bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of surface flux measurements in heterogeneous terrain during the Monsoon '90 experiment
Authors: Stannard D. I. , Blanford J. H. , Kustas W. P. , Nichols W. D. , Amer S. A. , Schmugge T. J. , Weltz M. A.
Published: February 2004

A network of 9‐m‐tall surface flux measurement stations were deployed at eight sparsely vegetated sites during the Monsoon '90 experiment to measure net radiation, Q, soil heat flux, G, sensible heat flux, H (using eddy correlation), and latent heat flux, λE (using the energy balance equation). At four of these sites, 2‐m‐tall eddy correlation systems were used to measure all four fluxes directly. Also a 2‐m‐tall Bowen ratio system was deployed at one site. Magnitudes of the energy balance closure (Q + G + H + λE) increased as the complexity of terrain increased. The daytime Bowen ratio decreased from about 10 before the monsoon season to about 0.3 during the monsoons. Source areas of the measurements are developed and compared to scales of heterogeneity arising from the sparse vegetation and the topography. There was very good agreement among simultaneous measurements of Q with the same model sensor at different heights (representing different source areas), but poor agreement among different brands of sensors. Comparisons of simultaneous measurements of G suggest that because of the extremely small source area, extreme care in sensor deployment is necessary for accurate measurement in sparse canopies. A recently published model to estimate fetch is used to interpret measurements of H at the 2 m and 9 m heights. Three sites were characterized by undulating topography, with ridgetops separated by about 200–600 m. At these sites, sensors were located on ridgetops, and the 9‐m fetch included the adjacent valley, whereas the 2‐m fetch was limited to the immediate ridgetop and hillside. Before the monsoons began, vegetation was mostly dormant, the watershed was uniformly hot and dry, and the two measurements of H were in close agreement. After the monsoons began and vegetation fully matured, the 2‐m measurements of H were significantly greater than the 9‐m measurements, presumably because the vegetation in the valleys was denser and cooler than on the ridgetops and hillsides. At one lowland site with little topographic relief, the vegetation was more uniform, and the two measurements of H were in close agreement during peak vegetation. Values of λE could only be compared at two sites, but the 9‐m values were greater than the 2‐m values, suggesting λE from the dense vegetation in the valleys was greater than elsewhere.
Variability of emissivity and surface temperature over a sparsely vegetated surface
Authors: Humes K. S. , Kustas W. P. , Moran M. S. , Nichols W. D. , Weltz M. A.
Published: February 2004

Radiometric surface temperatures obtained from remote sensing measurements are a function of both the physical surface temperature and the effective emissivity of the surface within the band pass of the radiometric measurement. For sparsely vegetated areas, however, a sensor views significant fractions of both bare soil and various vegetation types. In this case the radiometric response of a sensor is a function of the emissivities and kinetic temperatures of various surface elements, the proportion of those surface elements within the field of view of the sensor, and the interaction of radiation emitted from the various surface components. In order to effectively utilize thermal remote sensing data to quantify energy balance components for a sparsely vegetated area, it is important to examine the typical magnitude and degree of variability of emissivity and surface temperature for such surfaces. Surface emissivity measurements and ground and low‐altitude‐aircraft‐based surface temperature measurements (8–13 μm band pass) made in conjunction with the Monsoon '90 field experiment were used to evaluate the typical variability of those quantities during the summer rainy season in a semiarid watershed. The average value for thermal band emissivity of the exposed bare soil portions of the surface was found to be approximately 0.96; the average value measured for most of the varieties of desert shrubs present was approximately 0.99. Surface composite emissivity was estimated to be approximately 0.98 for both the grass‐dominated and shrub‐dominated portions of the watershed. The spatial variability of surface temperature was found to be highly dependent on the spatial scale of integration for the instantaneous field of view (IFOV) of the instrument, the spatial scale of the total area under evaluation, and the time of day. For the conditions which existed during most of the Monsoon '90 experiment, the differences in kinetic (physical) temperature between the vegetation and soil background were typically between 10° and 25°C at midday. These differences gave rise to large variations in radiometric composite surface temperatures observed with a ground‐based instrument configuration which allowed a ground IFOV of approximately 0.5 m. An evaluation of the frequency distribution for these observations indicated that the variance in surface temperature observed over an intensively sampled target area (approximately 500 m×120 m) increased significantly in the early to late morning hours of a typical diurnal heating cycle. For aircraft‐based composite radiometric temperature measurements at the watershed scale (with ground IFOV of approximately 40 m for each observation), much of the variability in surface temperature due to differences in soil and vegetation temperature was integrated into a single measurement; consequently, the variance between observations over the watershed was not significantly larger than those observed at length scales of 100 m.
Evaluation of hydrologic parameters in a semiarid rangeland using remotely sensed spectral data
Authors: Moran M. S. , Clarke T. R. , Kustas W. P. , Weltz M. , Amer S. A.
Published: February 2004

