bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐frequency wave propagation from mantle earthquakes in the Tyrrhenian Sea: New constraints for the geometry of the South Tyrrhenian Subduction Zone
Authors: Mele Giuliana
Published: February 2004

Propagation of shear waves produced by 25 mantle earthquakes (80–600 km depth) in the subduction zone of the south Tyrrhenian Sea (southern Italy) has been investigated to infer the geometry and extent of the descending lithosphere. From all hypocentral depths high‐frequency, high‐amplitude shear waves are recorded at most of the stations in southern Italy and easternmost Sicily. This shear‐wave energy is interpreted to travel as a guided wave within the descending slab. In contrast, shear waves are either not recorded at all or they are recorded as low‐frequency, low‐amplitude signals at stations located in the peninsular part of Italy north of the Calabrian arc, in western Sicily and in Sardinia. This systematic S‐wave attenuation is interpreted in terms of an active and continuous slab correlated with and limited to the Calabrian arc.
Retrieval of aerosol optical depth over land using two‐angle view satellite radiometry during TARFOX
Authors: Veefkind J. Pepijn , de Leeuw Gerrit , Durkee Phillip A.
Published: February 2004

A new aerosol optical depth retrieval algorithm is presented that uses the two‐angle view capability of the Along Track Scanning Radiometer 2 (ATSR‐2). By combining the two‐angle view and the spectral information this so‐called dual view algorithm separates between aerosol and surface contributions to the top of the atmosphere radiance. First validation of the dual view algorithm was performed during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX), which was conducted at the mid‐Atlantic coast of the United States in July 1996. The satellite retrieved spectral aerosol optical depth is in good agreement with the aerosol optical depth from ground‐based Sun/sky radiometers in three out of four cases. This shows the potential of aerosol retrieval over land using two‐angle view satellite radiometry.
Global distribution of atmospheric bromine‐monoxide from GOME on Earth Observing Satellite ERS‐2
Authors: Hegels E. , Crutzen P. J. , Klüpfel T. , Perner D. , Burrows J. P.
Published: February 2004

The remote sensing spectro‐photometer GOME installed on board of the polar orbiting ESA satellite ERS‐2 collects nadir scattered sunlight. The spectral intensity in the UV‐VIS‐region is measured and various atmospheric trace gases can be identified in the UV‐spectra. In this work BrO and NO2 have been followed. They are globally present and absolute column absorptions are obtained for BrO by comparison with direct sun light not having passed through the atmosphere. Average vertical columns of (3.1±1) × 1013 molec/cm² BrO are found in the equatorial region around noon. The omnipresence of BrO has some bearing on the global ozone depletion.
Unusual surface morphology from digital elevation models of the Greenland Ice Sheet
Authors: Ekholm Simon , Keller Kristian , Bamber Jonathan L. , Gogineni S. Prasad
Published: February 2004

In this study of the North Greenland ice sheet, we have used digital elevation models to investigate the topographic signatures of a large ice flow feature discovered in 1993 and a unique surface anomaly which we believe has not been observed previously. The small scale topography of the flow feature is revealed in striking detail in a high‐pass filtered elevation model. Furthermore, ice penetrating radar show that the sub‐stream bed is rough with undulation amplitude increasing downstream. The new feature consists of two large depressions in the ice sheet connected by a long curving trench. The low driving stresses in the region and the increased power of radio echo from the ice/bed interface over the feature clearly show presence of basal water. The shape of one of the two depressions and its location above a bedrock trough is indicative of a sub‐glacial lake but we also see evidence suggesting that water transport through a basal hydrological system may be occurring.
A 180th degree and order model of the Venus gravity field from Magellan line of sight residual Doppler data
Authors: Barriot J.‐P. , Valès N. , Balmino G. , Rosenblatt P.
Published: February 2004

We present a new 180th degree and order model of the Venus gravity field directly derived from line of sight Magellan residual Doppler data instead of usual line of sight residual acceleration data. We discuss the influence of the a priori covariance matrices on the deconvolution process, and compare our results with previous solutions.
Ionospheric signature of a magnetic flux rope in the magnetotail
Authors: Lui A. T. Y. , Brittnacher M. J. , Christon S. P. , Eastman T. E. , Kokubun S. , Liou K. , McEntire R. W. , Meng C.‐I. , Newell P. T. , Parks G. K. , Yamamoto T. , Williams D. J.
Published: February 2004

A flux rope was detected in the near‐Earth magnetotail at X ≈ −20 RE by Geotail with simultaneous viewing of the northern polar region by Polar on January 11, 1997. This offers the opportunity to ascertain the optical signature in the ionosphere of a flux rope for the first time. The magnetotail flux rope was associated with tailward streaming of energetic particles and had an estimated core radius of ∼ 1.5 RE. The composition of energetic ions within the flux rope showed a temporal increase in the abundance of ionospheric N+ and O+ ions. Simultaneous with the flux rope encounter were auroral activations at ∼23 MLT (substorm onset) and ∼ 18 MLT. An extensive consideration of magnetic field projection of the Geotail location to the ionosphere and the associated auroral and particle signatures of this event lead to the inference that the optical signature of the flux rope was an auroral arc system at ∼ 18 MLT, which had an ∼2 h extent in MLT and was moving progressively poleward and westward.
Uncertainty in the oceanic heat and carbon uptake and its impact on climate projections
Authors: Sokolov A. , Wang C. , Holian G. , Stone P. , Prinn R.
Published: February 2004

