bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of summertime ozone over North America
Authors: Jacob Daniel J. , Logan Jennifer A. , Yevich Rose M. , Gardner Geraldine M. , Spivakovsky Clarisa M. , Wofsy Steven C. , Munger J. William , Sillman Sanford , Prather Michael J. , Rodgers Michael O. , Westberg Hal , Zimmerman Patrick R.
Published: February 2008

The concentrations of O3 and its precursors over North America are simulated for three summer months with a three‐dimensional, continental‐scale photochemical model using meteorological input from the Goddard Institute for Space Studies (GISS) general circulation model (GCM). The model has 4°×5° grid resolution and represents non linear chemistry in urban and industrial plumes with a subgrid nested scheme. Simulated median afternoon O3 concentrations at rural U.S. sites are within 5 ppb of observations in most cases, except in the south central United States where concentrations are overpredicted by 15–20 ppb. The model captures successfully the development of regional high‐O3 episodes over the northeastern United States on the back side of weak, warm, stagnant anticyclones. Simulated concentrations of CO and nonmethane hydrocarbons are generally in good agreement with observations, concentrations of NOx are underpredicted by 10–30%, and concentrations of peroxyacylnitrates (PANs) are overpredicted by a factor of 2 to 3. The overprediction of PANs is attributed to flaws in the photochemical mechanism, including excessive production from oxidation of isoprene, and may also reflect an underestimate of PANs deposition. Subgrid nonlinear chemistry as captured by the nested plumes scheme decreases the net O3 production computed in the United States boundary layer by 8% on average.
Improved angular directional models for clear sky ocean derived from Earth radiation budget satellite shortwave radiances
Authors: Dlhopolsky Rose , Cess Robert D.
Published: February 2008

A clear sky ocean angular directional model (ADM) using Earth Radiation Budget Satellite (ERBS) shortwave (SW) radiances was developed and compared with the ADM for clear sky ocean used in processing the Earth Radiation Budget Experiment (ERBE) data. It differs from the ERBE operational ADM for clear sky ocean because the resolution of the angular bins which describe the anisotropy of the reflected shortwave radiation is higher. The largest errors occurred for small solar zenith angles and were as high as 67% when the satellite was in a position to measure the Sun's reflection from the surface. These errors are also related to findings that ERBE albedos for clear sky ocean retain some dependence on the satellite‐viewing geometry.
New measurements of the NO2 absorption cross section in the 440‐ to 460‐nm region and estimates of the NO2‐N2O4 equilibrium constant
Authors: Amoruso Antonella , Crescentini Luca , Fiocco Giorgio , Volpe Massimiliano
Published: February 2008

Absolute determinations of the NO2 absorption cross section in the 440‐ to 460‐nm region at different temperatures are reported. This region is of special interest for remote sensing applications. The interpretation of the results is rendered complex by the coexistence of NO2 and its dimer. In the experiment both NO2 and N2O4 absorption features are observed. Different approaches are utilized to obtain the partial pressure of NO2; a new estimate of the NO2‐N2O4 equilibrium constant from spectroscopic measurements is also obtained. Within experimental errors the overall shape of the spectrum does not show a dependence on temperature, but some features are affected; in particular, a slight increase of a few maxima and a decrease of the other maxima and of the minima when the temperature is lowered have been observed.
Metalloids in wet deposition on Bermuda: Concentrations, sources, and fluxes
Authors: Cutter Gregory A.
Published: February 2008

The concentrations of antimony, arsenic, and selenium were determined in wet deposition samples collected on a daily (event) basis from 1988 to 1990 on Bermuda as a part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). Isentropic back trajectories were used to identity air masses that passed over North America (59% of the events), Europe or North Africa (8%), or were largely marine in origin (33% of the events). The North American trajectories had the highest volume‐weighted average (VWA) concentrations and crustal enrichment factors for the three metalloids; the As/Se ratio and good correlations with acidity suggest inputs from fossil fuel combustion. The Euro‐African trajectories had the lowest VWA concentrations and enrichment factors that approached crustal values, indicating mineral aerosol inputs; values for marine events fell between these two extremes. The atmospheric flux of metalloids to the western Atlantic Ocean represents a major source of these elements in surface waters (up to 100% for Sb and Se; up to 61 % for As) and a corresponding sink in their global atmospheric budgets.
A new calculation of nitric oxide photolysis in the stratosphere, mesosphere, and lower thermosphere
Authors: Minschwaner K. , Siskind D. E.
Published: February 2008

Photodissociation of nitric oxide in the middle and upper atmosphere is examined using a line‐by‐line approach to describe absorption in the NO δ bands and O2 Schumann‐Runge bands. The new analysis of O2 absorption results in greater transmission of ultraviolet radiation in the Schumann‐Runge (5–0) band in comparison with previous studies, leading to increased rates for photolysis of nitric oxide in the δ(0–0) band. Reduced transmission in the O2 (9–0) and (10–0) Schumann‐Runge bands produces smaller photolysis rates for the NO δ(1–0) band. Absorption in strong lines of the NO δ bands is shown to make a nonnegligible contribution to atmospheric opacity at wavelengths which are important for NO photodissociation. Representative distributions of nitric oxide are used to quantify possible changes in the NO photolysis rate over the course of a solar cycle. As a result of changes in the NO abundance in the thermosphere, modulation of the photolysis frequency at lower altitudes may be opposite in phase to variations in the solar irradiance. For solar zenith angles greater than 60°, photolysis rates at altitudes below 100 km may be smaller during solar maximum compared to solar minimum. A method is described which enables rapid calculation of NO photolysis frequencies, allowing also for effects of varying opacity by nitric oxide.
Nonlinear kinetic energy transfer in the upper troposphere during summer monsoon 1979
Authors: Chakraborty D. R. , Mishra S. K.
Published: February 2008