A study was conducted to determine the relation between remotely sensed spectral data and measurements of vegetation‐related hydrologic parameters in a semiarid rangeland in southeast Arizona. Throughout the measurement periods, ranging from June to September 1990, eight sites in the U.S. Department of Agriculture's Agricultural Research Service Walnut Gulch experimental watershed were monitored for water and energy fluxes and other meteorological and biological parameters. Corresponding spectral data were acquired with ground‐based radiometers, low‐altitude aircraft‐mounted instruments, and Landsat thematic mapper sensors. Spectral indices were derived from measurements of surface reflectance, based on their response to variations in hydrologic parameters and sensitivity to unrelated variables, such as solar zenith angle and soil differences. A soil‐adjusted vegetation index, SAVI (derived from red and NIR reflectance factors), was found to be highly correlated with the temporal changes in vegetation cover and biomass, but less successful in discriminating spatial differences in cover and biomass across the watershed. Significant relations were found between the surface‐air temperature (Ts‐Ta) difference and measurements of soil moisture content, though the shape differed from that previously published for bare soil. The relation between daily evaporation rate and measurements of (Ts‐Ta) and daily net radiation was similar to that derived previously for irrigated pasture and dryland shortgrass in France but differed from that derived for irrigated wheat. These results emphasized the strengths and limitations of the use of spectral data for estimation of hydrologic characteristics of sparsely vegetated sites and suggested a need for reevaluation of common empirical relations between remotely sensed measurements and surface characteristics for application to rangeland areas.
Runoff simulation sensitivity to remotely sensed initial soil water content
Authors: Goodrich D. C. , Schmugge T. J. , Jackson T. J. , Unkrich C. L. , Keefer T. O. , Parry R. , Bach L. B. , Amer S. A.
Published: February 2004

A variety of aircraft remotely sensed and conventional ground‐based measurements of volumetric soil water content (SW) were made over two subwatersheds (4.4 and 631 ha) of the U.S. Department of Agriculture's Agricultural Research Service Walnut Gulch experimental watershed during the 1990 monsoon season. Spatially distributed soil water contents estimated remotely from the NASA push broom microwave radiometer (PBMR), an Institute of Radioengineering and Electronics (IRE) multifrequency radiometer, and three ground‐based point methods were used to define prestorm initial SW for a distributed rainfall‐runoff model (KINEROS; Woolhiser et al., 1990) at a small catchment scale (4.4 ha). At a medium catchment scale (631 ha or 6.31 km2) spatially distributed PBMR SW data were aggregated via stream order reduction. The impacts of the various spatial averages of SW on runoff simulations are discussed and are compared to runoff simulations using SW estimates derived from a simple daily water balance model. It was found that at the small catchment scale the SW data obtained from any of the measurement methods could be used to obtain reasonable runoff predictions. At the medium catchment scale, a basin‐wide remotely sensed average of initial water content was sufficient for runoff simulations. This has important implications for the possible use of satellite‐based microwave soil moisture data to define prestorm SW because the low spatial resolutions of such sensors may not seriously impact runoff simulations under the conditions examined. However, at both the small and medium basin scale, adequate resources must be devoted to proper definition of the input rainfall to achieve reasonable runoff simulations.
Local energy flux estimates for unstable conditions using variance data in semiarid rangelands
Authors: Kustas W. P. , Blanford J. H. , Stannard D. I. , Daughtry C. S. T. , Nichols W. D. , Weltz M. A.
Published: February 2004

A network of meteorological stations was installed during the Monsoon '90 field campaign in the Walnut Gulch experimental watershed. The study area has a fairly complex surface. The vegetation cover is heterogeneous and sparse, and the terrain is mildly hilly, but dissected by ephemeral channels. Besides measurement of some of the standard weather data such as wind speed, air temperature, and solar radiation, these sites also contained instruments for estimating the local surface energy balance. The approach utilized measurements of net radiation (Rn), soil heat flux (G) and Monin‐Obukhov similarity theory applied to first‐ and second‐order turbulent statistics of wind speed and temperature for determining the sensible heat flux (H). The latent heat flux (LE) was solved as a residual in the surface energy balance equation, namely, LE = −(Rn + G + H). This procedure (VAR‐RESID) for estimating the energy fluxes satisfied monetary constraints and the requirement for low maintenance and continued operation through the harsh environmental conditions experienced in semiarid regions. Comparison of energy fluxes using this approach with more traditional eddy correlation techniques showed differences were within 20% under unstable conditions. Similar variability in flux estimates over the study area was present in the eddy correlation data. Hence, estimates of H and LE using the VAR‐RESID approach under unstable conditions were considered satisfactory. Also, with second‐order statistics of vertical velocity collected at several sites, the local momentum roughness length was estimated. This is an important parameter used in modeling the turbulent transfer of momentum and sensible heat fluxes across the surface‐atmosphere interface.
Flow and solute transport through the soil matrix and macropores of a hillslope segment
Authors: Tsuboyama Yoshio , Sidle Roy C. , Noguchi Shoji , Hosoda Ikuhiro
Published: February 2004

