bluuebunny/crossref_metadata_2025 huggingface dataset:
The Upper Atmosphere Research Satellite microwave limb sounder instrument
Authors: Barath F. T. , Chavez M. C. , Cofield R. E. , Flower D. A. , Frerking M. A. , Gram M. B. , Harris W. M. , Holden J. R. , Jarnot R. F. , Kloezeman W. G. , Klose G. J. , Lau G. K. , Loo M. S. , Maddison B. J. , Mattauch R. J. , McKinney R. P. , Peckham G. E. , Pickett H. M. , Siebes G. , Soltis F. S. , Suttie R. A. , Tarsala J. A. , Waters J. W. , Wilson W. J.
Published: February 2008

The microwave limb sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) is the first satellite experiment using limb sounding techniques at microwave frequencies. Primary measurement objectives are stratospheric ClO, O3, H2O, temperature, and pressure. Measurements are of thermal emission: all are performed simultaneously and continuously and are not degraded by ice clouds or volcanic aerosols. The instrument has a 1.6‐m mechanically scanning antenna system and contains heterodyne radiometers in spectral bands centered near 63, 183, and 205 GHz. The radiometers operate at ambient temperature and use Schottky‐diode mixers with local oscillators derived from phase‐locked Gunn oscillators. Frequency tripling by varactor multipliers generates the 183‐ and 205‐GHz local oscillators, and quasi‐optical techniques inject these into the mixers. Six 15‐channel filter banks spectrally resolve stratospheric thermal emission lines and produce an output spectrum every 2 s. Thermal stability is sufficient for “total power” measurements which do not require fast chopping. Radiometric calibration, consisting of measurements of cold space and an internal target, is performed every 65‐s limb scan. Instrument in‐orbit performance has been excellent, and all objectives are being met.
Concentration gradients and dry deposition of nitric acid vapor at the Mauna Loa Observatory, Hawaii
Authors: Lee Gangwoong , Zhuang Liangzhong , Huebert Barry J. , Meyers Tilden P.
Published: February 2008

From August 14 to September 5, 1991, we measured the mixing ratio of nitric acid vapor and several aerosol species (nitrate, sulfate, ammonium and sodium) at three heights (2 m, 10 m and 30 m) at the Mauna Loa Observatory. Well‐defined logarithmic gradients of temperature and HNO3 vapor were measured throughout the experiment, indicating rapid HNO3 vapor deposition to the ground. Measured dry deposition velocities for HNO3 vapor ranged from 0.27 to 4 cm s−1. The collection efficiency for HNO3 vapor varied with sampler location and orientation on the sampling tower, due to concentration depletion by the tower or the sampler itself. We found that our long‐term samplers at 8 m may underestimate free tropospheric HNO3 mixing ratios by about 20% due to dry deposition.
On the interaction of isotopic exchange processes with photochemical reactions in atmospheric oxides of nitrogen
Authors: Freyer H. D. , Kley D. , Volz‐Thomas A. , Kobel K.
Published: February 2008

Gas‐phase isotopic exchange between NO and NO2 enriches the heavier 15N isotope in the more oxidized form. In the atmosphere the concentration of both gases, NO and NO2, is controlled during daytime by the Leighton relationship through the oxidation of NO with O3 and the photolytic reaction of NO2 to NO. For atmospheric concentrations (e.g., NOx, ∼10 ppb), isotopic exchange and photolytic reaction are very fast with characteristic time constants of a few minutes compared to other removing reactions of atmospheric NOx via OH radicals (daytime reaction) and O3 (nighttime reaction) with time constants of some hours and more. We have found from 15N/14N measurements of atmospheric NO2 and NOx at Jülich that both processes, isotopic exchange and photolytic reaction, interact and have an influence on the 15N/14N isotopic ratio. This interaction, together with seasonal variations of the NOx/O3 ratio at daytime and either complete oxidation of NO to NO2 or isotopic exchange between NO and NO2 at nighttime, explains the seasonal variation of the 15N/14N ratio of atmospheric NO2, which agrees with results from a simple model.
Greenland ice core “signal” characteristics: An expanded view of climate change
Authors: Mayewski P. A. , Meeker L. D. , Morrison M. C. , Twickler M. S. , Whitlow S. I. , Ferland K. K. , Meese D. A. , Legrand M. R. , Steffensen J. P.
Published: February 2008

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. We have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to ∼674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. We have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were “stationary” and by utilizing evolutionary spectral analysis, we were able to reveal periodic processes in the climate system which change in frequency, “turn on,” and “turn off” with other climate transitions such as'that between the little ice age and the medieval warm period.
Airborne measurements of gases and particles from an Alaskan wildfire
Authors: Nance J. David , Hobbs Peter V. , Radke Lawrence F. , Ward Darold E.
Published: February 2008

Airborne measurements of several gaseous and particulate chemical species were obtained in the emissions from a wildfire that burned in an old black spruce forest in Alaska during the summer of 1990. The relative proportions of most of the measured plume constituents are consistent with ground‐based and airborne measurements in the plumes of several other biomass fires, and with laboratory measurements. Possible exceptions include the mean fine‐particle emission factor, which was about 3 times larger than predicted from a regression relation based on measurements of the smoke from several prescribed biomass fires, and the mean CH4/CO molar emission ratio which was at the low end of a range of values measured for other biomass fires. Measurements of water‐soluble particulate ions in the smoke plume from the Alaskan wildfire indicate that acids formed from the oxides of sulphur and nitrogen were partially neutralized inside cloud droplets by NH3absorbed from the plume.
Surface‐based measurements and satellite retrievals of broken cloud properties in the equatorial Pacific
Authors: Chertock Beth , Fairall C. W. , White Allen B.
Published: February 2008

