bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability of sea‐ice draft off Hokkaido in the Sea of Okhotsk revealed by a moored ice‐profiling sonar in winter of 1999
Authors: Fukamachi Y. , Mizuta G. , Ohshima K. I. , Melling H. , Fissel D. , Wakatsuchi M.
Published: May 2003

Using a moored ice‐profiling sonar along with an ADCP, a spatial section of draft across 855 km of sea ice was obtained for the first time in the southwestern part of the Okhotsk Sea near Hokkaido in winter of 1999. The draft evolved from 0.20 m in mid‐February to 1.45 m in late March with the overall value of 0.72 m. The draft characteristics were quite different between February and March before and after the period of strong winds. The increase of the mean draft from February to March was associated with the increase of deformed ice. The maximum draft observed was ∼17 m. Ice volume was dominated by the contribution from portions of deformed ice especially in March. These results suggest that deformed ice dominated in the region of observation and dynamical processes were mainly responsible for the evolution of draft.
Summertime quadruplet heating pattern in the subtropics and the associated atmospheric circulation
Authors: Wu Guoxiong , Liu Yimin
Published: May 2003

A quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer based on data diagnosis. The ocean region to the west is characterized by strong longwave radiative cooling (LO); the western and eastern portions of the continent are dominated by sensible heating (SE) and condensation heating (CO), respectively; and the ocean region to the east is characterized by double dominant heating (D), with LO prevailing CO. These compose a LOSECOD heating quadruplet. Its general feature is heating over the continent and cooling over the oceans. A distinct circulation pattern accompanies this heating pattern: in the upper troposphere, anticyclonic circulation over the continent is accompanied by cyclonic circulations over the oceans on its western and eastern sides; near the surface, cyclonic circulation over the continent is accompanied by anticyclonic circulations over the oceans on both sides. This circulation feature is interpreted as the atmospheric thermal adaptation to the quadruplet heating. It is further demonstrated that the global summer subtropical heating and circulation may be viewed as “mosaics” of such a quadruplet heating and circulation patterns, respectively.
Frequencies of future extreme events under conditions of changing hydrologic regime
Authors: Clarke Robin T.
Published: May 2003

Estimating the future frequency of extreme hydrologic events remains a common problem. Present procedures use hydrologic records to estimate future frequencies of occurrence, assuming that hydrologic regimes are stationary, despite contrary evidence in South America. This paper is concerned with estimating frequencies of hydrologic extremes under conditions for which trends in hydrologic regime have been detected, and where it is not unreasonable to suppose that such trends will continue into the near future. Expressions are given (i) for the probability that a given critical extreme Qcrit (a critical flood discharge, for example) will occur at least once in the next K years, when trend has been found in the sequence of annual extreme values; (ii) for the probability that a peak flood equal to or larger than Qcrit will occur at least once during a period [0,T) where the 'peaks‐over‐threshold' method is used.
Anisotropy of magnetic susceptibility of Hannuoba basalt, northern China: Constraints on the vent position of the lava sequences
Authors: Zhu Rixiang , Shi Caidong , Liu Qingsong
Published: May 2003

Anisotropy of magnetic susceptibility (AMS) was determined for Hannuoba basaltic samples from 17 flows (21.4 ± 0.7Ma) distributed in three sections (Jianshaba, Yuershan and Manjing) around Zhangbei, northern China. The results show normal ‘flow’ fabrics with horizontal foliation planes. The typical ratios of the principal AMS axes are 1.01 for the magnetic lineation (L) and 1.02 for the foliation (F), respectively. Magnetic hysteresis loop, isothermal remanence, thermomagnetic properties, and optical observations indicate that pseudo‐single domain (PSD) low‐titanium magnetite particles dominate the low‐field susceptibility of samples. Thus the AMS of the magma at this area is believed to be originated from the lineation of the low‐Titanium magnetite particles driven by the lava flow. Since the Kmax trends coincide well with the observed flow directions, the intersection of the mean Kmax trends from these three sites perfectly defines the previously known vent position of the lava sequences.
Impact of deep‐ocean carbon sequestration on atmospheric CO2 and on surface‐water chemistry
Authors: Harvey L. D. Danny
Published: May 2003

The effectiveness of injection into the ocean of CO2 produced from the use of fossil fuels is investigated using a coupled climate‐carbon cycle model. Four fossil fuel emission scenarios are considered, in which emissions peak at 28 Gt C/yr in 2100 (scenario 1), 9 Gt C/yr in 2050 (scenario 2), or decrease to zero by 2100 or 2075 (scenarios 3 and 4). Sequestration sufficient to reduce the net emissions for scenarios 1–3 to that in scenario 4 is considered. Sequestration in scenario 1 results in a CO2 concentration of 857 ppmv by 3100, compared to a peak of 1614 ppmv without sequestration, and slows the accumulation of atmospheric CO2. The supersaturation of the non‐polar mixed layer with respect to calcite decreases from 486% pre‐industrial to about 250%, while mixed layer pH decreases by 0.66. Only for scenario 3 is sequestration sufficient to limit the peak impact on atmospheric CO2 and mixed layer chemistry to the impacts obtained in scenario 4.
On the decay rate of sunspots
Authors: Chapman G. A. , Dobias J. J. , Preminger D. G. , Walton S. R.
Published: May 2003

