bluuebunny/crossref_metadata_2025 huggingface dataset:
Near‐source velocity structure and isotropic moment tensors: A case study of the Long Valley Caldera
Authors: Panning Mark , Dreger Douglas , Tkalčić Hrvoje
Published: February 2004

The effect of near‐source velocity structure on the recovery of the isotropic component in moment tensor inversions is explored using a finite‐difference method. Synthetic data generated using a 3D Long Valley Caldera (LVC) velocity model (Vp +/− 20%) were inverted for the full moment tensor using a linear time‐domain scheme utilizing Green's functions calculated from 1D models. While inversions of synthetic data with input isotropic components recovered isotropic components with 95% significance according to an F‐test relative to deviatoric inversions (isotropic component constrained to zero), inversions of synthetic data with no input isotropic component recovered only nominal isotropic components with less than 75% significance. This study demonstrates near‐source structure does not appear to falsely produce significant isotropic components of moment tensor inversions in the passband typically employed by regional inversion methods.
Transport of biomass burning smoke to the upper troposphere by deep convection in the equatorial region
Authors: Andreae M. O. , Artaxo P. , Fischer H. , Freitas S. R. , Grégoire J.‐M. , Hansel A. , Hoor P. , Kormann R. , Krejci R. , Lange L. , Lelieveld J. , Lindinger W. , Longo K. , Peters W. , de Reus M. , Scheeren B. , Silva Dias M. A. F. , Ström J. , van Velthoven P. F. J. , Williams J.
Published: February 2004

During LBA‐CLAIRE‐98, we found atmospheric layers with aged biomass smoke at altitudes >10 km over Suriname. CO, CO2, acetonitrile, methyl chloride, hydrocarbons, NO, O3, and aerosols were strongly enhanced in these layers. We estimate that 80–95% of accumulation mode aerosols had been removed during convective transport. Trajectories show that the plumes originated from large fires near the Brazil/Venezuela border during March 1998. This smoke was entrained into deep convection over the northern Amazon, transported out over the Pacific, and then returned to South America by the circulation around a large upper‐level anticyclone. Our observations provide evidence for the importance of deep convection in the equatorial region as a mechanism to transport large amounts of pyrogenic pollutants into the upper troposphere. The entrainment of biomass smoke into tropical convective clouds may have significant effects on cloud microphysics and climate dynamics.
Joint interpretation of displacement and gravity data in volcanic areas. A test example: Long Valley Caldera, California
Authors: Fernández J. , Charco M. , Tiampo K. F. , Jentzsch G. , Rundle J. B.
Published: February 2004

Volcanic activity produces deformation and gravity changes that many times can be used as precursors of future eruptions. Applying geodetic techniques to monitoring activity involves interpretation using deformation models. Usually gravity change data and displacement data are interpreted separately. We show, using modeling of deformation and gravity change data in Long Valley Caldera, California, USA, that this can lead to incorrect interpretations. The results obtained show that displacements and gravity changes must be interpreted together whenever possible and that elastic‐gravitational models can be a far more appropriate approximation to problems of volcanic load in the crust than the more commonly used purely elastic models. Therefore it is necessary to change the philosophy normally used to interpret geodetic observations, improving the possibility of predicting future eruptions.
Enhanced pressure solution creep rates induced by clay particles: Experimental evidence in salt aggregates
Authors: Renard François , Dysthe Dag , Feder Jens , Bjørlykke Knut , Jamtveit Bjørn
Published: February 2004

Pressure solution is responsible for mechano‐chemical compaction of sediments in the upper crust (2–10 km). This process also controls porosity variations in a fault gouge after an earthquake. We present experimental results from chemical compaction of aggregates of halite mixed with clays. It is shown that clay particles (1–5 microns) greatly enhance the deformation by pressure solution in salt aggregates (100–200 micron), the strain rates being 50% to 200% faster in samples containing 10% clays than for clay‐free samples. Even the presence of 1% clay increases the strain rate significantly. We propose that clay particles enhance pressure solution creep because these microscopic minerals are trapped within the salt particle contacts where they allow faster diffusion of solutes from the particle contacts to the pore space and inhibit grain boundary formation.
Extra‐tropical response to ENSO as expressed in an ice core from the Saint Elias Mountain Range
Authors: Moore G. W. K. , Holdsworth Gerald , Alverson Keith
Published: February 2004

The El‐Niño Southern Oscillation (ENSO) is the dominant mode of inter‐annual variability of the atmosphere‐ocean system in the tropical Pacific and exerts its influence in the extra‐tropics through persistent large‐scale wave‐like patterns in the atmosphere known as teleconnections. Although the physics of ENSO in the tropics is relatively well understood, our knowledge of its extra‐tropical response is based on teleconnection patterns that are statistical in origin and derived from relatively short time series. In this paper we analyze the ENSO signal in an annually resolved record of snow accumulation covering the period 1736–1985 from an ice core obtained in the Saint Elias Mountains of the Yukon. This region is located in the center of an area with one of the most significant teleconnection signatures associated with ENSO. The high elevation of the site where the ice core was obtained allows it to sample the mid and upper‐tropspheric flow where the extra‐tropical response to ENSO has its largest amplitude. As we show these characteristics of the site result in a significant ENSO signal in the snow accumulation time series.
First results from the Radio Plasma Imager on IMAGE
Authors: Reinisch B. W. , Huang X. , Haines D. M. , Galkin I. A. , Green J. L. , Benson R. F. , Fung S. F. , Taylor W. W. L. , Reiff P. H. , Gallagher D. L. , Bougeret J.‐L. , Manning R. , Carpenter D. L. , Boardsen S. A.
Published: February 2004