Subsurface flow from various portions of a soil profile on a steep, forested hillslope was evaluated by two sets of step‐change miscible displacement tests at different application rates and antecedent hydrologic conditions. Solutions of NaCl (1000 mg L−1 Cl−) were applied at steady state rates (equivalent to 20 and 30 mm h−1 of standing water over the entire plot area) using a line irrigation source located 1.5 m upslope (lateral distance) from an excavated soil pit. Subsurface flow and tracer breakthrough from five portions (the organic‐rich soil layer including macropores, the mineral soil matrix, and three groups of macropores in the mineral soil layer) of the soil profile were individually measured and analyzed using a convective‐dispersive model. Matrix flow dominated discharge from the soil pit during tracer tests (70–93% of total discharge). However, during wet periods with upslope drainage, macropores (including organic‐rich soil) contributed proportionally more flow than during periods when upslope drainage was minimal. Outflow from macropores during the test with wet antecedent conditions had lower Cl− concentrations than drainage from the soil matrix, suggesting dilution in macropores from upslope drainage. Effective pore volumes calculated for the flow‐averaged breakthrough data from the entire profile were much less (<40%) than the estimates (measured by tensiometers) of total volume of pore water, suggesting that preferential flow significantly contributed to subsurface transport of tracer. The pore volume for the entire profile increased only slightly with increasing application rate; however, the relative proportions of pore volumes calculated for individual portions varied proportionally to antecedent hydrologic conditions. These changes are attributed to the expansion of individual macropores with surrounding soil and the lateral extension of macropore networks during wetter conditions.
Examining the contributions of glacial till water to storm runoff using two‐ and three‐component hydrograph separations
Authors: Hinton M. J. , Schiff S. L. , English M. C.
Published: February 2004

Two‐ and three‐component hydrograph separations based on 18O and dissolved silica are used to investigate the contributions of glacial till water to the storm runoff of a headwater stream on the Canadian Shield. Two‐component isotopic hydrograph separations based on 18O indicate that the volume and flux of event water could be accounted for by direct precipitation onto saturated areas. Three‐component hydrograph separations distinguish between event water, preevent soil water, and preevent till water. These results show that groundwater flow through coarse‐textured glacial tills can make a significant contribution to stream discharge during runoff events (29 and 62% in this study) despite the lower hydraulic conductivities of the tills compared to the overlying soils. The three‐component hydrograph separations also demonstrate that the relative contributions of preevent soil water and preevent till water changed during one runoff event such that the average water chemistry of the preevent component varied during the event. Two‐component hydrograph separations using dissolved silica indicate that seasonal changes in the till water contributions also occur and are related to groundwater levels. Measurements of vertical hydraulic gradients during runoff events indicate that the increase in flow from the tills to the soils is minimal and cannot account for the large and rapid increase in till water flow into the stream. Till water that has discharged to the soils prior to the event is probably being flushed from the soils into the stream during events.
Water and heat fluxes in desert soils: 1. Field studies
Authors: Scanlon Bridget R.
Published: February 2004

Soil physics parameters were monitored in a semiarid site in the Chihuahuan Desert of Texas to evaluate unsaturated flow processes under natural conditions. The bed of an ephemeral stream was instrumented with neutron probe access tubes to monitor water content for 3 years and with thermocouple psychrometers to monitor water potential and temperature for 2 years. Soil samples were collected from stream and interstream settings for laboratory measurement of water content, water potential, water retention, and saturated hydraulic conductivity. Absence of temporal variations in water content in deep (41‐m) profiles indicated that within the accuracy of the neutron probe measurements, water pulses were not moving through the system. Penetration of water after rainfall was generally restricted to the uppermost 0.2 m of the sediments. During rain‐free periods, the surficial sediments were extremely dry, as indicated by laboratory‐measured water potentials as low as −16 MPa. After rainfall, water potentials were highest at the surface and decreased sharply at the base of the wetting front, with gradients as steep as −13 MPa in 0.05 m. Water potentials were out of range of the in situ psychrometers down to 0.8 m throughout most of the monitoring period because the soils were very dry (≤−7 to −8 MPa). Seasonal fluctuations in water potential were recorded at depths of 1.1 and 1.4 m. Water potentials at greater depths remained fairly uniform with time. Except in the shallow subsurface after rainfall, water potentials generally decreased upward; this trend indicated an upward driving force for liquid and isothermal vapor movement. Soil temperatures displayed large seasonal and diurnal fluctuations. Temperatures generally increased with depth in the winter and decreased with depth in the summer. Downward summer temperature gradients opposed upward water potential gradients and resulted in a downward driving force for thermal vapor movement.
Water and heat fluxes in desert soils: 2. Numerical simulations
Authors: Scanlon Bridget R. , Milly P. C. D.
Published: February 2004

