bluuebunny/crossref_metadata_2025 huggingface dataset:
Water level fluctuations in the Plata Basin (South America) from Topex/Poseidon Satellite Altimetry
Authors: Maheu Caroline , Cazenave Anny , Mechoso Carlos R.
Published: May 2003

Time series of water level in major rivers of the Plata basin are examined using altimetry data from the Topex/Poseidon satellite over the period 1993–2001. Ten sites are selected on the Paraná, three on the Paraguay, one the Uruguay and seven on wetlands. It is confirmed that the seasonal cycle of river levels decreases in amplitude with increasing latitude of the site. The normalized time series for sites along the same river differ mainly by a time‐lag corresponding to propagation speeds of about 0.1 ms−1. The interannual variability of the Lower Paraná, with a strong peak in early 1998 and minima in early 1996 and 2000, shows the remote effects of El Niño/Southern Oscillation (ENSO). The variability of the Upper Paraná and Paraguay shows similar ENSO impacts with smaller amplitudes after 1995, and the effects of regional features climate variability before that date (e.g. the South American monsoon). The results support the usefulness of satellite altimetry for a dense and continuous monitoring of river water levels.
Secular total solar irradiance trend during solar cycles 21–23
Authors: Willson Richard C. , Mordvinov Alexander V.
Published: May 2003

A series of satellite total solar irradiance (TSI) observations can be combined in a precise solar magnetic cycle length composite TSI database by determining the relationship between two non‐overlapping components: ACRIM1 and ACRIM2. [Willson and Hudson, 1991; Willson, 1994] An ACRIM composite TSI time series using the Nimbus7/ERB results [Hoyt et al., 1992] to relate ACRIM1 and ACRIM2 demonstrates a secular upward trend of 0.05 percent‐per‐decade between consecutive solar activity minima. [Willson, 1997] A PMOD TSI composite using ERBS [Lee et al., 1995] comparisons to relate ACRIM1 and ACRIM2 [Fröhlich and Lean, 1998] differs from the ACRIM composite in two significant respects: a negligible trend between solar minima and lower TSI at solar maxima. Our findings indicate the lower PMOD trend and lower PMOD TSI at the maxima of solar cycles 22 and 23 are artifacts of ERBS degradation. Lower PMOD TSI during the maximum of cycle 21 results from modifications of Nimbus7/ERB and ACRIM1 published results that produces better agreement with a TSI/solar proxy model [Foukal and Lean, 1988; Lean et al., 1995; Fröhlich and Lean, 1998].
Control of acid polysaccharide production and 234Th and POC export fluxes by marine organisms
Authors: Santschi Peter H. , Hung Chin‐Chang , Schultz Gary , Alvarado‐Quiroz Nicolas , Guo Laodong , Pinckney Jay , Walsh Ian
Published: May 2003

Ratios of particulate organic carbon (POC) to particulate 234Th activities (POC/234Th) in the ocean are used to determine the POC export flux, and thus, the power of the biological pump. In order to understand the main reasons why this ratio frequently varies as a function of depth, size, and kind (suspended vs. sinking particles), we measured vertical profiles in a cold core ring and warm core ring in the Gulf of Mexico in May 2001. Here we show that particulate 234Th/POC ratios in the Gulf of Mexico are positively correlated to the content of different Th(IV)‐binding polysaccharide fractions (uronic acids, total acid polysaccharides, total polysaccharides) in both suspended and sinking particles as well as to prymnesiophyte abundance, but negatively correlated to bacterial production. Variations in acid polysaccharide compounds, produced by both algae and bacteria, but degraded only by bacteria, can account for observed variations in POC/234Th ratios seen in the ocean.
Continuing deflation by fumaroles at Kuju Volcano, Japan
Authors: Nakaboh M. , Ono H. , Sako M. , Sudo Y. , Hashimoto T. , Hurst A. W.
Published: May 2003

A phreatic eruption occurred at Kuju Volcano in October 1995. We deployed an EDM network around the active craters of the volcano just after the eruption. Slope distances of the survey lines in the northern network have tended to contract, whereas those in the southern one extended. The maximum contraction observed in the northern network was 70 cm over 6 years. A spherical volume decrease just beneath a fumarolic area called Iwoyama 700 m north of the new craters is a plausible model for these changes in slope distances. A noteworthy feature is that over 6 years after the phreatic eruption ended, the deflation rate is still approximately linear. We also estimated the thermal energy discharge by fumaroles in the new craters, which proved to be well correlated with the observed deflation rate. It is strongly suggested that deflation of a geothermal reservoir, not any magmatic effect, causes the ground deformation around Iwoyama.
Fluctuation in groundwater level prior to the critical failure point of the crustal rocks
Authors: Shibata Tomo , Matsumoto Norio , Akita Fujio
Published: May 2003

Groundwater level change observed prior to the 2000 eruption of Usu volcano demonstrates that the failure in rock obeys a scaling rule. Three months before the eruption, the observed groundwater level perturbedly decreased around a curve like a power law, which appeared as an oscillation pattern like self‐similarity. The fluctuation in groundwater level is considered to be the inherent critical phenomenon of crustal rock prior to rock failure. The critical phenomenon offers the potential for prediction of failure in rock. The failure point in rock can be foreseen, more than one month before the rock failure.
The spectral behaviour of Sphagnum canopies under varying hydrological conditions
Authors: Bryant Robert G. , Baird Andrew J.
Published: May 2003

