bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining sources and transit times of suspended sediment in the Murrumbidgee River, New South Wales, Australia, using fallout 137Cs and 210Pb
Authors: Wallbrink P. J. , Murray A. S. , Olley J. M. , Olive L. J.
Published: February 2004

Sediment budgets typically require an estimate of the proportional yield from erosion sources to sediments in transport and storage. This becomes increasingly difficult as catchments become larger, and erosion, storage, and deposition processes become more complex. We demonstrate how fallout radionuclides can be used to estimate the proportional contributions to sediment load, from a tripartite classification of erosion sources in a large catchment (the mid‐Murrumbidgee, 13,500 km2). The three major potential sources of sediment within this catchment are cultivated lands (∼22% of the surface area), uncultivated pastoral lands (∼78%), and the numerous channels and gullies found in this region. Concentrations of the fallout radionuclides 210Pbex and 137Cs in representative samples from each of these three sources are significantly different. Employing these values in a simple mixing model shows that the largest contribution of material is currently derived from subsoil channel/gully sources. Alterations to the suspended sediment 210Pbex signature by in situ labeling and decay are also considered. Applying the model with different concentrations of 210Pbex (decayed as a function of residence time in channels) suggests that the mean residence time of fine‐grained material within this system is 10±5 years. However, differences in 137Cs concentrations observed between flood and low‐flow sediments, and the presence of the short‐lived, cosmogenic 7Be, suggest that residence time of some of this fine‐grained material may be of the order of only weeks to months.
On the development of a new methodology for groundwater‐Driven health risk assessment
Authors: Maxwell Reed M. , Pelmulder Susan D. , Tompson Andrew F. B. , Kastenberg William E.
Published: February 2004

A methodology and hypothetical case study are presented for incorporation of uncertainty and variability into calculations of human health risk appropriate for regional, or basin‐scale, groundwater management problems. Uncertainty in well water concentration is introduced through complex contaminant migration patterns in the subsurface. Variability is considered in parameters related to individual behavior patterns and biological effects and to groundwater extraction and distribution networks. A joint uncertainty and variability (JUV) analysis is used to generate a two‐dimensional distribution or risk surface that spans both transport uncertainty as well as individual variability. Cuts in this distributional surface (fractiles of variability and percentiles of uncertainty) are presented and discussed. Comparisons with alternative approaches based upon deterministic transport models are also made. In addition, important distinctions are made between the case where household water is derived from the nearest well and the case where household water is mixed from many wells in a distribution system.
Numerical solutions to statistical moment equations of groundwater flow in nonstationary, bounded, heterogeneous media
Authors: Zhang Dongxiao
Published: February 2004

In this paper we investigate the combined effect of nonstationarity in log hydraulic conductivity and the presence of boundaries on flow in heterogeneous aquifers. We derive general equations governing the statistical moments of hydraulic head for steady state flow by perturbation expansions. Due to their mathematical complexity, we solve the moment equations by the numerical technique of finite differences. The numerical approach has flexibility in handling (moderately) irregular geometry, different boundary conditions, various trends in the mean log hydraulic conductivity, spatial variabilities in the magnitude and direction of mean flow, and different covariance functions, all of which are important factors to consider for real‐world applications. The effect of boundaries on the first two statistical moments involving head is strong and persistent. For example, in the case of stationary log hydraulic conductivity the head variance is always finite in a bounded domain while the head variance may be infinite in an unbounded domain. As in many other stochastic models, the statistical moment equations are derived under the assumption that the variance of log hydraulic conductivity is small. Accounting for a spatially varying, large‐scale trend in the log hydraulic conductivity field reduces the variance of log hydraulic conductivity. Although this makes the conductivity field nonstationary and significantly increases the mathematical complexity in the problem, it justifies the small‐variance assumption for many aquifers.
Concentration fluctuations and dilution in aquifers
Authors: Kapoor Vivek , Kitanidis Peter K.
Published: February 2004

The concentration of solute undergoing advection and local dispersion in a random hydraulic conductivity field is analyzed to quantify its variability and dilution. Detailed numerical evaluations of the concentration variance σc2 are compared to an approximate analytical description, which is based on a characteristic variance residence time (VRT), over which local dispersion destroys concentration fluctuations, and effective dispersion coefficients that quantify solute spreading rates. Key features of the analytical description for a finite size impulse input of solute are (1) initially, the concentration fields become more irregular with time, i.e., coefficient of variation, CV=σc/〈c〉, increases with time (〈c〉 being the mean concentration); (2) owing to the action of local dispersion, at large times (t > VRT), σc2 is a linear combination of 〈c〉2 and (∂〈c〉/∂xi)2, and the CV decreases with time (at the center, CV ≅ (N)1/2 VRT/t, N being the macroscopic dimensionality of the plume); (3) at early time, dilution and spreading can be severely disconnected; however, at large time the volume occupied by solute approaches that apparent from its spatial second moments; and (4) in contrast to the advection‐local dispersion case, under advection alone, the CV grows unboundedly with time (at the center, CV ∝ tN/4), and spatial second moment is increasingly disconnected from dilution, as time progresses. The predicted large time evolution of dilution and concentration fluctuation measures is observed in the numerical simulations.
A generalized growth model for simulating initial migration of dense non‐aqueous phase liquids
Authors: Ewing Robert P. , Berkowitz Brian
Published: February 2004

