bluuebunny/crossref_metadata_2025 huggingface dataset:
Chlorophyll modulation of sea surface temperature in the Arabian Sea in a mixed‐layer isopycnal general circulation model
Authors: Nakamoto S. , Kumar S. Prasanna , Oberhuber J. M. , Muneyama K. , Frouin R.
Published: September 2002

Remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) are used to estimate biological heating rate and investigate the biological modulation of the sea surface temperature (SST) in a bulk mixed layer model, embedded in the ocean isopycnal general circulation model (OPYC). A higher abundance of chlorophyll in October than in April in the Arabian Sea increases absorption of solar irradiance and heating rate in the upper ocean, resulting in decreasing the mixed layer thickness and lowering temperatures in the layers below the mixed layer than they would be under clear water condition. These changes in the model mixed layer were consistent with Joint Global Ocean Flux Study (JGOFS) observations during the 1994–1995 Arabian Sea experiment.
Loading‐unloading processes in the nightside ionosphere
Authors: Kallio E. I. , Pulkkinen T. I. , Koskinen H. E. J. , Viljanen A. , Slavin J. A. , Ogilvie K.
Published: September 2002

The loading‐unloading processes during magnetospheric substorms are examined using the ’IL index’ from the IMAGE magnetometer chain together with solar wind and IMF data from the WIND spacecraft. The IL index is a local, midnight sector, AL index. Energy input throughout the substorm is evaluated by integrating the epsilon parameter from the start of the growth phase until the end of the substorm. Energy dissipated in the ionosphere is estimated by integrating the IL index from the substorm onset to the end of the substorm. We show that the best correlation with the energy dissipated in the ionosphere is given by the energy input to the system after the substorm onset. Hence, we conclude that the energy loaded during the growth phase is necessary for the magnetospheric reconfiguration before the substorm onset, but that the size of the substorm as measured by the IL index is mostly governed by the direct energy input during the expansion phase.
Galactic cosmic ray diurnal modulation, interplanetary magnetic field intensity and the planetary index Ap
Authors: Ahluwalia H. S.
Published: September 2002

We have studied the data strings for the limiting rigidity (Rc) for the galactic cosmic ray (GCR) solar diurnal anisotropy, the interplanetary magnetic field (IMF) intensity (B), and the planetary index Ap for the period 1963 to 1998. The study covers three sunspot number (SSN) cycles (20, 21, 22). Our analysis brings out some of the steady state characteristics of the long term changes in Rc and other data strings and their interrelationships. Among other things, we relate the observed changes in Rc values to changes in B which are not related to SSN; the largest value of Rc occurs near 1982 when B has a high value 3 years away from SSN maximum for cycle 21. Rc bears a linear correlation with B and Ap but shows a low correlation with the power in the low frequency turbulence in IMF. The fit parameters with Ap data may be used to compute the values of Rc when in situ measurements of B do not exist; they may be applied to the cosmic ray data (available since 1937) to compute the amplitude and the phase of the diurnal anisotropy and to estimate more accurately the values of the key heliospheric transport parameters at high GCR rigidities near earth's orbit.
Thin current sheet evolution as seen in observations, empirical models and MHD simulations
Authors: Pulkkinen T. I. , Wiltberger M.
Published: September 2002

The inner and midtail current sheet is examined during a substorm on Dec 10, 1996 using multispacecraft observations, empirical models, and global MHD simulations. Both the simulation and empirical magnetic field model show good agreement with observations, which substantially increases the confidence in both methods. Both locate the thin current sheet inner edge at ∼7 RE, and give a scale size of ∼15 RE in tailward and cross‐tail directions. The MHD simulation confirms the empirical model result that the thin current sheet remained stable after a local auroral breakup and indicates that the activity followed from flow channels generated at ∼40 RE independent of the thin current sheet evolution closer to the Earth.
Amplitude variations of 1470‐year climate oscillations during the last 100,000 years linked to fluctuations of continental ice mass
Authors: Schulz Michael , Berger Wolfgang H. , Sarnthein Michael , Grootes Pieter M.
Published: September 2002

We describe amplitude variations of a 1470‐year (y) signal in the oxygen‐isotope record from the GISP2 ice‐core as a function of continental ice mass as recorded in sea‐level variations. The 1470‐y signal is closely tied to Dansgaard‐Oeschger interstadial events, which perturbed the climate system on a global scale. Large‐amplitude 1470‐y oscillations occur only if continental ice mass exceeds a threshold level, equivalent to sea level at approximately −45 m and are tied to times of change in ice mass. Minima of the 1470‐y signal in the Greenland ice are associated with short time intervals of relatively stable phases of sea level and with reduced climate variability in the entire periodicity range between approximately 550–5000 y.
Under the volcano: A new dimension in Ar‐Ar dating of volcanic ash
Authors: Smith Patrick E. , Evensen Norman M. , York Derek
Published: September 2002