Upper tropospheric (300–100 hPa) nonlinear kinetic energy (KE) converts to rotational and divergent motion and the conversion is computed in the wavenumber domain for July 1979 in the latitude belt 10°S–30°N. They are further partitioned into stationary and transient components. It is shown by comparing the rotational and divergent KE spectra for stationary and transient motions that the best nondivergent level is 300 hPa, and 200 hPa is the most representative level in the upper troposphere for monsoon studies. Wavenumbers 3 and 7 are identified as the most preferred transient waves from the rotational transient kinetic energy spectrum. It is concluded that in the planetary‐scale dynamics of the monsoon region, wave‐wave interaction plays a secondary role. The net gain of rotational kinetic energy is proportional to its value, and the proportionality constant is nearly the same for all wave categories. It is found that planetary and synoptic waves in the upper troposphere during the monsoon are maintained by energy transfer from divergent kinetic energy. KE in the monsoon region is transported by nonlinear wave‐wave interaction. In particular, transient synoptic‐scale eddies are also maintained by energy transfer from transient synoptic‐scale divergent motion. It is further inferred from the energy balance that the stationary‐transient wave‐wave interaction is important for the maintenance of transient subsynoptic waves. It is noticed that kinetic energy conversion for transient subsynoptic waves is from the divergent to the rotational component at 200 hPa only and is opposite to that in the upper troposphere. The energy budget for transient waves 3 and 7 is investigated.
A study of the reaction NaO2+ O → NaO+ O2: Implications for the chemistry of sodium in the upper atmosphere
Authors: Helmer Magdalena , Plane John M. C.
Published: February 2008

Sodium superoxide (NaO2) is believed to be a major sink for meteor‐ablated Na in the upper atmosphere. However, the rate constant for the reaction between NaO2 and O is not known, and its determination is the subject of this study. NaO2 was produced by the reaction between Na vapor, an excess of O2, and the carrier gas N2 in the upstream section of a fast flow tube reactor. Excess atomic O was then added, so that a steady state developed in which the sodium was partitioned between its atomic form and a variety of oxides. The steady state fraction of atomic Na, monitored by laser‐induced fluorescence, was then observed as a function of [O] and [O2], from which it was deduced that k(NaO2 + O) = (2.2 ± 1.0) × 10−11 cm3 molecule−1 s−1 at 300 K (3σ uncertainty). As a prelude to this experiment, the recombination reaction between O2 and Na was studied by the conventional flow tube technique, yielding k(Na + O2 + N2) = (3.14 ± 0.20) ×10−30 (300/T)−(1.52±0.27) cm6 molecule−2 s−1. These experimental results were then incorporated into a one‐dimensional model of sodium in the upper atmosphere between 65 and 110 km. It is shown that formation of NaHCO3 rather than NaO2 is the dominant removal process for atomic Na below 90 km. This new model, whose only important assumption is the rate constant for the reaction NaHCO3 + H → Na + H2CO3, predicts a seasonal variation of the atomic Na layer in excellent agreement with recent lidar observations at 40° and 69°N and also demonstrates that temperature fluctuations produced by gravity waves should induce significant chemical responses in the Na layer below 88 km.
Coupled surface‐atmosphere reflectance (CSAR) model: 1. Model description and inversion on synthetic data
Authors: Rahman Hafizur , Verstraete Michel M. , Pinty Bernard
Published: February 2008

Absorption and scattering processes in the atmosphere affect the transfer of solar radiation along its double path between the Sun, the Earth's surface, and the satellite sensor. These effects must be taken into account if reliable and accurate information on the surface must be retrieved from satellite remote sensing data. One approach consists in characterizing the state of the atmosphere from independent observations and correcting the data with the help of radiation transfer models. This approach requires a detailed and accurate description of the composition of the atmosphere (e.g., aerosol and water vapor profiles in the case of advanced very high resolution radiometer data) at the time of the satellite overpass and requires significant computer resources. An alternative method is to attempt to simultaneously retrieve surface and atmospheric parameters by inverting a coupled surface‐atmosphere model against remote sensing data. This study describes such a coupled model and the results of its inversion against synthetic data, using a nonlinear inversion technique. The results obtained are encouraging in that realistic directional reflectances at the top of the atmosphere can be produced, and the inversion of the model against these synthetic data is capable of estimating surface and atmospheric variables. The accuracy of the retrieval is studied as a function of the amount of noise added to the data. It is shown that some surface or atmospheric parameters are easier to retrieve than others with such a coupled model, and that although it appears to be difficult to accurately and reliably estimate the water vapor amount from channel 2, there is a definite possibility of retrieving the aerosol loading from simulated channel 1 data, if the type of aerosol can be assumed.
Onset of the summer monsoon over White Sands Missile Range, New Mexico, as seen by VHF radar
Authors: Nastrom G. D. , Eaton F. D.
Published: February 2008