Transient one‐dimensional fluxes of soil water (liquid and vapor) and heat in response to 1 year of atmospheric forcing were simulated numerically for a site in the Chihuahuan Desert of Texas. The model was initialized and evaluated using the monitoring data presented in a companion paper (Scanlon, this issue). Soil hydraulic and thermal properties were estimated a priori from a combination of laboratory measurements, models, and other published information. In the first simulation, the main drying curves were used to describe soil water retention, and hysteresis was ignored. Remarkable consistency was found between computed and measured water potentials and temperatures. Attenuation and phase shift of the seasonal cycle of water potentials below the shallow subsurface active zone (0.0‐ to 0.3‐m depth) were similar to those of temperatures, suggesting that water potential fluctuations were driven primarily by temperature changes. Water fluxes in the upper 0.3 m of soil were dominated by downward and upward liquid fluxes that resulted from infiltration of rain and subsequent evaporation from the surface. Upward flux was vapor dominated only in the top several millimeters of the soil during periods of evaporation. Below a depth of 0.3 m, water fluxes varied slowly and were dominated by downward thermal vapor flux that decreased with depth, causing a net accumulation of water. In a second simulation, nonhysteretic water retention was instead described by the estimated main wetting curves; the resulting differences in fluxes were attributed to lower initial water contents (given fixed initial water potential) and unsaturated hydraulic conductivities that were lower than they were in the first simulation. Below a depth of 0.3 m, the thermal vapor fluxes dominated and were similar to those in the first simulation. Two other simulations were performed, differing from the first only in the prescription of different (wetter) initial water potentials. These three simulations yielded identical solutions in the upper 0.2 m of soil after infiltration of summer rain; however, the various initial water potentials were preserved throughout the year at depths greater than 0.2 m. Comparison of all four simulations showed that the predominantly upward liquid fluxes below a depth of 0.2 m were very sensitive to the differences in water retention functions and initial water potentials among simulations, because these factors strongly affected hydraulic conductivities. Comparison of numerical modeling results with chemical tracer data showed that values of downward vapor flux below the surface evaporation zone were of the same order of magnitude as those previously estimated by analysis of depth distributions of bomb 3H (volatile) and bomb 36Cl (nonvolatile).
Falling rate evaporation and desorption estimates
Authors: Lockington D. A.
Published: February 2004

The second stage of evaporation from a bare soil has been described in terms of the desorptivity, a parameter related to the soil's hydraulic properties. Several formulas for desorptivity dependence on the soil water diffusivity have been proposed, but to date have not achieved the accuracy established for the sorptivity (i.e., <1% absolute relative error), the equivalent parameter for infiltration. A new formula is derived in the present study using a weighted residual approach. Comparison with precise numerical solutions for exponential and power law diffusivity functions shows that the new result has an absolute relative error less than 1%.
The Dole Effect and its variations during the last 130,000 years as measured in the Vostok Ice Core
Authors: Bender Michael , Sowers Todd , Labeyrie Laurent
Published: February 2004

We review the current understanding of the Dole effect (the observed difference between the δ18O of atmospheric O2 and that of seawater) and its causes, extend the record of variations in the Dole effect back to 130 kyr before present using data on the δ18O of O2 obtained from studying the Vostok ice core (Sowers et al., 1993), and discuss the significance of temporal variations. The Dole effect reflects oxygen isotope fractionation during photosynthesis, respiration, and hydrologic processes (evaporation, precipitation, and evapotranspiration). Our best prediction of the present‐day Dole effect, +20.8‰, is considerably lower than the observed value, +23.5‰, and we discuss possible causes of this discrepancy. During the past 130 kyr, the Dole effect has been 0.05‰ lower than the present value, on average. The standard deviation of the Dole effect from the mean has been only ±0.2‰, and the Dole effect is nearly unchanged between glacial maxima and interglacial periods. The small variability in the Dole effect suggests that relative rates of primary production in the land and marine realms have been relatively constant. Most periodic variability in the Dole effect is in the precession band, suggesting that changes in this global biogeochemical term reflects variations in low‐latitude land hydrology and productivity or possibly variability in low‐latitude oceanic productivity.
The sensitivity of the terrestrial biosphere to climatic change: A simulation of the Middle Holocene
Authors: Foley Jonathan A.
Published: February 2004

A process‐based ecosystem model, DEMETER, is used to simulate the sensitivity of the terrestrial biosphere to changes in climate. In this study, DEMETER is applied to the two following climatic regimes: (1) the modern observed climate and (2) a simulated mid‐Holocene climate (6000 years before present). The mid‐Holocene climate is simulated using the GENESIS global climate model, where shifts in the Earth's orbital parameters result in warmer northern continents and enhanced monsoons in Asia, North Africa, and North America. DEMETER simulates large differences between modern and mid‐Holocene vegetation cover: (1) mid‐Holocene boreal forests extend farther poleward than present in much of Europe, Asia, and North America, and (2) mid‐Holocene North African grasslands extend substantially farther north than present. The simulated patterns of mid‐Holocene vegetation are consistent with many features of the paleobotanical record. Simulated mid‐Holocene global net primary productivity is approximately 3% larger than present, largely due to the increase of boreal forest and tropical grasslands relative to tundra and desert. Global vegetation carbon is higher at 6 kyr B.P. compared to present by roughly the same amount (4%). Mid‐Holocene global litter carbon is larger than present by 10%, while global soil carbon is approximately 1% less. Despite the regional changes in productivity and carbon storage the simulated total carbon storage potential of the terrestrial biosphere (not including changes in peat) does not change significantly between the two simulations.
Soil‐atmosphere exchange of nitrous oxide, nitric oxide, and methane under secondary succession of pasture to forest in the Atlantic lowlands of Costa Rica
Authors: Keller Michael , Reiners William A.
Published: February 2004

