bluuebunny/crossref_metadata_2025 huggingface dataset:
Nighttime reactive nitrogen measurements from stratospheric infrared thermal emission observations
Authors: Abbas Mian M. , Kunde Virgil G. , Brasunas J. C. , Herman J. R. , Massie Steven T.
Published: February 2008

Infrared thermal emission spectra of the Earth's atmosphere in the 700–2000 cm−1 region were obtained with a cryogenically cooled high‐resolution interferometer spectrometer on a balloon flight from Palestine, Texas, on September 15–16, 1986. The observations exhibit spectral features of a number of stratospheric constituents, including important species of the reactive nitrogen family. In this paper we present an analysis of the observed data for simultaneously measured vertical distributions of O3, H2O, N2O, NO2, N2O5, HNO3, and ClONO2. These measurements permit the first direct determination of the nighttime total reactive nitrogen concentrations, and the partitioning of the important elements of the NOx family. Comparisons of the total reactive nitrogen budget are made with the measurements by the ATMOS experiment and with the predictions of one‐dimensional and two‐dimensional photochemical models.
Mesospheric KHI signatures in reconstructed broadband rocket probe data
Authors: Parker Jay W. , Bowhill Sidney A.
Published: February 2008

In an accepted method of measuring D region electron density with a rocket‐borne DC‐mode Langmuir probe, the resulting fine‐structure signal is modified by a high‐pass filter. While this form of data has been successfully used for power spectral analysis, it fails to reveal important spatial domain features without further processing. We demonstrate that the broadband signal can be recovered by use of a digital filter that corrects for the on‐board high‐pass filter effects. The D region broadband structure so recovered for a daytime equatorial flight shows variations in electron density consistent with a model of Kelvin‐Helmholtz billows, and not consistent with inertial range turbulence. The isolated regions of irregularity are ∼ 100 m thick near an altitude of 75 km, imbedded in a region with a staircase‐structure electron density profile with ∼ 200‐m steps. We show suggestive similarities to a numerical model of KHI and to undersea observations of KHI‐caused microstructure.
Isoprene and monoterpene emission rate variability: Observations with eucalyptus and emission rate algorithm development
Authors: Guenther Alex B. , Monson Russell K. , Fall Ray
Published: February 2008

Variability in the emission rates of isoprene and monoterpenes from individual leaves of Eucalyptus globulus was investigated with a laboratory gas exchange system and an environmental control leaf cuvette. For individual leaves, with constant environmental conditions, short‐term (1 hour) fluctuations in isoprene emission rates were less than 3% while day‐to‐day fluctuations averaged 14%. Leaf‐to‐leaf variations were much larger (62%). Fluctuations with time and leaf‐to‐leaf variability in CO2 assimilation rates were of the same order as isoprene, while monoterpene variations were higher. Leaf age was identified as one of the factors contributing to leaf‐to‐leaf variability in CO2 assimilation and isoprene and monoterpene emission rates. Monoterpene emission rates were not influenced by light intensity or CO2 mixing ratio. The observed temperature dependence was the same for α‐pinene and 1,8‐cineole (an oxygenated monoterpene) and is similar to the temperature dependence of monoterpene emission rates reported by other investigators. Isoprene emissions were slightly dependent on humidity (1–3% increase in emission per 10% increase in relative humidity) and responded only to very low (<100 ppm) or very high (>600 ppm) CO2 mixing ratios. Isoprene emission was associated with the abaxial leaf side, which contains stomatal pores, while monoterpenes were emitted primarily from the adaxial side, which lacks stomatal pores. The temperature and light dependence of isoprene emission closely resembles relationships observed for electron transport in plant chloroplasts. For this reason, we have used a mechanistic electron transport model as the basis for an empirical isoprene emission rate model. The emission rate variation predicted by this model was within 10% of observed values for 62% of the 255 observations at light‐saturated conditions and temperatures between 23° and 33°C. The entire data base includes over 600 observations at leaf temperatures ranging between 12° and 50°C and light intensities between 0 and 2000 μmol m−2 s−1. Nearly two thirds of the emission rates predicted for the entire data base were within a factor of 1.25, and 89% were within a factor of 2. The algorithms developed in this study provide a solid physiological basis for future efforts to model the biogenic flux of isoprene and monoterpenes into the atmosphere.
UV gas and liquid phase absorption cross section measurements of hydrochlorofluorocarbons HCFC‐225ca and HCFC‐225cb
Authors: Braun W. , Fahr A. , Klein R. , Kurylo M. J. , Huie R. E.
Published: February 2008

The environmental effect of chlorofluorocarbon (CFC) replacement compounds such as the hydrochlorofluorocarbons (HCFCs) requires accurate data for gas phase absorption cross sections. Such data are particularly important in the near uv wavelength region where the cross sections are often very low. Measurements of such low cross‐sections are difficult and unreliable. In the present work we have found that absorption cross sections derived from measurements in the liquid phase for two HCFCs, 1,1,1,2,2‐pentafluoro‐3,3‐dichloropropane (HCFC‐225ca) and 1,1,2,2,3‐pentafluoro‐l,3‐dichloropropane (HCFC‐225cb) can, with appropriate correction factors, be converted into accurate gas phase values. The method itself has a basis in theoretical treatments which relate liquid to gas phase absorption cross section conversions. Thus a reliable experimental technique is available for determining gas phase absorption cross sections of diffuse absorbers in regions of very low absorptions. The method minimizes some of the systematic errors that accompany the measurement of extremely low gas phase absorbtivity in the ultraviolet and can potentially cover a wide range of temperature.
A study of the dependence of rural ozone on ozone precursors in the eastern United States
Authors: McKeen S. A. , Hsie E.‐Y. , Liu S. C.
Published: February 2008

