bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of the geology and geomorphology of the 1999 Marsokhod test site
Authors: De Hon R. A. , Barlow N. G. , Reagan M. K. , Bettis E. A. , Foster C. T. , Gulick V. C. , Crumpler L. S. , Aubele J. C. , Chapman M. G. , Tanaka K. L.
Published: February 2004

The Marsokhod rover returned data from six stations that were used to decipher the geomorphology and geology of a region not previously visited by members of the geomorphology field team. Satellite images and simulated descent images provided information about the regional setting. The landing zone was on an alluvial apron flanking a mountain block to the west and a playa surface to the east. Rover color images, infrared spectra analysis of the mountains, and the apron surface provided insight into the rock composition of the nearby mountains. From the return data the geomorphology team interpreted the region to consist of compressionally deformed, ancient marine sediments and igneous rocks exposed by more recent extensional tectonics. Unconsolidated alluvial materials blanket the lower flanks of the mountains. An ancient shoreline cut into alluvial material marks a high stand of water during a past, wetter climate period. Playa sediments floor a present‐day, seasonally, dry lake. Observations made by the rover using panoramic and close‐up (hand specimens—scale) image data and color scene data confirmed the presence of boulders, cobbles, and fines of various provinces. Rover traverses to sites identified as geologically distinct, such as fan, channel, shoreline, and playa, provided useful clues to the geologic interpretations. Analysis of local rocks was given context only through comparison with distant geologic features. These results demonstrated the importance of a multifaceted approach to site interpretation through comparison of interpretations derived by differing geologic techniques.
Photochemical modeling of CH3 abundances in the outer solar system
Authors: Lee Anthony Y. T. , Yung Yuk L. , Moses Julianne
Published: February 2004

Recent measurements of methyl radicals (CH3) in the upper atmospheres of Saturn and Neptune by the Infrared Space Observatory (ISO) provide new constraints to photochemical models of hydrocarbon chemistry in the outer solar system. The derived column abundances of CH3 on Saturn above 10 mbar and Neptune above the 0.2 mbar pressure level are (2.5–6.0) × 1013 cm−2 and (0.7–2.8) × 1013 cm−2, respectively. We use the updated Caltech/Jet Propulsion Laboratory photochemical model, which incorporates hydrocarbon photochemistry, vertical molecular and bulk atmospheric eddy diffusion, and realistic radiative transfer modeling, to study the CH3 abundances in the upper atmosphere of the giant planets and Titan. We identify the key reactions that control the concentrations of CH3 in the model, such as the three‐body recombination reaction, CH3 + CH3 + M → C2H6 + M. We evaluate and extrapolate the three‐body rate constant of this reaction to the low‐temperature limit (1.8×10−16 T−3.75 e−300/T, T<300 K) and compare methyl radical abundances in five atmospheres: Jupiter, Saturn, Uranus, Neptune, and Titan. The sensitivity of our models to the rate coefficients for the reactions H + CH3 + M → CH4 + M, H + C2H3 → C2H2 + H2, 1CH2 + H2 → CH3 + H, and H + C2H5 → 2 CH3, the branching ratios of CH4 photolysis, vertical mixing in the five atmospheres, and Lyman α photon enhancement at the orbit of Neptune have all been tested. The results of our model CH3 abundances for both Saturn (5.1×1013 cm−2) and Neptune (2.2×1013 cm−2) show good agreement with ISO Short Wavelength Spectrometer measurements. Using the same chemical reaction set, our calculations also successfully generate vertical profiles of stable hydrocarbons consistent with Voyager and ground‐based measurements in these outer solar system atmospheres. Predictions of CH3 column concentrations (for p≤0.2 mbar) in the atmospheres of Jupiter (3.3×1013 cm−2), Uranus (2.5×1012 cm−2), and Titan (1.9×1015 cm−2) may be checked by future observations.
DIRTCam in the desert: The Silver Lake field test of the Robotic Arm Camera
Authors: Yingst R. Aileen , Smith Peter H. , Lemmon Mark T. , Marcialis Robert L. , Rice James W. , Weinberg Jon D.
Published: February 2004

The Robotic Arm Camera (RAC) is a panchromatic imager included as part of the Mars Volatiles and Climate Surveyor (MVACS) science experiment on Mars Polar Lander and on the Mars 2001 lander. It is designed to take both panoramic and microscopic images in order to gather data on the morphology and mineralogy of surface materials. In order to demonstrate these capabilities, a field test was conducted at Silver Lake playa in the Mojave Desert. The test consisted of going to a remote site unknown to the science team and providing that team with a data set of RAC panoramic, anaglyph, and microscopic images similar to what would be available during an actual landing. With only this information the science team attempted a determination of the position and the geology of the field test site. Using panoramic and anaglyph images provided by RAC, in conjunction with overflight images simulating data from a descent camera, the landing site for the field test was determined within 50 m of the actual site as lying near both a playa and an alluvial fan. Images of samples from the surface and within the trench revealed grain morphology, texture, and mineralogy indicating a soil dominated by quartz and feldspar, interspersed with a minor mafic component. Grain‐size distribution was bimodal, with small, rounded to subrounded grains dominant at lower depths and larger, more angular grains more plentiful near the surface. This mineralogy is confirmed by the geology of the site and the data provided by the descent images and mid‐IR measurements. RAC has demonstrated its ability to image the local geology and identify the major mineralogic components of an unknown site. These abilities will be crucial in understanding both the macroscopic and the microscopic geology of future Mars landing sites. This test also has demonstrated the crucial link between RAC data and complementary data sets such as context images and compositional data that can support the mineralogic observations made by RAC.
Convection in a catastrophic flood deposit as the mechanism for the giant polygons on Mars
Authors: Lane Melissa D. , Christensen Philip R.
Published: February 2004