A significant part of the history of the Greek island of Kos has been decoded from a handful of volcanic ash by argon‐argon laser probe dating of single crystals of the minerals sanidine, plagioclase and quartz. On a 3‐D argon isotope plot, the data define six straight lines, corresponding to four distinct volcanic events from 161 to 1728 ka. All four events produced plagioclase crystals, whose ages and Ca/K ratios are consistent with the known evolution of the rest of the Aegean arc. Sanidine appeared only in the final eruption at 161 ka. The joint occurrence of quartz and plagioclase at a 925 ka event implies that quartz did not reside for millennia in the magma, as has been suggested for quartz from the Bishop Tuff, California. The step‐heated cooling age of a schist fragment from the ash provides the first radiometric evidence for ∼250 Ma crust under the volcano.
Distribution of dicarboxylic acids and carbon isotopic compositions in aerosols from 1997 Indonesian forest fires
Authors: Narukawa M. , Kawamura K. , Takeuchi N. , Nakajima T.
Published: September 2002

Fine aerosol particles collected in Southeast Asia during 1997 Indonesian forest fires were studied for the concentrations of total carbon (TC), water‐soluble organic carbon (WSOC) and low molecular weight dicarboxylic acids (C2‐C12) as well as carbon isotopic ratios of TC (δ13CTC). TC and WSOC showed a large increase during the heavy forest fire event. At the same period, dicarboxylic acids, dominated by oxalic (C2) followed by succinic (C4) and malonic (C3) acids, also showed a concentration increase. Furthermore, the δ13CTC showed a decrease from ca. −25.5 to −27.5‰ during an intensified forest fire event, suggesting an addition of organic aerosols derived from C3 plants whose δ13C are lighter. These results indicate that the aerosol particles in Southeast Asia were significantly affected by the combustion processes of vegetations during the 1997 Indonesian forest fires that were extensively induced by El Ninõ event.
Evidence of convection as a major source of condensation nuclei in the northern midlatitude upper troposphere
Authors: Wang Y. , Liu S. C. , Anderson B. E. , Kondo Y. , Gregory G. L. , Sachse G. W. , Vay S. A. , Blake D. R. , Singh H. B. , Thompson A. M.
Published: September 2002

We examine concurrent measurements of CN (size > 8 nm), NO, and NOy in the upper troposphere over the North Atlantic during the SONEX Experiment (Oct.–Nov., 1997). High CN and NOy, observations are attributed largely to the enhancement in convective outflow. Using the ratio of NO/NOy as a chemical clock, we estimate that dilution of convective high‐CN plumes is rapid (on a time scale of < 2 days) and accounts for a large fraction of elevated CN concentrations above the background. We estimate that less than 7% of observed high‐CN (> 10000 cm−3) plumes may be attributed to aircraft emissions. The contribution by aircraft emissions to upper tropospheric CN concentrations is estimated to be significantly higher than 7% because aircraft plumes dilute much faster than convective plumes and hence are sampled less frequently.
The impact of rising atmospheric CO2 on Simulated sea ice induced thermohaline circulation variability
Authors: Holland Marika M. , Brasket Aaron J. , Weaver Andrew J.
Published: September 2002

The impact of rising atmospheric CO2 levels on the sea ice induced low frequency variability of the North Atlantic climate is examined using a coupled ice/ocean/atmosphere model. In particular, we focus on thermohaline circulation variability forced by fluctuations in ice export from the Arctic basin. Under 2XCO2 conditions, the thermohaline circulation variance is reduced to 7% of its simulated value under present day forcing. This decrease is caused by relatively low ice export variability and changes in the primary ice melt location in the northern North Atlantic under 2XCO2 conditions.
Discrete Field Line Resonances and the Alfvén Continuum in the Outer Magnetosphere
Authors: Mathie R. A. , Menk F. W. , Mann I. R. , Orr D.
Published: September 2002

Using Pc5 pulsation events observed with the IMAGE magnetometer array, we demonstrate that mHz frequency field line resonances (FLRs) represent local enhancements in the background Alfvén continuum of field line eigenfrequencies. By comparing resonance profiles for a typical event with the continuum frequency profile determined using cross‐phase techniques, we show that pulsation frequencies as low as 1–2 mHz can couple to FLRs on high latitude closed field lines. We also suggest that the transition to open field lines on days of higher geomagnetic activity may lead to a breakdown in pulsation characteristics at the highest latitudes of the IMAGE array. In addition, we show evidence of the U‐shaped diurnal variation in field line eigenfrequency and suggest that this is primarily due to field line stretching, especially on the magnetosphere flanks.
Type U burst and CME in the solar wind
Authors: Leblanc Yolande , Dulk George A. , Kaiser Michael L. , Bougeret Jean‐Louis
Published: September 2002

A type U burst was observed on 22 June 1998 with the WAVES radio receivers on the Wind spacecraft. It descended in frequency from 5 MHz to the turning frequency of about 1 MHz. It is extremely rare that a U burst is observed at such a low frequency, well out in the solar wind. Using a density model to convert frequency to radial distance we find that the radio emission started at 3 Ro, and that the electron stream turned back toward the Sun at about 8 Ro. The probable origin of the energetic electrons was in a B 6.8 X‐ray flare that was coincident with the onset time of the U burst. A series of images by the LASCO coronagraph show a slow (214 km/s) CME in progress on the west limb whose front was at 9 Ro at the time of the U burst. As no stable magnetic loops exist at radial distances such as 8–9 Ro, we attribute the U burst to a stream of energetic electrons accelerated in an active region at the footpoint of one leg of the expanding arch of the CME.
Forecasting auroral electrojet activity from solar wind input with neural networks
Authors: Weigel R. S. , Horton W. , Tajima T. , Detman T.
Published: September 2002