The Radio Plasma Imager (RPI) is a 3 kHz to 3 MHz radio sounder, incorporating modern digital processing techniques and long electronically‐tuned antennas, that is flown to large radial distances into the high‐latitude magnetosphere on the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) satellite. Clear echoes, similar to those observed by ionospheric topside sounders, are routinely observed from the polar‐cap ionosphere by RPI even when IMAGE is located at geocentric distances up to approximately 5 Earth radii. Using an inversion technique, these echoes have been used to determine electron‐density distributions from the polar‐cap ionosphere to the location of the IMAGE satellite. Typical echoes from the plasmapause boundary, observed from outside the plasmasphere, are of a diffuse nature indicating persistently irregular structure. Echoes attributed to the cusp and the magnetopause have also been identified, those from the cusp have been identified more often and with greater confidence.
Iodine oxide homogeneous nucleation: An explanation for coastal new particle production
Authors: Hoffmann Thorsten , O'Dowd Colin D. , Seinfeld John H.
Published: February 2004

A series of laboratory experiments on the chemical composition of aerosol particles formed after photodissociation of CH2I2, a major volatile alkyl halide released from macroalgae, have been performed in a laboratory scale reaction chamber using on‐line atmospheric pressure chemical ionization mass spectrometry (APCI/MS). Based on the mass spectrometric results and the molecular properties of iodine oxides, we suggest that the self‐nucleation of iodine oxides provides an efficient source of natural condensable material in coastal environments and discuss this concept focusing on OIO as one potential key species for new particle formation. The presented hypothesis not only fits the measured enrichment of iodine species in submicrometer particles, but also can explain the frequently observed nucleation bursts in the coastal boundary layer.
Observed changes in Arctic Ocean temperature structure over the past half decade
Authors: Gunn John T. , Muench Robin D.
Published: February 2004

Ocean temperature data obtained from the central Arctic Ocean during 1995–1999 show interannual changes in the temperature of the warm Atlantic Water core. Widespread warming continued from 1995 until 1998 but had ceased during 1998–1999 and was replaced by a slight cooling. The timing of these changes differed regionally, as the warming had occurred prior to 1995 in the Nansen and Amundsen basins, and between 1995 to 1998 in the Makarov Basin. The regional phase differences are consistent with advection along mid‐ocean ridges from the Eurasian margin slope current, which provides the source for warm Atlantic Water. Anomalous behaviors were associated with the Arctic Mid‐Ocean and Lomonosov ridges and probably reflected the presence of overlying topographically trapped circulations.
Coordinated thermospheric day‐night airglow and ionospheric measurements from low latitudes—First results
Authors: Taori Alok , Sridharan R. , Chakrabarty D. , Narayanan R. , Ramarao P. V. S.
Published: February 2004

The Dayglow photometer which monitors the O(¹D) 630.0 nm thermospheric airglow emission, has been converted into a day‐night photometer and was operated from Waltair (17.7°N, 83.3°E dip. Lat. 10.09°N) during March 1998 as a part of the Indian Solar Terrestrial Energy Programme (ISTEP) campaign. The first results on the day‐night airglow measurements together with ionosonde data from the same location are scrutinized in the present exercise. The base height of the F‐layer (h'F) showed a strong negative correlation with dayglow intensity similar to nighttime conditions and a new empirical relation (Barbier type) linking the F‐region electron densities and the h'F with the dayglow intensity has been worked out highlighting the importance of chemical processes in OI 630.0 nm dayglow and its variabilities.
Satellite observations of cloud plumes generated by Nauru
Authors: Nordeen M. L. , Minnis P. , Doelling D. R. , Pethick D. , Nguyen L.
Published: February 2004

A cloud plume is generated by the interaction of low‐level easterly flow and diurnal surface heating on the island of Nauru in the tropical Pacific. Diurnal and seasonal cycles of cloud plume length, frequency, and heading were obtained by inspection of a year of hourly daytime GMS images. The cloud plume extends downwind and typically grows during the day to a mean length of 125 km by late afternoon with a maximum observed length of 425 km. The longest average plumes occur during March and April. The afternoon plume frequency was 63% compared to 50% for all observations. Further evaluation of the plume effects is needed to fully assess their impact on the development of long‐term statistics of cloud and radiation parameters derived from surface instruments on the island's leeward side.
Global dynamics of the plasmasphere and ring current during magnetic storms
Authors: Burch J. L. , Mitchell D. G. , Sandel B. R. , Brandt P. C. , Wüest M.
Published: February 2004

Simultaneous global images of the plasmasphere and the ring current were obtained with the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft during the geomagnetic storms of 24 May 2000 and 29 July 2000. The plasmasphere images confirm the theoretically predicted development of long plasma tails in the dusk hemisphere during magnetic storms. They also reveal several unexpected structures, including a sharp azimuthal gradient or shoulder, which forms on the night side and corotates with the Earth for many hours, and a narrow ion trough, which is located well inside the main plasmapause in the late evening sector. The ring current images show the peak of the ring current to be nearly centered on the plasmapause, which is consistent with ring current decay models that include coulomb scattering and wave‐particle interactions as well as charge exchange.
Scattering phase functions and particle sizes in noctilucent clouds
Authors: Gumbel J. , Stegman J. , Murtagh D. P. , Witt G.
Published: February 2004