A formational mechanism for the large‐scale polygons that are defined by intersecting fractures in the northern plains of Mars is proposed in this work. The presented model is based on Rayleigh convection of interstitial water driven by an unstable density/temperature gradient within a saturated, porous medium. Catastrophic emplacement of water‐rich sediments into the Martian northern plain basins could have provided a thick sedimentary layer in which Rayleigh convection could have occurred. Convection within this active layer is proposed to have differentially thawed an underlying ice‐rich permafrost layer that had been at the planet's surface before being rapidly buried. The resulting morphology of the permafrost subsurface is thought to have resembled the scalloped solid‐liquid interface morphology produced in terrestrial convective flow visualization studies. The exact size and shape of the scallops on the frozen subsurface would have been controlled by the dimensions of the convection cells, which are estimated to have had width‐to‐depth ratios of between 3.4 and 4.5. Subsequent stresses (e.g., gravity and bending stresses) would have produced maximum tensile stresses in the overlying sediments preferentially above the subsurface topographic highs as described previously by McGill and Hills [1992]. Additional desiccation of the sediments would have required contraction of the sediment cover and would have produced large‐scale polygonal fractures along the preexisting weaknesses located above the raised subsurface topography. Thus the underlying subsurface geometric morphology would have been translated to the surface and would be represented by the large‐scale polygonal fractures visible in the Viking Orbiter and Mars Global Surveyor images of the Martian northern plains.
Terraces and Gilbert‐type deltas in crater lakes in Ismenius Lacus and Memnonia (Mars)
Authors: Ori Gian Gabriele , Marinangeli Lucia , Baliva Antonio
Published: February 2004

Paleolacustrine environments have been widely recognized from landform associations on the surface of Mars. In contrast to paleolakes in more open areas, putative crater lakes commonly display well‐developed sedimentary landforms, especially wave‐formed terraces and Gilbert‐type deltas. This study focuses on terraces and deltas of Western Memnonia and Ismenius Lacus. As on Earth, these landforms provide important indications of water dynamics and sedimentary processes. The putative Martian paleolakes must have been active for thousands of years to have permitted the water movement and wave formation necessary to form one or more terraces. Fan‐shaped landforms at the mouths of channels entering crater‐lake areas may indicate various channel water interaction. Of these, Gilbert‐type deltas are particularly informative. Their presence indicates multiple flooding events whereby the inlet channels conveyed coarse‐grained sediment to the crater lake. Both terraces and deltaic progradation indicate that the crater lakes of Memnonia and Ismenius Lacus were active for long time periods, at least for thousands of years, during the post heavy bombardment period of the later Martian history. The unequivocal presence of standing bodies of water of relatively long durations indicates that climatic settings very different from those prevailing today must have occurred, at least locally and temporarily, during parts of the Martian planetary history.
Sensitivity studies of methane photolysis and its impact on hydrocarbon chemistry in the atmosphere of Titan
Authors: Wilson Eric H. , Atreya Sushil K.
Published: February 2004

The photodissociation of methane at Lyman α (1216 Å) has been the focus of much scrutiny over the past few years. Methane photolysis leads to the formation of H2 molecules as well as H, CH, 1CH2, 3CH2, and CH3 radicals, which promote the propagation of hydrocarbon chemistry. However, recent studies [Mordaunt et al., 1993; Romani, 1996; Smith and Raulin, 1999] have not fully resolved the issue of methane photolytic product yields at this wavelength. We use a one‐dimensional photochemical model with updated chemistry to investigate the significance of these quantum yield schemes on the hydrocarbon chemistry of Titan's atmosphere, where Lyman α radiation accounts for 75% of methane photolysis longward of 1000 Å. Sensitivity studies show that while simple hydrocarbons like C2H2 (acetylene) and C2H4 (ethylene), which serve as important intermediates to the formation of more complex hydrocarbons, show virtually no variation in abundance, minor C3 molecules do show substantial sensitivity to choice of quantum yield scheme. We find that the C3H4 isomers (methylacetylene, allene) and C3H6 (propylene) display major variation in atmospheric mixing ratios under the implementation of these schemes, with a maximum variation of approximately a factor of 5 in C3H4 abundance and approximately a factor of 4 for C3H6. In these cases our nominal scheme, recommended by Romani [1996], offers an intermediate result in comparison with the other schemes. We also find that choice of pathway for non‐Lyman α methane absorption does affect hydrocarbon chemistry in the atmosphere of Titan, but this effect is minimal. A 65% variation in C2H6 (ethane) abundance, a value within observational uncertainty, is the largest divergence found for a wide range of possible non‐Lyman α photofragment quantum yields. These results will have significance in future modeling and interpretation of observations of the atmosphere of Titan.
Infrared reflectance spectroscopy of Martian analogues
Authors: Esposito Francesca , Colangeli Luigi , Palomba Ernesto
Published: February 2004

