bluuebunny/crossref_metadata_2025 huggingface dataset:
Ganymede's ionic radiation belts
Authors: Williams D. J.
Published: February 2004

During Galileo's fifth close encounter with Jupiter's moon Ganymede (May 20, 2000), energetic particle observations revealed the existence of trapped ions within Ganymede's closed field line region. Previously only trapped electrons had been observed within Ganymede's magnetosphere. Furthermore, the measured electron distributions displayed a normal sinn(α) pitch angle distribution as opposed to the butterfly distributions observed during the G8 encounter. The existence of trapped energetic ions in Ganymede's magnetosphere along with the existence of more stably trapped electrons shows the robustness of that magnetosphere and emphasizes the importance of modeling studies to determine particle drift paths within it and to reveal the processes that populate the closed field‐line region. Qualitatively such drift paths seem able to unify details of the pitch angle distributions measured during the two encounters for which trapped particles have been observed.
Tropical Pacific basin‐wide adjustment and oceanic waves
Authors: An Soon‐Il , Kang In‐Sik
Published: February 2004

This study examines the basin‐wide adjustment process associated with El Niño‐Southern Oscillation (ENSO) in terms of oceanic waves using the Cane‐Zebiak model. The Rossby waves induce not only the meridional mass divergence in the ocean interior but also the incoming zonal mass flux at the western boundary, which generally overcompensates the interior meridional divergence. Therefore, the Rossby waves alone cannot make a negative feedback. However, the outgoing zonal mass flux associated with the reflected Kelvin wave at the western boundary reduces the incoming boundary mass flux associated with the Rossby waves, resulting in the tendency of equatorial basin‐wide heat content varying in phase with the meridional divergence. Also shown is that the nonequilibrium adjustment of the tropical Pacific Ocean is mainly due to the free Kelvin waves reflected at the western boundary.
Surface wave waveform anomalies at the Saudi Seismic Network
Authors: Laske G. , Cotte N.
Published: February 2004

This paper describes surface wave waveforms observed at the Saudi Arabian Seismic Network. We identify records corresponding to events occuring in the Kuril Islands region as anomalous and discuss possible causes for the waveform distortions. Most likely, the waveform anomalies are caused by constructive and destructive interference of laterally refracted wave packets. Some waveform anomalies are probably of instrumental origin and we suspect a calibration error for the vertical component at station RIYD. For station AFIF, we find a significant clockwise rotation of the horizontal components with respect to geographic North by approximately 4 degrees.
Recent upward shift of the deep convection system in the Japan Sea, as inferred from the geochemical tracers tritium, oxygen, and nutrients
Authors: Gamo Toshitaka , Momoshima Noriyuki , Tolmachyov Sergei
Published: February 2004

The thermohaline circulation system in the Japan Sea, an almost land‐locked marginal sea in the northwest Pacific, is now in a transition state. Comparison of vertical profiles of tritium, oxygen and nutrients between 1984 and 1998 demonstrates the following two points: (1) the supply of dense surface seawater to the bottom layer (>2,500 m in depth) has almost ceased since 1984, and (2) the intrusion of surface seawater to an intermediate depth range (between ∼700 m and ∼2,000 m in depth) has been reinforced during this 14‐year period. Such transitional upward shift of the thermohaline conveyor belt in the Japan Sea is thought to have separeted the bottom water from the conveyor belt and brought about a stagnant mode of the bottom water.
Chlorophyll variability in eastern boundary currents
Authors: Thomas A. C. , Carr M.‐E. , Strub P. T.
Published: February 2004

The first three years of SeaWiFS data (1997–2000) provide the most complete quantification to date of chlorophyll seasonal variability along the full latitudinal extent of the four major eastern boundary currents (EBCs). Comparisons to previously published chlorophyll seasonal climatologies deduced from the relatively sparse coverage provided by the Coastal Zone Color Scanner (CZCS) show significant differences in both southern hemisphere EBCs, while northern hemisphere regions are qualitatively similar. Comparisons between chlorophyll and cross‐shelf Ekman transport seasonal cycles, calculated from coincident satellite scatterometer data, show seasonal maxima have similar phases over most of the California Current, at higher (>32°S) latitudes in the Peru‐Chile and Benguela Currents (>30°S) and at lowest latitudes (< 20°N) in the Canary Current. Latitudinal zones within which phases diverge are indicative of alternate and/or more distant forcing.
Tidal triggering of microearthquakes on the Juan de Fuca Ridge
Authors: Wilcock William S. D.
Published: February 2004

Tidal stresses beneath the oceans can be up to an order of magnitude higher than those found in the continents because of the effects of loading by ocean tides. I have analyzed 1899 microearthquakes recorded during a 55‐day experiment on the Endeavour segment of the Juan de Fuca Ridge for tidal triggering. The tidal phase of the full data set and of a declustered subset comprising 987 events appears non‐random to a high level of confidence. Earthquakes occur more frequently near low tides, especially the lowest spring tides, when the extensional stresses are a maximum in all directions.
Modeling broadscale deformation in northern California and Nevada from plate motions and elastic strain accumulation
Authors: Murray Mark H. , Segall Paul
Published: February 2004

