bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion cyclotron harmonic resonances driven by ion ring‐beam distributions
Authors: Wong H. K. , Goldstein M. L. , Smith C. W.
Published: February 2008

Enhanced magnetic fluctuations with frequencies peaking at the ion cyclotron frequency and its harmonics have been observed at comet Halley and also in the upstream regions of planetary bow shocks. It is thought that these waves are generated at comets by pickup ions that are unstable to the generation of waves at harmonics of the ion cyclotron wave number. In the spacecraft frame of reference these waves are observed as harmonics of the ion cyclotron frequency. In this report we show that the ring‐beam distributions of pickup ions observed in the cometary environment are capable of generating these waves if the beam speed component of the distribution (parallel to the ambient magnetic field) is much larger than the ring speed (perpendicular to the magnetic field). As the ring speed increases relative to the beam speed, other instabilities occur at the same wave number which have even larger growth rates. These additional instabilities do not lead to generation of harmonics.
Critical points in the 16‐moment approximation
Authors: Yasseen F. , Retterer J. M.
Published: February 2008

The singular points in steady state, field‐aligned plasma transport models based on velocity moment theory are examined. In particular, two separate singular points in the equations obtained from the 16‐moment approximation are identified. These equations are presented in a form that makes the singularities apparent, and they are solved in a simple illustrative case. The singular points, one occurring at the sonic point and the other at a critical value of the parallel heat flux, give rise to different outflow regimes, characterized generically by different asymptotic behavior. The existence of the different outflow regimes separated by the heat flux critical point has been only hinted at in previous discussions of numerical simulation of the polar wind.
A general statistical instrument theory of atmospheric and ionospheric radars
Authors: Woodman Ronald F.
Published: February 2008

Some basic functional relationships between the statistics of the signals received in a radar and the statistics of the density fluctuations of a scattering medium are derived. They vary in their degree of generality, but they are all very general in scope. They include monostatic and bistatic radars scattering from either atmospheric, ionospheric, or meteorological media. They are valid for refractive and slightly dispersive media, so they can also be used for HF ionospheric radars. They include the effects of filtering, including receiver filtering, pulse compression coding and decoding schemes, and coherent integration, or any alternative linear digital filtering scheme. Functional relationships to include cross‐correlation schemes, such as Faraday rotation experiments and interferometers, are included. Some simplified expressions are derived for frequently encountered situations, where different approximations can be made. These simplified expressions cover a large number of radar techniques currently in use for atmospheric and ionospheric applications.
Mesothermal plasma flow around a negatively wake side biased cylinder
Authors: Coggiola Éric , Soubeyran Amaury
Published: February 2008

We have made a numerical investigation of the wake potential and density perturbations caused by the presence of a large negative voltage on a sector situated on the wake side of a spacecraft moving at orbital speed through the ionosphere. The spacecraft is represented as an infinite cylinder moving in an unmagnetized plasma. The rest of the cylinder's surface is biased to a moderate negative voltage representing floating potential. It is shown that in the case of large Debye ratio (spacecraft size much larger than Debye length) the geometrical wake is almost ion‐empty for a high differential bias voltage on the sector, and that in the case of low Debye ratio and low Mach number, ion focusing effects can lead to the formation of a high‐ion‐density strip parallel to the surface when the differential bias is made very large. In the latter case, the results show evidence of an ionic emptying effect in the near wake and in the midwake. We propose a mechanism to explain this result. Ion collection on the biased sector is also addressed.
Velocity structure of the Vulsinian Volcanic Complex (Latium, Italy) from seismic refraction data and three‐dimensional inversion of travel times
Authors: Amato A. , Biella G. , de Franco R.
Published: February 2008

We have interpreted three reversed seismic refraction profiles and three related fans in the Monti Vulsini Volcanic Complex, modelling travel times and amplitudes calculated using the asymptotic ray theory. The interpretation of the refraction lines revealed complex structure in the shallow crust (0–7 km), characterized by strong lateral heterogeneities. The three‐layer seismic model of the volcanic area is characterized by relatively high P wave velocities, generally ranging from 4.0–4.5 km/s in the uppermost layer to 6.7–7.1 km/s at a depth of about 7 km. The upper layer (0.5–2.7 km thick) corresponds to the volcanic cover and the upper part of the flysch sequence. The depth to the top of the middle layer, corresponding to the lower part of the flysch unit and to the Meso‐Cenozoic carbonate sequence, is very irregular and is strongly controlled by the tectonic evolution of the area. The thickness of this layer ranges between 2.2 and 5.0 km. The third layer extends beneath the whole Vulsinian region and is characterized by high P velocity (6.7–7.1 km/s) at relatively shallow depth (5–7 km). We interpret the high velocity observed in the third layer as being caused by mafic intrusive rocks, such as gabbros, or by high‐grade metamorphic rocks, such as schists, granulates, or metatuffs. The results of the refraction modelling have been compared with a three‐dimensional (3‐D) P velocity model calculated by inverting travel time residuals from explosions and local earthquakes. Generally, close agreement is observed between refraction and inversion models. The fan profiles, as well as three unreversed refraction profiles and 3‐D inversion, showed a velocity decrease, as low as 5%, within the deepest layer in the central part of the volcanic complex. The low‐velocity zone in the central region could be related either to high temperatures and/or partial melt in the intrusive (or metamorphic) body, or to the deepening of the top of the third layer.
The history of Post‐Miocene sea level change: Inferences from stratigraphic modeling of Enewetak Atoll
Authors: Quinn Terrence M.
Published: February 2008