The MIDAS‐DROPPS campaign conducted in Norway in 1999 provided a comprehensive study of the high‐latitude summer mesopause region with rocket‐borne and ground‐based instrumentation. Optical photometers were flown on two rocket payloads through substantially different mesospheric conditions. On both flights, distinct noctilucent cloud (NLC) layers were detected. We present the first analysis of NLC scattering phase functions observed from sounding rockets. Applying Mie calculations, the angular dependence of the scattering is used to extract information about particle sizes. The first flight featured a weak NLC with small particles (r ≤ 20 nm) located below the core of a strong polar mesosphere radar echo (PMSE). The second flight took place in the absence of any detectable PMSE and probed a bright NLC optically dominated by particles in the size range 40–50 nm.
DROPPS: A study of the polar summer mesosphere with rocket, radar and lidar
Authors: Goldberg R. A. , Pfaff R. F. , Holzworth R. H. , Schmidlin F. J. , Voss H. D. , Tuzzolino A. J. , Croskey C. L. , Mitchell J. D. , Friedrich M. , Murtagh D. , Witt G. , Gumbel J. , von Zahn U. , Singer W. , Hoppe U.‐P.
Published: February 2004

DROPPS (The Distribution and Role of Particles in the Polar Summer Mesosphere) was a highly coordinated international study conducted in July, 1999 from the Norwegian rocket range (Andøya, Norway). Two sequences of rockets were launched. Each included one NASA DROPPS payload, containing instruments to measure the electrodynamic and optical properties of dust/aerosol layers, accompanied by European payloads (MIDAS, Mini‐MIDAS, and/or Mini‐DUSTY) to study the same structures in a complementary manner. Meteorological rockets provided winds and temperature. ALOMAR lidars and radars (located adjacent to the launch site) monitored the mesosphere for noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs), respectively. EISCAT radars provided PMSE and related information at a remote site (Tromsø, Norway). Sequence 1 (5–6 July) was launched into a strong PMSE with a weak NLC present; sequence 2 (14 July) occurred during a strong NLC with no PMSE evident. Here we describe program details along with preliminary results.
The Kaapvaal craton seismic anisotropy: Petrophysical analyses of upper mantle kimberlite nodules
Authors: Ben‐Ismail W. , Barruol G. , Mainprice D.
Published: February 2004

A dense network of seismic stations has been deployed on the Kaapvaal craton (South Africa) to investigate the upper mantle seismic structures. In order to bring independent petrophysical constraints, we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the Earth's surface by kimberlite eruptions. Seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants. Despite variations in the nodules compositions, microstructures and crystallographic preferred orientations, seismic anisotropy is rather homogeneous throughout the craton. Mean S‐wave anisotropy is weak (2.64%), which is compatible with the small measured SKS wave splitting (mean delay time of 0.62 s).
First common volume observations of layered plasma structures and polar mesospheric summer echoes by rocket and radar
Authors: Havnes O. , Brattli A. , Aslaksen T. , Singer W. , Latteck R. , Blix T. , Thrane E. , Trøim J.
Published: February 2004

We report the results from simultaneous radar and rocket measurements of a PMSE event where for the first time the rocket measured dust and plasma within the radar beam. We find very clear correspondence between the measured dust charge density profile and the radar backscatter profile as a function of height. We find that even very small amounts of charged dust is associated with an appreciable PMSE radar backscatter. Although we find it likely that the dust layer corresponds fully with the PMSE layer there is a possibility that the upper part of the PMSE layer may be influenced by ion clusters which are too small to be detected by the rocket dust probe.
Simultaneous measurements of the O2(¹Δ) and O2(¹Σ) Airglows and ozone in the daytime mesosphere
Authors: Mlynczak M. G. , Morgan F. , Yee J.‐H. , Espy P. , Murtagh D. , Marshall B. , Schmidlin F.
Published: February 2004

We report simultaneous measurements of the O2(¹Δ) and O2(¹Σ) airglow volume emission rate profiles in the daytime mesosphere. We use these measurements to derive ozone concentrations separately from each airglow. The measurements were made as part of the Mesosphere‐Thermosphere Emissions for Ozone Remote Sensing (METEORS) sounding rocket project launched from White Sands Missile Range, New Mexico. These data offer the opportunity to assess the consistency of ozone profiles derived from measurements of the oxygen airglows and thus provide a fundamental test of our understanding of dayglow physics and solar energy deposition. In both airglow‐derived profiles the ozone decreases with altitude throughout the middle mesosphere and a pronounced secondary maximum exists near 90 km. The derived ozone profiles are in agreement to within measurement uncertainty. This agreement confirms that the major processes responsible for the generation of mesospheric oxygen dayglow are well understood via measurement.
Intra‐seasonal modulation of convection in the West African Monsoon
Authors: Janicot Serge , Sultan Benjamin
Published: February 2004