One of the main goals of Mars exploration is to determine the characteristics of surface materials to shed light on its geological evolution. To this end, infrared spectra, acquired by ground‐based observations and by space‐borne remote sensing, represent one of the most diagnostic tools. In order to best interpret these data a careful comparison with laboratory spectra of Martian surface analogues is needed. In the present work we report the results of transmittance, specular, and diffuse biconical reflectance measurements of three materials potentially representative of bright regions on the surface of Mars: andesite, palagonite, and montmorillonite. Few spectroscopic data are available in the literature for andesite; the palagonite from Etna volcano exhibits important differences from Hawaiian palagonite. Although montmorillonite has been already studied by various authors, it was included here in order to build a self‐consistent set of data. The infrared spectral range covered by our measurements (400–6000 cm−1) matches most of the Mars radiance spectrum, and the spectral resolution of 2 cm−1 has allowed us to perform an accurate band identification. Using the measurements, we have computed the optical constants of the samples. The chemical and morphological characterization of the analyzed samples has allowed us to perform a careful interpretation of the observed spectral features. The dependence of the band intensities, observed in diffuse reflectance, on the particle size was used to identify fundamental and combination/overtone bands. This complex of laboratory data obtained by morphological, chemical, and spectroscopic analyses provides a reference for the Martian mineral identification through interpretation of remote observations.
Heat flows through the ice lithosphere of Europa
Authors: Ruiz Javier , Tejero Rosa
Published: February 2004

Some of the geological features on the surface of Europa's ice shell suggest the existence of a brittle lithosphere that in some regions is no more than 2 km thick. The surface heat flow needed to put the brittle‐ductile transition in ice at a depth of 2 km is at least ∼100 mW m−2, much higher than predicted by tidal heating models for a purely conductive ice shell. A possible explanation lies in the probable existence of a convective layer beneath the brittle lithosphere, which, owing to tidal dissipation in warm ice, could contribute to higher heat flows. If a convective subsurface layer and grain size dependent flow behavior of ice are admitted, the grain size at brittle‐ductile transition depth cannot be >1 mm, which is consistent with the required value for the onset of convection in an ice shell thinner than 20 km.
Stochastic‐ballistic eruption plumes on Io
Authors: Glaze Lori S. , Baloga Stephen M.
Published: February 2004

Some active volcanoes on Io are associated with bright annular deposits. Here we characterize the dimensions of the annulus observed at Prometheus. Assuming that relative brightness in images is directly related to areal particle concentration on the surface, we develop a model describing emplacement of particles whose motion is controlled by stochastic processes near the vent and ballistic transport beyond. Stochastic processes are expressed as probability distributions for the important transport variables. By varying the distribution parameters, high particle concentration annuli on the surface come and go. For isotropic ejection from the stochastic region with a fixed energy, subsequent ballistic transport to the surface produces singularities in the areal concentration at r = 0 and r = rmax. This areal concentration of particles features peaks corresponding to the singularities. Truncation of the ejection cone such that particles with a single energy are ejected isotropically between 0 and some maximum angle θ0 increases the relative importance of the peak near rmax. Extrapolating the model with a narrow Gaussian energy distribution introduces enough dispersion in the areal concentrations to produce broad annuli. Varying combinations of the truncation angle and relative standard deviation for the energy distribution changes the shape and magnitude of the surface deposit. A truncation angle of 75° and a relative standard deviation of 0.08 produce a symmetric annulus closest in shape and size to that observed at Prometheus. From examination of the energetics associated with thermalized particles, we find that many molecular compositions are admissible as annulus constituents at Prometheus.
Oxygenation history of bottom waters in the Cariaco Basin, Venezuela, over the past 578,000 years: Results from redox‐sensitive metals (Mo, V, Mn, and Fe)
Authors: Yarincik K. M. , Murray R. W. , Lyons T. W. , Peterson L. C. , Haug G. H.
Published: February 2004

We present results from analyses of the redox‐sensitive metals Mo, V, Mn, and Fe in sediment recovered from the Cariaco Basin (Ocean Drilling Program Leg 165, site 1002). Results are interpreted in the context of previous studies of δ15N, export production (percent total organic carbon), eolian input, and hemipelagic deposition in the basin. Variations in redox metal ratios over the past ∼578,000 years were compared to variations in δ18O at Milankovitch frequencies and show a strong relationship between glacial‐interglacial cycles in sea level, governed by the shallow sills encircling Cariaco Basin, and bottom water oxygen content. During 100 kyr and 41 kyr cyclicity, enrichments of Mo and V occur during highly productive interglacials, indicating bottom water anoxia. During glacials, sediments are less depleted or enriched in Mn and Fe relative to the interglacials, reflecting oxic conditions. During 23 kyr and 19 kyr cyclicity, however, these redox metal patterns are not observed, indicating that the Cariaco Basin responds differently to the higher‐frequency climate changes.
Export production and carbonate dissolution in the central equatorial Pacific Ocean over the past 1 Myr
Authors: Murray R. W. , Knowlton C. , Leinen M. , Mix A. C. , Polsky C. H.
Published: February 2004

