Two-source Model Research Articles

Strangeness production in heavy ion collisions at SPS and RHIC within two-source statistical model

The experimental data on hadron yields and ratios in central Pb + Pb and Au + Au collisions at SPS and RHIC energies, respectively, are analysed within a two-source statistical model of an ideal hadron gas. These two sources represent the expanding system of colliding heavy ions, where the hot central fireball is embedded in a larger but cooler fireball. The volume of the central source increases with rising bombarding energy. Results of the two-source model fit to RHIC experimental data at midrapidity coincide with the results of the one-source thermal model fit, indicating the formation of an extended fireball, which is three times larger than the corresponding core at SPS.

An Extended CO Source around Comet 29P/Schwassmann–Wachmann 1

Comet 29P/Schwassmann–Wachmann 1 has been studied during seven days in August 1998 with the SEST submillimeter telescope at ESO, La Silla, Chile. The CO (J=2−1) emission at 230 GHz was mapped by directing the telescope beam at the nucleus and six off-nucleus positions. The CO line profiles exhibit the blue- and redshifted components previously observed by various observers. The strength of the observed lines does not decrease with projected distance to the nucleus as expected if CO molecules were coming from the nucleus only. Instead, the line area is nearly constant throughout the map. This can be explained if CO molecules are being released from both the sunlit side of the nucleus and CO-bearing particles distributed in a shell-like cloud. The extended source must consist of icy grains globally moving toward the Sun at ∼50 m s−1 released ∼30 days before the observations were made. The nuclear and extended sources produce (7±1)×1027 and 2.4×1028 molecules s−1, respectively. Our 1996 observations of the comet (Festou, M., M. Gunnarsson, A. Winnberg, H. Rickman, and G. Tancredi 2001. Icarus150, 140–150) were reexamined using this new two-source model. In this case, the nuclear and extended CO sources produced 10±1×1027 and 2.9×1028 CO molecules s−1, respectively. It is not necessary to postulate night side outgassing, but a large quantity of solid grains has to be expelled into the coma.

Estimation of the incidence of stroke using a capture-recapture model including covariates.

Capture-recapture is often used to assess completeness of a register. However, the usual two-source model relies on assumptions of independence of sources and equality of capture probability which are rarely satisfied in epidemiology. An alternative is to include covariates in capture-recapture models. We use capture-recapture models including covariates to estimate incidence of stroke in South London. We estimate ascertainment-adjusted age-standardized incidence rates, and calculate confidence intervals for incidence which allow for the uncertainty in estimation of the total number of cases. The crude capture-recapture model (including no covariates) underestimated the number of non-fatal strokes. Demographic and stroke severity variables were associated with the probability of capture. Including covariates led to more plausible results for fatal and non-fatal strokes, and suggested that the stroke register was 88% complete. Adjusting for under-ascertainment increased the estimated incidence from 1.31 (95% CI : 1.21-1.42) to 1.49 (95% CI : 0.38-2.60) per 1000 people. Incidence and age-standardized incidence can be calculated using data from an incomplete register. However, sparse strata can lead to wide confidence intervals for adjusted rates. Cost-effectiveness of routine registers might be increased by using the combination of sources and covariates which most accurately estimates the total number of cases, rather than by aiming for 100% completeness.

A two-source model for electron beams: calculation of relative output factors.

A two-source model for the calculation of relative output factors (ROF) for clinical applications of electron beams has been developed. The model consists of (1) an effective extended source above the final field-defining aperture (cutout) plane and (2) a source due to scattering from the aperture. Calculations are based on Fermi-Eyges theory and a pencil beam algorithm with parameters determined independently for each major scattering component. The model predicts a modified inverse square law for determining the dose rate for the electron beams. It also generalizes the "square-root method" and "one-dimensional method" that are often used clinically for ROF calculations. A computer program based on the model has been developed to calculate ROF for irregular fields. The predictions of ROF values have been compared with measurements on a Varian CLINAC 2100C/D accelerator for different cutout size, energies, applicators, and SSDs for square fields, rectangular fields, circular fields, and irregular fields. The agreement between prediction and measurement of the ROF for these wide range of conditions is generally within 1% for energies from 6 to 20 MeV. This two-source model can be used for clinical applications and it requires a minimal set of measured input data.