Ship‐based measurements of marine clouds and radiation in the equatorial Pacific are used to address a critical question: What is the relationship of integrated cloud liquid to cloud albedo and solar flux at the Earth's surface in the broken cloud regime? These measurements, taken during a 21‐day on‐site period of the Tropical Instability Wave Experiment (TIWE), constitute the first comprehensive database for examining subgrid‐scale parameterizations of cloud and radiation interactions for nonhomogeneous cloud regimes. The high‐resolution field experiment data are used in combination with satellite‐based records to investigate the relationship between small‐scale (temporal and spatial) quantities and the large‐scale parameterizations of the effects. In the 21‐day ship‐based record the average cloud fraction was 0.26 and the average cloud optical depth was about 2. The temporally averaged ship‐based estimate of cloud liquid water for this period was 54 g m−2, and the temporally averaged satellite‐based estimate of cloud liquid water within 25 km of the ship was 50 g m−2.
Peroxy radicals as measured in ROSE and estimated from photostationary state deviations
Authors: Cantrell C. A. , Shetter R. E. , Calvert J. G. , Parrish D. D. , Fehsenfeld F. C. , Goldan P. D. , Kuster W. , Williams E. J. , Westberg H. H. , Allwine G. , Martin R.
Published: February 2008

Ambient measurements of peroxy radical concentrations were made using the chemical amplifier (CA) and determined independently from photostationary state deviations (PSSD), NO2 + hv (+O2) ⇌ NO + O3, derived from simultaneous measurements of O3, NO, NO2 and jNO2. The data were collected in the Rural Oxidants in the Southern Environment experiment during 19 days of July 1990. A reasonably good correspondence between the two methods is observed for many of the days, although estimates from the PSSD method for some of the days are higher by as much as a factor of 2. Scatter observed between estimates probably results from several sources: uncertainties in the calibration of the RO2‐HO2 instrument, rapid changes in the ozone background, rapid alterations in the solar flux induced by intermittent cloud cover, and imprecisions in making simultaneous measurements of [NO], [NO2], [O3], and jNO2 required for the PSSD method. Possible origins of bias in the two measurement techniques are discussed. Theoretical estimates of the peroxy radical concentrations were made using the measured suite of trace gas concentrations for 2 days, one for which the CA and PSSD estimates of peroxy radical concentrations differed significantly (July 14) and one for which they showed good agreement (July 11). Theoretical estimates for July 11 checked well with the results from both methods. Those for July 14 fell between the GA and PSSD estimates. These results suggest that the PSSD method may have a bias toward higher estimates on some days and/or that the CA method may have a bias for the lower estimates for reasons which are discussed.
A two‐dimensional model with coupled dynamics, radiative transfer, and photochemistry: 2. Assessment of the response of stratospheric ozone to increased levels of CO2, N2O, CH4, and CFC
Authors: Schneider Hans R. , Ko Malcolm K. W. , Shia Run‐Lie , Sze Nien‐Dak
Published: February 2008

The impact of increased levels of carbon dioxide (CO2), chlorofluorocarbons (CFCs), and other trace gases on stratospheric ozone is investigated with an interactive, two‐dimensional model of gas phase chemistry, dynamics, and radiation. The scenarios considered are (1) a doubling of the CO2 concentration, (2) increases of CFCs, (3) CFC increases combined with increases of nitrous oxide (N2O) and methane CH4, and (4) the simultaneous increase of CO2, CFCs, N2O, and CH4. The radiative feedback and the effect of temperature and circulation changes are studied for each scenario. For the double CO2 calculations the tropospheric warming was specified. The CO2 doubling leads to a 3.1% increase in the global ozone content. Doubling of the CO2 concentrations would lead to a maximum cooling of about 12°C at 45 km if the ozone concentration were held fixed. The cooling of the stratosphere leads to an ozone increase with an associated increase in solar heating, reducing the maximum temperature drop by about 3°C. The CFC increase from continuous emissions at 1985 rate causes a 4.5% loss of ozone. For the combined perturbation a net loss of 1.3% is calculated. The structure of the perturbations shows a north‐south asymmetry. Ozone losses (when expressed in terms of percent changes) are generally larger in the high latitudes of the southern hemisphere as a result of the eddy mixing being smaller than in the northern hemisphere. Increase of chlorine leads to ozone losses above 30 km altitude where the radiative feedback results in a cooler temperature and an ozone recovery of about one quarter of the losses predicted with a noninteractive model. In all the cases, changes in circulation are small. In the chlorine case, circulation changes reduce the calculated column depletion by about one tenth compared to offline calculations.
Rare Earth element composition of precipitation, precipitation particles, and aerosols
Authors: Sholkovitz Edward R. , Church Thomas M. , Arimoto Richard
Published: February 2008

