bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental evidence of randomness and nonuniqueness in unsaturated outflow experiments designed for hydraulic parameter estimation
Authors: Hollenbeck K. J. , Jensen K. H.
Published: February 2004

Single transient outflow experiments are commonly conducted for inverse estimation of unsaturated hydraulic parameters. We assess the validity of this procedure through several repeated experiments on the same sample, a medium sand contained in a pressure cell. Outflow was induced by. one or multiple step changes in bottom boundary suction, such that there were replicates for each of several step levels in suction. We observed that experiments with small initial step changes were poorly reproducible, even though our setup allowed reproduction of almost identical initial saturation for each run. Experiments with large step changes were well reproducible, but the outflow response was virtually the same for different step levels. Neither type of observation was predicted by a theoretical sensitivity analysis of the Richards equation, given the minimal inaccuracy in our experiments. Inverse estimation yielded incompatible apparent hydraulic parameters for different flow conditions. Our results imply experimental limitations of the inversion procedure.
Carbon storage during biodegradation of municipal solid waste components in laboratory‐scale landfills
Authors: Barlaz Morton A.
Published: February 2004

The objective of this research was to measure the amount of carbon associated with the major biodegradable components of municipal solid waste (MSW) that remains in long‐term storage after anaerobic decomposition in landfills. Tests were conducted in quadruplicate in 2‐L reactors operated to obtain maximum decomposition. Measured carbon storage factors (CSFs) for grass, leaves, branches, food waste, coated paper, old newsprint, old corrugated containers, office paper, and MSW were 0.32, 0.54, 0.38, 0.08, 0.34, 0.42, 0.26, 0.05, and 0.22 kg C sequestered dry kg−1, respectively. These values were then used to estimate an overall CSF for MSW that varied from 0.274 to 0.302 kg C sequestered wet kg−1 for waste mixtures that exclude and include recycling, respectively. On the basis of an overall CSF for MSW and data on global MSW generation, global carbon sequestration from MSW burial is estimated to be at least 119 million metric tons per year.
Dynamics of fossil fuel CO2 neutralization by marine CaCO3
Authors: Archer David , Kheshgi Haroon , Maier‐Reimer Ernst
Published: February 2004

A detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of CaCO3 diagenesis in deep sea sediments to simulate the millennium‐scale response of the oceans to future fossil fuel CO2 emissions to the atmosphere and deep sea. Simulations of deep sea injection of CO2 show that CaCO3 dissolution is sensitive to passage of high‐CO2 waters through the Atlantic Ocean, but CaCO3 dissolution has a negligible impact on atmospheric pCO2 or the atmospheric stabilization CO2 emission in the coming centuries. The ultimate fate of the fossil fuel CO2 will be to react with CaCO3 on the seafloor and on land. An initial CaCO3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years. The magnitude of the initial spike is sensitive to assumptions about the kinetics for CaCO3 dissolution, but subsequent behavior appears to be less model dependent. Neutralization by seafloor CaCO3 occurs on a timescale of 5–6 kyr, and is limited to at most 60–70% of the fossil fuel release, even if the fossil fuel release is smaller than the seafloor erodible inventory of CaCO3. Additional neutralization by terrestrial CaCO3 restores a balance between CaCO3 weathering and seafloor accumulation on a timescale of 8.5 kyr, while the deficit of seafloor CaCO3 (the lysocline) is replenished with an e‐folding timescale of approximately 18 kyr. The final equilibrium with CaCO3 leaves 7–8% of the fossil fuel CO2 remaining in the atmosphere, to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years.
Long‐term variability of the terrestrial and oceanic carbon sinks and the budgets of the carbon isotopes 13C and 14C
Authors: Joos Fortunat , Bruno Michele
Published: February 2004

The long‐term variability in the terrestrial and oceanic uptake of anthropogenic carbon is investigated. Ice core and direct observations of atmospheric CO2 and 13C are used for the last 200 years. An inverse method called double deconvolution is applied. It is found that the biosphere turned from a carbon source of about 0.5 Gt C yr−1 into a sink of 1 Gt C yr−1 during the first half of this century. This is in qualitative agreement with earlier reconstructions based on atmospheric CO2 data and implies a terrestrial sink to compensate land use emissions during the last five decades. Oceanic and biospheric carbon uptakes are estimated to be 0.9±1.0 and l.l±1.0 Gt C yr−1 as averaged over the 1970–1990 period. Hence ocean uptake is on the low side of current estimates, but our results may be biased as δ13C observations between 1956 and 1982 are missing. Additional uncertainties in calculated carbon sinks are due to uncertainties in model parameters and in fossil emission estimates. Prior to 1950, uncertainties are primarily related to uncertainties in the ice core δ13C data; a Monte Carlo analysis yields a l‐σ uncertainty in the terrestrial and oceanic uptake of ±0.36 Gt C yr−1 when ice core data are smoothed over a 50 year period. The budget of bomb‐produced radiocarbon is reinvestigated. We could not find model solutions that concomitantly match the bomb budget and the observed atmospheric δ13C and prebomb Δ14C decrease. The closure of the budget would require a relatively low oceanic and biospheric 14C uptake that conflicts with the relatively high isotopic uptake rates required to simulate the observed decrease in δ13C and Δ14C. We conclude that recent estimates of bomb test productions and/or the stratospheric 14C decrease are not compatible with published 13C and 14C observations.
On the influence of biomass burning on the seasonal CO2Signal as observed at monitoring stations
Authors: Wittenberg Uwe , Heimann Martin , Esser Gerd , McGuire A. David , Sauf Walter
Published: February 2004