Modification of DAISY SVAT model for potential use of remotely sensed data

The SVAT model DAISY is modified to be able to utilize remote sensing (RS) data in order to improve prediction of evapotranspiration and photosynthesis at plot scale. The link between RS data and the DAISY model is the development of the minimum, unstressed, canopy resistance r c min during the growing season. Energy balance processes are simulated by applying resistance networks and a two-source model. Modeled data is validated against measurements performed for a winter wheat plot. Soil water content is measured by time domain reflectometry. Crop dry matter content and leaf area index are modeled adequately. Modeled soil water content, based on a Brooks and Corey [Brooks, R.H., Corey, A.T., 1964. Hydraulic properties of porous media. Hydrology Paper no. 3, Colorado University, Fort Collins, CO, 27 pp.] parameterization, from 0 to 20, 0 to 50 and 0 to 100 cm is calibrated satisfactorily against measured TDR values. Simulated and observed energy fluxes are generally in good agreement when water supply in the root zone is not limiting. With decreasing soil moisture content during a longer drought period, modeled latent heat flux is lower than observed, which calls for both improved parameterizations for environmental controls and for a improved estimation of the r c min parameter.

Evaluating the Effects of Subpixel Heterogeneity on Pixel Average Fluxes

Radiometric temperature observations T R (φ) at a sensor view angle φ are routinely available from weather satellites such as the Geostationary Orbiting Environmental Satellite (GOES) and provide a unique spatially distributed boundary condition for surface energy balance modeling at regional scales. Reliable flux estimates over heterogeneous surfaces have been obtained using two-source models that implicitly account for differences between T R (φ) and aerodynamic temperature, T O , by considering separately the contributions of soil/substrate and vegetation to T R (φ) observations and to the turbulent fluxes. A simple two-source energy balance model developed to use T R (φ) observations has been applied successfully to a wide range of vegetation cover conditions at the field scale. However, its application with course resolution weather satellite data (i.e., pixel resolution≳1 km) will invariably result in errors in pixel-averaged heat flux estimation for surfaces with significant variability in vegetation cover and stress conditions. Indeed, with the highest resolution of satellite T R (φ) data∼100 m, subpixel heterogeneity will still be significant for many landscapes, especially arid and semiarid areas. Uncertainty in flux estimation due to significant subpixel heterogeneity is examined using the simplified two-source model with T R (φ) inputs from simulations using a detailed plant-environment model (Cupid) under six different “homogeneous” surface conditions commonly found in semiarid and arid regions and under high and low winds. These surface types are comprised of shrub and tall riparian vegetation, high and low canopy cover, wet and dry surface soil moisture state, and stressed versus unstressed vegetation condition. From six homogeneous surface conditions defined by vegetation type, cover, surface moisture and stress, four mixed-pixel cases were constructed, each containing two contrasting surface types. Significant or unacceptable errors (i.e., ∼50 W m −2 ) in pixel-average heat fluxes are found in all four mixed-pixel cases, but the significant errors primarily occur when the fraction of the extreme surface condition (e.g., riparian wetland) comprises between ∼20% and 80% of the mixed-pixel. Additionally, the results are influenced by the wind conditions with a higher wind speed tending to reduce errors. This preliminary analysis suggests that when there is a significant discontinuity in surface conditions, particularly under low winds, the subpixel variability in energy fluxes will likely cause unacceptable errors in two-source model predictions. However, daytime wind speeds are typically >2 m s −1 and the resolution of T R (φ) observations from weather satellites are relatively coarse (i.e., ∼5–10 km), which means riparian areas are likely to comprise less than 10% of a pixel. Both of these factors are likely to reduce errors in heat flux predictions at these large spatial scales caused by using pixel-average inputs. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument proposed for NASA's Earth Observing System (EOS) has 90 m resolution. This will be useful for evaluating the impact of subpixel variability on flux predictions with coarser resolution data more routinely available from weather satellites.