We report the rare earth element (REE) composition of aerosols and precipitation (dissolved and particle phases) from Bermuda, Lewes (Delaware), and Woods Hole (Massachusetts). There is large‐scale fractionation of REEs between the continents, atmosphere, and the oceans. The REE compositions of atmospheric samples are highly fractionated relative to (1) each other (e.g., aerosol/precipitation pairs), (2) the upper crust of the Earth, and (3) seawater. Precipitation samples exhibit markedly convex‐up shale‐normalized patterns, large negative Eu anomalies and large and systematic depletions in the heavy REE (Lu > Yb > Er > Dy). Aerosols are strongly depleted in the heavy REE which dissolutions experiments show are attributable to the presence of HREE‐enriched refractory minerals. We argue that in situ selective dissolution of mineral aerosol particles is responsible for the unusual REE composition of precipitation. This has major implications for the interpretation of the biogeochemical cycles of REEs in the oceans, particularly the partitioning between solution and particle phases, residence times, and the composition of seawater.
An empirical analysis of the strength of the phytoplankton‐dimethylsulfide‐cloud‐climate feedback cycle
Authors: Lawrence Mark G.
Published: February 2008

The possible influence of the marine biogeochemical sulfur cycle on the global climate has been a topic of much recent research. Based on the hypothesis that phytoplankton could affect cloud albedo by producing dimethylsulfide, which is a precursor to aerosols and cloud condensation nuclei, and that cloud albedo could in turn affect the productivity of the phytoplankton, the presence of such a feedback cycle would have significant implications for models of global climate change. By considering available data on the relationships between individual components of the proposed feedback, an empirical model is developed of the cycle as a whole, allowing an assessment to be made of the degree to which the cycle could thermostatically regulate the climate. It is estimated that the feedback strength is about 20% (10% – 50%) of that which would be necessary to completely counteract a perturbation to the global climate, such as is anticipated due to accumulation of anthropogenic greenhouse gases.
Use of Fourier transforms for asynoptic mapping: Applications to the upper atmosphere research satellite microwave limb sounder
Authors: Elson Lee S. , Froidevaux Lucien
Published: February 2008

Fourier analysis has been applied to data obtained from limb viewing instruments on the Upper Atmosphere Research Satellite. A coordinate system rotation facilitates the efficient computation of Fourier transforms in the temporal and longitudinal domains. Fields such as ozone (O3), chlorine monoxide (ClO), temperature, and water vapor have been transformed by this process. The transforms have been inverted to provide maps of these quantities at selected times, providing a method of accurate time interpolation. Maps obtained by this process show evidence of both horizontal and vertical transport of important trace species such as O3 and ClO. An examination of the polar regions indicates that large‐scale planetary variations are likely to play a significant role in transporting midstratospheric O3 into the polar regions. There is also evidence that downward transport occurs, providing a means of moving O3 into the polar vortex at lower altitudes. The transforms themselves show the structure and propagation characteristics of wave variations.
Visible spectra and chromaticity of noctilucent clouds
Authors: Ostdiek Vern J. , Thomas Gary E.
Published: February 2008

A computational scheme was developed to predict the visible spectra and chromaticity of noctilucent clouds (NLC) for arbitrary viewing geometries. The spectrum of a cloud in the visible is computed at 5‐nm intervals using the spherical shape of the stratified atmosphere, the measured solar irradiance spectrum, wavelength‐dependent extinction by air molecules, ozone, and aerosols, and scattering by a specified size distribution of cloud particles. The chromaticity calculated from each spectrum is used to evaluate the cloud's color. A comparison is made of the abilities of two proposed cloud particle size distributions to account for published spectra measured from the ground and from Earth orbit. A lognormal distribution of “small” particles with an effective radius of 42.6 nm is found to be better at reproducing measured spectra of NLC than a Junge (power law) distribution of “large” particles with an effective radius of 700 nm. Chromaticities of the small‐particle spectra show much better agreement with those of spectra measured from orbit and with the visual appearance of NLC viewed from the ground. Chromaticities are found to be weakly dependent on the atmospheric aerosol loading. However, NLC brightness is strongly dependent upon both tropospheric and stratospheric aerosols.
Biogenic sulfur aerosol in the Arctic troposphere: 1. Contributions to total sulfate
Authors: Li Shao‐Meng , Barrie Leonard A.
Published: February 2008

Long‐term observations from 1980 to 1990 of aerosol methanesulfonate (MSA), sulfate, sodium, and other related chemical species as well as a shorter time series of aerosol sulfur isotope composition (δ34S) at Alert, Northwest Territories, Canada, were used in two separate methods to determine the contributions of sea salt, biogenic sources, and pollution to aerosol SO4=. The first method, based on sulfur isotope composition, assumed a three‐source model of anthropogenic, biogenic, and sea‐salt sources for aerosol SO4=. Applying a Monte Carlo uncertainty propagation technique to the three‐source model, the MSA/biogenic SO4= mass ratio was estimated to be between 0.2 and 0.6 in summer and much lower in October to March (<0.08). The second method, based on a multivariate statistical analysis technique, apportioned aerosol SO4= into three major components attributable to the same three sources and yielded an estimate of MSA/biogenic SO4= of 0.2 to 0.9 for the summer months, in agreement with the isotopic estimate. Based on the isotopic composition, aerosol SO4= in summer is 25 to 30% biogenic, 1 to 8% sea‐salt, and the rest (62 to 74%) anthropogenic in origin. At other times of year it is <14% biogenic, 1 to 8% sea salt, and the rest anthropogenic in origin.
Parameters of triggered‐lightning flashes in Florida and Alabama
Authors: Fisher R. J. , Schnetzer G. H. , Thottappillil R. , Rakov V. A. , Uman M. A. , Goldberg J. D.
Published: February 2008