We tested the extent to which the spectral response (0.4–2.5 μm) of Sphagnum can be used to indicate changes in near‐surface hydrological conditions in northern wetlands. Via laboratory experimentation on three typical Sphagnum species we found that: (1) there is a clear link between (a) a ratio of SWIR/NIR reflectance (ETM+ Ch 5/Ch4) and (b) the relative depth of the water absorbion feature centred at 1.205 μm (RDI), and near‐surface volumetric moisture content (VMC) of the three species, (2) the changes in this ratio seem to be distinct for each species, and (3) data relating to the red‐edge inflection point (REIP) for the Sphagnum species may also yield important information on variations in photosynthetic activity with near‐surface VMC.
In situ photolysis of deep ice core contaminants by Çerenkov radiation of cosmic origin
Authors: Colussi A. J. , Hoffmann M. R.
Published: May 2003

Ice core contaminants should provide permanent paleoclimatic records if, as it is generally assumed, they remained frozen in place and isolated from sunlight by the reflective overlaying snow layers. The excess CO levels recently detected in 1100–1600 AD Greenland ice core air bubbles relative to their Antarctic counterparts [Haan and Raynaud, 1998] amount, however, to an average production of about 5 ± 2 CO molecules cm−3 ice s−1 in that period. Here we show that such rates are quantitatively consistent with the in situ photodecarbonylation of the chromophoric organic matter present in Greenland, but not in the cleaner Antarctic, ice under the Çerenkov radiation fluxes generated by penetrating muons of cosmic origin. The normal CO levels of modern (1600–1800 AD) Greenland records, and their variability earlier in the last millennium correlate significantly with the occurrence of boreal fires and the associated release of organic aerosol [Savarino and Legrand, 1998].
Effects of dry fractures on matrix diffusion in unsaturated fractured rocks
Authors: Seol Yongkoo , Liu Hui Hai , Bodvarsson Gudmundur S.
Published: May 2003

Matrix diffusion has been recognized as an important mechanism affecting solute transport through unsaturated fractured rock, where a significant portion of the fracture network remains relatively dry and inactive in conducting liquid flow. This simulation study shows that dry fractures act as strong diffusion barriers to solute transport when such fractures divide the matrix into discrete blocks. Where fracture surface roughness causes certain amount of direct contact between matrix blocks separated by a dry fracture, the contacts of the matrix blocks provide conduits for liquid flow and molecular diffusion across dry fractures. Simulation results indicate that the presence of dry fractures and their discontinuities can considerably affect solute transport in unsaturated fractured rock, depending on the magnitude of molecular diffusion.
Tropical Atlantic seasonal predictability: The roles of El Niño remote influence and thermodynamic air‐sea feedback
Authors: Chang Ping , Saravanan R. , Ji Link
Published: May 2003

Recent studies suggest that the thermodynamic feedback and the remote influence of El Niño Southern Oscillation (ENSO) are two dominant factors affecting climate variability in the tropical Atlantic sector. Given that both of these processes are included in an atmospheric general circulation model (AGCM) coupled to a mixed layer ocean (ML), such a simple coupled system is expected to possess useful skills in predicting regional climate variability on seasonal time scales. This letter reports some preliminary results from a set of prediction experiments using a coupled AGCM‐ML model. These results show promise for prospects of seasonal climate prediction in the tropical Atlantic sector using the simple dynamical seasonal prediction system.
Solar impact on the lower mesospheric subtropical jet: A comparative study with general circulation model simulations
Authors: Kodera Kunihiko , Matthes Katja , Shibata Kiyotaka , Langematz Ulrike , Kuroda Yuhji
Published: May 2003

The seasonal and interannual variation in the lower mesospheric subtropical jet (LMSJ) and their dependence on the 11‐year solar cycle are studied by comparing observational data with simulations by two general circulation models. In the model simulations, a strengthening of the LMSJs is found in both hemispheres during the winter under the solar maximum condition, similar to the observation. However the model responses are substantially smaller except for one case in the southern hemisphere. It is also found that the stronger LMSJ due to an enhanced solar forcing appears during the period which follows an increasing period of interannual variation. Analysis of the observed seasonal march of the LMSJ in each year shows two different regimes of behavior. For a successful simulation, the model should realistically reproduce the observed interannual variability as well as the climatological mean.
A double sodium layer event observed over Wuhan, China by lidar
Authors: Gong S. S. , Yang G. T. , Wang J. M. , Cheng X. W. , Li F. Q. , Wan W. X.
Published: May 2003

A double sodium layer (DSL) structure was observed during the night of June 13, 2000 over Wuhan, China (31°N, 114°E) by our Na lidar. The unique feature of this DSL is that a normal sodium layer at altitudes of 80 ∼ 105 km was accompanied by a secondary sodium layer at altitudes of 105 ∼ 125 km for about 2 hours. The lidar observation result together with that obtained from the nearby ionosonde and geomagnetic equipments are presented. While the exact mechanism responsible for this DSL formation is still unclear, some possible explanations and corresponding observation evidences are discussed.
Patterns and sources of multidecadal oscillations in drought‐sensitive tree‐ring records from the central and southern Rocky Mountains
Authors: Gray Stephen T. , Betancourt Julio L. , Fastie Christopher L. , Jackson Stephen T.
Published: May 2003