The history of post‐Miocene sea level change has been investigated using a quantitative, one‐dimensional stratigraphic forward model. The stratigraphic model produces synthetic stratigraphies, including mineralogy and sediment age versus depth, in response to changes in sea level, subsidence, sedimentation, and diagenesis. Model outputs, using sea level curves inferred from passive margin sequence stratigraphy and deep‐sea foraminiferal oxygen isotope stratigraphy, were compared to the post‐Miocene stratigraphy of Enewetak Atoll. Modeling results support high‐frequency (104 to 105 years) fluctuations of post‐Miocene sea level. Post‐Miocene sea level elevations significantly greater than modern sea level elevation are not easily reconciled with the stratigraphy of Enewetak Atoll. Model/data fit is maximized when a rapid subsidence rate for Enewetak Atoll is used. Alternatively, model/data fit may be maximized using a lower subsidence rate for Enewetak and having post‐Miocene sea level elevations significantly lower than modem sea level elevation. Given the present state of knowledge, much work is still needed to accurately decipher the record of post‐Miocene sea level change.
Comparison of observed and predicted gravity profiles over Aphrodite Terra, Venus
Authors: Black Martin T. , Zuber Maria T. , McAdoo David C.
Published: February 2008

We compare observed Pioneer Venus orbiter (PVO) gravity profiles over Aphrodite Terra to profiles predicted from models of thermal isostasy, mantle convection, and Airy compensation. Similar approaches are used in order to investigate how well the models can be distinguished with the PVO data. Topography profiles across Aphrodite are compared to model spreading ridge profiles in order to further assess this model. Airy compensation depths and convection layer thicknesses are greater under eastern Aphrodite than western Aphrodite. Compensation depths in the east are greater than most estimates of lithospheric thickness, suggesting that this part of the ridge is dynamically supported. In parts of western Aphrodite, the spreading ridge model gravity provides a better fit to the data than either Airy compensation or mantle convection. Best‐fit spreading rates are between 0.3 and 1.6 cm/yr. Airy compensation and mantle convection cannot be distinguished in most places using only PVO data.
Seismic modeling of the decollement zone at the base of the Barbados Ridge Accretionary Complex
Authors: Bangs Nathan L. B. , Westbrook Graham K.
Published: February 2008

Wide‐aperture seismic reflection profiling of the northern Barbados Ridge accretionary complex at 16°12′N has imaged the decollement horizon across more than 100 km of the accretionary complex revealing prominent changes in the amplitude of the decollement reflection. Synthetic seismograms from models of the variation of velocity and density with depth were compared with selected seismic traces between 2.5 km seaward of the toe of the accretionary complex and 20 km landward of the toe to determine the changes in velocity‐density properties along the decollement thrust zone. Modeling requires a thin, low‐velocity layer to develop landward along the decollement beneath the complex, while no such layer exists at the corresponding stratigraphic boundary in the undeformed sediments seaward of the complex. Two‐dimensional modeling that incorporated lateral variations in topography, velocity, and density was performed on a 7‐km section of the decollement 20 km landward of the deformation front. The best fitting model includes a 20‐m‐thick low‐velocity layer at the decollement horizon with a relative velocity decrease in the layer of 0.2 km/s. Changes in the reflection amplitude along this 7‐km section could be produced by either a change in the velocity anomaly within the layer or a thinning of the decollement layer to less than 4 m. The shape of the reflected wavelet from the decollement indicates that the principal cause of the amplitude variation is a change in the velocity contrast rather than a change in thickness. The low‐velocity layer can be explained by a decollement shear zone that has high porosity maintained by elevated pore fluid pressure. High fracture permeability within the decollement permits dewatering of sediment attached to the oceanic crust and thrust beneath the accretionary complex.
Determination of defect equilibria in minerals
Authors: Hirsch L. M. , Shankland T. J.
Published: February 2008

We have developed a general computation procedure DEFEQ that enables equilibrium defect concentrations in minerals to be quantitatively determined over the range of thermodynamic conditions that encompasses both laboratory experiments and Earth conditions. The governing equations are the quasichemical reactions between defects, conservation of lattice site ratios, and conservation of charge. The input parameters are the enthalpies and entropies for the defect reactions and the thermodynamic conditions which include temperature, gaseous fugacity, and chemical activities. A modified Newton‐Raphson algorithm is used to simultaneously solve the nonlinear set of equations without a priori simplifications on charge balance or lattice site conservation. Our method is general and can be applied to materials other than minerals such as oxide superconductors, semiconductors, and ceramics. The method is illustrated with results from the study of (Mg,Fe)O.
Comparison of a stochastic seafloor model with SeaMARC II Bathymetry and Sea Beam data near the East Pacific Rise 13°–15°N
Authors: Goff John A. , Jordan Thomas H. , Edwards Margo H. , Fornari Daniel J.
Published: February 2008