Channel base currents from triggered lightning were measured at the NASA Kennedy Space Center, Florida, during summer 1990 and at Fort McClellan, Alabama, during summer 1991. Additionally, 16‐mm cinematic records with 3‐ or 5‐ms resolution were obtained for all flashes, and streak camera records were obtained for three of the Florida flashes. The 17 flashes analyzed here contained 69 strokes, all lowering negative charge from cloud to ground. Statistics on interstroke interval, no‐current interstroke interval, total stroke duration, total stroke charge, total stroke action integral (∫ i2dt), return stroke current wave front characteristics, time to half peak value, and return stroke peak current are presented. Return stroke current pulses, characterized by rise times of the order of a few microseconds or less and peak values in the range of 4 to 38 kA, were found not to occur until after any preceding current at the bottom of the lightning channel fell below the noise level of less than 2 A. Current pulses associated with M components, characterized by slower rise times (typically tens to hundreds of microseconds) and peak values generally smaller than those of the return stroke pulses, occurred during established channel current flow of some tens to some hundreds of amperes. A relatively strong positive correlation was found between return stroke current average rate of rise and current peak. There was essentially no correlation between return stroke current peak and 10–90% rise time or between return stroke peak and the width of the current waveform at half of its peak value. Parameters of the lightning flashes triggered in Florida and Alabama are similar to each other but are different from those of triggered lightning recorded in New Mexico during the 1981 Thunderstorm Research International Program. Continuing currents that follow return stroke current peaks and last for more than 10 ms exhibit a variety of wave shapes that we have subdivided into four categories. All such continuing currents appear to start with a current pulse presumably associated with an M component. A brief summary of lightning parameters important for lightning protection, in a form convenient for practical use, is presented in an appendix.
A two‐particle‐size model and measurements of radon progeny near the Earth's surface
Authors: Schery S. D. , Wasiolek P. T.
Published: February 2008

Measurements of radon progeny in the attached‐to‐aerosol and unattached‐to‐aerosol states were made in central New Mexico. Simultaneous measurements of attached and unattached progeny at 0.2 and 2 m were carried out over a range of meteorological and terrain conditions. The ratio of the average progeny concentrations at 2.2 to 0.2 m was 1.06 for total progeny and 1.35 for unattached progeny, indicating a net downward flux, with the unattached progeny dominating removal to the Earth's surface. Progeny/parent activity ratios greater than 1 were clearly detected (for example, at 0.2 m, the average 214Pb/218Po ratio was 1.43 ± 0.10), providing partial support for some previous observations. A two‐particle‐size model for radon progeny is able to account for the observed gradients, progeny/parent activity ratios greater than 1, and some trends in the experimental measurements as a function of meteorological conditions.
Transport and residence times of tropospheric aerosols inferred from a global three‐dimensional simulation of210Pb
Authors: Balkanski Yves J. , Jacob Daniel J. , Gardner Geraldine M. , Graustein William C. , Turekian Karl K.
Published: February 2008

A global three‐dimensional model is used to investigate the transport and tropospheric residence time of210Pb, an aerosol tracer produced in the atmosphere by radioactive decay of222Rn emitted from soils. The model uses meteorological input with 4°×5° horizontal resolution and 4‐hour temporal resolution from the Goddard Institute for Space Studies general circulation model (GCM). It computes aerosol scavenging by convective precipitation as part of the wet convective mass transport operator in order to capture the coupling between vertical transport and rainout. Scavenging in convective precipitation accounts for 74% of the global210Pb sink in the model; scavenging in large‐scale precipitation accounts for 12%, and scavenging in dry deposition accounts for 14%. The model captures 63% of the variance of yearly mean210Pb concentrations measured at 85 sites around the world with negligible mean bias, lending support to the computation of aerosol scavenging. There are, however, a number of regional and seasonal discrepancies that reflect in part anomalies in GCM precipitation. Computed residence times with respect to deposition for210Pb aerosol in the tropospheric column are about 5 days at southern midlatitudes and 10–15 days in the tropics; values at northern midlatitudes vary from about 5 days in winter to 10 days in summer. The residence time of210Pb produced in the lowest 0.5 km of atmosphere is on average four times shorter than that of210Pb produced in the upper atmosphere. Both model and observations indicate a weaker decrease of210Pb concentrations between the continental mixed layer and the free troposphere than is observed for total aerosol concentrations; an explanation is that222Rn is transported to high altitudes in wet convective updrafts, while aerosols and soluble precursors of aerosols are scavenged by precipitation in the updrafts. Thus210Pb is not simply a tracer of aerosols produced in the continental boundary layer, but also of aerosols derived from insoluble precursors emitted from the surface of continents. One may draw an analogy between210Pb and nitrate, whose precursor NOxis sparingly soluble, and explain in this manner the strong correlation observed between nitrate and210Pb concentrations over the oceans.
Fractal analysis of high‐resolution rainfall time series
Authors: Olsson Jonas , Niemczynowicz Janusz , Berndtsson Ronny
Published: February 2008