We investigated changes in soil‐atmosphere flux of CH4, N2O, and NO resulting from the succession of pasture to forest in the Atlantic lowlands of Costa Rica. We studied a dozen sites intensively for over one year in order to measure rates and to understand controlling mechanisms for gas exchange. CH4flux was controlled primarily by soil moisture content. Soil consumption of atmospheric CH4was greatest when soils were relatively dry. Forest soils consumed CH4while pasture soils which had poor drainage generally produced CH4. The seasonal pattern of N2O emissions from forest soils was related exponentially to soil water‐filled pore space. Annual average N2O emissions correlated with soil exchangeable NO3−concentrations. Soil‐atmosphere NO flux was greatest when soils were relatively dry. We found the largest NO emissions from abandoned pasture sites. Combining these data with those from another study in the Atlantic lowlands of Costa Rica that focused on deforestation, we present a 50‐year chronosequence of trace gas emissions that extends from natural conditions, through disturbance and natural recovery. The soil‐atmosphere fluxes of CH4and N2O and of NO may be restored to predisturbance rates during secondary succession. The changes in trace gas emissions following deforestation, through pasture use and secondary succession, may be explained conceptually through reference to two major controlling factors, nitrogen availability and soil‐atmosphere diffusive exchange of gases as it is influenced by soil moisture content and soil compaction.
Methane in the Baltic and North Seas and a reassessment of the marine emissions of methane
Authors: Bange H. W. , Bartell U. H. , Rapsomanikis S. , Andreae M. O.
Published: February 2004

During three measurement campaigns on the Baltic and North Seas, atmospheric and dissolved methane was determined with an automated gas chromatographic system. Area‐weighted mean saturation values in the sea surface waters were 113 ± 5% and 395 ± 82% (Baltic Sea, February and July 1992) and 126 ± 8% (south central North Sea, September 1992). On the bases of our data and a compilation of literature data the global oceanic emissions of methane were reassessed by introducing a concept of regional gas transfer coefficients. Our estimates computed with two different air‐sea exchange models lie in the range of 11–18 Tg CH4 yr−1. Despite the fact that shelf areas and estuaries only represent a small part of the world's ocean they contribute about 75% to the global oceanic emissions. We applied a simple, coupled, three‐layer model to evaluate the time dependent variation of the oceanic flux to the atmosphere. The model calculations indicate that even with increasing tropospheric methane concentration, the ocean will remain a source of atmospheric methane.
Exports of carbon and nitrogen from river basins in Canada's Atlantic Provinces
Authors: Clair T. A. , Pollock T. L. , Ehrman J. M.
Published: February 2004

The loss of carbon and organic nitrogen from the terrestrial ecosystem via streams and rivers is dependent on a number of factors such as basin vegetation, geography, geology, climate, and hydrology. We studied the export of dissolved carbon and nitrogen from 26 rivers varying in size from 45 to 92,500 km2 located in Atlantic Canada. Twenty‐four of the basins studied were free of significant anthropogenic activity and were covered with coniferous and mixed hardwood forests. Our results showed that total organic carbon loss from the region, normalized for area, was approximately 29 kg ha−1 yr−1, while inorganic C was considerably lower at 4.3 kg ha−1 yr−1. We developed predictive statistical models using total precipitation, basin size, and basin slope to predict the export of organic carbon and nitrogen. Our results suggest that increases in regional precipitation will most likely increase the loss of organic carbon and nitrogen from terrestrial systems. We also found that inorganic carbon and nitrogen were not influenced by precipitation. Inorganic carbon seemed more influenced by geology, and inorganic nitrogen seemed more influenced by basin slope.
Carbon monoxide budget in the northern hemisphere
Authors: Bakwin Peter S. , Tans Pieter P. , Novelli Paul C.
Published: February 2004

To improve urban air quality the major industrialized nations of the West took steps during the 1970s and 1980s to reduce carbon monoxide (CO) emissions from automobiles and other industrial sources. Overall, CO/CO2 emission ratios from the mix of fossil fuel combustion sources have been reduced by about half during 1976–1990. Also, the tropospheric abundance of hydroxyl radical (OH), which is the main sink for CO, is proposed to have increased globally by about 1.0±0.8% yr−1 [Prinn et al., 1992]. We use a simple two‐box model to examine the impact of shrinking emissions and increasing OH on the global abundance of CO. We find that these factors contribute about equally in reducing CO levels in the Northern Hemisphere troposphere by about 1.8±0.8 ppb yr−1 on average.
Decomposition of halomethanes on α‐alumina at stratospheric temperatures
Authors: Robinson Gary N. , Freedman Andrew , Kolb Charles E. , Worsnop Douglas R.
Published: February 2004

We present data that suggest the possibility of a previously unsuspected heterogeneous process involving the decomposition of halocarhon source gases on alumina solid‐propellant rocket motor exhaust particles deposited in the stratosphere. These results, obtained under ultrahigh vacuum conditions, provide evidence that halomethane compounds undergo dissociative chemisorption on α‐alumina surfaces at stratospheric temperatures, leading to the release of more reactive halogen containing species. Simple calculations indicate that halocarbon concentrations will be severely depleted in the immediate wake of the rocket plume; any serious global impact at current projected launch rates requires the existence of one or more processes that regenerate active sites on the surface subsequent to the dissociative chemisorption of halocarbons.
The contribution of evaporation from the Great Lakes to the continental atmosphere: estimate based on stable isotope data
Authors: Gat Joel R. , Bowser Carl J. , Kendall Carol
Published: February 2004

