variability in the depth of the surface evaporation duct and the relationship with the mesoscale structure of air‐sea interaction processes. The 2‐dimensional fields of near‐surface wind, stress, wind‐stress curl, air and sea‐surface temperature are measured directly for flow around a headland. The sea surface temperature field indicates cold upwelling driven by the wind‐stress curl. Boundary‐layer stability responds rapidly to the spatial changes in surface temperature. These changes result in modification of the evaporation duct, which decreases significantly in depth over the cooler upwelling water.
The North Atlantic Oscillation and the occurrences of ozone miniholes
Authors: Orsolini Yvan J. , Limpasuvan Varavut
Published: February 2004

The North Atlantic Oscillation (NAO) induces a clear signature on synoptic‐scale ozone fluctuations over the Euro‐Atlantic sector, as revealed by a band‐pass filtering analysis of the Total Ozone Mapping Spectrometer (TOMS) satellite observations over a 20‐year period. Low‐ozone episodes, or miniholes, appear more frequent over the Euro‐Atlantic sector in the high NAO phase, when the prevailing, upper tropospheric westerly jet is displaced pole‐ward and acquires a stronger northward tilt relative to climatology. Thus, the tendency of the NAO to remain in its high phase in late eighties and nineties accounts for recent observations of more frequent minihole conditions and episodes of low‐latitude, ozone‐poor intrusions into high‐latitude region of this sector.
Comparison of POLDER cloud phase retrievals to active remote sensors measurements at the ARM SGP site
Authors: Riedi J. , Goloub P. , Marchand R. T.
Published: February 2004

In our present study, cloud boundaries derived from a combination of active remote sensors at the ARM SGP site are compared to POLDER cloud top phase index which is derived from polarimetric measurements using an innovative method. This approach shows the viability of the POLDER phase retrieval algorithm, and also leads to interesting results. In particular, the analysis demonstrates the sensitivity of polarization measurements to ice crystal shape and indicates that occurrence of polycrystalline ice clouds has to be taken into account in order to improve the POLDER phase retrieval algorithm accuracy. Secondly, the results show that a temperature threshold of 240 K could serve for cloud top particle phase classification. Considering the limitations of the analysis, the temperature threshold could be biased high, but not by more than about 5 degrees.
Slip‐length scaling in large earthquakes: Observations and theory and implications for earthquake physics
Authors: Shaw Bruce E. , Scholz Christopher H.
Published: February 2004

For twenty years there has been a dilemma in earthquake physics, because the observed scaling law for large earthquakes did not appear to be consistent with the stress‐drop invariance of small earthquake scaling. Surprisingly, slip was seen to continue to increase with rupture length L even for events with lengths much longer than the event widths W (the brittle crust down‐dip depth), whereas it might have been expected to saturate for lengths much beyond the width. If this implies that the physics of great earthquakes is somehow different from that of their smaller counterparts, this casts serious doubts on predicting the effects of the rare and damaging great events from observations of the more common smaller events. Here we bring together recently compiled observations of very large aspect ratio earthquakes with results of a 3 dimensional dynamic earthquake model to show that slip‐length scaling observations are, in fact, consistent with a scale‐invariant physics. Further, we discuss the origin of the large earthquake scaling in the model.