By using daily gridded rainfall data and NCEP/NCAR 925 hPa wind reanalyses over the period 1968–1990, it is shown the evidence of large and coherent fluctuations in the rainfall and wind fields at intra‐seasonal time scale (10–60‐day period) over West Africa. A composite analysis based on the dates of maximum (minimum) of a regional rainfall index in wet (dry) sequences shows that these sequences belong to a quasi‐periodic signal of about 15 days. These enhanced (weakened) phases in the West African monsoon are characterized by a westward propagation of positive (negative) rainfall anomalies north of 10°N associated with a more cyclonic (anticyclonic) circulation over the Sahel consistent with a stronger (weaker) moisture advection over West Africa.
Volcanic gas emission rates measured by solar occultation spectroscopy
Authors: Duffell Hayley , Oppenheimer Clive , Burton Mike
Published: February 2004

We report here the first measurements of volcanic gas fluxes obtained with a Sun‐tracking Fourier transform infrared spectrometer. The experiment was carried out at Masaya volcano in Nicaragua, in April 2000, and yields ratios and emission rates for five gases: H2O, CO2, SO2, HCl, and HF. Traverses beneath the plume were made by road 15 km downwind from the summit, and indicate SO2 and HCl fluxes of 11 and 3 kg s−1, respectively. These values are a good guide to source strengths since we observed no significant change in SO2/HCl ratios (∼3 by mass) between the summit and downwind sites, suggesting negligible removal of SO2 or HCl from the gas phase prior to observation. Combining the HCl flux, with the ratios of HF/HCl, CO2/HCl and H2O/HCl determined spectroscopically at the summit, yields fluxes for HF, CO2 and H2O of 0.26, 11 and 160 kg s−1, respectively. The technique heralds considerable promise for volcano monitoring.
A new type of intra‐plate volcanism; Young alkali‐basalts discovered from the subducting Pacific Plate, Northern Japan Trench
Authors: Hirano N. , Kawamura K. , Hattori M. , Saito K. , Ogawa Y.
Published: February 2004

Alkali pillow basalts were collected from the toe of the oceanward slope of the northern Japan Trench. These alkali‐basalts formed as a result of a low degree of partial melting of Pacific Ocean mantle and rapid rise of the magma (no fractionation in shallow magma chambers). Reconstructing Pacific Plate motion based on 40Ar‐39Ar age dates of 5.95±0.31 Ma for these basalts indicates that they erupted outboard of outer swell or forebulge of the Japan Trench in the NW Pacific. We suggest that these alkali‐basalts represent a new form of intra‐plate volcanism, whereby magmatic activity occurs off the forebulge of the downgoing Pacific slab, perhaps using conduits related to fracturing of the slab during bending prior to subduction.
Unsuccessful initial search for a midmantle chemical boundary with seismic arrays
Authors: Vidale John E. , Schubert Gerald , Earle Paul S.
Published: February 2004

Compositional layering of the midmantle has been proposed to account for seismic and geochemical patterns [van der Hilst and Karason, 1999], and inferred radiogenic heat source concentrations [Kellogg et al., 1999]. Compositional layering would require thermal boundary layers both above and below an interface. We construct a minimal 1‐D model of a mid‐mantle boundary consistent with the observed nearly adiabatic compressional velocity structure [Dziewonski and Anderson, 1981] and the proposed high heat flow from the lower mantle [Albarede and van der Hilst, 1999; Kellogg et al., 1999]. Ray tracing and reflectivity synthetic seismograms show that a distinct triplication is predicted for short‐period P waves. Although topography on a boundary would cause uncertainty in the strength and the range of the triplication, many clear observations would be expected. We examine data from the US West Coast regional networks in the most likely distance range of 60° to 70° for a 1770‐km‐depth boundary, and find no evidence for P wave triplications.
Radon groundwater monitoring at underground laboratories of Gran Sasso (Italy)
Authors: Plastino Wolfango , Bella Francesco
Published: February 2004

An automatic multiparametric equipment (groundwater temperature, electrical conductivity, pH, 222Rn) has been planned and realized to study the correlations between the variations of radon with the strain processes of the rock and transport properties related to the groundwater geochemistry. The monitoring activity at underground laboratories of Gran Sasso with a groundwater sampling period of twelve hours has been started from May 1996. From geochemical data recorded during the first year a high dynamic behaviour of shallow aquifer has been emphasized due to high permeability of the cretaceous limestones that form part of the Gran Sasso massif. Also, the residual time series analysis of the geochemical parameters has emphasized pre‐co seismic anomalies in electrical conductivity and post‐seismic in radon content in groundwater related to local seismicity.
Accurate evaluation of ocean tide loading effects for gravity in nearshore region: The FG5 measurements at Sakurajima Volcano in Kagoshima Bay, Japan
Authors: Yamamoto Keigo , Ishihara Kazuhiro , Okubo Shuhei , Araya Akito
Published: February 2004

We detected 5–10 microgal diurnal/semidiurnal gravity signals of ocean tide origin by the FG5 absolute gravimeter at two stations in Sakurajima volcano located 300 m and 2500 m away from the shore. We computed the gravity originating both from the global ocean tides and from the local ones in Kagoshima Bay, considering the fine‐scale sealand distribution around the stations. The observed FG5 records and the theoretical ocean tides agreed well with each other in both amplitude and phase, indicating that the oceanic loading effects can be predicted to an accuracy better than 2 microgal within several hundred meters of the shore in Sakurajima. The apparently puzzling errors that have so far arisen on nearshore LaCoste measurements were resolved by the correction of the effects.
Structure of the Kaapvaal Craton from surface waves
Authors: Freybourger Marion , Gaherty James B. , Jordan Thomas H. ,   Kaapvaal SeismicGroup
Published: February 2004