Tree‐ring records spanning the past seven centuries from the central and southern Rocky Mountains were studied using wavelet analysis to examine multidecadal (>30–70 yr) patterns of drought variation. Fifteen tree‐ring series were grouped into five regional composite chronologies based on shared low‐frequency behavior. Strong multidecadal phasing of moisture variation was present in all regions during the late 16th century megadrought. Oscillatory modes in the 30–70 yr domain persisted until the mid‐19th century in two regions, and wet‐dry cycles were apparently synchronous at some sites until the 1950s drought. The 16th/17th century pattern of severe multidecadal drought followed by decades of wet conditions resembles the 1950s drought and post‐1976 wet period. The 16th century megadrought, which may have resulted from coupling of a decadal (∼20–30 yr) Pacific cool phase with a multidecadal warm phase in the North Atlantic, marked a substantial reorganization of climate in the Rocky Mountain region.
On the non‐linear response of the ocean thermohaline circulation to global deforestation
Authors: Renssen H. , Goosse H. , Fichefet T.
Published: May 2003

An experiment of 1750‐yr duration has been performed with a three‐dimensional coupled atmosphere‐sea‐ice‐ocean‐vegetation model to study the transient effect of global deforestation on climate. The response consists of two phases. First, the initial global cooling due to increased surface albedo (forest replaced by grassland) is enhanced by a significant expansion of the sea‐ice cover in both hemispheres, which increases the surface albedo further. Second, a non‐linear response of the ocean thermohaline circulation results in a southward shift of the main deep‐convection site and reduced northward heat transport in the Atlantic Ocean, leading to enhanced global cooling due to a further expansion of Arctic sea ice. Ultimately, surface temperatures over northwestern North America become sufficiently low to prevent the snow pack to melt in summer. Our results thus suggest that large‐scale changes in forest cover may lead to non‐linear changes in the climate system.
The dynamics of submarine geothermal heat pipes
Authors: Bai Wuming , Xu Wenyue , Lowell Robert P.
Published: May 2003

To better understand natural two‐phase hydrothermal systems, we have constructed one‐dimensional heat‐pipe solutions for NaCl‐H2O fluids and explored the effects of basal heat flux and permeability on their behavior. For seafloor conditions, saline brines form quickly at the base of the heat pipe; and in some cases halite is precipitated. NaCl‐H2O heat pipes may become liquid or vapor dominated but, in contrast to their pure‐water counterparts, often do not achieve steady state. When steady state solutions do exist, they are characterized either by broad, weak counter‐flow or by vigorous counter‐flow across a thin layer. The latter behavior may be analogous to that occurring in the Salton Sea Geothermal System, California.
Small‐scale lateral variations in D″ attenuation and velocity structure
Authors: Fisher Jesse L. , Wysession Michael E. , Fischer Karen M.
Published: May 2003

Combined ScS‐S differential attenuation and travel‐time studies, with data from temporary and permanent arrays, produce quality factor, Qμ(D″), estimates for D″ beneath Central America. Similarities between S and ScS ray paths through the upper mantle reduce the upper mantle elastic and anelastic contributions to differential studies. Differential attenuation correlates with ScS attenuation but not S attenuation, indicating that the attenuation primarily stems from lower mantle interactions. We image a ∼250 km wide high‐attenuation low‐velocity anomaly within a ∼600 km wide low‐attenuation high‐velocity region at the core‐mantle boundary (CMB). The observed inverse exponential relationship between attenuation and velocity is consistent with a 200 ± 50 km thermal anomaly, but does not preclude chemical, phase, or structural variations. Observation of a small‐scale thermal anomaly within D″ may provide significant evidence in favor one kind of plume formation at the CMB.
Spectral beam attenuation coefficient retrieved from ocean color inversion
Authors: Roesler Collin S. , Boss Emmanuel
Published: May 2003

A reflectance inversion model in presented in which particle backscattering is parameterized by the particle backscattering ratio, attenuation and absorption coefficients rather than a hyperbolic function. This parameterization removes backscattering spectral constraints and yields independent estimates of the magnitude and spectral slope of the particle beam attenuation, which have been found to correlate with the particle concentration and size distribution, respectively. The model yields estimates of component absorption and backscattering consistent with observations and Mie models, particularly for environments dominated by phytoplankton and other strongly absorbing particles.
NAO signal recorded in the stable isotopes of Greenland ice cores
Authors: Vinther B. M. , Johnsen S. J. , Andersen K. K. , Clausen H. B. , Hansen A. W.
Published: May 2003

The winter δ18O signal is extracted from 7 Greenland ice cores covering the past ∼700 years. To filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data. A comparison between the time series of the first principal component (PC1) with 67 years of winter (December to March) temperature measurements from 3 southern Greenland synoptic stations shows highly significant correlations. Southern Greenland winter temperatures are known to be greatly influenced by the North Atlantic Oscillation (NAO). A good proxy for southern Greenland temperatures is therefore expected to reveal at least parts of the NAO signal. It is shown that the PC1 time series indeed is significantly correlated to the NAO during the winter months. The inclusion of ice core winter season δ18O time series in future multiproxy NAO reconstructions is therefore recommended.
Toward stochastic deep convective parameterization in general circulation models
Authors: Lin Johnny Wei‐Bing , Neelin J. David
Published: May 2003