We investigated the role of biomass burning in simulating the seasonal signal in both prognostic and diagnostic analyses. The prognostic analysis involved the High‐Resolution Biosphere Model, a prognostic terrestrial biosphere model, and the coupled vegetation fire module, which together produce a prognostic data set of biomass burning. The diagnostic analysis involved the Simple Diagnostic Biosphere Model (SDBM) and theHao and Liu[1994] diagnostic data set of biomass burning, which have been scaled to global 2 and 4 Pg C yr−1, respectively. The monthly carbon exchange fields between the atmosphere and the biosphere with a spatial resolution of 0.5° × 0.5°, the seasonal atmosphere‐ocean exchange fields, and the emissions from fossil fuels have been coupled to the three‐dimensional atmospheric transport model TM2. We have chosen eight monitoring stations of the National Oceanic and Atmospheric Administration network to compare the predicted seasonal atmospheric CO2signals with those deduced from atmosphere‐biosphere carbon exchange fluxes without any contribution from biomass burning. The prognostic analysis and the diagnostic analysis with global burning emissions of 4 Pg C yr−1agree with respect to the change in the amplitude of the seasonal CO2concentration introduced through biomass burning. We find that the seasonal CO2signal at stations in higher northern latitudes (north of 30°N) is marginally influenced by biomass burning. For stations in tropical regions an increase in the CO2amplitude of more than 1 ppmv (up to 50% with respect to the observed trough to peak amplitude) has been calculated. Biomass burning at stations farther south accounts for an increase in the CO2amplitude of up to 59% (0.6 ppmv). A change in the phase of the seasonal CO2signal at tropical and southern stations has been shown to be strongly influenced by the onset of biomass burning in southern tropical Africa and America. Comparing simulated and observed seasonal CO2signals, we find higher discrepancies at southern tropical stations if biomass burning emissions are included. This is caused by the additional increase in the amplitude in the prognostic analysis and a phase shift in a diagnostic analysis. In contrast, at the northern tropical stations biomass burning tends to improve the estimates of the seasonal CO2signal in the prognostic analysis because of strengthening of the amplitude. Since the SDBM predicts the seasonal CO2signal reasonably well for the northern hemisphere tropical stations, no general improvement of the fit occurs if biomass burning emissions are considered.
Optimised rooting depth and its impacts on the simulated climate of an atmospheric general circulation model
Authors: Kleidon Axel , Heimann Martin
Published: February 2004

Rooting depth determines how much water can be stored in the soil which is accessible to the vegetation for transpiration. Here, we derive a global distribution of rooting depth with an optimisation principle: A simple formulation of Net Primary Production (NPP) is incorporated into a General Circulation Model and then NPP is maximised in respect to rooting depth. The obtained rooting depths are considerably larger to those used in present‐day models but are consistent with observations. NPP increases substantially with the use of optimised rooting depths, mainly in tropical regions during the dry season accompanied with enhanced transpiration. The increased flux of latent heat leads to a considerable decrease in 2m air temperature, which leads to a better agreement with observations. We conclude that rooting depth is an important vegetation property, especially in the tropics, and tropical deforestation might have a much larger impact on climate than previously thought.
In situ measurements of the vertical structure of a noctilucent cloud
Authors: Gumbel Jörg , Witt Georg
Published: February 2004

During the NLC‐93 rocket campaign at Esrange, Sweden, the vertical structure of a noctilucent cloud layer has been investigated in situ. As in earlier rocket flights, combinations of scattered light detectors and electrostatic impact probes have been applied. While the photometric measurement provides the total downward radiance scattered from the cloud particles, the impact probe yields local information about the particle properties. The responses of both techniques scale differently with the particle size. This feature is utilized to derive information about the height dependence of the particle population. The analysis of three NLC passages indicates little vertical variation of the population throughout most of the layer. The lower part of the cloud is characterized by an increase in particle size and a decrease in particle density towards the cloud base. This is to be expected for an NLC brightness peak caused by large particles sedimenting out of the cloud. Implications for the dynamical structure of the cloud are discussed.
Airborne observations of aircraft aerosol emissions I: Total nonvolatile particle emission indices
Authors: Anderson B. E. , Cofer W. R. , Bagwell D. R. , Barrick J. W. , Hudgins C. H. , Brunke K. E.
Published: February 2004

We report airborne measurements of total and nonvolatile (at T < 290°C) fine and ultrafine aerosol emission indices (EI's) generated by a variety of jet aircraft. The data were obtained using an instrumented jet aircraft, flown repeatedly through aircraft wakes. These aircraft were observed to produce 0.5hyphen;10 × 1015 nonvolatile particles kg−1 of fuel burned. Their numbers varied as a function of aircraft type, age, and engine operating parameters, but less with atmospheric conditions. Large numbers of volatile aerosols were measured in all cases. Volatile EI's ranged from 0.1 to 40×1016 kg−1 fuel burned. The observed soot emissions are estimated to have only a minor impact on atmospheric aerosol loading, but a future fleet producing such high concentrations of implied sulfate aerosols could perturb cloud formation and heterogeneous chemical processes in the upper troposphere/lower stratosphere.
The relationship between electrostatic shocks and kinetic Alfvén waves
Authors: Lysak Robert L.
Published: February 2004