A case study is presented of the onset of the seasonal transition from the dry conditions characteristic of early summer over southern New Mexico to the more humid conditions of late summer. Observations of Cn2 from the VHF radar wind profiler at White Sands Missile Range, New Mexico, are used as proxy indicators of humidity in the troposphere. The observations are made each 3 min at heights from about 5 to 20 km and are presented as hourly means. During June 1991, a sudden shift in the mean value of Cn2 of about 10 dB took place throughout the troposphere, in a time span of only a few hours. Surface and upper air charts, local weather observations, weather surveillance radar, and satellite imagery are used to establish the synoptic events associated with this shift. No distinct feature changed in the flow patterns aloft or in the analyzed air mass boundaries. The shift in moisture observed by the VHF radar is found to persist on time scales of a month or more from inspection of time series of precipitable water from radiosonde data at nearby El Paso, Texas.
Characteristics of gravity waves (10 min‐6 hours) at Saskatoon (52°N, 107°W): Observations by the phase coherent medium frequency radar
Authors: Manson A. H. , Meek C. E.
Published: February 2008

Height‐time cross sections of the power spectral density in two bands (10–100 min, 2–6 hours) for gravity waves (IGW) are formed from horizontal (u, v) and vertical (w) wind measurements made during 1989 and 1990 using the Saskatoon MF radar (52N, 107W). These climatologies are compared with the seasonally varying mean winds, and are consistent with data from previous years (1979–1984), which demonstrated semiannual variations (solstitial maxima) below ∼90 km and annual (winter maximum) above 90 km. Directions of preferred propagation are inferred by forming the wind perturbation
covariances and fitting ellipses to the perturbation velocities; the preferred orientations are closer to meridional (NS) than to zonal (EW) especially for the shorter periods. Finally the
,
products, which are the vertical fluxes of horizontal momenta, are formed in cross section and time series formats for the longer periods. The zonal momenta
have a seasonal variation below 85 km apparently modulated by the zonal mean winds, with mainly westward/eastward momenta in winter/summer months. The divergences of the flux provide accelerations of +10 m s−1 d−1 in summer (65–80 km) and −15 ms−1 d−l in winter (75–90 km), which are somewhat less than (but often opposite in sign to) the Coriolis torque on the meridional flow. Such comparisons suggest that shorter period waves must also contribute important fluxes of momentum. The fluctuations in IGW intensities and covariances over time scales of several days may be considerable and will affect the sampling needed to obtain seasonal means. Fluctuations due to planetary waves and stratwarms are observed.
A photostationary state analysis of the NO2‐NO system based on airborne observations from the subtropical/tropical North and South Atlantic
Authors: Davis D. D. , Chen G. , Chameides W. , Bradshaw J. , Sandholm S. , Rodgers M. , Schendal J. , Madronich S. , Sachse G. , Gregory G. , Anderson B. , Barrick J. , Shipham M. , Collins J. , Wade L. , Blake D.
Published: February 2008

The Chemical Instrumentation Test and Evaluation 3 (CITE 3) NO‐NO2 database has provided a unique opportunity to examine important aspects of tropospheric photochemistry as related to the rapid cycling between NO and NO2. Our results suggest that when quantitative testing of this photochemical system is based on airborne field data, extra precautions may need to be taken in the analysis. This was particularly true in the CITE 3 data analysis where different regional environments produced quite different results when evaluating the photochemical test ratio (NO2)Expt/(NO2)Calc, designated here as RE/RC. The quantity (NO2)Calc was evaluated using the following photostationary state expression: [NO2]Calc = (k1[O3] + k4[HO2] + k5[CH3O2] + k6[RO2]) [NO]Expt/J2. The four most prominent regional environmental data sets identified in this analysis were those labeled here as free‐tropospheric northern hemisphere (FTNH), free‐tropospheric tropical northern hemisphere (FTTNH), free‐tropospheric southern hemisphere (FTSH), and tropical‐marine boundary layer (plume) (TMBL(P)). The respective RE/RC mean and median values for these four data subsets were 1.74, 1.69; 3.00, 2.79; 1.01, 0.97; and 0.99, 0.94. Of the four data subsets listed, the two that were statistically the most robust were FTNH and FTSH; for these the respective RE/RC mean and standard deviation of the mean values were 1.74 ± 0.07 and 1.01, ± 0.04. The FTSH observations were in good agreement with theory, whereas those from the FTNH data set were in significant disagreement. An examination of the critical photochemical parameters O3, UV(zenith), NO, NO2, and non‐methane hydrocarbons (NMHCs) for these two databases indicated that the most likely source of the RE/RC bias in the FTNH results was the presence of a systematic error in the observational data rather than a shortcoming in our understanding of fundamental photochemical processes. Although neither a chemical nor meteorological analyses of these data identified this error with complete certainty, they did point to the three most likely possibilities: (1) an NO2 interference from a yet unidentified NOy species; (2) the presence of unmeasured hydrocarbons, the integrated reactivity of which would be equivalent to ∼2.7 parts per billion by volume (ppbv) of toluene; or (3) some combination of points (1) and (2). Details concerning hypotheses (1) and (2) as well as possible ways to minimize these problems in future airborne missions are discussed.
Monitoring the evolution of 1991 Pinatubo aerosols over Beijing by combining twilight observations with lidar detection
Authors: Wu Beiying , Lu Daren
Published: February 2008