We present a first‐order method for modeling broadscale deformation consistent with both plate tectonic motions and elastic strain accumulation on plate boundary faults. Interseismic deformation is assumed to be a superposition of long‐term rigid‐body motions between faults, defined by angular velocities of spherical plates, and backslip on shallow locked portions of faults in an elastic half‐space. This method is applied to 1993–2000 continuous GPS data from 35 sites in a profile from the San Francisco Bay area, northern California, to eastern Nevada. Deformation is consistent, within the 1 mm yr−1 uncertainties of the estimated site velocities, with a simple 10‐parameter model using 6 rigid plates and 3 locked San Andreas system faults.
The effect of stratospheric ozone depletion on the phase of the Antarctic Oscillation
Authors: Sexton D. M. H.
Published: February 2004

The effect of stratospheric ozone loss on Southern Hemispheric extratropical circulation is explored using an atmosphere‐only model. The main tropospheric response is a sudden shift in the leading mode of month‐to‐month variability, the Antarctic Oscillation, during November and December towards its high phase. Therefore, this change consists of a shift in atmospheric mass from high‐latitudes poleward of 60°S to a mid‐latitude band centred on 45°S. This response provides a plausible explanation for the increase in westerly circulation at 60°S observed since the early 1980's. There is also a strong response in January–March but this may be unrealistic as the observed lower stratospheric temperature changes are poorly simulated in that season.
Comparison between crustal density and velocity variations in southern California
Authors: Langenheim V. E. , Hauksson Egill
Published: February 2004

We predict gravity from a three‐dimensional Vp model of the upper crust and compare it to the observed isostatic residual gravity field. In general this comparison shows that the isostatic residual gravity field reflects the density variations in the upper to middle crust. Both data sets show similar density variations for the upper crust in areas such as the Peninsular Ranges and the Los Angeles basin. Both show similar variations across major faults, such as the San Andreas and Garlock faults in the Mojave Desert. The difference between the two data sets in regions such as the Salton Trough, the Eastern California Shear Zone, and the eastern Ventura basin (where depth to Moho is <30 km), however, suggests high‐density middle to lower crust beneath these regions. Hence the joint interpretation of these data sets improves the depth constraints of crustal density variations.
Survey of deep tail plasma sheet crossings: Plasma sheet distributions resulting from reconnection
Authors: Mist R. T. , Owen C. J. , Mukai T.
Published: February 2004

We illustrate the structure of the distant (X < −60 Re) plasma sheet and separatrix layers in terms of low energy ion distributions observed by Geotail. In a statistical survey, ion distributions are classified as single or multi‐component. Multi‐component populations are clearly observed in 68% of tailward flows. In two crossings only multi‐component populations are observed and in two crossings no multi‐component populations are identified. Although multi‐component plasmas occur throughout the plasma sheet, they are observed more often in the outer region. Previous plasma sheet formation models do not predict multi‐component distributions in the centre of the plasma sheet. However, this data supports the Owen and Mist [2001] model that predicts a similar plasma sheet structure.
Relationship between zonal and meridional modes in the tropical Atlantic
Authors: Murtugudde Ragu G. , Ballabrera‐Poy Joaquim , Beauchamp James , Busalacchi Antonio J.
Published: February 2004

The tropical Atlantic displays two main modes of variability; the meridional or dipole mode and the equatorial zonal mode. It was proposed recently, that these two modes are correlated and are both forced within the tropics by latitudinal displacements of the ITCZ. This modeling study shows that while the two modes are correlated for limited record lengths prior to and after 1976, the correlation falls apart when longer time‐series from 1949 to 2000 are considered. The 1976 ‘climate shift’ also occurred in the tropical Atlantic seen as a thermocline shift similar to the Pacific, forced dynamically within the tropics. The first EOF of the simulated thermocline depth captures the inter‐decadal mode with the 1976 shift. The first EOF of SST anomalies prior to (after) 1976 represents the meridional (zonal) mode, consistent with the previous finding that the relation between the eastern Pacific and Atlantic ITCZ is stronger in the 1980‐90's.
Rayleigh lidar observations of a mesospheric inversion layer during night and day
Authors: Duck Thomas J. , Sipler Dwight P. , Salah Joseph E. , Meriwether John W.
Published: February 2004

A narrow field of view Rayleigh lidar has been constructed at Millstone Hill / MIT Haystack Observatory (42.6°N, 71.5°W) for observations of middle atmospheric temperatures throughout the diurnal cycle. During a 31.5 h measurement on 19–21 March 2001 a mesospheric thermal inversion layer was observed in both the night and day. It developed near 60 km in altitude, progressed downward at 0.40±0.06 km/h, and had an overlying adiabatic lapse rate. The inversion amplitude correlated with the evolution of stratospheric gravity wave activity, although the mesospheric perturbations were too large to be due to conservative gravity‐wave growth alone. The 24 h mean temperature profile shows no evidence of a residual inversion layer.
Arabian Sea and Bay of Bengal exchange of salt and tracers in an ocean model
Authors: Jensen Tommy G.
Published: February 2004

Exchanges of mass and salt between the mixed layers in the Arabian Sea and the Bay of Bengal are examined in a model of the Indian Ocean using passive tracers as a tool to map the pathways. Inflow of high salinity water from the Arabian Sea into the Bay of Bengal is significant and occurs after the mature phase of the southwest monsoon. Freshwater transport out of the Bay of Bengal is southward throughout the year along the eastern boundary of the Indian Ocean. Low salinity water transport into the Arabian Sea occurs in the Somali Current during the southwest monsoon, closing a clockwise path of water mass transport. Only a small fraction of low salinity water is advected into the eastern Arabian Sea from the Bay of Bengal.
Losses of ring current ions by strong pitch angle scattering
Authors: Walt M. , Voss H. D.
Published: February 2004