Neural networks are developed for reconstructing the chaotic attractor in the nonlinear dynamics of the solar wind driven, coupled magnetosphere‐ionosphere (MI) system. Two new methods which improve predictive ability are considered: a gating method which accounts for different levels of activity and a preconditioning algorithm which allows the network to ignore very short time fluctuations during training. The two networks are constructed using the Bargatzeet al.[1985] substorm database that contains solar wind speed and interplanetary magnetic field (IMF) along with ionospheric electrojet index, AL. Both networks are found to produce improvements in predictability, and the significance of the performance increase of the gated network is demonstrated using the bootstrap model testing method.
Shear‐wave structure of the lithosphere above the Hawaiian Hot Spot from two‐station Rayleigh wave phase velocity measurements
Authors: Priestley Keith , Tilmann Frederik
Published: September 2002

We have measured fundamental mode Rayleigh wave phase velocity dispersion from seismograms of five earthquakes recorded at stations on the islands of Hawaii and Oahu and inverted these data for upper mantle velocity structure. The seismic lithosphere of the velocity model is 88±7 km thick, which is similar to that of 80–90 Myr oceanic lithosphere, indicating that no significant lithospheric thinning takes place above the mantle plume. Below the lithosphere the shear wave velocity decreases to ∼4.0 km s−1. The seismic model is consistent with the structure of the Hawaiian plume model of Watson and McKenzie [1991] which has a 72‐km thick mechanical boundary layer with the shallowest melting occurring at 82 km depth. The difference between the dispersion measured on the Hawaii‐Oahu path and that observed by Woods and Okal [1996] on the Oahu‐Midway path can be explained by the cooling of the injected hot plume material.
Daytime variation of marine stratocumulus microphysical properties as observed from geostationary satellite
Authors: Greenwald Thomas J. , Christopher Sundar A.
Published: September 2002

Daytime changes in the droplet effective radius (re) and cloud liquid water path (LWP) were examined over a large area of marine stratocumulus off the coast of California over a six‐day period using Geostationary Operational Environmental Satellite (GOES) 9 imager measurements. Amplitude and phase of the first harmonic of the Fourier series were used to represent the daytime cycle. Complex spatial variation in the amplitude was found. Mean amplitudes were 0.65 µm (re) and 13.8 g m−2 (cloud LWP). For cloud LWP the cycle peaked predominantly in the morning while re maxima occurred in both morning and afternoon. While attention has focused on the re afternoon maximum, these observations show that in fact the morning maximum is more common and has a stronger cycle, underscoring the poorly understood nature of the diurnal cycle of marine stratocumulus microphysical properties.
In situ ground deformation measurements from the summit of Axial Volcano during the 1998 volcanic episode
Authors: Fox Christopher G.
Published: September 2002

Since September 1987, seafloor instrumentation monitoring ground deformation has been maintained on the summit of Axial Volcano on the central Juan de Fuca Ridge. During a January 1998 volcanic episode, pressure records from the central caldera showed a significant increase in pressure, indicating caldera subsidence of over 3 m. This observed subsidence is interpreted to represent volcanic deflation as magma is erupted and/or injected into the volcanic flanks. Temperature anomalies of nearly 0.45°C were also observed. A comparison of the subsidence record with hydroacoustic recordings indicates a continuous volcanic tremor signal coincident with the subsidence event. The time‐coincidence of subsidence of the summit caldera with migration of epicenters into the volcanic rift zones confirms that during the 1998 episode, the volcanic flanks were supplied by lateral dike injection from a central magma body, rather than locally derived magma sources.
Two‐fluid theory of the drift kink instability
Authors: Daughton William
Published: September 2002

A simple two‐fluid theory of the drift kink instability is developed. The validity of the theory is restricted to the regime where the ion gyroradius is small in comparison with the sheet thickness ρi ≪ L and wavelength ρiky ≪ 1. Analytic expressions are derived for the real frequency and growth rate. For the limited region of parameter space where two‐fluid theory is applicable, the analytic expressions are in excellent agreement with a full Vlasov solution [Daughton, 1999].
Magnetotail waveguide: Fast and Alfvén waves in the plasma sheet boundary layer and lobe
Authors: Allan W. , Wright Andrew N.
Published: September 2002

Numerical simulations of MHD wave propagation and coupling in a realistic magnetotail are presented. Fast mode waves are observed to disperse and couple resonantly to Alfvén waves over a broad layer rather than on an isolated field line. Indeed, the layer is likely to be so broad as to include the entire tail lobe as well as the plasma sheet boundary layer (PSBL). It appears that small ky modes (where ky is the cross‐tail wave number) will provide the most efficient coupling as they will tend to propagate along the magnetotail field lines rather than across them and out of the tail boundaries. (Moreover, it is only small ky fast modes that will be able to penetrate the lobe.) Alfvén waves in the PSBL are shown to phase mix rapidly resulting in strong field‐aligned currents with an equatorward phase motion. These properties are in agreement with observations of optical auroral emissions. The lobe Alfvén waves do not phase mix, and are not expected to excite optical emissions. They may, however, provide a significant ponderomotive force and could account for the transport of oxygen ions from the ionosphere into the distant tail lobes.
Constraints on the Kurile slab from shear wave residual sphere analysis
Authors: Pankow Kris L. , Lay Thorne
Published: September 2002