A comprehensive three‐dimensional mesoscale model, with detailed treatment of meteorology and photochemistry, is applied to the eastern United States and southeastern Canada to address the issue of ozone production over rural regions. Simulations with various anthropogenic emission reductions over a 4‐day high‐pressure period, for which the eastern U.S. experienced elevated O3 levels, are compared to the results of a reference case that incorporates the most recent National Acid Precipitation Assessment Program (1985) emissions inventory. Our focus is on the relative effects of anthropogenic NOx versus nonmethane hydrocarbons (NMHC) emission reductions on O3 concentrations within this photochemical regime. The model results are consistent with earlier studies that predict a reasonably high O3 sensitivity to NMHC emission reductions, and O3 increases for NOx emission reductions in regions of strong urban influence. However, the total area that exhibits these distinctly urban characteristics comprises less than 10% of the continental area within the model. O3 production for the majority of the eastern United States is found to be limited by NOx availability rather than NMHC. Thus the sensitivity to NOx emission reductions averaged over the continental regions of the model domain is about a factor of 3 higher than that of NMHC. Because of large uncertainties in the natural and anthropogenic NMHC emissions, additional sensitivity runs are performed with increased anthropogenic NMHC emissions and natural NMHC emissions excluded. These alterations do not effect our basic conclusions with respect to rural O3 formation but do impact urban locations. When anthropogenic NMHC emissions are increased by a factor of 4, control Of NOx emissions has nearly the same effect in both urban and rural areas. The nonlinear nature of regionally averaged O3 with respect to anthropogenic and natural precursors is also illustrated from the results of the sensitivity studies.
Extension of the Diendorfer‐Uman lightning return stroke model to the case of a variable upward return stroke speed and a variable downward discharge current speed
Authors: Thottappillil R. , McLain D. K. , Uman M. A. , Diendorfer G.
Published: February 2008

A new lightning return stroke model has recently been proposed by Diendorfer and Uman (1990). In this model, if one specifies a current at the channel base (ground), a constant return stroke speed, and a channel discharge time constant, one can derive analytically the current and charge as a function of time and height associated with the channel above ground. Here we present a more general and more straightforward derivation of the Diendorfer‐Uman model. In the new formulation we allow a variable return stroke speed that can be any arbitrary function of height. The influence of a decrease in speed with height, as occurs in nature, on the channel current and charge distributions and on the radiated electric and magnetic fields is determined and compared with the constant speed case. For a given channel base current, a decreasing speed with height does not change the initial peak electric and magnetic fields appreciably from the values found for a constant speed having the same value as the variable speed at the channel base, but a decreasing speed can cause considerable changes in field waveshapes for both the distant radiation fields and the near electrostatic fields. In addition to allowing an arbitrary return stroke speed, the new formulation of the Diendorfer‐Uman model allows the downward propagating current waves released by the return stroke front also to have an arbitrary variable speed, whereas the original model assumed that speed to be constant at the speed of light.
Seasonal and annual carbon fluxes in a boreal forest landscape
Authors: Bonan Gordon B.
Published: February 2008

Ecosystem process models were used to estimate seasonal and annual landscape carbon fluxes in the boreal forests near Fairbanks, Alaska. The forest landscape is a successional mosaic of recently burned to old‐growth stands and productive to unproductive stands growing on a variety of soil types. A model of forest dynamics simulated annual production and decomposition for a successional mosaic of 250 stands growing on five representative sites. A model of daily ecosystem photosynthesis and respiration decomposed these annual carbon fluxes into a seasonal cycle. Simulated annual aboveground tree production, annual moss production, and annual forest floor decomposition were not significantly different from observed data. Monthly estimates of the normalized difference vegetation index derived from NOAA's AVHRR sensor, which is thought to represent canopy photosynthesis, accounted for 85% of the seasonal variation in landscape‐averaged tree carbon flux. On average the landscape absorbed 74 g C m−2 yr−1. Carbon uptake by trees was the dominant flux (225 g C m−2 yr−1). Carbon loss during microbial respiration was of secondary importance (144 g C m−2 yr−1). Carbon uptake during moss growth and carbon loss during fire were less important (23 and 30 g C m−2 yr−1, respectively). Potential model errors indicate that the net landscape carbon uptake represents the lower bounds of the possible uptake. If valid for the circumpolar taiga, this net flux extrapolates to an uptake of 0.85 to 1.11 Gt C per year.
Spectral analysis of temperature and Brunt‐Väisälä frequency fluctuations observed by radiosondes
Authors: Tsuda Toshitaka , VanZandt Thomas E. , Mizumoto Masahiro , Kato Susumu , Fukao Shoichiro
Published: February 2008

