bluuebunny/crossref_metadata_2025 huggingface dataset:
Coastal zone color scanner retrospective
Authors: Mitchell B. Greg
Published: February 2004

The following special section of the Journal of Geophysical Research is dedicated to a retrospective of scientific studies using the coastal zone color scanner (CZCS) instrument. The CZCS was launched in late 1978 aboard the Nimbus 7 satellite as a “proof‐of‐concept” instrument to demonstrate the feasibility of using satellite platforms to monitor the distribution of oceanic phytoplankton in the world's oceans. It provided data until the middle of 1986. Phytoplankton primary production contributes approximately one half of the global biospheric fixation of organic matter by photosynthesis, thereby forming the base of the oceanic food web and providing a major sink for atmospheric CO2.
Observations of bottom currents and estimates of resuspended sediment transport at the New York Bight 12‐mile dumpsite
Authors: Manning J. P. , Oey L. Y. , Packer D. , Vitaliano J. , Finneran T. W. , You K. W. , Fromm S.
Published: February 2004

To document storm events that may induce a redistribution of sediment in the vicinity of the New York Bight 12‐mile sewage sludge dumpsite, current meter moorings were deployed in water depths from 20 m (near the mouth of New York Harbor) to 53 m (within the Hudson Shelf Valley) from July 1986 through June 1989. Ten usable instrument records ranging from one month to one year in duration were obtained; eight of them near‐bottom records. Seasonal and geographic variability of wind‐induced flow were examined. The wind is most efficient in driving the subtidal currents in the 2–10 day frequency band during winter when the water column is well mixed and when the eastward component of the wind often induces and sustains an up‐valley (northward) bottom flow. Maximum efficiency occurs for wind from 300° (WNW) and at sites located within the Hudson Shelf Valley. A continental shelf bottom boundary layer model (Glenn and Grant, 1987) was used to estimate resuspended sediment transport. Model inputs include bottom currents (observed), orbital wave velocities (estimated), and sediment grain size (from the literature). Model output indicates that sediment resuspension at the current meter sites occurs approximately 5% of the time, primarily during winter months. The difference in along‐valley flux between two moorings provides a rough estimate (6‐month time series) of deposition and erosion. The net deposition (+.02 mm) was no greater than the deposition and erosion resulting from individual storms. A three‐dimensional circulation model (You et al., 1991) is applied to increase the spatial resolution of the near‐bottom current field (4 km grid) for a storm event in May of 1987. Given these velocities that vary in space and time, the redistribution of sediment was modeled for different surface wave conditions. Areas of deposition aligned with the Hudson Shelf Valley due to less wave‐induced resuspension in deeper waters. Given all the uncertainties in the input variables (grain size, surface waves) and the simplistic assumptions made in modeling the deposition and erosion, it is still uncertain how much sludge is permanently removed from the area, but episodic redistribution of surficial sediment evidently occurs throughout the Inner New York Bight.
Wind‐forced variations in the Brazil‐Malvinas confluence region as simulated in a coarse resolution numerical model of the South Atlantic
Authors: Smith Linda T. , Chassignet Eric P. , Olson Donald B.
Published: February 2004

The observed seasonal and interannual fluctuations in the Brazil‐Malvinas confluence region are investigated using a wind‐driven isopycnic coordinate model of the South Atlantic Ocean south of 10°S. The model is configured on a rotated Mercator grid with 2° horizontal resolution and five constant‐density layers in the vertical. In order to model the passage of the Antarctic Circumpolar Current (ACC) across the basin, the grid is augmented by a channel extension to the west of Drake Passage and east of 50°E, having the width of Drake Passage. A series of benchmark experiments with annual mean climatological forcing shows that (1) when bottom topography is included, one observes a reduction in Drake Passage transport in agreement with previous studies, as well as a northward shift in the Brazil Current separation latitude, (2) an increase in Drake Passage transport to realistic values does not cause any further northward shift in the separation point, and (3) the model is relatively insensitive to the choice of lateral boundary conditions. A second set of experiments, in which the forcing is by seasonal climatological wind data and the Drake Passage transport is relaxed to a constant annual mean value, indicates the presence of a semiannual signal in the annual transport cycles for the Malvinas Current and for the ACC through Drake Passage. That signal is significantly damped in the Brazil Current region, and the amplitude of each cycle is reduced in comparison to observations. When the value to which the Drake Passage transport is relaxed is allowed to vary in time, the semiannual wind‐forced oscillation in the Malvinas region remains evident, with additional superimposed variations related to the variations in the transport forcing. The final experiments are forced by a 10‐year data set of realistic wind stress values, providing 10‐year time series of model output for analysis of the interrelationships of the principal Southwestern Atlantic currents. A high correlation at the semiannual period is found to exist among the cycles of Drake Passage transport, Malvinas Current transport, and seasonal movements of the Brazil‐Malvinas confluence latitude, while the Brazil Current transport cycle exhibits a significant energy peak only at the annual period. We conclude that the locally wind‐forced semiannual signal south of the confluence is significantly damped before reaching the Brazil Current region by several factors: friction, the opposing flow of the current itself, and the inability of the Malvinas to penetrate the subtropical circulation that is confined to the upper model layers.
Minimizing systematic errors from atmospheric multiple scattering and satellite viewing geometry in coastal zone color scanner level IIA imagery
Authors: Martin D. L. , Perry M. J.
Published: February 2004