We have analyzed the decay of 32 sunspots observed during the years 1988 through 2001 at the San Fernando Observatory (SFO). The data are from digital images obtained in the red (672 nm) with the Cartesian Full Disk Telescope No.1 (CFDT1). We find that the rate of decay is strongly correlated with the total sunspot area and the umbral to total area ratio. The multiple correlation coefficient is 0.93. Thus, the unexplained variance from this simple model is (1–0.87). We find that for the sunspots of this study, the decay rate is not a constant and that there is no significant correlation between the decay rate and the square root of the total spot area.
Respiration in the dark ocean
Authors: Arístegui Javier , Agustí Susana , Duarte Carlos M.
Published: May 2003

The dark ocean, the waters below 200 m depth, comprises about 95% of the volume of the ocean, but its contribution to the metabolism of the ocean is poorly quantified. Here we show that the respiration rate of microplankton declines exponentially at a rate of 0.53 km−1 in the dark ocean, and is enhanced at the interface between the mesopelagic and the abyssal layers (1,000–2,000 m). The respiratory CO2 production in the dark ocean, estimated at 20 to 33.3 Gt C yr−1, renders it a major component of the carbon flux in the biosphere.
The equation of state of CsCl‐structured FeSi to 40 GPa: Implications for silicon in the Earth's core
Authors: Dobson David P. , Crichton Wilson A. , Bouvier Pierre , Vočadlo Lidunka , Wood Ian G.
Published: May 2003

We have measured the compressibility of CsCl‐structured FeSi to 40 GPa by X‐ray powder diffraction using synchrotron radiation. A third order Birch‐Murnaghan equation of state fit to the experimental data yields V0 = 21.74 ± 0.02 Å, with a K0 of 184 ± 5 GPa and K′0 = 4.2 ± 0.3. The measured density and elastic properties of CsCl‐FeSi are consistent with silicon being a major element in the Earth's core.
On the surface currents of the Caribbean Sea
Authors: Centurioni Luca R. , Niiler Pearn P.
Published: May 2003

Velocity observations from near surface drifters made between 1996 and 2001 were used to construct surface circulation maps of the Caribbean Sea. In the Venezuela Basin the strongest westward currents (0.3 ms−1) are found south of 14°N and at 17°N. Two jets occur over the deep gaps of the Jamaica Ridge and move northwestward across the Cayman Basin. The two jets feed a current that impinges on Yucatan, slows down while turning north and accelerates again to become the Yucatan Current. A cyclonic gyre occurs in the southern Colombia Basin, with mean currents along the south coast in excess of 0.7 m s−1. To the east, the gyre is highly variable. Eddy motions dominate most of the Eastern Caribbean as well as the eastern Yucatan Basin, where the average surface circulation is not well defined.
Absolute transport from the sea level difference across the Korea Strait
Authors: Lyu Sang Jin , Kim Kuh
Published: May 2003

A strong linear relationship is found between the transport through the Korea Strait and the sea level difference (SLD) between Moji, Japan and Pusan, Korea after a correction is applied to SLD using cross‐strait hydrographic sections to remove baroclinic effects, which lead to an overestimate of the transport by up to 40% in summer. The conversion factor from SLD to the transport is estimated as Λ = (10.2 ± 1.1) × 106 m2 s−1 with a reference value of SLD, Δη0 = 197 ± 3 cm. Therefore, SLD provides a means to investigate long‐term variations of the transport through the Korea Strait and their relation to changes in the Pacific Ocean, such as El Niño and decadal climate variations.
Differential mixing by breaking internal waves
Authors: Hebert Dave , Ruddick Barry R.
Published: May 2003

Diapycnal mixing occurs at spatial scales which are unresolved in numerical models of the ocean. Thus, it is essential to understand small‐scale mixing processes properly in order to parameterize their fluxes in numerical models, especially those used in climate studies. In the ocean, diapycnal mixing is actually a process of mixing two variables, heat (or temperature) and salt (or salinity), which both contribute to the density of ocean water. Presently, numerical ocean models parameterize the unresolved diapycnal fluxes as an eddy diffusivity times a mean property gradient normal to the isopycnals. Most models also use the same eddy diffusivities for heat and salt. Mixing in the ocean interior is due mainly to breaking internal waves. In this paper, vertical fluxes and diffusivities of two tracers, with different molecular diffusivities, were obtained for a wide range of breaking internal wave activity in the laboratory.
Assessment of 15N15N16O as a tracer of stratospheric processes
Authors: Kaiser Jan , Röckmann Thomas , Brenninkmeijer Carl A. M.
Published: May 2003

Isotopic fractionation of mono‐substituted N2O species by the stratospheric sinks, photolysis and reaction with O(1D), has been investigated previously by atmospheric and laboratory measurements. Here, we report on photolysis of the most abundant poly‐substituted isotopologue, 15N15N16O. The associated fractionation constant equals the sum of individual fractionation constants at central and terminal nitrogen sites. Based on statistical considerations, a more general “additivity rule” is proposed that extends to the remaining poly‐substituted N2O species and is compared to predictions from two theories. Atmospheric mixing effects do not lead to measurable deviations from random isotope distributions since variations of isotope ratios are too small. Fractionation by the O(1D) sink likely also follows the “additivity rule”. Consequently, the stratospheric 15N15N16O abundance is expected to reflect its statistically dictated value. The value of 15N15N16O as a potential new tracer of stratospheric processes may thus be limited, but this remains to be verified by actual measurements.
Normal modes and long period seismograms in a 3D anelastic elliptical rotating Earth
Authors: Millot‐Langet Raphaële , Clévédé Eric , Lognonné Philippe
Published: May 2003