Two‐year series of 1‐min rainfall intensities observed by rain gages at six different points are analyzed to obtain information about the fractal behavior of the rainfall distribution in time. First, the rainfall time series are investigated using a monodimensional fractal approach (simple scaling) by calculating the box and correlation dimensions, respectively. The results indicate scaling but with different dimensions for different time aggregation periods. The time periods where changes in dimension occur can be related to average rainfall event durations and average dry period lengths. Also, the dimension is shown to be a decreasing function of the rainfall intensity level. This suggests a multidimensional fractal behavior (multiscaling), and to test this hypothesis, the probability distribution/multiple scaling method was applied to the time series. The results confirm that the investigated rainfall time series display a multidimensional fractal behavior, at least within a significant part of the studied timescales, which indicates that the rainfall process can be described by a multiplicative cascade process.
The bromine content of micrometeorites: Arguments for stratospheric contamination
Authors: Rietmeijer Frans J. M.
Published: February 2008

Bromine‐salt nanocrystals are associated with a porous chondritic micrometeorite (W7029E5) that was collected in the lower stratosphere. These salt nanocrystals occur together with volcanic Na and K salt nanocrystals embedded in sulfuric acid droplets that were originally adhered to the particle. These materials were concentrated during hexane rinsing as part of routine curation procedures at the NASA Johnson Space Center Cosmic Dust Curatorial Facility. This observation is fortuitous to the extent that the concentration of nanocrystals and sulfuric acid is an experimental artifact of curation. If bromine is a stratospheric contaminant due to surface adsorption, there should be a positive linear relationship between the mass‐normalized residence time and bromine content of individual micrometeorites. I show that the predicted correlation exists using a new model to calculate the stratospheric residence time of individual nonspherical micrometeorites in the slow‐settling Wilson‐Huang regime of the stratosphere.
Five populations of interplanetary meteoroids
Authors: Divine Neil
Published: February 2008

A description of the interplanetary meteoroid environment is proposed in terms of distinct populations, each of which has separable distributions in particle mass and in orbital inclination, eccentricity, and perihelion distance. This treatment leads to expressions for particle concentration and flux which explicitly incorporate both Keplerian dynamics in heliocentric orbit and the directional properties of particle impact velocities for a spacecraft detector. Data which represent radar meteors, the zodiacal light, and fluxes from impact detectors aboard the Pioneer 10 and 11, Helios 1, Galileo, and Ulysses spacecraft have been combined with the interplanetary flux near Earth (from lunar crater counts and orbiting spacecraft) to evaluate parameter values for the mass and orbital distributions. Five distinct meteoroid populations are needed to successfully match all the data, and they span the ranges from 10−18 to 1.0 g in mass and from <0.1 to 20 AU in heliocentric distance. The five populations, each named for a distinctive characteristic of their orbital distributions, and in increasing order of mean particle mass, carry the labels eccentric, inclined, halo, core, and asteroidal.
Mercury: full‐disk radar images and the detection and stability of ice at the North Pole
Authors: Butler Bryan J. , Muhleman Duane O. , Slade Martin A.
Published: February 2008

The first full‐disk radar images of Mercury were obtained on August 8 and 23, 1991. These images were constructed using the Very Large Array (VLA) in Socorro, New Mexico, to receive and map radar flux at 3.5 cm (X band) which was continuously transmitted from the 70‐m Jet Propulsion Laboratory/Deep Space Network antenna at Goldstone, California. Approximately 77% of the surface was imaged, at resolutions as good as 150 km. About half of the hemisphere photographed by Mariner 10 was imaged, as well as most of the hemisphere which has not previously been photographed. At the time of the observations, the north pole was visible, and the feature with the highest same sense (SS) circular reflectivity in the images is near the nominal polar position. The peak SS reflectivity of this feature was 7.9%, and the circular polarization ratio throughout much of the feature is >1. Our best estimate of the size of the feature is that its diameter is ≲350 km. We interpret the feature to be indicative of the presence of ices because of the signal strength and polarization characteristics. The ices must be very clean and were thus probably deposited in a relatively short time period. The most likely place to find these ices is in any permanently shadowed areas in the polar regions, which would be very cold. In comparison to absolute reflectivities of other icy bodies and regions in the solar system, the reflectivity of the north polar feature is slightly depressed. This is probably because the ices do not fill an observational resolution cell (i.e., there is incomplete areal coverage), or are covered by a layer of dust or soil, which absorbs some of the incoming and outgoing radar energy, or both. A covering layer would also protect any ices from erosion by energetic sources. Other prominent features on the unphotographed hemisphere correspond to positions where atmospheric sodium enhancements have been measured from Earth. This may indicate that these locations are large basins similar to the Caloris basin, where an atmospheric potassium enhancement has been measured, which may be the result of increased degassing in the disrupted surface and near surface. Direct comparison of the radar echoes from our features with those from the Caloris basin are hard to make, as Caloris was not imaged by us in a favorable geometry. Features on the photographed hemisphere are smaller and mostly associated with craters and crater complexes, most notably the Kuiper crater and its environs.
Variable phenomena in Jovian planetary systems: Introduction
Authors: Kostiuk Theodor , McGrath Melissa , Bergstralh Jay
Published: February 2008