In order to quantify changes in export production and carbonate dissolution over the past 1 Myr in the central equatorial Pacific Ocean we analyzed Ba, P, Al Ti, and Ca in 1106 samples from five piston cores gathered from 5°S to 4°N at 140°W. We focused on Ba/Ti, Al/Ti, and P/Ti ratios as export proxies and employed areally integrated time slice as well as time series strategies. Carbonate maxima from 0–560 kyr are characterized by 15–30% greater export than carbonate minima. The increases in export fall on glacial δ18O transitions rather than glacial maxima. From 560–800 kyr, overlapping with the mid‐Pleistocene transition, there is a very large increase in total export yet no glacial‐interglacial variability. The highest latitudes (5°S and 4°N) record minimal absolute export change from glacials to interglacials and yet record the most extreme minima in percent CaCO3, indicating that carbonate records there are dominated by dissolution, whereas near the equator they are more influenced by changes in export.
Increased Pliocene North Atlantic Deep Water: Cause or consequence of Pliocene warming?
Authors: Kim Seong‐Joong , Crowley Thomas J.
Published: February 2004

Raymo et al. [1996] suggested that the mid‐Pliocene (∼3 Ma) warm period was associated with increased North Atlantic Deep Water (NADW) production. Is this circulation change a cause or consequence of Pliocene warming? We test the hypothesis that increased strength of NADW was a consequence of the warming around Antarctica affecting deep Antarctic outflow. A sensitivity experiment with an ocean general circulation model with Pliocene surface conditions changed only over the Southern Ocean (SO) indicates that warmer temperatures around Antarctica result in lower rates of sea ice formation and SO deep water outflow. The decreased abyssal density gradient in the SO directly leads to about a 20% increase in NADW outflow at 30°S, a 10% increase in NADW overturning in the subpolar North Atlantic, and a 20% increase in poleward heat transport in the North Atlantic. We postulate that the largest initial Pliocene climate change was in the SO because the greater sea ice area in this region is more sensitive to inferred slightly higher CO2 levels in the mid‐Pliocene.
Upper ocean circulation in the glacial North Atlantic from benthic foraminiferal isotope and trace element fingerprinting
Authors: Willamowski Claudia , Zahn Rainer
Published: February 2004

Benthic Cd/Ca and δ13C records from the midlatitude and northern North Atlantic are used to derive nutrient inventories and water mass distribution patterns for the past 50,000 years. Inferred Holocene water column Cd concentrations (CdW′) and δ13C values are 0.17–0.24 nmol kg−1 and 1.0–1.3‰ Peedee belemnite (PDB), which document the dominance of nutrient‐depleted Mediterranean Outflow Water (MOW) and Upper North Atlantic Deep Water (UNADW). Glacial benthic Cd/Ca and δ13C indicate a continued contribution of UNADW to the northern North Atlantic and upper Portuguese margin (CdW′=0.08 nmol kg−1; δ13C=+1.86‰ PDB). At the upper Moroccan margin, glacial CdW′ (0.23 nmol kg−1) is higher, and δ13C (+1.44‰ PDB) is lower. During “Heinrich” events, benthic δ13C decreases by up to 1.3‰, and peak Cd/Ca increases by 0.1–0.14 µmol mol−1; water column phosphorus equivalents are 1.8–2.8 µmol kg−1. The combined Cd/Ca and δ13C pattern indicates that during mean glacial conditions Antarctic Intermediate Water, (AAIW) reached the midlatitude northeast Atlantic (30°N). During Heinrich events, AAIW contribution maximized so that Southern Hemisphere waters filled the North Atlantic basin from bottom water to middepth levels.
On sharp spectral lines in the climate record and the millennial peak
Authors: Wunsch Carl
Published: February 2004

The existence of a narrow spectral line in the internal oscillations of the climate system would be a physical discovery of the first order. Thus the appearance of such a spectral peak, with a Q > 20 near 1500 years period, in the physical properties of the Greenland ice core is intriguing (bandwidth less than two cycles in 110,000 years). Apparently similar phenomena exist in some deep sea cores. It is shown, however, that the peak appears at precisely the period predicted as a simple alias of the seasonal cycle inadequately (under the Nyquist criterion) sampled at integer multiples of the common year. If this peak is therefore discounted, climate variability appears, as expected, to be a continuum process in the millennial band. More generally, however, aliasing of high frequencies must be a concern in any core analysis.
Variations in the Zn/Si record over the Last Interglacial Glacial Transition
Authors: Ellwood Michael J. , Hunter Keith A.
Published: February 2004