The impact of uncertainty in the rate of heat and carbon uptake by the deep ocean on climate response to increases in greenhouse gas concentrations is studied by means of simulations with a two‐dimensional climate‐chemistry model. We assume that mixing of both heat perturbations and carbon into the deep ocean can be parameterized by effective diffusion. Comparison of two‐dimensional model and coupled atmosphere‐ocean GCM simulations justifies such an approach for projections 100–150 years ahead. Rates of vertical mixing for temperature perturbations and carbon are assumed to be positively correlated. We consider the uncertainty range of transient projections of climate change when the above correlation is taken into account. Compared to taking into account changes just in the rate of heat uptake, we find that the range of projections of global surface warming is increased, but the range of projections of sea level rise due to thermal expansion is decreased.
Methane in surface waters of the Arabian Sea
Authors: Bange H. W. , Ramesh R. , Rapsomanikis S. , Andreae M. O.
Published: February 2004

More than 2000 measurements of atmospheric and dissolved methane (CH44) were performed in the central and northwestern Arabian Sea as part of the German JGOFS Arabian Sea Process Study during three cruises in March, May/June, and June/July 1997. Mean CH4 saturations in the surface waters of the central Arabian Sea were in the range of 103–107%. Significantly enhanced saturations were observed in the coastal upwelling area at the coast of Oman (up to 156%) and in an upwelling filament (up to 145%). The CH4 surface concentrations in the upwelling area were negatively correlated to sea surface temperatures. Area‐weighted, seasonally adjusted estimates of the sea‐air fluxes of CH4 gave annual emissions from the Arabian Sea of 11–20 Gg CH4, suggesting that previously reported very high surface CH4 concentrations might be atypical owing to the interannual variability of the Arabian Sea and that the emissions derived from them are probably overestimates.
Assessment of the future development of the ozone layer
Authors: Dameris M. , Grewe V. , Hein R. , Schnadt C. , Brühl C. , Steil B.
Published: February 2004

ECHAM3/CHEM is used to estimate the future development of the ozone layer. The general circulation model ECHAM3 and the chemistry module CHEM are coupled in a CTM‐like mode, i.e. no feedback of simulated chemical species on radiation is considered. Currently CHEM does not include bromine chemistry. Two time‐slice experiments representing 1991 and 2015 conditions are carried out. Chemical species are transported by winds calculated with different CO2 mixing ratios as a proxy for other greenhouse‐gases. For 2015, the adopted increase of CO2 and the corresponding modification of the sea‐surface temperature lead to a warming of the troposphere and a cooling of the stratosphere. The assessment for 2015 indicates that the ozone layer will not homogeneously recover, despite the employed decrease of chlorine in the model. Whereas in low and mid‐latitudes an ascent of stratospheric O3 is obvious, no significant increase of O3 is found in the polar regions during spring time.
A reexamination of “interstellar ion waves” previously identified in Pioneer 10 magnetic field data
Authors: Murphy Neil , Smith Edward J. , Wolf Joyce , Intriligator Devrie S.
Published: February 2004

Pioneer 10 magnetic field measurements, believed to include waves associated with the pick‐up of interstellar hydrogen atoms, have been further analyzed. Power spectra and waveform data reveal that the signals previously interpreted as waves are an artifact. They resulted from a very low telemetry/sampling rate, associated with the large distance of Pioneer 10 from Earth, which caused aliasing of a sinusoidal signal at the spacecraft spin frequency to a low frequency just above the proton gyrofrequency. Thus the Pioneer 10 plasma analyzer evidence for interstellar pickup ions must be considered separately from the magnetometer data: The validity of the plasma measurements is not affected by this data artifact.
A new auroral feature: The nightside gap
Authors: Chua D. , Brittnacher M. , Parks G. , Germany G. , Spann J.
Published: February 2004

Using images from the Ultraviolet Imager (UVI) aboard the Polar spacecraft, we identify an unusual morphological feature of the auroral oval marked by roughly a factor of four decrease in auroral luminosity near local midnight during some substorms. This feature has not been previously described in detail. The nightside gap appears in roughly 7% of the substorms observed by UVI during our study period from December, 1996 to February, 1997. Two nightside gap events from this period are characterized in detail as case studies of this phenomenon. We suggest that the nightside gap may be due to a significant reduction in field‐aligned currents along with an insufficient ionospheric potential to accelerate precipitating electrons within the gap region, perhaps associated with the Harang discontinuity.
The January 10–11, 1997 magnetic cloud: Multipoint measurements
Authors: Šafránková J. , Němeček Z. , Přech L. , Zastenker G. , Paularena K. I. , Nikolaeva N. , Nozdrachev M. , Skalsky A. , Mukai T.
Published: February 2004