Water‐leaving radiances and phytoplankton pigment concentrations are calculated from coastal zone color scanner (CZCS) radiance measurements by removing atmospheric Rayleigh and aerosol radiances from the total radiance signal measured at the satellite. The single greatest source of error in CZCS atmospheric correction algorithms is the assumption that these Rayleigh and aerosol radiances are separable. Multiple‐scattering interactions between Rayleigh and aerosol components cause systematic errors in calculated aerosol radiances, and the magnitude of these errors is dependent on aerosol type and optical depth and on satellite viewing geometry. A technique was developed which extends the results of previous radiative transfer modeling by Gordon and Castaño to predict the magnitude of these systematic errors for simulated CZCS orbital passes in which the ocean is viewed through a modeled, physically realistic atmosphere. The simulated image mathematically duplicates the exact satellite, Sun, and pixel locations of an actual CZCS image. Errors in the aerosol radiance at 443 nm are calculated for a range of aerosol optical depths. When pixels in the simulated image exceed an error threshold, the corresponding pixels in the actual CZCS image are flagged and excluded from further analysis or from use in image compositing or compilation of pigment concentration databases. Studies based on time series analyses or compositing of CZCS imagery which do not address Rayleigh‐aerosol multiple scattering should be interpreted cautiously, since the fundamental assumption used in their atmospheric correction algorithm is flawed.
The diurnal cycle of the upper equatorial ocean: Turbulence, fine‐scale shear, and mean shear
Authors: Peters Hartmut , Gregg Michael C. , Sanford Thomas B.
Published: February 2004

Physical processes within the diurnal cycle of the upper ocean in the Pacific Equatorial Undercurrent are investigated based on observations at 0°/140°W of April 1987. The cycle extended below the surface mixed layer into the pycnocline, where nighttime maxima and daytime minima occurred in turbulent dissipation rates ε, fine‐scale shear variance, and in “large‐scale,” low‐frequency zonal shear, buoyancy frequency, and gradient Froude number. The time‐of‐day average e varied by a factor of 40 at 20 m, near the base of the mixed layer. Its night/day ratio decreased with increasing depth, the diurnal signal extending to 45–60 m, compared to nighttime mixed layer depths of 10–25 m. The daily variation of ε extended throughout the layer of high shear and high gradient Froude number Fr, above the Undercurrent core, being cut off where the large‐scale Fr dropped below 1. The diurnal cycle of ε remained unaffected by changes in the large‐scale shear and stratification. The nighttime fine‐scale shear variance in the 5–10 m vertical wavelength band exceeded daytime minima by a factor of 2 on average, the daily variation decaying rapidly with increasing depth. Turbulent overturns were smaller than 5 m, so that we suspect that the fine‐scale shear was related to internal waves. Fine‐scale shear was large enough to be a factor in local shear instability. A zone some 20 m thick below the mixed layer showed weak nighttime maxima in the large‐scale, low‐frequency zonal shear, stratification, and Froude number. We suspect that these variations were a product of turbulent mixing. They could become a discriminative tool in a future comparison of our observations with upper ocean models. The application of such models is encouraged by indications of a local control of the upper ocean heat budget by the surface heat flux. In apparent response to a weaker Undercurrent, stronger stratification, and weaker trade winds, mean and nighttime dissipation rates were lower in 1987 than in November 1984. The night/day ratio, however, was larger in 1987 owing to the absence of daytime high‐ε events.
Analysis of tropospheric aerosol number density for aerosols of 0.2‐ to 3‐μm diameter: Central and northeastern Canada
Authors: Gregory Gerald L. , Anderson Bruce E. , Barrick John D. , Hudgins Charles H. , Bagwell Donald R. , Blake Donald R.
Published: February 2004

NASA's Atmospheric Boundary Layer Experiment conducted during the summer of 1990 focused on the distribution of trace species in central and northeastern Canada (altitudes <6 km) and the importance of surface sources/sinks, local emissions, distant transport, tropospheric/stratospheric exchange. Aircraft flights were based from North Bay, Ontario, and Goose Bay, Labrador, Canada. As part of the aircraft measurements, aerosol number density (0.2‐ to 3‐μ diameter) was measured using an optical laser technique. Results show that summertime aerosol budgets of central and northeastern Canada can be significantly impacted by the transport of pollutants from distant source regions. Biomass burning in Alaska and western and central Canada exerts major influences on regional aerosol budgets. Urban emissions transported from the U.S./Canadian border regions are also important. Aerosol enhancements (mixed layer and free troposphere) were most prevalent in air with carbon monoxide mixing ratios >110 parts per billion by volume (ppbv). When data were grouped as to the source of the air (5‐day back trajectories) either north or south of the polar jet, aerosol number density in the mixed layer showed a tendency to be enhanced for air south of the jet relative to north of the jet. However, this difference was not observed for measurements at the higher altitudes (4 to 6 km). For some flights, mixed layer aerosol number densities were >100 higher than free‐tropospheric values (3‐ to 6‐km altitude). The majority of the observed mixed layer enhancement was associated with transport of effluent‐rich air into the Canadian regions. Aerosol emissions from natural Canadian ecosystems were relatively small when compared to transport.
Seasonal trends of isoprene, C2–C5 alkanes, and acetylene at a remote boreal site in Canada
Authors: Jobson B. T. , Wu Z. , Niki H. , Barrie L. A.
Published: February 2004