Auroral satellites and sounding rockets frequently observe large electric fields perpendicular to the magnetic field that have a narrow scale length perpendicular to the magnetic field if they are interpreted as spatial structures. These fields have been variously attributed to electrostatic shock structures or to kinetic Alfvén waves. These two models can be distinguished by considering the ratio of the magnetic field perturbation to the electric field. This ratio is calculated within the context of the electrostatic approximation, the fully kinetic Alfvén wave dispersion relation considered by Lysak and Lotko [1996], and the cold fluid model including ionospheric reflection presented by Lysak [1991, 1993]. Results for this model show that the ratio of the electric to magnetic field is not always equal to the Alfvén speed, especially for structures that are very narrow in the direction perpendicular to the magnetic field. These narrow structures have electric fields that are enhanced with respect to the Alfvénic value, and thus may appear as electrostatic.
Large earthquake nucleation associated with stress exchange between middle and upper crust
Authors: Huc Mireille , Hassani Riad , Chéry Jean
Published: February 2004

Earthquake nucleation and propagation can be explained using two basic concepts, crustal strength and fault rheology. Despite numerous experimental and modeling studies, the way in which a faulted crust generates a seismic cycle under loading is still controversial. We discuss earthquake generation using a 2‐D Finite Element Model which includes relevant features of geodynamical problems such as rheological layering, dynamic Coulomb faulting and relative plate velocity. The occurrence of a deep nucleation is explained by the strong viscosity drop at the base of the seismogenic layer, without any transition of frictional properties of the fault. Rather, viscosity contrast causes a stress transfer around the fault that reloads the fault plane during the postseismic phase. We argue that this mechanism may explain the seismic cycle for large faults in the continental crust.
Kinetic and spectroscopic requirements for the measurement of mesospheric ozone at 9.6 µm under non‐LTE conditions
Authors: Mlynczak Martin G. , Zhou Daniel K.
Published: February 2004

Radiative emission from transitions involving the vibration‐rotation bands of ozone in the 9.6 µm spectral region is readily detected by limb‐scanning instruments on orbiting satellites and such measurements are used to infer the ozone profile in the middle atmosphere. In the terrestrial mesosphere and lower thermosphere these transitions are predicted to depart from local thermodynamic equilibrium (LTE). The occurrence of non‐LTE complicates the interpretation of emission measurements in terms of the ozone abundance as the vibrational temperatures must be known a priori or calculated directly as part of the retrieval process. This in turn requires accurate knowledge of various kinetic and spectroscopic parameters used in a statistical equilibrium model to calculate the vibrational temperatures. Through detailed simulations of the forward and inverse retrieval problem we find that in order to achieve retrieved ozone concentrations accurate to 15% the collisional quenching rates must be known to better than 25% accuracy and that the distribution of energy within ozone upon recombination of O and O2 must be significantly improved. Collisional quenching rates are currently uncertain by more than a factor of 2.
Dehydration and denitrification in the Arctic Polar Vortex during the 1995–1996 winter
Authors: Hintsa E. J. , Newman P. A. , Jonsson H. H. , Webster C. R. , May R. D. , Herman R. L. , Lait L. R. , Schoeberl M. R. , Elkins J. W. , Wamsley P. R. , Dutton G. S. , Bui T. P. , Kohn D. W. , Anderson J. G.
Published: February 2004

Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (θ∼450–465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NOy) had also been removed, with layers of enhanced NOy at lower altitudes. Back trajectory calculations show that air parcels sampled inside the vortex had experienced temperatures as low as 188 K within the previous 12 days, consistent with a small amount of dehydration. The depth of the dehydrated layer (∼1 km) and the fact that trajectories passed through the region of ice saturation in one day imply selective growth of a small fraction of particles to sizes large enough (>10 µm) to be irreversibly removed on this timescale. Over 25% of the Arctic vortex in a 20–30 K range of θ is estimated to have been dehydrated in this event.
A model for calculating acoustic gravity wave energy and momentum flux in the mesosphere from OH airglow
Authors: Swenson Gary R. , Liu Alan Z.
Published: February 2004

Acoustic gravity and tidal waves propagating in the mesosphere/lower thermosphere (80–110 km) perturb the airglow layer intensities. The OH airglow has recently been modeled to determine the relationship between the relative perturbed atmospheric density and temperature (ρ′/ρ, T′/T) to the OH intensity (I′OH/IOH) at the OH emission altitudes [Swenson and Gardner, 1997]. A model is presented here which relates wave perturbed OH airglow to the wave energy and momentum flux as they propagate through the emission layer. The model is dependent on the wave horizontal and vertical wavelengths (or phase speed as related through the dispersion relationship), and the relative perturbed airglow intensity, I′OH/IOH. The model can be used by optical experimenters to relate their measurements to wave energy and momentum flux in the stated altitude region.
Coupling an AGCM with an ISM to investigate the ice sheets mass balance at the Last Glacial Maximum
Authors: Fabre Adeline , Ramstein Gilles , Ritz Catherine , Pinot Sophie , Fournier Nicolas
Published: February 2004