Modeling the migration of spilled non–aqueous phase liquids (NAPLs) is currently difficult because the physics governing their movement is complex and knowledge of the local geology is always incomplete. NAPL movement is subject to buoyancy, capillary, and viscous forces in addition to being directed by the particular structural and hydraulic properties of the porous medium. Consideration of buoyancy forces suggests that the flow regime diagram of Lenormand et al. [1988] can be expanded to a third dimension. We develop a generalized growth model, based on invasion percolation, that captures the essential physics of initial NAPL migration but is simple enough computationally that simulations can be conducted much faster than by using continuum simulation models that attempt to capture all details of the physics. In comparison with available experimental data, our model realistically simulates movement of a NAPL for a wide range of values of Bond and capillary numbers, in any kind of porous medium. Because this approach allows much faster and simpler simulation than other approaches, a higher spatial resolution and/or the use of Monte Carlo methods to reduce the effect of geological uncertainty becomes a realistic possibility.
Simulating carbon dynamics along the Boreal Forest Transect Case Study (BFTCS) in central Canada: 1. Model testing
Authors: Peng Changhui , Apps Michael J. , Price David T. , Nalder Ian A. , Halliwell David H.
Published: February 2004

CENTURY 4.0, a simulation model of carbon and nitrogen dynamics of terrestrial ecosystems based on the relationships between climate, soil texture, plant productivity, decomposition and human management, was tested against observed data along the boreal forest transect case study (BFTCS) in central Canada. The results show that the simulated average aboveground biomass and net N mineralization were consistent with observed data. The modeled estimates for soil carbon were consistent with those from regional‐scale empirical regression models. High correlation (R2= 0.92) with data was obtained for the simulation of soil carbon dynamics of the boreal forest, but the model overestimated soil carbon (O–20 cm) by 2–8% for fine‐textured soil and underestimated soil carbon by 5–18% for sandy soil. The effects of climatic variation on temporal changes in biomass and soil carbon storage over the past century were found to be very different for southern and northern sites but relatively insensitive to site‐specific soil texture. The main discrepancies between observed data and CENTURY 4.0 results are associated with the effects of soil texture and an inadequate representation of fire disturbance on C dynamics of boreal forests. Further improvements, particularly in the representation of disturbance regimes and in the simulation of slow pool C dynamics, are suggested to enhance its predictive capability.
Variabilities in the fluxes and annual emissions of nitrous oxide from the Arabian Sea
Authors: Lal Shyam , Patra Prabir K.
Published: February 2004

Extensive measurements of nitrous oxide (N2O) have been made during April–May 1994 (intermonsoon), February–March 1995 (northeast monsoon), July–August 1995 and August 1996 (southwest monsoon) in the Arabian Sea. Low N2O supersaturations in the surface waters are observed during intermonsoon compared to those in northeast and southwest monsoons. Spatial distributions of supersaturations manifest the effects of larger mixing during winter cooling and wind‐driven upwelling during monsoon period off the Indian west coast. A net positive flux is observable during all the seasons, with no discernible differences from the open ocean to coastal regions. The average ocean‐to‐atmosphere fluxes of N2O are estimated, using wind speed dependent gas transfer velocity, to be of the order of 0.26, 0.003, and 0.51, and 0.78 pg (pico grams) cm−2 s−1 during northeast monsoon, intermonsoon, and southwest monsoon in 1995 and 1996, respectively. The lower range of annual emission of N2O is estimated to be 0.56–0.76 Tg N2O per year which constitutes 13–17% of the net global oceanic source. However, N2O emission from the Arabian Sea can be as high as 1.0 Tg N2O per year using different gas transfer models.
Atmospheric iron supply and enhanced vertical carbon flux in the NE subarctic Pacific: Is there a connection?
Authors: Boyd P. W. , Wong C. S. , Merrill J. , Whitney F. , Snow J. , Harrison P. J. , Gower J.
Published: February 2004

Recent studies have confirmed the relationship between iron supply and phytoplankton growth rates in all three high‐nitrate low‐chlorophyll (HNLC) oceanic provinces. However, there is little evidence, so far, of the role of iron in altering the efficiency of the biological pump via increased downward export of particulate organic carbon (POC). The NE subarctic Pacific is unique among HNLC regions in that long time series pelagic observations and deep‐moored sediment trap records exist which may provide the best opportunity thus far to test aspects of the iron hypothesis. Episodic elevated levels of chlorophyll a (> 2.0 μg L−1) were observed 6 times between 1964 and 1976 at the former site of Ocean Station Papa (OSP). In addition, between 1984 and 1990 on at least three occasions, concurrent pulses of POC and biogenic silica were recorded in deep‐moored traps at OSP. Possible explanations for these events, such as lateral advection of more productive waters, iron‐mediated blooms, or grazing by salp swarms are discussed and tested using an existing downward POC flux model. Owing to the episodic nature of such events, no available data are sufficiently comprehensive to unequivocally rule out any of these explanations. Nevertheless, from the data available, the occurrence of pelagic or deep water pulses, approximately once every 3 years, are most consistent with iron‐mediated diatom blooms, and of the sinking of POC and biogenic silica (from such a bloom) to depth, respectively. A comparison of the timing of these iron‐mediated pulses with that of the transport probabilities of atmospheric dust supply from Asia and Alaska provides an opportunity to assess the likelihood of a coupling between the atmosphere and the ocean.
Methane emissions from above ground open manure slurry tanks
Authors: Kaharabata S. K. , Schuepp P. H. , Desjardins R. L.
Published: February 2004