We analyze residual spheres for teleseismic S wave arrival times from 10 intermediate and deep focus earthquakes in the Kurile subduction zone. Long‐period WWSSN and CSN recordings of transverse component S and ScS arrivals provide good azimuthal coverage for each event, with arrival time estimates that compare well with short‐period observations. In order to isolate the near‐source structure, substantial lower mantle and receiver path effects are suppressed both by using empirical station/path statics derived from S, sS, ScS, and sScS arrivals for a total of 28 northwestern Pacific events and by constructing differential residual spheres. Ray tracing through three‐dimensional aspherical shear velocity models supports the inferred large magnitude of the deep mantle and near receiver effects, although existing models do not appear to provide accurate corrections. The events are relocated in the PREM structure, and a modest spatial smoothing of the residuals is applied. The resulting residual spheres are modeled using a finite difference travel time method that accounts for three‐dimensional ray path perturbations. Our starting models are derived from slab structures determined by previous P wave residual sphere analyses. We explore the compatibility of the P and S wave observations to constrain the Vs/Vp velocity ratio of the slab and to test whether the S wave arrival times place additional constraints on the slab geometry. The modeling supports the previous results favoring penetration of the Kurile slab to at least 800 km depth for most of the length of the arc, with some evidence that the northern portion of the slab broadens by as much as a factor of 3 upon entering the lower mantle. The preferred slab shear velocity models have relatively low (2–3%) shear velocity contrasts below 670 km depth, which can be accounted for by slab temperature reductions of 300°–400°.
Hysteresis and two‐dimensional nonlinear wave propagation in Berea Sandstone
Authors: Xu Heming , Day Steven M. , Minster Jean‐Bernard H.
Published: September 2002

We have further developed a two‐dimensional endochronic constitutive model applicable to rock in the intermediate strain regime, i.e., approximately 10−6 to 10−3, where nonlinear losses, pulse distortion, and harmonic distortions have been documented in the laboratory. An accurate and efficient computation algorithm has been established and used to fit a set of triaxial laboratory data on Berea Sandstone, obtained by G. N. Boitnott of New England Research, Inc., including nonlinear hysteresis for both hydrostatic compression and shear deformation. The constitutive model has been incorporated into a two‐dimensional pseudospectral scheme for simulating nonlinear wave propagation. We compare our numerical pseudospectral scheme with the perturbation solutions to nonlinearly elastic plane wave propagation and find that the two solutions are in close agreement. Applying the numerical scheme to the endochronic constitutive model for Berea Sandstone, we find the following results, which confirm and extend previous results obtained with a one‐dimensional model: (1) nonlinear propagation from a monochromatic source excites odd harmonics of the source frequency, (2) the interaction of two monochromatic wave fields leads to energy transfer to other bands corresponding to various combinations of the two source frequencies, (3) amplitudes of the harmonics change with distance and show a trade‐off between nonlinearity, intrinsic attenuation (hysteresis), and geometrical spreading, (4) for a broadband pressure source, energy is transferred from the principal band to a higher band at the expense of the components at intermediate frequencies; this is diagnostic of nonlinear interactions, and (5) the harmonic amplitude and energy transfer increase nonlinearly with strain amplitude; i.e., higher strain levels lead to higher energy exchange. These simulations of harmonic generation, interaction, and band expansion, based on a model developed from quasistatic experimental observations, agree with dynamic experimental observations.
Equation of state and strength of natural majorite
Authors: Kavner A. , Sinogeikin S. V. , Jeanloz Raymond , Bass J. D.
Published: September 2002

The bulk modulus of a natural sample of cubic majorite, one of the primary components of the Earth's transition zone, has been determined by two independent methods: quasi‐hydrostatic compression in the diamond anvil cell and Brillouin spectroscopy at room pressure. The two measurements agree well, and together yield a zero‐pressure isothermal bulk modulus KOT = 162.7 (±3.3) GPa, and a pressure derivative KOT = 6.6 (±0.8). Additional compression experiments under nonhydrostatic conditions show that majorite supports shear stresses of at least 2 to 3 GPa at pressures of 7–11 GPa, among the highest values yet documented in silicates or oxides at comparable pressures. These results imply a high strength for majorite, suggesting that the transition zone could be strong to a degree that may influence deformation and heat transfer within the Earth.
Sources of aerosol sulphate at Alert: Apportionment using stable isotopes
Authors: Norman A. L. , Barrie L. A. , Toom‐Sauntry D. , Sirois A. , Krouse H. R. , Li S. M. , Sharma S.
Published: September 2002