Assessment of evapotranspiration models applied to a watershed of Canadian Prairies with mixed land-uses

Using meteorological data collected in the summer of 1996 and 1997, three evapotranspiration (ET) models, the Penman–Monteith (PM), the modified Penman for non-saturated surface, and the two-source models were applied to estimate hourly ET from different land-use covers of the Paddle River Basin (area = 265 km2). By assuming closed canopy conditions, the PM model could estimate the ET of coniferous forest and agricultural land because the contribution of soil evaporation under these land covers is not significant. For mixed forest and pasturelands that are partially vegetated, however, the amount of soil evaporation is significant and so PM underestimated the total ET. The modified Penman model mainly underestimated hourly ET during daytime when the atmosphere is unstable, but overestimated ET during early morning and late afternoon (stable atmosphere), particularly for pastureland. By re-establishing a relationship for the relative evaporation, the ET simulated by the modified Penman model improved. Both PM and the modified Penman are assessed with respect to the comprehensive, two-source model's simulated ET because the latter agrees favourably with the ET obtained from the basin water balance. The water balance ET is reliable because it is based on the streamflow, surface temperature, net radiation and soil moisture simulated by the semi-distributed hydrological model, Semi-distributed Physically based Hydrologic Model–Remote Sensing, DPHM-RS (host to the two-source model), all of which have been demonstrated to agree well with the observed data. Copyright © 2000 John Wiley & Sons, Ltd.

Estimating surface fluxes over the SGP site with remotely sensed data

The estimation of surface energy fluxes using remotely sensed data requires the combination of data from several sources, including land use, vegetation cover and surface temperature. Land use and vegetation cover were obtained from visible and near infrared (VNIR) data, while the state variable, surface temperature, was obtained from thermal infrared (TIR) data. An approach to combine these data with an energy balance model was studied as part of the 1997 Southern Great Plains Experiment (SGP97). Toward this end, VNIR and TIR images for 2 July 1997 were analyzed over the El Reno, Oklahoma (OK) site using data from the Thermal Infrared Multispectral Scanner (TIMS) and Thematic Mapper Simulator (TMS) airborne instruments. Intensive ground measurements constrained leaf area indices, canopy height and surface meteorological inputs required by the model. The observed brightness temperatures, when corrected for atmospheric effects using MODTRAN, nearby radiosoundings and the temperature-emissivity separation (TES) algorithm, were mostly within VC of ground based temperatures. The resulting surface temperatures were used in a two-source model that considers the heat flux and temperature contributions from the soil and vegetation. The heat flux predictions on average agree within 50 W m−2 of tower-based observations.

LARGE SOLAR EVENT OF SEPTEMBER 29, 1989: TEN YEARS AFTER

Out of the 56 Ground Level Enhancements (GLEs) of solar cosmic rays (SCRs) observed since 1942 until the present, 15 events were recorded in the 22nd cycle of solar activity (1986–1996). Solar proton events (SPEs) in that cycle displayed some peculiarities, which may need an interpretation on a new concept base. The event of September 29, 1989 is of special interest. Since the well-known event of February 23, 1956, it proved to be the most intense in the relativistic range of proton energies. This GLE affords a unique opportunity to study the propagation of SCRs over a wide range of rigidity. In spite of its occurrence behind the western solar limb, the originating major flare could be observed over a wide range of the wavelengths and particle energy spectra – from gamma rays to decametric radio waves, from >2 MeV electrons to multi-GeV protons; there were also measurements of the energy spectra and charge states of solar heavy nuclei. The flare was followed by some energetic solar phenomena (large magnetic loops, coronal eruptions and mass ejections, shocks, etc.). Due to the very hard rigidity spectrum, this was the first GLE recorded by underground muon detectors. The event also has a number of other unusual features, for example, an extended component of gamma-ray emission and the change in direction of the probable particle source during the event's initial stage. In addition, the intensity-time profile of the GLE is notable for its non-classic shape, showing a two-peak structure. The latter implies the possibility of a two-component (or two-source) ejection of accelerated particles from the Sun. The available observational data for the event is described in detail, the main focus of this paper is concentrated on different attempts to interpret the data within the framework of traditional and non-traditional concepts: shock and/or post-eruption acceleration, two-component (dual) ejection, two-source model of particle acceleration in large (extended) coronal structures, etc. None of the models put forward for explaining this event is exhaustive. The rigidity spectrum of ejected protons is estimated and the problem of the maximum rigidity, R m, of the accelerated particles is discussed. In the relativistic range, this event proved to be by 1–2 orders less intense than the event of February 23, 1956. It is also shown that the event of September 29, 1989 could not have been recorded with the present-day neutrino detectors.

Evidence for the distortion product frequency place as a source of distortion product otoacoustic emission (DPOAE) fine structure in humans. I. Fine structure and higher-order DPOAE as a function of the frequency ratio f2/f1.