A recent SeaMARC II survey along the Hanks and crest of the East Pacific Rise between 13° and 15° N (Edwards et al., 1988) provides us with a unique opportunity to compare stochastic models of the seafloor against bathymetric data. Stochastic models can be used to quantitatively characterize intermediate to small‐scale (<100 km) seafloor features such as abyssal hills. In a recent paper, Goff and Jordan (1988) introduced a model for the two‐point covariance function having five free parameters which describe the amplitude, orientation, characteristic wavelengths, and Hausdorff (fractal) dimension of seafloor topography. These parameters can be estimated from multibeam data such as Sea Beam by inverting auto‐ and cross‐covariance functions for the beams. The stochastic model can be used to generate synthetic topography to arbitrary resolution and scale. By assuming appropriate Sea Beam noise and response characteristics we can use the synthetic topography to produce synthetic data sets. Comparison of real and synthetic data is an important means of assessing the performance of the stochastic model. Unfortunately, the limited spatial extent of Sea Beam in the across‐track direction and lack of 100% coverage over large areas severely limit our ability to compare the full two‐dimensional stochastic model with real seafloor morphology, especially with respect to abyssal‐hill length characteristics. The recent SeaMARC II survey included sufficient off‐axis topography (over 100 km, 70,000 km2) to permit a comparison of a complete two‐dimensional synthetic topographic field with a region of abyssal hill terrain that has close to 100% data coverage. We have estimated stochastic models for various regions of the SeaMARC II survey area from several Sea Beam tracks which cross it. Synthetic fields are generated from these models using a Fourier method. These comparisons indicate the extent to which the model succeeds in characterizing seafloor topography, and the directions we will need to take to improve our modeling. A change in ridge complexity at 14° N and the location of a propagator pseudofault appear to be correlated with changes in stochastic character modeled in this region. Such correlations may provide important new constraints on the understanding of ridge processes.
Frequency‐magnitude distribution of earthquakes in Vrancea: Relevance for a discrete model
Authors: Trifu Cezar‐Ioan , Radulian Mircea
Published: February 2008

A high‐resolution analysis of a homogeneous and complete data set of intermediate depth microearthquakes (h > 60 km), extending over an interval of 9.3 years emphasizes a significant deviation at low magnitudes (ML < 4) in a linear frequency‐magnitude distribution. It appears as a distinct change in the slope of the cumulative distribution and as a seismicity deficit followed by a relative enhancement in the corresponding noncumulative curve. This is in agreement with the presence of two characteristic mechanisms and allows the identification of both the magnitude threshold of asperity‐like earthquakes and the transition zone (ML = 3.3 ‐ 3.9) from crack‐like earthquakes (background seismicity) to asperity‐like events. These features are better pointed out on well individualized active zones. The background seismicity shows a tremendeous decrease in its b slope, from 1.03 to 0.57, during a 6‐year interval before the occurrence of a major earthquake in 1986 ( Mw = 7.3), followed by a fast recovery to 1.03 in 2 years after this event. Such a behavior could be correlated to the continuous growth of the shear stress‐free surface on the fault, as in a percolation process, followed by its sudden diminution due to the locking of the fault. The above results provide relevance for the discrete character of faulting and enable a coherent modeling of the earthquake generation process from microearthquake to major event scale lengths.
Crustal structure of accreted terranes in southern Alaska, Chugach Mountains and Copper River Basin, from seismic refraction results
Authors: Fuis Gary S. , Ambos Elizabeth L. , Mooney Walter D. , Christensen Nikolas I. , Geist Eric
Published: February 2008

Seismic refraction data were collected along a 320‐km‐long “Transect” line in southern Alaska, crossing the Prince William, Chugach, Peninsular, and Wrangellia terranes, and along several shorter lines within individual terranes. Velocity structure in the upper crust (less than 9‐km depth) differs among the four terranes. In contrast, layers in the middle crust (9‐ to 25‐km depth) in some cases extend across projected terrane boundaries. The following observations can be made: (1) An intermediate‐velocity layer (6.4 km/s) at 9‐km depth extends across the deep projection of the suture between the Chugach and Peninsular terranes, suggesting that the northern Chugach and southern Peninsular terranes are detached and rest on a deeper terrane of unknown origin. (2) The top of a gently north dipping sequence of low‐ and high‐velocity layers (5.7–7.8 km/s), more than 10 km thick, extends from near the surface in the southern Chugach terrane to more than 20‐km depth beneath the southern Peninsular terrane. This sequence, truncated by the suture between the Prince William and Chugach terranes, is interpreted to be an underplated “terrane” made up of fragments of the Kula plate and its sedimentary overburden that were accreted during subduction in the late Mesozoic and/or early Tertiary, during or between times of accretion of the Prince William and Chugach terranes. (3) A thick crustal “root”, with a laminated sequence at its top, extends from a depth of 19 km to as much as 57 km beneath the northern Peninsular and Wrangellia terranes. This root extends across the deep projection of the suture between the Peninsular and Wrangellia terranes, although resolution of this apparent crosscutting relationship is relatively poor. This root may represent tectonically or, possibly, magmatically emplaced rocks. The lower crust beneath the Prince William, Chugach, and southern Peninsular terranes includes a north dipping, 3‐ to 8‐km‐thick section of subducting oceanic crust.
Rapid subsidence of small oceanic basins: A study of the Marsili Basin, central Mediterranean
Authors: Wang Chi‐Yuen , Kastens Kim , Hwang Win‐Twang
Published: February 2008