The isotopic composition of precipitation and river runoff in the vicinity of the North American Great Lakes is characterized by a higher deuterium‐excess value than observed in the advecting air masses. It is suggested that this indicates that evaporated moisture from the surface waters is mixed with the atmosphere waters. A preliminary estimate of the atmospheric water balance during summer and autumn indicates that between 4.6%–15.7% of the atmospheric water content downwind from the Great Lakes is derived from lake evaporation during summer.
Changes in the Character of Polar Stratospheric Clouds Over Antarctica in 1992 Due to the Pinatubo Volcanic Aerosol
Authors: Deshler Terry , Johnson Bryan J. , Rozier William R.
Published: February 2004

Vertical profiles of aerosol concentration were measured on 8 occasions from McMurdo Station, Antarctica (78°S), between late August and early October 1992. Polar stratospheric clouds (PSCs) were observed on 6 of these soundings. The characteristics of PSCs, are ozone, were quite different above and below about 16 km. Above 16 km PSCs were variable in time, with particles >1.0 μm radius contributing significantly to the surface area, generally <8 μm2 cm−3. Below 16 km PSCs were much more stable and were dominated by high concentrations of smaller particles, <1.0 μm, with surface areas of 20–30 μm2 cm−3. This lower layer coincided with the altitude of the primary Pinatubo volcanic aerosol as measured in mid September and October, and with the 4 km region of the atmosphere where ozone was virtually completely destroyed over Antarctica in 1992.
Stratospheric warmings during February and March 1993
Authors: Manney G. L. , Zurek R. W. , O'Neill A. , Swinbank R. , Kumer J. B. , Mergenthaler J. L. , Roche A. E.
Published: February 2004

Two stratospheric warmings during February and March 1993 are described using UKMO analyses, calculated PV and diabatic heating, and N2O observed by the CLAES instrument on the UARS. The first warming affected temperatures over a larger region, while the second produced a larger region of reversed zonal winds. Tilted baroclinic zones formed in the temperature field, and the polar vortex tilted westward with height. Narrow tongues of high PV and low N2O were drawn off the polar vortex, and irreversibly mixed. Tongues of material were drawn from low latitudes into the region between the polar vortex and the anticyclone; diabatic descent was also strongest in this region. Increased N2O over a broad region near the edge of the polar vortex indicates the importance of horizontal transport. N2O decreased in the vortex, consistent with enhanced diabatic descent during the warmings.
Experimental diagenesis: Exploratory results
Authors: Scholz Christopher H. , Léger Albert , Karner Stephen L.
Published: February 2004

We conducted experiments in which a granular mixture of quartz and labradorite was deformed in compression at elevated temperatures (200–350°C) and pressures (100 MPa) in the presence of deionized water. Following initial consolidation of the material by application of the loads at room temperature, a second, hydrothermal phase of consolidation was observed when the temperature was increased with the loads fixed. The strain rate during this hydrothermal consolidation decayed approximately exponentially with time and was accompanied by only minor porosity reduction. The sample permeability decreased rapidly during the hydrothermal consolidation and continued to decrease following cessation of the deformation. The rate of this self‐sealing process was a complex function of temperature. Scanning electron microscopy and microprobe analysis of the indurated post‐experimental material showed albitization of the feldspar, especially in highly deformed regions. Analysis of post‐experimental fluids show that Si in solution increased with increasing flow and temperature. Fluid‐rock equilibrium was not achieved within the short durations of the experiments (50–60 hours). Our interpretation is that deformation occurred by grain boundary sliding aided by solution and reaction at high stress contacts, and sealing occurred by precipitation in low stress regions in the throats of pores.
Palaeomagnetic rotations in opposite senses in southeastern Spain
Authors: Calvo Manuel , Osete María Luisa , Vegas Romón
Published: February 2004

20 volcanic and 3 sedimentary sites of upper Miocene age were sampled in the Cabo de Gata region in southeastern Spain. Palaeomagnetic and rockmagnetic investigations yielded useful results in 15 volcanic and 1 sedimentary site. Clockwise and anticlockwise block rotations of adjacent blocks could be observed. The age of these rotations is younger than Tortonian. Deformation in the eastern part of the Betics seems to follow a different pattern than in the central and western part of the Subbetic. This behaviour can be related to the crustal structure in the eastern Betics.
On the thermal noise “temperature” in an anisotropic plasma
Authors: Meyer‐Vernet Nicole
Published: February 2004

Electrostatic waves are often detected with wire dipoles longer than the wave‐lengths. The electrostatic directivity pattern of such antennas has lobes roughly perpendicular to those of short dipoles. As a consequence, in a plasma where the electron temperatures are different along (T║) and across (T⟂) the magnetic field, the thermal noise “temperature” is T⟂ if the antenna is parallel to B and (T║+T⟂)/2 if it is perpendicular. Practical applications for space plasma and wave polarization measurements are given.
Space shuttle observations of collisionally excited outgassed water vapor
Authors: Dean D. A. , Huppi E. R. , Smith D. R. , Nadile R. M. , Zhou D. K.
Published: February 2004