The degree of polarization of skylight in the zenith direction before and after the eruption of the Mount Pinatubo observed with a newly developed multiwavelength photometer as well as the profiles of backscattering ratio detected by a lidar are used along with a Monte Carlo radiative transfer model to evaluate the optical depth of stratospheric aerosols at 0.7‐μm wavelength over Beijing (39°57′N, 116°21′E). Observations show that the stratospheric aerosols over Beijing significantly increased after the eruptions of the Mount Pinatubo. A large temporal variation was found. The optical depth of the aerosols reached the maximum during the period from February 1992 to April 1992, then decreased gradually. Although significantly decreased, the optical depth of stratospheric aerosols had not recovered to the background level until September 1992. The retrieved results show that there was a layer of aerosols in the layer 8–11 km with an optical depth of 0.01 after the eruption. This layer of aerosols may interfere with the deduction of the aerosol backscattering ratio from the lidar detection and might also affect the formation of ice crystals in cirrus clouds and therefore influence the climate.
Introduction to the MSATT special section
Authors: Haberle Robert M.
Published: February 2008

This special section of JGR‐Planets was motivated by the tremendous increase in scientific activities that deal with the planet Mars. For the past decade, many of these activities have been nurtured by NASA's Mars Data Analysis Program, which has been structured around a series of 3‐year research programs that sequentially address topics with the greatest potential for study. The latest of these programs is MSATT: the Martian Surface and Atmosphere Through Time which began in October 1990. The general goal of MSATT is to understand the processes that have developed and modified the Martian surface and atmosphere through time.
Stratigraphy and erosional landforms of layered deposits in Valles Marineris, Mars
Authors: Komatsu G. , Geissler P. E. , Strom R. G. , Singer R. B.
Published: February 2008

The complex stratigraphy of layered deposits suggests a diversity of origins, ages, and post‐depositional modification histories. The complexities within some layered deposits indicate changes in the dominant source materials in space and time. The stratigraphy of layered deposits in the isolated Martian chasmata Hebes, Juventae and Gangis is not well correlated. This indicates that at least these chasmata had isolated depositional environments resulting in different stratigraphic sequences. Separated layered deposits in Ophir‐Candor and Melas Chasmata might have been a single continuous deposit in each chasma. Chaotic terrains are found in conjunction with layered deposits in Juventae, Gangis and Capri‐Eos Chasmata. In these chasmata, layered deposits unconformably overlie chaotic terrains. Chaotic terrain formation may have provided water to form paleolakes, and lacustrine deposition of thick layered deposits may have occurred if the canyons were closed. A very thick sequence of the layered deposits has been exposed by erosion. A combination of gradual processes such as evaporation of ice and eolian and fluvial transport in addition to structural processes may be responsible for this erosion. Another alternative is that catastrophic water release under the layered deposits disrupted and initiated erosion of the layered deposits. Newly identified units of anomalous color are confined to the depressions or reentrants in western Candor Chasma. The difference in color between these units and the surrounding terrain is most consistent with a somewhat greater content of bulk crystalline hematite in these anomalous units. The presence of the Candor units is a result of original and/or secondary deposition which is different from the primary and dominant formation of the layered deposits.
Magnetic fields of the terrestrial planets
Authors: Russell C. T.
Published: February 2008

The four terrestrial planets, together with the Earth's Moon, provide a significant range of conditions under which dynamo action could occur. All five bodies have been visited by spacecraft, and from three of the five bodies (Earth, Moon and Mars) we have samples of planetary material upon which paleomagnetic studies have been undertaken. At the present time, only the Earth and Mercury appear to have a significant dipole magnetic field. However, the Moon, and possibly Mars, appear to have had ancient planetary dynamos. Venus does not now have a significant planetary magnetic field, and the high surface temperatures should have prevented the recording of evidence of any ancient magnetic field. Since the solidification of the solid inner core is thought to be the energy source for the terrestrial magnetic field, and since smaller bodies evolve thermally more rapidly than larger bodies, we conjecture that the terrestrial planets are today in three different phases of magnetic activity. Venus is in a predynamo phase, not having cooled to the point of core solidification. Mercury and the Earth are in the middle of their dynamo phase, with Mercury perhaps near the end of its activity. Mars and the Moon seem to be well past their dynamo phase. Much needs to be done in the study of the magnetism of the terrestrial planets. We need to characterize the multipole harmonic structure of the Mercury magnetic field plus its secular variation, and we need to analyze returned samples to attempt to unfold the long‐term history of Mercury's dynamo. We need to more thoroughly map the magnetism of the lunar surface and to analyze samples obtained from a wider area of the lunar surface. We need a more complete survey of the present Martian magnetic field and samples from a range of different ages of Martian surface material. Finally, a better characterization of the secular variation of the terrestrial magnetic field is needed in order to unfold the workings of the terrestrial dynamo.
Temperature and abundances in the Jovian auroral stratosphere: 1. Ethane as a probe of the millibar region
Authors: Livengood Timothy A. , Kostiuk Theodor , Espenak Fred , Goldstein Jeffrey J.
Published: February 2008