We examined the zinc content of diatom frustules as an indicator of past changes in surface seawater Zn2+ concentration. Zn/Si data of samples from three cores located in the South Atlantic sector of the Southern Ocean spanning the last interglacial‐glacial transition are presented. Changes in the Zn/Si record are linked to changes in the surface water Zn2+ concentration. The source of variation in Zn2+ concentration appears to be via changes in deep water upwelling and circulation. We rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the Zn/Si record. Likewise, the Zn/Si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects. The Zn/Si results presented do not support the zinc hypothesis. There is no link between the uptake of CO2 by phytoplankton, as inferred from the δ13C record, and the Zn/Si record.
Reconciling Bølling Warmth with peak deglacial meltwater discharge
Authors: Lohmann Gerrit , Schulz Michael
Published: February 2004

Paleoclimatic data indicate warm conditions during the Bølling period, whereas climate modeling studies predict significant cooling, triggered by the concomitant deglacial meltwater flux into the Atlantic Ocean. We suggest that the lack of an adequate representation of deep water flow over the Greenland‐Scotland Ridge in ocean circulation models can account for this discrepancy.
Late Quaternary changes of western equatorial Atlantic surface circulation and Amazon lowland climate recorded in Ceará Rise deep‐sea sediments
Authors: Rühlemann Carsten , Diekmann Bernhard , Mulitza Stefan , Frank Martin
Published: February 2004

Today the western tropical Atlantic is the most important passage for cross‐equatorial transfer of heat in the form of warm surface water flowing from the South into the North Atlantic. Circulation changes north of South America may thus have influenced the global thermohaline circulation system and high northern latitude climate. Here we reconstruct late Quaternary variations of western equatorial Atlantic surface circulation and Amazon lowland climate obtained from a multiproxy sediment record from Ceará Rise. Variations in the illite/smectite ratio suggest drier climatic conditions in the Amazon Basin during glacials relative to interglacials. The 230Thex‐normalized fluxes and the 13C/12C record of organic carbon indicate that sea level fluctuations, shelf topography, and changes of the surface circulation pattern controlled variations and amplitude of terrigenous sediment supply to the Ceará Rise. We attribute variations in thermocline depth, reconstructed from vertical planktic foraminiferal oxygen isotope gradients and abundances of the phytoplankton species Florisphaera profunda, to changes in southeast trade wind intensity. Strong trade winds during ice volume maxima are associated with a deep western tropical Atlantic thermocline, strengthening of the North Brazil Current retroflection, and more vigorous eastward flow of surface waters.
A 900 year stable isotope record of interdecadal and centennial change from the California Current
Authors: Field David B. , Baumgartner Tim R.
Published: February 2004

This paper describes the development of a high‐resolution record of interdecadal and centennial variability of ocean climate of the California Current from continuous 5 year sampling intervals based on varve counts from Santa Barbara Basin sediments. We show the importance of the choice of species and size fraction as well as the practice of making multiple measurements per interval to obtain a clear environmental signal capable of resolving interdecadal change. Changes in temperature and salinity from oceanographic surveys of the past 50 years indicate that thermal variability dominates the δ18O signal. A δ18O record from Neogloboquadrina dutertrei spanning 1030–1905 A.D. contains interdecadal thermal fluctuations within the upper thermocline that are centered around periods of roughly 55, 70, and 90 years. The interdecadal changes comprise the major share of total variability compared to a low‐amplitude mode of underlying multicentennial variability corresponding to the Medieval Warm Period and the Little Ice Age.
The quasi‐biennial oscillation
Authors: Baldwin M. P. , Gray L. J. , Dunkerton T. J. , Hamilton K. , Haynes P. H. , Randel W. J. , Holton J. R. , Alexander M. J. , Hirota I. , Horinouchi T. , Jones D. B. A. , Kinnersley J. S. , Marquardt C. , Sato K. , Takahashi M.
Published: February 2004

The quasi‐biennial oscillation (QBO) dominates the variability of the equatorial stratosphere (∼16–50 km) and is easily seen as downward propagating easterly and westerly wind regimes, with a variable period averaging approximately 28 months. From a fluid dynamical perspective, the QBO is a fascinating example of a coherent, oscillating mean flow that is driven by propagating waves with periods unrelated to that of the resulting oscillation. Although the QBO is a tropical phenomenon, it affects the stratospheric flow from pole to pole by modulating the effects of extratropical waves. Indeed, study of the QBO is inseparable from the study of atmospheric wave motions that drive it and are modulated by it. The QBO affects variability in the mesosphere near 85 km by selectively filtering waves that propagate upward through the equatorial stratosphere, and may also affect the strength of Atlantic hurricanes. The effects of the QBO are not confined to atmospheric dynamics. Chemical constituents, such as ozone, water vapor, and methane, are affected by circulation changes induced by the QBO. There are also substantial QBO signals in many of the shorter‐lived chemical constituents. Through modulation of extratropical wave propagation, the QBO has an effect on the breakdown of the wintertime stratospheric polar vortices and the severity of high‐latitude ozone depletion. The polar vortex in the stratosphere affects surface weather patterns, providing a mechanism for the QBO to have an effect at the Earth's surface. As more data sources (e.g., wind and temperature measurements from both ground‐based systems and satellites) become available, the effects of the QBO can be more precisely assessed. This review covers the current state of knowledge of the tropical QBO, its extratropical dynamical effects, chemical constituent transport, and effects of the QBO in the troposphere (∼0–16 km) and mesosphere (∼50–100 km). It is intended to provide a broad overview of the QBO and its effects to researchers outside the field, as well as a source of information and references for specialists. The history of research on the QBO is discussed only briefly, and the reader is referred to several historical review papers. The basic theory of the QBO is summarized, and tutorial references are provided.
Measuring snow and glacier ice properties from satellite
Authors: König Max , Winther Jan‐Gunnar , Isaksson Elisabeth
Published: February 2004