We observed profiles of the temperature, T, and Brunt‐Väisälä frequency squared, N2, from 0 to 30 km in altitude using radiosondes with 150 m height resolution launched from the MU observatory, Japan (34°51′N, 136°06′), from September 27, 1986, to February 24, 1989. We analyzed vertical wavenumber spectra of the normalized temperature T/T and N2 fluctuations in the 2.0–8.5 km (troposphere) and 18.5–25.0 km (lower stratosphere) altitude ranges and compared them with model spectra based on saturated gravity wave theory. In the winter stratosphere the slope of the mean T/T spectra in the wavenumber range from 7.0×10−4 to 2.0×10−3 (cycles per meter) was very close to the −3 predicted by the model, and the spectral amplitudes were 1.3–1.9 times larger than the predicted values, which is within the possible range of variability of the model. On the other hand, in the summer stratosphere the spectral slope ranged from −2.2 to −2.4, which is more gradual than the model, and the spectral amplitudes were only 0.4 to 0.5 of the predictions. The spectral shape in the troposphere did not show a significant difference between summer and winter. The spectral amplitudes, however, exceeded the model values by factors of about 3.2 and 1.9 in winter and summer, respectively. The overall shape of the profile for fluctuations with vertical scales from 150 to 900 m was generally similar to the shape of the background value of N4, consistent with the saturated gravity wave model, but the details of the altitude variations were rather complicated. That is, just below the tropopause usually exceeded the model by a factor of 2 to 4, and it became significantly smaller than the model in the summer stratosphere and in a region above 25 km in winter.
The influence of dynamics on two‐dimensional model results: Simulations of 14C and stratospheric aircraft NOx injections
Authors: Jackman Charles H. , Douglass Anne R. , Brueske Kurt F. , Klein Stephen A.
Published: February 2008

A two‐dimensional (2D) photochemical model (latitude range from −85° to +85° and altitude range from the ground to 0.23 mbar (about 60 km)) has been used to investigate the influence of dynamics on model results. We tested three representations of atmospheric transport to simulate total ozone and 14C amounts after nuclear tests in the early 1960s. We also simulated three scenarios of NOx. injections from a proposed fleet of stratospheric aircraft and their effects on ozone. The three dynamical formulations used were Dynamics A, a base dynamics used in previous work with this model; Dynamics B, a strong circulation dynamics discussed by Jackman et al. [1989a] and Dynamics C, the dynamics used by Shia et al. [1989]. The advective component of the stratosphere to troposphere mass exchange rate (advective strat/trop exchange rate (ASTER)) is largest for Dynamics B (5.8×1017 kg yr−1) and smallest for Dynamics C (1.4×1017 kg yr−1), with the ASTER for Dynamics A (2.4×1017 kg yr−1) being between these two extremes. Simulations of both total ozone and 14C were worst with Dynamics B. Simulations of total ozone were best with Dynamics A and for 14C best with Dynamics C. This illustrates the difficulty of simultaneously modeling constituents with different altitude and latitude dependencies. Ozone depletion from NOx injections of stratospheric aircraft showed a strong sensitivity to dynamics. Generally, if eddy diffusion is not changed, then a large ASTER leads to reduced ozone loss while a small ASTER leads to increased ozone loss from a given stratospheric NOx injection.
Thermal stress tectonics on the satellites of Saturn and Uranus
Authors: Hillier John , Squyres Steven W.
Published: February 2008

Most of the major Saturnian and Uranian satellites have undergone some form of extensional tectonism and/or resurfacing early in their histories. We examine the stresses created by the early thermal evolution of these satellites and consider the geologic implications of these stresses. Starting from an initial accretional temperature profile, we calculate the satellites' temperature profiles as they evolve by conduction. Solid state convection, when it occurs, is handled using a simple parameterized convection scheme. The effects of radiogenic heating and release of heat of phase change are included. The thermal stresses built up in the satellites are then calculated, assuming the satellites to have a Maxwell viscoelastic rheology. The stress calculation takes into account both the effects of thermal stresses and of shifts in the position of the ice I/ice II phase boundary in some satellites. If accretion takes place in a cold, gas‐free environment, the stresses that build up in the smaller satellites (Mimas, Miranda, and Enceladus) are minor. In the larger satellites, however, stresses are large enough to cause fracturing and extensional tectonism under these circumstances. The stresses result largely from rapid cooling contraction of a thin outer shell; the ice II → ice I phase transition also contributes significantly for the largest satellites. If accretion occurs in a warm gaseous nebula that dissipates rapidly, stresses large enough to cause failure are attained in all of the satellites. In all cases, the material immediately underlying the zone of failure is the warmest in the satellite and hence may be buoyant and mobile enough to be extruded to the surface through fractures created by the extension. We conclude that thermal stresses following accretion led to a substantial early episode of extensional tectonism and perhaps also associated resurfacing on many of the Saturnian and Uranian satellites. If evidence of this early episode of extensional tectonism has survived subsequent impacts, then the process may have been responsible for much of the early tectonism and resurfacing observed on these satellites. If not, then it may only be responsible for the very early global resurfacing that some of the satellites are inferred to have undergone.
The sodium zenocorona
Authors: Smyth William H. , Combi Michael R.
Published: February 2008