We report infrared heterodyne spectroscopy (λ/Δλ ∼ 106) of C2H6 emission at 11.9 μm from the northern Jovian auroral region, in observations conducted over December 2–7, 1989. Accurately measured line shapes provide information on C2H6 abundance as well as temperature and permit retrieval of the source pressure region. Enhanced emission was observed in the longitude range ∼150°–180° at ∼60° north latitude, approximately corresponding to the CH4 7.8‐μm hot spot and the region of brightest UV aurora. Significant brightness variations were observed in the hot spot emissions on a time scale of ∼20 hours. Analysis of the brightest hot spot spectra indicates C2H6 mole fractions of ∼(6.3–6.8) × 10−6 at temperatures of ∼182–184 K at 1 mbar, compared to mole fractions of (3.8 ± 1.4) × 10−6 averaged over spectra outside the hot spot at a temperature of ∼172 K at the same pressure. Fixing the mole fraction to the lower limit retrieved in the quiescent (non‐hot spot) region allows the temperature at 1 mbar to be as high as ∼200 K within the hot spot. These results provide upper limits to the temperature increase near the source of the C2H6 thermal infrared emission. Combined with results from similar measurements of ethylene emission probing the ∼10‐μbar region (Kostiuk et al., this issue), altitude information on the thermal structure of the Jovian auroral stratosphere can be obtained for the first time.
Development of a dust mantle on the surface of an insolated ice‐dust mixture: results from the KOSI‐9 experiment
Authors: Grün Eberhard , Gebhard Jürgen , Bar‐Nun Akiva , Benkhoff Johannes , Düren Helmi , Eich Günter , Hische Ralf , Huebner Walter F. , Keller Horst Uwe , Klees Gabriele , Kochan Hermann , Kölzer Gabriele , Kroker Harald , Kührt Ekkehard , Lämmerzahl Peter , Lorenz Eckehard , Markiewicz Wojciech J. , Möhlmann Diedrich , Oehler Achim , Scholz Joachim , Seidensticker Klaus J. , Roessler Kurt , Schwehm Gerhard , Steiner Gerhard , Thiel Klaus , Thomas Hubertus
Published: February 2008

Astronomical observations indicate that formation and destruction of dust mantles on cometary nuclei may be the cause for erratic and systematic variations of cometary activity, i.e. emission of dust. A laboratory experiment (KOSI‐9) has been performed to study the evolution of a dust mantle on top of a sublimating ice‐dust mixture in vacuum. A sample consisting of water ice with a 10% (by weight) admixture of olivine grains has been insolated in three periods at variable intensities from 200 to 1900 W/m2. Both increasing surface temperature of the sample and decreasing gas and particle emissions indicated the formation of a dust mantle during the first period. During the second insolation period after the gas flux had reached a critical value of a few 1021 water molecules m−2 s−1, avalanches of mantle material occurred on the inclined sample surface, broke up the mantle locally, and opened up a fresh icy surface. Enhanced ice and dust particle emission resumed for some time from these spots. A large number of the emitted dust particles were of a fluffy aggregate structure, i.e., they had large cross section to mass ratios compared to compact particles. During the third period the critical gas flux was not reached and no enhanced dust and ice emission was observed. A dry dust mantle of a few millimeters thickness developed during the course of the experiment. Consequences of these findings for cometary scenarios are discussed.
Specular scattering on a terrestrial playa and implications for planetary surface studies
Authors: Shepard Michael K. , Arvidson Raymond E. , Guinness Edward A.
Published: February 2008

Multiangle Advanced Solid State Array Spectroradiometer and Portable Apparatus for Rapid Acquisition of Bidirectional Observations of Land and Atmosphere visible and near infrared reflectance data covering the Lunar Lake playa, Nevada, were modeled using specular and volume scattering theory. The volume component used to model the data was based on the Hapke (1986) model and the specular scattering component was based on Fresnel reflection from surface facets with a distribution of tilts. Specular scattering was needed to explain the several‐fold increase in reflectance observed at high phase angles in the solar principal plane. Results imply single scattering albedos of approximately 0.93 to 0.95, a real index of refraction value of approximately 1.52 (at a wavelength of 0.66 μm), a small imaginary index of refraction and an exponential facet tilt probability function for the playa. Electron micrographs showed the playa surface to consist of ensembles of smooth, micrometer‐scale ellipsoidal particles on gently undulating topography at the millimeter to centimeter scale. The exponential probability function is consistent with this observation. Mars and the icy satellites are discussed as possible places to look for a significant specular scattering component.
Calcareous nannofossils and the origin of eastern Mediterranean sapropels
Authors: Castradori Davide
Published: February 2008