Critical experiments were performed in order to validate the two-source hypothesis of distortion product otoacoustic emissions (DPOAE) generation. Measurements of the spectral fine structure of DPOAE in response to stimulation with two sinusoids have been performed with normal-hearing subjects. The dependence of fine-structure patterns on the frequency ratio f2/f1 was investigated by changing f1 or f2 only (fixed f2 or fixed f1 paradigm, respectively), and by changing both primaries at a fixed ratio and looking at different order DPOAE. When f2/f1 is varied in the fixed ratio paradigm, the patterns of 2 f1-f2 fine structure vary considerably more if plotted as a function of f2 than as a function of fDP. Different order distortion products located at the same characteristic place on the basilar membrane (BM) show similar patterns for both, the fixed-f2 and fDP paradigms. Fluctuations in DPOAE level up to 20 dB can be observed. In contrast, the results from a fixed-fDP paradigm do not show any fine structure but only an overall dependence of DP level on the frequency ratio, with a maximum for 2f1-f2 at f2/f1 close to 1.2. Similar stimulus configurations used in the experiments have also been used for computer simulations of DPOAE in a nonlinear and active model of the cochlea. Experimental results and model simulations give strong evidence for a two-source model of DPOAE generation: The first source is the initial nonlinear interaction of the primaries close to the f2 place. The second source is caused by coherent reflection from a re-emission site at the characteristic place of the distortion product frequency. The spectral fine structure of DPOAE observed in the ear canal reflects the interaction of both these sources.

The prevalence of multiple sclerosis in Tayside, Scotland: do latitudinal gradients really exist?

To determine the prevalence of multiple sclerosis (MS) in the Tayside Health Board Area, Scotland, we carried out a population-based survey using four intersecting sources (Neurology Department records, a survey of general practitioners, Scottish Morbidity Records of discharges from hospitals and visual evoked response requests). A two-source capture-recapture model estimated survey coverage, and direct age-sex standardisation was used to take account of different population structures. Comparisons were made between the prevalence in Scotland and that in the rest of the United Kingdom. A total of 727 (definite and probable) and 880 cases (early, probable and possible) were identified using the criteria of Poser et al. and those of Allison and Millar in a population of 395,600 (1995 mid-year estimate). The prevalence of MS on 1 September 1996 was 184/100,000 (95% confidence interval 171-198) and 222/100,000 (95% confidence interval 210-240), respectively. The two-source capture-recapture model estimated that the survey was between 93% and 99% complete. Age-sex standardisation eliminated certain north-south differences in prevalence when comparisons were made with previous surveys. Diagnostic misclassification may also have influenced reported prevalence statistics. The prevalence is similar to that found in revised figures from the Grampian region in Scotland but significantly higher than recent estimates from England and Wales. Methodological differences may account for most of the reported differences between north and south, although there is still evidence to suggest that MS is more prevalent in northern Great Britain and Northern Ireland than in England and Wales.

Estimation of Regional Evapotranspiration through Remote Sensing

Models used for the remote estimation of evapotranspiration are evaluated using aircraft observations over two distinct vegetation regimes in southwestern Australia. Single-source models using an empirically determined excess resistance term performed better than a two-source model, which does not require such a parameterization. The mean absolute difference between measured and estimated values of the sensible heat flux is below 17 W m−2 in comparison with approximately 40 W m−2 for evapotranspiration. Estimates of evapotranspiration depend on the closure of the surface energy balance and incorporate all residual errors in this closure. All models performed better over the agricultural vegetation than over the native vegetation.

Evaluation of soil and vegetation heat flux predictions using a simple two-source model with radiometric temperatures for partial canopy cover