Satellite remote sensing is a convenient tool for studying snow and glacier ice, allowing us to conduct research over large and otherwise inaccessible areas. This paper reviews various methods for measuring snow and glacier ice properties with satellite remote sensing. These methods have been improving with the use of new satellite sensors, like the synthetic aperture radar (SAR) during the last decade, leading to the development of new and powerful methods, such as SAR interferometry for glacier velocity, digital elevation model generation of ice sheets, or snow cover mapping. Some methods still try to overcome the limitations of present sensors, but future satellites will have much increased capability, for example, the ability to measure the whole optical spectrum or SAR sensors with multiple polarization or frequencies. Among the methods presented are the satellite‐derived determination of surface albedo, snow extent, snow volume, snow grain size, surface temperature, glacier facies, glacier velocities, glacier extent, and ice sheet topography. In this review, emphasis is put on the principles and theory of each satellite remote sensing method. An extensive list of references, with an emphasis on studies from the 1990s, allows the reader to delve into specific topics.
Estimates of the direct and indirect radiative forcing due to tropospheric aerosols: A review
Authors: Haywood James , Boucher Olivier
Published: February 2004

This paper reviews the many developments in estimates of the direct and indirect global annual mean radiative forcing due to present‐day concentrations of anthropogenic tropospheric aerosols since Intergovernmental Panel on Climate Change [1996]. The range of estimates of the global mean direct radiative forcing due to six distinct aerosol types is presented. Additionally, the indirect effect is split into two components corresponding to the radiative forcing due to modification of the radiative properties of clouds (cloud albedo effect) and the effects of anthropogenic aerosols upon the lifetime of clouds (cloud lifetime effect). The radiative forcing for anthropogenic sulphate aerosol ranges from −0.26 to −0.82 W m−2. For fossil fuel black carbon the radiative forcing ranges from +0.16 W m−2 for an external mixture to +0.42 W m−2 for where the black carbon is modeled as internally mixed with sulphate aerosol. For fossil fuel organic carbon the two estimates of the likely weakest limit of the direct radiative forcing are −0.02 and −0.04 W m−2. For biomass‐burning sources of black carbon and organic carbon the combined radiative forcing ranges from −0.14 to −0.74 W m−2. Estimates of the radiative forcing due to mineral dust vary widely from +0.09 to −0.46 W m−2; even the sign of the radiative forcing is not well established due to the competing effects of solar and terrestrial radiative forcings. A single study provides a very tentative estimate of the radiative forcing of nitrates to be −0.03 W m−2. Estimates of the cloud albedo indirect radiative forcing range from −0.3 to approximately −1.8 W m−2. Although the cloud lifetime effect is identified as a potentially important climate forcing mechanism, it is difficult to quantify in the context of the present definition of radiative forcing of climate change and current model simulations. This is because its estimation by general circulation models necessarily includes some level of cloud and water vapor feedbacks, which affect the hydrological cycle and the dynamics of the atmosphere. Available models predict that the radiative flux perturbation associated with the cloud lifetime effect is of a magnitude similar to that of the cloud albedo effect.
Ionogram analysis using fuzzy segmentation and connectedness techniques
Authors: Tsai Lung‐Chih , Berkey Frank T.
Published: February 2004

We present a new procedure for the analysis of ionograms that evolves from methods developed for image analysis and utilizes techniques based on the concepts of fuzzy segmentation and connectedness. Ionogram traces are often not “crisply” defined, and we demonstrate that it is possible to approximate them as fuzzy subsets within the two‐dimensional space defined by the time‐of‐flight and the radio frequency. A real number between 0 and 1 is assigned to each pixel in an ionogram, thereby defining the membership of that pixel to each of the fuzzy subsets, effectively creating a “gray scale” ionogram. In this context, ionogram analysis becomes a problem in fuzzy geometry, and various geometrical properties, including the topological concepts of connectedness, adjacency, height, width, and major axis, can be defined. It is shown that not only does the fuzzy segmentation process separate signals from the chaotic noise background that often characterizes ionograms, but that it can also be applied to classify ionospheric echoes according to standard nomenclature, e.g., normal E, F, or Es layers. Furthermore, in reference to the skeleton or thinning extraction procedures employed in imaging processing, the fuzzy connectedness between echoes in selected segments can be used to determine the primary layers that are characteristic of vertical incidence ionospheric reflection. This information can be provided as input to automatic scaling or true‐height inversion routines, which can then be used to derive either the standard URSI set of ionospheric parameters or the electron density distribution in the overhead ionosphere, or both. This fuzzy algorithm approach has been successfully applied to midlatitude ionogram data from advanced digital ionospheric sounders operated by the National Central University and Utah State University.
Forecasting of the ionospheric quiet and disturbed ƒoF2 values at a single location
Authors: Stanislawska Iwona , Zbyszynski Zbigniew
Published: February 2004