The WIND and IMP 8 spacecraft detected a magnetic cloud upstream of Earth's bow shock on January 10–11, 1997 while the INTERBALL‐1, MAGION‐4, GEOTAIL, and LANL‐084 satellites were in the vicinity of the magnetopause and crossed it many times. Based on these multipoint observations we have determined the velocity of the magnetopause motion induced by the abrupt changes in the solar wind dynamic pressure during this event, and also the velocity of propagation through the magnetosheath of the structures connected with the magnetic cloud. Using the determined velocities, we tried to find the spatial orientations and dimensions of the observed disturbances. The estimated orientation of the interplanetary shock driven by the magnetic cloud is interpreted as a consequence of the local deformation of the cloud surface. The timing of measurements made by the aforementioned satellites suggests that the strong density enhancement behind the magnetic cloud is limited in spatial extent. We attribute this enhancement to the interaction of the magnetic cloud with the ambient solar wind plasma.
The outer radiation belt during the 10 January, 1997 CME event
Authors: Bühler P. , Johnstone A. , Desorgher L. , Zehnder A. , Daly E. , Adams L.
Published: February 2004

On 10 January 1997 a magnetic cloud of a coronal mass ejection impinged upon the earth magnetosphere and caused considerable variations of the relativistic electron population in the earth's outer radiation belt in the following days. Data obtained with radiation detectors on board a pair of satellites, STRV‐1a and STRV‐1b in a nearly equatorial geostationary transfer orbit show that the electron flux variations during the days following the arrival of the magnetic cloud can be characterized by four phases during which the fluxes alternatingly decreased and increased. The close relation between flux and Dst variations suggest the magnetic field variations in the inner magnetosphere to play an important role. However, the observed injection of electrons into the trapping region in the morning of 10 January seems to be crucial for the large electron flux enhancement during the afternoon of 10 January.
Synoptic measurements of Martian winds using the Hubble Space Telescope
Authors: Mischna Michael A. , Bell James F. , James Philip B. , Crisp David
Published: February 2004

We used the Hubble Space Telescope to make wind speed and wind direction measurements of the Martian atmosphere during early northern summer (Ls=97°). Our strategy utilized a series of near‐UV images with optimal temporal sampling to track observable cloud features and to determine the direction and speed of cloud motion. Several techniques were used to identify similar features between images, including Fourier transform and cross‐correlation. In these measurements, which span 19–75° N lat and 319° E to 135° W Ion, we find average wind speeds of 26.2 ± 10.1 m/s and a range of wind directions from 51° to 162° with an average error of ±23°.
Specific distribution of ground motion during the 1995 Kobe Earthquake and its generation mechanism
Authors: Furumura T. , Koketsu K.
Published: February 2004

The 1995 Kobe (Hyogo‐ken Nanbu) earthquake (Mw 6.9) is the most damaging in the recent Japanese history, and its notable feature is that most of the damage and over 6000 casualties occurred in a narrow belt through Kobe and neighboring cities (the Kobe‐Hanshin area). Usually a fault‐rupture propagation generates strong ground motions along the direction of propagation, and this directivity effect should be significant above the source faults and beyond its leading end. However, the damage zone of the Kobe earthquake is migrated noticeably from the fault trace into the center of Kobe city. Three‐dimensional (3‐D) simulations of ground motion in Kobe show that this migration is due to the strong amplification and ray bending in the sedimentary basin below the city in cooperation with the multipathing effects at a basin/bedrock boundary.
Elemental composition of the January 6, 1997, CME
Authors: Wurz P. , Ipavich F. M. , Galvin A. B. , Bochsler P. , Aellig M. R. , Kallenbach R. , Hovestadt D. , Grünwaldt H. , Hilchenbach M. , Axford W. I. , Balsiger H. , Bürgi A. , Coplan M. A. , Geiss J. , Gliem F. , Gloeckler G. , Hefti S. , Hsieh K. C. , Klecker B. , Lee M. A. , Managadze G. G. , Marsch E. , Möbius E. , Neugebauer M. , Reiche K.‐U. , Scholer M. , Verigin M. I. , Wilken B.
Published: February 2004

Using solar wind particle data from the CELIAS/MTOF sensor on the SOHO mission, we studied the abundance of the elements O, Ne, Mg, Si, S, Ca, and Fe for the time period around the January 6, 1997, coronal mass ejection event (CME). In the interstream and coronal hole regions before and after this event we found elemental abundances consistent with the expected abundance patterns of the respective flow regimes. However, during the passage of the CME and during the passage of the erupted filament, which followed the CME, we found that the elemental composition differed markedly from the interstream and coronal hole regions before and after this event. During the passage of the CME and the passage of the erupted filament we found a mass‐dependent element fractionation, with a monotonic increase toward heavier elements. We observed Si/O and Fe/O abundance ratios of about one half during these time periods, which is significantly higher than for typical solar wind.
Diffusion in MgO at high pressure: Implications for lower mantle rheology
Authors: Ita Joel , Cohen Ronald E.
Published: February 2004

Theoretical calculations of diffusion in periclase were performed to model the rheological properties of the lower mantle. Gibbs free energy values derived from molecular dynamics simulations using a non‐empirical interatomic potential to accurately predict diffusion in MgO at zero pressure. Diffusion coefficients were computed for pressures and temperatures up to 140 GPa and 5000 K. We find that Mg vacancies required for diffusive transport are likely extrinsic (due to impurities), and the resulting O vacancies would then be too few to support bulk O transport. Estimates of viscosity from these results are consistent with those inferred for the lower mantle from geophysical observations if grain boundary diffusion is responsible for O transport.
Evaluation of repeatability of baseline lengths in the VLBI network around the Tokyo metropolitan area
Authors: Kondo Tetsuro , Kurihara Noriyuki , Koyama Yasuhiro , Sekido Mamoru , Ichikawa Ryuichi , Yoshino Taizoh , Amagai Jun , Sebata Kohichi , Furuya Masato , Takahashi Yukio , Kiuchi Hitoshi , Kaneko Akihiro
Published: February 2004