High angular resolution measurements of 155 keV ions in the ring current during the magnetic storm of August 6, 1998 show filled loss cones indicating that very rapid pitch angle scattering is taking place above the satellite location. The measurements were made with the SEPS detector on the Polar satellite during its passages through the ring current regions, usually at magnetic latitudes near ±45° and at magnetic local times of about 04:00 and 16:00 hrs. The observed strong pitch angle scattering implies a trapping lifetime of less than an hour and may explain the early rapid recovery of Dst during magnetic storms.
Sprites over Europe
Authors: Neubert T. , Allin T. H. , Stenbaek‐Nielsen H. , Blanc E.
Published: February 2004

Results are presented from the first European campaign for observation of sprites, conducted during the summer of 2000 from the French astronomical observatory, Observatoire Midi‐Pyrénées. The primary objective was to establish if sprites are generated over Europe and to identify the characteristics of the associated thunderstorms. During the one‐month campaign local weather conditions allowed observations approximately half of the nights. Sprites were observed two nights over the Alps and one night over southeastern France in connection with cold fronts moving in from the Atlantic. In all, 40 sprites were recorded, including dancing sprites, multiple carrot sprites and c‐sprites. The weather conditions were almost identical during the 3 nights, with the active area forming on the front‐side of the cold fronts. The storms are not of the same magnitude as active systems often observed over the North American plains. Even so, sprites seem to be a common occurrence also over Europe.
Contribution of “Old” carbon from natural marine hydrocarbon seeps to sedimentary and dissolved organic carbon pools in the Gulf of Mexico
Authors: Wang Xu‐Chen , Chen Robert F. , Whelan Jean , Eglinton Lorraine
Published: February 2004

Natural radiocarbon (14C) abundances and stable carbon isotope (δ13C) compositions were measured for sediment total organic carbon (TOC), and total lipid fractions of sediments, bottom water, and hydrate‐water collected from two hydrocarbon seepage sites in Green Canyon, Northern Gulf of Mexico to determine the contribution of “old” carbon from seeps to sediment TOC and dissolved organic carbon (DOC) pools. Our results indicate that 40–60% of the organic carbon preserved in the sediments and 30% of the DOC in the deep water above the seeps were seep‐derived 14C‐depleted organic carbon. This new evidence along with our previous studies suggest that natural marine hydrocarbon seepage could be a significant source contributing “old” carbon to the marine environment. Our findings suggest that the global importance and the long‐term impact of this contribution to biogeochemical carbon cycling in the ocean need to be more thoroughly investigated.
Structure of the upper mantle under the Antarctic Plate from surface wave tomography
Authors: Danesi S. , Morelli A.
Published: February 2004

We have analyzed surface wave data for 245 events occurring in Antarctica and surrounding oceans during years 1991‐1999. We first apply dispersion analysis to the fundamental mode of Rayleigh waves for periods ranging from 20 to 150 sec. We then invert path‐averaged dispersion curves to obtain 2D maps of group velocity for different periods, represented by splines on a grid with 250 km spacing, with considerably more detail than that achieved by global models. We finally use group velocity maps in a nonlinear inversion for the regional 3D υSV structure of the upper mantle. The resulting model shows thick continental roots under East Antarctica, reaching depths below 200 km; low velocities under oceanic ridges, mostly confined to the upper 150 km; and a slow area under the Ross Sea volcanic centres, extending all the way down to 200 km, beyond which our data loose resolving power.
Footprinting: A seasonal connection between the tropics and mid‐latitudes
Authors: Vimont Daniel J. , Battisti David S. , Hirst Anthony C.
Published: February 2004

A connection between the mid‐latitude and tropical Pacific is identified in a coupled general circulation model (CGCM). The connection involves a seasonal coupling between winter mid‐latitude atmospheric circulation anomalies, and summer equatorial wind stress anomalies. The seasonal coupling results from a “footprinting” mechanism, in which the summer tropical atmosphere responds to subtropical sea surface temperature (SST) anomalies that are generated by the mid‐latitude atmospheric variability during the previous winter. Details of the connection, and of the footprinting mechanism are presented. Implications for interannual ENSO and decadal ENSO‐like variability are discussed.
Stratospheric ozone isotope enrichments—Revisited
Authors: Mauersberger Konrad , Lämmerzahl Peter , Krankowsky Dieter
Published: February 2004

Ozone isotope data for 49O3 and 50O3 are presented, that were obtained from 28 stratospheric samples collected over 10 years onboard balloon payloads. Enrichments for 49O3 range from 7 to 9% in the middle stratosphere. This is in very good agreement with laboratory‐derived isotope predictions. For 50O3 most enrichments are between 7 and 11%, a few, however, are too high to be of atmospheric origin. Arguments are presented that stratospheric ozone isotope data are consistent with enrichments determined in laboratory studies when pressure and temperature dependence of the isotope effect is included. Results from recent remote sensing experiments support the values obtained during balloon‐borne sample collections. Very high enrichments occasionally measured in the past should be disregarded.
A chemical ionization technique for measurement of pernitric acid in the upper troposphere and the polar boundary layer
Authors: Slusher D. L. , Pitteri S. J. , Haman B. J. , Tanner D. J. , Huey L. G.
Published: February 2004