A weekly air sampling program at Fraserdale, Ontario (latitude 50° N, longitude 82° W) has revealed distinct seasonal trends in the isoprene, alkane, and acetylene concentrations over the period April 1990 to October 1992. Concentration of the biogenic hydrocarbon isoprene peaked in July to August (≤5 parts per billion by volume (ppbv)), with concentrations above 0.1 ppbv from May through September. In contrast, alkane and acetylene concentrations displayed a summer minimum (July to August) and a winter maximum (January to February). Back trajectory data showed that prevailing airflow to Fraserdale was from the northwest sector when samples were collected, and throughout most of the year Fraserdale received air originating from northern Canada. An analysis of changes in hydrocarbon concentration ratios over the period provided evidence that the seasonal trend of the C2‐C4 hydrocarbons is dominated by seasonal changes in HO reaction rates. In general, the amplitude of the seasonal oscillation for the C2‐C5 anthropogenic hydrocarbons increased with HO rate constant. Comparison with Toronto data indicates the long‐range transport of acetylene and C2‐C5 alkanes of urban origin to this boreal site.
Exchange of nitrous oxide within the Hudson Bay lowland
Authors: Schiller C. L. , Hastie D. R.
Published: February 2004

The source strength of atmospheric trace gases from natural ecosystems must be quantified in order to assess the effect of such inputs on the background tropospheric chemistry. A static chamber technique and a gas exchange technique were used to determine the emissions of nitrous oxide from five sites within the Hudson Bay Lowland, as part of the Northern Wetland Study. Two mechanisms, one diffusive and the other episodic, were found likely to be responsible for the emissions of nitrous oxide, The annual diffusive flux ranged from −3.8 mg(N2O)/m2 in a treed bog to 7.9 mg(N2O)/m2 in an open fen. The addition of the episodic flux, increased this range to −2.1 mg(N2O)/m2 and 18.5 mg(N2O)/m2 respectively. These episodic emissions occurred in from 2.5% to 16.7% of the samples during the late summer peak emission period. Since the gas exchange rate could not detect the episodic emissions, it was found to be a poor method for water emission rate determination within the wetland. LANDSAT‐Thermatic Mapper (TM) imagery was used to scale the emissions, from the chamber level to an integrated average over the entire Hudson Bay Lowland. The total emission rate of N2O from the Hudson Bay Lowland, was determined to be 1.2 Gg(N2O)/year, of which 80% was attributed to episodic emissions.
Carbon monoxide and methane over Canada: July–August 1990
Authors: Harriss R. C. , Sachse G. W. , Collins J. E. , Wade L. , Bartlett K. B. , Talbot R. W. , Browell E. V. , Barrie L. A. , Hill G. F. , Burney L. G.
Published: February 2004

Carbon monoxide (CO) and methane (CH4) were measured in the 0.15‐ to 6‐km portion of the troposphere over subarctic and boreal landscapes of midcontinent and eastern Canada during July–August 1990. In the mid‐continent region, Arctic air entering the region was characterized by relatively uniform CO concentrations (86–108 parts per billion by volume (ppbv)) and CH4concentrations (1729–1764 ppbv). Local biomass burning and long‐range transport of CO into the area from industrial/urban sources and distant fires did frequently produce enhanced and variable concentrations. Emissions of CH4from the Hudson Bay lowlands was the primary source for enhanced and variable concentrations, especially at altitudes of 0.15–1 km. In eastern Canada, most of the observed variability in CO and CH4was similar in origin to the phenomena described for the midcontinent region. However, unexpectedly low concentrations of CO (51 ppbv) and CH4(1688 ppbv) were measured in the midtroposphere on several flights. Combined meteorological and chemical data indicated that the low CO‐CH4events were the result of long‐range transport of tropical Pacific marine air to subarctic latitudes.
The Northern Wetlands Study (NOWES): An overview
Authors: Glooschenko W. A. , Roulet N. T. , Barrie L. A. , Schiff H. I. , McAdie H. G.
Published: February 2004

The Northern Wetlands Study (NOWES) was undertaken to better define the role of northern wetlands and particularly of the large continuous wetland of the Hudson Bay lowland. CO2, CH4, N2O, O3, and nonmethane hydrocarbons (NMHC)between the surface and the atmosphere were measured across a 140‐km transect, representing approximately 5000 years of peatland evolution. This transect was located in the southern portion of the Hudson Bay lowland. A second study of surface exchange was conducted in the subarctic region of the northern Hudson Bay lowland. Regional flux surveys were conducted by aircraft between the two study areas. An integral part of the study was to determine the size of the source/sink of various gases and to compare the flux estimates made by several different techniques.
High‐precision measurements of mercury vapor in air: Design of a six‐port‐manifold mass flow controller system and evaluation of mass flow errors at atmospheric pressure
Authors: Kim Ki‐Hyun , Lindberg Steven E.
Published: February 2004