From July 1993 to September 1994, seasonal variations in the sources of SO42− aerosols in the Arctic lower atmosphere at Alert, Canada, (82°30′N, 62°20′W) were investigated using the sulphur isotope abundance of as little as 10 μg of sulphur analyzed by combustion‐flow isotope‐ratio mass spectrometry. In conjunction with air mass trajectories and in parallel with measurements of aerosol composition, the sulphur isotope composition was used to discern sources of aerosol SO42−. Total SO42− is composed of sea‐salt SO42−, marine biogenic, and nonmarine SO42−. From June through September the fraction of biogenic SO42− in the non‐sea‐salt (nss) component ranged from 0.09 to 0.40 with an average of 0.31 ± 0.11. Summertime nonmarine SO42− is likely anthropogenic in origin since it is isotopically indistinguishable from SO42− in the polluted winter/spring period of arctic haze (δ34S = +5‰). In summer there was no significant difference in isotope composition of aerosol sulphate between air which recently traversed Eurasia and the Arctic Ocean and air arriving from North America. In contrast to summer and late winter/spring, δ34S values for nonmarine SO42− in fall and early winter were often less than +5‰. These isotopically light samples were divisible into two groups: (1) those associated with air mass trajectories potentially affected by North American soils and/or smelters and (2) three weekly samples between October and December which could be attributed to fractionated sea‐salt aerosol formed on refrozen Arctic Ocean leads. For the latter the ratio of SO42−/Na was estimated to be a factor of 3.6 lower than in bulk seawater. From November to May, nonmarine aerosol SO42− was apportioned into 10 aerosol components using positive matrix factor analysis of 18 aerosol ions and trace elements [Sirois and Barrie, this issue]. In turn, a multiple linear regression of δ34S values against the scores of the components was used to predict the isotope composition of six components. It was concluded that the main mass of anthropogenic SO42− had a δ34S value near +5‰ and that biogenic SO42− had a δ34S of +16 ± 3.9‰. Reasonable agreement between model results and sulphur isotope measurements at Alert show that SO42− apportionment using positive matrix factor analysis is a reasonable approach which gives realistic results.
Carbon isotopic compositions of C2‐C5 hydrocarbons and methyl chloride in urban, coastal, and maritime atmospheres over the western North Pacific
Authors: Tsunogai Urumu , Yoshida Naohiro , Gamo Toshitaka
Published: September 2002

C2‐C5 non‐methane hydrocarbons (NMHCs) and methyl chloride in the remote maritime atmosphere over the western North Pacific are analyzed in regard to their variation of mixing ratio and 13C/12C ratio (δ 13C), together with those in polluted urban (Nagoya and Yokohama) and coastal (Tokyo Bay) atmospheres in Japan. NMHCs show large atmospheric mixing ratio differences between urban (coastal) and maritime atmospheres probably due to emission from urban areas and degradation within the maritime atmosphere. Reflecting isotopic fractionation during the degradation within the maritime atmosphere, ethane shows large and systematic δ13C variation between urban (around −27‰ Peedee belemnite(PDB)) and maritime atmospheres (up to −22‰ PDB). Except for ethane, however, alkanes show small isotopic variation around δ13C = −27±2‰ PDB (1σ) without systematic isotopic differences between urban and maritime atmospheres, suggesting both small δ13C variation within major emission sources and also little isotopic fractionation during atmospheric degradation for alkanes other than ethane. Alkenes show large δ13C variation from −37 to −12‰ PDB for ethylene and from −27 to −14‰ PDB for propylene. Combination of both large δ13C differences between major sources (especially between land and maritime sources) and large isotopic fractionation effect during atmospheric degradation can be suggested for alkenes. Methyl chloride also shows large isotopic variation from −44 to −30‰ PDB in spite of their similar atmospheric mixing ratios from 580 to 710 parts per trillion by volume (pptv), probably due to the contribution of highly 13C‐depleted, anthropogenic methyl chloride especially to urban atmospheres. The general δ13C pattern of NMHCs and methyl chloride in polluted urban city air agrees strongly with those of biomass (C‐3 plant) burning plumes, suggesting that thermal breakdown of C‐3 plant (or related organic matter) is one of the representative sources of these hydrocarbons in urban atmospheres. Further investigations of the isotopic signature of source materials as well as laboratory studies of isotopic fractionation processes resulting from atmospheric degradation will improve our understanding of the sources, sinks, and atmospheric distributions of NMHCs and methyl chloride.
Laboratory studies of particle nucleation: Initial results for H2SO4, H2O, and NH3 vapors
Authors: Ball S. M. , Hanson D. R. , Eisele F. L. , McMurry P. H.
Published: September 2002

Particle formation in the binary H2SO4‐H2O vapor system was studied at 295 K in a series of experiments employing a flow reactor. The concentration of H2SO4 was detected by chemical ionization mass spectrometry, and an ultrafine particle condensation nucleus counter was used to count the newly nucleated particles. Results yield a particle formation rate that is approximately proportional to [H2SO4] raised to the eighth power and to [H2O] raised to the fifth power. The power dependencies measured here are significantly different from those determined in previous experimental work, and furthermore, the water dependence is markedly different from that predicted from current theories. The effect of adding ammonia vapor to the binary system was investigated; concentrations of NH3 in the many tens of parts per trillion by volume range were observed to promote dramatically the rate of particle nucleation.
Impact of the ozone profile on the surface UV radiation: Analyses of the Umkehr and UV measurements at Belsk (52°N, 21°E), Poland
Authors: Krzyścin Janusz W.
Published: September 2002