For the first time, a stochastic deep convective parameterization to represent variability arising from small‐scale processes that are unresolved by traditional deterministic moist convective parameterizations is tested in a general circulation model. Two physical pathways of representing small‐scale variability as a stochastic process are explored. First, the relationship between cloud‐base mass flux Mb and large‐scale convective available potential energy (CAPE) is posited to have a stochastic component (the CAPE‐Mb scheme). Second, the vertical structure of heating is modified by a simple random process about the structure given by the traditional convective scheme (the VSH scheme). The CAPE‐Mb scheme increases the overall variance of precipitation toward observations with a realistic spatial pattern. The VSH scheme has smaller impacts on precipitation variance but yields preferential enhancement at large spatial scales and low frequencies.
Mixing‐driven diagenesis and mineral deposition: CaCO3 precipitation in salt water – fresh water mixing zones
Authors: Berkowitz Brian , Singurindy Olga , Lowell Robert P.
Published: May 2003

We perform a novel set of laboratory experiments that depict CaCO3 precipitation upon mixing between saturated fresh and salt water solutions, thus simulating mixing diagenesis in a coastal aquifer. The experimental results are shown to agree with the result predicted from a relatively simple mathematical model, thus suggesting that the model may be extrapolated to natural environments. Application of the model to the coastal aquifer of Mallorca, Spain indicates calcite precipitation is reducing porosity at a rate of ∼13% per 10,000 years. Consideration of precipitation processes can thus explain contradictory interpretations of natural evolution in carbonate formations.
Measuring the sea breeze from QuikSCAT Scatterometry
Authors: Gille Sarah T. , Llewellyn Smith Stefan G. , Lee Shira M.
Published: May 2003

Differences between morning and evening winds from QuikSCAT scatterometer measurements are analyzed to diagnose the diurnal variability of the wind over the ocean. A statistically significant signal, associated with the sea breeze, is present along most of the world's coastlines. Significant diurnal variability is also present mid‐ocean in the easterly trade wind belts.
Along‐shore variations of offshore flow
Authors: Moore Erin , Mahrt L.
Published: May 2003

Using eddy correlation data collected by the LongEZ research aircraft, the adjustment of atmospheric flow downstream from a coastline is examined. Along‐shore variation of the turbulence over the water is generated by the varying width of the upstream land strip between the sea and inland water. Over the coastal zone, the turbulence is strongest downstream from the widest part of land. The along‐shore variation of the turbulence decreases with increasing sea fetch due to horizontal mixing. In other terms, the footprint of the flux farther offshore includes a larger width of upstream land. Beyond 5 km sea fetch, the along‐shore variation becomes small.
Inherently three dimensional magnetic reconnection: A mechanism for bursty bulk flows?
Authors: Shay M. A. , Drake J. F. , Swisdak M. , Dorland W. , Rogers B. N.
Published: May 2003

We examine the development of mesoscale structure during 3‐D magnetic reconnection which initiates from random perturbations. Reconnection develops as multiple x‐line segments with characteristic scale lengths of ∼1–4 Re in the cross tail direction. For relatively wide initial current sheets (several c/ωpi), these finite length x‐lines remain spatially isolated and drive reconnection which is strongly reminiscent of bursty bulk flows (BBFs) in the magnetotail. In narrower initial current layers the x‐line segments merge together to a state in which large scale magnetic energy release takes place. Thus, the degree of compression of the magnetotail may ultimately determine if energy is released in local bursts or globally as a substorm.
Presunrise ion temperature enhancement observed at 600 km low‐ and mid‐latitude ionosphere
Authors: Chao C. K. , Su S.‐Y. , Yeh H. C.
Published: May 2003

The quiet‐time low‐ and mid‐latitude topside ionospheric ion temperature measured with ROCSAT‐1/IPEI instrument is studied for local time, longitudinal, latitudinal, and seasonal variations for the solar maximum year of 2000. The statistical result shows two significant observations at the presunrise sector. Namely, the earliest presunrise ion temperature increase at 600 km low‐ and mid‐latitude ionosphere always starts in the winter hemisphere for both summer and winter seasons; and the strongest presunrise ion‐heating region is located in the longitudinal region between 165° and 195° during June summer and between 285° and 345° during December winter. Our simple calculation indicates that the temperature increase at the satellite altitude results from the heating process of photoelectrons that are produced at the magnetic conjugate‐point where sunrise is at an earlier time. However, the mechanism to enhance the photoelectron heating at the strongest presunrise ion‐heating region is still not clear, because the observed ion density and the field flow data fail to lend a clear support to the proposed heating mechanism for the current observations.
Orbital control of low‐latitude seasonality during the Eemian
Authors: Winter Amos , Paul André , Nyberg Johan , Oba Tadimichi , Lundberg Joyce , Schrag Dan , Taggart Bruce
Published: May 2003

We used Sr/Ca and stable isotope data from well dated and preserved corals from the northeastern Caribbean to determine the seasonal environmental conditions for four continuous years during the Eemian, the last time the Earth was in a prolonged warm phase. We determined that the seasonal range in SST during the Eemian was 25°–30° C. This is ∼1–2° larger than at present and caused primarily by winter cooling and, only to a small degree, by summer warming. As climate modeling studies indicate, the bias towards colder winters can be explained by changes in low latitude insolation induced by altered orbital parameters, modulated by atmospheric CO2 levels that were lower than today. Milankovitch forcing at higher latitudes was probably less important.
Turbulence at the tropopause due to breaking Kelvin waves observed by the Equatorial Atmosphere Radar
Authors: Fujiwara Masatomo , Yamamoto Masayuki K. , Hashiguchi Hiroyuki , Horinouchi Takeshi , Fukao Shoichiro
Published: May 2003