We constructed an atmospheric sampling system for Hg vapor that utilizes a single vacuum pump connected via a manifold to six separate mass flow controllers (MFC). The manifold system reduces the size and power requirements for collection of replicate samples, is ideally suited for use on meteorological towers, and achieves the precise control of air‐sampling volumes required for computing air/surface exchange rates from concentration gradients of Hg vapor. In testing our air sampling systems, we found consistent calibration errors between the manufacturer's calibrations and a standard bubble flow meter. Errors as high as 30% decreased systematically with increasing flow rate to values of 3–5% at near‐maximum flow. The relative error patterns established between adjacent MFC units in each system were found to be relatively stable over time. Using gold‐coated sand amalgamation traps for Hg vapor and the flow correction factors computed from our calibrations, we routinely achieve precision for replicate measurements of Hg vapor in background air of 0.5–2% (expressed as relative standard errors of mean concentrations of 1.5–3.5 ng/m3). Application of the flow correction factors measurably decreases the level of bias between mean concentrations of Hg vapor measured with adjacent sampling systems and is necessary to reduce uncertainty associated with quantifying gradients in atmospheric concentrations.
Origins and variations of fluoride in Greenland precipitation
Authors: De Angelis M. , Legrand M.
Published: February 2004

Summit‐Greenland firn and ice core sections have been analyzed to determine the fluoride background level of high northern latitude precipitation and to investigate its temporal variations over various time periods. A continuous profile covering the last century and a discontinuous study of the last 27,000 years spanning the entire Holocene time period (0 to 11,500 years B.P.) and the late part of the last glaciation have been achieved. This first detailed study of the fluoride content of polar ice help us obtain a better understanding of the atmospheric cycle of inorganic fluoride in remote atmospheres. First, our data suggest that blown dust is among the nonvolcanic sources that contributed to the natural fluoride background level of this high‐latitude precipitation. Primary sea‐salt emissions represent an insignificant contribution. Our study also indicates that high‐latitude biomass burning debris which sometimes reaches the Greenland ice cap represents an additional weak source of fluoride for Greenland precipitation. Second, this work provides useful information for evaluating the impact of the volcanic activity on the fluoride budget of these high northern latitude regions. Indeed, our data demonstrate that although the natural background fluoride content of Greenland snow is very often sporadically disturbed by volcanic emissions from Iceland (numerous Hekla eruptions and the 1783 Laki eruption, for instance), located relatively close to the Greenland ice cap, large explosive eruptions (Tambora in 1815, for instance) only weakly disturb this background level. Our data suggest that even in the case of significant input within the stratosphere, fluoride is rapidly scavenged probably along with ash particles. Finally, our study of recent snow layers suggests that man‐made sources (mainly coal burning) represent an important contribution which has dominated this high northern hemisphere fluoride budget for the three last decades. Furthermore, over the last 10 years, a possible influence of the stratospheric reservoir builded up from the chlorofluorocarbons' degradation cannot be ruled out and in the future this growing contribution may represent a significant part of the anthropogenic fluoride input compared to the input derived from coal burning.
Ozone within the El Chichón aerosol cloud inferred from solar backscatter ultraviolet continuous‐scan measurements
Authors: Wen Guoyong , Frederick John E.
Published: February 2004

Large amounts of SO2injected into the stratosphere by the El Chichón volcanic eruption greatly enhanced the sulfuric acid aerosol loading. According to laboratory studies, the increase in aerosol surface area would lead to a loss of ozone. Radiation measurements from the solar backscatter ultraviolet spectroradiometer are used to probe the absorbing and scattering properties of the stratosphere after the eruption. The backscattered radiation is enhanced for wavelengths greater than 290 nm, with a peak at about 302 nm. The enhancements associated with aerosol backscattering and ozone change can be separated. A decrease in column ozone of 8 to 30 Dobson units was deduced within the aerosol layer at an altitude between 20 and 30 km following the month of the eruption.
Climatology and natural variability of the global hydrologic cycle in the GLA atmospheric general circulation model
Authors: Lau K.‐M. , Mehta V. M. , Sud Y. C. , Walker G. K.
Published: February 2004