A two-source model developed to use radiometric temperature observations for predicting component surface energy fluxes from soil and vegetation was evaluated with data from a row crop (cotton). The total or combined heat fluxes from the soil and vegetation agreed to within 20% of the observed values, on average. Component heat flux predictions from the soil and vegetation indicated that soil evaporation was generally higher than canopy transpiration. This result contradicts an earlier study which showed that soil evaporation was ∼1/3 of canopy transpiration rates with a significant source of sensible heat from the soil being advected to the canopy ( Kustas, 1990). Moreover, the modeled derived canopy temperatures were ∼6 K higher and soil temperatures were ∼4 K lower than the radiometric temperature observations. In order to obtain more physically realistic soil and vegetation component heat fluxes and better agreement between the predicted and observed soil and canopy temperatures, two model parameterizations required modification. One adjustment was to the magnitude of the Priestley–Taylor coefficient α PT used in estimating canopy transpiration. The magnitude of α PT was increased by ≈50% from its `universal constant' α PT ∼ 1.3 to α PT ∼ 2. The other modification was to the free convective velocity, U CV, defined as constant in the original formulation for estimating soil resistance to sensible heat flux transfer, R S. The new formulation is based on the recent experimental results from Kondo and Ishida (1997)who found that U CV ∝ Δ T 1/3 where Δ T is the surface–air temperature difference. Both of these modifications are shown to be supported by observations from the literature and therefore are not considered merely model `tuning'. Furthermore, component heat fluxes predicted by the model using canopy and soil radiometric temperature observations support the higher α PT value and new free convective formulation for estimating R S. Two other changes to model algorithms are described which are relevant to all dual-source modeling schemes. One is replacing the commonly used Beer's law type expression for estimating the divergence of net radiation in partial canopy covered surfaces with a more physically-based algorithm. The other is a simple method to address the effects of clumped vegetation (common in row crops and sparse canopies) on radiation divergence and wind speed inside the canopy layer.

Prevalence of tuberous sclerosis estimated by capture-recapture analysis

time. Unfortunately, in human populations these assumptions are frequently violated. The problem can be minimised by the use of techniques such as log-linear modelling but a high degree of accuracy in the estimate of numbers of missing cases should not be expected. We carried out a capture-recapture analysis of data collected in the survey of prevalence of tuberous sclerosis in Wessex. Cases had been identified from a large number of different sources. Data from these individual sources were pooled to construct three summary sources: cases identified by paediatricians; cases identified by other medical practitioners; and cases identified from other sources (for example, the Tuberous Sclerosis Association or Hospital Activity Analysis). We used the method described by Hook and Regal to first derive estimates for the total number of cases from each of the three possible two-source models and finally from all three sources. The figure shows the number of cases identified from each source and the overlap between sources. No cases were identified from all three sources. Maximum likelihood estimates are given for the total number of people with tuberous sclerosis in this population derived from each of the two-source models and from the three-source model. Dependency between sources was investigated by including terms for interaction between sources in the loglinear model; none of these terms was statistically significant. The Wessex survey originally identified 131 cases of tuberous sclerosis in a population of 3·4 million. The results of the capture-recapture analysis suggest that, despite the efforts of the investigators to locate all cases, more than half remained undetected. A revised estimate of prevalence, taking account of unascertained cases, is 8·8 per 100 000 population (95% CI 6·8–12·4). One implication is that many people with tuberous sclerosis do not receive either genetic counselling or specialist medical supervision.

Monitoring land surface fluxes using ASTER observations

This paper presents a review of methods for using remotely sensed data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to estimate the energy fluxes from the land surface. The basic concepts of the energy balance at the land surface are presented along with an example of how remotely sensed surface brightness temperatures can be used to estimate the sensible heat. The example is from the Monsoon 1990 experiment conducted over an arid watershed in Arizona. In this case, surface temperatures derived from an aircraft thermal-infrared (TIR) sensor and vegetation and land use characteristics derived from a Landsat Thematic Mapper (TM) image were used in a two-source model to predict the surface heat fluxes. The agreement with ground measurements is reasonably good for the three days of observations.

A two-source time-integrated model for estimating surface fluxes using thermal infrared remote sensing

We present an operational two-source (soil+vegetation) model for evaluating the surface energy balance given measurements of the time rate of change in radiometric surface temperature (T RAD) during the morning hours. This model consists of a two-source surface component describing the relation. between T RAD and sensible heat flux, coupled with a time-integrated component connecting surface sensible heating with planetary boundary layer development. By tying together the time-dependent behavior of surface temperature and the temperature in the boundary layer with the flux of sensible heat from the surface to the atmosphere, the need for ancillary measurements of near-surface air temperature is eliminated. This is a significant benefit when TRAD is acquired remotely. Air temperature can be strongly coupled to local biophysical surface conditions and, if the surface air and brightness temperature measurements used by a model are not collocated, energy flux estimates can be significantly corrupted. Furthermore, because this model uses only temporal changes in radiometric temperatures rather than absolute temperatures, time-independent biases in T RAD , resulting from atmospheric effects or other sources, do not affect the estimated fluxes; only the time-varying component of corrections need be computed. The algorithm also decomposes the surface radiometric temperature into its soil and vegetation. contributions; thus the angular dependence of T RAD can be predicted from an observation of T RAD at a single view angle. This capability is critical to an accurate interpretation of off-nadir measurements from polar orbiting and geosynchronous satellites. The performance of this model has been evaluated in comparison with data collected during two large-scale field experiments: the first International Satellite Land Surface Climatology Project field experiment, conducted in and around the Konza Prairie in Kansas, and the Monsoon '90 experiment, conducted in the semiarid rangelands of the Walnut Gulch Watershed in southern Arizona. Both comparisons yielded uncertainties comparable to those achieved by models that do require air temperature as an input and to measurement errors typical of standard micrometeorological methods for flux estimation. A strategy for applying the two-source time-integrated model on a regional or continental scale is briefly outlined.

