bluuebunny/crossref_metadata_2025 huggingface dataset:
Surficial slip distribution on the central Emerson fault during the June 28, 1992, Landers earthquake, California
Authors: McGill Sally F. , Rubin Charles M.
Published: September 2002

We present the results of our mapping of a 5.6‐km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right‐lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right‐lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left‐lateral or thrust displacement. The maximum net vertical displacement was 175 cm, east‐side‐up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike‐slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as 1 m or more over distances ranging from 1–2 km to a few tens of meters, suggesting that strains of the order of 10−1may have occurred locally within the surficial sediments. The long‐wavelength (kilometer‐scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.
Effect of lateral migration of melt on chemical compositions: Implications for the local variations of mid‐ocean ridge basalts
Authors: Ichihara M. , Ida Y.
Published: September 2002

The decompressional melting process involving dynamically induced migration of melt in the residual country rock is analyzed to formulate the effects of melt migration on the chemical compositions of mid‐ocean ridge basalt (MORB). It is rigorously proved that if the relative motion between melt and solid is unidirectional and steady, the composition of the melt is the same as that expected from the batch melting because it is determined by equations that are separable from those concerning the relative melt motion. The present proof is more general than the previous treatments and is applicable to any system consisting of arbitrary numbers of phases and components. The effect of lateral melt motion on the concentration of a minor component is formulated more specifically using two parameters. One of the parameters is the lateral gradient of melt flux that represents degree of convergence or divergence of melt in the flow. The other parameter that specifies the gradient of the chemical composition is introduced to evaluate the so‐called chromatographic effect that separates the minor component migration paths in the flow by their partition coefficients. The parameterization gives a good tool to predict the flow field from the known chemical variations. It is shown that some local variations of MORB compositions observed in individual mid‐ocean ridges can be modeled as a result of lateral melt migration convergent in some places and divergent in others.
Poisson's ratio structure of young oceanic crust
Authors: Collier J. S. , Singh S. C.
Published: September 2002

We have applied full waveform inversion to wide‐aperture seismic reflection data from the southern East Pacific Rise near 14°S. The data contain clear compressional wave and doubly converted shear wave arrivals that provide good constraints on the P and S‐wave velocities (Vp, Vs, and hence Poisson's ratio σ) and seismic attenuation (Qp, Qs) structure of seismic layer 2. Layer 2A is highly attenuating (Qp = 18–30 and Qs = 8–15) and layer 2B is moderately attenuating (Qp = 30–50 and Qs = 20–25). Our results show high σ at the seafloor and in layer 2A (σ = 0.48). Across the top of the 2A/B transition the rapid increase in Vp is accompanied by a sharp drop in σ to 0.25 within just 200 m of the seafloor. We perform simple calculations to gain an insight into the porosity and crack distribution with depth. These calculations suggest that porosity is in excess of 30% in layer 2A but reduces to 6–7% at the top of the 2A/B transition and to about 5% at a depth of 600 m below seafloor within layer 2B. Our results suggest that there is an increase in the average aspect ratio with depth across the 2A/B transition. The most likely explanation is that numerous thin cracks either mechanically close or are infilled at depth. Our results show there to be an abrupt change in the pore structure across the 2A/B transition which is consistent with a lithologic transition from extrusives to dykes but is equally consistent with a transition (mechanical or hydrothermal) within the extrusive pile.
The structure of Cretaceous oceanic crust of the NW Pacific: Constraints on processes at fast spreading centers
Authors: Reston T. J. , Ranero C. R. , Belykh I.
Published: September 2002

A 725 km long transect along a flow line in the NW Pacific provides new images of the internal structure of Cretaceous oceanic crust formed at fast spreading rates. Reflections from the Moho transition zone document changes in crustal travel time along the profile: variations with a wavelength of 100–150 km may representing fluctuations in the magma supply with a 2–3 m.y. periodicity; to the south the crust may be several kilometers thicker than “normal” in places, possibly resulting from increased magma supply due to the distal effects of the Shatsky hotspot. At about the depth expected for the boundary between seismic layers 2 and 3, sub‐horizontal reflections are imaged over much of the profile; the clearest are positive polarity and of an amplitude consistent with a reflection coefficient of ∼0.1, implying a sharp velocity and density discontinuity. Northward (ridgeward) dipping reflections in the lower crust are imaged over much of the profile, particularly toward the north (away from the region possibly affected by the hotspot). These reflections stop at the Moho reflection but die out perhaps 1 s beneath top basement; they probably represent lithological layering as predicted by models of ductile flow accompanying passive upwelling during plate separation, although they could represent secondary shears generated by basal drag during active mantle upwelling beneath the spreading center. The discrete character and, in places, regular spacing (every ∼8 km) of these features hint at a cyclicity in the layering and thus at some episodicity in magmatic processes over a timescale of 0.1–0.2 m.y.
Spatial distribution of hotspot material added to the lithosphere under La Réunion, from wide‐angle seismic data
Authors: Charvis Philippe , Laesanpura Agus , Gallart Josep , Hirn Alfred , Lépine Jean‐Claude , de Voogd Béatrice , Minshull Tim A , Hello Yann , Pontoise Bernard
Published: September 2002