Many small backarc basins show subsidence rates significantly greater than those in major ocean basins of similar ages. In this study we test, by numerical modeling, the hypothesis that small backarc basins are formed by the same fundamental processes as major oceanic basins, i.e., by accretion, spreading and cooling, and that the rate of subsidence is modified and accelerated by lateral heat loss from the hot, subbasinal asthenosphere to the surrounding cooler continental lithosphere. Bathymetric, seismic, and drilling data in the Marsili Basin, a small and young backarc basin in the central Mediterranean, are used to constrain the models. The results of this analysis confirm the above hypothesis. They further suggest that for actively spreading backarc basins, the most rapid subsidence occurs in a zone near the margin of the basin during the earliest stage of basin spreading, whereas after spreading terminates the location for rapid subsidence migrates towards the basin center.
Analysis of remotely forced oceanic Rossby waves off California
Authors: Shriver Jay F. , Johnson Mark A. , O'Brien James J.
Published: February 2008

Complex empirical orthogonal function (CEOF) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial structure function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originating in the equatorial Pacific. The spatial structure function is used to extract the interannual Rossby wave response from observed 300‐m‐depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike features observed in the projection mode are order 1000 km long with most periods ranging between 2 and 4 years. The wave numbers and frequencies found are consistent with Rossby dynamics. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s−1, in agreement with the theoretical Rossby wave phase speed at 40°N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2–4 years was identified by Pares‐Sierra and O'Brien (1989) as poleward propagating Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a majority of their periods ranging between 2 and 4 years, their forcing can be attributed to long‐period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3–4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propagation. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300‐m‐depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300‐m depth temperature anomalies.
A study of the use of scatterometer data in the European Centre for Medium‐Range Weather Forecasts operational analysis‐forecast model: 1. Quality assurance and validation
Authors: Anderson D. , Hollingsworth A. , Uppala S. , Woiceshyn P.
Published: February 2008

This paper is Part 1 of a study concerned with the feasibility of using wind scatterometer data in a real‐time data assimilation system. The potential that such a system offers for quality assurance and validation of scatterometer data is illustrated using Seasat A satellite scatterometer (SASS) data. The results of passive assimilations of scatterometer data (where the SASS data are passed to the assimilation system but not used), and of active assimilations of scatterometer data (where the data are used), are presented. It is shown that assimilation allows validation and quality assurance of the scatterometer data, through comparisons with collocated ship data and through comparison with the wind fields generated by the assimilation. Intercomparison can be carried out quickly and efficiently at an operational weather centre where large amounts of data are collected, so allowing comprehensive quality assurance and validation of wind scatterometer data to be carried out in near‐real‐time. A number of comparisons are made which illustrate a speed‐dependent bias between SASS and ship observations and between SASS and forecast model, as well as directional irregularities in the SASS data.
Refinement of the statistical relationship between Straits of Florida sea level difference and Florida‐Bahamas cable voltages
Authors: Mayer Dennis A. , Maul George A.
Published: February 2008

Analyses of a composite 6.5‐year record of Bahamas minus Miami sea level difference (SLD) and Florida‐Bahamas volume transport determined from submarine cable voltages (CABLE) support the hypothesis advanced by Maul et al. (1990) that SLD is the better variable for monitoring volume transport than western side sea level alone. In the subseasonal frequency band BW1 (393−1–182−1 cycles per day), modeled CABLE, when using SLD, accounts for 79% of the variance of observed CABLE. Further, the phase relationships of modeled CABLE with respect to SLD in BW1 represent approximately a simple time shift in that SLD leads CABLE by a little more than 2 weeks.
On the numerical simulation of the sea ice ridging process
Authors: Hopkins M. A. , Hibler W. D. , Flato G. M.
Published: February 2008