Time average climatology and low‐frequency variabilities of the global hydrologic cycle (GHC) in the Goddard Laboratory for Atmospheres (GLA) general circulation model (GCM) were investigated in the present work. A 730‐day experiment was conducted with the GLA GCM forced by insolation, sea surface temperature, and ice‐snow undergoing climatological annual cycles. Influences of interactive soil moisture on time average climatology and natural variability of the GHC were also investigated by conducting 365‐day experiments with and without interactive soil moisture. Insolation, sea surface temperature, and ice‐snow were fixed at their July levels in the latter two experiments. Results show that the model's time average hydrologic cycle variables for July in all three experiments agree reasonably well with observations. Except in the case of precipitable water, the zonal average climates of the annual cycle experiment and the two perpetual July experiments are alike, i.e., their differences are within limits of the natural variability of the model's climate. Statistics of various components of the GHC, i.e., water vapor, evaporation, and precipitation, are significantly affected by the presence of interactive soil moisture. Even with fixed external conditions, the GHC exhibits a variety of low‐frequency natural variabilities. A long‐term trend is found in the principal empirical modes of variability of ground wetness, evaporation, and sensible heat. Dominant modes of variability of these quantities over land are physically consistent with one another and with land surface energy balance requirements. The dominant empirical modes of ground wetness variability in the annual cycle and perpetual July experiments have similar spatial patterns. The dominant mode of precipitation variability is found to be closely related to organized convection over the tropical western Pacific Ocean. The precipitation variability has timescales in the range of 2 to 3 months and can be identified with the stationary component of the Madden‐Julian Oscillation. The precipitation mode is not sensitive to the presence of interactive soil moisture but is closely linked to both the rotational and divergent components of atmospheric moisture transport. The present results indicate that globally coherent natural variability of the GHC in the GLA GCM has two basic timescales in the absence of annual cycles of external forcings: a long‐term trend associated with atmosphere‐soil moisture interaction which affects the model atmosphere mostly over midlatitude continental regions and a large‐scale 2‐ to 3‐month variability associated with atmospheric moist processes over the western Pacific Ocean.
Dependence of boundary layer structure near an ice‐edge coastal front upon geostrophic wind direction
Authors: Glendening John W.
Published: February 2004

The dependence of boundary layer (BL) features within a “coastal front” (created by temperature and roughness differences across a surface interface) upon the direction of a large‐scale geostrophic wind is examined with idealized simulations, using parameters appropriate to an ice edge. Maximum vertical velocities and strongest horizontal gradients occur when the vertically averaged BL velocity near the ice edge parallels the ice edge; this occurs at the on‐ice geostrophic angle for which frictional modification of the geostrophic wind optimally counters thermally induced cross‐interface flow at the ice edge. This optimal angle is greater for “ice‐on‐right” (when looking downwind, assuming northern hemisphere rotation) flow than for “ice‐on‐left” flow due to asymmetry introduced by surface friction. The associated vertical velocity maxima also vary asymmetrically with geostrophic wind direction. The optimal angle depends upon the average surface roughness at the interface, whereas the vertical velocity maxima depend upon the differential surface roughness across the interface. For a prototype ice edge, the optimal on‐ice angle is 20° larger and its vertical velocity maximum 3 times larger for ice‐on‐right flow, with differential surface roughness accounting for nearly half of the magnitude asymmetry. Along‐ice velocity jets develop only when the large‐scale geostrophic wind nearly parallels the ice edge. The curl of the surface stress is sensitive to changes in geostrophic wind direction, changing sign over the water when the large‐scale geostrophic wind approximately parallels the ice edge. Because of frontal collapse the width of the surface transition region has a relatively minor influence on these results.
Stratospheric aerosol acidity, density, and refractive index deduced from SAGE II and NMC temperature data
Authors: Yue G. K. , Poole L. R. , Wang P.‐H. , Chiou E. W.
Published: February 2004

Water vapor concentrations obtained by the Stratospheric Aerosol and Gas Experiment II (SAGE II) and collocated temperatures provided by the National Meteorological Center from 1986 to 1990 are used to deduce seasonally and zonally averaged acidity, density, and refractive index of stratospheric aerosols. It is found that the weight percentage of sulfuric acid in the aerosols increases from about 60 just above the tropopause to about 86 at 35 km. The density increases from about 1.55 to 1.85 g cm−3between the same altitude limits. Some seasonal variations of composition and density are evident at high latitudes. The refractive indices at 1.02, 0.694, and 0.532 μm increase, respectively, from about 1.425, 1.430, and 1.435 just above the tropopause to about 1.445, 1.455, and 1.458 at altitudes above 27 km, depending on the season and latitude. The aerosol properties presented can be used in models to study the effectiveness of heterogeneous chemistry, the mass loading of stratospheric aerosols, and the extinction and backscatter of aerosols at different wavelengths. Computed aerosol surface areas, rate coefficients for the heterogeneous reaction ClONO2+ H2O → HOCl + HNO3and aerosol mass concentrations before and after the Pinatubo eruption in June 1991 are shown as sample applications.
Thermal and albedo mapping of the polar regions of Mars using Viking thermal mapper observations: 1. North polar region
Authors: Paige David A. , Bachman Jennifer E. , Keegan Kenneth D.
Published: February 2004