Estimates of methane (CH4) emissions from slurry tanks or lagoons in the past have been made primarily by using chamber techniques, which are point specific and interfere with conditions at the slurry‐atmosphere interface. This study is based on the use of sulphur hexafluoride (SF6) as a tracer gas to estimate CH4 transport from the slurry surface. The tracer was released from the surface of the swine slurry, and air samples were taken at the downwind rim of the tank over a 165 day period from June 12 to November 20, 1995, at the McGiIl University ‐ Macdonald Campus Farm, Ste‐Anne‐de‐Bellevue, Quebec, and analyzed for CH4 and SF6 concentrations (C). Knowing the SF6 source strength (Q), CH4 source strength was then determined from the measured downwind concentrations using the C/Q ratio. Using this method, annual CH4 emission from the swine slurry tank was estimated at 56.5 kg CH4 m−2 tank surface yr−1 (± 20%). Assuming that diffusion processes at the nearby dairy tank were similar to those at the swine tank, the same C/Q ratio was used to determine CH4 emissions from the dairy slurry based on downwind CH4 concentrations measured over the same period as at the swine tank. Annual methane emission from the dairy tank was estimated at 74 kg CH4m−2 tank surface yr−1 (± 45%). On the basis of these estimates, CH4 emissions from outdoor holding tanks for swine and dairy slurry in Canada were approximated at 0.71 Tg CH4 yr−1 (± 40%) and 0.24 Tg CH4 yr−1 (± 70%), respectively, giving a combined annual emission of approximately 0.95 Tg yr−1(± 50%).
A new method to study simultaneous methane oxidation and methane production in soils
Authors: Andersen B. L. , Bidoglio G. , Leip A. , Rembges D.
Published: February 2004

Results of laboratory experiments show that 14C‐labeled methane added to soil was consumed faster than atmospheric 12C methane. This implies a source of methane, presumably through methanogenesis, in a soil that is a net consumer of atmospheric methane. The soil was well‐drained forest soil from Ispra, Italy. An undisturbed sample was taken with a steel corer and incubated under oxic conditions in a jar. Headspace samples were taken at time intervals and analyzed for total methane by gas chromatography and analyzed for 14C methane by liquid scintillation counting. Fluxes calculated from the decreasing headspace mixing ratios were, for example, −6.5 and −7.1 μmol m−2 hr−1 for 12C methane and 14C methane, respectively. A simple model is considered which reproduces reasonably well the observed mixing ratios as function of time.
Determination of the isotopic(13C/12C) discrimination by terrestrial biology from a global network of observations
Authors: Bakwin Peter S. , Tans Pieter P. , White James W. C. , Andres Robert J.
Published: February 2004

We analyze data from the National Oceanic and Atmospheric Administration / Climate Monitoring and Diagnostics Laboratory global air sampling network in order to extract the signatures of isotopic (13C/12C) discrimination by the terrestrial biota and of fossil fuel combustion for the regions surrounding the sampling sites. We utilize measurements of carbon monoxide (CO) to give an estimate of the contribution of fossil fuel combustion to the short‐term variability of carbon dioxide (CO2). In general, variations of CO2 are more strongly dominated by biological exchange, so the isotopic signature of fossil fuel combustion, while consistent with inventory estimates, is not well constrained by the observations. Conversely, results for isotope discrimination by the terrestrial biosphere are not strongly dependent on assumptions about fossil fuel combustion. Our analysis appears valid primarily for stations fairly near continental source/sink regions, particularly for midlatitude regions of the northern hemisphere. For these stations we derive a mean discrimination of −16.8 per mil (‰), with site‐to‐site variability of 0.8‰ (1 standard deviation) and with little or no consistent latitudinal gradient.
Three‐dimensional magnetospheric response to variations in the solar wind dynamic pressure
Authors: Ostapenko A. A. , Maltsev Yu. P.
Published: February 2004

Several thousand magnetic measurements at distances from 3 to 10 RE from the database of Fairfield et al. [1994] have been used for studying the magnetic field response to variations of the hourly‐averaged values of the solar wind dynamic pressure. The response differs from that predicted by the Mead [1964] model. Increase in the dynamic pressure compresses the magnetospheric field in the dayside sector mainly. In the most part of the nightside a depression dominates. The depression is connected with the growth of the cross‐tail current.
A comparison of the microphysical and optical properties of particles in an aircraft contrail and mountain wave cloud
Authors: Baumgardner Darrel , Gandrud Bruce E.
Published: February 2004

The freezing of deliquesced aerosols is the most likely formation mechanism of ice particles in wave clouds. A similar microphysical process has been postulated for the formation of aircraft contrails. Aerosol and cloud particle measurements have been made in contrail and wave clouds that formed under similar environmental conditions. Microphysical and optical properties are compared for these two types of clouds using a number of unique capabilities of the MASP particle probe, i.e., direct detection of forward and backscattered light, and the measurement of particle spacing to determine small scale cloud structures relevant to microphysical processes. The data indicate similarities in optical properties, but significant differences in the number concentrations, liquid water contents and the spatial organization of the cloud particles in the two types of clouds.
Strength and water weakening of mantle minerals, olivine, wadsleyite and ringwoodite
Authors: Chen Jiuhua , Inoue Toru , Weidner Donald J. , Wu Yujun , Vaughan Michael T.
Published: February 2004