A two‐dimensional particle simulation model of the sea‐ice ridging process is developed. In this model, ridges are formed from a floating layer of rubble compressed between converging multiyear floes. The energy consumed in ridge growth, including dissipation, is explicitly calculated. A series of experiments are performed to establish the dependence of the energy consumed in ridging on the velocity of the multiyear floes and on the shape, the friction coefficient, and the inelasticity of the rubble blocks. The experiments show that shape and friction between ice blocks are the most significant factors in determining the energy required to ridge ice. In large‐scale sea ice modeling, using a variable thickness approach, it is convenient to parameterize total ridging work in terms of the increase of potential energy. The results of the ridging simulations with block‐shaped rubble suggest that the total ridging work may be 4–5 times the increase in potential energy. At the same time, an analytical model of the ridging process is developed from classical Mohr‐Coulomb‐Rankine theory for a cohesionless granular material. The predictions of this model, using values of porosity and the passive pressure coefficient derived from the ridge simulations, are in fair agreement with the numerical experiments. However, several violations of the basic assumptions underlying the Mohr‐Coulomb‐Rankine model are noted in the ridge simulations.
Mixing in warm‐core rings of the Kuroshio
Authors: Rogachev Konstantin , Goryachev Vladimir
Published: February 2008

Water mass evolution and ventilation in warm‐core rings of the Kuroshio is discussed using hydrographic (T‐S) data, remote sensing, and tritium measurements. The Kuroshio warm‐core ring A3 detached from the Kuroshio in 1986, migrated northwest along the Japan and Kuril trenches, and reached the southern Kuril Islands in 1989. This ring is characterized by weak stratification to a depth of about 700 m. In its upper layer the ring displayed a pronounced thermostad and a high tritium concentration; in its lower portion, however, temperature and salinity were density compensated. On the basis of tritium data analyses, the thermostad water was shown to originate in intermediate layers of the Kuroshio south of the subarctic front. This implies that the warm‐core rings are a major factor influencing the tritium transport in this region and that they are an important link for water exchange between the subtropical and subpolar gyres in the North Pacific. The tritium data confirm the idea about the origin of the thermostad water of anticyclonic ring from intermediate layers of the Kuroshio. Therefore a mechanism must exist in the Kuroshio frontal zone, which selectively draws water from the Kuroshio to the rings and acts to ventilate the subtropical gyre. It is also noted that during the ring cooling period a surface layer of low tritium content was formed above the ring.
Particle (plankton) size structure across the Azores Front (Joint Global Ocean Flux Study North Atlantic Bloom Experiment)
Authors: Kahru Mati , Nômmann Sulev , Zeitzschel Berndt
Published: February 2008

The horizontal distributions of particle size spectrum and chlorophyll a concentration across the northern edge of the North Atlantic subtropical gyre along 21°W were studied as part of the Joint Global Ocean Flux Study North Atlantic Bloom Experiment in March–April, 1989. An abrupt change in the particle size spectrum at 32°40′N was located within the broad thermohaline front between the central gyre water in the south and the Azores Current in the north. Whereas the small particulate fraction (1–10 μm) and chlorophyll a concentration were similar (within a factor of 2), the abundance of the “diatom” size fraction (28–72 μm ) showed a drastic increase by more than an order of magnitude in the Azores Current. The diatom fraction seemed to contribute little to the chlorophyll pool, indicating a postbloom condition. Different trophic pathways, i.e., grazing of the picoplankton in the gyre versus the diatom bloom with the following detrital loop in the Azores Current and northward, can be conjectured. The increased scattering versus absorption due to the different particle size spectrum and composition could bias the algorithms of pigment retrieval from remote sensing data.
Ozone and other trace gases in the Arctic and Antarctic regions: Three‐dimensional model simulations
Authors: Granier Claire , Brasseur Guy
Published: February 2008

A three‐dimensional mechanistic model of the middle atmosphere with calculated dynamics and chemistry (Rose and Brasseur, 1989) is used to study the behavior of chemically active trace gases at high latitudes in winter and spring, and to simulate the formation of an ozone hole in Antarctica. The dynamics of both hemispheres is simulated by applying at the lower boundary of the model (8.5 km) a wavelike perturbation representing qualitatively a climatological tropospheric forcing. The chemical heterogeneous processes converting chlorine reservoirs into active chlorine in cold air masses are parameterized. The model simulates the behavior of nitrogen oxides, nitric acid, water vapor, methane, hydrogen radicals, chlorine compounds, and ozone. It reproduces important features observed during different Antarctic and Arctic observation campaigns. The ozone hole in the southern hemisphere can only be simulated when the heterogeneous polar chemistry is taken into account. The springtime ozone depletion over Antarctica calculated in the model is thus mostly the result of chemical removal although the dynamics is responsible for the low temperature that triggers the large ozone loss rates. Unresolved questions are related to the strength of the vertical exchanges inside the vortex, the preconditioning of trace gases before and during the winter season, the behavior of the different trace gases as the vortex breaks down (dilution effects), accurate determination of the ozone sink inside the vortex, and a better quantitative estimation of the role of polar stratospheric clouds. Despite elevated concentrations of active chlorine at high latitudes in the northern hemisphere in late winter, no ozone hole is produced by the model, even with chlorine levels as high as 6 ppbv. This conclusion could, however, be modified for very stable and cold winters with delayed final warming.
Vertical distribution of aerosol particles, water vapor, and insoluble trace gases in convectively mixed air
Authors: Kleinman Lawrence I. , Daum Peter H.
Published: February 2008