We present results of a direct method to compute realistic long period (>200 s in this example) synthetic seismograms using higher order perturbation theory (up to the 3rd order). Normal modes are computed for the Earth, taking into account rotation, ellipticity, 3D elastic lateral heterogeneities (SAW12D) for the whole mantle, and anelastic lateral variations in the upper mantle (QR19). Coupling between different modes and branches is included in the computation. We study the sensitivity of the waveform to 3D anelasticity and the biases between 3D elastic and 3D anelastic variations. The resulting seismograms can be computed to higher frequency and may then be used to perform whole mantle joint inversions for elastic and anelastic structure.
Seismic focusing by a single planar fracture
Authors: Oliger A. , Nolte D. D. , Pyrak‐Nolte Laura J.
Published: May 2003

A single plane fracture with an axially symmetric stress distribution behaves as a seismic lens that focuses seismic energy to a beam “waist” at a focal plane. Both phase and amplitude effects on a seismic wave propagating across the fracture contribute to the lensing behavior. Radial gradients in the fracture specific stiffness cause wave refraction through a radially varying group time delay, while the fracture transmission amplitude approximates a Fresnel zone plate. This work demonstrates that a two‐dimensional planar fracture, contrasted with three‐dimensional geologic structures such as basins and domes, can focus seismic waves. Focusing of seismic waves by fractures should be considered in the interpretation of seismic data from fractured strata with heterogeneous stress distributions.
Modeling catchment‐scale mixing in the near‐stream zone—Implications for chemical and isotopic hydrograph separation
Authors: Chanat Jeffrey G. , Hornberger George M.
Published: May 2003

The saturated region immediately surrounding the stream channel has been characterized as a zone of active mixing, but the dynamics of this process are not accounted for in conventional hydrograph separations. We employ a simple mixing model to explore the possible consequences. Chemically distinct “hillslope” and “groundwater” runoff components are routed through a “near‐stream” reservoir, representing the channel and surrounding alluvium, to produce streamflow. For physically plausible near‐stream zones, groundwater contributions estimated from hydrograph separation on streamflow ranged from 45 to 80 percent larger than the “true” inflow values on the rising limb, and 19 to 57 percent larger at peak flow. The overestimates resulted from a near‐stream reservoir‐induced lag in the hillslope chemical signature relative to increases in hillslope water flux, and were consistent for reservoir dynamics ranging from constant‐volume to linear. The results suggest that caution be exercised when interpreting hydrograph separations without knowledge of the hydrology of the near‐stream zone.
Open‐ocean convection in the Irminger Sea
Authors: Bacon Sheldon , Gould W. John , Jia Yanli
Published: May 2003

Open‐ocean deep convection is known to occur in a very few locations in the present climate. Convection is important for the ventilation of the oceans, and for the operation of the meridional overturning circulation. Using data from ships and profiling floats, we present evidence for the occurrence of convection in the Irminger Sea of the North Atlantic, south‐east of Greenland. Confirmation of this convective site in the North Atlantic will influence our understanding of the connection of the atmosphere to the ocean depths, and of the mechanisms of climate variability.
The North Atlantic Oscillation and snow avalanching in Iceland
Authors: Keylock C. J.
Published: May 2003

The number of snow avalanche cycles occurring in Iceland is correlated to a major source of variability in climate, the North Atlantic Oscillation. A new index for this oscillation is produced that reflects the cumulative effect of snow build‐up in a starting zone. An analysis of the time‐series for this index shows that recent avalanche tragedies in Iceland are linked to a rise in this index. Consequently, estimations of avalanche return periods and thus, avalanche hazard zones, may need re‐evaluation. Because the oscillation has an impact upon climate throughout the Northern Hemisphere, this may be necessary in a number of other countries.
The N:Si:P molar ratio in the Strait of Gibraltar
Authors: Dafner Evgeny V. , Boscolo Roberta , Bryden Harry L.
Published: May 2003

All existing descriptions of nutrient distributions in the Strait of Gibraltar suggest that the Atlantic water brings to the Mediterranean Sea nutrients in the Redfield ratio (N:Si:P = 16:15:1). Here, the N:Si:P molar ratios (±Standard Error), obtained in April 1998, are used to show that in the Atlantic water at the western entrance of the Strait this ratio is lower (13.8(±0.5):12.1(±1.0):1) than the classical Redfield ratio; it is close to the Redfield ratio in the middle of the Strait (15.6(±0.6):10.7(±0.9):1), and increases dramatically to 23.6(±3.4):29.1(±4.5):1 at the eastern entrance of the Strait. In the Mediterranean water, the N:Si:P ratio has a quite similar trend with 31.5(±6.0):26.5(±3.6):1 in the east, 20.4(±0.2):31.5(±11.1):1 in the middle and 18.1(±0.6):17.6(±0.7):1 in the west of the Strait. The physical and biological processes that account for the observed spatial variability of the N:Si:P ratio along the Strait are identified. We estimated that in the Atlantic water entering the Mediterranean Sea, about 84% of the variability in N:Si:P molar ratio is due to biological and 16% to physical processes.
Threshold of geomorphic detectability estimated from geologic observations of active low slip‐rate strike‐slip faults
Authors: Kaneda Heitaro
Published: May 2003