The Equatorial Atmosphere Radar (EAR) installed in Sumatra Island, Indonesia, observed significant enhancement of turbulence in the tropopause region, 15–17 km, intermittently for ∼5 days in November 2001. The turbulence intensity was estimated with the spectral width of the radar echo power spectrum, and the turbulence during the period was a factor of up to ∼5 larger in kinetic energy than that in other periods. Further analyses confirm that the enhanced turbulence was convectively generated in the breaking phase of an equatorial Kelvin wave. Between July and December 2001, we observed at least three more prominent cases of the turbulence generation by breaking Kelvin waves in the tropopause region.
The impact of a No‐Net‐Rotation Condition on ITRF2000
Authors: Altamimi Zuheir , Sillard Patrick , Boucher Claude
Published: May 2003

The realization of the International Terrestrial Reference System (ITRS) for 2000 (ITRF2000), provides an accurate estimation of relative motions for 6 major tectonic plates. In order to comply with the ITRS specification, a No‐Net‐Rotation Condition (NNRC) was applied by aligning the orientation time evolution of the ITRF2000 to that of the geophysical model NNR‐NUVEL‐1A. This implicit application of the NNRC, since the NNR‐NUVEL‐1A satisfies that condition, is achieved by using a consistent geodetic method, minimizing the global rotation rate between the ITRF2000 and the NNR‐NUVEL‐1A model. The main focus of this paper is to examine how the ITRF2000 satisfies this condition by computing rotation rate components with respect to the Tisserand frame which is the basis of the NNRC. Numerical tests based on several approaches illustrate the sensitivity of the alignment to NNR‐NUVEL‐1A and they also show that the ITRF2000 is aligned at the 1 mm/yr level.
Diurnal signals in satellite sea surface temperature measurements
Authors: Gentemann Chelle L. , Donlon Craig J. , Stuart‐Menteth Alice , Wentz Frank J.
Published: May 2003

During the daytime, solar heating may lead to the formation of a near‐surface diurnal warm layer, particularly in regions with low wind speeds. This effect can be clearly seen in global, satellite‐derived, maps of the difference between daytime and nighttime SSTs. Analysis of TMI and AVHRR SSTs revealed that the onset of warming begins as early as 8 AM and peaks near 3 PM., with a magnitude of 2.8 C during favorable conditions. After this peak, the signal decays gradually until 11 PM, when the skin temperature approaches the bulk temperature. An empirical model is calculated from satellite SST and wind speed data, then used to derive daily global maps of diurnal warming. When modeled warming is removed from daytime SSTs, the mean and standard deviation of day minus night SST differences are diminished.
Are there spurious temperature trends in the United States Climate Division database?
Authors: Keim Barry D. , Wilson Adam M. , Wake Cameron P. , Huntington Thomas G.
Published: May 2003

The United States (U.S.) Climate Division data set is commonly used in applied climatic studies in the United States. The divisional averages are calculated by including all available stations within a division at any given time. The averages are therefore vulnerable to shifts in average station location or elevation over time, which may introduce spurious trends within these data. This paper examines temperature trends within the 15 climate divisions of New England, comparing the NCDC's U.S. Divisional Data to the U.S. Historical Climate Network (USHCN) data. Correlation and multiple regression revealed that shifts in latitude, longitude, and elevation have affected the quality of the NCDC divisional data with respect to the USHCN. As a result, there may be issues with regard to their use in decadal‐ to century‐scale climate change studies.
Riverine inorganic carbon flux and rate of biological uptake in the Mississippi River plume
Authors: Cai Wei‐Jun
Published: May 2003

Inorganic carbon parameters were studied for the first time in the Mississippi River estuary and plume. Area‐integrated biological uptake rates (1.5–3 gC m−2 d−1) derived from riverine total dissolved inorganic carbon (DIC) and total alkalinity (TAlk) fluxes as well as that based on the consumptions of DIC and TAlk in the plume are comparable to earlier results of 14C incubation in individual water samples. This rate is among the highest in the estuaries and plumes of the world's largest rivers. Fluvial DIC flux (13.5 × 1012 gC yr−1) indicates a 16% increase in the inorganic carbon flux over the earlier estimate and perhaps an increase in the weathering rate in the Mississippi River basin over the past four decades.
Observation of Electrostatic Solitary Waves associated with reconnection on the dayside magnetopause boundary
Authors: Matsumoto H. , Deng X. H. , Kojima H. , Anderson R. R.
Published: May 2003

When a Coronal Mass Ejection struck the Earth on January 10, 1997, Electrostatic Solitary Waves (ESW) and Amplitude Modulated Electrostatic Waves (AMEW) were detected as GEOTAIL skimmed along the dayside magnetopause and observed 3‐dimensional multiple x‐line magnetic reconnection. The ESW had amplitudes up to ∼20mV/m and evolved from two‐dimensional structures with smaller amplitudes to one‐dimensional structures with larger amplitudes. The observation of ESW and AMEW show that the enhanced broadband electrostatic emissions associated with reconnection are not random noises but are nonlinear coherent structures which may provide important dissipation in the electron diffusion region during reconnection.
The 1978 shift in the NCEP reanalysis stratospheric quasi‐biennial oscillation
Authors: Huesmann Amihan S. , Hitchman Matthew H.
Published: May 2003