The potential of SF6− for the detection of pernitric acid in air by chemical ionization mass spectrometry was studied in the laboratory via its reactions with HO2NO2, O3, H2O, and NO2. Measurements of HO2NO2 using SF6− ion chemistry were then performed at the South Pole. SF6− reacts at the gas kinetic rate with HO2NO2 to form SF5−, NO4−(HF), NO2−(HF), and NO3−. The NO4−(HF) product provides a unique signature for HO2NO2. The rate coefficient for this channel is 2.9 × 10−10 cm³ molecule−1s−1 at 16.5 torr in N2 and decreases as the total pressure increases. NO4−(HF) undergoes ligand switching with H2O and HO2NO2, implying the existence of a NO4− core ion in the gas phase. SF6− reacts with H2O to produce a large number of product ions that increase nonlinearly with [H2O]. This limits the use of SF6− to regions of the atmosphere with low absolute humidities. However, our lab studies indicate that HO2NO2, can be selectively detected in air with an ozone mixing ratio up to 550 ppbv and a dew point of −25°C or less, which corresponds to regions of the troposphere where HO2NO2 is expected to be thermally stable. We present field data from the South Pole showing typical HO2NO2 mixing ratios of 20 pptv.
Experimental mixing variability in intersecting natural fractures
Authors: Johnson Joel , Brown Stephen
Published: February 2004

Laboratory experiments of flow through epoxy replicas of intersecting natural fractures show that solute transport deviates significantly from predictions of two‐dimensional streamline routing through parallel plate intersections. Surface roughness in intersecting fractures causes two major discrepancies between mixing experiments and the parallel plate predictions. First, the fluids exiting the intersection are not uniformly mixed, but consist of ribbons with varied solute concentrations which tend to follow streamlines in the flow. Some of these streams maintain a nearly pure inlet fluid composition as they exit the intersection and traverse the outlet fracture. Second, when the outlet fluids are collected and homogenized, we find that this complex redirection of streamlines within natural rough‐walled fracture intersections results in more total mixing than is predicted by the parallel plate model.
A nonlinear vacillating dynamo induced by an electrically heterogeneous mantle
Authors: Chan Kit H. , Zhang Keke , Zou Jun , Schubert Gerald
Published: February 2004

This paper reports the first spherical numerical dynamo based on a three‐dimensional finite element method. We investigate a nonlinear dynamo in a turbulent electrically conducting fluid spherical shell of constant electric conductivity surrounded by an electrically heterogeneous mantle. Magnetic fields in the form of a three‐dimensional azimuthally traveling dynamo wave are generated by a prescribed time‐dependent α in the fluid shell. In the inner sphere, we assume that there is a solid electrical conductor with the same conductivity as that of the fluid shell. Equilibration of the generated magnetic fields is achieved by the nonlinear process of α‐quenching. We show for the first time that finite element methods can be effectively and efficiently employed to simulate three‐dimensional dynamos in spherical systems. We also show that an electrically heterogeneous mantle can modulate the core dynamo, leading to a vacillating dynamo whose amplitude depends upon the relative phases between the generated magnetic field and the heterogeneous mantle.
Correction to “Titan, Mars and Earth: Entropy production by latitudinal heat transport”
Authors: Lorenz Ralph D.
Published: February 2004

Small corrections are made, which do not affect the results of the paper.
Seawater temperature trends at Usa Tide Gauge sites
Authors: Maul George A. , Davis Andria M. , Simmons Jeffrey W.
Published: February 2004

Seawater temperatures have been measured at United States tide gauges throughout most of the 20th century. All available records have been digitized, and the longest 14 have been analyzed by linear least‐square regression. The largest positive trend is from Boston MA (+3.6±0.4°C per century), and the largest negative trend is at Charleston SC (−0.1±0.3°C per century). No consistent latitudinal or east‐coast vs. west‐coast patterns are discernable, but air temperature trends are typically greater than seawater changes.
Influence of aerosol dry deposition on photosynthetically active radiation available to plants: A case study in the Yangtze Delta Region of China
Authors: Bergin M. H. , Greenwald R. , Xu J. , Berta Y. , Chameides W. L.
Published: February 2004

In this paper, a new mechanism is proposed by which aerosols decrease the amount of photosynthetically active radiation (PAR) available to plants for photosynthesis. The mechanism involves the scattering and absorption of PAR by water insoluble aerosol particles (WIA) which deposit on leaves and are not washed off by precipitation. A simple model is developed that predicts the change in the transmittance of PAR, TPAR, for plant leaves due to WIA dry deposition as a function of aerosol chemical, physical, and optical properties. Model estimates for the agricultural Yangtze delta region of China indicate that over a 2‐month period during a growing season, dry deposition of WIA may account for a ∼35% reduction in PAR available for plant photosynthesis. Although, the estimate is sensitive to several factors that are uncertain including aerosol dry deposition velocity, leaf area index, and removal rate of particles by precipitation. Results suggest that impacts on crop yields due to aerosol dry deposition could be considerable in this region and suggest a previously neglected economic incentive for China to mitigate air pollution. Additionally, WIA dry deposition may influence carbon uptake by plants in other locations that experience regional haze.
The role of the non‐axisymmetric antarctic orography in forcing the observed pattern of variability of the Antarctic climate
Authors: Lachlan‐Cope Tom A. , Connolley William M. , Turner John
Published: February 2004