Rheological properties of olivine and its high pressure polymorphs, both dry and hydrous, have been studied by monitoring x‐ray diffraction peak broadening as a function of pressure, temperature and time. The measurements were carried out up to a pressure of 10 GPa and a temperature of 600°C for olivine and wadsleyite, and a pressure of 20 GPa and a temperature of 1000°C for ringwoodite. The observations indicate that olivine is much weaker than the other two minerals for this range of conditions, and furthermore, water weakens olivine dramatically but only slightly weakens wadsleyite and ringwoodite. When the temperature increases from 25°C to 400°C the yield strength in the olivine drops by 39% without water and 62% with water, however there is hardly any change in strength for wet or dry wadsleyite and ringwoodite.
Neoproterozoic Earth‐Moon dynamics: Rework of the 900 Ma Big Cottonwood Canyon tidal laminae
Authors: Sonett C. P. , Chan Marjorie A.
Published: February 2004

The tidal rhythmites in the Proterozoic Big Cottonwood Formation (BCC) of Utah, the Neoproterozoic Elatina Formation of the Flinders Range of Southern Australia, and the lower Pennsylvanian Mansfield Formation of Indiana indicate that the rate of retreat of the lunar orbit has been approximately constant since the late Precambrian and closely matches the present epoch value determined from Apollo lasers. Examination of a new (BCC) core leads to a slightly revised length of day (LOD) and modified values for other Earth‐Moon dynamical parameters, thus implying the length of day 900 million years ago, reported earlier by Sonett et al. [1996] should be modified to ∼ 18.9 hrs.
CO2 ice clouds in the upper atmosphere of Mars
Authors: Clancy R. Todd , Sandor Brad J.
Published: February 2004

Recent (Sept. 1996–Sept. 1997) observations of Mars submillimeter CO lines from the James Clerk Maxwell Telescope (JCMT) on Mauna Kea, Hawaii have revealed surprisingly cold temperatures as typical of the Mars atmosphere over the 50–80 km altitude region. Measurements of these J=2‐>3 and J=3‐>4 rotational transitions of Mars atmospheric 12CO provide unique seasonal coverage of global‐averaged, dayside temperatures within this poorly observed mesophere of Mars. At solar longitudes (Ls) of 8°, 90°, 150°, and 187° in 1996–97, the mean atmospheric temperature for the 70–80 km (2.0–0.3 µbars) altitude region is observed to be at or below 120 K, which is only 10–15 K above the vapor saturation temperature for the CO2 Mars atmosphere. Consequently, local CO2 saturation conditions at these altitudes would be likely to exist and, in fact, were observed during the 3 AM descent entry of the Pathfinder spacecraft, on July 4, 1997. We argue that the blue wave clouds imaged from the Pathfinder lander 35–100 minutes prior to sunrise on Sol 39 are evidence of such CO2 ice formation within the 60–100 km altitude region; and that the 4.3 µm CO2 lines of solar scattered flux, in Mariner 6 and 7 infrared limb spectra of Mars are a direct spectral identification of CO2 ice cloud formation in the dayside Mars mesosphere. Simple considerations of these Pathfinder and Mariner 6 and 7 observations suggest 0.1–0.3 µm cloud particle radii, and particle number densities of the order 10² cm−3. On the basis of a variety of such day and night time measurements, we assert that the mesosphere of Mars does not exhibit extreme (25 K) diurnal temperature variations as maintained by the Pathfinder meteorology team; and that it is often substantially colder (>20 K) than determined from the Viking descent measurements in 1976 due to temporal variations in dust loading of this region.
Ground detection of trans‐ionospheric pulse pairs by stations in the National Lightning Detection Network
Authors: Zuelsdorf R. S. , Casler C. , Strangeway R. J. , Russell C. T. , Franz R.
Published: February 2004

Trans‐Ionospheric Pulse Pairs (TIPPs), as detected by the Blackbeard instrument on board the ALEXIS satellite, correlate with signals that the National Lightning Detection Network (NLDN) classifies as “cloud” lightning with a positive signal polarity (+IC). Correlation is only found for +IC pulses occurring in the 10 ms interval prior to TIPP occurrence. Apart from this single peak, there is no general change in lightning rates around TIPP time. Correlation between TIPPs and +IC strokes is statistically significant with 99.94% confidence. The amplitudes of +IC pulses that are associated with TTPPs are indistinguishable from the amplitudes of pulses that are not. The rise time of +IC pulses correlating with TIPPs, however, does appear to be longer than the noncorrelating +IC pulses, the median value being about 3 times greater than all other +IC pulses. By assuming TIPPs to be generated close to the detecting ground station, we can use the pulse separation time to calculate the source heights for the ground reflection model. The calculated height of TIPPs is consistent with a cloud source.
Gross deformation of the dayside magnetopause
Authors: Sibeck D. G. , Borodkova N. L. , Zastenker G. N. , Romanov S. A. , Sauvaud J.‐A.
Published: February 2004

On July 24, 1996, the entire magnetosheath moved past the Interball‐1 spacecraft twice within 7 min. Such rapid transits through the magnetosheath suggest the passage of an antisunward‐moving boundary wave with an amplitude in excess of 5 RE. A wave of this amplitude requires an order of magnitude decrease in the pressure confining the magnetosphere. Such decreases have been reported only in conjunction with hot flow anomalies, features accompanying interplanetary magnetic field discontinuities, bounded by narrow shocks, and identified on the basis of heated deflected flows transverse to the Earth‐Sun line. We identify all these features just outside the Interball‐1 magnetopause crossings on July 24, 1996.
Topography and gravity across subduction zones
Authors: Harabaglia Paolo , Doglioni Carlo
Published: February 2004