Since 1995, VLBI measurements using fixed VLBI stations around the Tokyo metropolitan area have been continually producing data of station positions and baseline lengths. The accuracy of baseline length measurements is evaluated in terms of repeatability, conventionally defined as a standard deviation of those obtained by five continuous sessions. Continuous improvement both in system hardware and in the observation method have resulted in a remarkable improvement in measurement accuracy. Repeatability reaches about a 2‐mm level in baseline length in our VLBI network.
Oxygen‐18 variations in a global ocean model
Authors: Schmidt Gavin A.
Published: February 2004

The ratio of 18O to 16O in water of the world oceans is examined using the GISS ocean general circulation model. This ratio is governed by fractionation during evaporation and sea‐ice formation and by the isotopic content of precipitation and runoff entering the oceans. The δ18Oω at any point depends on a balance between local evaporation, precipitation, and regional ocean and sea‐ice processes. Surface δ18Oω equilibrates after 30–50 model years to produce a pattern of high values (0.5–1.5 ‰ ) in the sub‐tropics (highest in the Indian and Atlantic oceans) and low values (−15‐−1‰ ) in the mid‐to‐high latitudes. Arctic values are low especially where runoff enters from Arctic rivers. Comparisons with data show that regional linear relationships between δ18Ow and salinity are reasonably captured by the model. Surface data from the entire ocean show a clear distinction in slope between the tropical oceans and the extra‐tropics, however, departures from the linear relationships are significant. Importantly for attempts at calculating paleo‐salinities, the seasonal and longer‐term temporal gradients (Δδ18Ow/ΔS at a fixed point) are not generally equal to the spatial gradient (at a fixed time).
Transient flux enhancements in the magnetosheath
Authors: Němeček Z. , Šafránková J. , Přech L. , Sibeck D. G. , Kokubun S. , Mukai T.
Published: February 2004

This study presents INTERBALL‐1, and MAGION‐4 observations of transient ion flux variations in the magnetosheath which cannot be related to similar changes in the solar wind observed by WIND and GEOTAIL. The duration of the transient events varies from tens of seconds to a few minutes and their amplitude can exceed background levels by a factor of 2 or more. We use the closely‐spaced INTERBALL‐1 and MAGION‐4 satellites to estimate that the spatial dimensions of the events are on the order of ∼ 1RE. The interaction of foreshock discontinuities with the bow shock is identified as a possible source of these events.
Polar plumes and fine‐scale coronal structures ‐ On the interpretation of coronal radio sounding data
Authors: Pätzold M. , Bird M. K.
Published: February 2004

Variations in total electron content at high heliographic latitudes, observed during the 1995 solar conjunction of the Ulysses spacecraft when the radio ray path was embedded in the southern coronal hole, were interpreted by Woo and Habbal [1997b] as polar plume structures extending to at least 30 solar radii from the Sun. Somewhat surprisingly, we detected a 24‐hour sinusoidal oscillation of the total electron content with a peak‐to‐valley amplitude of about 10%. Model calculations were performed under the assumption that these electron content variations are indeed the signature of plumes moving in and out of the radio ray path. If the density contrast between plume and interplume regions is low, then the plume structure must occupy a significant fraction of the radio ray path. If the plume extent along the line‐of‐sight is similar to their observed width in the plane of the sky, then the density contrast is very high (factor 8 or more). Neither scenario seems reasonable under the given geometry. A more likely explanation for this 24‐hour variation would be an unaccounted bias at one of the ground stations which imposes an apparent diurnal periodicity onto the measurements. In short, there is no evidence for high latitude coronal plumes in radio sounding data near 30 solar radii.
Impact of diurnally‐varying skin temperature on surface fluxes over the tropical Pacific
Authors: Zeng Xubin , Dickinson Robert E.
Published: February 2004

Multi‐year hourly data of air temperature, wind speed, and humidity from the TOGA TAO moored buoys over the tropical Pacific along with our derived hourly sea surface skin temperature data are analyzed to show that there are substantial diurnal variations of monthly averaged surface fluxes of latent heat, sensible heat, and momentum (e.g., one‐third of the cases show monthly averaged latent heat diurnal amplitudes greater than 20 Wm−2). Daily or monthly average surface temperatures cannot provide such flux variations, suggesting that numerical modeling may require the inclusion of the diurnal variation of surface skin temperature.
Effect of sea roughness on bistatically scattered range coded signals from the Global Positioning System
Authors: Garrison James L. , Katzberg Stephen J. , Hill Michael I.
Published: February 2004