The pattern of inter‐annual variability in the atmospheric circulation around Antarctica has a maximum over the Amundsen‐Bellinghausen Sea (ABS), which is particularly strong during the winter (June, July and August). By using an atmosphere‐only general circulation model the causes of this maximum have been investigated. In particular we study the effect of the non‐axisymmetric nature of the local surface forcing (sea surface temperatures, sea ice and orography) by imposing axi‐symmetric forcing fields at high southern latitudes. The results of these experiments show that the non‐axisymmetric nature of the Antarctic orography is sufficient to explain the variability maximum in the ABS.
Ulysses in the south polar cap at solar maximum: Heliospheric magnetic field
Authors: Smith E. J. , Balogh A. , Forsyth R. J. , McComas D. J.
Published: February 2004

Observations during the recent ascent of Ulysses to the south polar region are reported. Large variations in field magnitude are associated principally with solar wind interaction regions. The observed spiral angle agrees reasonably well with the Parker model. The magnetic flux, the product of the radial field component and the square of the radial distance (r² BR), is independent of latitude implying non‐radial expansion of the solar wind. Two magnetic sectors are present up to a latitude of ≈ −78° above which a single negative (inward) polarity is observed consistent with the polar field not yet having reversed. Crossings between sectors, extrapolated back to the sun, appear consistent with a single warped current sheet tilted slightly to the rotation axis. Field lines in the polar region passing near the current sheet originate at low latitudes. They provide access of high energy solar particles to the polar region.
Strain partitioning during the elastic deformation of an olivine + magnesiowüstite aggregate
Authors: Covey‐Crump S. J. , Schofield P. F. , Stretton I. C.
Published: February 2004

In order to measure directly the extent of elastic strain partitioning between the phases in a two phase material, room temperature uniaxial compression experiments have been performed on an olivine + magnesiowüstite sample within the neutron beam at the ISIS neutron spallation source, Rutherford Appleton Laboratory, U.K. Neutron diffraction data were collected at fourteen different applied loads. At each load the olivine and magnesiowüstite lattice parameters in directions parallel and normal to the direction of applied load, were extracted from the diffraction data, and the axial and radial elastic strains experienced by each phase were calculated from these parameters. The observed strain partitioning is in close agreement with that predicted by the widely used Hashin‐Shtrikman analysis of the elastic properties of composites, confirming both the validity of that analysis, and the potential which the experimental technique has for providing insight into the controls on the mechanical properties of polymineralic materials.
Interannual upper ocean variability in the tropical Indian Ocean
Authors: Feng Ming , Meyers Gary , Wijffels Susan
Published: February 2004

Empirical orthogonal function (EOF) analysis is used to characterize interannual upper ocean temperature variability since mid‐1980s along two repeated XBT sections across the Indian Ocean. The mode 1 EOF loadings have deepened thermocline in the western tropical Indian Ocean and a shoal thermocline in the east/southeast Indian Ocean during the 1994 and 1997/98 Indian Ocean dipole (IOD) events. Reversed anomalies occur during 1988/89, 1996, and 1998/99. The mode 2 EOF loadings only have significant magnitudes related to the IOD, with upwelling (downwelling) along the Sumatra‐Java coast and downwelling (upwelling) in the southern subtropics leading (lagging) the IOD peaks. Lagged correlations between sea level anomaly and westward wind stress anomaly along the equatorial Indian Ocean (an IOD index) support the EOF analysis: the two EOF modes are linked by propagation and reflection of subtropical Rossby waves and equatorial Kelvin waves, which also contribute to reverse the IOD through a delayed action.
First absolute dating of Miocene Langbeinite evaporites by 40Ar/39Ar laser step‐heating: [K2Mg2(SO4)3] Stebnyk Mine (Carpathian Foredeep Basin)
Authors: Léost I. , Féraud G. , Blanc‐Valleron M. M. , Rouchy J. M.
Published: February 2004

Four langbeinite [K2Mg2(SO4)3] single grains from the Stebnyk evaporite mine have been dated with the laser step‐heating 40Ar/39Ar method. These yield very clustered ages, including a high quality plateau age of 14.31 ± 0.06 Ma for 99.5% 39ArK released. These Middle Miocene ages disagree with the inferred Early Miocene age of the Stebnyk deposit [Peryt and Kovalevich, 1997]. Therefore, langbeinite may be formed after primary evaporite deposition in a maximum time interval around 7.5 Ma, during a diagenetic process or as a result of a fluid circulation. However the stratigraphic age may have been also overestimated due to a complicated tectonic history and the absence of clear stratigraphic markers. This work confirms the suitability of langbeinite for 40Ar/39Ar dating. Langbeinite in evaporites may thus be used for stratigraphic dating when primary, or for dating diagenesis or fluid circulation when secondary.
Towards the time dependent modeling of sediment core data on a global basis
Authors: Heinze Christoph
Published: February 2004