We consider changes of the ozone vertical profile using Umkehr observations taken at Belsk (52°N, 21°E) by means of the Dobson spectrophotometer in the period 1963–1998. The ratio of ozone content in the Umkehr layers 1–4 (0–23.5 km) to total column ozone (layers 1–10) is used as a proxy characterizing the shape of the ozone profile. The long‐term tendency in the ratio appears statistically insignificant for the periods 1963–1979 and 1980–1998. Analysis of the residuals from the multiple‐regression model, which relates fluctuations in the measured daily UV doses (erythemally weighted) at Belsk with those in total ozone and global radiation (surrogate for the cloud and/or aerosol property variations) for the period 1993–1998, reveals that a 0.1 decrease (increase) of the ratio manifests as ∼ 2–3% increase (decrease) of the daily dose relative to its normal value. Extreme change in the vertical structure of the atmosphere yields about a 5% change in the UV daily dose. The simulations by means of a radiative transfer model also show that possible changes of the vertical structure of the atmosphere are rather a minor source of day‐to‐day variations in surface UV radiation. It is suggested that the temporal variations of the ratio may give an insight into the year‐to‐year variations of dynamical processes affecting total ozone content in the Northern Hemisphere midlatitudes.
A textbook example of long‐range transport: Simultaneous observation of ozone maxima of stratospheric and North American origin in the free troposphere over Europe
Authors: Stohl Andreas , Trickl Thomas
Published: September 2002

We describe an episode of a stratospheric intrusion into the free troposphere over Europe followed by a long‐range transport of ozone from the North American boundary layer. Observational data showed the presence of a thin tongue of stratospheric air in the free troposphere for at least 36 hours. This filament was found in data from two ozone soundings and was recorded continuously for 26 hours by a high‐resolution ozone lidar. The stratospheric air also intercepted two high Alpine summits, causing elevated ozone and beryllium 7 concentrations. Trajectory, particle dispersion model, and potential vorticity analyses confirmed the stratospheric nature of the tongue. In the lidar data, following the intrusion, pockets of elevated ozone concentrations (80–100 ppb) were found in the free troposphere close to the tropopause. The low potential vorticity values and high water vapor content in these ozone‐rich pockets and trajectory analyses suggest that the ozone was photochemically produced in the boundary layer over eastern North America, followed by rapid uplifting in a warm conveyor belt over the Atlantic Ocean ahead of a frontal system. This was confirmed by ozone and water vapor measurements aboard commercial airliners crossing the warm conveyor belt. The air mass trajectories in both the stratospheric intrusion and the warm conveyor belt were tightly bundled, emphasizing the importance of the coherency of airstreams for long‐range ozone transport.
Behavior of NO2 and O3 columns during the eclipse of February 26, 1998, as measured by visible spectroscopy
Authors: Gil M. , Puentedura O. , Yela M. , Cuevas E.
Published: September 2002

Observations of the NO2 and O3 columns using zenith‐viewing differential absorption spectroscopy in the visible range (450–540 nm) were carried out at Izaña Observatory (Tenerife, 28°N, 16°W, 2370 m above sea level.) during the eclipse of February 26, 1998 (95% occultation over the station). Ozone has been retrieved using two different spectral ranges to minimize the effect of the continuous change of the solar spectrum shape as the Sun is being occulted. Small variations before the maximum phase in agreement with previous observations are found, but because of the change in the shape of the solar spectrum, it cannot conclusively be determined whether the ozone changes are real or due to interferences with changing Fraunhofer lines. The difficulties in observing small changes of absorbing gases during solar eclipse when using remote sensing technique that uses the solar UV and visible radiation as the source are discussed. NO2 displays an increase in phase with the degree of solar occultation, as compared to a non eclipse day of 1.55±0.09. A simple model assuming that changes over short times scales are only due to changes in photodissociation, using O3 and temperatures obtained from an ozone sounding station close to the observatory, reproduces the observed variation when the NO2 bulk is assumed to be at an altitude of 28 km. Correction for differences between local solar zenith angle (SZA) and the SZA where the absorption takes place is taken into account.
Aerosol detection by TOMS and POLDER over oceanic regions
Authors: Chiapello Isabelle , Goloub Philippe , Tanré Didier , Marchand Aurelia , Herman Jay , Torres Omar
Published: September 2002

In this paper we investigate the aerosol content retrieved by Earth‐Probe Total Ozone Mapping Spectrometer (TOMS) and ADEOS POLDER over oceanic regions for the period November 1996 to June 1997. We combine the aerosol index (AI) derived from TOMS corresponding to UV‐absorbing aerosols (desert dust and biomass‐burning particles) and the POLDER aerosol optical thickness (AOT) and Angström coefficients. The seasonal composited images from the two sensors show in general consistent spatial distributions of the aerosol over oceans, with the highest aerosol content retrieved over the north tropical and equatorial Atlantic. Over the different oceanic regions investigated (i.e., Atlantic Ocean, Mediterranean Sea, Indian Ocean, and Pacific Ocean), TOMS and POLDER show a good correspondence in the aerosol seasonal variability. At all sites with the exception of the region of the Sea of Japan, we show that during the time periods of maximum aerosol amounts, a linear correlation exists between the TOMS AI and POLDER AOT. For the Sea of Japan the influence of different aerosol types (i.e., desert dust and sulfates) is likely to complicate the TOMS detection. For the other oceanic regions, our results suggest a large variability in the relationship between the TOMS AI and the POLDER AOT, which is likely to be related to changes in aerosol composition and/or altitude.
Power spectral artifacts in published balloon data and implications regarding saturated gravity wave theories
Authors: Dewan E. M. , Grossbard N.
Published: September 2002