The analysis of CIRRIS 1A (Cryogenic InfraRed Radiance Instrumentation for Shuttle) interferometric and radiometric data obtained during the flight of STS‐39 (28 Apr–6 May 1991) reveals the presence of IR emission in the 400–900 cm−1 (11–25 μm) region not attributable to atmospheric emission. In this paper, data are shown which identify the signal as near‐field water vapor present during all CIRRIS 1A observations. Variability of the near‐field water vapor emissions is characterized, and further investigation indicates that the water is excited to high effective temperatures, possibly in excess of 2000 K. The data presented support the conclusion that water outgassed from the shuttle tiles is highly excited by collisions with atmospheric O, classifying it as a type of shuttle‐induced glow whose spectrum has never previously been measured in the LWIR. Measured results are compared to current models which predict radiance for collisionally excited outgassed molecules.
A third volcanic chain in Kamchatka: thermal anomaly at transform/convergence plate boundary
Authors: Tatsumi Yoshiyuki , Furukawa Yoshitsugu , Kogiso Tetsu , Yamanaka Yoshiko , Yokoyama Takuo , Fedotov Sergei A.
Published: February 2004

The Kamchatka volcanic arc, which is located at the northern edge of the Kurile arc, consists of three volcanic chains, all parallel to the trench axis. In contrast, most subduction zones have only two subparallel volcanic chains. The third chain in Kamchatka, which is farthest from the trench, is characterized by the occurrence of voluminous plateau lavas; volcanoes in the two chains closer to the trench are stratovolcanoes typical in arc magmatism. The third chain magmatism is also unusual in that lavas show concentrations of incompatible elements intermediate between those in the two trenchward chains. Both the unusual occurrence of the third volcanic chain and the unusual lava chemistry could be caused by partial melting of K‐amphibole bearing peridotites in the downdragged hydrous layer at the base of the mantle wedge under anomalously high‐temperature conditions associated with the characteristic tectonic setting of transform/convergence transition in the region.
Impact of Pinatubo aerosols on the partitioning between NO2 and HNO3
Authors: Koike M , Jones N. B. , Matthews W. A. , Johnston P. V. , McKenzie R. L. , Kinnison D. , Rodriguez J.
Published: February 2004

Ground based infrared observations of HNO3 column amount at Lauder, New Zealand (45°S, 170°E), show significant increases in HNO3 following the arrival of Pinatubo volcanic aerosols. The increase first became apparent in September 1991 when the HNO3 amount was higher than that expected from the regular seasonal variation by 2.3 × 1015 cm−2, which corresponds to 16% of the unperturbed value. Between September 1991 and May 1993, the observed HNO3 amounts were systematically higher, typically by 1.5 to 3.5 × 1015 cm−2 or 10 to 30%. After June 1993, the observed HNO3 amounts were close to the unperturbed values. The decrease in stratospheric NO2 due to the volcanic aerosols was observed at Lauder after August 1991 [Johnston et al., 1992, 1993]. The start of the HNO3 increase and the general trend are in agreement with those expected from the NO2 decrease when heterogeneous reactions on the sulfate aerosols are considered. Model calculations, in which observed aerosol fields have been used, qualitatively agree with these observed trends, although the magnitude of the changes have been underestimated. These results provide further understanding of the impact of heterogeneous chemistry on the partitioning between NO2 and HNO3.
Chaotic transport in a double gyre ocean
Authors: Yang Huijun , Liu Zhengyu
Published: February 2004

Lagrangian trajectories in a deterministic simple flow can exhibit complex behavior. This is called the chaotic advection, which can induce the chaotic transport and mixing (which oceanographers conventionally call stirring) in the fluid particles and fine structure in the tracer fields. We propose the chaotic transport as a gyre‐scale transport mechansim in oceans. Our model ocean has double gyres, subtropical and subpolar gyres, driven by the surface wind. When the wind is allowed to seasonally migrate, the inter‐gyre transport and across streamline transport within each gyre will be excited. The fastest inter‐gyre transport occurs when the wind migrates about 1000km in north‐south direction with a period of interannual to decadal time. The estimate of the effective diffusion coefficient by this gyre‐scale mixing is about 3 × 107cm2s−1, comparable to those derived for synoptical eddies. The results shed some light on gyre‐scale exchange of water and heat flux in general oceans and implications for the studies of ocean climate. The concepts and methods used here will find applications in coastal oceanography, ocean biology and chemistry.
Implications of laboratory electrical measurements on interpretation of EM‐surveys and origin of the Sudbury Structure
Authors: Katsube T. J. , Salisbury M.
Published: February 2004

Electrical resistivity and effective porosity have been measured for 52 drillcore samples representing major sedimentary and igneous lithologies exposed in the Sudbury Structure (SS). The purpose was to constrain interpretation of high conductivity anomalies observed by surface electromagnetic (EM) surveys conducted across the SS, and to provide information on its origin. While zones of low resistivity are known to exist in the upper sedimentary formations, rocks at depth are generally characterized by high resistivities (104–7×104 Ω‐m), leaving the source of the deep EM anomaly unexplained. However, samples with low resistivities (7–20 Ω‐m) have been unexpectedly found in the cores from lower sections of the SS, depths possibly corresponding to that of the EM anomaly. These samples are characterized by low porosities (0.3–0.6%), normal bulk densities (2.78–2.81), and a porphyritic texture with a blackish matrix, suggesting carbon as the likely cause of the low resistivities.
Effects of non‐welded interfaces on guided SH‐waves
Authors: Nihei Kurt T. , Myer Larry R. , Cook Neville G. W. , Yi Weidong
Published: February 2004