Wide‐angle seismic lines recorded by ocean bottom and land seismometers provide a pseudo three‐dimensional investigation of the crust and upper mantle structure around the volcanically active hotspot island of La Réunion. The submarine part of the edifice has fairly low seismic velocities, without evidence for intrusives. An upper unit with a velocity‐depth gradient is interpreted as made of material erupted subaerially then transported and compacted downslope. Between this unit and the top of the oceanic plate, imaged by normal incidence seismic reflection, a more homogeneous unit indicated by shadow zones on several wide‐angle sections may correspond to lavas of a different nature, extruded underwater in the earlier phase of volcanism. Coincident wide angle and normal incidence reflections document that the oceanic plate is not generally downwarping toward the island but doming instead toward its southeastern part, with limited evidence for some intracrustal intrusion. Deeper in the lithosphere, the presence of a layer of intermediate velocity between the crust and mantle is firmly established. It is interpreted as resulting from the advection of hotspot magmatic products, possibly partially molten, and of a composition for which the crust is a density barrier. The extensive wide‐angle coverage constrains the extent of this body. It does not show the elongated shape expected from plate drift above a steady hotspot supply. Alternative propositions can hence be considered, for example, that La Réunion is caused by a solitary wave of hotspot material or by a young hotspot. The size of the underplate, 140 km wide and up to 3 km thick, corresponds to less than half the volume of the edifice on top of the plate.
Nonlinear shear instabilities of alongshore currents over barred beaches
Authors: Slinn Donald N. , Allen J. S. , Newberger P. A. , Holman R. A.
Published: September 2002

The nonlinear dynamics of finite amplitude shear instabilities of alongshore currents in the nearshore surf zone over barred beach topography are studied using numerical experiments. These experiments extend the recent study of Allen et al. [1996], which utilized plane beach (constant slope) topography by including shore‐parallel sandbars. The model involves finite‐difference solutions to the nonlinear shallow water equations for forced, dissipative, initial‐value problems and employs periodic boundary conditions in the alongshore direction. Effects of dissipation are modeled by linear bottom friction. Forcing for the alongshore currents is specified using a model formulated by Thornton and Guza [1986] (T‐G). Distinct classes of flows develop depending on the dimensionless parameter Q, the ratio of an advective to a frictional timescale. For Q greater than a critical value Qc the flows are linearly stable. For ΔQ=Qc–Q >0 the flow is unstable. For small values of ΔQ, equilibrated shear waves develop that propagate alongshore at phase speeds and wavelengths that are in agreement with predictions from linear theory for the most unstable mode. At intermediate values of ΔQ, unsteady vortices form and exhibit nonlinear interactions as they propagate alongshore, occasionally merging, pairing, or being shed seaward of the sandbar. At the largest values of ΔQ examined, the resulting flow field resembles a turbulent shear flow. A net effect of the instabilities at large AQ is to distribute the time‐averaged alongshore momentum from local maxima of the T‐G forcing, located over the sandbar and near the shore, into the region of the trough. The across‐shore structure of the time‐averaged alongshore current is in substantially better qualitative agreement with observations than that given by a steady frictional balance with T‐G forcing. The results point to the possible existence in the nearshore surf zone of an energetic eddy field associated with instabilities of the alongshore current.
Space‐time properties of radar sea spikes and their relation to wind and wave conditions
Authors: Frasier Stephen J. , Liu Yong , McIntosh Robert E.
Published: September 2002

Low‐grazing angle (LGA) radar sea spikes were observed with a high‐resolution, dual‐polarization, X band imaging radar deployed on the floating instrument platform (FLIP) during the Marine Boundary Layer Experiment (MBLEX) held off the California coast during April–May 1995. Spatiotemporal statistics of observed sea spike events are presented, including duration, velocity, and directional distributions. The dependence of these parameters on wind and wave conditions is compared to theoretical predictions and to similar measurements of breaking wave signatures obtained with passive acoustic techniques by Ding and Farmer [1994]. The density of sea spikes (events per unit time per unit area) and the fractional surface coverage are estimated as a function of friction velocity and compared to theoretical predictions. Though we find consistency between the dynamical aspects of sea spike events and of acoustic wave‐breaking signatures, we do not observe a predicted cubic u* dependence of sea spike density. Differences may be a consequence of the specific nature of low‐grazing angle scattering at X band (and higher) frequencies. We observe an approximately quadratic dependence on u* of sea spike fractional surface coverage which is insensitive to the choice of backscattered power threshold over a 9 dB range.
A numerical investigation of the transport process of dense shelf water from a continental shelf to a slope
Authors: Kikuchi Takashi , Wakatsuchi Masaaki , Ikeda Motoyoshi
Published: September 2002