A recent narrow‐band‐filtered CCD image by Mendillo et al. (1990) has shown that a sodium corona, produced near Io, extends at least 400 Jupiter radii in the planet's equatorial plane. Isophotes indicate that the polar to equatorial extents are in ∼1 to 3 proportions. The image can be reproduced by a model which includes both a high‐ and an intermediate‐speed distribution, with source rates of 2.2 and 1.1 × 1026 atoms s−1, respectively. The high−speed distribution was ejected from Io with a velocity tangential to the satellite orbit of 57 km s−1 (∼74 km s−1 relative to Jupiter) plus an isotropic Maxwellian velocity distribution of ∼25 km s−1. This distribution likely corresponds to a charge exchange source of plasma torus sodium ions which are neutralized in the near‐Io atmosphere and are ejected relative to Jupiter with a corotational velocity (74 km s−1) plus a thermal ion (25 km s−1) Maxwellian distribution. The intermediate speed distribution was ejected from Io with a tangential speed near 20 km s−1 (37 km s−1 relative to Jupiter) plus an isotropic Maxwellian velocity distribution of ∼12 km s−1. This distribution corresponds to the same nonthermal sodium atoms earlier identified near Io in the sodium directional features (Pilcher et al., 1984). Modeled Doppler profiles of the sodium D lines show that moderate resolution spectroscopy would prove to be highly diagnostic of both the velocity distribution of the source near Io and the resulting periodic time variations expected. On the scale of a few astronomical units, the sodium corona displays a cometary comalike appearance because of the acceleration of sodium atoms induced by solar radiation pressure. Finally, at distances of roughly 1000 planetary radii the effects of the ∼400‐hour photoionization lifetime of sodium atoms should begin to become apparent in observed radial profiles.
Near‐Mars space
Authors: Luhmann J. G. , Brace L. H.
Published: February 2008

The space environment of Mars is largely determined by its lack of a substantial planetary magnetic field. In contrast to Earth, Mars does not have radiation belts or an auroral “oval,” and its perturbation of the interplanetary medium or solar wind is confined to a relatively small volume. Moreover, the direct interaction of the solar wind plasma with the Martian atmosphere produces a distinctive local energetic particle population of planetary origin, which provides evidence of the possibly significant scavenging of certain elements from Mars over the life of the solar system. In this paper we describe the general characteristics of near‐Mars space, as it is known today, including both the ambient interplanetary environment and the ionosphere, upper atmosphere, and regions above that are affected by the presence of Mars.
Evolution of gravity anomalies across collisional mountain belts: Clues to the amount of continental convergence and underthrusting
Authors: Lillie Robert J.
Published: February 2008

A series of density models illustrates the gross form of free air and Bouguer gravity anomalies anticipated during ocean basin closure and consequent development of collisional orogens. When compared to gravity anomalies observed across some mountain belts, the hypothetical anomalies provide a clue to the degree of under thrusting of crust associated with one lithospheric plate beneath crust of the opposing plate margin. The results of the study suggest very early stage collision in the Ouachita Mountains of Arkansas and the Sulaiman Range of Pakistan, with thin transitional or oceanic crust still intact on the lower plate. In contrast, the Himalaya of Pakistan represent a much more advanced stage of collision, where continental crust may have underthrust the mountains for 600 km.
From transcurrent faulting to frontal subduction: A seismotectonic study of the Northern Caribbean Plate Boundary from Cuba to Puerto Rico
Authors: Calais Eric , Béthoux Nicole , de Lépinay Bernard Mercier
Published: February 2008

Recent marine and onland geophysical and geological investigations along the northern Caribbean plate boundary call for a review of its tectonic interpretation, in the light of a new compilation of the seismological data avalaible from Cuba to Puerto Rico. We show that the shallow seismicity in the northeastern Caribbean is concentrated along an east‐west trending lineament corresponding to the trace of the major strike‐slip fault system. The most intense seismicity is located around restraining bends such as southern Cuba and northern Hispaniola. The stress and strain distribution deduced from focal mechanisms and microtectonic analysis lead us to infer a small N‐S convergence component associated with the major eastward strike‐slip motion of the Caribbean plate versus North America. Earthquake distribution and focal mechanisms suggest the existence of a lithospheric slab inherited from the frontal subduction under the Lesser Antilles diping down under Puerto Rico and eastern Hispaniola. We propose a model in which this slab is disconnected from the Atlantic oceanic lithosphere by transcurrent faulting along the plate boundary.
Seasonal variations of stable hydrogen and carbon isotope ratios of methane in subtropical freshwater sediments
Authors: Burke Roger A. , Barber Timothy R. , Sackett William M.
Published: February 2008