Vertical distributions of submicrometer size aerosol particles, water vapor, and the insoluble gases (O3, CO, and NOy) were determined from measurements made during 12 aircraft flights conducted in June 1987 near Columbus, Ohio. Measurements extended from the surface to 290 mbar (∼9.5 km) and were made primarily in the vicinity of convective storms. The mixing ratio of aerosol particles decreased strongly with altitude, from an average value of 1800 scm−3 (SCM, standard centimeter) (at 20°C, 1 atm) near the surface to a value in the upper troposphere (30 scm−3, above 300 mbar) that was, on average, less than 2% of the near‐surface mixing ratio. This decrease was similar to that exhibited by water vapor. CO and NOy, in contrast, were more uniformly distributed. Average upper tropospheric mixing ratios were 128 and 0.8 ppb, 51 and 35%, respectively, of boundary layer values. Compact plumelike features were observed at high altitude in which concentrations of boundary layer constituents increased by 50% or more over a distance of several kilometers. These features are attributed to boundary layer air that had been transported upward in convective storms. Such boundary layer air encountered aloft could contain higher mixing ratios of water vapor and aerosol particles than found in adjacent regions, but on an absolute basis these soluble substances were always severely depleted relative to the insoluble gases, CO and NOy. We ascribe the qualitative difference between the vertical distributions of soluble and insoluble substances as being due to in‐cloud processes occurring during upward transport. The upward transport of soluble material is limited by dissolution in cloud water and subsequent conversion of cloud water to downward moving precipitation, whereas insoluble pollutants are not affected by this process.
Solar total irradiance variations and the global sea surface temperature record
Authors: Reid George C.
Published: February 2008

The record of globally averaged sea surface temperature (SST) over the past 130 years shows a highly significant correlation with the envelope of the 11‐year cycle of solar activity over the same period. This correlation could be explained by a variation in the sun's total irradiance (the solar “constant”) that is in phase with the solar‐cycle envelope, supporting and updating an earlier conclusion by Eddy (1976) that such variations could have played a major role in climate change over the past millennium. Measurements of the total irradiance from spacecraft, rockets, and balloons over the past 25 years have provided evidence of long‐term variations and have been used to develop a simple linear relationship between irradiance and the envelope of the sunspot cycle. This relationship has been used to force a one‐dimensional model of the thermal structure of the ocean (Hoffert et al., 1980), consisting of a 100‐m mixed layer coupled to a deep ocean and including a thermohaline circulation. The model was started in the mid‐seventeenth century, at the time of the Maunder Minimum of solar activity, and mixed‐layer temperatures were calculated at 6‐month intervals up to the present. The total range of irradiance values during the period was about 1%, and the total range of SST was about 1°C. Cool periods, when temperatures were about 0.5°C below present‐day values, were found in the early decades of both the nineteenth and twentieth centuries. There is direct evidence for the latter period from the historical SST record and some indirect evidence for the earlier cool period. While many aspects of the study are unavoidably simplistic, the results can be taken as indicating that solar variability has been an important contributor to global climate variations in recent decades. It has probably not been the only contributor, however, and in particular, the growing atmospheric burden of greenhouse gases may well have played an important role in the immediate past. This role is likely to become even more important in the near future.
Assessment of the accuracy of atmospheric temperature profiles retrieved from TOVS observations by the 3I method in the European Arctic; Application for mesoscale weather analysis
Authors: Claud Chantal , Scott Noelle A. , Chedin Alain , Gascard Jean‐Claude
Published: February 2008

In recent years, polar orbiting satellites have greatly increased the number of meteorological measurements in the Arctic, passing over the pole nearly once every hour. The Improved Initialization Inversion (3I) algorithm, which has been designed for retrieving meteorological parameters from observations of the satellites of the TIROS‐N series, has been applied to 17 passes covering the European Arctic in order to check its ability to provide reliable temperature profiles in polar areas. Issues such as sea ice/cloud detection and better estimation of the tropopause level have been addressed and are discussed. Validation of temperature profiles through comparison with radiosonde reports and conventional analyses show the good quality of the retrievals. This quality is also illustrated by the early detection of two storms: one having gone undetected by the standard synoptic network, and one having been incorrectly described by conventional products, confirming the new opportunity offered by satellites to improve our knowledge of polar meteorology.
Consistency of Earth Radiation Budget Experiment bidirectional models and the observed anisotropy of reflected sunlight
Authors: Baldwin Daniel G. , Coakley James A.
Published: February 2008