The effect of clumping and stomatal response on evaporation from sparsely vegetated shrublands

The development of two-source models of evaporation has improved estimates of evaporation from sparsely vegetated surfaces over those of single-source models. This paper investigates the importance of clumping of vegetation, as defined by the fractional vegetative cover, for evaporation from soil and shrubs. A sensitivity analysis; of a model that includes clumping of vegetation and three sources of water for evaporation, shrubs, soil under shrubs and bare soil outside shrubs, is presented. Resistances to vapour transfer were derived experimentally for a shrubland in southeastern Spain, which was dominated by the leguminous shrub Retama sphaerocarpa. Stomatal conductances of the shrub were found to decline linearly with the in-canopy water vapour saturation deficit (D 0). The slope of this relationship increased linearly with volumetric soil water content. Soil surface resistances were found to increase quadratically with time after wetting of the soil surface. The model that included clumping (the C model) was compared with single- and two-source models. The tested models included feedbacks between plant resistances, in-canopy vapour pressure saturation deficits, and total evaporation from the surface ( λE t ). The single-source and two-source models overestimated evaporation from the plant ( λE p ) by 1% and 8%, respectively, whereas the C model underestimated λE p by 5%. The overestimates of λE p by the conventional two-source model resulted primarily from over-estimation of the radiation being absorbed by the canopy. The underestimation by the C model may have resulted from underestimation of the radiation absorbed by the canopy resulting from high reflected short-wave and emitted long-wave radiation from the soil. The C and two-source models predicted D 0 within 4%, whereas the single-source model underestimated D 0 by 19%, resulting from the omission of energy fluxes from the soil. The good prediction of evaporation from the plant by the single source model resulted from the combination of under-estimating D 0 and overestimating stomatal conductance.

Dynamics of Particulate Organic Matter in the Tamagawa Estuary and Inner Tokyo Bay

The distribution of carbon isotope ratio (δ 13C) in suspended particulate organic matter (POM) and sedimentary organics in the Tamagawa River and Inner Tokyo Bay was investigated. The objective was to assess the origin and fate of organic particles with emphasis on the growth of phytoplankton in the highly eutrophic estuarine and coastal environments. Variations in the δ 13C of POM ( δ 13C POM) in the intertidal river waters and seawaters are explained clearly in the δ 13C POM-salinity figure. The δ 13C POMof land-derived organics showed an almost constant value (−26·9±1·1‰) throughout the year. However, δ 13C POMand salinity in the intertidal zone exhibited a significant difference between warm (summer and early autumn) and cold (late autumn and winter) seasons. In the warm season, δ 13C POMwas highly variable in the Tamagawa Estuary and Inner Tokyo Bay. Growth of phytoplankton was notable, and the POM with high chlorophyll aconcentration could be categorized into two groups with light (around −30‰) and heavy (around −15‰) δ 13C POM, which appeared in the low- and high-salinity areas, respectively. The former light δ 13C POMvalue was caused by the light δ 13C POMvalue (−13·7‰) of substrate CO 2under the normal algal growth rate. The heavy δ 13C POMvalues were observed at sites where pH of the water was significantly high (around 8·5). It was thus suggested that a rapid algal growth rate such as a red-tide phenomenon was highly limited by the CO 2uptake process in this type of blooming. This is because the substrate δ 13C value was kept almost constant (0·0‰) with its high dissolved inorganic carbon concentration (2 mM) in the seawater. Due to the light δ 13C value of autochthonous particles in the high-salinity area in winter, no significant difference in the δ 13C POMlevel was found from the upper to lower tidal zones, regardless of changes in salinity. Consequently, the δ 13C POM-salinity figure was successfully constructed, and a framework assessing the dynamics of POM involving the phytoplankton growth rate was proposed for the highly eutrophic estuarine and inner bay areas. The δ 13C of sedimentary organics in Inner Tokyo Bay reflected the heavy δ 13C POMin the overlying water. The δ 13C value tended to decrease from the shallow coastal areas to the deep open bay. This trend clearly corresponded to the annual mean δ 13C POMin the water column of overlying seawater. Variations in the δ 13C value of the coastal sediments from the estuary to the open bay were illustrated by a dynamic model rather than a two-source model.