Topographic and Free‐air gravimetric profiles across subduction zones show two distinct signatures. Average low topography (−1250 m) and pronounced gravimetric anomalies characterize west‐directed subduction zones. Average elevated topography (1200 m) and smoother gravimetric waves are peculiar to east‐ or northeast‐directed subduction zones. These differences are particularly evident along the Pacific margins, but they persist also along the other subduction zones of the world in the Atlantic, Mediterranean, Himalayas and Indonesia regions. Therefore topography and gravimetry confirm the existence of two separate classes of subduction zones which appear to be independent of the age and nature of the subducting slab. It is suggested that these differences might be linked to the ‘westward’ drift of the lithosphere relative to the underlying upper mantle.
P‐SV conversions of teleseismic waves beneath the Chyulu Hills Volcanic Field, Kenya
Authors: Kaspar Tilo , Ritter Joachim R. R.
Published: February 2004

Observations of P‐SV converted waves provide new insights on the structure of the lithosphere beneath the Chyulu Hills, a Quaternary volcanic field on the SE shoulder of the Kenya rift (East Africa). A 3D teleseismic delay‐time tomography and a seismic refraction model revealed a zone of reduced P‐wave velocity (−3.5%) extending from the lower crust into the uppermost mantle (limited to about 70 km depth). In this paper, waveform and particle‐motion analyses are used to identify P‐SV conversions in teleseismic recordings and to search for lateral variations of seismic discontinuities. Data from 9 teleseisms contain clear SV‐phases within the first 8 seconds of the P‐coda. The depth of the generating interfaces is determined with a local velocity‐depth function based on the seismic refraction model. Our results show that there are no lateral depth variations of the Conrad (19–21 km) and Moho (43–45 km) discontinuities, indicating no large‐scale modification of the crustal structure through the magmatic processes. In the time window between the SV‐arrivals from the Conrad and Moho discontinuities additional SV‐energy is observed at some stations, but its origin cannot be located.
Evidence and mechanism of Hurricane Fran‐Induced ocean cooling in the Charleston Trough
Authors: Xie Lian , Pietrafesa L. J. , Bohm E. , Zhang C. , Li X.
Published: February 2004

Evidence of enhanced sea surface cooling during and following the passage of Hurricane Fran in September 1996 over an oceanic depression located on the ocean margin offshore of Charleston, South Carolina (referred to as the Charleston Trough), [Pietrafesa, 1983] is documented. Approximately 4C° of sea surface temperature (SST) reduction within the Charleston Trough following the passage of Hurricane Fran was estimated based on SST imagery from Advanced Very High Resolution Radiometer (AVHRR) on the NOAA‐14 polar orbiting satellite. Simulations using a three‐dimensional coastal ocean model indicate that the largest SST reduction occurred within the Charleston Trough. This SST reduction can be explained by oceanic mixing due to storm‐induced internal inertia‐gravity waves.
vertical distribution of methyl bromide in the stratosphere
Authors: Kourtidis Kostas , Borchers Reinhard , Fabian Peter
Published: February 2004

Seven vertical profiles of methyl bromide measured between 1987 and 1995 in the tropical, mid‐latitude and Arctic stratosphere are reported. Three of these profiles are previously unpublished, and four are previously published and are here reevaluated and brought on to the same calibration scale as the other ones. The profiles were derived by the analysis of air samples collected by the MPAE balloon‐borne cryogenic sampler at various latitudes and at heights from around 6 km to around 30 km. Methyl bromide was not detected above the first 7 km of the tropical stratosphere, while at higher latitudes it sometimes persisted to altitudes greater than 13 km above the tropopause. Concurrent measurements of the man‐made Halons 1211 (CBrClF2) and 1301 (CBrF3) and the natural compound CH2Br2 indicate that methyl bromide accounts for 55–70% of the bromine transported into the stratosphere from these four species.
Evolution of microseismicity during frictional sliding
Authors: Sammonds Peter , Ohnaka Mitiyasu
Published: February 2004

We have done frictional sliding experiments on Inada granite in double shear and monitored the acoustic emission (AE) produced and temporal changes in the microseismic b‐value (where b is defined as the log‐linear slope of the AE frequency‐amplitude distribution), using both rough and smooth ground simulated fault surfaces. We have found, (i) the maximum amplitudes of AE events during stable sliding are strongly dependent on the surface roughness with smooth‐ground surfaces giving smaller maximum AE amplitudes; (ii) b‐values are related to the surface topographic fractal dimensions, so that in steady‐state stable sliding smooth surfaces exhibit lower b‐values than rough surfaces; (iii) the b‐value falls before stick‐slip instability. The change of b with slip we interpret in terms of evolving fractal crack damage during frictional sliding of the fault surfaces.
Observations of the Spectral Distribution of Solar Irradiance at the Ground During SUCCESS
Authors: Pilewskie Peter , Goetz Alexander F. H. , Beal David A. , Bergstrom Robert W. , Mariani Peter
Published: February 2004

During SUCCESS two independent and independently calibrated spectrometers were deployed at a surface site to determine the spectrally resolved downwelling solar irradiance. Preliminary evidence shows that for cloud‐free conditions there is general agreement between measurements and model derived irradiance, at least to within instrumental and model uncertainties of 5%, with greatest disagreement occurring in the 400 nm–700 nm band. Cirrus effects are most prominent in the near‐infrared bands beyond 1500 nm while the influence of very thin (subvisual) cirrus is evident in the scattered flux at the surface. Further remote sensing applications and the assessment of cloud absorption is contingent upon measurements of the surface spectral albedo.
Solar Cycle 23 forecast update
Authors: Schatten Kenneth , Hoyt Douglas
Published: February 2004