The aim of this paper is to investigate the consistency between the ice sheets reconstruction at the LGM and the climate simulated by AGCM. In particular, to investigate whether the laurentian and the fennoscandian ice sheets have an equilibrated mass balance, we use two complementary approaches. First we analyze the changes of snow and water budgets over the ice sheets, only using the model results of LGM runs. Second, we use a thermomechanical ice sheet model [Ritz et al., 1997] forced with the AGCM simulated climate, to perform long term runs at finer spatial resolution. Analyzing the results obtained with both approaches, we show that the ice sheet mass balance computed directly from AGCM results may be biaised. Moreover we show, using two versions of the LMD AGCM, that the ice sheet mass balance computed by the ISM is drastically sensitive to the summer surface temperatures simulated by the AGCM.
On the origin of radio emissions associated with the January 6–11, 1997, CME
Authors: Reiner M. J. , Kaiser M. L. , Fainberg J. , Bougeret J.‐L. , Stone R. G.
Published: February 2004

Unusual type II radio emissions were generated by an Earth‐directed CME that originated at the sun on Jan. 6, 1997. The intensities of the observed radio emissions were significantly higher than for typical type II events, while the source sizes and the overall frequency drift rate were significantly smaller. By introducing a new way of presenting the radio data that inherently reveals the dynamics of the type II radio source, we used these type II radio emissions, observed by the WAVES experiment on Wind, to track this CME through the interplanetary medium (IPM). From an analysis of the observed frequencies, the frequency drift rates and the results of the Wind radio direction finding, we were able to identify specific interplanetary structures such as a CIR that were the probable sources of at least some of the type II radio emissions associated with this event. This is the first time that type II emissions have been traced to specific interplanetary structures.
Geothermal evidence for deforestation induced warming: Implications for the Climatic impact of land development
Authors: Lewis Trevor J. , Wang Kelin
Published: February 2004

Analyses of temperatures from boreholes in previously forested areas in western Canada disclose sudden increases of one to two degrees in ground surface temperature at the times of deforestation at each site. This is the first clear evidence for deforestation induced warming. These findings suggest that any land development changing climatic parameters such as the amounts of water evaporated from the earth's surface contributes to regional climatic change. A warming of the ground surface over a large area of central Canada, synchronous with the deforestation of southern Ontario and neighbouring regions in the nineteenth century, may be an example of climate change linked to the widespread creation of agricultural lands. Such a warming also affects the surrounding regions
Influence of vertical transport on free tropospheric aerosols over the central USA in springtime
Authors: Talbot R. W. , Dibb J. E. , Loomis M. B.
Published: February 2004

Measurements of the atmospheric aerosol chemical composition during the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) indicate substantial vertical transport of boundary layer aerosol to the free troposphere over the south‐central United States during springtime. Mixing ratios of water‐soluble aerosol Ca2+ at 6–12 km altitude exhibited a median mixing ratio of 20 pptv, with 15% of the measurements ≥ 100 pptv and a maximum of 1235 pptv. In air parcels with enhanced Ca2+, the ratios K+/Ca2+, Mg2+/Ca2+, and Na+/Ca2+ in the bulk aerosol were distinctly characteristic of those in limestone and/or cement. Significantly enhanced mixing ratios of aerosol SO42−, NO3−, and NH4+ were also concomitant with the elevated Ca2+, suggesting transport of both crustal and anthropogenic aerosols to the upper troposphere. The mass concentration of water‐soluble aerosol material was in the range 0.1–6 µg m−3 STP, and estimated crustal dust levels were 7–160 µg m−3 STP.
Modelling signatures of pulsed magnetopause reconnection in cusp ion dispersion signatures seen at middle altitudes
Authors: Lockwood M. , Davis C. J. , Onsager T. G. , Scudder J. D.
Published: February 2004

It is shown that the open magnetosphere model can reproduce both the down‐going and the up‐going magnetosheath ions seen in the cusp and mantle regions by the Polar satellite at middle altitudes. The pass studied shows a series of discontinuities in the ion dispersion, most of which are shown to arise from pulses of magnetopause reconnection rate. A total of 9 pulses are detected in an interval estimated to be about 30 min long, giving a mean repetition period of about 3 min: they vary in length between 0.5 min and 3.5 min and are separated by periods of much slower reconnection of duration 1–3 min. One step is not as predicted for reconnection rate pulses but is explained in terms of compressive motions caused by a pulse of solar wind dynamic pressure. The reconnection site is found to be 16 ± 3 RE from the ionosphere along the separatrix field line, placing it at low latitudes on the dayside magnetopause.
2D modeling of melt percolation in the mantle: The role of a melt dependent mush viscosity
Authors: Khodakovskii G. , Rabinowicz M. , Genthon P. , Ceuleneer G.
Published: February 2004