The National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP) reanalysis exhibits interdecadal changes in the structure of the quasi‐biennial oscillation (QBO) and annual mean fields in the tropical stratosphere during 1958–2001. A sudden temperature increase occurred around 1978, with equatorial maxima of ∼3 K at 10 hPa and near the tropopause. When this 1978 jump is removed, a moderate cooling trend is found throughout the tropical lower stratosphere, with an equatorial maximum cooling of 3 K over 40 years near 30 hPa. While the QBO in zonal wind is similar in both the 1958–1978 and 1979–2001 periods, the QBO in temperature is significantly reduced in amplitude and latitudinally contracted after 1978, and the QBO meridional circulation is stronger. Vertical temperature variations in the annual mean and QBO have been underestimated since the introduction of nadir‐sounding satellites. A mechanism is suggested for how this may affect meridional circulations in data assimilation models.
Rain‐on‐snow events impact soil temperatures and affect ungulate survival
Authors: Putkonen J. , Roe G.
Published: May 2003

Field data from Spitsbergen and numerical modeling reveal that rain‐on‐snow (ROS) events can substantially increase sub‐snowpack soil temperatures. However, ROS events have not previously been accounted for in high latitude soil thermal analyses. Furthermore such events can result in widespread die‐offs of ungulates due to soil surface icing. The occurrence of Spitsbergen ROS events is controlled by the North Atlantic Oscillation. Globally, atmospheric reanalysis data show that significant ROS events occur predominantly over northern maritime climates, covering 8.4 × 106 km2. Under a standard climate change scenario, a global climate model predicts a 40% increase in the ROS area by 2080–2089.
Dependence of the annular mode in the troposphere and stratosphere on orography and land‐sea heating contrasts
Authors: Körnich H. , Schmitz G. , Becker E.
Published: May 2003

Using an idealized general circulation model, we explore the influence of orography and land‐sea heating contrasts on the development of Annular Modes (AM) under perpetual January conditions. In the troposphere, model experiments with different stationary wave forcing all show an internally induced AM, but with significantly different amplitudes. Only the combined forcing of orography and land‐sea heating contrast leads to a localization of the AM similar to the North Atlantic Oscillation, and additionally, to a stratospheric AM and its downward propagation. A tropospheric feedback mechanism between the anomalies of zonal‐mean wind and stationary waves applies in the simulation with the combined forcing only, where the coupling of orographically and thermally forced waves reproduces the observed stationary waves, and where the simulated diabatic heating supports the feedback mechanism. In contrast, transient forcing dominates the variability in the experiments without orography, comparable to the Southern AM.
Postseismic deformation following the 1997 Umbria‐Marche (Italy) moderate normal faulting earthquakes
Authors: Aoudia A. , Borghi A. , Riva R. , Barzaghi R. , Ambrosius B. A. C. , Sabadini R. , Vermeersen L. L. A. , Panza G. F.
Published: May 2003

We combine aftershock strain mapping, GPS measurements and leveling profiles with forward modeling of viscoelastic relaxation to study the postseismic deformation of the 1997 Umbria‐Marche (Central Apennines) earthquake sequence. We explore the feasibility of GPS monitoring of postseismic transients, for the first time in Italy, generated by shallow and moderate sources. Our data allow us to distinguish a preferred coseismic faulting model as well as insight into the rheology of the Central Apennines Earth's crust. The faulting model requires a listric geometry with most of the energy released in the lower half part of the elastic crust. The rheological model consists of an elastic thin upper crust, a transition zone of about 1018 Pa s underlain by a low‐viscosity lower crust, ranging from 1017 to 1018 Pa s. The postseismic deformation is, both distributed in the transition zone ‐ lower crust and confined to the fault zone.
The potential role of snow cover in forcing interannual variability of the major Northern Hemisphere mode
Authors: Saito Kazuyuki , Cohen Judah
Published: May 2003

Decadal trends have been noted in the leading mode of boreal winter variability. Given that this mode is thought to be an internal mode of the atmosphere it remains unclear as to what is responsible for interannual to interdecadal oscillations of this mode. We demonstrate that continental‐scale snow cover varies at the same multi‐year time periods as the atmosphere but leads the atmosphere by several months through their mutual oscillations. Therefore we propose snow cover as a potential contributor to the interannual variability of the leading boreal winter mode of the atmosphere.
Diffusion in MgO at high pressures: Constraints on deformation mechanisms and chemical transport at the core‐mantle boundary
Authors: Van Orman James A. , Fei Yingwei , Hauri Erik H. , Wang Jianhua
Published: May 2003

High‐pressure experiments on diffusion in MgO were performed to model the rheological and chemical transport properties of the lower mantle. Lattice and grain boundary diffusion coefficients for Mg, O and Al were determined at 2273 K and pressures up to 25 GPa. The results for pure MgO are in excellent agreement with first‐principles calculations. In samples doped with Al2O3, cation vacancies were found to attach to Al impurities with a binding energy of ∼0.7 eV. Our results predict that a transition from diffusion creep to dislocation creep will occur in the deep lower mantle if the shear stress exceeds ∼1–10 MPa, for a grain size of ∼0.1–1 mm. Diffusion through periclase is fast enough to allow substantial chemical exchange across the core‐mantle boundary since core formation, with length scales of ∼1–10 km for lattice diffusion and 100 km for grain boundary diffusion.
Large historical changes of fossil‐fuel black carbon aerosols
Authors: Novakov T. , Ramanathan V. , Hansen J. E. , Kirchstetter T. W. , Sato M. , Sinton J. E. , Sathaye J. A.
Published: May 2003