The procedure for the simulation of a time dependent sediment stratigraphy for 4 different sediment species with a global biogeochemical ocean general circulation model is presented. In this feasibility study, a sediment column for the last 131 kyr was accumulated through use of a variable ocean velocity field (mixed from preindustrial and glacial ocean time slices in a kinematic approach). The biogenic components of sediment are entirely a model product. Artificial sediment cores were “recovered” from the simulated stratigraphy. The approach is the foundation for a systematic comparison of paleoclimate simulations with the sediment record. Through use of adjoint model codes the direct 4‐dimensional data assimilation of paleoclimate observations will become possible in the long range.
Formation and maintenance of the extratropical tropopause by baroclinic eddies
Authors: Haynes Peter , Scinocca John , Greenslade Michael
Published: February 2004

Numerical simulations in a simple atmospheric model show that a realistic extratropical tropopause structure, marked by a strong change both in meteorological variables such as lapse rate and in transport characteristics, may be achieved solely through the stirring effects of baroclinic eddies acting against a smooth thermal relaxation. The flow self‐organizes to give a transport structure that has a sharp transition in the vertical. Below the transition level the eddies stir across entire isentropic surfaces. The transition level corresponds to the extratropical tropopause height. Above the transition level there is a midlatitude transport barrier, corresponding to the subtropical transport barrier in the real atmosphere, with eddy stirring on poleward and equatorward sides. Similar self‐organizing mechanisms are likely to be relevant in the stratosphere and in oceanic flows.
Characterization of surface heterogeneity detected at the MISR/TERRA subpixel scale
Authors: Widlowski Jean‐Luc , Pinty Bernard , Gobron Nadine , Verstraete Michel M. , Davis Anthony B.
Published: February 2004

Vegetation structure can have a significant impact on the degree of anisotropy in the reflected radiation field. With the appropriate characterization of these effects, the analysis of multiangular data, such as provided by the Multi‐angle Imaging SpectroRadiometer (MISR) instrument on board TERRA, can yield statistical information about the type of surface heterogeneity that exists at the subpixel scale.
Depth‐dependent time‐clustering behaviour in seismicity of southern California
Authors: Telesca Luciano , Cuomo Vincenzo , Lapenna Vincenzo , Macchiato Maria
Published: February 2004

Temporal fluctuations in seismicity of southern California have been investigated by means of two methods, the Allan Factor Analysis and the Detrended Fluctuation Analysis, which are used to detect the scaling behaviour of an nonstationary observational time series. Performing the time‐clustering analysis varying the depth of the events, we found that the seismicity of the area reveals a tendency toward Poissonian behaviour near the depth ranges 14–16 km.
The effect of CO2 variability on the retrieval of atmospheric temperatures
Authors: Engelen Richard J. , Stephens Graeme L. , Denning A. Scott
Published: February 2004

The effect of spatial variability of the atmospheric CO2 distribution on temperature and water vapor retrievals from high spectral resolution observations of infrared emission is estimated by performing 4 different retrieval experiments. Using a global mean CO2 value, as currently routinely used, introduces errors in the retrieved temperature profile of up to 0.85 K compared to a retrieval in which the CO2 profile is known exactly. Including CO2 in the retrieval vector reduces these errors to 0.3 K. A more practical alternative, especially for data assimilation, is to use a monthly mean zonal mean CO2 value, which produces errors of up to 0.35 K in the temperature profile.
Simulations of diurnal tides due to tropospheric heating from the NCEP/NCAR Reanalysis Project
Authors: Forbes Jeffrey M. , Zhang Xiaoli , Hagan Maura E.
Published: February 2004

Diurnal tides are forced in a global‐scale wave model using monthly mean tropospheric heating rates from the NCEP/NCAR Reanalysis Project. The heating rates give rise to a semiannual variation in the migrating (sun‐synchronous) tidal wind response near 95 km altitude with equinoctial maxima (∼50–70 ms−1) similar in magnitude to those derived from observational data. Nonmigrating (longitude‐dependent) tides with zonal wavenumbers s=−3 (eastward) to s=+5 (westward) are also generated. Many of these oscillations are characterized by wind and temperature amplitudes of order 20–30 ms−1 and 10–20 K in the lower thermosphere (100–130 km), and suggest that the tidal response in this regime varies considerably with longitude.
Latitudinal distribution of aerosols and clouds in the western Pacific observed with a lidar on board the Research Vessel Mirai
Authors: Sugimoto Nobuo , Matsui Ichiro , Liu Zhaoyan , Shimizu Atsushi , Asai Kazuhiro , Yoneyama Kunio , Katsumata Masaki
Published: February 2004

We observed vertical distributions of aerosols and clouds with a lidar on board R/V Mirai and analyzed latitudinal features using the data of four cruises in the western Pacific. According to the measured backscattering coefficient, aerosol density was generally high at latitudes above 25° N where the westerly from the Asian continent prevailed. The wavelength dependence of the retrieved aerosol backscattering showed that the characteristics of aerosols in the continental air mass were clearly different from those at lower latitudes. Aerosol concentration in the boundary layer varied significantly in the lower latitudes and was correlated with surface wind speed. The wavelength dependence of aerosol backscattering indicated that aerosol particles were larger when surface wind speed was high.
Impact of the AVHRR sea surface temperature on atmospheric forcing in the Japan/East Sea
Authors: Chen Shuyi S. , Zhao Wei , Tenerelli Joseph E. , Evans Robert H. , Halliwell Vicki
Published: February 2004