Phase delays of Rayleigh and Love waves from teleseismic earthquakes recorded during the Southern Africa Seismic Experiment have been inverted for upper‐mantle seismic velocities along the propagation paths and beneath the station array. Successful models of subarray structure displayed significant radial anisotropy in the uppermost mantle but no shear‐wave low‐velocity zone, supporting the hypothesis that the lithosphere beneath the Kaapvaal craton is thick. The azimuthal variations of Rayleigh‐wave slowness are not consistent with simple models based on SKS splitting observations and anisotropy measurements of Kaapvaal mantle xenoliths. This discrepancy may imply some amount of small‐scale heterogeneity in anisotropy.
Wind induced sea level variability in the Red Sea
Authors: Sofianos Sarantis S. , Johns William E.
Published: February 2004

Analysis of TOPEX/Poseidon altimetry data for the Red Sea shows a large seasonal sea level signal in agreement with the few available coastal sea level stations. The results are compared with the predictions from a simple model that balances the sea surface elevation against the wind stress. The winter sea level field in the central and northern Red Sea is shown to be a response to the convergent wind pattern associated with the Indian Monsoon, consisting of NNW winds in the northern Red Sea and SSE winds in the south. There is a very good agreement between the model and observations, indicating that the basic mechanism responsible for the variability of the sea surface height inside the Red Sea on seasonal time scales is the wind pattern.
Direct measurements reveal insignificant storage of anthropogenic CO2 in the Abyssal Weddell Sea
Authors: Hoppema Mario , Roether Wolfgang , Bellerby Richard G. J. , de Baar Hein J. W.
Published: February 2004

In the northern Weddell Gyre at the prime meridian, Total TCO2 changes in the Weddell Sea Bottom Water (WSBW) have been investigated. Following a suggestion by [Poisson and Chen, 1987], the TCO2 difference at potential temperatures of 0.2°C and −0.8°C was determined using data from 1996 and 1998. No significant difference was found to similar differences for the years 1973 and 1981 reported by Poisson and Chen. Thus, over a period of 25 years an at most minor amount of anthropogenic CO2 has penetrated into the WSBW at this location. This suggests that this abyssal subpolar region is relatively unimportant for the storage of anthropogenic CO2. The same core of WSBW exhibited a marked increase of chlorofluorocarbon (CFC). For the Southern Ocean, therefore, CFCs are apparently of limited value as analogues of anthropogenic CO2, in contrast to some other ocean provinces.
Seasonal cycle of water storage in major river basins of the world
Authors: Masuda Kooiti , Hashimoto Yukie , Matsuyama Hiroshi , Oki Taikan
Published: February 2004

The seasonal cycle of water storage of each of the 70 major river basins of the world is evaluated by means of basin‐atmosphere water budgets. The atmospheric data of National Centers for Environmental Prediction (NCEP) Reanalysis is used together with river runoff data.

In the tropics and in the temperate zone of East Asia, storage becomes largest at the end of the rainy season and smallest at the beginning of the rainy season. In the cold region and in the temperate zone of North America, storage becomes largest in spring and smallest in summer or autumn. The global sum of storage becomes largest in spring of the northern hemisphere, when the contribution of the northern cold region and the southern tropics coincide.
Relationship between errors in AVHRR‐derived sea surface temperature and the TOMS aerosol index
Authors: Diaz J. P. , Arbelo M. , Expósito F. J. , Podestá G. , Prospero J. M. , Evans R.
Published: February 2004

We investigate the effects of various types of atmospheric aerosols on satellite‐derived sea surface temperature (SST) retrievals. The association between aerosol presence identified by the Earth Probe Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) and systematic errors in Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST retrievals is explored. We find a significant increase in systematic PFSST errors in the presence of dust aerosols. Average errors range from 0.34°C for AI values between 0.5 and 1.0 to 1.74°C for AI ≥ 1.5. The bias is introduced by the AVHRR channel brightness temperature difference (T4–T5) which is intended to correct for atmospheric absorption normally due primarily to water vapor. Our study shows that (T4– T5) is sensitive to the dust aerosols (i.e., TOMS AI values). In contrast, smoke aerosols do not seem to have a significant effect on PFSST errors.
Ion outflow observed by IMAGE: Implications for source regions and heating mechanisms
Authors: Fuselier S. A. , Ghielmetti A. G. , Moore T. E. , Collier M. R. , Quinn J. M. , Wilson G. R. , Wurz P. , Mende S. B. , Frey H. U. , Jamar C. , Gerard J.‐C. , Burch J. L.
Published: February 2004

Images of the Earth's proton aurora from the IMAGE spacecraft on 8 June 2000 indicate a temporally and spatially isolated ionospheric response to a shock that impinged on the Earth's magnetopause. Sometime after this ionospheric response, the Low Energy Neutral Atom imager on IMAGE detected enhanced ionospheric outflow. The time delay between the ionospheric response and the enhanced outflow is consistent with the travel time of ∼30 eV neutral Oxygen (created by charge exchange of outflowing O+ with the exosphere) from the low altitude ionosphere to the spacecraft. The prompt ionospheric outflow implies that the shock deposited sufficient energy in the topside ionosphere near or above the O+ exobase to initiate the outflow.
Near surface atmospheric characteristics over the North Bay of Bengal during the Indian Summer Monsoon
Authors: Bhat G. S.
Published: February 2004