A quantitative analysis of calcareous nannofossil assemblages was carried out, with an optical microscope, on four deep‐sea cores raised from the eastern Mediterranean and selected to form a NW‐SE transect. A total of 748 samples were studied, including a very detailed analysis of sapropels S5 and S6 in two, out of the four cores. This paper is restricted to the discussion of the results obtained on Florisphaera profunda which provided important insights on the mechanisms of sapropel formation, an intricated and unravelled puzzle for the scientists of the last decades. On the basis of abundance variations of F. profunda, the only species of calcareous nannoplankton which inhabits the lower part of the photic zone, I suggest that sapropel formation was triggered by increased primary production, either confined to a Deep Chlorophyll Maximum (DCM) (a concept previously introduced by Rohling and Gieskes, [1989]) or extended to a thicker layer of the photic zone. When increased primary production was confined to the DCM (sapropel S3, S4, S5, S7, and S1, this latter only in the eastern part of the basin), the abundance of F. profunda was enhanced greatly with respect to all other species living in the higher part of the photic zone. On the contrary, when the increased primary production was extended to a thicker layer of the photic zone (“glacial” sapropels S6 and S8) the production of most nannoplankton species was favored, decreasing the relative proportion of F. profunda.
Effect of Drake and Panamanian Gateways on the circulation of an ocean model
Authors: Mikolajewicz Uwe , Maier‐Reimer Ernst , Crowley Thomas J. , Kim Kwang‐Yul
Published: February 2008

Geologic studies indicate that prior to ∼40 Ma the Drake Passage was closed and the Central American Isthmus was open. The effect of these changes has been examined in an ocean general circulation model. Several sensitivity experiments were conducted, all with atmospheric forcing and other boundary conditions from the present climate, but with different combinations of closed and open gateways. In the first experiment, the only change involved closure of the Drake Passage. In agreement with earlier studies the barrier modified the geostrophic balance that now maintains the circumpolar flow in the southern ocean, with the net effect being decreased transport of the Antarctic Current and an approximate fourfold increase in outflow of Antarctic deep‐bottom waters. The very large increase in Antarctic outflow suppresses North Atlantic Deep Water (NADW) formation. In addition to corroboration of results from earlier studies, our simulations provide several new insights into the role of a closed Drake Passage. A more geologically realistic closed Drake/open central American isthmus experiment produces essentially the same pattern of deepwater circulation from the first experiment, except that Antarctic outflow is about 20% less than the first experiment. The resultant unipolar deepwater circulation pattern for the second experiment is consistent with paleoceanographic observations from the early Cenozoic. A third experiment involved an open Drake and open central American isthmus. In this experiment, Antarctic outflow is diminished to slightly above present levels but NADW production is still low due to free exchange of low‐salinity surface water between the North Pacific and North Atlantic. The low level of thermohaline overturn should have reduced oceanic productivity in the Oligocene (∼30 Ma), a result in agreement with geologic observations. Finally, simulations with an energy balance model demonstrate that the changes in surface heat flux south of 60°S due to breaching of the Drake barrier do not result in temperature changes large enough to have triggered Antarctic glaciation. This last result suggests that some other factor (CO2?) may be required for Antarctic ice sheet expansion in the Oligocene (∼30–34 Ma). Our results lend further support to the concept that even in the absence of changing boundary conditions due to ice sheet growth, variations in the geometry of the ocean basins can significantly influence ocean circulation patterns and the sediment record. The results also suggest that the primary polarities of the Cenozoic deepwater circulation may have been controlled by opening and closing of these two gateways.
Strontium isotope stratigraphy in the Late Cretaceous: Numerical calibration of the Sr isotope curve and intercontinental correlation for the campanian
Authors: McArthur J. M. , Thirlwall M. F. , Chen M. , Gale A. S. , Kennedy W. J.
Published: February 2008

The white Chalk exposed in quarries at Lägerdorf and Kronsmoor, northwestern Germany, provides a standard section for the European Upper Cretaceous. The 87Sr/86Sr values of nannofossil chalk and belemnite calcite increase upward through 330 m of section, from ≤0.70746 in the Upper Santonian to ≥0.70777 in the Lower Maastrichtian. The data define three linear trends separated by major points of inflection at stratigraphic heights in the section of 162 m (75.5 Ma) in the Upper Campanian Galerites vulgaris zone and at −6 m (82.9 Ma), just above the base of the Campanian in the Inoceramus lingua/Gonioteuthis quadrata zone. The temporal rate of change of 87Sr/86Sr was constant through each of the linear segments of our isotope “curve” when viewed at the resolution of our average sampling interval (0.15 m.y.). Fine structure, if real, may record brief (<100 kyr) excursions of 87Sr/86Sr from values expected from the overall trends. In Lägerdorf, the boundary between the Santonian and Campanian stages, taken here as the level of first occurrence of the belemnite Gonioteuthis granulataquadrata, has an 87Sr/86Sr of 0.707473±5. This is within error of the values of 0.707457±16 for this boundary in the U.S. western interior (base of the Scaphites leei III zone) and 0.707479±9 for this boundary in the English Chalk (top of the Marsupites testudinarius zone). In Kronsmoor, the boundary between the Campanian and Maastrichtian stages, taken here as the level of first occurrence of the belemnite Belemnella lanceolata, has an 87Sr/86Sr of 0.707723±4. This is within error of the values of 0.707725±20 for this boundary in the U.S. western interior (base of the Baculites eliasi zone) and 0.707728±5 for this boundary in the English Chalk (defined as in Germany).
A proof of the Woodward‐Lawson sampling method for a finite linear array
Authors: Somers Gary A.
Published: February 2008