The Earth Radiation Budget Experiment (ERBE) uses bidirectional models to estimate radiative fluxes from observed radiances. The anisotropy of the radiance field derived from these models is compared with that observed with the ERBE scanner on the Earth Radiation Budget Satellite (ERBS). The bidirectional models used by ERBE were derived from NIMBUS 7 Earth radiation budget (ERB) scanner observations. Because of probable differences in the radiometric calibrations of the ERB and ERBE scanners and because of differences in their field of view sizes, we expect to find systematic differences of a few percent between the NIMBUS 7 ERB‐derived radiation field anisotropy and the ERBS scanner‐observed anisotropy. The differences expected are small compared with the variability of the anisotropy which arises from the variability in cloud cover allowed to occur within the individual scene types. By averaging over groups of 40 ERBE scanner scan lines (equivalent to an average over approximately 2000 km) for a period of a month, we detect significant differences between the modeled and observed anisotropy for particular scene types and Sun‐Earth‐satellite viewing geometries. For a typical 2.5° latitude‐longitude region these differences give rise to a bias in the radiative flux that is at least 0.3% for the monthly mean and an rms error that is at least 4% for instantaneous observations. By comparing the fluxes derived using the observed anisotropy with those derived assuming isotropic reflection, we conclude that a reasonable estimate for the maximum error due to the use of incorrect bidirectional models is a bias of approximately 4% for a typical 2.5° latitude‐longitude, monthly mean and an rms error of 15%.
Simulations of continental ice sheet growth over the last glacial‐interglacial cycle: Experiments with a one‐level seasonal energy balance model including realistic geography
Authors: Deblonde G. , Peltier W. R.
Published: February 2008

A global, two‐dimensional, one‐level seasonal energy balance model (linear in temperature) is asynchronously coupled to vertically integrated ice‐flow models (which depend on latitude and longitude) in order to study the response of the atmosphere‐ocean‐cryosphere‐lithosphere system to variable solar forcing during the last ice age cycle of late Pleistocene time. At the last glacial maximum, the model is shown to satisfactorily simulate both the geographic distribution of ice volume and the individual ice sheet masses within the North American and European ice sheet complexes as they have recently been inferred on the basis of relative sea level data (Tushingham and Peltier, 1991). Because the energy balance model employed here does not take mean ocean currents into account, the absence of the moderating influence of the warm currents in the North Atlantic Ocean leads to a simulation such that surface temperatures are too cold over Scandinavia and the Barents and Kara seas, which leads to an erroneous European ice sheet even in the interglacial phase of the glacial‐interglacial cycle. The sensitivity of the coupled model to variable solar forcing is also insufficient to explain the terminations that are such a striking feature of individual ice age cycles (e.g., Broecker and van Donk, 1970), and this suggests that further physical mechanisms will have to be added to the model in order to explain this important phenomenon. Suggestions are provided as to what these missing physical ingredients might be.
Zonal contributions to global momentum variations on intraseasonal through interannual time scales
Authors: Rosen Richard D. , Salstein David A. , Wood Tamara M.
Published: February 2008

We separate the variability in a 13‐year time series of daily values of the relative angular momentum of the atmosphere (M) into three frequency bands: intraseasonal, seasonal, and interannual. Two methods are used to achieve this separation, and the amount of variance attributable to intraseasonal fluctuations, in particular, is sensitive to the choice made. Seasonal time scales clearly dominate the global momentum series; included in this frequency band is a notable dip in the series early in almost every calendar year. To localize the sources of the frequency band‐dependent fluctuations in M, we decompose the data into series of angular momentum values within each of 46 equal‐area zonal belts over the globe and form covariances between these belt series and M. Seasonal variations in M represent the residual of opposing contributions from the subtropical jets of the northern and southern hemispheres. Both intraseasonal and interannual variations in M result mostly from behavior in the tropics.
Ozone loss rates calculated along ER‐2 flight tracks
Authors: Murphy D. M.
Published: February 2008

Local ozone loss rates due to the ClO+ClO and BrO+ClO cycles are calculated using ClO, pressure, and temperature from in‐situ aircraft measurements and representative BrO mixing ratios. Ozone loss during the vertical profiles executed by the ER‐2 near 72°S usually extended over a deep altitude range rather than reaching a maximum at the top of the profiles. This is due to the strong pressure dependence of the rate determining steps. In the Antarctic, very high ozone loss rates (>5·106 cm−3 s−1) were observed at altitudes with potential temperatures below 400 K, where advective exchange is likely to be much more rapid than at higher altitudes. On September 22, 1987, the ER‐2 measured an ozone loss rate of about 2.8 Dobson units (DU) per 12 sunlit hours in the 350–400 K range and 2.0 DU in the 400–450 K range near 72°S. Rapid ozone loss in the Arctic did not extend below 400 K in the available data. The calculated average loss rate, which is nonlinear, in general depends on the order in which the terms are averaged. Loss rates calculated by averaging the ClO, pressure and temperature for up to 2400 s (about 500 km) generally agree with the average of the local loss rate to within one percent except at the edge of the vortex, where the difference can be up to 30%. Adiabatic temperature changes of up to 10 K change the ozone loss rate by less than 10% because the temperature and pressure effects nearly cancel. Thermal decomposition of Cl2O2 was not important along sunlit portions of ER‐2 flight tracks if equilibrium is assumed between ClO and Cl2O2. The effect of recalibration of the ClO data on the calculated loss rates is discussed.
Atmospheric fate of hydrofluoroethanes and hydrofluorochloroethanes: 1. Rate coefficients for reactions with OH
Authors: Gierczak Tomasz , Talukdar Ranajit , Vaghjiani Ghanshyam L. , Lovejoy Edward R. , Ravishankara A. R.
Published: February 2008