Solar activity, although virtually impossible to forecast a month in advance, has succumbed to scientific methods on long time scales, much as climate or seasonal weather predictions are simpler than weekly weather forecasting. Moderately accurate solar activity forecasts on decadal time scales now seem possible. The methods that work fall into a class of prediction techniques called “precursor methods.” We utilize solar, interplanetary field, and geomagnetic precursors to update our cycle 23 prediction to provide a mean smoothed sunspot number of 153 ± 30 and mean smoothed Fl0.7 cm Radio flux of 200 ± 30. This is comparable to, but somewhat smaller than, the NOAA SEC panel findings that the next solar cycle would peak at a sunspot number near 160 ± 30. This paper also provides some discussion relating solar and interplanetary field components to serve as a bridge in interplanetary space, helping to forge Sun‐Earth connections.
Aerosol size distribution in a coagulating plume: Analytical behavior and modeling applications
Authors: Turco Richard P. , Yu Fangqun
Published: February 2004

In a previous paper (Turco and Yu, 1997), a series of analytical solutions were derived for the problem of aerosol coagulation in an expanding plume, as from a jet engine. Those solutions were shown to depend on a single dimensionless time‐dependent number, NT, which is related to the particle coagulation kernel and the plume volume. Here, we derive a new analytical expression that describes the particle size distribution in an expanding plume in terms of NT. We show how this solution can be extended to include the effects of soot particles on the evolving volatile sulfuric acid aerosols in an aircraft wake. Our solutions apply primarily to cases where changes in the size distribution—beyond an initial period encompassing emission and prompt nucleation/condensation—is controlled mainly by coagulation. The analytical size distributions allow most of the important properties of an evolving aerosol population—mean size, number greater than a minimum size, surface area density, size dependent reactivities, and optical properties—to be estimated objectively. We have applied our analytical solution to evaluate errors associated with numerical diffusion in a detailed microphysical code, and demonstrate that, if care is not exercised in solving the coagulation equation, substantial errors can result in the predictions at large particle sizes. This effect is particularly important when comparisons between models and field observations are carried out. The analytical expressions derived here can also be employed to initialize models that do not resolve individual aircraft plumes, by providing a simple means for parameterizing the initial aerosol properties after an appropriate mixing time.
Kinetic and spectroscopic requirements for the inference of chemical heating rates and atomic hydrogen densities from OH Meinel band measurements
Authors: Mlynczak Martin G. , Zhou Daniel K. , Adler‐Golden Steven M.
Published: February 2004

We present the accuracy requirements for specific kinetic and spectroscopic parameters used in modeling populations of vibrationally excited hydroxyl. The requirements are based on simulations of the inference of chemical energy deposition rates and atomic hydrogen densities from satellite observations of the hydroxyl Meinel band emission rates. Improvement in the rate constants which describe the collisional removal of the high‐lying υ states of OH and the reaction of highlying υ states with atomic oxygen is required in addition to improved specification of the nascent distribution of energy within OH upon reaction of atomic hydrogen and ozone. These improvements are necessary for the interpretation of Meinel band measurements to be made from a new spaceflight experiment in less than 3 years.
Evidence for a high‐latitude origin of lower latitude high‐speed wind
Authors: Roberts D. Aaron , Goldstein M. L.
Published: February 2004

Using low‐frequency spectra of the wind speed, density, and magnetic field strength, we show that the near‐streamer belt solar wind at solar minimum exhibits many harmonics of fundamental frequencies corresponding to 26‐ and 34‐day periods. Nearly all the low‐frequency peaks in the spectra can be explained by these harmonics. The 26‐day period is that of coronal hole rotation, and the 34‐day period is naturally associated with the photospheric rotation period at about 70° S latitude. Thus we find evidence that the wind flow near 25° S comes from a region poleward of 60° S, consistent with magnetic field models.
Airborne volcanic plume measurements using a FTIR spectrometer, Kilauea Volcano, Hawaii
Authors: McGee Kenneth A. , Gerlach Terrence M.
Published: February 2004

A prototype closed‐path Fourier transform infrared spectrometer system (FTIR), operating from battery power and with a Stirling engine microcooler for detector cooling, was successfully used for airborne measurements of sulfur dioxide at Kilauea volcano. Airborne profiles of the volcanic plume emanating from the erupting Pu′u′O′o vent on the East Rift of Kilauea revealed levels of nearly 3 ppm SO2 in the core of the plume. An emission rate of 2,160 metric tons per day of sulfur dioxide was calculated from the FTIR data, which agrees closely with simultaneous measurements by a correlation spectrometer (COSPEC). The rapid spatial sampling possible from an airborne platform distinguishes the methodology described here from previous FTIR measurements.
Species dependent energies in upward directed ion beams over auroral arcs as observed with FAST TEAMS
Authors: Möbius E. , Tang L. , Kistler L. M. , Popecki M. , Lund E. J. , Klumpar D. , Peterson W. , Shelley E. G. , Klecker B. , Hovestadt D. , Carlson C. W. , Ergun R. , McFadden J. P. , Mozer F. , Temerin M. , Cattell C. , Elphic R. , Strangeway R. , Pfaff R.
Published: February 2004