This special section contains papers from the International Workshop on Variable Phenomena in Jovian Planetary Systems held in Annapolis, Maryland, July 13–16, 1992. As Galileo approaches Jupiter and the planning for the Cassini mission to Saturn progresses, the time was appropriate to assess the current knowledge of Jovian planetary systems and to evaluate what the near‐Earth observing community could do to optimize the observations from these missions. This is the second such workshop; the first was held in Flagstaff, Arizona, on August 25–27, 1987 [Belton et al., 1989]. The recent workshop occurred just 3½ years before Galileo's Jupiter orbit insertion (JOI) and provided an opportunity for the community to examine and define the relevant observational, theoretical, and laboratory research in time to influence final planning for the mission science sequences.
Evaluation of infrared emission spectroscopy for mapping the moon's surface composition from lunar orbit
Authors: Nash Douglas B. , Salisbury John W. , Conel James E. , Lucey Paul G. , Christensen Philip R.
Published: February 2008

Infrared thermal emission spectroscopy is evaluated for its possible application to compositional mapping of the Moon's surface from lunar orbit. Principles of the mid‐IR (∼4–25 μm) technique, previous lunar ground‐based observations, and laboratory studies of Moon samples are reviewed and summarized. A lunar thermal emission spectrometer experiment is described, patterned after a similar instrument on the Mars Observer spacecraft. Thermal emission spectrometry from a polar‐orbiting lunar spacecraft could provide a valuable mapping tool to aid in exploration for lunar resources and help provide understanding of the origin of the Moon and history of lunar surface processes.
Diffusion of Na and K in the uppermost regolith of Mercury
Authors: Killen R. M. , Morgan T. H.
Published: February 2008

We examine the conditions under which ions impacting the Hermean surface can act as a regional source of enhanced atmospheric column through ion implantation and subsequent release at the surface. At most latitudes, energetic (a few keV) Na or K ions which impact the nightside surface, are released quickly (well before noon) upon warming of the surface. We show that the relative sunrise/sunset difference produced by ion implantation is {[n]SR − [n]ss}/[n]Ave = ƒ, where ƒ is the fraction of the photo‐ions recycled, [n]SR is the average zenith column above the sunrise portion of the illuminated hemisphere, [n]ss is the average zenith column in the sunset portion, and [n]Ave is the average column over the sunlit disk. Thus, to produce a large sunrise/sunset difference via ion implantation and subsequent release requires efficient (close to total) recycling. We show that the most extensive set of available data reduced to Na column abundance does not show any sunrise enhancement. We argue that the K data do not permit an unambiguous interpretation in favor of sunrise/sunset differences. We further find that if an efficient surface loss process for the alkali is not operating after sunrise, the initial Na and K distribution will relax into the bulk of the solid. Preserved abundance gradients of Na and K in lunar glasses suggest that the Arrhenius coefficients for impact glasses are likely more modest than those for laboratory glasses derived from rock by nonimpact processes, but the effect of the more modest diffusion rates is only to delay the efficient loss of Na by a few Earth days. We argue that implantation can lead to observable regional increases in the observed Na or K column densities only if it occurs at very high latitudes, where diffusion is slow. It is typically lower energy ions which impact at high latitude and these are both more numerous than the high energy ions and possess smaller average penetration depths; thus there are additional reasons to favor a high‐latitude locus for any possible prompt return related increases in zenith column. We find that we cannot rule out sputtering as a source process, as the low‐energy ions are efficient sputterers. Finally, we argue that the observed Na/K ratio in the atmosphere may be the expression of their different asymptotic rates of loss from the interiors of the regolith grains. If so, this allows us to fix the importance of sputtering and photon stimulated desorption relative to impact vaporization.
Plio‐Pleistocene Nannofossil Biostratigraphy and Calibration to Oxygen Isotope Stratigraphies from Deep Sea Drilling Project Site 607 and Ocean Drilling Program Site 677
Authors: Raffi Isabella , Backman Jan , Rio Domenico , Shackleton Nicholas J.
Published: February 2008