We present the first maps of the apparent thermal inertia and albedo of the north polar region of Mars. The observations used to create these maps were acquired by the infrared thermal mapper (IRTM) instruments on the two Viking orbiters over a 50‐day period in 1978 during the Martian early northern summer season. The maps cover the region from 60°N to the north pole at a spatial resolution of 1/2° of latitude. The analysis and interpretation of these maps is aided by the results of a one‐dimensional radiative convective model, which is used to calculate diurnal variations in surface and atmospheric temperatures, and brightness temperatures at the top of the atmosphere for a wide range of assumptions concerning aerosol optical properties and aerosol optical depths. The results of these calculations show that the effects of the Martian atmosphere on remote determinations of surface thermal inertia are more significant than have been indicated in previous studies. The maps of apparent thermal inertia and albedo show a great deal of spatial structure that is well correlated with surface features. The north residual polar cap has a very high apparent thermal inertia, and is interpreted to contain dense, coarse‐grained, or solid water ice that extends from within 2 mm of the surface to depths of at least l m below the surface. Detached, bright water ice deposits surrounding the residual cap also have very high apparent thermal inertias, and are interpreted to have similar properties. Polar layered deposits surrounding the north residual cap also have high apparent thermal inertias, and are also interpreted to contain near‐surface water ice. Mariner 9 images of the north residual cap obtained in 1972 show much less bright water frost coverage than Viking images obtained three Mars years later in 1978, and it is suggested that layered deposits may be actively forming in these areas over interannual timescales. Dark transverse dune deposits adjacent to the north residual cap have relatively low apparent thermal inertias, as do arcuate scarp regions within the polar layered deposits that appear to be major sources of polar dune material. The apparent thermal inertias of these north polar dune deposits are significantly lower than those of intracrater dune deposits at lower latitudes. The north polar dunes are interpreted to be composed of dark unconsolidated material that is being eroded from the layered deposits and transported away from the pole by saltation. The region poleward of 60°N contains no large low thermal inertia regions, which is interpreted as evidence that atmospheric dust is not accumulating in the north polar region under present climatic conditions.
Remote sensing of potential lunar resources: 2. High spatial resolution mapping of spectral reflectance ratios and implications for nearside mare TiO2 content
Authors: Melendrez David E. , Johnson Jeffrey R. , Larson Stephen M. , Singer Robert B.
Published: February 2004

High spatial resolution maps illustrating variations in spectral reflectance 400/560 nm ratio values have been generated for the following mare regions: (1) the border between southern Mare Serenitatis and northern Mare Tranquillitatis (including the MS‐2 standard area and Apollo 17 landing site), (2) central Mare Tranquillitatis, (3) Oceanus Procellarum near Seleucus, and (4) southern Oceanus Procellarum around Flamsteed. We have also obtained 320–1000 nm reflectance spectra of several sites relative to MS‐2 to facilitate scaling of the images and provide additional information on surface composition. Inferred TiO2 abundances for these mare regions have been determined using an empirical calibration which relates the weight percent TiO2 in mature mare regolith to the observed 400/560 nm ratio. Mare areas with high TiO2 abundances are probably rich in ilmenite (FeTiO3) a potential lunar resource. The highest potential TiO2 concentrations we have identified in the nearside maria occur in central Mare Tranquillitatis. Inferred TiO2 contents for these areas are >9 wt % and are spatially consistent with the highest‐TiO2 regions mapped previously at lower spatial resolution. We note that the morphology of surface units with high 400/560 nm ratio values increases in complexity at higher spatial resolutions. New telescopic spectra of landing sites successfully reproduce the Charette relation, although we find that the 400/560 nm value is strongly a fimction of the sample area size. The increased spectral contrast of the 400/730 nm ratio over the 400/560 nm ratio demonstrates the potential increased precision with which the 400/730 nm ratio might be used to estimate TiO2 abundances. Comparisons have been made with previously published geologic maps, Lunar Orbiter IV, and ground‐based images, and some possible morphologic correlations have been found between our mapped 400/560 nm ratio values and volcanic landforms such as lava flows, mare domes, and collapse pits.
Galileo infrared imaging spectrometry measurements at the Moon
Authors: McCord Thomas B. , Soderblom Larry A. , Carlson Robert W. , Fanale Fraser P. , Lopes‐Gautier Rosaly , Ocampo Adriana C. , Forsythe Jennifer , Campbell Bruce , Granahan James C. , Smythe W. D. , Weissman P. R. , Becker K. J. , Edwards K. , Kamp Lucas , Lo Juliana , Mehlman R. , Torson J. , Danielson G. E. , Maison D. L. , Kieffer H. H. , Johnson T. V.
Published: February 2004

Imaging spectrometer observations were made of the surface of the Moon during the December 1990 flyby of the Earth‐Moon system by the Galileo spacecraft. This article documents this data set and presents analyses of some of the data. The near infrared mapping spectrometer (NIMS) investigation obtained 17 separate mosaics of the Moon in 408 spectral channels between about 0.7 and 5.2 μm. The instrument was originally designed to operate in orbit about Jupiter and therefore saturates at many spectral channels for most measurement situations at 1 AU. However, sufficient measurements were made of the Moon to verify the proper operation of the instrument and to demonstrate its capabilities. Analysis of these data show that the NIMS worked as expected and produced measurements consistent with previous ground‐based telescopic studies. These are the first imaging spectrometer measurements of this type from space for the Moon, and they illustrate several major points concerning this type of observation and about the NIMS capabilities specifically. Of major importance are the difference between framing and scanning instruments and the effects of the spacecraft and the scan platform on the performance of such an experiment. The science return of subsequent NIMS and other investigation measurements will be significantly enhanced by the experience and results gained.
Glacial‐interglacial history of Antarctic Intermediate Water: Relative strengths of Antarctic versus Indian Ocean sources
Authors: Lynch‐Stieglitz Jean , Fairbanks Richard G. , Charles Christopher D.
Published: February 2004