We investigate the offshore transport process of dense shelf water, using a three‐dimensional, primitive equation model. We focus on the effects of bottom topography, in particular, inclination of a bottom slope from a continental shelf to a deep basin. For the numerical domain we use an idealized bottom topography in which the bottom deepens gradually from a shallow continental shelf region to a steep slope region. In the continental shelf region we use a salt flux which represents the typical brine rejection in a coastal polynya. Results of the numerical experiments show that dense shelf water is transported offshore by eddy flux and a dense plume. The transport by eddy flux occurs mainly over a continental shelf, while that by the dense plume occurs over a continental slope. A boundary between the regions where the above two processes are dominant corresponds locally to a shelf break. A salinity front is developed in the boundary over the shelf break, separating the dense shelf water from the offshore water. We also investigate the stability of the surface westward current over the shelf break front, using a simple analytical model. The analytical model investigation shows that shelf break topography plays an important role in determining a neutral point of the stability of the shelf break current and preventing dense shelf water from being transported farther offshore by eddy flux. We suggest that eddy activity on a continental shelf contributes not only to the development of the shelf break front but also to the water exchange between a continental shelf and a slope region.
Measuring inorganic nitrate species with short time resolution from an aircraft platform by dual‐channel ozone chemiluminescence
Authors: Tanner Roger L. , Valente Ralph J. , Meagher James F.
Published: September 2002

A measurement technique for determining nitrate (the sum of nitric acid and particulate nitrate) with a few seconds time resolution in plumes is needed to resolve within‐plume features. A technique using dual ozone‐chemiluminescent NO detectors with a selective nitrate scrubber in one sampling train is promising if used with an appropriate sampling inlet, and if nitrate is the desired analyte. We report the design of, and preliminary results from a dual channel ozone‐chemiluminescent system, each channel containing a gold‐CO catalyzed converter which reduces all odd nitrogen species (NOy) quantitatively to NO; one channel also contains a nylon filter to remove nitrate from the air stream prior to the converter (this signal is termed NOy*). This system was deployed successfully in a Bell 205 helicopter during the 1995 Southern Oxidants Study Nashville Ozone Study. The converters were mounted forward near the air intake, and zero air and calibration gases admitted simultaneously to both channels during flight operations. The difference signal between the two channels (NOy‐NOy*) indicated apparent nitrate levels in the sampled air with a time resolution of <5 s and a limit of detection of about 1 ppbv. Nitrate levels observed with this system in plumes and background air during the Nashville Ozone Study were highly correlated with ozone and varied from below detection limits to ≈20 ppbv. Nitrate levels were also highly correlated with the calculated difference between NOy and the sum of NO and NO2 (NOz). Higher nitrate levels as a fraction of NOz were found in power plant plumes (≥60%) compared with urban plumes (≈50%) and background air, consistent with apparently lower ozone production efficiencies in power plant plumes vis‐à‐vis urban plumes.
Sequential oxidation products from tropospheric isoprene chemistry: MACR and MPAN at a NOx‐rich forest environment in the southeastern United States
Authors: Nouaime G. , Bertman S. B. , Seaver C. , Elyea D. , Huang H. , Shepson P. B. , Starn T. K. , Riemer D. D. , Zika R. G. , Olszyna K.
Published: September 2002

Measurements of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and peroxymethacryloyl nitrate (MPAN) were made during the Southern Oxidants Study 1995 Nashville/Middle Tennessee Ozone Study at the Youth Inc. Ranch southeast of Nashville from June 29 to July 26. These measurements were made along with those of isoprene and its oxidation products methacrolein (MACR) and methyl vinyl ketone (MVK), other carbonyl compounds, and supporting measurements. This data set represents the first high‐frequency, simultaneous measurements of MPAN and its precursor, MACR as well as PPN and its precursor propanal. The NOx sensitivity of isoprene chemistry can be studied with data from this site because large and widely fluctuating levels of NOx were experienced as a result of the proximity to the Nashville urban center. Mean mixing ratios of PAN, PPN, MPAN, and MACR were 485, 50, 30, and 290 parts per trillion by volume respectively. The mean diurnal cycle of MPAN closely tracks that of MACR and was found to be considerably sharper than the mean diurnal cycles of PAN, PPN, and O3, showing that MPAN is closely dependent on the availability of MACR. Considerable levels of MPAN and MACR appear to develop at night above a nocturnal boundary layer and are partly responsible for a commonly observed morning increase. Early morning OH reaction with MACR also produces MPAN in the morning. With the high summer temperatures at Youth Inc., the MPAN lifetime is largely determined by thermal decomposition, although OH and O3 chemistry could substantially reduce the ambient lifetime. Additional loss mechanisms for MPAN and dependence on a single source make MPAN more sensitive to photochemical activity and NOx. than is PAN. Unless quickly advected to colder, less photochemically active regions of the atmosphere, the contribution of MPAN to O3 formation through long‐range transport of NOx is likely to be less significant in comparison with PAN and PPN. Its influence is more limited to local O3 production, so MPAN can be a useful indicator of local‐scale, active biogenic photochemistry.
Volatile organic compounds and isoprene oxidation products at a temperate deciduous forest site
Authors: Helmig Detlev , Greenberg Jim , Guenther Alex , Zimmerman Pat , Geron Chris
Published: September 2002