Abstract. Stable hydrogen (δD) and carbon (δ13C) isotope ratios of sedimentary methane from five subtropical Florida freshwater sites exhibited smaller, less distinct seasonal variations than previously observed in temperate sediments, apparently due to the smaller range of temperatures forcing the subtropical environments. Negative correlations observed between δD‐CH4 and δ13C‐CH4 at these sites probably resulted from mixing methane produced via acetate fermentation with methane formed from CO2 and H2. The inverse δD/δ13C trends, high sedimentary gas methane concentrations (up to 80 mole%), and visual observations imply that ebullition dominates methane transport from the sediments during at least part of the seasonal cycle. Many values deviated from the main inverse δD/δ13C trend such that bacterial oxidation was not indicated. The deviation may result from the reduction of CO2 with varying δ13C under conditions of elevated H2 concentrations or enhanced interspecies hydrogen transfer, which may cause relatively greater hydrogen isotopic fractionation. Alternatively, the deviation may result from fermentation of autotrophically formed, 13C‐depleted acetate. Differences in the δ13C of bulk organic matter from two of the sites potentially account for about half of the difference in mean δ13C‐CH4 between the two sites. In other cases, however, the immediate methanogenic precursor (e.g., acetate versus CO2/H2) appeared to be the major determinant of methane stable isotopic composition.
Rising slope of moment rate functions: The 1989 earthquakes off east coast of Honshu
Authors: Ishihara Yasushi , Fukao Yoshio , Yamada Isao , Aoki Harumi
Published: February 2008

A series of large earthquakes occurred off east coast of Honshu, Japan, during the period of October to November 1989. Mechanisms were studied for the foreshock (M=6.5), the mainshock (M=7.1) and the two aftershocks (M=5.2 and 5.3) using the STS‐I broadband records at station INU about 700km away from the epicenters. The lowpass filtered seismograms of these earthquakes show mutually very similar waveforms, in good agreement with those calculated for a known mechanism by an extended reflectivity method. The mainshock is 10 times as large as the foreshock and 2000 times as large as the aftershocks in terms of seismic moment. Assuming that the mainshock (or foreshock) is a collection of some elementary sources at a focal point and that aftershock seismograms represent the responses to such elementary sources, the broadband seismogram of the mainshock (or foreshock) for the first 60s was deconvolved with that of an aftershock to obtain the moment rate function. The moment rate functions of the mainshock and foreshock are both triangle‐like with durations of 14 and 9s respectively. Their rising slopes are mutually very different, a greater slope is associated with the greater shock. This and the similar results for other pairs of earthquakes suggest that the rising slope of moment rate function is causaly related to the eventual size of seismic rupture.
Acoustic emissions produced by anticrack faulting during the olivine→spinel transformation
Authors: Green H. W. , Scholz C. H. , Tingle T. N. , Young T. E. , Koczynski T. A.
Published: February 2008

Anticrack faulting during the phase transformations of olivine to its denser polymorphs is a principal contender for the mechanism of deep‐focus earthquakes. The original work on Mg2GeO4 established that initiation of faulting by this mechanism is not due to brittle fracture and subsequent experiments on olivine of mantle composition showed that it can operate at pressures of at least 14 GPa. Here we report acoustic emissions accompanying anticrack faulting in Mg2GeO4, thereby confirming that this mechanism involves a dynamic instability accompanied by elastic radiation.
Comparisons of observed ozone and temperature trends in the lower stratosphere
Authors: Miller A. J. , Nagatani R. M. , Tiao G. C. , Niu X. F. , Reinsel G. C. , Wuebbles D. , Grant K.
Published: February 2008

One result of the Ozone Assessment [WMO, 1989] is that there is a significant negative ozone trend in the lower stratosphere and upper troposphere from 1970 through 1986. In this paper we examine the relationship of this trend in ozone to that of temperature in the same altitude region utilizing a 62 station set of rawinsonde data, and compare the results to the changes in temperature determined from a radiative equilibrium model calculation. The calculated and observed trends in lower stratospheric temperature indicate substantive agreement in shape and magnitude of the vertical profiles.
Non‐relativistic solar electron events during December 1990: Results from Ulysses
Authors: Anderson K. A. , Chaizy P. , Lin R. P. , Sommers J.
Published: February 2008

Several groups of impulsive flare accelerated non‐relativistic solar electron events occurred in November and December 1990. In a total of 18 separate events, most show the characteristic dispersion in arrival times at the Ulysses spacecraft corresponding to travel time for the various particle energy groups. After maximum development, the electron intensities generally decay smoothly with characteristic times of 10 to 15 hours. In a few cases there are marked departures from this “classic” behavior. On 15 December 1990, these departures are associated with a structure in the interplanetary magnetic field having a width of ∼4 × 106 km at 1.37 A.U. The particle intensities inside this structure varied greatly with spatial position. Some of the changes occurred over distances as small as 3 × 104 km. We believe that this interplanetary structure had its origin in the complex magnetic fields that overlay the solar active region in which the electron accelerating flares occurred, and that it is these fields near the Sun that determine access of the flare accelerated electrons to interplanetary field lines. A solar electron event on 11 December 1990 is similar in many respects to the one on 15 December. Neither of these events is directly related to an interplanetary shock wave.
Dynamic rupture processes of inland earthquakes in Japan weak and strong asperities
Authors: Miyatake Takashi
Published: February 2008

Reconstruction of dynamic rupture process of four large earthquakes in Japan shows two types of high stress drop region on the fault planes, i.e., high stress drop part with low strength excess, and that with high strength excess, where the strength excess is the difference between strength and applied initial stress. Here, we call the first type of the above high stress drop part “weak asperity” or “asperity with low strength” and the second one “strong asperity” or “asperity with high strength”.
Fractal model for sunspot evolution
Authors: Milovanov A. V. , Zelenyi L. M.
Published: February 2008