Determination of the extent of anthropogenic Pb migration through fractured sandstone using Pb isotope tracing

The extent of vertical migration of anthropogenic Pb beneath a medieval smelting site in Derbyshire, U.K. has been estimated using the determination of total Pb concentrations and 206Pb/ 207Pb isotope ratio from samples taken down 6 m of drill core. Preliminary studies of total Pb concentrations established that the surface slag derived from the smelting contained up to 16% Pb and that the normal background levels in uncontaminated sandstone were 10±2 ppm. Sample analyses beneath the site revealed elevated Pb concentrations in fracture infill clays (270 ppm Pb) and sandstone (76–83 ppm Pb). Both are well above the background Pb concentration. Lead isotope analysis of the slag wastes, the underlying contaminated sandstone and fracture infill has shown that all 3 contain very similar isotope ratios for 206Pb/ 207Pb (1.1802–1.1820). However, matched control sandstone samples show that the background 206Pb/ 207Pb isotope ratio (1.1670 ± 0.003) is distinctly different. This would indicate that both the sandstone and fracture infill underlying the historical smelting site contain a substantial proportion of Pb that has been derived from the overlying contamination. The application of total Pb concentrations along the core and isotope analysis suggest that anthropogenically derived Pb from the smelting site (that was operated between 665 and 445 a BP) has migrated to a depth of 4.50 m. Assuming a uniform migration rate and a mean time of migration of 555 a, then the mean migration rate is estimated to be 8 ± 2 mm/a. The proportion of natural versus anthropogenic Pb in the samples has been estimated from small variations in the 206Pb/ 207Pb isotope ratio. If the slag is considered to contain 100% anthropogenic Pb and the uncontaminated sandstone considered to contain 100% natural Pb, the linear interpolation can be applied between the 2 end members of the isotope ratio. The use of this approach to the 206Pb/ 207Pb ratio measurements has shown that 88% of the Pb in the contaminated sandstone (i.e. 69 ppm from a mean total Pb concentration of 78.5 ppm) has been derived from the anthropogenic Pb at the surface. For the fracture infill sample taken at a depth of 4.50 m, and with a total Pb concentration of 270 ppm, the % of Pb that has been derived from the slag wastes is approximately 98% (equivalent to 265 ppm Pb). The remaining Pb in both these samples (9.4 and 5 ppm, respectively) is deduced to have originated from the natural background concentration of Pb in the sandstone. The closeness of these estimates to the measured background concentration, suggests that a simple two-source model of Pb contamination is valid for this site.

On using mixed-layer transport parameterizations with radiometric surface temperature for computing regional scale sensible heat flux

Recent mixed-layer formulations for computing large-scale surface energy fluxes under daytime convective conditions do not require the estimation of surface-layer parameters, such as the roughness lengths for momentum and heat. This greatly simplifies approaches using operational satellite measurements of surface temperature for computing the surface energy balance at regional scales because the surface roughness parameters are not well known for many landscapes. The utility of such mixed-layer formulations is tested using data from several recent multidisciplinary field experiments (HAPEX-MOBILHY, FIFE and Monsoon 90). The results indicate that specific mixed-layer formulations adequately simulate surface sensible heat fluxes in the grassland and shrubland sites. However, use of the original values of proposed empirical coefficients for the forested site yield poor results. This is probably due to the fact that the forested site has significantly different surface geometry and associated distribution of temperature among the surface components (especially the relative importance of soil background temperatures) compared to the other sites. Therefore, the relationship between aerodynamic and radiometric surface temperature may have greatly differed between the forested site and the other locations. However, differences in aerodynamic roughness between the experimental sites were not correlated with changes required in the values of the coefficients. Instead, a two-source model which makes the distinction between aerodynamic and radiative temperature is proposed, as a means to determine which surface properties significantly affect the magnitude of the mixed-layer coefficients.