Evolutionary events within early Pleistocene Gephyrocapsa assemblages provide at least four biostratigraphically useful events occurring in the Matuyama Chron after the Olduvai Subchron. We establish an informal taxonomy based on three size groups (< 4.0 µm, 4.0–5.5 µm, > 5.5 µm) resulting in four reproducible biostratigraphic events that reflect episodes of adaptive radiation within the Gephyrocapsa lineage. Four additional, late Pliocene‐early Pleistocene events are also investigated. The successful astronomical calibration of oxygen isotope stratigraphies from Deep Sea Drilling Project site 607 and Ocean Drilling Program site 677 in the Matuyama Chron permits calibration of the biostratigraphic events to these uniquely resolved isotope chronologies. Shackleton et al.'s [1990] time scale gives the following age estimates (in million years): (reemG) reentrance of medium‐sized Gephyrocapsa (1.028, 0.957) (677, 607); (tlG) top large Gephyrocapsa (1.240, 1.227); (blG) base large Gephyrocapsa (1.457, 1.479); (bmG) base medium‐sized Gephyrocapsa (1.670, 1.700); (tHS) top H. sellii (1.470, 1.241); (tCM) top C. macintyrei (1.597, 1.640); (tDB) top D. brouweri (1.950) (607 only); (baDT) base acme D. triradiatus (2.153) (607 only). Further comparison with other, less resolved, ∂18O stratigraphies indicate that event reemG is diachronous by 71 kyr, consistently being younger in the mid‐latitudes. Event tlG appears synchronous, clustering in stage 37 in all sites. Event blG is slightly older (22 kyr) in the mid‐latitudes than in the equatorial Pacific. Also, event bmG is older in the mid‐latitudes (30 kyr). Event tHS shows the largest difference, occurring 229 kyr later at site 607, corresponding to 12 isotope stages. The critical paleoisotherm separating “young” from “old” last occurrences of H. sellii was probably located between ∼11°N and 18°N in the Atlantic Ocean. Event tCM is clearly time transgressive, occuring 43 kyr earlier at site 607. Event tDB occurred a few kiloyears within basal Olduvai at site 607.
Oceanographic and climatic changes over the past 160,000 years at Deep Sea Drilling Project Site 594 off southeastern New Zealand, southwest Pacific Ocean
Authors: Nelson Campbell S. , Cooke Penelope J. , Hendy Chris H. , Cuthbertson Alison M.
Published: February 2008

High‐resolution textural, carbonate, microfossil, and oxygen (δ18O) and carbon (δ13C) stable isotopic analyses are presented for the late Quaternary (isotopic stages 1 to 6) interval of a core at Deep Sea Drilling Project site 594, situated just south of the present Subtropical Convergence in northernmost Subantarctic surface waters on the southern flank of Chatham Rise in the southwest Pacific. Downcore alternations of pelagic and hemipelagic oozes correspond to interglacial and glacial episodes, respectively. Interglacial oozes contain a northern Subantarctic assemblage of planktonic foraminifera, with rare cool subtropical species, while glacial oozes are characterized by species typical of southern(most) Subantarctic waters and include radiolaria with affinity for Antarctic waters. The planktonic δ18O record for the site supports a 3°–6°C temperature change in near‐surface waters between interglacial and glacial stages and indicates that during stage 5e, the near‐surface waters were about 1°C warmer than at present. A pronounced cooling during stage 5d matches that of the Vostok ice core δD record, and negative excursions at the end of stages 2 and 6 support a southern latitude warming preceding northern hemisphere deglaciation. Benthic foraminifera typical of cold intermediate to deep waters can increase dramatically in abundance in the hemipelagic ooze intervals when δ18O results suggest a temperature drop in glacial stage bottom waters of 2°–4°C, possibly a result of upward displacement of Antarctic Intermediate Water by Circumpolar Deep Water at the site. The foraminiferal δ13C records support a reduced influence of North Atlantic Deep Water in the southwest Pacific during glacial stages, when nutrient enhancement occurred in both bottom and surface waters. Despite the pronounced changes between interglacial and glacial conditions inferred at site 594, contributed to by a substantial northward shift by at least 5° of latitude in the position of the Antarctic Convergence south of New Zealand during glacial episodes, we conclude that the Subtropical Convergence remained locked to Chatham Rise (approximately 44°S) throughout stages 1 to 6. Major compression of the intervening belt of Subantarctic water during glacial episodes, and the associated very steep thermal gradients and intensified atmospheric and oceanic circulation patterns that developed in this part of the southwest Pacific, account for the harsh, frigid environment reported for on‐land southern New Zealand at these times.
A low‐order model of the Heinrich Event Cycle
Authors: MacAyeal D. R.
Published: February 2008

If Heinrich events result from free oscillations in the size and basal melting conditions of the Laurentide ice sheet, a rigorous quantitative analysis of ice sheet physics should describe their dynamics. To explore this possibility, I exploit two characteristic timescales which arise from ice sheet physics to construct a relaxation oscillator model of the North Atlantic's Heinrich events. The numerical implementation of this model confirms the notion that the periodicity of Heinrich events (approximately 7,000 years) is determined by the gross properties of a steady glacial climate (e.g., an annual average sea level temperature of −10° C and an adiabatic lapse rate).
Turbidite systems: State of the art and future directions
Authors: Normark William R. , Posamentier Henry , Mutti Emiliano
Published: February 2008

The study of turbidite systems covering a wide range of physical scales has led to confusion regarding the use of certain key terms and hence a breakdown in communication between workers involved in turbidite research. There are three fundamentally different scales and types of observations derived from the study of outcrop data (ancient systems), high‐resolution seismic reflection and side scan sonar data (modern systems), and multichannel seismic reflection data (modern and older buried systems). Despite the variability of scale the same terms are used to describe features that may have little in common. Consequently, turbidite system terminology has become imprecise and even misleading in some cases, thus providing impediments to developing useful predictive models for processes, depositional environments, and lateral and vertical distribution of sand bodies within turbidite systems. To address this concern, we review the principal elements critical to deepwater systems: slump scars, submarine canyons, channels, channel fill deposits, overbank deposits, and lobes and discuss some of their recognition criteria with each different type of data base. Local and regional tectonic setting, relative sea level variations, and bottom current activity are probably the main factors that control size, external geometry, internal stratal configuration, and facies characteristics of both modern and ancient turbidite systems. These factors ultimately control the timing and bounding characteristics between stages of growth of deepwater systems. If comparison of elements from different turbidite deposits using various data types is carried out at similar physical and temporal scales, predictive models eventually may be improved.
A statistical comparison of spaced antenna and spatial interferometry wind estimation
Authors: Sheppard E. Lamar , Larsen M. F. , Palmer Robert D. , Fukao Shoichiro , Yamamoto Mamoru , Tsuda Toshitaka , Kato Susumu
Published: February 2008