Sources of catastrophic earthquakes include not only major active faults, but also those with low slip rates. Geologic observations of two Japanese surface‐rupturing earthquakes on low slip‐rate strike‐slip faults (the 1927 Kita‐Tango and the 1943 Tottori earthquakes) suggests a concept of “threshold of geomorphic detectability” for strike‐slip faults in humid mountainous regions. This threshold must be exceeded in order that progressive coseismic surface offset can be preserved as detectable faulted topography that may be otherwise erased by surface processes. The determined threshold minimum slip rates for both examples are about 0.1 mm/yr, which can be a quantitative explanation for lack of recognition and mapping of many active faults with slip rates of less than 0.1 mm/yr in Japan islands. Although this threshold is probably negligible in arid regions, it can produce another type of unrecognized active fault in humid mountainous regions, in addition to blind thrusts beneath thick sediments.
Fresh air in the 21st century?
Authors: Prather Michael , Gauss Michael , Berntsen Terje , Isaksen Ivar , Sundet Jostein , Bey Isabelle , Brasseur Guy , Dentener Frank , Derwent Richard , Stevenson David , Grenfell Lee , Hauglustaine Didier , Horowitz Larry , Jacob Daniel , Mickley Loretta , Lawrence Mark , von Kuhlmann Rolf , Muller Jean‐Francois , Pitari Giovanni , Rogers Helen , Johnson Matthew , Pyle John , Law Kathy , van Weele Michiel , Wild Oliver
Published: May 2003

Ozone is an air quality problem today for much of the world's population. Regions can exceed the ozone air quality standards (AQS) through a combination of local emissions, meteorology favoring pollution episodes, and the clean‐air baseline levels of ozone upon which pollution builds. The IPCC 2001 assessment studied a range of global emission scenarios and found that all but one projects increases in global tropospheric ozone during the 21st century. By 2030, near‐surface increases over much of the northern hemisphere are estimated to be about 5 ppb (+2 to +7 ppb over the range of scenarios). By 2100 the two more extreme scenarios project baseline ozone increases of >20 ppb, while the other four scenarios give changes of −4 to +10 ppb. Even modest increases in the background abundance of tropospheric ozone might defeat current AQS strategies. The larger increases, however, would gravely threaten both urban and rural air quality over most of the northern hemisphere.
Waveform inversion for seismic source processes using ABIC with two sorts of prior constraints: Comparison between proper and improper formulations
Authors: Fukahata Yukitoshi , Yagi Yuji , Matsu'ura Mitsuhiro
Published: May 2003

For inversion analysis using Akaike's Bayesian Information Criterion (ABIC) we obtained a proper formulation to incorporate two sorts of partially‐dependent prior information into observed data by Bayes' rule. In previous improper formulations, complete independence of the two sorts of prior information has been assumed. Through comparison of the solutions obtained by the improper formulation with those by the proper formulation, we demonstrated the validity of the proper formulation. The results show that the previous improper formulation gives proper solutions, if and only if the data used for inversion are accurate and sufficient. If the data are inaccurate and/or insufficient, the improper formulation gives somewhat biased and oversimplified solutions. From a poor data set, if we employed the improper formulation, we could not find any solution because of the vanishing of the local minimum of ABIC.
Thermal inertia and reversing buoyancy in flow in porous media
Authors: Menand Thierry , Raw Alan , Woods Andrew W.
Published: May 2003

The displacement of fluids through porous rocks is fundamental for the recharge of geothermal and hydrocarbon reservoirs [Grant et al., 1982; Lake, 1989], for contaminant dispersal through the groundwater [Bear, 1972] and in controlling mineral reactions in permeable rocks [Phillips, 1991]. In many cases, the buoyancy force associated with density differences between the formation fluid and the displacing fluid controls the rate and pattern of flow through the permeable rock [Phillips, 1991; Barenblatt, 1996; Turcotte and Schubert, 2002]. Here, using new laboratory experiments, we establish that a striking range of different flow patterns may develop depending on whether this density contrast is associated with differences in temperature and/or composition between the two fluids. Owing to the effects of thermal inertia in a porous rock, thermal fronts lag behind compositional fronts [Woods and Fitzgerald, 1993; Turcotte and Schubert, 2002], so that two zones of different density develop in the region flooded with injected fluid. This can lead to increasing, decreasing or even reversing buoyancy in the injected liquid; in the latter case it may then form a double‐flood front, spreading along both the upper and lower boundary of the rock. Recognition of these different flow regimes is key for predicting sweep efficiency and dispersal patterns in natural and engineered flows, and offers new opportunities for the enhanced recovery of natural resources in porous rocks.
Disproportionate impact of particulate emissions on global cloud condensation nuclei concentrations
Authors: Adams P. J. , Seinfeld J. H.
Published: May 2003