A series of aircraft experiments was performed using a specialized GPS receiver and a nadir‐oriented left hand circularly polarized antenna. This apparatus received reflections of the GPS signals from water surfaces under a variety of sea states. The cross‐correlation between the reflected signal and a reference pseudo‐random noise code was recorded as a function of the relative time delay. The shape of this function showed a dependence on the roughness of the reflecting surface. This dependence generally followed that predicted by theory for bistatic scattering of range‐coded signals. Use of this information as a remote sensing technique for the determination of sea state is discussed.
Atmospheric dust under glacial and interglacial conditions
Authors: Andersen Katrine K. , Armengaud Alexandre , Genthon Christophe
Published: February 2004

The uplift, transport and deposition of dust have been implemented in the LMDz AGCM. Simulations of atmospheric dust transport have been performed under present day (PD) and Last Glacial Maximum (LGM) conditions. For the PD climate the large‐scale atmospheric dust transport as inferred from atmospheric measurements is reproduced. Increased dust amounts are simulated almost everywhere for the LGM climate, and the concentration of dust in Antarctic ice is increased as inferred from ice cores. The model simulates substantially increased dust concentrations in Greenland ice, however they are still lower than values reported from ice cores.
Transient CO2 Experiment using the ARPEGE/OPAICE non flux corrected coupled model
Authors: Barthelet P. , Terray L. , Valcke S.
Published: February 2004

A transient CO2 experiment using the ARPEGE/ OPAICE coupled general circulation model with no flux correction has been performed at CERFACS. Despite a warm initial climate drift, the main features of the observed climate are reasonably captured in the control simulation. In particular, the simulated oceanic circulation is satisfactory. The transient CO2 simulation shows a global warming of 1.6°C in surface air temperature at the time of CO2 doubling. This value and the main geographical patterns of climate change are in agreement with previous studies using either flux corrected or non flux corrected models. The absence of flux correction does not prevent the too strong atmospheric water fluxes to produce an unrealistic freshening of the upper layer of the Northern North Atlantic which leads to a reduction of the thermohaline circulation in the control simulation. As a consequence, the weakening of the thermohaline circulation in response to the anthropogenic radiative forcing is less than expected.
High Rayleigh number thermo‐chemical models of a dense boundary layer in D″
Authors: Montague Nancy L. , Kellogg Louise H. , Manga Michael
Published: February 2004

We simulate the effects of an intrinsically dense boundary layer at the base of the mantle on the thermal structure of D″ and the dynamics of the lower mantle. Using a finite element model of thermo‐chemical convection in 2‐D with a Rayleigh number of 107, we investigate the dynamic consequences of varying the density and of increasing thermal diffusivity in the basal layer to simulate enrichment in metals. Convection may occur within a stable layer at the base of the model mantle, leading to short (400 km) wavelength temperature variations that contrast with the longer wavelength (1500–2000 km) variations above the dense layer. Strong small‐scale convection within the layer is not observed if the layer is only marginally stable and easily deformed.
Path correction using interpolated amplitude residuals: An example from central China
Authors: Phillips W. Scott , Randall George E. , Taylor Steven R.
Published: February 2004

To isolate effects of the laterally varying lithosphere on regional seismograms, we geographically smoothed source‐ and distance‐corrected amplitudes from 853 events recorded at station LZH in central China. This procedure was applied to Pn, Pg, Sn and Lg phases and various coda windows for eight bands between 0.5 and 8 Hz. We assume smoothing reduces effects such as source radiation, leaving an estimate of the path effect that can be used to correct data. A cross‐validation procedure showed that path corrections performed best with low‐frequency Lg data, reducing variance up to 39% for 1 Hz Lg, and up to 57% for 0.75 Hz P/Lg ratios, compared to correction for distance alone. These corrections reduce scatter in magnitude estimates and discriminant ratios without needing to know detailed geological structure and will be important for effective test‐ban monitoring.
The density of the Io plasma torus ribbon
Authors: Küppers Michael , Schneider Nicholas M.
Published: February 2004

We investigate two contradictory determinations of the density of the “ribbon” feature within the Io plasma torus. A value of ∼2000 cm−3 was measured by the Voyager 1 Plasma Science and Planetary Radio Astronomy instruments. Volwerk et al. [1997] recently suggested a value at least 5 times higher, and possibly much greater. Their upward revision is based on rapid EUV intensity variations observed by the Voyager Ultraviolet Spectrometers: Short radiative cooling times are only possible with higher plasma densities. We have modeled emissions from both the Voyager‐based torus model and the high‐density case suggested by Volwerk, and show that the latter is inconsistent with the intensity and morphology of numerous observations. We suggest that the observations by Volwerk et al. [1997] can be explained by a closer examination of the radiative cooling process and possibly by short‐term temperature variations caused by variability of the dawn‐dusk electric field in the Jovian magnetosphere.
Pacific‐Farallon relative motion 42‐59 Ma determined from magnetic and tectonic data from the Southern Austral Islands
Authors: Jordahl Kelsey A. , McNutt Marcia K. , Zorn Heather
Published: February 2004