Biogenic volatile organic compounds (BVOCs) and their role in atmospheric oxidant formation were investigated at a forest site near Oak Ridge, Tennessee, as part of the Nashville Southern Oxidants Study (SOS) in July 1995. Of 98 VOCs detected, a major fraction were anthropogenic VOCs such as chlorofluorocarbons (CFCs), alkanes, alkenes and aromatic compounds. Isoprene was the dominant BVOC during daytime. Primary products from BVOC oxidation were methylvinylketone, methacrolein and 3‐methylfuran. Other compounds studied include the BVOCs α‐pinene, camphene, β‐pinene, p‐cymene, limonene and cis‐3‐hexenyl acetate and a series of light alkanes, aromatic hydrocarbons and seven of the CFCs. The correlation of meteorological parameters, with the mixing ratios of these different compounds, reveals information on atmospheric oxidation processes and transport. Long‐lived VOCs show very steady mixing ratio time series. Regionally and anthropogenically emitted VOCs display distinct diurnal cycles with a strong mixing ratio decrease in the morning from the breakup of the nocturnal boundary layer. Nighttime mixing ratio increases of CFCs and anthropogenic VOCs are suspected to derive from emissions within the Knoxville urban area into the shallow nocturnal boundary layer. In contrast, the time series of BVOCs and their oxidation products are determined by a combination of emission control, atmospheric oxidation and deposition, and boundary layer dynamics. Mixing ratio time series data for monoterpenes and cis‐3‐hexenyl acetate suggest a temporarily emission rate increase during and after heavy rain events. The isoprene oxidation products demonstrate differences in the oxidation pathways during night and day and in their dry and wet deposition rates.
Measurement of nitrogen oxide emissions from an agricultural soil with a dynamic chamber system
Authors: Roelle Paul , Aneja Viney P. , O'Connor J. , Robarge W. , Kim Deug‐Soo , Levine Joel S.
Published: September 2002

Biogenic soil emissions of nitric oxide (NO) were measured from an intensively managed agricultural row crop (corn, Zea mays) during a 4 week period (May 15 through June 9, 1995). The site was located in Washington County, near the town of Plymouth, which is in the Lower Coastal Plain of North Carolina. Soil NO flux was determined using a dynamic flowthrough chamber technique. The measurement period was characterized by two distinguishing features: an application of nitrogen (N) fertilizer at the midpoint of the experiment and a nontypical rainfall pattern. Average NO flux prior to the application of N fertilizer was 31.5 ± 10.1 ng N m−2 s−1, and more than doubled (77.7 ± 63.7 ng N m−2 s−1) after the application of a side‐dressing of N fertilizer. Average soil extractable nitrogen values did not change significantly following application of the side‐dressing of N fertilizer. We attribute this failure to detect a significant difference in soil extractable nitrogen following N fertilization to the method in which the fertilizer was applied, the subsequent rainfall pattern, and the technique of soil sampling. NO flux followed the same diurnal trend as soil temperature, with maximum NO emissions coinciding with maximum soil temperature, and minimum NO emissions coinciding with minimum soil temperature. NO flux was found to increase exponentially with soil temperature, but only after fertilization. Due to subsurface irrigation practices employed by the farmer, changes in soil water content were minimal, and no relation could be drawn between soil water content and NO flux. Simultaneous measurements of NOy, NO2, and NO emissions revealed that NO and NO2 emissions represent 86 and 8.7%, respectively, of NOy emissions leaving the soil. Simultaneous NO flux measurements made by a closed box flux technique, at the same site, revealed no statistically significant differences between the two different methodologies for measuring NO flux.
Meteorological conditions during the 1995 Southern Oxidants Study Nashville/Middle Tennessee Field Intensive
Authors: McNider Richard T. , Norris William B. , Song Aaron J. , Clymer Robert L. , Gupta Shekhar , Banta Robert M. , Zamora Robert J. , White Allen B. , Trainer Michael
Published: September 2002

As a background for other papers presented in this issue on the 1995 Southern Oxidants Study (SOS) Nashville/Middle Tennessee Field Intensive, the role of meteorology in the field study is reviewed. Descriptions of the meteorological observing systems are given, and the strategy behind the observational network is defined. The tools used in making forecasts and their use for operational decisions are described. In particular, the use in real time of a dynamic boundary layer model coupled with a Lagrangian plume model to forecast power plant and urban plumes is examined. The weather occurring during the field intensive is summarized and put into a climatological perspective. Specific attention is given to the episodes of July 1–3 and July 10–14, 1995, when some of the highest ozone values were recorded. The role of nocturnal, low‐level jets observed by the boundary layer wind profiler network in dispersing urban emissions into the regional background is explored.
Atmospheric chemistry and distribution of formaldehyde and several multioxygenated carbonyl compounds during the 1995 Nashville/Middle Tennessee Ozone Study
Authors: Lee Y.‐N. , Zhou X. , Kleinman L. I. , Nunnermacker L. J. , Springston S. R. , Daum P. H. , Newman L. , Keigley W. G. , Holdren M. W. , Spicer C. W. , Young V. , Fu B. , Parrish D. D. , Holloway J. , Williams J. , Roberts J. M. , Ryerson T. B. , Fehsenfeld F. C.
Published: September 2002