Observations were made from a ship at 17.5°N & 89°E in the North Bay of Bengal during July–August 1999. The Bay was convectively active during this period with almost one convective event every week. The surface wind speed varied from 3 to 15 m s−1. SST decreased by 0.5° to 1° C following convection. The latent heat flux was about 25–35% lower over the Bay compared to that over the West Pacific at comparable wind speeds. High resolution radiosonde observations have been made for the first time in the North Bay. The values of atmospheric mixed layer height, equivalent potential temperature, convective available potential energy and convection inhibition energy over the North Bay are comparable to those observed over the western Pacific warm pool region. The recovery timescale of the atmospheric variables such as mixed layer height, equivalent potential temperature and convective available potential energy is one to two days.
Analytic potentials for the forward and inverse modeling of SP anomalies caused by subsurface fluid flow
Authors: Sailhac Pascal , Marquis Guy
Published: February 2004

Classical interpretation techniques developed primarily for gravity and magnetic data have been adapted to electric self‐potential (SP) data. From a recently developed wavelet‐based technique for potential field interpretation, we propose a novel approach for the forward and inverse modeling of SP anomalies caused by subsurface fluid flow. We use analytic signals and wavelets associated with the electric and fluid flow potentials. Fluid flow singularities have typical signatures in the wavelet‐domain SP data that can be used in the inversion scheme. For cases where electrokinetics is unambiguously the origin of SP anomalies, our interpretation method provides key parameters of the subsurface fluid flow (e.g. position, geometry, flow rate). To illustrate the theory, we consider synthetic 2D flows for which analytic solutions exist and actual SP data acquired around the Vulcarolo fissure on Mount Etna that show sources between 3 to 18 m depths.
Palaeolake evolution and abrupt climate changes during Last Glacial Period in NW China
Authors: Zhang H. C. , Ma Y. Z. , Li J. J. , Qi Y. , Chen G. J. , Fang H. B. , Wünnemann B. , Pachur H.‐J.
Published: February 2004

Field investigations and laboratory analyses show that there existed long‐lasting and extensive palaolakes between 18,000 and 42,000 yr B.P. in the Tengger Desert, NW China. This palaolake phase developed in a mild humid‐warm climate that was very different from that of present. Geochemical data, palynological evidence and grain size variations demonstrate that the lake levels had fluctuated greatly with the climate changes and these fluctuations can be correlated with the Dansgaard‐Oeschger and Heinrich events.
Correlation of ocean mass and temperature fluxes among hydrographic sections in the southern oceans
Authors: Sloyan Bernadette M. , Schröter J.
Published: February 2004

Two dominant correlations of ocean mass and temperature fluxes are found among distant hydrographic sections in the southern ocean. Mass transports are highly correlated among sections crossing the Antarctic Circumpolar Current at Drake Passage, south of Africa, and south of Australia, while there is a smaller temperature transport correlation among these sections. A second correlation is found in the mass and temperature fluxes between subtropical sections across the Indian and Pacific Oceans via south of Australia, and a temperature flux correlation between the Indian and the Atlantic Oceans via south of Africa. Knowledge of the property flux correlation among distant hydrographic sections provides information on the role of the Southern Ocean in the global overturning circulation.
Active crustal extension in the Central Apennines (Italy) inferred from GPS measurements in the interval 1994–1999
Authors: D'Agostino N. , Giuliani R. , Mattone M. , Bonci L.
Published: February 2004

We present the first GPS estimate of crustal extension in the central Apennines (Italy) through the analysis of the deformation of a sub‐network of the National GPS Geodetic network IGM95 in the interval 1994–1999. The selected sub‐network spans the entire active deformation belt perpendicularly to its axis and allows the evaluation of (1) the total extension rate absorbed in this sector of the Apennines and (2) the seismogenic potential of the normal faults active in the Late Pleistocene‐Holocene interval within the network. Results of this reoccupation are consistent with an extensional strain rate of 0.18 × 10−6 yr−1 concentrated in an area of about 35 km width, giving an average extension rate of 6±2 mm/yr across the central Apennines. The pattern of active deformation suggests active elastic strain accumulation on the westernmost of the two fault systems active in the Late Pleistocene‐Holocene interval and may also suggest the presence of another active fault system not recognized so far.
Precursory changes in well water level prior to the March, 2000 eruption of Usu Volcano, Japan
Authors: Shibata Tomo , Akita Fujio
Published: February 2004

The height of water levels in two wells located near Usu volcano, Japan, changed in a systematic fashion for several months prior to the eruption of Usu volcano on 31 March 2000. In one well, water‐level decrease relative to normal levels was first observed at the beginning of October 1999. The decreasing water‐level is postulated to result from groundwater flow into cracks widened by intruding magma during dike formation. From the beginning of January 2000, the rate of decrease became higher. During this time, the water level of the second well increased by 0.05 m and then gradually decreased. The water‐level changes are consistent with volumetric expansion of magma inside the magma chamber, followed by intrusion of magma into the fracture system associated with widening of cracks. We conclude that water‐level observations can provide information that may potentially be used to predict further volcanic eruptions.
The global mass of ozone: 1978–1998
Authors: Bodeker G. E. , Connor B. J. , Liley J. B. , Matthews W. A.
Published: February 2004