Estimates of indirect aerosol radiative forcing have focused on increased sulfate aerosol mass concentrations caused by anthropogenic emissions of gas‐phase sulfur dioxide, implicitly neglecting the impact of direct particulate emissions. Emissions of primary particles and gas‐phase precursors have different effects on cloud condensation nuclei (CCN) concentrations as they impact CCN concentrations via different microphysical pathways. We present a theoretical analysis and evidence from a three‐dimensional global model of aerosol microphysics to show that particulate emissions are more efficient per unit mass than gas‐phase emissions at increasing CCN concentrations. Both analyses show that the few percent of anthropogenic sulfur emitted as particulate sulfate results in an increase in CCN concentrations comparable to that resulting from much larger emissions of gas‐phase sulfur dioxide. Therefore, models should explicitly distinguish between the microphysical impacts of particulate and gas‐phase emissions to accurately estimate the magnitude of the indirect effect of aerosols on climate.
The Southern Oscillation in the Early 1990s
Authors: van Loon Harry , Meehl Gerald A. , Milliff Ralph F.
Published: May 2003

Two aspects of the onset of a warm event in the Southern Oscillation are 1) the subtropical South Pacific High is weakened in early southern winter which weakens subtropical sea level pressure (SLP) gradients, and thus reduces the trade winds and upwelling along the equator, and 2) in the months that follow, and particularly during the mature phase of the warm event during southern summer, the negative SST anomalies in the equatorial cold‐water tongue are displaced by positive anomalies and the water along the tropical Peruvian coast usually warms. To highlight the role of Southern Hemisphere subtropical processes in warm events, we focus on the first half of the 1990s. That period has been viewed as a five year warm event, but actually two warm events developed during this period according to the criteria in 1) and 2): in 1991 and 1994. This study emphasizes the importance of interactions between the subtropical and equatorial Pacific in warm events.
Evidence for periods of wetter and cooler climate in the Sahel between 6 and 40 kyr BP derived from groundwater
Authors: Beyerle Urs , Rueedi Joerg , Leuenberger Markus , Aeschbach‐Hertig Werner , Peeters Frank , Kipfer Rolf , Dodo Abdelkader
Published: May 2003

Concentrations of noble gases, stable isotopes and 14C in samples from the Continental Terminal groundwaters of Niger provide evidence for more humid and cooler climate phases in West Africa in the Holocene and the late Pleistocene. During humid phases, even within the Holocene, the soil temperature was up to 5.5°C cooler than today, which is partly attributed to atmospheric cooling, but also to a change in the relationship between air and soil temperature due to increased vegetation. Intense rainfall events and increased groundwater recharge are consistently indicated by stable isotope data and excess air concentrations, i.e., the component of dissolved atmospheric gases in excess of solubility equilibrium. This finding encourages the use of excess air as an additional, humidity‐related climate indicator.
Wind observations pertaining to current disruption and ballooning instability during substorms
Authors: Chen Li‐Jen , Bhattacharjee A. , Sigsbee K. , Parks G. , Fillingim M. , Lin R.
Published: May 2003

The westward propagation of wave disturbances associated with current disruption is observed in the near‐Earth plasma sheet by the Wind satellite. By analyzing the time delay between earthward and tailward flux enhancements of energetic ions, the propagation velocity is estimated to be several hundred kilometers per second. A large anisotropy between the duskward and dawnward fluxes of energetic ions is observed to persist until the local onset of a current disruption. This anisotropy is consistent with an earthward density gradient which is significantly reduced after the magnetic fluctuations that accompany the current disruption cease. The reduction process is impulsive and bursty, suggesting that the underlying dynamics is nonlinear. The westward propagation of the unstable wave disturbances, the radial density gradient and its subsequent reduction support the drift ballooning instability as a possible mechanism for triggering substorms.
The aerodynamic roughness with a blowing sand boundary layer (BSBL): A redefinition of the Owen effect
Authors: Dong Zhibao , Liu Xiaoping , Wang Hongtao
Published: May 2003

Attempt is made to define the aerodynamic roughness length with a blowing sand boundary layer. Two methods, the log curve‐fit method and power curve‐fit method, have been tried to determine the aerodynamic roughness length based on the measured wind profiles in a wind tunnel. The results suggest that a good linear relation exists between the aerodynamic roughness lengths obtained by the two methods. But the power curve‐fit method yields greater aerodynamic roughness length for the same blowing sand boundary layer. The aerodynamic roughness tends to increase with sand transport rate. The relationship between the aerodynamic roughness length and shear velocity with a blowing sand cloud is much more complicated than that proposed by Owen and others due to the variation with height of the shear stress caused by the blown sand movement.
Penetration of the solar wind electric field into the magnetosphere/ionosphere system
Authors: Kelley Michael C. , Makela Jonathan J. , Chau Jorge L. , Nicolls Michael J.
Published: May 2003

On April 17, 2002 an intense, long duration electric field penetration event was captured by the Jicamarca incoherent scatter radar. Other radars in the U. S. chain detected the event as well, although not with as much clarity. The Interplanetary Electric Field (IEF) is available from the ACE satellite as well. The ratio of the dawn‐to‐dusk component of the IEF to the dawn‐to‐dusk electric field in the equatorial ionosphere for periods less than about two hours is 15:1. We suggest that this corresponds to the ratio of the size of the magnetosphere to the length of the connection line between the Interplanetary Magnetic Field (IMF) and the Earth's magnetic field. Simultaneous magnetic field measurements at Piura (off the magnetic equator) and at Jicamarca (under the magnetic equator) in Peru, reveal the same high frequency components and suggest that a chain of stations or an equatorial fleet of satellites in low earth orbit could be used to monitor the connection length continuously.
Ice stream D flow speed is strongly modulated by the tide beneath the Ross Ice Shelf
Authors: Anandakrishnan S. , Voigt D. E. , Alley R. B. , King M. A.
Published: May 2003