This paper analyzes the model for the evolution of sunspots considered as fractal clusters of magnetic flux tubes. Formation of sunspots is regarded as a result of magnetic tubes aggregation to the cluster. It is proved that magnetic field dissipation in the tubes results in effective sunspot decay. Sunspot formation and decay times deduced by the model as well as the rate of magnetic flux loss are in a good agreement with the observational data. The diffusion of magnetic flux tubes in sunspot penumbra is considered as a random walk on a fractal geometry. Disappearance of umbra in decaying sunspots is interpreted as a phase transition.
Evidence for a missing carbon monoxide sink based on tropospheric measurements of 14CO
Authors: Mak John E. , Brenninkmeijer Carl A. M. , Manning Martin R.
Published: February 2008

An important problem in atmospheric chemistry is the determination of the oxidative capacity of the troposphere, which provides an index of how quickly trace gas species are destroyed. Central to this question are the abundance and distribution of hydroxyl radical, which is responsible for the destruction of a large proportion of chemical compounds such as CH4, CO, and nonmethane hydrocarbons. 14CO can be used as a chemical tracer to help constrain the OH concentration, as oxidation via OH is the major sink for all carbon monoxide. We present the first 14CO observations in the free troposphere during different seasons from 90°S to 34°N. Model simulations suggest that a large increase in the carbon monoxide sink strength may be needed in order to accommodate the experimental results.
Lidar conversion parameters derived from SAGE II extinction measurements
Authors: Thomason L. W. , Osborn M. T.
Published: February 2008

SAGE II multiwavelength aerosol extinction measurements are used to estimate mass‐ and extinction‐to‐backscatter conversion parameters. The basis of the analysis is the principal component analysis of the SAGE II extinction kernels to estimate both total aerosol mass and aerosol backscatter at a variety of wavelengths. Comparisons of coincident SAGE II extinction profiles with 0.694‐μm aerosol backscatter profiles demonstrate the validity of the method.
Altimetric gravity anomalies in the Norwegian‐Greenland Sea ‐ Preliminary results from the ERS‐1 35 days repeat mission
Authors: Knudsen Per , Andersen Ole Baltazar , Tscherning C. Christian
Published: February 2008

New fast delivery 35 days repeat ERS‐1 altimeter data have been used to recover the gravity field in the Norwegian‐Greenland Sea. Furthermore the spectral characteristics of the gravity field have been investigated from 18 arcs of 3 days repeat period data. The recovered gravity field correlates exclusively with the major geological structures, which clearly demonstrates the potential of these new ERS‐1 altimeter data.
Thermal buoyancy on Venus: Underthrusting vs subduction
Authors: Burt Jeffrey D. , Head James W.
Published: February 2008

In an effort to define the conditions distinguishing underthrusting and subduction in the Venus environment, we have modeled the thermal and buoyancy consequences of the subduction endmember. Predictions of the thermal evolution of a slab subducting at a fixed angle into the Venusian mantle are used to find slab densities based on slab composition and changes of temperature, pressure, and phase. The sustainability of subduction is assessed by considering the effects of slab buoyancy and mantle flow on the subduction angle. Mantle flow induced by slab motion applies torques on the slab, which are compared to buoyancy torques. Flow torques tend to decrease the angle of subduction. Buoyancy torques also act to decrease the subduction angle when the slab is positively buoyant. The basalt‐eclogite phase transition dominates the transformation of positively buoyant slabs to negative buoyancy. Slabs that have descended to depths less than about 275 km remain positively buoyant. Beyond 275 km slabs become negatively buoyant. We predict that the combination of flow and buoyancy torques will tend to force initially subducted slabs to assume an underthrusting position, leading to crustal thickening, deformation, melting, and volcanism. This may provide a model explaining the association of compressional mountain belts and tessera blocks with apparent flexural rises, foredeeps, and voluminous volcanic deposits. Only special circumstances appear capable of promoting the conditions for negative slab buoyancy. These might include one where an underthrust slab becomes attached to or included in a densified crustal root created in a zone of crustal thickening. The subsequent delamination and sinking of the root may then lead to the subduction of the slab.
Spring measurements of tropospheric bromine at Barrow, Alaska
Authors: Sturges William T. , Schnell Russell C. , Dutton Geoffrey S. , Garcia Samuel R. , Lind John A.
Published: February 2008

The partitioning of bromine in the lower troposphere between particulate, inorganic gaseous, and organic gaseous phases was measured during the arctic spring. Rapid photochemical production of particulate Br− from organic gaseous Br was indicated by 1) an inverse correlation between particulate bromide and organic gaseous bromine (r²=−0.67), 2) a diurnal cycle in the ratio of these two phases, and 3) a diurnal cycle in the ratio of organic gaseous Br to Cl. Organic gaseous Br and Cl were correlated (r²=0.67) indicating a common, possibly marine, source.
High resolution measurements of density structures in the Jovian plasma sheet
Authors: Ansher J. A. , Kurth W. S. , Gurnett D. A. , Goertz C. K.
Published: February 2008