There are several theories of atmospheric gravity wave power spectral densities (PSDs) which have been published. These, in turn, have inspired numerous experimental tests. The spectra involved are in the class denoted “stochastic, red noise spectra.” This means that most of the power is at the low‐frequency end and obeys a power law falloff in going to higher frequency. The present paper describes how some published experimental spectra are flawed by an artifact of spectral analysis which has not heretofore been recognized in the literature. It involves both an amplitude fluctuation enhancement and a coupling between spectral amplitude and slope, and it can be avoided only by stringent control of spectral leakage. Because of “trade‐off” considerations every data set, depending on its length and signal characteristics, requires a different method of analysis. It is therefore required that PSD analysis programs must be adjusted and tested to fit each situation. For this purpose a simple method is described to simulate data of known general characteristics for test purposes (to avoid the pitfalls). Since the papers by Nastrom et al. [1997] and de la Torre et al. [1997] have the unfortunate artifact in their analyses, their conclusions regarding saturated gravity wave theories should be reexamined.
Observed and modeled seasonal variation of 13C, 18O, and 14C of atmospheric CO at Happo, a remote site in Japan, and a comparison with other records
Authors: Kato Shungo , Kajii Yoshizumi , Akimoto Hajime , Bräunlich Maya , Röckmann Thomas , Brenninkmeijer Carl A. M.
Published: September 2002

Measurements of the 13C/12C and 18O/16O ratios and 14C of atmospheric CO were carried out for 2 years (1997 and 1998) at Happo (36°41′N, 137°48′E, 1840 m above sea level) in Japan. This is the first measurement of time series for isotopic compositions of CO at a remote site in Asia. The seasonal cycle of the 18O/16O ratio shows a maximum of 10‰ (Vienna SMOW) in February and a minimum of 2‰ in July. This minimum value is heavier than the values reported for high latitude in the Northern Hemisphere, and this indicates that CO from fossil fuel combustion, which has a large 18O/16O ratio, affects midlatitude in the Northern Hemisphere considerably. On the contrary, the 13C/12C ratio shows a clear seasonal variation with little scatter; maximum −24.5‰ (Vienna Peedee belemnite) in April and minimum −28.5‰ in July‐August. The seasonal variation at Happo has different values and phases compared to those in the Southern Hemisphere and in the northern high latitude. 14CO concentration at Happo is similar to that at high latitude in the Northern Hemisphere. A simple box model calculation is presented for these seasonal variations, and the model reproduces the observed seasonal cycles of CO concentration, 18O/16O ratio, and 14CO concentration within the limitations of the simplified model, but not 13C/12C ratio. To reproduce the spring maximum of CO concentration, an enhanced CO production from biomass burning or other CO sources in spring are inferred in east Asia.
The great lunar hot spot and the composition and origin of the Apollo mafic (“LKFM”) impact‐melt breccias
Authors: Korotev Randy L.
Published: September 2002

Thorium‐rich, mafic impact‐melt breccias from the Apollo 14–17 missions, that is, those breccias identified with the composition known as “LKFM,” are regarded largely as products of basin‐forming impacts that penetrated the feldspathic crust and sampled underlying mafic material and magma‐ocean residuum carrying the compositional signature of KREEP (potassium, rare earth elements, phosphorous). Despite considerable compositional variation among such breccias, compositions of all of them correspond to mixtures of only four components: (1) a norite with composition generally similar to that of Apollo 15 basalt (mean abundance: 58%; range: ∼30–95%), (2) Fo∼90 dunite (mean: 13%, range: 1–27%), (3) feldspathic upper crust (mean: 29%, range: 4–50%), and FeNi metal (0.1–1.7%). Petrographic evidence has shown that much of the feldspathic component, but none of the KREEP component, is clastic. This observation and the high proportion of KREEP norite component in the breccias suggest that the melt zone of the impact or impacts forming the breccias contained little feldspathic material but consisted predominantly of material with the average composition of KREEP norite. The dunite component probably derives ultimately from the upper mantle. These conclusions support the hypothesis that the breccias were not formed in typical feldspathic crust but instead by one or more impacts into what is designated here “the great lunar hot spot,” that is, the anomalous Th‐rich terrane in the Imbrium‐Procellarum area identified by the Apollo and Lunar Prospector gamma‐ray spectrometers. The LKFM composition is a special product of the great lunar hot spot and is not the average composition of the lower crust in typical feldspathic highlands. Similarly, Mg‐suite and alkali‐suite plutonic rocks of the Apollo collection are likely all differentiation products of the hot spot, not of plutons that might occur in typical feldspathic crust.
Compositional studies of the Orientale, Humorum, Nectaris, and Crisium lunar basins
Authors: Bussey D. Ben J. , Spudis Paul D.
Published: September 2002