The flow velocity of ice stream D, West Antarctica has been measured to vary by a factor of three over the course of a day. These fluctuations are measured at the grounding line as well as upstream of the grounding line in the ice plain of ice stream D. The diurnal velocity fluctations appear to be driven by the tide beneath the Ross Ice Shelf. These results suggest that there is significant, and heretofore poorly understood, influence of the ocean tide and of the ice shelf on the dynamics of ice stream flow.
The role of Pc1‐2 waves in spectral broadening of SuperDARN echoes from high latitudes
Authors: Ponomarenko Pavlo V. , Waters Colin L.
Published: May 2003

Previous studies of Super Dual Auroral Radar Network (SuperDARN) echoes from high latitudes have shown large spectral widths (≥200 m/s), which cannot be interpreted in terms of ionospheric drifts. A recent model of André et al. [1999, 2000a, 2000b] invoked modulation of ionospheric plasma drift velocity by ultra low frequency (ULF) waves within the Pc1‐2 band (0.1–5 Hz). Their simulated signal was processed in the same way as real radar echoes, and the output spectral width was much larger than the input signal bandwidth. This was attributed to signal undersampling. After re‐examining their model we found that the spectral broadening was caused by the way the signal was simulated. This paper presents a revised model that gives spectral width estimates close to the input signal bandwidth. An alternative explanation of the experimental data involves spatio‐temporal non‐uniformity of the ionospheric irregularities due to particle precipitation.
A sub‐tropical cirrus clouds climatology from Reunion Island (21°S, 55°E) lidar data set
Authors: Cadet B. , Goldfarb L. , Faduilhe D. , Baldy S. , Giraud V. , Keckhut P. , Réchou A.
Published: May 2003

The aim of this work is to document cirrus characteristics using ground‐based measurements. A climatology of sub‐tropical cirrus clouds is presented from the analysis of the Rayleigh‐Mie lidar data collected at the “Observatoire de Physique de l'Atmosphere de la Reunion” (OPAR) over the period 1996–2001. The lidar laser operates at 532 nm. This climatology is based on the analysis of upward laser beam over 533 nights corresponding to 1643 hours of lidar probing. In this sub‐tropical zone, two main seasons prevail for cirrus clouds occurrence: an austral winter, from May to October, and an austral summer, from November to April. As expected, cirrus are present more frequently during the austral summer, 13% of measurements, than during the austral winter, 1%. Subvisible cirrus clouds, characterised by an optical thickness below 0.03, compose a significant fraction, 65%, of the total cirrus observations.
Polar low‐speed solar wind reappeared at the solar activity maximum of cycle 23
Authors: Ohmi T. , Kojima M. , Fujiki K. , Tokumaru M. , Hayashi K. , Hakamada K.
Published: May 2003

The heliospheric tomography of the interplanetary scintillation (IPS) showed that low‐speed (≤350 km s−1) solar wind reappeared at the polar regions during the solar activity maximum of cycle 23. Comparing the distribution of solar wind velocity with the computed coronal magnetic structures, we found that the polar‐low speed streams at the north polar regions appeared just before the polar open fields were about to disappear. The actual existence of the calculated polar open fields was confirmed in the coronal hole maps from the He I 10830 Å absorption line, 195 Å Fe XII emission line, and white‐light images. This situation is very similar to the polar low‐speed streams observed at the previous solar activity maximum of cycle 22.
Estimation of land surface window (8–12 μm) emissivity from multi‐spectral thermal infrared remote sensing — A case study in a part of Sahara Desert
Authors: Ogawa Kenta , Schmugge Thomas , Jacob Frederic , French Andrew
Published: May 2003

Land surface window emissivity is an important parameter for estimating the longwave radiative budget. This study focuses on estimating the window (8–12 μm) emissivity from the waveband emissivities of the five thermal infrared channels of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). ASTER data along with the Temperature‐Emissivity Separation (TES) algorithm allows us to estimate surface channel emissivities with 90 m spatial resolution globally. Multiple regression was used to relate window emissivity to the five ASTER emissivities. This regression was developed using spectral libraries. Its residual error was less than 0.005 (RMSE) for values ranging between 0.81 and 1.00. We applied this regression to ASTER emissivities extracted from data acquired in 2001 and 2002 over a 240 × 1200 km area in a desert of North Africa. A comparison against a classification based emissivity map showed significant differences ranging between −0.08 and +0.06.
Global gas flux from mud volcanoes: A significant source of fossil methane in the atmosphere and the ocean
Authors: Milkov Alexei V. , Sassen Roger , Apanasovich Tatiyana V. , Dadashev Farid G.
Published: May 2003