A recent effort to determine the plasma density by using the low‐frequency cutoff of trapped continuum radiation in the vicinity of the Jovian plasma sheet has revealed the existence of sharply defined density structures in the plasma sheet. These structures typically have a plasma density which is relatively constant, but of order 50% greater or less than that of the surrounding plasma. The transitions from low to high density occur on time scales of about ten seconds, which correspond to spatial dimensions of the order of a few ion Larmor radii. Voyager requires time intervals of less than a minute to more than five minutes to traverse the structures themselves, corresponding to size scales from a fraction of a Jovian radius to more than a Jovian radius. The existence of such structures in the Jovian magnetosphere raises obvious questions as to their three‐dimensional nature as well as their origin. We suggest that the structures might represent flux tubes of varying plasma content, but on the basis of single‐point measurements, we do not have the observations necessary to describe the three‐dimensional form of the structures. A Fourier transform of the density variations yields a featureless spectrum which displays an inverse frequency dependence. This spectrum is consistent with the square wave‐like form of the density variations observed. The observations of flux tubes in the middle magnetosphere of widely varying plasma content may be the result of a centrifugally‐driven plasma transport mechanism acting inwards of the point of observation. We conclude that the structures observed are not consistent with an eddy‐diffusion model.
Determination of electron polytropic indices in the environment of comet P/Halley
Authors: Mazelle Christian , Belmont Gerard
Published: February 2008

We present a general experimental method to investigate the relations between the density variations and the pressure variations (parallel and perpendicular to the ambient magnetic field) for one particle population of a hot collisionless plasma. The theoretical aspects of this problem have already been discussed in a recent paper [Belmont and Mazelle, 1992]. The aim of this letter is to provide a complete description of the data analysis technique for an experimental case, from GIOTTO electron and magnetic field data measured in the environment of comet P/Halley, used to verify the theory. The correlations between the electron characteristics, density and pressures (parallel and perpendicular), and the magnetic field strength are investigated. In this case, the method shows that the relations between the electron density and pressures can be satisfactorily represented by two polytropic laws. The values inferred for the polytropic indices strongly differ from those usually found in the literature, but are nevertheless fully quantitatively explained from the theoretical analytical calculations.
Teleseismic interpretation of the 1968 Dasht‐e Bayaz, NE Iran, Earthquake
Authors: Gheitanchi M. R. , Kikuchi M. , Mizoue M.
Published: February 2008

The 1968 Dasht‐e Bayaz earthquake is the oldest destructive earthquake in north‐east Iran recorded by the WWSSN network at teleseismic distances. These records are well distributed in azimuth and allow a detailed study of the rupture process of the main shock. We invert the WWSSN long‐period body waves of the Dasht‐e Bayaz earthquake and its principal aftershock, which occurred about 20 hours later, to their sources to study the complexity of the sources. The results of our analysis suggest that the main shock consists of three major subevents while the principal aftershock is a single event. Mechanisms of the subevents of the main shock are mainly strike‐slip and consistent with the observed fault movement. The principal aftershock has a dip‐slip mechanism. The sum of the seismic moments of the main shock is ∑M0 = 4.5×1026 dyn cm. The moment of the largest subevent of the main shock is M0 = 2.4×1026 dyn cm and its stress drop is about 200 bar. This shows that the main shock has a high stress drop nature. The largest subevent with shallow depth and large lateral displacement mostly caused the great destruction during the source process of the main shock. The moment of the principal aftershock is M0 = 1.9×1025 dyn cm and its stress drop is about 40 bar. Mechanism of the earthquakes suggest that there is a shortening in north‐east Iran mostly due to the north‐east compressional stress in the Iranian plateau.
Arctic sea ice albedo: A comparison of two satellite‐derived data sets
Authors: Schweiger Axel J. , Serreze Mark C. , Key Jeffrey R.
Published: February 2008

Spatial patterns of mean monthly surface albedo for May, June, and July, derived from DMSP Operational Line Scan (OLS) satellite imagery are compared with surface albedos derived from the International Satellite Cloud Climatology Program (ISCCP) monthly data set. Spatial patterns obtained by the two techniques are in general agreement, especially for June and July. Nevertheless, systematic differences in albedo of 0.05 – 0.10 are noted which are most likely related to uncertainties in the simple parameterizations used in the DMSP analyses, problems in the ISCCP cloud‐clearing algorithm and other modeling simplifications. However, with respect to the eventual goal of developing a reliable automated retrieval algorithm for compiling a long‐term albedo data base, these initial comparisons are very encouraging.
A comparison of several cooling schedules for simulated annealing implemented on a residual statics problem
Authors: Mirkin Gerri , Vasudevan Kris , Cook Frederick A. , Laidlaw William G. , Wilson William G.
Published: February 2008

A study of several cooling schedules for the simulated annealing optimization algorithm, as applied to a residual statics problem in seismic data processing, is undertaken and discussed. A variety of schedules which depend on user‐controlled parameters and an adaptive annealing schedule which depends on the system itself are considered. The algorithm, with each schedule implemented in turn, is tested on a residual statics estimation where the optimization function is a coherence function between adjacent common depth point (CDP) gathers. Results of this study suggest the usefulness of a hybrid cooling schedule to reduce the number of cycles. Constrained adaptive annealing schedule offers a viable alternative.
Source parameters of the June 29, 1992 Little Skull Mountain Earthquake from complete regional waveforms at a single station
Authors: Walter William R.
Published: February 2008