Anthropogenic emissions of fine black carbon (BC) particles, the principal light‐absorbing atmospheric aerosol, have varied during the past century in response to changes of fossil‐fuel utilization, technology developments, and emission controls. We estimate historical trends of fossil‐fuel BC emissions in six regions that represent about two‐thirds of present day emissions and extrapolate these to global emissions from 1875 onward. Qualitative features in these trends show rapid increase in the latter part of the 1800s, the leveling off in the first half of the 1900s, and the re‐acceleration in the past 50 years as China and India developed. We find that historical changes of fuel utilization have caused large temporal change in aerosol absorption, and thus substantial change of aerosol single scatter albedo in some regions, which suggests that BC may have contributed to global temperature changes in the past century. This implies that the BC history needs to be represented realistically in climate change assessments.
Bragg reflection of ocean waves from sandbars
Authors: Elgar Steve , Raubenheimer B. , Herbers T. H. C.
Published: May 2003

Resonant Bragg reflection of ocean surface waves by a field of natural shore‐parallel sandbars was observed in Cape Cod Bay, MA. Waves transmitted through the bars were reflected strongly from the steep shoreline, and the observed cross‐shore variations in the onshore‐ and offshore‐directed energy fluxes are consistent with theory for resonant Bragg reflection, including a 20% decay of the incident wave energy flux that is an order of magnitude greater than expected for wave‐orbital velocity induced bottom friction. Bragg reflection was observed for a range of incident wave conditions, including storms when sediment transported toward and away from nodes and antinodes caused by the reflecting waves might result in growth and maintenance of the sandbars.
Strong El Niño events and nonlinear dynamical heating
Authors: Jin Fei‐Fei , An Soon‐Il , Timmermann Axel , Zhao Jingxia
Published: May 2003

We present evidence showing that the nonlinear dynamic heating (NDH) in the tropical Pacific ocean heat budget is essential in the generation of intense El Niño events as well as the observed asymmetry between El Niño (warm) and La Niña (cold) events. The increase in NDH associated with the enhanced El Niño activity had an influence on the recent tropical Pacific warming trend and it might provide a positive feedback mechanism for climate change in the tropical Pacific.
Interferometric observations of filamentary structures associated with plasma instability in the auroral ionosphere
Authors: Grydeland T. , La Hoz C. , Hagfors T. , Blixt E. M. , Saito S. , Strømme A. , Brekke A.
Published: May 2003

We present evidence of filamented structure in the auroral ionosphere, observed through enhanced radar echoes produced by plasma instabilities in the filaments. Enhancements are observed in up‐ or down‐shifted ion‐acoustic peaks, or both, with power well above thermal levels. Detailed theoretical understanding of these enhancements is still lacking, and several different theories are currently used to explain the observations. Using an interferometric technique, we have measured the horizontal scales of the structures, and their evolution in time, with unprecedented resolution. To explain simultaneous up‐ and down‐shifted enhancements using theories that could only enhance one of these shoulders, spatial and/or temporal averaging has previously been suggested. However, the present observations show that enhancements occur simultaneously and in the same volume. The observed scale size in the plane perpendicular to the magnetic field is comparable to the smaller scale size of optical aurora, which, despite extensive attempts, has not been successfully explained.
The seasonal cycle of wind stress curl and its relationship to subsurface ocean temperature in the Northeast Pacific
Authors: Murphree Tom , Green‐Jessen Phaedra , Schwing Franklin B. , Bograd Steven J.
Published: May 2003

We examine the seasonal evolution of analyzed wind stress curl (WSC) over the northeast Pacific Ocean. The strongest WSC features are associated with wind maxima on the flanks of the North Pacific High and Aleutian Low, especially in coastal regions. A strong, seasonally‐migrating WSC dipole (positive inshore, negative offshore) is evident year‐round over the California Current System (CCS). We compare the WSC fields to observed upper ocean temperatures to test the hypothesis that seasonal variations in overlying WSC strongly impact temperatures just below the seasonal thermocline. The hypothesis is supported along most of the west coast, where the WSC seasonal cycle is strong and subsurface temperature data are relatively abundant. In open ocean regions, there is little clear evidence for or against the hypothesis due to weak WSC signals and a lack of subsurface data.
A study of the effect of non‐spherical dust particles on the AVHRR aerosol optical thickness retrievals
Authors: Zhao Tom X.‐P. , Laszlo Istvan , Dubovik Oleg , Holben Brent N. , Sapper John , Tanré Didier , Pietras Christophe
Published: May 2003

Non‐spherical assumption of particle shape has been used to replace the spherical assumption in the AVHRR aerosol optical thickness (τ) retrievals for dust particles. Retrieved τ with both spherical and non‐spherical assumptions have been compared to the surface AERONET observations at two desert dust sites to evaluate and quantify the effect of non‐spherical dust particles on the satellite aerosol retrievals. The errors (especially the random error) in the satellite retrieved τ have been reduced as a result of adopting the non‐spherical assumption in the NOAA/NESDIS AVHRR aerosol retrieval algorithm. This result suggests the importance of taking into account the effects of non‐sphericity in the retrieval of dust particles from AVHRR measurements.
Waveform analysis of the 1999 Hector Mine foreshock sequence
Authors: Zanzerkia Eva E. , Beroza Gregory C. , Vidale John E.
Published: May 2003

By inspecting continuous Trinet waveform data, we find 42 foreshocks in the 20‐hour period preceding the 1999 Hector Mine earthquake, a substantial increase from the 18 foreshocks in the catalog. We apply waveform cross‐correlation and the double‐difference method to locate these events. Despite low signal‐to‐noise ratio data for many of the uncataloged foreshocks, correlation‐based arrival time measurements are sufficient to locate all but three of these events, with location uncertainties from ∼100 m to 2 km. We find that the foreshocks fall on a different plane than the initial subevent of the mainshock, and that the foreshocks spread out over the plane with time during the sequence as the time of the mainshock approaches.
Photochemical activity of organic compounds in ice induced by sunlight irradiation: The Svalbard project
Authors: Klán P. , Klánová J. , Holoubek I. , Čupr P.
Published: May 2003