There are yet unidentified sources of fossil methane (CH4) in the atmosphere. Mud volcanoes (MVs) are a potentially significant but poorly quantified geologic source of fossil hydrocarbon gases and CO2 to the atmosphere and the ocean not included in the current models of sources and sinks. Our statistical analysis of 36 previous measurements and estimates of gas flux from individual MVs suggests that the global gas flux may be as high as ∼33 Tg yr−1 (∼15.9 Tg yr−1 during quiescent periods plus ∼17.1 Tg yr−1 during eruptions). Onshore and shallow offshore MVs are estimated to contribute ∼6 Tg yr−1 of greenhouse gases directly to the atmosphere. MVs may contribute ∼9% of fossil CH4 missing in the modern atmospheric CH4 budget, and ∼12% in the preindustrial budget. Large volumes (∼27 Tg yr−1) of gas may escape from deep‐water MVs, suggesting that global gas flux from the seafloor may be underestimated.
Polar cap observations of mesospheric and lower thermospheric 4‐hour waves in temperature
Authors: Won Y.‐I. , Wu Q. , Cho Y. M. , Shepherd G. G. , Killeen T. L. , Espy P. J. , Kim Y. , Solheim B.
Published: May 2003

Lower thermospheric and upper mesospheric rotational temperatures have been derived from ground‐based measurements of the O2(0–1) and OH(6–2) nightglow emissions over Resolute Bay, Canada (74.68°N, 94.90°W) and OH(4–2) nightglow emission over Kiruna, Sweden (67.90°N, 21.10°E). From measurements taken during two nights in November, 2001, we have observed a dominant and coherent 4‐hr oscillation in both the O2 and OH airglow emission rates and rotational temperatures. The phases for the two oscillation events remain almost constant at each location, indicating that these oscillations may not be caused by transient passage of instantaneous gravity waves. More importantly, there is little phase difference in universal time between the 4‐hr oscillations in temperature at Resolute and Kiruna. The small phase difference gives a strong indication that the oscillation maybe related to a zonally symmetric tide, since any tidal waves in temperature with a nonzero zonal wavenumber are very weak at high latitudes. Waves in both events have large vertical wavelengths (76 and 175 km). The 4‐hr wave shows almost no latitudinal variation from Resolute to Kiruna.
Typhoon Vamei: An equatorial tropical cyclone formation
Authors: Chang C.‐P. , Liu Ching‐Hwang , Kuo Hung‐Chi
Published: May 2003

Due to the diminishing Coriolis effect, the belt 300 km either side of the equator has been considered tropical cyclone‐free. Typhoon Vamei, which developed near Singapore on 27 December 2001, was the first recorded tropical cyclone formation within 1.5 degrees of the equator. The development was the result of two interacting systems, a weak Borneo vortex that drifted into the southern tip of the South China Sea and remained there for four days, and a strong and persistent cold surge that created the large background cyclonic vorticity at the equator. The probability of a similar equatorial development is estimated to be once every 100–400 years.
Timing and localization of reconnection signatures – Is there a substorm model problem?
Authors: Krauss‐Varban Dietmar , Karimabadi Homa
Published: May 2003

Observations place ionospheric substorm onset signatures on field lines that map to the near‐Earth plasma sheet, and field‐aligned currents (FACs) are observed before dipolarization, equatorward of open field lines. The near‐Earth neutral line (NENL) model, however, appears to suggest perturbations to originate from the x‐line on newly reconnected field lines, which map to much higher latitudes. Its order of dipolarization, FACs, and subsequent ionospheric signatures contradicts the observations. Using large‐scale kinetic simulations, we demonstrate that these “flaws” of the NENL model are misconceptions and that the timing and location of signatures in the model are indeed consistent with observations. In a thinned current sheet, energetic ions are virtually unmagnetized, get further energized when passing through the neutral sheet, and travel earthward quickly and close to the neutral sheet, thus providing a pathway for early substorm signatures at relatively low latitudes.
Causes of atmospheric temperature change 1960–2000: A combined attribution analysis
Authors: Jones Gareth S. , Tett Simon F. B. , Stott Peter A.
Published: May 2003

We investigate the causes of temperature change over the last four decades, both near the surface and in the free atmosphere, using a coupled atmosphere/ocean general circulation model, HadCM3, which requires no flux correction. We use an 'optimal detection' methodology to examine zonal mean temperatures near the surface and on nine diagnosed pressure levels throughout the atmosphere over the last four decades of the 20th Century. This produces a space‐time‐multivariable detection analysis which for the first time includes both solar and volcanic forcings in addition to anthropogenic forcings. Our results strengthen the case for an anthropogenic influence on climate. Unlike previous studies we attribute observed decadal‐mean temperature changes both to anthropogenic emissions, and changes in stratospheric volcanic aerosols. The temperature response to change in solar irradiance is also detected but with a lower confidence than the other forcings.
Seasonality and trends of snow‐cover, vegetation index, and temperature in northern Eurasia
Authors: Dye Dennis G. , Tucker Compton J.
Published: May 2003

We examine seasonal variability in snow‐cover, normalized difference vegetation index (NDVI), and temperature in a broad region of northern Eurasia, and the spatial and temporal correspondence among trends in these variables between 1982 and 1999. Our results support the contention that the previously reported springtime “greening” trend in northern Eurasian land areas arises from a combination of: (1) the direct effects of declining snow‐cover on surface spectral reflectance and NDVI, and (2) enhanced vegetation growth and green biomass stimulated by warmer air temperatures and potentially greater vegetation absorption of photosynthetically active radiation (PAR) during the period of annual peak solar irradiance.
La Nina and El Nino—induced variabilities of ozone in the tropical lower atmosphere during 1970–2001
Authors: Ziemke J. R. , Chandra S.
Published: May 2003