The autocovariance prediction method has been used for ionospheric forecasting of ƒoF2 values for 1, 2, 4, 8, and 12 hours ahead at a single location. Time series of ƒoF2 data for ionospheric quiet and disturbed conditions for February 1986 and September and December 1990 at different European stations were studied in order to clarify the forecasting capabilities of the method for ionospheric purposes. The accuracy of the method varies within reasonable limits depending on the time range of the forecast for different conditions. Samples of the results for representative periods are presented. The forecast is compared with observations, monthly median recommendations of the Radiocommunication Sector of the International Telecommunication Union (ITU‐R), and persistence models.
Modeling and inverting radio occultation signals in the moist troposphere
Authors: Sokolovskiy Sergey V.
Published: February 2004

Accurate modeling of radio occultation signals is performed by solving the Helmholtz equation with the use of a multiple‐phase‐screen technique. Refractivity is assumed spherically symmetric, and vertical profiles are reproduced from high‐resolution tropical radiosondes. As a result, the characteristics of the signals, which are important for their tracking in low Earth orbit, are evaluated: the spectral bandwidth, ∼50 Hz, and the random phase acceleration, ∼1000 Hz/s. The complex signals are inverted with the use of two radio holographic methods: back propagation and sliding spectral (radio optics). For the back propagation method, finding the position of the auxiliary trajectory which provides an unambiguous bending angle function of impact parameter appears to be a problem. For the sliding spectral method a simple technique, which takes into account the whole spectral content of the signal without identification and selection of local spectral maxima, is introduced and tested. The sliding spectral method allows for the stable reconstruction of bending angles and refractivity with vertical resolution of ∼0.5 km. The small‐scale laminated structure of refractivity results in propagation of radio occultation signals down to significantly lower observation altitudes than in the case of smooth refractivity. Information content of radio occultation signals at those low altitudes is important for the radio holographic inversions.
Numerical study of diffraction of a normally incident plane wave at a hollow wedge with different impedance sheet faces by the method of parabolic equation
Authors: Zhu Ning Yan , Lyalinov Mikhail A.
Published: February 2004

The problem of diffraction of a normally incident plane wave at a hollow wedge formed by two different semi‐infinite planar impedance sheets is studied numerically by using the parabolic equation (PE) method. It is assumed that either the electric or the magnetic field is parallel to the edge of the wedge. After having proved the uniqueness of the solution of the parabolic equation for passive wedge faces, the PE is solved via Crank‐Nicolson finite difference scheme. A good agreement between the PE numerical results and available results for specific cases has been shown. In addition, the diffraction behavior dependent upon the parameters of the wedge faces has been displayed by several examples.
Ionospheric specification algorithms for precise GPS‐based aircraft navigation
Authors: Harris I. L. , Mannucci A. J. , Iijima B. A. , Lindqwister U. J. , Muna D. , Pi X. , Wilson B. D.
Published: February 2004

The Federal Aviation Administration (FAA) is implementing an aircraft navigation scheme for the United States using the Global Positioning System (GPS) L1 signal (1575.42 MHz). To achieve position accuracies of a few meters, sufficient to allow precision airfield approaches, it will be necessary to broadcast corrections to the direct GPS signal. A significant component of these corrections is the delay in the GPS signal introduced by its propagation through the ionosphere. Ionospheric delay corrections will be derived using a ground network of at least 24 dual‐frequency GPS receivers distributed across the continental United States. This network is part of the FAA's wide area augmentation system (WAAS) and will provide real‐time total electron content (TEC) measurements. We present a technique for converting these TECs into gridded vertical delay corrections at the GPS L1 frequency, which will be broadcast to users every 5 min via geosynchronous satellite. Users will convert these delays to slant corrections for their own particular lines of sight to GPS satellites. To preserve user safety, estimates of the error in the user delay corrections will also be broadcast. However, the error algorithm must not resort to excessive safety margins as this reduces the expected accuracy, and thus utility, of the navigation system. Here we describe an error algorithm and its dependence on various factors, such as user location with respect to the WAAS ground network and ionospheric conditions.
Deformation history of tectonic melange and its relationship to the underplating process and relative plate motion: An example from the deeply buried Shimanto Belt, SW Japan
Authors: Onishi C. T. , Kimura G. , Hashimoto Y. , Ikehara‐Ohmori K. , Watanabe T.
Published: February 2004