2D‐melt percolation models in the partially molten mantle are presented. Previous work has shown that melt solitary waves develop in response to the non‐linear dependence of mush permeability to melt concentration. The present study focuses on the wave evolution when the mush viscosity abruptly drops, around a critical concentration fc. 2D‐waves develop with a diameter, that shortens as the melt concentration increment for viscosity drop narrows. They are initiated inside 1D‐maturing horizontal waves at melt concentration of about 4×fc. Both 1D‐ and 2D‐waves collect all the melt whose concentration exceeds fc. These features may help to explain the distribution and organization of some melt impregnations observed in mantle outcrops.
An examination of cirrus cloud characteristics using data from millimeter wave radar and lidar: The 24 April SUCCESS Case Study
Authors: Mace Gerald G. , Sassen Kenneth , Kinne Stefan , Ackerman Thomas P.
Published: February 2004

We examine the characteristics of a cirrus system that moved over north central Oklahoma on 24 April 1996 during the Subsonic Aircraft: Contrail and Cloud Effects Speical Study. This system was probed by aircraft and several surface‐based active and passive remote sensors located at the Department of Energy's Atmospheric Radiation Measurement faclity. Several layers of cirrus were identified and tended to be organized in bands that were maintained by turbulent motions associated with unstable lapse rates. The microphysical properties of two events sampled by a cloud radar were quite different with the earlier event composed, on average, of larger particles and lower concentrations than the later event.
Nature of surface electrical conductivity in natural sands, sandstones, and clays
Authors: Revil A. , Glover P. W. J.
Published: February 2004

The electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid/grain interface. The nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined. Surface conduction is characterized by the specific surface conductance which is the sum of three contributions: (i) Conduction within the electrical diffuse layer, which makes a negligible contribution to the total specific surface conductance, (ii) Conduction in the Stern layer, which is shown to vary significantly with the salinity of the pore fluid at low salinities (10−6 to 10−3 mol 1−1), but becomes independent of salinity at higher salinities, (iii) A mechanism operating directly on the mineral surface, independent of salinity, and perhaps associated with proton transfer. At salinities higher than 10−3 mol 1−1 and at 25°C, the specific surface conductance of quartz and clays is equal to 8.9×10−9 S and 2.5×10−9 S respectively. Equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands, sandstones, and shales are also developed.
Cloud and radiative fields derived from GOES‐8 during SUCCESS and the ARM‐UAV spring 1996 flight series
Authors: Minnis Patrick , Smith William L.
Published: February 2004

Cloud and radiative properties were derived for the southern Great Plains for April 9–May 9, 1996 from GOES‐8 to provide a large‐scale context for SUCCESS and a dataset for mesoscale modeling of cirrus processes. The analyses indicate that cloudiness over the domain was below normal during April 1996. Thin cirrus with optical depths less than 6 was the predominant cloud type over much of the domain, however, providing a considerable number of measurement opportunities for the suite of SUCCESS instruments. Diurnal variation of cloudiness was substantial over the ARM southern Great Plains central facility. Total albedos were below normal because of the diminished thick cloudiness, while surface temperature and total longwave fluxes were relatively high. The data are on a 0.5° grid and are available electronically.
Quasi‐periodic echoes observed with the Chung‐Li VHF Radar during the SEEK Campaign
Authors: Pan C. J. , Tsunoda R. T.
Published: February 2004

The 52‐MHz Chung‐Li VHF radar, located in Taiwan, was operated during the SEEK (Sporadic‐E Experiment over Kyushu) campaign to investigate the so‐called quasi‐periodic (QP) echoes that occur from nighttime sporadic E (Es) layers. Highlights of this study are presented in this paper, using measurements made on August 17, 1996, to illustrate the echo characteristics. QP echoes displaying 5 to 10 minute periods were observed throughout this night. A new finding is the occurrence of QP echoes whose striations were almost vertically oriented when plotted using a height‐time‐intensity (HTI) format. This observation provides the first unambiguous evidence for the existence of steep spatial tilts in Es layers that are responsible for QP echoes. Other characteristics from three periods during this night are described including striations with positively sloped striations. These characteristics are discussed in light of existing models for QP echoes.
Characteristics of magnetic fluctuations within coronal mass ejections: The January 1997 event
Authors: Leamon Robert J. , Smith Charles W. , Ness Norman F.
Published: February 2004

We determine the geometry of the fluctuations of the magnetic field at frequencies just above the proton gyrofrequency for the January 10, 1997 CME and the magnetic cloud within. The transverse magnetic fluctuations represent a greater fraction of the magnetic energy than is the case in the typical undisturbed solar wind. The break in the power spectrum that is associated with the the onset of magnetic dissipation falls within the frequency range of interest. The fluctuation geometry is markedly different above and below the spectral break frequency. The inertial range geometry remains unchanged in the cloud with only ∼30% of the energy associated with field‐aligned wave vectors. The dissipation range wave vectors are highly oblique to the mean magnetic field B with up to 96% of the energy associated with oblique wave vectors.
Direct observation of the rapid turnover of the Japan Sea bottom water by means of AMS radiocarbon measurement
Authors: Kumamoto Yu‐ichiro , Yoneda Minoru , Shibata Yasuyuki , Kume Hiroshi , Tanaka Atsushi , Uehiro Takashi , Morita Masatoshi , Shitashima Kiminori
Published: February 2004