This study provides the first evidence from several decades of satellite measurements that both La Nina and El Nino events have a comparable and dramatic impact in altering the interannual variability and distribution of tropospheric ozone in the tropics. Measurements of tropospheric ozone were combined from several total ozone mapping spectrometer (TOMS) and backscatter ultraviolet (BUV) satellite instruments to establish long time series in the tropics extending from April 1970 through December 2001. The changes in tropospheric column ozone (TCO) for both La Nina and El Nino are sizeable when compared to local values which average from less than 15 Dobson Units (DU) up to 25 DU over the year. It is suggested that interannual changes in TCO from combined La Nina and El Nino are the dominant source of decadal variability in the tropics.
Statistical analysis of tropical explosive volcanism occurrences over the last 6 centuries
Authors: Ammann Caspar M. , Naveau Philippe
Published: May 2003

Explosive volcanic eruptions are very violent events, each with clearly individual characteristics. Instead of looking at specific eruptions, we focus here on the long term record of tropical explosive volcanism. To assess the distribution of volcanic occurrences over several centuries we employ sulfate measurements from polar ice cores. From these measurements, we compile a binary time series of sulfate deposition events that left a signature at both poles. Because of the binary nature of this problem, a series of logistic statistical models are compared to best represent the data. These models demonstrate the existence of a strong multi‐decadal variation in the occurrence of sulfur rich tropical eruptions. More precisely, a combination of a trend and a cycle explains best the evolution of eruption history. To corroborate this result with a record independent of the ice cores, we confirm these long‐term variations with the most recent Volcanic Explosivity Index (VEI).
Physical‐biological sources for dense algal blooms near the Changjiang River
Authors: Chen Changsheng , Zhu Jianrong , Beardsley Robert C. , Franks Peter J. S.
Published: May 2003

Harmful algal blooms (“red tides”) occur primarily in a confined region on the inner shelf off the Changjiang River in the East China Sea during May–August. The areal extent of these blooms has increased dramatically in the last decade, and is thought to be associated with the rapid increase in nutrient supply via the Changjiang River. An interdisciplinary survey conducted in August 2000 identified three areas of high chlorophyll‐a concentration in this region: the near‐surface Changjiang River plume with high dissolved oxygen and pH, the thermocline above Taiwan Warm Current (TWC) water, and near the bottom north of the Zhoushan Island complex, an area of strong sediment deposition from the Changjiang River with low dissolved oxygen and pH. These results imply that the formation of phytoplankton blooms is controlled by a complex interplay of physical, geological, biological, and chemical processes associated with the Changjiang River discharge, sediment deposition, and TWC intrusions. The predicted increase in nutrient loading in the Changjiang River due to further economic development of Shanghai and reduction in sediment discharge due to the Three Gorges dam suggest that this part of the East China Sea could become an ecosystem disaster, with possible downstream contamination of Korea and Japan, unless the nutrient loading from Shanghai and surrounding cities and aquaculture activities along the coast are reduced.
Revealing the nature of radar reflections in ice: DEP‐based FDTD forward modeling
Authors: Eisen Olaf , Wilhelms Frank , Nixdorf Uwe , Miller Heinrich
Published: May 2003

Successful simulation of ground penetrating radar (GPR) traces in polar ice is achieved by numerical finite‐difference time‐domain (FDTD) forward modeling. Properties of the modeled medium are taken from high resolution dielectric profiling (DEP) of the upper 100 m of an ice core from Dronning Maud Land, Antarctica. The GPR reference trace is calculated from stacking of a normal moveout corrected common‐midpoint survey, carried out near the borehole location. The excellent agreement of synthetic and GPR‐based results demonstrates the capability of FDTD models to reproduce radargrams from ice core properties for interpretation of radio echo sounding data, and emphasizes the exploitation of radar data for improved interpretations of glaciological climate proxys. In addition to presenting modeling results, we perform sensitivity experiments to investigate the nature and origin of radar reflection in ice, discuss reasons for the failure of modeling studies in the past, and indicate new approaches.
Hybrid simulations of the expanding solar wind: Temperatures and drift velocities
Authors: Hellinger Petr , Trávníček Pavel , Mangeney André , Grappin Roland
Published: May 2003

We study the evolution of the expanding solar wind using a one‐dimensional and a two‐dimensional expanding box model [Grappin et al., 1993] implemented here within a hybrid code [Liewer et al., 2001]. We first consider a plasma with protons and 5% of alpha particles, without drift between the protons and alphas, considering successively the low‐beta and high‐beta cases. Then we consider a strong drift between protons and alphas, again separately the low‐beta and high‐beta case. Without drift, the evolution of the low‐beta plasma is adiabatic. In the high‐beta plasma without drift, the fire hose instabilities (both parallel and oblique) disrupt the adiabatic evolution. Finally, with a drift, the adiabatic evolution is stopped by the oblique Alfvén instability and the parallel magnetosonic instability for low‐beta plasma and for high‐beta plasma, respectively. The two instabilities slow down thealphas and heat alphas and protons.