Sediment cores from the southern continental margin of Australia are near the formation region of Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water and record the changes in these water masses from the last glacial maximum through the present. Carbon and oxygen isotopes were measured on the benthic foraminiferal species Planulina wuellerstrorfi for both the Recent and last glacial maximum sections of the cores and were then used to reconstruct temperature and carbon isotopic water column profiles. The glacial oxygen isotope profile indicates a vertical temperature structure for this region similar to that in today's Subantarctic Zone. Although intermediate water δ13C cannot be used as a nutrient tracer in this region because of the large influence of air‐sea carbon isotopic exchange on this water mass, δ13C can be used as a water mass tracer. Today, AAIW properties reflect contributions from cool, fresh Antarctic Surface Waters (2/3) and warm, salty waters from the Indian Ocean (1/3). When examined in conjuction with the glacial δ13C and δ18C data from the north Indian and Southern Oceans, our data suggest a much reduced contribution of North Indian Ocean intermediate water to glacial Antarctic Intermediate Water relative to the contribution of Antarctic Surface Water. This fresher, cooler glacial Antarctic Intermediate Water would be distributed to the intermediate‐depth ocean, thus decreasing the transport of salt produced in the North Indian Ocean to the rest of the world's oceans. Combined with evidence for a reduced influence of North Atlantic Deep Water, these results suggest major changes in the pathways for the redistribution of heat and salt in the glacial ocean.
Discrete barite particles and barium as tracers of paleoproductivity in south Atlantic sediments
Authors: Gingele Franz , Dahmke Andreas
Published: February 2004

Geochemical analyses as well as X ray diffraction measurements were carried out on five sediment cores from the eastern Angola Basin and the equatorial divergence of the South Atlantic. Barite concentrations were calculated from total barium concentrations by subtracting the estimated barium background supplied by “nonbarite” barium carriers. Barite concentrations assessed by this geochemical method show a good correspondence to barite concentrations determined by quantitative X ray diffraction measurements. Barite proved to be an important carrier of barium in the pelagic cores, contributing up to 90% of the total barium concentrations in the sediment, while clastic material provides an important source of barium at sites closer to the African continent. Barite accumulation rates were calculated in order to eliminate the diluting effects of varying inputs of terrigenous and biogenic material. Barite accumulation rates show cyclic variations with maxima corresponding to glacial and minima to interglacial stages. Absolute paleoproduction rates were computed from barite accumulation rates. At the Congo fan and the equatorial divergence they are consistent with calculations based on total organic carbon (TOC) accumulation. At the Walvis Ridge, glacial‐interglacial cycles contrast to a constant paleoproductivity computed from TOC accumulation.
dendrohydrology and long‐term hydrologic phenomena
Authors: Loaiciga Hugo A. , Haston Laura , Michaelsen Joel
Published: February 2004

Dendrohydrology provides accurate methods for studying long‐term hydrologic variability at regional scales. A substantial literature and body of knowledge exists, attesting to the value of tree ring based hydrologic reconstructions to discern patterns of long‐term hydrologic variability. Application studies encompass drought analysis, analysis of extremes, periodicity of rare hydrologic phenomena, regional interdependence of surface moisture conditions, and, in general, the probabilistic analysis of key hydroclimatic variables such as runoff, precipitation, and temperature. The probabilistic analysis includes distributional properties, frequency duration analysis, severity of events, and spatial variability of hydrologic indicators. This paper reviews some fundamental aspects of dendrohydrology, with a perspective on its value to hydrologists in pursuit of an understanding of long‐term hydrologic spatial‐temporal behavior and provides also a selective citation of previous work conducted within the dendrohydrologic discipline.
Gas hydrates—geological perspective and global change
Authors: Kvenvolden Keith A.
Published: February 2004

Natural gas hydrates occur worldwide in polar regions, normally associated with onshore and offshore permafrost, and in sediment of outer continental and insular margins. The total amount of methane in gas hydrates likely exceeds 1019 g of methane carbon. Three aspects of gas hydrates are important: their fossil fuel resource potential, their role as a submarine geohazard, and their effects on global climate change. Because gas hydrates represent a large amount of methane within 2000 m of the Earth's surface, they are considered to be an unconventional, unproven source of fossil fuel. Because gas hydrates are metastable, changes of pressure and temperature affect their stability. Destabilized gas hydrates beneath the seafloor lead to geologic hazards such as submarine slumps and slides, examples of which are found worldwide. Destabilized gas hydrates may also affect climate through the release of methane, a “greenhouse” gas, which may enhance global warming and be a factor in global climate change.
Interactions between biological and physical processes in Arctic Seas: Investigations using numerical models
Authors: Smith Walker O. , Niebauer H. J.
Published: February 2004