Global measurements of total column ozone from five inter‐compared satellite‐based instruments were used to calculate the daily global mass of ozone from November 1978 to December 1998. Missing data in polar darkness were estimated by interpolation across the polar caps. Global ozone mass and ozone mass totalled over 30° latitude zones were examined for the mean annual cycle, its evolution over the 20 year period, the impacts of volcanic eruptions and hemispheric differences in these impacts. Ozone mass for the globe or within a latitude zone is more suitable than mean column amount (e.g. in Dobson Units) because it is invariant under transport within zones and is a direct measure of exchange between zones. Furthermore, the relative contribution of impacts at different latitudes to global changes in ozone can be more easily quantified. While global ozone mass is significantly perturbed by high latitude wintertime ozone depletion, the impact of the Mt. Pinatubo eruption on northern midlatitude ozone mass was larger than any single Antarctic ozone hole event.
Non‐systematic errors of monthly oceanic rainfall derived from Passive Microwave Radiometry
Authors: Chang Alfred T. C. , Chiu Long S.
Published: February 2004

We compute the non‐systematic errors of monthly oceanic rainfall over 5° latitude by 5° longitude boxes derived from data taken by the Special Sensor Microwave Imager (SSM/I) on board the Defense Meteorological Satellite Program (DMSP) satellites and TRMM Microwave Imager (TMI). The mean rain rates between 1998 and 1999 are calculated to be 3.0, 2.85, 2.89 mm day−1 and the non‐systematic errors 22.2%, 22.4% and 19.7% for SSM/I onboard the DMSP F13, F14 and TMI, respectively. The non‐systematic error for the TMI is smaller than that for one SSM/I at the low rain rates but is comparable at rain rates higher than about 5mm day−1. The TRMM objective of 1mm day−1 for non‐systematic error is met by TMI for rain rates up to 5–6mm day−1. Improved space‐borne sampling strategy, such as that proposed for the Global Precipitation Mission (GPM), is needed to achieve errors better than 10% at the higher rain rates.
Strong zonal winds from thermal convection in a rotating spherical shell
Authors: Aurnou Jonathan M. , Olson Peter L.
Published: February 2004

Zonal wind (ZW) generation by thermal convection in rotating spherical shells is studied using numerical calculations. Strong ZW accompany quasi‐geostrophic, high Rayleigh number convection in shells with stress‐free boundaries. In a thin shell (radius ratio 0.75) with stress‐free boundaries, nearly 90% of the total kinetic energy is contained in the ZW at Rayleigh number 106 and Taylor number 4.4 × l07. The same parameters in a thicker shell produce weaker convection and weaker ZW. Rigid boundaries reduce the kinetic energy in the ZW to less than 20% of the total. The ZW are eastward (prograde) in the equatorial region and westward at higher latitudes, and are driven by Reynolds stresses associated with the convection. Episodes with strong ZW alternate with episodes of strong convection. Although far from the dynamical regime of Jupiter and Saturn, our results support the interpretation that the prograde equatorial jets on these planets originate from deep convection.
The salinity front of the Río de la Plata ‐ A numerical case study for winter and summer conditions
Authors: Simionato Claudia G. , Nuñez Mario N. , Engel Manfred
Published: February 2004

A 3‐D baroclinic model has been applied to investigate the location of the salinity front of the Río de la Plata. River run‐off, tides and mean winds for summer and winter conditions respectively were considered in order to find out the most important factors for the observed seasonal variability of this location. The results show that wind forcing is responsible for the observed variability in summer. In winter, wind forcing is not important, but the river discharge. The resulting surface salinity distributions show a surprisingly good agreement with the present knowledge from observations.
Detection of excitations of free core nutation of the Earth and their concurrence with huge earthquakes
Authors: Shirai Toshimichi , Fukushima Toshio
Published: February 2004

We detected the excitations of Free Core Nutation (FCN) of the Earth directly from the analysis of the Very Long Baseline Interferometry (VLBI) observation for the period 1979.9–2000.1. During the period, the FCN had 4 significant excitations at 1989.90, 1994.47, 1994.76, and 1998.99 where the timing uncertainty is 0.40 year. These epochs coincide with the occurrence of 4 of 5 huge (Mw ≥8.0) earthquakes within the same uncertainty. The probability of the coincidence by happenings is as quite low as 2 × 10−5.
Origin of postseismic streamflow changes inferred from baseflow recession and magnitude‐distance relations
Authors: Manga Michael
Published: February 2004

The effects of earthquakes on baseflow, the component of streamflow provided by groundwater, are analyzed for streams that exhibit large coseismic increases in streamflow and discharge large volumes of excess water. Although discharge Q may increase rapidly, the rate of baseflow recession dlogQ/dt is unchanged suggesting that the hydraulic conductivity of groundwater system providing baseflow does not change. For (at least) the studied streams, the coseismic increase of discharge therefore requires increased hydraulic head gradients resulting from the rapid release of water from some source of storage. The relationship between the response of streams, earthquake magnitude, and the distance of the drainage basin from the epicenter, is consistent with subsurface liquefaction being the mechanism that increases head gradients.
On the origin of reverse polarity TCRs
Authors: Moldwin Mark B. , Collier M. R. , Slavin J. A. , Szabo A.
Published: February 2004