The impact of high resolution sea surface temperature (SST) data on the atmospheric forcing in the Japan/East Sea (JES) is investigated using a high‐resolution mesoscale atmospheric model. We use the Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST (PFSST) and the operational NCEP (National Center for Environmental Prediction) global SST analysis (NCEPSST) as the lower boundary conditions for two numerical experiments. A sharp SST gradient associated with the subpolar front in JES, well‐resolved by PFSST, has a significant influence on both synoptic scale and monthly mean surface winds and heat fluxes in JES. These results have an important implication for research related to coastal atmosphere and ocean circulation and air‐sea interactions.
A new estimate for present‐day Cocos‐Caribbean Plate motion: Implications for slip along the Central American Volcanic Arc
Authors: DeMets Charles
Published: February 2004

Velocities from 153 continuously‐operating GPS sites on the Caribbean, North American, and Pacific plates are combined with 61 newly estimated Pacific‐Cocos seafloor spreading rates and additional marine geophysical data to derive a new estimate of present‐day Cocos‐Caribbean plate motion. A comparison of the predicted Cocos‐Caribbean direction to slip directions of numerous shallow‐thrust subduction earthquakes from the Middle America trench between Costa Rica and Guatemala shows the slip directions to be deflected 10° clockwise from the plate convergence direction, supporting the hypothesis that frequent dextral strike‐slip earthquakes along the Central American volcanic arc result from partitioning of oblique Cocos‐Caribbean plate convergence. Linear velocity analysis for forearc locations in Nicaragua and Guatemala predicts 14±2 mm yr−1 of northwestward trench‐parallel slip of the forearc relative to the Caribbean plate, possibly decreasing in magnitude in El Salvador and Guatemala, where extension east of the volcanic arc complicates the tectonic setting.
A two‐phase response of the Southern Ocean to an increase in greenhouse gas concentrations
Authors: Goosse Hugues , Renssen Hans
Published: February 2004

The response of the Southern Ocean to an increase in atmospheric greenhouse gas concentrations simulated by a global atmosphere‐ocean‐sea‐ice model can be decomposed in two different phases. Firstly, the ocean damps the surface warming because of its large heat capacity. Secondly, one century after the major increase in greenhouse gases, the warming is amplified because of a positive feedback that is associated with a stronger oceanic meridional heat transport toward the Southern Ocean. Consequently, the long‐term decrease in ice area in the Southern Ocean is much larger than in the Northern Hemisphere. This large but delayed response has consequences for the interpretation of both observations and model results.
In situ measurements of the majorite‐akimotoite‐perovskite phase transition boundaries in MgSiO3
Authors: Hirose Kei , Komabayashi Tetsuya , Murakami Motohiko , Funakoshi Ken‐ichi
Published: February 2004

Here we report the phase boundaries between majorite, akimotoite (ilmenite), and perovskite in MgSiO3 determined by in situ measurements in a multi‐anvil apparatus. We used both gold and platinum as internal pressure standards at high pressure and temperature. Our results obtained at 1400‐2000°C, together with previous results obtained at 1000‐1200°C by Ono et al. [2001], precisely locate the akimotoite‐perovskite transition boundary at P (GPa) = 25.09 ‐ 0.0027 × T (°C), based on the P‐V‐T equation of state of gold [Anderson et al., 1989]. Our new experimental data show the position of triple point to be 20.0 GPa and 1920°C. The present measurements reconfirm our earlier study [Hirose et al., 2001] that Anderson's gold pressure scale gives slightly higher pressures than the platinum pressure scale proposed either by Jamieson et al. [1982] or Holmes et al. [1989].
QBO signal found at the extratropical surface through northern annular modes
Authors: Coughlin Katie , Tung Ka‐Kit
Published: February 2004

A QBO (quasi‐biennial oscillation) signal is found in 150‐year, Northern Hemisphere, surface air temperatures which have been projected onto an annular mode at the surface. The signal is tied to the equatorial QBO by demonstrating coherence in the extratropical stratosphere and tracing the signal, using the annular modes as a filter, down through the atmosphere to the surface. Then the statistical significance of the surface signal is established.
Evolution of subducting mantle lithosphere at a continental plate boundary
Authors: Pysklywec Russell N.
Published: February 2004

Although it is apparent that at continental convergence mantle lithosphere can be accommodated by a subduction‐like style of deformation, it is not clear how this process evolves and how it is different from “classical” plate subduction. Using numerical models of the crust‐mantle system these issues are considered for the case of a simplified continent‐continent plate collision. The results suggest that subducting mantle lithosphere is prone to detach, resulting in a reversal of subduction polarity; alternatively it may undergo symmetric plate consumption with steepening and possible roll‐over/polarity reversal. The style of post‐collisional subduction is largely controlled by the strength (e.g., dependent on temperature, assumed rheology) of the mantle lithosphere.
Early marine diagenesis in corals and geochemical consequences for paleoceanographic reconstructions
Authors: Müller Anne , Gagan Michael K. , McCulloch Malcolm T.
Published: February 2004