We have used recently collected magnetic profiles and high resolution multibeam bathymetry data near the southern Austral Islands in French Polynesia to constrain the relative motion of the Pacific and Farallon plates between chron 25 and chron 18 (42–59 Ma). A change in plate motion at about chron 21 (50 Ma), which reoriented spreading direction in the area by 10‐12° clockwise was apparently accommodated by a southward propagating rift which transferred 160 km of Pacific crust to the Farallon plate, the outer pseudofault of which is preserved as the Adventure Trough. These new constraints significantly revise previous estimates of Pacific‐Farallon relative motion at the crucial time period encompassing the bend in the Hawaiian‐Emperor chain, believed to represent an abrupt change in the absolute motion of the Pacific plate. Disrupted lithosphere at the Adventure Trough has apparently been a preferred site for later midplate volcanic activity.
Case study on the influence of inhomogeneous surface albedo on UV irradiance
Authors: Degünther M. , Meerkötter R. , Albold A. , Seckmeyer G.
Published: February 2004

The influence of inhomogeneous surface albedo on UV irradiance is investigated for cloud free conditions using a recently developed 3‐dimensional radiative transfer model. From the calculations the relative enhancement of UV irradiance due to (partial) snow coverage as well as an 1‐dimensional effective albedo is derived. This 1d‐albedo is a quantity allowing to account for effects of inhomogeneous surface albedo in 1‐dimensional radiative transfer models. The results indicate that the surface albedo must be known on an area with considerable size: even if surface albedo is specified on an area with 40km radius around the measuring site the influence of areas outside this range on UV irradiance can be still up to 3%.

Although we already found encouraging agreement between modeled and measured spectral irradiance for clear skies and low surface albedo, the general evaluation of the 3‐dimensional model remains an open issue.
A capillary‐column chromatographic system for efficient chlorofluorocarbon measurement in ocean waters
Authors: Bulsiewicz Klaus , Rose Henning , Klatt Olaf , Putzka Alfred , Roether Wolfgang
Published: February 2004

We describe a new gas chromatographic analytical system for the joint measurement of the chlorofluorocarbons CFC‐11, CFC‐12, and CFC‐113 and of CC14 in ocean waters. From measurements at sea and in the laboratory we find overall precisions for surface waters of ±0.6, 0.6, 1.5, and 2.4% and detection limits of 0.002, 0.002, 0.008, and 0.003 pmol/kg, for CFC‐12, CFC‐11, CFC‐113, and CC14, respectively (1‐σ equivalents). The measurement repeat period is 17 min. A purge‐and‐trap approach, and other details, pay tribute to the work of Bullister and Weiss [1988]. A capillary column in combination with a low‐volume trap yields higher resolution than reported for other systems. There is füll separation of CFC‐12 from N2O and a satisfactory one of CFC‐113 from CH3I; to achieve the latter, a short packed column is operated in series with the main column. Slow purging of CC14 from the water samples contributes to its analytical error. The system is fully automated, allowing eight water samples and associated calibration measurements to be carried out unattented. Water samples are transferred into the system by means of flow‐through containers incorporating glass ampoules. Alternatively, the ampoules can be flame‐sealed, allowing sample storage for later analysis ashore. The performance of the system is assessed in some detail to serve as reference information for other CFC measurement systems and to direct future system tuning and developments. The system has been successfully employed at sea repeatedly. Sections from cruise M30/2, 1994 (Atlantic, 48° N), are presented as an example.
Temporal evolution of the tracer signal in the Deep Western Boundary Current, tropical Atlantic
Authors: Rhein Monika , Plähn Olaf , Bayer Reinhold , Stramma Lothar , Arnold Matthias
Published: February 2004

Four World Ocean Circulation Experiment (WOCE) repeat cruises (October 1990 to March 1994) in the tropical Atlantic off Brazil are used to study the spatial and temporal evolution of the chlorofluorocarbon (CFC) (components CFC‐11 and CFC‐12) and tritium signal in the upper North Atlantic Deep Water (NADW). Its shallowest part, located in the tropical Atlantic around 1600‐m depth, is the shallow upper North Atlantic Deep Water (SUNADW). It is characterized by a distinct tracer maximum, which is presumably received through winter time convection in the subpolar North Atlantic. Here we discuss the tracer fields and the temporal evolution of the tracer signal of the SUNADW in the tropical Atlantic along two meridional sections at 44° and 35°W and two zonal sections at 5° and 10°S off Brazil. The spatial and temporal development of the tracer field in the tropical Atlantic as well as the correlation with hydrographic parameters show that the temporal tracer change being due to the arrival of “younger” water is disturbed by other processes. In particular, the impact of variable mixing and spreading pathways on the observed tracer variability in the SUNADW is evident in the observations.
Tritium and CFC input functions for the Weddell Sea
Authors: Mensch Manfred , Simon André , Bayer Reinhold
Published: February 2004

On the basis of the International Atomic Energy Agency/World Meteorological Organization (IAEA/WMO) data set of the monthly tritium concentration in precipitation, the temporal and spatial pattern of the tritium concentration in marine precipitation of the southern hemisphere has been reconstructed. A numerical model that couples the tritium concentrations in the atmosphere and in the Weddell Sea's surface layer by parameterizing the relevant flux and exchange mechanisms, as well as the surface layer dynamics, has been used to calculate the time history of tritium in near‐surface waters of the Weddell Sea. The model also simulates the gas transfer of the chlorofluorocarbons CFC 11 and CFC 12 and of helium across the ocean‐atmosphere interface. The model accounts for the pronounced seasonality of the climatological and oceanographic conditions of the Weddell Sea. The calculated input functions of tritium, CFC 11 and CFC 12 provide the surface boundary conditions for numerical studies of the distributions of these transient tracers in the sub‐surface water masses of the Weddell Sea.
Identification of rain‐freshened plumes in the coastal ocean using Ra isotopes and Si
Authors: Moore Willard S. , Kjerfve Björn , Todd James F.
Published: February 2004