Upward flowing field‐aligned ion beams over auroral arcs have been observed with the 3‐dimensional ion mass spectrograph TEAMS on FAST. We have performed a statistical study on a sample of 77 ion beams from the auroral campaign in early 1997. All observed beams contain substantial amounts of H+, He+ and O+. A clear ordering of the total energies according to mass is found, with H+ having the lowest and O+ the highest energy. The composition varies significantly from beam to beam, with O+/H+ ratios ranging from ≈ 0.1 to 10. No variation of the energy ratio between species is observed as a function of relative abundance. These results are discussed in the light of earlier observations of higher energies for O+ in statistical studies of beams during solar minimum and attempts to explain this behavior in terms of beam instabilities.
The effect of soil anisotropy on the radiance field emerging from vegetation canopies
Authors: Pinty Bernard , Verstraete Michel M. , Gobron Nadine
Published: February 2004

The solution of the radiation transfer equation in a vegetation canopy requires the specification of appropriate boundary conditions, especially at the interface between the vegetation layer and the soil. This short paper documents the effect of soil brightness and anisotropy on the field of radiances emerging at the top of the vegetation canopy in the solar domain. The study is based on the analysis of the sensitivity of an advanced radiation transfer model. It is shown that the scattering properties of the soil must be carefully assigned to ensure a correct interpretation of data collected over optically thin vegetation canopies.
Pressure dependence of permeability and Earth tide induced fluid flow
Authors: Millich E. , Neugebauer H. J. , Huenges E. , Nover G.
Published: February 2004

New in situ measurements of the pressure dependence of permeability at the Continental‐Deep‐Drilling Project in Windisch‐Eschenbach/Germany (KTB) indicate a much stronger sensitivity compared to measurements of core samples. The non‐linear pressure‐dependent permeability combined with the oscillating tidal forces provide the basis for a pumping mechanism in porous rocks. Numerical simulations of the interaction between tidal strain and fluid pore pressure show a residual flow beside fluid oscillations for the simplified model of a u‐shaped fault system. The magnitude of the residual flow is dependent on the permeability and the scale of the area considered. A residual Darcy velocity of 4·10−14m/s was calculated with KTB permeabilities.
Comment on “A new hydrous silicate, a water reservoir, in the upper part of the lower mantle” by Eiji Ohtani, Hiroki Mizobata, Yasuhiro Kudoh, Toshiro Nagase, Haruo Arashi, Hisayoshi Yurimoto, and Isoji Miyagi
Authors: Liu Lin‐gun , Irifune T.
Published: February 2004

On the basis of the available powder X‐ray diffraction data, chemical composition, Raman spectrum and synthesis P‐T conditions, it is concluded that the so‐called new phase claimed by Ohtani et al. [1997] is in reality the phase D reported earlier by Liu [1987], Irifune et al. [1996] and Kuroda and Irifune [1997]. Phase F first reported by Kanzaki [1991] is also probably in reality the phase D. The powder X‐ray diffraction pattern of the so‐called phase F studied by Kudoh et al. [1995] bears no resemblance to that reported by Kanzaki [1991], suggesting a totally different material was employed in the study of Kudoh et al. [1995].
Observations of large amplitude parallel electric field wave packets at the plasma sheet boundary
Authors: Cattell C. , Wygant J. , Dombeck J. , Mozer F. S. , Temerin M. , Russell C. T.
Published: February 2004

We report the first observation of large amplitude electric fields parallel to the earth's magnetic field at radial distances of ∼6 RE on magnetic field lines linking the plasma sheet boundary to the auroral zone. The parallel fields, with magnitudes up to 40 mV/m, occur in three different electrostatic structures: unipolar wave packets with a net potential drop, bipolar wave packets, and solitary waves. Examples from one boundary crossing are presented which show that the wave packets have durations of <1s, are traveling at velocities of ≤100 k/s, and are consistent with ion acoustic waves. The waves can contribute to the acceleration of auroral electrons and modify the pitch angle distributions. The wave packets occur in a region of large‐scale field‐aligned currents and are often associated with perpendicular waves near the lower hybrid frequency with strongly modulated amplitudes. The velocities determined for the solitary waves are faster than those of the wave packets.
Geomagnetic activity and the solar wind during the Maunder Minimum
Authors: Cliver Edward W. , Boriakoff Valentín , Bounar Khaled H.
Published: February 2004

We used a strong (r = 0.96) correlation between 11‐year averages of sunspot number (SSN) and the geomagnetic aa index to infer that the mean level of geomagnetic activity during the Maunder Minimum (1645–1715) was approximately a third of that observed for recent solar cycles (∼7 nT vs. ∼24 nT). We determined the variation of 11‐year averages of solar wind speed (v) and the southward component of the interplanetary magnetic field (Bs) with cycle‐averaged SSN for the two most recent cycles and also compared cycle‐averaged variations of v²Bs and aa for the same interval. We then extrapolated these observed solar wind variations to Maunder Minimum conditions (mean SSN of ∼ 2 and mean aa value of ∼ 7 nT) to deduce that, on average, the solar wind during that period was somewhat slower (v = 340 ± 50 km s−1), and the interplanetary magnetic field much smoother (Bs = 0.3±0.1 nT), than at present (∼ 440 km s−1 and ∼ 1.2 nT). Various lines of evidence (including 10Be data) suggest that, despite the virtual absence of sunspots that characterized the Maunder Minimum, the 11‐year geomagnetic (solar wind) cycle persisted throughout this period.
POLAR magnetic observations of the low‐altitude magnetosphere during the January 1997 coronal mass ejection/magnetic cloud event
Authors: Le G. , Russell C. T. , Luhmann J. G.
Published: February 2004