The rate coefficients for the reactions of OH with five halocarbons [CF3CH2F (HFC 134a), CF3CHClF (HCFC 124), CF3CHCl2 (HCFC 123), CH3CHF2 (HFC 152a), and CH3CF2Cl (HCFC 142b)], which are proposed as alternatives to chlorofluoromethanes, have been measured. A pulsed photolysis system and a discharge flow apparatus were used to measure the rate coefficients between approximately 210 and 425 K. Use of the complementary techniques enabled identification of systematic errors and minimization of these errors. The obtained values are compared with values previously measured by other groups. This data base is used in the subsequent paper to calculate the atmospheric lifetimes of the five compounds.
Stratospheric water vapor measurements during CHEOPS‐3
Authors: Ovarlez Joëlle
Published: February 2008

During January 1990, in situ stratospheric water vapor measurements were performed over the Arctic during the CHEOPS experiment at Kiruna. The instrument used is a balloon‐borne frost‐point hygrometer. Results of two flights are shown: one of the flights showed thermal structure indicative of cooling induced by orographic forcing and favourable to PSC formation. Mixing ratio were the same for the two flights, 4–5 ppmv between 12 and 22 km. However, above 22 km, an increase in mixing ratio to 7.5 ppmv is observed. Because this increase is much higher than at mid‐latitudes, we examine it in detail.
Horizontal structures in sporadic sodium layers at 23°S
Authors: Batista Paulo P. , Clemesha Barclay R. , Simonich Dale M.
Published: February 2008

During 1979 and 1980 the INPE lidar located at São José dos Campos, Brazil was operated in a steerable mode, measuring the sodium profiles sequentially at three points in the sky. Twelve sporadic sodium layer events (SSLs) which occurred in this period are studied in the present work. The evolution of the sporadic peaks at the three positions shows short time structures generally separated by consistent time lags in almost all events. On some occasions, the time evolution at one position is very different than at the other two. These data indicate that short duration SSLs have cloud‐like structures which are advected over the measuring station by the horizontal winds, and the long duration layers show a patchy and wave‐like structure. In no case did we observe rapid growth in the sodium density to occur simultaneously at all 3 measuring points. On this basis we believe that there is no evidence for fast production of sodium, and consequently that there is no need for theories for the formation of SSLs to be consistent with such fast production.
A probability method for local earthquake focal mechanisms
Authors: De Natale Giuseppe , Ferraro Anna , Virieux Jean
Published: February 2008

We propose a method for obtaining focal mechanisms of earthquakes recorded on a local network. It is based on the non‐linear estimation of the probability function for strike, dip and slip of the focal mechanism from P polarities, S polarizations and S/P amplitude ratios. The method is shown to be effective for the analysis of small earthquakes recorded by local networks. In particular, the S/P amplitude ratios bring strong constraints on fault parameters, even if large errors are present. An application to a small earthquake recorded at the volcanic zone of Campi Flegrei (Naples, Italy) during a seismic outburst is presented.
Eiscat radar observations of enhanced incoherent scatter spectra; Their relation to red aurora and field‐aligned currents
Authors: Collis P. N. , Häggström L. , Kaila K. , Rietveld M. T.
Published: February 2008

Enhancements of one, or both, of the ion‐acoustic peaks of incoherent scatter spectra in the auroral ionosphere have been observed with the EISCAT UHF and VHF radars. All occurrences for which optical data are available show these events to coincide with active, unusually intense, red auroral forms in the vicinity of the radar beam at high altitudes. Both the optical and the radar signatures are expected to be caused by large fluxes of low energy electrons. Analyses of the measured spectra, in which the electron drift speed is estimated, imply field‐aligned current densities up to several mA m−2. The vertically‐directed VHF observations from ∼1000 km altitude reveal that the spectral enhancements, which are transient features in field‐aligned measurements, can exist for up to several minutes.
Geometry and mechanisms of fluid flow at 15 to 45 kilometer depths in an Early Cretaceous Accretionary Complex
Authors: Bebout Gray E.
Published: February 2008

The Catalina Schist (southern California), contains variably metamorphosed mafic, sedimentary, and ultramafic rocks that were accreted at depths of 15 to 45 km during early Cretaceous subduction. Fluid flow in the Catalina Schist was concentrated along fractures and shear zones, as indicated by the textures and abundance of veins and evidence in melange zones for metasomatism and homogenization of stable isotope compositions. Slab‐parallel orientations of major melange zones with enhanced permeability may dictate that the majority of fluid released by devolatilization at depths >15 km in subduction zones moves updip toward the seafloor. Such transport could contribute to fluid budgets in shallower parts of accretionary wedges and facilitate large‐scale mass and energy transfer in forearc regions.