A statistical comparison of spaced antenna and spatial interferometry methods for estimating horizontal winds in the troposphere and lower stratosphere is presented. The data analyzed were obtained with the middle and upper atmosphere radar from 1910 LT on June 29, 1990, through 0950 LT on July 2, 1990. At all heights, velocity estimates based on frequency domain analysis are within 4% of those based on the time domain analysis. We conclude that frequency domain techniques provide an alternative method for estimating the so‐called true velocity. It is not clear, however, that they offer a significant advantage over the time domain methods. Some analysis parameters are easier to extract in the frequency domain, while others can be extracted more easily and efficiently in the time domain.
Effects of the acoustic and radar pulse length ratio on the accuracy of radio acoustic sounding system (RASS) temperature measurements with monochromatic acoustic pulses
Authors: Adachi Tatsuhiro , Tsuda Toshitaka , Masuda Yoshihisa , Takami Tomoyuki , Kato Susumu , Fukao Shoichiro
Published: February 2008

This paper is concerned with the accuracy of temperature measurements with radio acoustic sounding system (RASS) consisting of a pulsed Doppler radar and an acoustic source, where the latter excites short monochromatic pulses. Through the use of a numerical model and middle and upper atmosphere (MU) radar experiments, we found that the accuracy is significantly affected by the acoustic and radar pulse length ratio. When the Bragg condition is not strictly satisfied, a numerical model predicted that the mean frequency shift fm of a RASS echo spectrum is detected between the Doppler‐shifted frequency corresponding to the sound speed fs and the transmitted acoustic frequency fa. When the ratio is close to or larger than unity, fm becomes almost identical with fa, while fm approaches fs as the ratio decreases. RASS experiments involving the MU radar operating at 46.5 MHz (6.45‐m wavelength) and an acoustic transmitter with a frequency of about 100 Hz showed that the observed characteristics of RASS echoes for various acoustic pulse lengths agreed quite well with model predictions. Although the numerical model suggested that a small value of the ratio is preferable for accurate measurement of temperature with RASS, the minimum value of the ratio was determined to be about 0.2 by taking into account the system sensitivity of the MU radar, since the RASS echo intensity decreases as the acoustic pulse length becomes shorter. When the lengths of the acoustic and radar pulses were set equal to about 60 m (18 acoustic wave cycles) and 300 m (l μs in pulse duration), respectively, which gives a ratio of the acoustic pulse length to the radar pulse length of approximately 0.2, we were able to obtain temperature profiles at 5 to 9 km every 3 min with an accuracy of about 0.5°C.
Impulse response function for a transionospheric signal through a Gaussian filter
Authors: Massey Robert S.
Published: February 2008

This short communiqué presents calculations of the output of a Gaussian filter to an electromagnetic impulse that has propagated through a nonmagnetized ionosphere. The rather simple result is interpreted on a physical basis. Useful expressions for the peak power and for the optimum bandwidth are obtained.
Nocturnal disturbances of total electron content and their correlation with VHF radio wave scintillations in the Pacific‐Asia region
Authors: Xu J. S. , Yeh K. C.
Published: February 2008

We have collected 136‐MHz Faraday rotation and scintillation data of signals transmitted by the satellite ETS‐2 and received at 13 ground stations in the Pacific‐Asia region. Using this data base, a statistical analysis has been carried out by correlating the nocturnal TEC disturbances with the amplitude scintillations. Also presented are several typical events observed simultaneously over this network. An important result in the present paper is that the occurrence of amplitude scintillations is closely associated with the wavelike disturbances in TEC with periods below 2 hours. These periods agree with the TIDs produced by atmospheric gravity waves in the ionosphere. Furthermore, simultaneous recordings at several spaced stations indicate the disturbances are traveling. It is therefore deduced that wavelike disturbances in TEC observed are manifested as the ionospheric response to gravity waves in the neutral atmosphere.
Thin crust at the western Iberia Ocean‐Continent transition and ophiolites
Authors: Whitmarsh R. B. , Pinheiro L. M. , Miles P. R. , Recq M. , Sibuet J.‐C.
Published: February 2008

Western Iberia is bounded by a nonvolcanic rifted continental margin made up of three apparently independent segments. The age of breakup decreases from south to north. Seismic refraction and reflection profiles, and magnetic and gravity data from each segment, show a consistent pattern of geophysical observations across the ocean‐continent transition (OCT) zone, which is a few tens of kilometers wide. We emphasize here the discovery of thin (2–4 km) oceanic crust underlain by 7.6 km s−1 material within the OCT. The available evidence favors the suggestion that the 7.6 km s−1 layer is serpentinized peridotite and that the thin oceanic crust is primarily the result of a poor magma supply for a few million years immediately after continental breakup. This thin crust may be the source of some ophiolites which exhibit thin crustal sections and continental margin affinities.