Airborne measurements of formaldehyde (FA), glycolaldehyde (GA), glyoxal (GL), methylglyoxal (MG), and pyruvic acid (PD) were made on board instrumented aircraft platforms, the Department of Energy G1 and National Oceanic and Atmospheric Administration P3 (FA only), during the 1995 Nashville/Middle Tennessee Ozone Study. FA data determined on these two aircraft during three intercomparison flights agreed to within ∼10%. The mean and median (in parentheses) concentrations observed within the boundary layer (<2000 m) for FA, GA, GL, MG, and PD were 4.2 (3.9), 0.78 (0.70), 0.07 (0.06), 0.14 (0.10), and 0.24 (0.23), respectively (all in parts per billion by volume (ppbv)). At the observed concentrations, FA accounted for a substantial fraction of the OH reactivity, comparable to isoprene and CO. Further, it served as an important free radical precursor, contributing 25–30% of the radical production during midday and even greater during morning and late afternoon periods. Source attribution of FA was assessed using measured concentrations of hydrocarbons, their reaction kinetics with the OH radicals, and FA yields. The results showed that isoprene was the dominant source of FA, responsible for ∼67%, methane and peroxyacetyl nitrate contributed equally at ∼13% each, and alkanes and alkenes which are largely of anthropogenic origin accounted for only ∼7%. This assessment based on reaction kinetics is consistent with the strong correlations (r > 0.8) observed between FA and two other isoprene products, GA and MG. Further, the magnitudes of the nonzero FA intercept exhibited in these correlation plots are found to qualitatively agree with the fraction of precursors that did not concomitantly produce GA and MG. Inspection of specific flights showed direct evidence of the dominance of isoprene as a precursor for FA, appreciable contribution of FA to CO, and negligible decay of FA overnight. Because of the dominant role isoprene plays as a precursor of FA, FA could be used as a proxy of isoprene for assessing the applicability of various versions of biogenic emission inventory.
Ozone production during an urban air stagnation episode over Nashville, Tennessee
Authors: Valente R. J. , Imhoff R. E. , Tanner R. L. , Meagher J. F. , Daum P. H. , Hardesty R. M. , Banta R. M. , Alvarez R. J. , McNider R. T. , Gillani N. V.
Published: September 2002

The highest O3 levels observed during the 1995 Southern Oxidants Study in middle Tennessee occurred during a period of air stagnation from July 11 through July 15. Extensive airborne (two fixed wing and one helicopter) and ground‐based measurements of the chemistry and meteorology of this episode near Nashville, Tennessee, are presented. In situ airborne measurements include O3, NOy, NO, NO2, SO2, CO, nitrate, hydrocarbons, and aldehydes. Airborne LIDAR O3 measurements are also utilized to map the vertical and horizontal extent of the urban plume. The use of multiple instrumented research aircraft permitted highly detailed mapping of the plume chemistry in the vertical and horizontal dimensions. Interactions between the urban Nashville plume (primarily a NOx and hydrocarbon source) and the Gallatin coal‐fired power plant plume (primarily a NOx and SO2 source) are also documented, and comparisons of ozone formation in the isolated and mixed urban and power plant plume are presented. The data suggest that during this episode the background air and the edges of the urban plume are NOx sensitive and the core of the urban plume is hydrocarbon sensitive. Under these worst case meteorological conditions, ambient O3 levels well over the level of the new National Ambient Air Quality Standard (NAAQS) for ozone (80 ppb) were observed over and just downwind of Nashville. For example, on July 12, the boundary layer air upwind of Nashville showed 60 to 70 ppb O3, while just downwind of the city the urban plume maximum was over 140 ppb O3. With a revised ozone standard set at 80 ppb (8 hour average) and upwind levels already within 10 or 20 ppb of the standard, only a slight increase in ozone from the urban area will cause difficulty in attaining the standard at monitors near the core of the urban plume during this type of episode. The helicopter mapping and LIDAR aircraft data clearly illustrate that high O3 levels can occur during stagnation episodes within a few kilometers of and even within the urban area. The extremely light boundary layer winds (1–3 m s−1) contributed to the creation of an ozone dome or blob which stayed very near to the city rather than an elongated plume. The small spatial scale of the zone of high O3 concentrations is mapped in detail demonstrating that the regulatory monitoring network failed to document the maximum O3 concentrations. Modelers using such regulatory data to test photochemical algorithms need to bear in mind that magnitude and frequency of urban ozone may be underestimated by monitoring networks, especially in medium‐sized urban areas under slow transport conditions. Finally, this effort shows the value of collaborative field measurements from multiple platforms in developing a more complete picture of the chemistry and transport of photochemical O3.
Polar stratospheric clouds climatology over Dumont d'Urville between 1989 and 1993 and the influence of volcanic aerosols on their formation
Authors: David C. , Bekki S. , Godin S. , Mégie G. , Chipperfield M. P.
Published: September 2002