An extension of the continuous aperture Woodward‐Lawson sampling theorem has been developed for a finite linear array of equidistant identical elements with arbitrary excitations. It is shown that by sampling the array factor at a finite number of specified points in the far field, the exact array factor over all space can be efficiently reconstructed in closed form. The specified sample points lie in real space and hence are measurable provided that the interelement spacing is greater than approximately one half of a wavelength. This paper provides insight as to why the length parameter used in the sampling formulas for discrete arrays is larger than the physical span of the lattice points in contrast with the continuous aperture case where the length parameter is precisely the physical aperture length.
An extended range‐modified gradient technique for profile inversion
Authors: Kleinman R. E. , van den Berg P. M.
Published: February 2008

A method for reconstructing the complex index of refraction of a bounded inhomogeneous object from measured scattered field data is presented. The index and the unknown fields within the object are simultaneously reconstructed in an iterative algorithm. The method is a refinement of earlier work which incorporates a more effective way to update the unknowns at each stage of the iteration. Considerable efficiency in the algorithm is achieved. Some numerical examples are given indicating the limits on the contrasts which can be reconstructed. These limits show that the range of contrasts that may be reconstructed is extended over that achievable with the earlier work.
Geometrical optics based on wave‐normal rays: Application to dielectric waveguides
Authors: Hashimoto Masahiro
Published: February 2008

The theory of stationary optics, which has recently been developed for guided waves in dielectric waveguides, is briefly reviewed. The various rules for the stationary rays, called the wave‐normal rays, are discussed in comparison with the conventional dynamical optics rules. However, our attention is restricted to the simplest example of applications to illustrate the basic idea of new geometrical optics. Mathematical details of derivation are omitted.
Vectorial analysis of bends in optical strip waveguides by the method of lines
Authors: Pascher Wilfrid , Pregla Reinhold
Published: February 2008

The vectorial analysis by the method of lines is extended to investigate optical waveguides consisting of several circularly bent strips. Bessel functions of very large and complex order are employed to calculate radiation loss and intensity distribution, for example, for a rib waveguide.
A new type of alternating code for incoherent scatter measurements
Authors: Sulzer Michael P.
Published: February 2008

An alternating code set is employed as one of several possible techniques used in incoherent scatter radar transmissions to obtain ambiguity‐free measurements of autocorrelation functions or spectra with good range resolution. An alternating code set consists of several codes; typically, each successive radar pulse is modulated with a different code in the sequence. This technique is useful in other types of radar transmissions when the target is overspread, assuming the targets have certain statistical properties. Code sets for a new type of alternating code are presented for code lengths 8–12. This new type of alternating code differs from the first kind in two ways: it is subject to a slightly different condition for the elimination of ambiguity, and it is not restricted to lengths that are powers of 2. The new lengths are useful because they allow greater freedom in designing a multipurpose radar waveform best utilizing the available duty cycle of the radar. The alternating code technique is described in detail sufficient to allow an understanding of the two types and to show that the new condition for ambiguity‐free measurements is a useful one. A search program was used to find the new sets; the aspects of the program important for decreasing the size of the search space are described. The code sets are presented, and their significance and uses are discussed.
An indentation model for the North and South China collision and the development of the Tan‐Lu and Honam Fault Systems, eastern Asia
Authors: Yin An , Nie Shangyou
Published: February 2008

Passive continental margins are geometrically irregular as a consequence of either triple‐junction evolution or the development of transfer zones in detachment fault systems, whereas active continental margins are smoothly arc‐shaped due to subduction of plates on the Earth's spherical surface. We propose that this basic difference in boundary geometry has played an important role in the latest Paleozoic‐early Mesozoic collision of North and South China. In particular, we suggest that prior to collision, the active southern margin of the North China Block (NCB) was contiguous across the Qilian Shan, Qinling, Dabie Shan, Shandong peninsula of east central China to the Imjingang area of central Korea. The passive northern margin of the South China Block (SCB), in contrast, had a more irregular shape, such that its northeastern segment in northern Jiangsu and eastern Anhui provinces of China extended some 500 km farther north than its western counterparts in northern Sichuan, southern Shaanxi, and northern Hubei provinces. Collision of the NCB and the SCB began by indentation of the northeastern SCB into the eastern NCB in the late Early Permian and lasted until the Late Triassic‐Early Jurassic. The indentation produced the left‐slip Tan‐Lu fault in northeastern China and the right‐slip Honam shear zone in southeastern Korea and caused the northward displacement of the Shandong and the Imjingang metamorphic belts. This model predicts that collision along the Dabie and Qinling metamorphic belt occurred significantly later than along the Shandong belt, which is consistent with radiometric and depositional constraints on the time of collision. The proposed model accounts for the abrupt termination of the Tan‐Lu fault at its south end and the drastic decrease in slip along the Tan‐Lu fault north of the Shandong metamorphic belt. The model also predicts the distribution and ages of metamorphism along the suture and the observed local but intense Triassic deformation (=Indosinian orogeny) in northeastern China and northern Korea, which was previously an enigmatic feature in this region.
Trench‐proximal volcanism following ridge crest‐trench collision along the Antarctic Peninsula
Authors: Hole M. J. , Larter R. D.
Published: February 2008