We have used full‐resolution (250 m/pixel) Clementine images to map the compositions of ejecta from four multiring basins on the Moon: Orientale, Humorum, Nectaris, and Crisium. All basins have relatively feldspathic ejecta, with iron contents ranging from 2 to 6 wt% FeO. Some basins show remarkably homogeneous ejecta blankets (Orientale), while others display distinct compositional zoning within exterior sectors of the basin (Crisium); in some cases this zoning correlates with morphologically observed ejecta facies (Nectaris). The iron‐poor composition of most basin ejecta indicates that the crust of the Moon at these locations is feldspathic down to depths of at least several tens of kilometers, the likely sampling depth of basin‐forming impacts. The inner rings of all four basins display massifs and small crater floors of nearly pure anorthosite (FeO <1 wt%), virtually the only such occurrences of this rock type on the Moon. Because basin rings are structurally emplaced topographic elements derived from depths of at least 10–20 km into the Moon, we postulate that basin inner rings are sampling a unique stratigraphic level in the Moon and at these depths, the primordial, pristine anorthositic crust of the Moon is largely preserved. Below this zone of anorthosite is the more mafic region of the lower crust, probably having “highland basalt” composition (FeO ∼ 10 wt%, Al2O3 ∼ 18–22 wt%). The petrologic nature of lower crustal levels remains uncertain but must at least in part include members of the mafic highland suite, such as norites and troctolites.
Crustal analysis of Venus from Magellan satellite observations at Atalanta Planitia, Beta Regio, and Thetis Regio
Authors: Leftwich Timothy E. , von Frese Ralph R. B. , Kim Hyung R. , Noltimier Hallan C. , Potts Laramie V. , Roman Daniel R. , Tan Li
Published: September 2002

We investigated an improved quantitative method for interpreting attributes of the Venusian crust from Magellan spacecraft imagery and spherical harmonic topographic and gravity models. We used spectral correlation theory to compare gravity effects of topography against free‐air gravity anomalies for three tectonically disparate crustal regions. Adjusting terrain gravity effects for correlated free‐air anomalies yields compensated effects that we used to estimate the Moho and crustal thickness variations. For Atalanta Planitia, the crust may be less than 10 km thick, but thickened peripherally at concentric ridge belts and tessera terrain. Crustal thickness may increase rapidly between the interior of this lowland plain and the peripheral ridge belts. For Beta Regio, the crustal thickness may exceed 40 km. Of the three regions considered, the crust of Beta Regio may be the most poorly compensated because its free‐air anomalies are largest relative to corresponding terrain gravity effects. For Thetis Regio, crustal thicknesses may exceed 50 km. The thickened crust of Thetis Regio may also have been rifted and embayed by plains forming lavas. The lavas appear to embay and cover complexly ridged areas except where these units remained above the reach of the plains forming lavas. Crosscutting relationships, which are evident from Magellan imagery, together with our crustal thickness estimates, suggest that the complexly ridged terrain (or tesserae) may be the oldest crustal units within the three study regions. Hence these units may represent relict surfaces that predate emplacement of the plains.
Late Quaternary insolation forcing on total organic carbon and C37 alkenone variations in the Arabian Sea
Authors: Budziak Dörte , Schneider Ralph R. , Rostek Frauke , Müller Peter J. , Bard Edouard , Wefer Gerold
Published: September 2002

We here present records of total organic carbon (TOC) and C37 alkenones, used as indicators for past primary productivity, from the western (WAS) and eastern Arabian Sea (EAS). New data from an open ocean site of the WAS upwelling area are compared with similar records from Ocean Drilling Program (ODP) Site 723 from the continental margin off Oman and MD 900963 from the EAS. These records together with other proxies used to reconstruct upwelling intensity, indicate periods of high productivity in tune with precessional forcing. On the basis of their phase relationship to boreal summer insolation they can be divided into three groups: in the WAS differences between monsoonal proxies (1) and productivity (2) document a combined signal of moderate SW monsoon winds and of strengthened and prolonged NE monsoon winds, whereas in the EAS phasing indicates maximum productivity (3) at times of stronger NE monsoon winds associated with precession‐related maxima in ice volume.
Climatically linked oscillations in Arabian Sea denitrification over the past 1 m.y.: Implications for the marine N cycle
Authors: Altabet Mark A. , Murray David W. , Prell Warren L.
Published: September 2002

Water column and core‐top δ15N data show that Arabian Sea denitrification produces large nitrogen isotopic enrichments that are regionally recorded with fidelity in the sediments. These results facilitate interpretation of a 1 m.y. δ15N record for Ocean Drilling Program site 722B on the Owen Ridge in terms of climatically linked oscillations in denitrification at the major orbital periods. As at present, denitrification was greatest during interglacial periods and, apparently, was not active during most glacial intervals. Cross‐spectral analysis of δ15N with foraminiferal δ18O (global climate/sea level index) and lithogenic grain size (monsoon strength index) suggests forcings by changes in hydrography and productivity acting through the extent and intensity of the oxygen minimum zone. The data suggest that denitrification may be an internal forcing mechanism for climate change during major glacial/interglacial transitions through influence on marine N inventory and atmospheric CO2. However, compensation or amplification may occur from other sinks (sediment denitrification) or sources (nitrogen fixation).
Virus transport in unsaturated porous media
Authors: Sim Youn , Chrysikopoulos Constantinos V.
Published: September 2002

A numerical model for one‐dimensional virus transport in homogeneous, unsaturated porous media was developed. The model accounts for virus sorption onto liquid‐solid and air‐liquid interfaces as well as inactivation of viruses suspended in the liquid phase and viruses attached at both interfaces. The effects of the moisture content variation on virus transport in unsaturated porous media were investigated. In agreement with previous experimental studies, model simulations indicated that virus sorption is greater at air‐liquid than liquid‐solid interfaces. Available data from experiments of colloid transport through unsaturated columns were successfully simulated by the virus transport model developed in this study.