The first polar stratospheric clouds (PSCs) climatology ever established from lidar data and relative to a specific site is presented here. It is based on lidar backscatter and depolarization measurements of PSCs carried out between 1989 and 1993 at Dumont d'Urville (66°S, 140°E), which is a primary station of the Network for Detection of Stratospheric Changes (NDSC). The climatology was subdivided based on the stratospheric sulphuric acid aerosol content (background aerosols in 1989–1991 and volcanic aerosols in 1992–1993 following the Mount Pinatubo eruption). PSCs were mainly observed in July and August. Very few water ice clouds (type II) were detected. Most of the PSCs tended to form around the peak in sulphuric acid aerosol, between 17 and 23 km in 1989–1991 and between 11 and 20 km in 1992–1993. This tendency suggests that sulphuric acid aerosols are very likely to act as condensation nuclei for PSCs. As shown by previous lidar studies [Browell et al, 1990], two type I subclasses were identified: depolarizing (nonspherical) particles (type Ia) and nondepolarizing (spherical) particles (type Ib). No type Ia PSCs were detected above the nitric acid trihydrate (NAT) saturation temperature, TNAT, lending support to the theory that NAT is the main component of type Ia PSCs. There was also no evidence of the existence of sulphuric acid tetrahydrate (SAT) in the data. Some type Ib PSCs were observed close to the frost point, showing that supersaturation with respect to NAT is a necessary, but not sufficient, condition for the existence of solid PSCs. No type Ib PSCs were clearly detected above TNAT in 1989–1991 whereas 18% of the PSCs seem to be found at temperatures above TNAT in 1992–1993. This difference might be linked to the HNO3 uptake by volcanic sulphuric acid particles starting at higher temperatures. The fraction of type Ia out of the total PSCs observations was lower in 1992–1993 than in 1989–1991. This difference was not found to be highly statistically significant.
Vertical profiles and horizontal transport of atmospheric aerosols and trace gases over central Ontario
Authors: Isaac G. A. , Banic C. M. , Leaitch W. R. , Anlauf K. G. , Couture M. D. , Liu P. S. K. , Macdonald A. M. , MacQuarrie K. I. A. , Puckett K. J. , Wiebe H. A.
Published: September 2002

The Canadian intensive measurement periods of the Eulerian Model Evaluation Field Study (EMEFS) were conducted in the summer of 1988 and the spring of 1990 in central Ontario, Canada. The project involved using instrumented research aircraft to measure vertical profiles of atmospheric aerosols and trace gases over special ground observing sites. Oxidant concentrations were often highest aloft. There were no strong diurnal variations in O3 and H2O2, suggesting that oxidant concentrations reported in this paper, as well as other species, seem to be most influenced by transport mechanisms rather than local chemical transformations. Aerosol and SO2 concentration vertical profiles tended to be similar to those of water vapor mixing ratio, showing a maximum near the surface, which points to a ground level source for these constituents. The inorganic aerosol was dominated by sulphate during the summer measurements, but particulate nitrate was important during the spring. The horizontal transport of these species was calculated for air with back trajectories from the north or south, showing transport to occur primarily from west to east for both cases, with components to the south or north, respectively. The sulphur is transported primarily as SO2 in the spring and about half as SO2 and half as SO4= in the summer. Air from the south is a source of particles, S, H2O, O3, H2O2 and NO2 to this region. Similarly, cloud water concentrations of sulphate and nitrate were higher with southerly trajectories, as were aircraft filter measurements of sulphate, nitrate, ammonium, and nitric acid.
On cloud radar and microwave radiometer measurements of stratus cloud liquid water profiles
Authors: Frisch A. S. , Feingold G. , Fairall C. W. , Uttal T. , Snider J. B.
Published: September 2002

We show a method for determining stratus cloud liquid water profiles using a microwave radiometer and cloud radar. This method is independent of the radar calibration and the cloud‐droplet size distribution provided that the sixth moment of the size distribution can be related to the square of the third moment. We have calculated these moments with a wide variety of in situ measurements and show that this is a reasonable assumption. Examples of droplet distributions that meet this requirement are the lognormal and gamma distributions.
Impact of the horizontal wind profile on the convective transport of chemical species
Authors: Wang Chien , Prinn Ronald G.
Published: September 2002

The impact of the vertical profile of the horizontal wind in the troposphere and lower stratosphere on the vertical transport of chemical species induced by deep convective events has been studied using a two‐dimensional cloud ensemble model. Seven horizontal wind profiles, including one observed during the Central and Equatorial Pacific Experiment (CEPEX) have been chosen. These represent typical wind profiles over the tropical Pacific including upper level westerly and easterly cases and have been applied to the model as initial conditions to carry out the sensitivity runs. We have found that the pattern of the shear in the horizontal wind in the vicinity of the tropopause plays a significant role in controlling the development of deep convective clouds. As a result, the fluxes of chemical species from the planetary boundary layer to the free troposphere and from the free troposphere to the lower stratosphere are very different for different assumed profiles. It has been found specifically that a moderate wind shear crossing tropopause favors vertically advective transport of chemical species. Strong positive shear, though enhancing turbulent mixing from the troposphere to the stratosphere, generates the weakest vertically advective transport primarily due to its influence in limiting the vertical development of convective turrets. In addition, we have found that the smoothed wind profile derived from a more fluctuating observed profile produces clear differences in cloud development and associated tracer vertical transport compared with the results of the run with the nonsmoothed profile.
A multi‐instrument approach for characterizing the vertical structure of aerosol properties: Case studies in the Pacific Basin troposphere
Authors: Redemann J. , Turco R. P. , Pueschel R. F. , Fenn M. A. , Browell E. V. , Grant W. B.
Published: September 2002