Two transient plumes of freshened water in the South Atlantic Bight off the coast of South Carolina were measured and mapped during a continental shelf cruise in July 1994. Salinity in the plumes was depressed 1–2 parts per thousand compared to surrounding shelf waters. One plume was at least 160 km long, 20 km wide, and 5–7 m deep. The other was 75 km long, 25 km wide and 5–7 m deep. Both plumes disintegrated almost completely in 6 days due to mixing or advection away from the sampling area. Measurement and analysis of short‐lived Ra isotopes and Si indicated that the plumes were not caused by river discharge but were rather due to an intense rain event a few days prior to the sampling cruise. With only salinity measurements we would have incorrectly concluded that the freshened water was a result of river plumes having entered the shelf. The rain was associated with the system that spawned tropical storm Alberto. We estimate that 220–330 mm of rain fell on the coastal ocean immediately before the cruise. Accompanying the rain were pesticides and nutrients. We estimate that the flux of nitrate from the rain was twice the riverine flux of nitrate to the study area in the month preceding the cruise.
Semidiurnal tides observed in the western equatorial Pacific during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment
Authors: Feng Ming , Merrifield Mark A. , Pinkel Robert , Hacker Peter , Plueddemann Albert J. , Firing Eric , Lukas Roger , Eriksen Charles
Published: February 2004

The semidiurnal tide within a 100 km square region of the western equatorial Pacific centered at 1.8° S, 156.1° E is examined using shipboard survey and mooring data collected during the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE). Baroclinic and barotropic tidal amplitudes and phases are estimated from the survey and mooring observations in the upper 300 m of the 1800 m deep ocean by specifying their horizontal and vertical structures. The barotropic tide is assumed to have zero horizontal wavenumber over the domain, while a component of the baroclinic tide that is phase‐locked to the barotropic tide is determined by a searching method using plane wave fits to the data. The estimated barotropic tidal current is in good agreement with tide models derived from TOPEX/POSEIDON observations. The plane wave analysis indicates a dominant mode one baroclinic wave propagating toward the northeast. The second vertical mode can also be detected. Given the phase differences between the M2 and S2 constituents in the barotropic and baroclinic tides, the source of the baroclinic tidal signal is determined to be about 320 km southwest of the observing region, at a series of islands and shallow ridges. The combined estimates of the barotropic and baroclinic tides typically account for only 40–60% of the observed semidiurnal band current variance in the mooring data, indicating the high degree of temporal and spatial variability of the baroclinic tide in this region. The results of this study suggest, however, that coherent barotropic and baroclinic tidal signals can be successfully distinguished in the deep ocean using shipboard survey data, even when the data are limited to the upper 300 m.
Influence of intermediate water in the western Okinawa Trough by the outflow from the South China Sea
Authors: Chen Chen‐Tung Arthur , Wang Shu‐Lun
Published: February 2004

Although the Kuroshio and the South China Sea (SCS) waters flow in and out of the Luzon Strait near surface, the SCS water mainly flows out of the SCS at mid depth between 350 and 1350 m in all seasons and years that we studied. The eastward flowing SCS intermediate water is blocked by and joins the northward flowing Kuroshio at about 122°E. Thus the Kuroshio Intermediate Water (KIW) is composed of the West Philippine Sea (WPS) proper water on the east, centered at 600 m depth. Because the ridge east of Taiwan separating the Okinawa Trough from the WPS is mostly shallower than 600 m, the eastern portion of the KIW is largely blocked by the ridge and is forced to turn eastward. This water does not enter the Okinawa Trough freely until it reaches a deep gap in the Ryukyu Ridge farther north, subsequently forming the eastern portion of the intermediate water in the trough. The western portion of the KIW is the mixed water of SCS and WPS. The nutrient‐rich SCS Intermediate Water, centered at 500 m, is less influenced by the ridge and is able to flow into the Okinawa Trough. The SCS Intermediate Water thus retains its signature in the southern and western Okinawa Trough, upwells onto the East China Sea shelf, and becomes a major source of nutrients to the shelf water.
Heat and salt changes on the continental shelf west of the Antarctic Peninsula between January 1993 and January 1994
Authors: Klinck John M.
Published: February 2004