Reverse polarity, or South‐then‐North (SN) bipolar, traveling compression regions (SN TCRs) are often observed in the Earth's magnetotail lobes. These events have been interpreted as either slowly earthward propagating “proto‐plasmoids” during extremely quiet geomagnetic conditions, or due to pressure pulses in the solar wind or magnetosheath compressing the magnetotail. This study presents a survey of 21 IMP 8 observations of SN TCRs and the corresponding solar wind pressure conditions as measured by WIND. We found that solar wind or magnetosheath pressure pulses nicely explain most (17), though not all, of the SN TCR observations. Therefore, it appears that both explanations previously given are needed to explain SN TCRs. We also found that most of these events occurred during northward Interplanetary Magnetic Field (IMF) conditions. This suggests that the magnetotail may respond differently to solar wind dynamic pressure pulses for different orientations of the IMF.
ENSO‐monsoon relationships in a greenhouse warming scenario
Authors: Ashrit R. G. , Kumar K. Rupa , Kumar K. Krishna
Published: February 2004

Recent studies based on observed climatic data indicate weakening of the relationship between El Niño‐Southern Oscillation (ENSO) and Indian summer monsoon rainfall, possibly due to global warming. Transient climate change simulations of a coupled ocean‐atmosphere GCM (ECHAM4/OPYC3) project a change towards enhanced ENSO activities in the tropical Pacific, as well as increase in mean monsoon rainfall and variability over India. However, the interannual correlations between the two are strong throughout the 240 year simulation. Analysis of monsoon viz‐a‐viz ENSO in the model simulations suggest a diminished impact of warm ENSO (El Niño) events on monsoon, while the impact of cold ENSO (La Niña) events remains unchanged in the scenario. Anomalous warming over the Eurasian landmass as well as enhanced moisture conditions over the Indian monsoon region in the global warming scenario have possibly contributed to the weakening of the impact of warm ENSO events on monsoon.
Recent change in organic carbon flux to Arctic Ocean deep basins: Evidence from acid volatile sulfide, manganese and rhenium discord in sediments
Authors: Gobeil C. , Sundby B. , Macdonald R. W. , Smith J. N.
Published: February 2004

Evidence of recent large‐scale change in redox conditions in Arctic Ocean basin sediments is found in profiles of solid phase acid volatile sulfide (AVS), Mn, and Re. AVS occurs at 2.5–5.5 cm in sediment cores collected from all major Arctic basins implying that presently there is a sufficient supply of organic carbon (OC) to deplete O2 and form sulfide. Re, which is mobile under oxic conditions but precipitates under suboxic or anoxic conditions, is not found enriched in the sediments suggesting that AVS is a recent product of enhanced OC fluxes. Estimated diffusion rates suggest that AVS production is recent and that a change from oxic to anoxic diagenesis has taken place within the past 50 y. The most likely origin for such widespread change is the ice climate, and we infer that reduction in ice cover over the past several decades has led to enhanced OC fluxes to the sea floor.
Response of the equatorial Pacific to chlorophyll pigment in a mixed layer isopycnal ocean general circulation model
Authors: Nakamoto S. , Kumar S. Prasanna , Oberhuber J. M. , Ishizaka J. , Muneyama K. , Frouin R.
Published: February 2004

The influence of phytoplankton on the upper ocean dynamics and thermodynamics in the equatorial Pacific is investigated using an isopycnal ocean general circulation model (OPYC) coupled with a mixed layer model and remotely sensed chlorophyll pigment concentration from the Coastal Zone Color Scanner (CZCS). In the equatorial Pacific heat accumulation due to a higher abundance of chlorophyll pigments in the equatorial Pacific leads to a decrease of the mixed layer thickness. This generates anomalous westward geostrophic currents north and south of the equator. In the western equatorial Pacific, these anomalous geostrophic currents merge into and strengthen the equatorial undercurrent (EUC), supplying water mass from the 200 m depth to the eastern equatorial Pacific. This chlorophyll‐induced response of the undercurrent enhances upwelling around 110W, resulting in a lower sea surface temperature (SST) than without chlorophyll. Thus, thermal gradients due to absorption of solar radiation by phytoplankton may contribute remotely to equatorial upwelling in the eastern Pacific.
On the origin of the deep CFC maximum in the Eastern Weddell Sea—Numerical model results
Authors: Schodlok Michael P. , Rodehacke Christian B. , Hellmer Hartmut H. , Beckmann Aike
Published: February 2004

CFC tracer observations indicate that Prydz Bay in the Indian sector of the Southern Ocean is a region of deep and bottom water formation. Results of a circumpolar ocean circulation model which includes CFC, an age tracer, and numerical floats indicate Prydz Bay as being a convection site which contributes to the reservoir of freshly ventilated waters in the Weddell Sea. In contrast to the newly formed Weddell Sea Bottom Water, captured near bottom, water masses of Prydz Bay origin spread on horizons which pass the ridges confining the Weddell Sea, therefore, contributing directly to the ventilation of the global abyss.
The climate of 6000 years BP in near‐equilibrium simulations with a coupled AOGCM
Authors: Voss Reinhard , Mikolajewicz Uwe
Published: February 2004

The response of a coupled atmosphere‐ocean general circulation model and an uncoupled atmosphere general circulation model to boundary conditions for 6000 years ago has been studied. The set of quasi‐equilibrium simulations enables a separation of the contributions from changes in the ocean circulation, the CO2 concentration, and the insolation to the total response. The results indicate that all three factors have considerable impact on the climate change signal and here especially on the northern African and Indian monsoon. Multi‐century adjustment processes associated with the inertia of the deep ocean play only a minor role for the climate change signal of the upper ocean and the atmosphere.