Detecting the potential geochemical consequences of early marine diagenesis is essential for establishing the validity of past climate reconstructions from coral. We present coral skeletal δ18O and Sr/Ca data for two long coral cores spanning 1839‐1994 AD at Ningaloo Reef, Western Australia, one of which includes significant secondary precipitation of marine inorganic aragonite. Long‐term trends in reconstructed sea surface temperatures (SSTs) for the well preserved coral correlate strongly with instrumental SST records spanning the 20th century. In contrast, the δ18O and Sr/Ca for the diagenetically altered coral give identical cool SST anomalies of 4‐5°C, as a consequence of the addition of secondary aragonite enriched in 18O and Sr. Our results indicate that cross‐checking of paleoclimate reconstructions with two supposedly independent paleothermometers may not be valid, and that coral records showing cooler SSTs in the past need to be interpreted with caution. Furthermore, modern coral records with long‐term trends in δ18O indicating recent warming and freshening of the ocean can be potentially explained by early marine diagenesis.
Electrical conductivity beneath the volcanoes of the NW Argentinian Puna
Authors: Lezaeta Pamela , Brasse Heinrich
Published: February 2004

The detection of a high conductivity anomaly below the northern (Bolivian) part of the Altiplano‐Puna plateau motivated a new analysis of magnetotelluric (MT) data which were formerly collected further south in NW Argentina. After appropriate dimensionality analysis from a profile located in the magmatic arc and backarc of the south‐central Andean subduction zone, two‐dimensional (2‐D) electrical conductivity modelling of the crust and upper mantle in the eastern sector could be performed, i.e., in the eastern Puna and backarc zone. The 2‐D conductivity models show a conductive zone beneath the eastern Puna shoshonitic volcanoes and nearby Tuzgle volcano, which reaches from the upper crust to the upper mantle. We suggest that this conductor is related to the Puna volcanism of enriched mantle composition. Whether the western Puna is also characterized by anomalous conductivities at crust‐mantle depths, is still an open question.
Coherent intraseasonal oscillations of ocean and atmosphere during the Asian Summer Monsoon
Authors: Sengupta Debasis , Goswami B. N. , Senan Retish
Published: February 2004

The space‐time evolution of the ocean and atmosphere associated with 1998–2000 monsoon intraseasonal oscillations (ISO) in the Indian Ocean and west Pacific is studied using validated sea surface temperature (SST) and surface wind speed from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager, and satellite outgoing longwave radiation. Monsoon ISO consist of alternating episodes of active and suppressed atmospheric convection moving northward in the eastern Indian Ocean and the South China Sea. Negative/positive SST anomalies generated by fluctuations of net heat flux at the ocean surface move northward following regions of active/suppressed convection. Such coherent evolution of SST, surface heat flux and convection suggests that air‐sea interaction might be important in monsoon ISO.
Anomalous surface currents in the tropical Indian Ocean
Authors: Grodsky Semyon A. , Carton James A. , Murtugudde Raghu
Published: February 2004

An anomalous climate event occurred in 1997 in the Indian Ocean with severe consequences for the surrounding continental areas. In response to an intensification of the trade winds, a westward gradient of SST and an anomalous reversal of the eastward surface currents with peak velocity anomalies exceeding 1 m/s were evident in boreal autumn. A similar but weaker event took place in 1994. In this study we examine the observational record during the 1990s including surface drifter velocities, SST and altimeter sea level to confirm these dramatic changes. We examine the key momentum balance between wind‐induced momentum flux and the pressure gradient force as well as the important role of horizontal temperature advection in the mixed layer heat response.
Anomalies in the seasonal cycle of sea level pressure in Iceland and the North Atlantic Oscillation
Authors: Jónsson Trausti , Miles Martin W.
Published: February 2004

This letter presents an analysis of a new homogenized time series of daily mean sea level pressure (SLP) from Reykjavík and Stykkishólmur, Iceland from 1823–1999. Time series statistical techniques including harmonic analysis are used to identify the seasonal march of pressure and its variability through the record. The results are assessed regarding the North Atlantic Oscillation (NAO) index. In addition to the annual cycle, the seasonal march of SLP has an appreciable semi‐annual cycle, as well as anomalies (abrupt rises and falls) occurring at remarkably distinct times in spring and winter. Multidecadal variability is apparent in the seasonal cycle and the anomalies. A shift in intraseasonal variability is observed in recent decades, including an extension of the winter Icelandic Low enhancement period into March. Increasing failure or delay of the “usual” abrupt pressure rise in Iceland in late February has contributed to the unusually positive winter NAO index values since the 1960s.
PMCs and the water frost point in the Arctic summer mesosphere
Authors: Stevens Michael H. , Conway Robert R. , Englert Christoph R. , Summers Michael E. , Grossmann Klaus U. , Gusev Oleg A.
Published: February 2004

In August, 1997 the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) obtained vertical profiles of OH number density and polar mesospheric cloud (PMC) brightness by scanning the limb up to 71° N while the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) obtained co‐located vertical profiles of temperature. MAHRSI OH densities are converted to water vapor using a one‐dimensional model that assumes photochemical equilibrium. By combining water vapor profiles with CRISTA temperatures we map the frost point both vertically and horizontally in the Arctic summer mesosphere. Our data show that supersaturation can exist between 80‐87 km suggesting that growth of ice particles is limited to these altitudes. Additionally, we find that not only is supersaturation an insufficient condition for a PMC but also that PMCs can exist in apparently unsaturated air.