Hydrographic measurements from four cruises between January 1993 and January 1994 over the continental shelf west of the Antarctic Peninsula allow analysis of seasonal changes in heat and salt content of this region. Changes above the permanent pycnocline (about 150 m) follow a seasonal pattern of cooling and increasing in salt from summer to winter and warming and freshening from winter to summer. These near‐surface changes, expressed as net heating or salting rate, were above 80 W m−2 and 4 mg salt m−2 s−1. The year to year difference was small compared to the seasonal changes. There was no seasonal pattern to the changes below the permanent pycnocline; heat and salt content increased or decreased together, with magnitudes about half (50 W m−2 and 2.0 mg salt m−2 s−1) that observed near the surface. Subpycnocline water warmed (10 W m−2) and increased salt (0.5 mg salt m−2 s−1) from one January to the next. Exchange of Upper Circumpolar Deep Water (UCDW), an oceanic water mass, and West Antarctic Peninsula modified Circumpolar Deep Water, a cooled version of UCDW on the shelf, is responsible for these changes. During the exchange process, UCDW cools by loosing heat to the cold, near‐surface Winter Water left by the deep mixing during the previous winter. Subpycnocline heat and salt changes occur as a difference between onshore and vertical diffusion with vertical diffusivities of (1.0,0.36) × 10−4 m2 s−1, for heat and salt, respectively, and a horizontal diffusivity of 37 m2 s−1. The annual change is due to a net flux of UCDW onto the shelf during 1993, with most of the exchange occurring fall and winter. Meandering of the Antarctic Circumpolar Current along the shelf break in this area seems to cause these exchanges. Deep across‐shelf cuts in the bottom topography may also play a role.
Large scale circulation in the Bellingshausen and Amundsen seas as a variational inverse of climatological data
Authors: Grotov A. S. , Nechaev D. A. , Panteleev G. G. , Yaremchuk M. I.
Published: February 2004

Atmospheric and oceanic climatological data are combined with the World Ocean Circulation Experiment S4 section hydrology in the framework of a variational data assimilation scheme into a steady state nonlinear model of the large‐scale circulation. The reconstructed fields of density and three‐dimensional velocity are dynamically balanced and provide qualitative and quantitative estimates of the circulation features of the Amundsen and Bellingshausen seas. Natural assumptions on the spatial structure of the density covariance matrices enable us to obtain realistic coastal currents near the continental slopes of Antarctica within the framework of model equations. The horizontal circulation pattern reveals along shore westward current with typical velocities of 1 cm s−1 and cyclonic gyres in the Amundsen and Bellingshausen seas transporting 2 and 0.5 Sv, respectively. Three eastward branches of the Antarctic Circumpolar Current are observed in offshore regions. Their transports are diagnosed as 19, 12, and 6 Sv. The lower layer is characterized by westward countercurrent in the northwestern part of the basin with the transport of 8 Sv. Average Ekman upwelling rate in the major part of the basin amounts to 20–25 m yr−1. Downwelling in the shelf regions of the Bellingshausen and Amundsen seas is estimated as 250–350 m yr−1.
Optimal averaging of NOAA/NASA Pathfinder satellite sea surface temperature data
Authors: Walker Alison E. , Wilkin John L.
Published: February 2004

Statistical interpolation is applied to 8 years of cloud‐interrupted satellite radiometer data to produce estimates of sea surface temperature (SST) at 10‐day intervals in the Indo‐Australian region. The data are 9‐km resolution daily “best SST” values calculated globally by the NOAA/NASA Pathfinder project reanalysis of advanced very high resolution radiometer (AVHRR) data. The optimal averaging technique determines an unbiased estimate of the signal that has the minimum mean square variance from the data, within the limits of the expected measurement error. Previous studies have shown that the method is superior to other linear averaging techniques, especially that of simple composite averaging. The method is applied in the time domain only, preserving the 9‐km spatial resolution of the data. The signal and noise covariances were evaluated from the data. This was done with care so that accurate estimates of the error bounds that bracket the optimally averaged values might be obtained. These error bounds were then verified against in situ data. A Markov function, (1 + τ/a) exp (−τ/a), where τ is the time lag and a is a characteristic timescale, was fitted to the data and used for the signal correlation function. This was selected after evaluation of functional forms proposed in other studies. The effect on the analysis of geographical variation in the correlation function was considered. The computational demand of the repeated matrix operations in optimal interpolation was reduced by using a limited duration data window. The complete analysis procedure for the 8‐year data set, comprising over 106 time series, was tractable on a modern workstation. The result is a set of SST maps for 1987–1994 at an interval of 10 days and a spatial resolution of 9 km. The analyses are suitable for applications such as high‐resolution ocean and atmosphere modeling where the timescales and space scales of interest are comparable to the analysis (i.e., of the order of 10 days, 9 km) and for which the presence of gaps due to clouds is problematic. Some features of Indo‐Australian regional mesoscale circulation that the analysis highlights are examined, including examples of detailed mesoscale SST evolution and interannual variability.
Investigation of the dynamic sea ice component of a coupled atmosphere‐sea ice general circulation model
Authors: O'Farrell Siobhan P.
Published: February 2004

This paper discusses the development of a coupled atmospheric‐ice model with a comprehensive ice dynamics, cavitating fluid rheology and an open water parameterization. The results center on the ice thickness and concentration distribution in the Arctic basin where the inclusion of ice rheology has maximum impact. The influence of the wind stresses calculated by an atmospheric model with stability dependent surface drag coefficients is discussed along with the role of the ocean currents and ocean‐ice drag coefficient. Under winter wind stress conditions the model had a tendency to buildup ice on the Siberian coast. The introduction of a partial slip condition at land‐ice boundaries in the model designed to prevent this buildup is discussed, and the best choice for the amplitude of the slip at the land boundaries in this model is found to be 0.4. The ice model results are compared with the available observational data sets on ice thickness, concentration and ice velocity fields to test the validity of the model simulations.