During the January 1997 coronal mass ejection/magnetic cloud event, the POLAR spacecraft experienced three successive perigee passes with dramatically different interplanetary magnetic field (IMF) and solar wind conditions on January 9, 10 and 11. The magnetic field observations during these three successive perigee passes are used to examine the response of the low‐altitude polar and auroral magnetosphere to different IMF and solar wind conditions. We find that field‐aligned currents are controlled mainly by the southward IMF component. They are greatly enhanced during strongly southward IMF conditions on January 10, but the solar wind dynamic pressure has little effect on their strength during the passage of the high‐density solar wind filament on January 11. Thus, drag on the magnetosphere is principally due to reconnection at the magnetopause, with little due to viscous effects. Effects of the ring current and the magnetopause current can be identified in the magnetic field data in the low‐altitude magnetosphere. During the magnetic storm of January 10, the ring current exhibits strong dawn‐dusk asymmetry. It is much stronger in the dusk sector than in the dawn sector.
Characteristics of electromagnetic proton cyclotron waves along auroral field lines observed by FAST in regions of upward current
Authors: Chaston C. C. , Ergun R. E. , Delory G. T. , Peria W. , Temerin M. , Cattell C. , Strangeway R. , McFadden J. P. , Carlson C. W. , Elphic R. C. , Klumpar D. M. , Peterson W. K. , Moebius E. , Pfaff R.
Published: February 2004

Preliminary studies from FAST observations indicate that auroral ion cyclotron waves (ICWs) above the helium cyclotron frequency (ΩHe+) occur at all MLTs have amplitudes sometimes >1 V/m and often have a magnetic component even above the proton cyclotron frequency (Ωp) with amplitudes up to 2nT. Waves with transverse amplitudes greater than 100 mV/m often exhibit large spiky downward pointing field‐aligned components with amplitudes that may exceed that of transverse fluctuation. The ratio of electric to magnetic fluctuation amplitude (E1/B1) is close to c. Using the 3 dimensional electric and magnetic field measurements available from FAST it is demonstrated that these waves are in most cases polarized transverse to the ambient magnetic field (B0) and have linear polarization with wavelengths perpendicular to B0 ranging from hundreds of meters to kilometers. Calculations of the Poynting vector associated with these ICWs indicates Poynting fluxes directed downwards along B0 for waves below the local Ωp and generally upwards for waves observed close to and above this frequency with fluxes which may exceed 10% of the total field‐aligned electron beam energy flux.
Evolution of HCL concentrations in the lower stratosphere from 1991 to 1996 following the eruption of Mt. Pinatubo
Authors: Webster C. R. , May R. D. , Michelsen H. A. , Scott D. C. , Wilson J. C. , Jonsson H. H. , Brock C. A. , Dye J. E. , Baumgardner D. , Stimpfle R. M. , Koplow J. P. , Margitan J. J. , Proffitt M. H. , Jaeglé L. , Herman R. L. , Hu H. , Flesch G. J. , Loewenstein M.
Published: February 2004

In situ measurements of hydrochloric acid in the lower stratosphere reveal that its mean abundance relative to that of total inorganic chlorine (Cly) has evolved upwards from HCl/Cly = 40% in late 1991 to 70% in 1996. This fraction is generally anticorrelated with aerosol surface area concentration, which has been diminishing since the 1991 volcanic eruption of Mt. Pinatubo. Calculations incorporating new laboratory results of faster heterogeneous chemistry show that air parcels with high aerosol loading exposed to temperatures below 205 K can experience enough chlorine activation to drive the HCl/Cly below 50%, but overestimate observed ClO/Cly.
Phase transformations of the ternary system (NH4)2SO4‐H2SO4‐H2O and the implications for cirrus cloud formation
Authors: Martin Scot T.
Published: February 2004

Homogeneous and heterogeneous growth mechanisms for cirrus cloud formation are considered in light of recent measurements showing the presence of NH4+ ions in the aerosol of the upper troposphere. Low‐temperature ternary phase diagrams of (NH4)2SO4‐H2SO4‐H2O are presented, and the thermodynamic and the kinetic data of the phase transitions are employed to consider the implications of NH4+ ions on the mechanisms of cirrus cloud formation. The analysis concludes that changes in the degree of ammoniation can lead to a crossover in the cloud growth system from homogeneous to heterogeneous nucleation. A corresponding change in the cloud's particle distribution alters the cloud's radiative properties, persistence, and surface area available for heterogeneous chemistry.
Dissolved niobium and tantalum in the North Pacific
Authors: Sohrin Yoshiki , Fujishima Yukiyo , Ueda Kazumasa , Akiyama Shoji , Mori Koji , Hasegawa Hiroshi , Matsui Masakazu
Published: February 2004

Niobium and tantalum were measured in North Pacific seawater. The concentration of Nb shows a slight depletion in surface water and that of Ta shows a slight increase near the bottom. The mean concentrations of Nb in surface and deep Pacific water are 3.0 and 3.8 pmol/kg, respectively, and for Ta, 0.08 and 0.20 pmol/kg. Their relatively uniform distribution suggests that Nb and Ta are less reactive with particles in seawater than Zr and Hf. In analogy with V, the species of Nb and Ta may be oxyacids rather than hydroxides.