During February/March 1994, a series of aircraft‐based aerosol measurements were carried out in the Pacific Basin troposphere using a differential absorption lidar system deployed by NASA Langley, and optical spectrometer probes and a wire‐impactor system operated by NASA Ames. A modified Klett inversion algorithm was applied to extract altitude profiles of aerosol backscattering from the IR lidar signal. The algorithm that we have designed for this purpose utilizes the in situ aerosol measurements to normalize the lidar profile at the aircraft altitude and to supply the lidar ratio as a function of height. The lidar‐derived aerosol backscattering coefficients were then compared to the backscattering coefficients calculated from the in situ measurements. During several local aircraft descents, we found good agreement between the remote lidar and in situ results for the absolute value of the aerosol backscattering coefficient and its altitude variation only when we allowed for several layers with different aerosol refractive indices. The agreement validates our lidar calibration method and provides an indication of the variation in aerosol refractive index as a function of altitude. Two of the three case studies performed in this paper reveal layers of anthropogenic aerosols transported long distances into the Pacific Basin troposphere. A third case implies the existence of a layer of dustlike aerosol particles in the lower troposphere, most likely of Asian origin.
Analysis of Kelvin waves in High‐Resolution Doppler Imager and Microwave Limb Sounder stratosphere measurements using a constrained least squares method
Authors: Srikanth R. , Ortland D. A.
Published: September 2002

The equatorial stratospheric wind and temperature fields have been observed by the High‐Resolution Doppler Imager (HRDI) and the Microwave Limb Sounder (MLS) instruments, both aboard the Upper Atmospheric Research Satellite (UARS). These independent data sets are analyzed for Kelvin waves through a constrained least squares projection of the data sets onto a basis consisting of Hermite and Fourier functions. This method is developed specifically for HRDI wind measurements since conventional methods do not work well for the irregular nature of HRDI sampling. The recovered eastward spectra from HRDI zonal winds and MLS temperatures are compared for zonal periods from 5 to 10 days per cycle for zonal wavenumbers 1 and 2. The vertical wavelengths of each Kelvin wave event in the two fields compare well. The temperature and the zonal wind fields are not in exact quadrature due to the first‐order effects of dissipation, density gradient, and shear. The observed values of zonal wind‐temperature correlation and the vertical flux of zonal momentum are studied using a numerical model which involves these first‐order effects.
Intercomparison of two stratospheric analyses: Temperatures relevant to polar stratospheric cloud formation
Authors: Pawson Steven , Krüger Kirstin , Swinbank Richard , Bailey Michael , O'Neill Alan
Published: September 2002

Two independent daily stratospheric data sets are compared for 16 northern winters. The objective is to assess the consistency of temperatures low enough for polar stratospheric cloud (PSC) formation at 50 hPa. The first data set is the subjective analysis produced from the radiosonde network at the “Freie Universität Berlin” (FUB), which is constrained by hydrostatic and thermal wind balance. The second is the satellite‐based analysis of geopotential height, compiled from the TIROS Operational Vertical Sounding system by the United Kingdom Meteorological Office; temperatures are derived from the hypsometric equation. The stratospheric sounding units (SSU) provide most of the stratospheric data in that system. The FUB data are generally colder, particularly at low temperatures, but there is a large dispersion about the mean difference. The uncertainties of the values of the lowest temperatures are around 1 K and 2 K in the mean and rms, respectively. There may be a geographical bias in the data sets. There is a clear relationship between the vertical temperature gradient and the difference between the two data sets, the satellite‐derived values becoming relatively colder when the temperature decreases at pressures lower than 50 hPa. Regarding PSC formation: adequately low temperatures occur more often in the FUB data, but on 25% of winter days the areas Aτ where PSCs might form are larger in the SSU data. Seasonally integrated values of Aτ show a fairly good agreement between the two data sets, the satellite‐derived values generally being smaller. Both systems give stable and consistent estimates of the areas of low temperature at 50 hPa. On the basis of data quality alone, it is not possible to recommend either analysis system in preference to the other for studies of the coldness of the polar stratosphere.
Inventorying emissions from nature in Europe
Authors: Simpson David , Winiwarter Wilfried , Börjesson Gunnar , Cinderby Steve , Ferreiro Antonio , Guenther Alex , Hewitt C. Nicholas , Janson Robert , Khalil M. Aslam K. , Owen Susan , Pierce Tom E. , Puxbaum Hans , Shearer Martha , Skiba Ute , Steinbrecher Rainer , Tarrasón Leonor , Öquist Mats G.
Published: September 2002