Map to microscopic‐scale structural analysis of the Hanazono Assemblage of the Shimanto Belt in SW Japan, an excellent example of a deeply buried accretionary complex, indicates a detailed process from underthrusting to underplating. The earliest underthursting process is recorded in fabric of melange, which has deformed by shear along the decollement, characterized by thinning strain due to extensional breakage of blocks of sandstone and exotic materials, such as basalt and pelagic sediments of oceanic affinities. The deformation mechanism for melange formation for domain I is plastic flow, concordant with metamorphic grade, which is higher than that of domain II. The deformation mechanism for domain II is predominantly pressure solution partly with grain‐scale brittle breakage for the less metamorphosed part of the Hanazono Assemblage. The posterior underplating process recorded is contraction and thickening due to thrust stacking and folding. Locations of the folds developed beneath thrusts are emphasized because they are a line of evidence of thickening. The main deformation mechanism of the second stage is plastic flow for domain I and cataclasis for domain II. The cataclasis in domain II may be a result of change in strain rate and seems to be related to seismicity at the time of underplating. Kinematics deduced from fabric analysis of the earliest deformed melange indicates a good consistency with a relative plate motion between the Eurasian and oceanic plates that is estimated from a hot spot reference plate circuit model by Engebretson et al. [1985], while that of the subsequent thrusting is not. This fact suggests that strain partitioning in association with oblique subduction of oceanic plate was minimum during subduction. Another possibility for strain partitioning is the requirement of coupling between plates that are recorded by the deformation mechanisms.
Terrane accretion and upward extrusion of high‐pressure granulites in the Neoproterozoic nappes of southeast Brazil: Petrologic and structural constraints
Authors: da Costa Campos Neto Mario , Caby Renaud
Published: February 2004

The high‐grade crystalline nappes exposed southeast of the São Francisco craton comprise two distinct units of mainly granulite facies rocks that represent a composite section of Neoproterozoic deep continental crust: the Socorro‐Guaxupé nappe above, derived from an arc terrane, and the Três Pontas‐Varginha nappe below. Metamorphism in the Três Pontas‐Varginha nappe is characterized by the exceptional preservation of kyanite granulites (700–750°C, 15 kbar), and followed by limited retrogression. Maximum temperatures around 900–950°C were reached toward the base of the overlying Socorro‐Guaxupé nappe during the intrusion of charnockitic‐mangeritic magmas. Lower‐pressure metamorphism, accompanied by anatexis, prevailed at shallower crustal levels. Our petrological results document an inverted thermal structure with isobaric heating of the top of the high‐pressure granulite nappe. Both granulite nappes were transported more than 200 km eastward above lower nappes involving reworked basement and passive margin units, both metamorphosed to high‐pressure but lower‐temperature conditions. Significant thinning and cooling of the two granulite nappes may have occurred before their emplacement onto the lower nappes. The proposed geodynamic scenario considers that continental subduction took place westward underneath Neoproterozoic oceanic lithosphere. The two granulite units crystallised at ∼ 45 km depths under distinct paleogeotherms within this subduction zone around 630 Ma. The kyanite granulites were rapidely exhumed through the mechanism of low‐angle “forced” extrusion, whereas syncollisional collapse affected the soft, anatectic middle crust of the overlying arc terrane. The final emplacement of the thinned nappe pile onto the cold São Francisco craton and its platform cover, with at most, anchizonal to greenschist‐facies metamorphism, occurred around 600 Ma.
Novel biogenic iodine‐containing trihalomethanes and other short‐lived halocarbons in the coastal east Atlantic
Authors: Carpenter L. J. , Malin G. , Liss P. S. , Küpper F. C.
Published: February 2004

Reactive halogen photochemistry and its impact on tropospheric oxidant levels have recently attracted intense research interest following the observation of the iodine oxide radical at midlatitudes. During September 1998, short‐lived organoiodines including CH3I, C2H5I, CH2ICl, CH2IBr, CH2I2, and the hitherto undetected CHIBr2, as well as the organobromines CHBr3, CH2Br2, CHBr2Cl, CH3Br, and C2H5Br, were measured in air and seawater at and around Mace Head, on the west coast of Ireland. The release rates of organic bromines and iodines from seaweeds were determined from incubations of 10 species of brown, red, and green macroalgae collected in the intertidal or subtidal zones of the rocky shore. For all the brown algae studied, iodine was released mainly as CH2I2. However, for several seaweeds, the novel iodine‐containing trihalomethanes CHIBr2 and CHI2Cl represented a significant fraction of the released organic iodine. The macroalgae incubation experiments as well as monitoring of the in situ concentrations in a rock pool indicated that natural halocarbon production by seaweeds was stimulated by incident light. The halocarbon fluxes derived from the seaweed incubations, coupled with published detailed biomass surveys, enabled coastal organohalogen seawater concentrations to be estimated. The CHBr3, CH2Br2, and CHBr2Cl concentrations calculated by this method compared well with coastal surface seawater measurements, implying that macroalgae were the major sources of the polybromomethanes. Measured CH3Br, CH3I, and CH2ICl levels were higher than calculated, which may be due to the existence of additional sources. CH3Br production by macroalgae accounted for less than 10% of measured levels in coastal waters. Short‐lived iodocarbons such as CH2I2 and CHIBr2 were depleted in surface seawater compared to calculated levels, implying their photolytic loss within the upper water column.