The effects of non‐welded interfaces on guided SH‐waves are examined analytically and numerically using the displacement‐discontinuity model to describe the mechanical shear stiffnesses of the interfaces. A modal solution for guided SH‐waves is developed for a layer in non‐welded contact with underlying and overlying half‐spaces. For low interface stiffnesses, the modal solution degenerates to the SH‐plate wave solution and for high interface stiffnesses, to the Love channel wave solution. It is demonstrated that a single non‐welded interface separating two half‐spaces is incapable of supporting an SH‐interface wave. The effects of interface stiffness on the phase velocities and displacement profiles of guided SH‐waves are examined for a low velocity layer in non‐welded contact with bounding half‐spaces using the modal solution and a numerical boundary integral equation code. The results of this analysis demonstrate that the magnitude of the interface stiffness can have a first order effect on the velocities, amplitudes and displacement profiles of guided SH‐waves in a low velocity layer which should make these waves highly detectable in crosshole seismic surveys.
Are magnetite spherules capable of carrying stable magnetizations?
Authors: Xu Weixin , Van der Voo Rob , Peacor Donald R.
Published: February 2004

To determine if magnetite spherules extracted from ancient carbonate rocks can carry ancient remanent magnetizations, electron microscope observations and magnetic data have been obtained for more than 100 individual spherules extracted from the Jurassic Twin Creek limestone, Wyoming, and the Mississippian Leadville limestone, Colorado. Two categories of surface textures (smooth and patterned) correlate with different hysteresis parameters. Spherules with patterned surfaces (Group A) have ratios of saturation remanent magnetization to saturation magnetization (Msr/Ms) < 0.1 and ratios of remanent coercive force to coercive force (Hcr/Hc) mostly > 3. Most spherules with smooth surfaces (Group B) have 0.1 < Msr/Ms < 0.3 and Hcr/Hc< 3. The patterned surfaces consist of (1) parallel dendritic nets with units ≈ 1 μm wide, (2) platelets with widths of 1 to 3 μm, (3) mosaic surface units with diameters between 2 and 5 μm; each of these surface elements consists of a single crystal, as verified by selected‐area electron diffraction patterns showing sharp spots, whereas the spherules as a whole show multicrystalline patterns by X‐ray diffraction. The Msr/Ms and Hc values of group A increase with decrease in grain size; these Group A magnetite spherules are undoubtedly multi‐domain in character and are unlikely to carry stable ancient remanences. The smooth‐surfaced Group B spherules are not very abundant (< 8% of the entire population) and have pseudo‐single‐domain (PSD) or multi‐domain (MD) magnetic properties; they may carry ancient remanences, although we infer that single‐domain (SD), non‐spherical, submicrometer magnetite is the principal carrier of remanence in most carbonates.
Upper tropospheric humidity observations from Meteosat compared with short‐term forecast fields
Authors: Schmetz Johannes , van de Berg Leo
Published: February 2004

Monthly mean brightness temperature observations from the water vapor channel (WV: 5.7–7.1 μ m) aboard the geostationary weather satellite METEOSAT‐4 are presented for July 1992. The WV channel is sensitive to the atmospheric column water vapor in the upper troposphere above 600 to 500 hPa. The WV channel has been recalibrated with a radiative transfer model using quality controlled radiosondes. The observations are compared with brightness temperature calculations based on short‐term forecast fields (12 and 24 h) of the general circulation model of the European Centre for Medium Range Weather Forecasts (ECMWF). While the model humidity field closely resembles the observed large‐scale distribution it is too moist in the subtropics and slightly too dry in areas associated with the Inter Tropical Convergence Zone (ITCZ). A simple method is suggested that quantifies the moisture bias in the general circulation model by adjusting the model based brightness temperatures.
Decay of the virtual dipole moment during polarity transitions and geomagnetic excursions
Authors: Lu Lin Jin , Verosub Kenneth L. , Roberts Andrew P.
Published: February 2004

We have analyzed paleointensity data from five polarity transitions and geomagnetic excursions recorded by lava flows. We find a significant correlation between the logarithm of the virtual dipole moment and the angle between the virtual geomagnetic pole and the Earth's rotation axis. This correlation implies that any physical model for geomagnetic field behavior during transitions and excursions must address the question of how changes in direction are linked to changes in intensity. In addition, large changes in paleointensity may occur even when the virtual geomagnetic pole is still at high latitude so the concept of transitional direction must be redefined.
Observation of mass loading in the Io plasma torus
Authors: Brown Michael E.
Published: February 2004

Ground‐based high‐resolution spectra of emission from the Io plasma torus obtained during 53 nights of observation over a seven month period are used to measure the torus rotation speed and discern regions of the torus that are slowed by mass loading of newly ionized materials. The amount of torus slowing implies that between 2000 and 3000 kg sec−1 are being ionized by the torus. The slowing is spread azimuthally throughout the orbit of Io, suggesting that neutral materials emanating from Io are distributed around Jupiter much more uniformly than currently believed.