Increase of 14C in the bottom water of the Japan Sea for the last 16 years (1979–1995) was observed by means of AMS radiocarbon measurement. This increment is due to penetration of surface bomb radiocarbon, which obviously suggests a rapid turnover of the bottom water of the Japan Sea. The turnover time is estimated to be ca. 100 years which coincides with results obtained by other chemical tracers. By an application of the estimated turnover time to a box model of Δ14C change, pre‐bomb surface Δ14C in the northern Japan Sea where the bottom water is formed is calculated to be ca. −90‰.
In‐situ mass spectrometric observation of impact vaporization of water‐ice at low temperatures
Authors: Sugi N. , Arakawa M. , Kouchi A. , Maeno N.
Published: February 2004

Impact experiments on water ice targets were carried out to investigate the partitioning of energy and the mass of water vaporized. A copper projectile accelerated by an electromagnetic gun impacted a low‐temperature ice target under a high vacuum condition. The mass of vaporized water gas was measured as a function of impact velocity (54–329 m/s) and ice temperature (130–185 K). Some 0.01–0.03 % of the impact energy is partitioned into ice vaporization at velocities ≤ 100 m/s. For impacts in the 100–180 m/s range, the energy partitioned into water vaporization drastically increases to 18–26 % of the impact energy. The estimated shock pressure is 277 MPa for a copper‐ice impact at 100 m/s. This is close to the pressure at the Hugoniot elastic limit for ice. It is considered that the drastic change in energy partition at 100 m/s is due to the large increases in surface area and localized heating via shear banding occurring at the Hugoniot elastic limit.
Banded electron structure formation in the inner magnetosphere
Authors: Liemohn M. W. , Khazanov G. V. , Kozyra J. U.
Published: February 2004

Banded electron structures in energy‐time spectrograms have been observed in the inner magnetosphere concurrent with a sudden relaxation of geomagnetic activity. In this study, the formation of these banded structures is considered with a global, bounce‐averaged model of electron transport, and it is concluded that this structure is a natural occurrence when plasma sheet electrons are captured on closed drift paths near the Earth followed by an extended period of quiet time for more than a day. These bands do not appear unless there is capture of plasma sheet electrons; convection along open drift paths making one pass around the Earth do not have time to develop this feature. The separation of high‐energy bands from the injected population due to the preferential advection of the gradient‐curvature drift creates spikes in the energy distribution above a keV, which overlap to form a series of bands in energy. The lowest band is the bulk of the injected population in the sub‐keV energy range. Using the Kp history for an observed banded structure event, a cloud of plasma sheet electrons is captured and the formation of their distribution function is examined.
Source and aftershock properties of the 1996 Flores Sea Deep Earthquake
Authors: Wiens Douglas A.
Published: February 2004

The June 17, 1996 (Mw 7.8) Flores Sea event is one of the largest deep earthquakes, and also produced an energetic aftershock sequence, allowing study of the spatial relationships between moment release, aftershock occurrence, and slab geometry. The locations of the mainshock, rupture sub‐events, aftershocks, and background slab seismicity are determined using a relative location algorithm. The event occurred at the edge of a 150 km wide aseismic region that represents a tear in the lowermost part of the Indonesian slab. The aftershocks define a 90 km long region parallel to slab strike. Two other aftershocks locate 10–25 km outside the previously active slab. The mainshock propagated about 75 km eastward along an E‐W striking, southward dipping plane, with a rupture velocity of 3.5 km/s. There was a substantial change in focal mechanism during the rupture, with the fault plane strike changing by about 25°. Overall, the Flores Sea deep earthquake shows numerous large aftershocks, and a moderate rupture velocity (3.5 km/s) and stress drop (∼ 7‐20 MPa.) These characteristics are similar to the 1994 Tonga deep earthquake, but different from the 1994 Bolivia event, suggesting they may be typical of large deep earthquakes in colder slabs. Systematic differences in rupture parameters for deep earthquakes in warm and cold slabs suggest that the rupture mechanism is highly sensitive to temperature.
Utilization of sky‐wave backscatter sounders for real‐time monitoring of ionospheric structure over extended geographic regions
Authors: Fridman Sergey V. , Berkey Frank T.
Published: February 2004

Backscatter ionograms (BI) and quasi vertical incidence (QVI) ionograms are routinely collected at over‐the‐horizon radar (OTHR) installations operated by the U.S. Navy. The BI provides information about the downrange ionosphere up to several thousand km from the sounder. In this paper, a method for the quantitative extraction of this information by means of a leading edge inversion technique is described and applied to data acquired by the BI sounder operating at the Chesapeake, VA OTHR facility. Because this sounder is used to sample 8 azimuthal sectors, maps of plasma frequency at a constant altitude can be derived over a geographic region that covers a 64° angular sector out to distances of ∼2000 km. The unique capability of the OTHR BI sounders to provide realtime monitoring of the ionosphere over a large geographical area is demonstrated.
Simulating Late Pliocene northern hemisphere climate with the LLN 2‐D Model
Authors: Li X. S. , Berger A. , Loutre M. F. , Maslin M. A. , Haug G. H. , Tiedemann R.
Published: February 2004