On the basis of multichannel seismic reflection, magnetics and bathymetry data, a Pleistocene‐Holocene (<0.1Ma) volcanic seamount has been identified at a location very close to the shelf edge off the west coast of the Antarctic Peninsula. The seamount overlies the subducted trace of a transform fracture zone which divides segments of the margin along which collision took place 3.1 and 6.0 Ma ago. New trace element and isotopic data from dredged samples demonstrate that the seamount appears to be predominantly formed of relatively primitive undersaturated alkali basalt. The basalts have geochemical signatures that are indistinguishable from ocean island basalts and some continental alkali basalts, (e.g. Th/Ta 1.0–1.5, Rb/Nb<0.5, 87Sr/86Sr 0.70265–0.7028, 143Nd/144Nd approximately 0.5129) and are totally lacking in any evidence for interaction with subduction‐enriched mantle. Geochemical similarities with other, more trench distal, postsubduction alkalic basalts along the Antarctic Peninsula are striking, strongly implying that all the postsubduction basalts were derived from a chemically similar asthenospheric source region. The basalts were most likely to have been generated as a result of the formation of a slab window beneath the Antarctic Peninsula following ridge crest‐trench collision. Subduction component‐free subslab asthenosphere upwelled into the incipient void left by the continued sinking of the leading plate following collision, and decompressional melting resulted. This type of trench‐proximal volcanism following ridge crest‐trench collision differs from that in other locations where calc‐alkaline volcanism persisted or ophiolite obduction occurred.
Denali Fault System of southern Alaska: An interior strike‐slip structure responding to dextral and sinistral shear coupling
Authors: Redfield Thomas F. , Fitzgerald Paul G.
Published: February 2008

The Denali fault system (DFS) extends for ∼1200 km, from southeast to south central Alaska. The DFS has been generally regarded as a right‐lateral strike‐slip fault, along which post late Mesozoic offsets of up to 400 km have been suggested. The offset history of the DFS is relatively unconstrained, particularly at its western end. For this study we calculated relative motion vectors at discrete points along the length of the DFS, based on the well‐understood kinematic interaction between the North American, Pacific, and Kula plates, and the following assumptions: (1) The arcuate geometry of the DFS has existed essentially unchanged since the Late Cretaceous; (2) The Yukon‐Tanana terrane and other terranes north of the DFS were fixed, in situ, prior to the accretion of the southern Alaskan terranes; and (3) Tangential and normal relative motion vector components calculated for points along the DFS using the plate model of Kelley [1993] describe the plate kinematics of the DFS since the Late Cretaceous. The consequent kinematic model for the DFS predicts that left‐lateral stresses have acted upon the western end of the DFS for much of its history, and conflicting senses of shear exist between the eastern and western ends of the system. The offset history of the western end of the Denali fault system should be significantly different than the history of the central and eastern sections; consequently, individual crustal blocks in southeast and southwest Alaska may have undergone, respectively, clockwise and counterclockwise rotations. The sense of rotation predicted by our model is in agreement with rotations determined by paleomagnetic studies and provides an alternative model to the “Alaskan orocline” hypotheses.
Interpretation of magnetic anomalies over the Grenada Basin
Authors: Bird Dale E. , Hall Stuart A. , Casey John F. , Millegan Patrick S.
Published: February 2008

The Grenada Basin is a back arc basin located near the eastern border of the Caribbean Plate. The basin is bounded on the west by the north‐south trending Aves Ridge (a remnant island arc) and on the east by the active Lesser Antilles island arc. Although this physiography suggests that east‐west extension formed the basin, magnetic anomalies over the basin exhibit predominantly east‐west trends. If the observed magnetic anomalies over the basin are produced by seafloor spreading, then the orientation of extension is complex. Extension in back arc basins is roughly normal to the trench, although some basins exhibit oblique extension. Present models for the formation of the Grenada Basin vary from north‐south extension through northeast‐southwest extension to east‐west extension. An interpretation of magnetic anomalies over the Grenada Basin supports basin development by nearly east‐west extension. Low amplitude magnetic anomaly trends subparallel to the island arc magnetic anomaly trends over the southern part of the basin and the results of forward three‐dimensional (3‐D) magnetic modeling are consistent with this conclusion. Late Cenozoic tectonic movements may have been responsible for disrupting the magnetic signature over the northern part of the basin. On the basis of our 3‐D analysis, we attribute the prominent east‐west trending anomalies of the Grenada Basin to fracture zones formed during seafloor spreading at low latitude. This east‐west trend is not interpreted as indicating north‐south extension of the basin.