Field experiments in Ny‐Ålesund, Spitsbergen Island (Svalbard) demonstrated that water ice can be a suitable reaction medium for photochemical transformations of organic pollutants. Several aromatic carbonyl, chloro, nitro or hydroxy compounds, frozen in the ice‐matrix samples, underwent very efficient sunlight‐induced chemical changes. The photoproducts, in many cases completely different from those obtained from liquid solution photolysis, might pose a high toxicological risk to biota when they enter the environment. It is concluded that the results could be applicable to natural snow and ice, and that possible photochemical transformations should be considered in the ice‐core record studies.
Rossby wave and ocean color: The cells uplifting hypothesis in the South Atlantic Subtropical Convergence Zone
Authors: Charria G. , Mélin F. , Dadou I. , Radenac M.‐H. , Garçon V.
Published: May 2003

Rossby waves signatures on filtered ocean color data are detected in the subtropical convergence zone of the South Atlantic ocean. We investigate whether these chlorophyll anomalies can be accounted for by the uplifting mechanism of phytoplanktonic cells associated with the passage of a Rossby wave. We consider vertical chlorophyll profiles exhibiting a subsurface chlorophyll maximum typical of the South Atlantic Subtropical Convergence Province. Chlorophyll remotely‐sensed concentrations resulting from an academic uplifting of the three chlorophyll profiles are reconstructed with a radiative transfer model. Amplitude of the chlorophyll enrichments found with this hypothesis (0.06 mg chl.m−3) compares well with propagative ocean color anomalies detected in the SeaWiFS data. However, other processes such as the Rototiller effect [Siegel, 2001] or advection of chlorophyll gradients could also play a non negligible role.
Influence of a cyclonic eddy on microheterotroph biomass and carbon export in the lee of Hawaii
Authors: Bidigare Robert R. , Benitez‐Nelson Claudia , Leonard Carrie L. , Quay Paul D. , Parsons Michael L. , Foley David G. , Seki Michael P.
Published: May 2003

A multi‐platform sampling strategy was used to investigate carbon cycling in a cold‐core eddy that formed in the lee of Hawaii during September 2000. Microheterotroph biomass and 234Th‐derived carbon export rates within the eddy were 2 to 3 times higher than those observed for adjacent waters. If this eddy is representative of other cyclonic eddies that are frequently formed in the lee of Hawaii, then eddy activity may significantly enhance the areal efficiency of the biological pump and facilitate the transfer of organic carbon to organisms inhabiting the mesopelagic and abyssal‐benthic zones of this subtropical ecosystem.
In situ X‐ray observation of iron using Kawai‐type apparatus equipped with sintered diamond: Absence of β phase up to 44 GPa and 2100 K
Authors: Kubo Atsushi , Ito Eiji , Katsura Tomoo , Shinmei Toru , Yamada Hitoshi , Nishikawa Osamu , Song Maoshuang , Funakoshi Kenichi
Published: May 2003

Stability relations of iron have been studied by means of in situ X‐ray observations using an eight cubic anvil system (Kawai‐type apparatus) equipped with sintered diamond (SD), in order to explore the stability of β‐iron. By observing the forward and reverse transitions, it has been confirmed that ε‐iron directly transforms into γ phase up to ca. 44 GPa and 2100 K, excluding the stability of β phase. The constrained ε‐γ phase boundary is expressed by the equation T (K) = 25 × P (GPa) + 540.
The 2000 Mw 6.8 Uglegorsk earthquake and regional plate boundary deformation of Sakhalin from geodetic data
Authors: Kogan M. G. , Bürgmann R. , Vasilenko N. F. , Scholz C. H. , King R. W. , Ivashchenko A. I. , Frolov D. I. , Steblov G. M. , Kim Ch. U. , Egorov S. G.
Published: May 2003

Interseismic GPS velocities in Sakhalin indicate that the island moves to the west at 3–4 mm/yr with respect to the Eurasian plate, which is about half of the relative Eurasia ‐ North America plate convergence rate. GPS measurements across the central Sakhalin fault system provide evidence of compressive and strike‐slip strain accumulation at a rate ≤3 mm/yr. Coseismic vertical displacements produced by the August 4, 2000 Mw 6.8 Uglegorsk earthquake in Sakhalin were analyzed by constrained nonlinear inversion which provided evidence for a reverse faulting mechanism on an east‐dipping fault plane.
Massive atmospheric sulfur loading of the AD 1600 Huaynaputina eruption and implications for petrologic sulfur estimates
Authors: Costa Fidel , Scaillet Bruno , Gourgaud Alain
Published: May 2003

We combine petrological, analytical, and thermodynamical data to constrain the sulfur yield of the AD 1600 Huaynaputina eruption which has been associated with the largest Earth's temperature shift in the last 600 years. The calculated amount of S (26–55 Tg), partly overlaps, but ranges to almost twice the amount estimated from ice‐core data (16–32 Tg), the higher values of our estimate probably reflect that not all S released by the eruption reached the stratosphere. Our study also shows that it is possible to estimate the atmospheric sulfur loading from the volcanic products themselves, which opens the possibility to explore volcano‐climate links beyond the time period covered by ice‐core archives.