Deep‐sea sediment records suggest Northern Hemisphere glaciation intensified at approximately 2.75 Ma. In this paper we simulate the fluctuations of the late Pliocene Northern Hemisphere ice‐sheets volume using the LLN 2‐D model, forced by the astronomically derived insolation and by scenarios of CO2 concentrations. The model simulates the waxing and waning of the Northern Hemisphere ice volume in an acceptable agreement with geological reconstructions, and in particular supports the geological evidence that the development of significant Northern Hemisphere ice sheets started between 2.75 and 2.55 Ma, a time interval accompanied by quite high and stable eccentricity values, and increased obliquity amplitude. When the CO2 concentration is lower than a threshold value, the Milankovitch forcing explains the suddenness and specific timing of this entrance into the Ice Age during the late Pliocene.
Observed and predicted potential distributions during the October 1995 magnetic cloud passage
Authors: Burke W. J. , Fehringer T. L. , Weimer D. R. , Huang C. Y. , Gussenhoven M. S. , Rich F. J. , Gentile L. C.
Published: February 2004

Ion drift measurements from DMSP F13 provide the first opportunity to study the evolution of high latitude potentials in both hemispheres as a magnetic cloud passed Earth. Early in the event with IMF BZ strongly southward, the polar cap expanded and the potential measured across it reached 174 kV, then decreased as the IMF rotated toward BY < 0. During the initial northward IMF phase convection in the polar cap was dominated by large lobe cells, clockwise in the southern and counterclockwise in the northern hemisphere. With purely northward IMF, convection patterns had four cells and were irregular on the day and night sides of the magnetic dawn‐dusk meridian. Potential distributions measured with a southward or westward IMF agree with predictions of the Weimer [1996] model, suggesting that some global MHD simulations overestimate dayside merging rates.
E region observations over Chung‐Li during the SEEK Campaign
Authors: Pan C. J. , Liu C. H. , Roettger J. , Su S. Y. , Liu J. Y.
Published: February 2004

During the Sporadic E Experiment over Kyushu (SEEK) campaign E‐region field aligned irregularities (FAI) were observed with the Chung‐Li VHF Radar (operated on 52 MHz) in Taiwan between August 15–22, 1996. The characteristics of the quasi‐periodical echoes from the E‐region about 80 km north of the Chung‐Li radar are studied. During the same period ionogram records were taken with the Digisonde located at the Chung‐Li radar site. Strong sporadic‐E layers were detected with the Digisonde when the FAI, observed with the VHF radar, were also very intense. The variations of sporadic E‐layer critical frequency and of the field‐aligned irregularities were studied. The latter were estimated to be located at altitudes 95–115 km occurring in layers of 5–15 km thickness, moving downwards at a rate of about 2.5 km/h. There seemed to be a change over of the FAI echoes from lower to upper E‐region every night approximately at 23 hour LT. The distinction between post‐sunrise and post‐sunset FAI echoes observed earlier by MU radar was not clearly seen in Chung‐Li. A preliminary examination of the morphology of the fine structures within the layers indicates quasi‐periodic features with 5–10 minutes period. Many of these periodic fine structures were observed at the Chung‐Li VHF radar to have opposite slopes than those detected earlier with the MU radar in Japan, which is located 1500 km north of the Chung‐Li VHF radar.
The solar origin of the January 1997 coronal mass ejection, magnetic cloud and geomagnetic storm
Authors: Webb D. F. , Cliver E. W. , Gopalswamy N. , Hudson H. S. , St. Cyr O. C.
Published: February 2004

The magnetic cloud and geomagnetic storm on January 10–11, 1997 were associated with a halo‐type Coronal Mass Ejection (CME) observed by the SOHO/LASCO coronagraphs near the sun on January 6. We summarize the solar activity related to this CME and the subsequent storm at Earth. This solar activity was remarkably weak and unimpressive. If the wide CME had not been observed, the storm would not have been forecast. Thus this case represents an extreme example of so‐called “problem” magnetic storms that lack obvious surface signatures of eruptive solar activity. It supports the view that CMEs involve the destabilization of large‐scale coronal structures which may or may not have associated surface activity, and that CMEs, not the surface activity, are the key causal link between solar eruptions and space weather at Earth.
The interplanetary events of January–May, 1997 as inferred from energetic particle data, and their relationship with solar events
Authors: Cane H. V. , Richardson I. G. , St Cyr O. C.
Published: February 2004

We use observations from the Goddard particle detectors on IMP 8 to investigate near‐Earth interplanetary disturbances and the associated solar events in January–May 1997. We infer the presence of high‐speed streams and ejecta (material in the solar wind associated with coronal mass ejections (CMEs) at the Sun) using depressions in the counting rate of >60 MeV/amu particles measured by the anti‐coincidence guard. In addition to a sequence of high‐speed streams, the guard detected four ejecta. A fifth ejecta (January 10–11), evident in solar wind observations, did not produce a particle decrease. During the study period there were five particle enhancements, indicating the occurrence of energetic CMEs at the Sun. All the particle enhancements were associated with halo CMEs observed by the SOHO LASCO coronagraphs. Five of the total of nine halo CMEs in this period impacted the Earth. None of the other ∼120 CMEs detected by LASCO did so. Only the four CMEs associated with traditional flare signatures were also associated with >10 MeV particle increases.
The influence of time‐dependent ocean‐continent geometry on predictions of post‐glacial sea level change in Australia and New Zealand
Authors: Milne Glenn A. , Mitrovica Jerry X.
Published: February 2004