The marginal ice zones of the Arctic are regions of extreme importance to global biogeochemical cycles, in that they are sites of accumulation and transfer of organic matter within the food web and locations of significant fluxes of carbon, both inorganic and organic. Yet a complete seasonal description over the relevant time and space scales has not been conducted. Properly validated numerical models extend our ability to understand these oceanographic features because field studies are limited in their spatial and temporal coverage. Our knowledge of the mosaic of complex air‐sea‐ice interactions is good enough to relate the forces, through models, which control sea and ice motion, as well as the growth of phytoplankton. We review the use of models in investigations of marginal ice zones in the Arctic and conclude that the primary factor in regulating the initiation, development, and dissipation of ice edge phytoplankton blooms is vertical stratification. Furthermore, the spatial domain of the bloom is controlled by the ice dynamics and the response to local winds. Upwelling does occur at ice edges, but it is generally ineffective in directly stimulating phytoplankton growth. Any stimulation that does occur is via changes in the local ice cover (hence irradiance) field. Other mesoscale features such as eddies, fronts, or current meanders also influence the local biophysical interactions. The use of properly validated models in oceanographic research is a powerful tool for both posing and answering questions dealing with complex interactions that occur in the ocean.
Polar mesosphere summer radar echoes: Observations and current theories
Authors: Cho John Y. N. , Kelley Michael C.
Published: February 2004

The remarkably strong radar echoes from the summer polar mesosphere have been an enigma to atmospheric and radar scientists since their discovery more than a decade ago. Since then, more sophisticated radar experiments and in situ rocket measurements have shed some light on the underlying physics and chemistry, and theories have been formulated to explain the generation of the intense radar backscatter and the remarkable physical conditions associated with it. First, we review the key observations and examine the proposed theories. We then evaluate the progress that has been made in understanding this phenomenon and explore its connection to global change, to the newly recognized material referred to as a dusty plasma, and to the highest clouds in the Earth's atmosphere. Finally, we end with suggestions for future research.
Orogen‐scale decollements
Authors: Cook Frederick A. , Varsek John L.
Published: February 2004

The continental lithosphere responds to stress by deforming as a generally layered medium. Deep seismic reflection data, coupled with a variety of ancillary geological and geophysical data, are interpreted to provide images of fault zones that tend to form moderately dipping ramp structures in mechanically rigid layers, and flat detachments in mechanically weak layers. This geometry is similar to ramp and flat structures observed at smaller scales in thrust and fold belts and leads to the interpretation that most orogens are underlain by orogen‐scale décollements in a manner that is analogous to so‐called “thin skin” deformation in sedimentary rocks. Décollements may occur within the crust (for example, near the base of a sedimentary section or in the middle crust), near the Moho, in the subcrustal lithosphere, or in the asthenosphere. Even intracratonic basement‐cored (“thick skin”) uplifts that occasionally occur in foreland regions such as the Wyoming province are probably large (crustal) scale versions of ramp/flat features observed in supracrustal rocks and are thus likely caused by the same fundamental tectonic processes.
Properties of the F layer plasma in the midday throat ridge and trough
Authors: Whalen J. A.
Published: February 2004

The tongue or ridge of the F layer plasma in the region of the dayside throat of the convection pattern is studied in order to determine its source and its relation to the daytime trough. A global array of six ionospheric sounders near 75° MLAT situated in both hemispheres provide the observations spanning 19 consecutive months at solar maximum. The ridge is often stable for many hours and magnetically conjugate; it is variable day to day but is so persistent that it is evident in the monthly medians. The ridge maximum has a seasonal dependence consistent with ionization by solar radiation rather than by particle precipitation, and a local time dependence that is consistent with the transport from elsewhere on the dayside by convection rather than with production at the observing sites. The ridge is not an isolated structure but is flanked by the two troughs of low‐density plasma transported to the dayside by the dawn and dusk convection cells. Accordingly, the structure of the throat is a ridge between two valleys that is entirely a product of convection.
Spatial structure of the E region field‐aligned irregularities revealed by the MU radar
Authors: Yamamoto Mamoru , Komoda Norio , Fukao Shoichiro , Tsunoda Roland T. , Ogawa Tadahiko , Tsuda Toshitaka
Published: February 2004

The MU radar (34.9°N, 136.1°E, geomagnetic latitude 25.0°N) is utilized to observe the spatial structures of the field‐aligned irregularities in the midlatitude E region. The multibeam observation in 12 directions has found that the “quasi‐periodic” echoes have a monochromatic wave structure propagating toward SSW. Much smaller‐scale structure of the irregularities has been observed by the interferometry techniques with three receivers. The results are consistent with a model in which a southward propagating gravity wave modulates the sporadic E layer to generate the quasi‐periodic echoes of the irregularities.
Natural resonance extraction from multiple data sets using physical constraints
Authors: Ilavarasan Ponniah , Rothwell Edward J. , Chen Kun Mu , Nyquist Dennis P.
Published: February 2004

This paper presents a scheme to extract natural frequencies from multiple data sets using an E pulse technique. Physical constraints are placed on the amplitudes of the E pulse basis functions to prevent the extracted damping coefficients from being positive, as often happens with low signal‐to‐noise ratio (snr) data. The constrained technique is compared to the usual E pulse extraction technique to show the improvement in the estimated natural frequencies.