As part of the work of the Economic Commission for Europe of the United Nations Task Force on Emission Inventories, a new set of guidelines has been developed for assessing the emissions of sulphur, nitrogen oxides, NH3, CH4, and nonmethane volatile organic compounds (NMVOC) from biogenic and other natural sources in Europe. This paper gives the background to these guidelines, describes the sources, and gives our recommended methodologies for estimating emissions. We have assembled land use and other statistics from European or national compilations and present emission estimates for the various natural/biogenic source categories based on these. Total emissions from nature derived here amount to ∼1.1 Tg S yr−1, 6–8 Tg CH4yr−1, 70 Gg NH3(as N) yr−1, and 13 Tg NMVOC yr−1. Estimates of biogenic NOxemissions cover a wide range, from 140 to 1500 Gg NOx(as N) yr−1. In terms of relative contribution to total European emissions for different pollutants, then NMVOC from forests and vegetation are clearly the most important emissions source. Biogenic NOxemissions (although heavily influenced by nitrogen inputs from anthropogenic activities) are very important if the higher estimates are reliable. CH4from wetlands and sulphur from volcanoes are also significant emissions in the European budgets. On a global scale, European biogenic emissions are not significant, a consequence of the climate and size (7% of global land area) of Europe and of the destruction of natural ecosystems since prehistoric times. However, for assessing local budgets and for photochemical oxidant modeling, natural/biogenic emissions can play an important role. The most important contributor in this regard is undoubtedly forest VOC emissions, although this paper also indicates that NMVOC emissions from nonforested areas also need to be further evaluated. This paper was originally conceived as a contribution to the collection of papers arising as a result of the Workshop on Biogenic Hydrocarbons in the Atmospheric Boundary Layer, August 24–27, 1997. (Several papers arising from this workshop have been published inJournal of Geophysical Research, 103(D19) 1998.)
JIM: A time‐dependent, three‐dimensional model of Jupiter's thermosphere and ionosphere
Authors: Achilleos N. , Miller S. , Tennyson J. , Aylward A. D. , Mueller‐Wodarg I. , Rees D.
Published: September 2002

We present the Jovian Ionospheric Model (JIM), a time‐dependent, three‐dimensional model for the thermosphere and ionosphere of Jupiter. We describe the physical inputs for the hydrodynamic, thermodynamic and chemical components of the model, which is based on the UCL Thermosphere Model of Fuller‐Rowell and Rees [1980]. We then present the results of an illustrative simulation in which an initially neutral homogeneous planet evolves for approximately 4 Jovian rotations, under the influence of solar illumination and auroral (electron) precipitation at high latitudes. The model shows that solar zenith angle, auroral activity, ion recombination chemistry and, to a lesser degree, magnetic field orientation, all play a role in forming the dayside and nightside global ionization patterns. We compare auroral and nonauroral/equatorial ionospheric compositions and find the signature of ion transport by fast winds. We also include a localized “spot” of precipitation in our model and comment on the associated ionization signatures which develop in response to this Io‐like aurora. The simulation also develops strong outflows with velocities up to ∼600 m s−1 from the auroral regions, driven mainly by pressure gradients. These pressure gradients, in turn, arise from the differences in chemical composition between the auroral and nonauroral upper thermospheres, as evolution proceeds. This preliminary study indicates a strong potential for JIM in analysis of two‐dimensional image data and simulation of time‐dependent global events.
Paleoclimatic Significance of Eolian Carbonates Supplied to the Japan Sea during the Last Glacial Maximum
Authors: Oba Tadamichi , Pedersen Thomas F.
Published: September 2002

Laminated sediments deposited under anoxic bottom waters in the Japan Sea during the last glacial maximum (LGM) contain extremely well preserved calcareous microfossils and eolian carbonates. The radiocarbon age‐difference between bulk sediment and monospecific planktonic foraminifera in discrete laminae from a core in the southern Japan Sea implies that ∼40% of the total carbonates in the sediments at the LGM are of eolian origin. Extrapolation of this result yields a rate of supply of eolian carbonates of ∼2800 tons d−1 to the entire Japan Sea during the LGM. The climatic significance of this flux potentially lies in its broader geographic extension, particularly in the interaction of the carbonate‐bearing dust with shallow, corrosive North Pacific waters and with rain in the atmosphere. By increasing the alkalinity of such waters and by enhancing the biological pump the dust flux could have increased CO2 absorption by both the ocean and rain during the LGM.
High‐frequency over‐the‐horizon radar and ionospheric backscatter studies in China
Authors: Li Le‐Wei
Published: September 2002

China is one of the countries that employs high‐frequency over‐the‐horizon radars for both military and civil applications. The first Chinese high‐frequency over‐the horizon backscatter radar was developed in the 1970s. This paper briefly introduces the first Chinese over‐the‐horizon backscatter radar system and reviews ionospheric backscatter and propagation studies in China. The paper discusses the motivation for establishing over‐the‐horizon radar systems in China, the experimental system, target recognition and detection,and estimation of over‐the‐horizon radar availability. Observations of aircraft, large‐scale traveling ionospheric disturbances, and the effects of a remote nuclear explosion are also presented. Finally, the real‐time Chinese ionosonde network and frequency predictions using backscatter ionograms are discussed.