We describe predictions of post‐glacial relative sea level (RSL) variations in Australia and New Zealand that incorporate a realistic evolution of the ocean‐continent margin and compare these to predictions which assume that the ocean‐continent interface is fixed to the present‐day coastline geometry. We find that the predicted amplitude of Holocene sea level highstands in this region can be increased by more than 2 m when a time‐dependent ocean‐continent margin is incorporated into the modeling procedure. Future attempts to refine both mantle viscosity and Late Holocene melting events based on the prediction of a set of these highstands should adopt a theory that includes this extension.
Ground rotational motions recorded in near‐source region of earthquakes
Authors: Takeo Minoru
Published: February 2004

Large rotational motions excited by earthquakes are recorded during an earthquake swarm of March, 1997, offshore Ito in Izu peninsula, Japan. The largest rotational velocity recorded at KAW is 2.6×10−2 rad/s around the north‐south axis during an earthquake of magnitude 5.2 at 14:09 (GMT) on March 3. The rotational motions around the vertical axis excited by the largest event is 3.3×10−3 rad/s. Considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion, we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis.
The CG lightning activity of a storm causing a flash‐flood
Authors: Soula S. , Sauvageot H. , Molinié G. , Mesnard F. , Chauzy S.
Published: February 2004

On August 7, 1996, a flood of the Rio Gallego, in Aragon (Spanish central Pyrénées) wiped out the Biescas' campground, killing more than 80 persons. From the observations of two meteorological radars, this thunderstorm exhibited some of the radar characteristics of a supercell. It spread almost exactly over the Rio Gallego catchment area, up‐stream of Biescas, and it remained above this area for about two hours, without any advection. The rainfall reached 100 mm h−1 and the total cumulative amount locally reached 200 mm. The cloud‐to‐ground (CG) flash density averaged over 5 × 5 km² areas, was exceptionally high, around 2 km−2, and the peak flash rate averaged over 5‐minute periods reached 11.6 min−1 within the cell area. The evolution of the CG flash rate and the radar reflectivity were closely correlated. The flash rate reached high values before the arrival of the precipitation at the ground. We observe also a very good agreement between the location of the intense rain at the ground and the high CG flash density. The rainfall water volume per flash was 3×104 m³, a value in agreement with previous work. We propose that quantitative measurements of the lightning activity may provide valuable information for flash‐flood nowcasting and short‐term forecasting in mountainous areas.
Waveform analysis of seismoacoustic signals radiated during the fall 1996 eruption of Pavlof Volcano, Alaska
Authors: Garcés Milton A. , Hansen Roger A.
Published: February 2004

Theoretical modeling of acoustic and seismic signals associated with the 1996 strombolian eruption of Pavlof volcano suggests that volcanic tremor at Pavlof originates in the deeper part of the magma conduit, and is generated by random fluid oscillations in the magma flow. Explosions are believed to occur in the shallower part of the magma conduit, and to be caused by the rapid and violent expansion of metastable magma‐gas mixtures. The effect of increasing the exsolved quantities of H2O and CO2 gas with reduced pressure in the melt is to decrease the sound speed and density of the magma‐gas mixture. This causes an acoustic decoupling of the upper and lower parts of the magma conduit. The reduced sound speed and density of the melt at shallow depths present a sharp impedance contrast, which strongly reflects acoustic energy originating at depth and traps it in the lower part of the magma conduit. Alternatively, acoustic energy originating from the upper part of the conduit remains trapped in the low‐velocity region formed by the exsolved gas in the melt, and hence shallow explosions may preferentially couple into the atmosphere. Explosion signals may be triggered by an increased flow of melt at depth, and may be preceded and accompanied by vigorous mass flux transients.
FAST satellite wave observations in the AKR source region
Authors: Ergun R. E. , Carlson C. W. , McFadden J. P. , Mozer F. S. , Delory G. T. , Peria W. , Chaston C. C. , Temerin M. , Elphic R. , Strangeway R. , Pfaff R. , Cattell C. A. , Klumpar D. , Shelley E. , Peterson W. , Moebius E. , Kistler L.
Published: February 2004

The Fast Auroral SnapshoT (FAST) satellite has made observations in the Auroral Kilometric Radiation (AKR) source region with unprecedented frequency and time resolution. We confirm the AKR source is in a density depleted cavity and present examples in which cold electrons appeared to have been nearly evacuated (nhot> ncold). Electron distributions were depleted at low‐energies and up‐going ion beams were always present. Source region amplitudes were far greater than previously reported, reaching 2×10−4 (V/m)²/Hz (300 mV/m) in short bursts with bandwidths generally <1 kHz. Intense emissions were often at the edge of the density cavity. Emissions were near or below the cold plasma electron cyclotron frequency in the source region, and were almost entirely electromagnetic. The |E|/|B| ratio was constant as a function of frequency and rarely displayed any features that would identify a cold plasma cutoff or resonance.