The June 29, 1992, mb=5.5, Little Skull Mountain earthquake occurred 20 km southeast of Yucca Mountain within the boundaries of the Nevada Test Site. This event was recorded at a very broadband station located about 310 km to the east at Kanab, Utah. Both body and surface waves from this single station were used in a grid search technique for the best fitting double couple moment tensor. The technique minimizes the misfit between reflectivity generated complete synthetic seismograms and the three‐component displacement data via a search over the strike, dip and rake of the source. In the passband of 50–15 s period, the grid search results in a well defined, nearly pure normal mechanism with a strike of 35°, a dip of 54°, a rake of −87°, and a seismic moment of 4.1 × 1017 N‐m. Applying the same technique to the large aftershock on July 5, 1992 we obtain a somewhat less well defined minimum with a strike of 358°, a dip of 36°, a rake of −177°, and a moment of 4.3 × 1015 N‐m. The minimum‐compression axes of these mechanisms are consistent with northwest‐southeast extension in the Basin and Range.
Correlation between magnetic and electric field perturbations in the field‐aligned current regions deduced from DE 2 observations
Authors: Ishii M. , Sugiura M. , Iyemori T. , Slavin J. A.
Published: February 2008

Satellite observations have shown high correlation between magnetic and electric field perturbations in the high‐latitude field‐aligned current regions. The high correlation has been interpreted by two models. In the first, the Static model, the observed perturbations are regarded as being static spatial variations, and the ratio of the orthogonal magnetic and electric field components ΔBz/Ex represents the height‐integrated ionospheric Pedersen conductivity ΣP. In the second, Alfvén wave model, the observed perturbations are interpreted as being Doppler‐shifted Alfvén waves, and the inverse of the ratio gives the Alfvén wave velocity VA. In this paper we investigate changes of this ratio with spatial scale length, using the DE 2 observations. The ratio ΔBz/Ex is found to change little with scale length for variations of scale lengths longer than 64 km, or 8.0 s in time. While for variations of smaller scale lengths, which are obtained using numerical filters with cutoff periods shorter than 4.0 s, the same ratio shows a significant dependence on scale length. The calculated ratios are nearly equal to ΣP based on an ionospheric model for long‐wavelength structures and to 1/VA for short‐wavelength variations. The transition from the former to the latter usually begins around 4.0‐8.0 s on the time scale. On the dayside the correlation between ΔBz and Ex is generally high, and the transition is clearly seen. Thus the static model is applicable to valuations of scale lengths greater than 8.0 s (or 64 km); while the Alfvén wave effect becomes increasingly dominant for scale lengths less than 4.0 s (or 32 km). For scale lengths below about 5 km (∼0.6 s) the short‐circuiting effect at ionospheric altitudes higher than the altitudes at which the horizontal Pedersen closure current usually flows becomes appreciable. However, this effect alone cannot explain the observed decrease in the ratio ΔBz/μ0Ex. The relation between the ratio ΔBz/μ0Ex and the solar zenith angle is consistent with the relationship between the Pedersen conductivity and the solar zenith angle in the published conductivity models.
A generalized hinged‐magnetodisc model of Jupiter's nightside current sheet
Authors: Khurana Krishan K.
Published: February 2008

For each of the three spacecraft that have visited the magnetotail of Jupiter, independent hinged‐magnetodisc models have been constructed for Jupiter's nightside current sheet. Model parameters (especially the hinge point distance) derived from any one encounter were found to be inapplicable to data from other encounters. For example, for the Pioneer 10 current sheet crossings, Goertz (1976, 1979) found that the current sheet does not significantly bend away from the dipole magnetic equator. On the other hand, Behannon et al. (1981) and Goertz (1981) found it necessary to introduce hinging of the current sheet in their models near a cylindrical radial distance of 60 RJ for Voyager 1 observations. The hinge distance was found to be even smaller (∼ 40 RJ) for Voyager 2 by Behannon et al. (1981). Vasyliunas and Dessler (1981) have criticized hinged magnetodisc models for their failure to organize current sheet crossing data from all three of the spacecraft by using a single set of parameters. Khurana and Kivelson (1989) in a study that evaluated several models of Jupiter's current sheet pointed out that if the hinging of the magnetotail is caused by solar wind forcing then the hinging distance should be parameterized in terms of Jupiter‐Sun‐magnetospheric (JSM) x coordinate instead of the cylindrical (or planetocentric) radial distance. In this paper we develop a quantitative hinged‐magnetodisc generalized model that incorporates this suggestion and explains the current sheet crossing data from all three of the flybys with the introduction of only three fitting parameters. The present model is comparable to or slightly superior than the models published previously in terms of rms error of fit between the modeled and observed current sheet crossing locations. The added novelty is that unlike the previous models the generalized model does not require a different set of parameters for each of the three encounters. A comparison of our results with the earlier models is presented.